Deficit Hyperactivity Disorder ● Autism ● Developmental Delays
Roughly one in six children in the U.S. has one or more developmental disabilities, ranging from a learning disability to a serious behavioral or emotional disorder. Scientists believe that the amount of toxic chemicals in the environment that cause developmental and neurological damage are contributing to the rise of physical and mental effects being found in children. Studies show children’s developing organs create “early windows of great vulnerability” during which exposure to pesticides can cause great damage. In the U.S., requirements for testing pesticides and other chemicals for potential developmental and learning disorders are minimal.
A developing brain is much more susceptible to the toxic effects of chemicals than an adult brain. During development, the brain undergoes a highly complex series of processes at different stages. Interference from toxic substances that disrupt these processes can have permanent consequences. That vulnerability extends from fetal development through infancy and childhood to adolescence. Research has shown that environmental toxicants, such as pesticides, at low levels of exposure can have subclinical effects—not clinically visible, but still important adverse effects, such as decreases in intelligence or changes in behavior.
Attention Deficit Hyperactivity Disorder (ADHD)
- Prenatal exposure to organophosphate pesticides and reciprocal social behavior in childhood.
Prenatal exposure to organophosphate pesticides (OPs) has been associated with adverse neurodevelopmental outcomes in childhood, including low IQ, pervasive developmental disorder (PDD), attention problems and ADHD. Many of these disorders involve impairments in social functioning. Authors investigated the relationship between biomarkers of prenatal OP exposure and impaired reciprocal social behavior in childhood, as measured by the Social Responsiveness Scale (SRS). Using a multi-ethnic urban prospective cohort of mother-infant pairs in New York City recruited between 1998 and 2002 (n=404) study examined the relation between third trimester maternal urinary levels of dialkylphosphate (ΣDAP) OP metabolites and SRS scores among 136 children who returned for the 7-9year visit. Overall, there was no association between OPs and SRS scores, although in multivariate adjusted models, associations were heterogeneous by race and by sex. Among blacks, each 10-fold increase in total diethylphosphates (ΣDEP) was associated with poorer social responsiveness.
There was no association among whites or Hispanics, or for total ΣDAP or total dimethylphosphate (ΣDMP) biomarker levels. Additionally, stratum-specific models supported a stronger negative association among boys for ΣDEPs, with no notable association among girls. Results support an association of prenatal OP exposure with deficits in social functioning among blacks and among boys, although this may be in part reflective of differences in exposure patterns.
[Furlong MA, Engel SM, et al. 2014. Environ Int.70:125-31.]
- Acetylcholinesterase activity and neurodevelopment in boys and girls.
Organophosphate exposures can affect children's neurodevelopment, possibly due to neurotoxicity induced by acetylcholinesterase (AChE) inhibition, and may affect boys more than girls. Authors tested the hypothesis that lower AChE activity is associated with lower neurobehavioral development among children living in Ecuadorian floricultural communities. In 2008, authors examined 307 children (age: 4-9 years; 52% male) and quantified AChE activity and neurodevelopment in 5 domains: attention/executive functioning, language, memory/learning, visuospatial processing, and sensorimotor (NEPSY-II test). Mean ± standard deviation AChE activity was 3.14 ± 0.49 U/mL (similar for both genders). The range of scores among neurodevelopment subtests was 5.9 to 10.7 U. Girls had a greater mean attention/executive functioning domain score than boys. In boys only, there were increased odds ratios of low neurodevelopment among those in the lowest tertile versus the highest tertile of AChE activity after adjustment for socioeconomic and demographic factors, height-for-age, and hemoglobin. Within these domains, attention, inhibition and long-term memory subtests were most affected.Overall, low AChE activity was associated with deficits in neurodevelopment, particularly in attention, inhibition, and memory in boys but not in girls. These critical cognitive skills affect learning and academic performance. Added precautions regarding secondary occupational pesticide exposure would be prudent.
[Suarez-Lopez JR1, Himes JH, et al. 2013. Pediatrics.132(6):e1649-58.]
- Urinary 3,5,6-trichloro-2-pyridinol (TCPY) in pregnant women from Mexico City: Distribution, temporal variability, and relationship with child attention and hyperactivity.
The etiology of ADHD and ADHD-related behavior is unclear, but genetic and environmental factors, such as pesticides, have been hypothesized. The objective of this study was to investigate the relationship between in utero exposure to chlorpyrifos, chlorpyrifos-methyl, and/or 3,5,6-trichloro-2-pyridinol (TCPY) and ADHD in school-age Mexican children using TCPY as a biomarker of exposure. Third trimester urinary TCPY concentrations were measured in 187 mother-child pairs from a prospective birth cohort. Child neurodevelopment in children 6-11 years of age was assessed using Conners' Parental Rating Scales-Revised (CRS-R), Conners' Continuous Performance Test (CPT), and Behavior Assessment System for Children-2 (BASC-2). Authors did not observe any statistically significant associations between tertiles of maternal TCPY concentrations and ADHD-related outcomes in children. However, compared to the lowest tertile we found suggestive evidence for increased ADHD index in the highest TCPY tertile in boys and increased attention problems for the middle tertile in girls. Considering the continued widespread agricultural and possible residential use of chlorpyrifos and chlorpyrifos-methyl in Mexico and the educational implications of cognitive and behavior deficits, these relationships deserve further study.
[Fortenberry GZ, Meeker JD, Sánchez BN, Barr DB, et al. 2013. Int J Hyg Environ Health. pii: S1438-4639(13)00112-0]
- Review of current evidence on the impact of pesticides, polychlorinated biphenyls and selected metals on attention deficit / hyperactivity disorder in children.
The aim of this review was to investigate the association between attention deficit / hyperactivity disorder (ADHD) or ADHD-related symptoms and industrial chemicals, such as organophosphates and organochlorine pesticides, polychlorinated biphenyls (PCBs), lead, mercury and manganese. The review is restricted to human studies published in English in peer-reviewed journals since 2000. Most of the presented studies focused on pesticides, PCB and lead. The impact of mercury and manganese was investigated less frequently. The findings indicate that children's exposure to organophosphate pesticides may cause symptoms consistent with pervasive developmental disorder, ADHD or attention problems. Exposures to organochlorine pesticides and PCBs were associated with ADHD-like behaviors such as alertness, quality of alert response, and cost of attention. The studies provided evidence that blood lead level below 10 μg/dl was associated with ADHD or ADHD-related symptoms. Two studies indicated that exposure to manganese is related to ADHD; such exposure and its impact on children neurodevelopment need to be further investigated. Future studies should use a prospective design with multiple biological samples collected over time for better assessment of exposure and its critical windows. Additionally, inclusion of potential confounding factors and co-exposures is crucial.
[Polańska K, Jurewicz J, Hanke W. 2013. Int J Occup Med Environ Health. 26(1):16-38]
- Chemical exposure early in life and the neurodevelopment of children--an overview of current epidemiological evidence.
A number of chemicals have been shown to demonstrate neurotoxic effects either in human or laboratory animal studies. This article aims at evaluating the impact of exposure to several chemicals including: organophosphate, organochlorine pesticides, polychlorinated biphenyls (PCBs), mercury and lead on the neurodevelopment of children by reviewing the most recent published literature, and answer the question whether any progress has been made in the epidemiology of the neurodevelopment of children induced by exposure to those chemicals. The result of the presented studies show that exposure to the above-mentioned chemicals may impair the neurodevelopment of children. Neonates exposed to organophosphate pesticides demonstrated a higher proportion of abnormal reflexes, and young children had more attention problems. Exposure to organochlorine pesticides in children was associated with alertness, quality of alert responsiveness, cost of attention and other potential attention associated measures. Because the neurotoxicants may cross the placenta and the fetal brain, exposure consideration regarding the reduction of exposure to those chemicals should be implemented.
[Jurewicz J, Polańska K, Hanke W. 2013. Ann Agric Environ Med. 20(3):465-86]
- Neuropsychological measures of attention and impulse control among 8-year-old children exposed prenatally to organochlorines
The goal of this study was to corroborate these findings using neuropsychological measures of inattentive and impulsive behaviors. Authors investigated the association between cord serum polychlorinated biphenyls (PCBs) and p,p'-dichlorodiphenyl dichloroethylene (p,p'-DDE) and attention and impulse control using a Continuous Performance Test (CPT) and components of the Wechsler Intelligence Scale for Children. Participants came from a prospective cohort of children born during 1993-1998 to mothers residing near a PCB-contaminated harbor in New Bedford. Study detected associations between PCBs and neuropsychological deficits for 578 and 584 children with CPT and WISC-III measures, respectively, but only among boys. For example, boys with higher exposure to ΣPCB4 had a higher rate of CPT errors of omission and slower WISC-III Processing Speed. Weaker associations were found for p,p'-DDE. For girls, associations were in the opposite direction for the CPT and null for the WISC-III. These results support an association between organochlorines (mainly PCBs) and neuropsychological measures of attention among boys only.
[Sagiv SK, Thurston SW, Bellinger DC, et al. 2012. Environ Health Perspect. 120(6):904-9]
- Longitudinal association between early life socio-environmental factors and attention function at the age 11 years
Prenatal and early-life exposures can affect the course of children's neuropsychological development well into pre-adolescence, given the vulnerability of the developing brain. However, it is unknown which socio-environmental factors at early childhood can influence specific cognitive processes like attention at a later age. This study aimed to determine social and environmental exposures in early childhood that may be associated with attention function of 11-year-olds. Attention function using the continuous performance test-II (CPT-II) on 393 11-year old children from the Menorca's birth-cohort within the INMA-project (Spain), and pre-selected a list of socio-environmental observations taken when they were up to 4 years of age was measured. Earlier socio-environmental characteristics, such as parental social class, educational level and maternal mental health were found to be associated with later inattentive and impulsive symptomatology through a higher rate of omission and commission errors. Breastfeeding played a protective role against commission errors, while higher DDE and PCBs levels at age 4 were associated with slow speed response. Our findings suggest that a number of life socio-environmental factors during prenatal life and early childhood, such as socio-demographic characteristics, breastfeeding, maternal nutritional supplementation with folic acid and vitamins and exposure to some organochlorine compounds may influence inattentive and hyperactive/impulsive symptomatology during pre-adolescence.
[Forns J, Torrent M, Garcia-Esteban R, et al. 2012. Environ Res. 117:54-9]
- Pesticide exposure and child neurodevelopment: summary and implications.
Widely used around the world, pesticides play an important role in protecting health, crops, and property. However, pesticides may also have detrimental effects on human health, with young children among the particularly vulnerable. Recent research suggests that even low levels of pesticide exposure can affect young children's neurological and behavioral development. Evidence shows a link between pesticides and neonatal reflexes, psychomotor and mental development, and attention-deficit hyperactivity disorder. Implications include a need for improved risk assessment and health histories by clinicians, greater education at all levels, more common use of integrated pest management, and continued policy and regulatory strategies to mitigate the effects of and the need for pesticides.
[Liu J, Schelar E. 2012. Workplace Health Saf. 60(5):235-42]
- Urinary trichlorophenol levels and increased risk of attention deficit hyperactivity disorder among US school-aged children.
Trichlorophenols (TCPs) are organochlorine compounds which are ubiquitous in the environment and well known for their carcinogenic effects. However, little is known about their neurotoxicity in humans. The goal was to examine the association between body burden of TCPs (ie, 2,4,5-TCP and 2,4,6-TCP) and attention deficit hyperactivity disorder (ADHD). Study reports children with low levels (<3.58 μg/g) and high levels (≥3.58 μg/g) of urinary 2,4,6-TCP had a higher risk of parent-reported ADHD compared to children with levels below the limit of detection after adjusting for covariates. No association was found between urinary 2,4,5-TCP and parent-reported ADHD. Exposure to TCP may increase the risk of behavioural impairment in children. The potential neurotoxicity of these chemicals should be considered in public health efforts to reduce environmental exposures/contamination, especially in countries where organochlorine pesticides are still commonly used.
[Xu X, Nembhard WN, Kan H, et al. 2011. Occup Environ Med. 68(8):557-61]
- Organophosphate Pesticide Exposure and Attention in Young Mexican-American Children
OP exposure, as measured by maternal urinary dialkyl phosphate (DAP) metabolites during pregnancy, was non-significantly associated with maternal report of attention problems and ADHD at age 3½, but were significantly related at age 5. Some outcomes exhibited interaction by sex with associations found only among boys.
[Marks AR, Harley K, Bradman A, Kogut K, Barr DB, et al. 2010. Environ Health Perspect. doi:10.1289/ehp.1002056]
- Prenatal organochlorine exposure and behaviors associated with attention deficit hyperactivity disorder in school-aged children.
Organochlorines are environmentally persistent contaminants that readily cross the placenta, posing a potential risk to the developing fetus. Evidence for neurodevelopmental effects at low levels of these compounds is growing, though few studies have focused on behavioral outcomes. The authors investigated the association between prenatal polychlorinated biphenyl (PCB) and p,p'-dichlorodiphenyl dichloroethylene (p,p'-DDE) levels and behaviors associated with attention deficit hyperactivity disorder (ADHD), measured with the Conners' Rating Scale for Teachers (CRS-T), in a cohort of 607 children aged 7-11 years (median age, 8.2 years) born in 1993-1998 to mothers residing near a PCB-contaminated harbor in New Bedford, Massachusetts. The authors found higher risk for ADHD-like behaviors assessed with the CRS-T at higher levels of PCBs and p,p'-DDE. These results support an association between low-level prenatal organochlorine exposure and ADHD-like behaviors in childhood.
[Sagiv SK, Thurston SW, Bellinger DC, et al. 2010. Am J Epidemiol. 171(5):593-601]
Disorder and Urinary Metabolites of Organophosphate Pesticides
Study's findings support the hypothesis that organophosphate exposure, at
levels common among US children, may contribute to ADHD prevalence.
[Bouchard, M. et al. 2010. Pediatrics (doi:10.1542/peds.2009-3058)]
sex selective hormonal and behavior alterations in mice exposed to low
doses of chlorpyrifos in utero
Exposure to low levels of
the organophosphate insecticide chorpyrifos during pregnancy can impair
learning, change brain function and alter thyroid levels of offspring
into adulthood for tested mice, especially females.
[Haviland, Butz, Porter. 2009. Reprod Toxicol, doi:10.1016/j.reprotox.2009.10.008]
of environmental chemicals on the thyroid hormone function in pituitary rat
disrupting chemicals (EDCs) are widespread in the environment and suspected
to interfere with the function of thyroid hormones (THs). Study showed that
EDCs have the potential to exert TH disruption
increasing the risk or a negative impact on fetal brain development, resulting
in cognitive dysfunctions.
[Ghisari M, Bonefeld-Jorgensen EC. 2005. Mol Cell Endocrinol;244(1-2):31-41]
and endocrine disruption.
Article explores the possibility that contaminants contribute to the increasing
prevalence of attention deficit hyperactivity disorder, autism, and associated
neurodevelopmental and behavioral problems in developed countries. It discusses
the exquisite sensitivity of the embryo and fetus to thyroid disturbance and
provide evidence of human in utero exposure to contaminants that can interfere
with the thyroid.
[Colborn T. 2004. Environ Health Perspect;112(9):944-9]
defects, season of conception, and sex of children born to pesticide applicators
living in the Red River Valley of Minnesota, USA.
A 2002 peer-reviewed study finds children born to parents exposed to glyphosate
(Roundup®) show a higher incidence of attention deficit disorder and hyperactivity.
[Garry, V.F. et al. 2002. Environ. Health Persp. 110 (Suppl. 3):441-449]
- Neurodevelopmental Disorders and Prenatal Residential Proximity to Agricultural Pesticides: The CHARGE Study.
To evaluate whether residential proximity to agricultural pesticides during pregnancy is associated with autism spectrum disorders (ASD) or developmental delay (DD) in the Childhood Autism Risks from Genetics and Environment (CHARGE) Study.The CHARGE study is a population-based case-control study of ASD, developmental delay (DD), and typical development. For 970 participants, commercial pesticide application data from the California Pesticide Use Report (1997-2008) were linked to the addresses during pregnancy. Pounds of active ingredient applied for organophophates, organochlorines, pyrethroids, and carbamates were aggregated within 1.25km, 1.5km, and 1.75km buffer distances from the home. Approximately one-third of CHARGE Study mothers lived, during pregnancy, within 1.5 km (just under one mile) of an agricultural pesticide application. Proximity to organophosphates at some point during gestation was associated with a 60% increased risk for ASD, higher for 3rd trimester exposures, and 2nd trimester chlorpyrifos applications: OR = 3.3. Children of mothers residing near pyrethroid insecticide applications just prior to conception or during 3rd trimester were at greater risk for both ASD and DD, with OR's ranging from 1.7 to 2.3. Risk for DD was increased in those near carbamate applications, but no specific vulnerable period was identified.This study of ASD strengthens the evidence linking neurodevelopmental disorders with gestational pesticide exposures, and particularly, organophosphates and provides novel results of ASD and DD associations with, respectively, pyrethroids and carbamates.
[Shelton JF, Geraghty EM, Tancredi DJ, et al. 2014. Environ Health Perspect. DOI:10.1289/ehp.1307044]
- Autism spectrum disorder, flea and tick medication, and adjustments for exposure misclassification: the CHARGE (CHildhood Autism Risks from Genetics and Environment) case-control study.
The environmental contribution to autism spectrum disorders (ASD) is largely unknown, but household pesticides are receiving increased attention. This study examined associations between ASD and maternally-reported use of imidacloprid, a common flea and tick treatment for pets.The analytic dataset included complete information for 262 typically developing controls and 407 children with ASD. Compared with exposure among controls, the odds of prenatal imidacloprid exposure among children with ASD were slightly higher, with an odds ratio (OR) of 1.3. A susceptibility window analysis yielded higher ORs for exposures during pregnancy than for early life exposures, whereas limiting to frequent users of imidacloprid, the OR increased to 2.0.Within plausible estimates of sensitivity and specificity, the association could result from exposure misclassification alone. The association between imidacloprid exposure and ASD warrants further investigation, and this work highlights the need for validation studies regarding prenatal exposures in ASD.
[Keil AP1, Daniels JL, Hertz-Picciotto I.2014. Environ Health. 13(1):3.]
- Environmental toxicants and autism spectrum disorders: a systematic review.
Although the involvement of genetic abnormalities in autism spectrum disorders (ASD) is well-accepted, recent studies point to an equal contribution by environmental factors, particularly environmental toxicants. Authors compiled publications investigating potential associations between environmental toxicants and ASD and arranged these publications into the following three categories: (a) studies examining estimated toxicant exposures in the environment during the preconceptional, gestational and early childhood periods; (b) studies investigating biomarkers of toxicants; and (c) studies examining potential genetic susceptibilities to toxicants.In the first category examining ASD risk and estimated toxicant exposures in the environment, the majority of studies (34/37; 92%) reported an association. Toxicants implicated in ASD included pesticides, phthalates, polychlorinated biphenyls (PCBs), solvents, toxic waste sites, air pollutants and heavy metals, with the strongest evidence found for air pollutants and pesticides. In the second category of studies investigating biomarkers of toxicants and ASD, a large number was dedicated to examining heavy metals. Such studies demonstrated mixed findings, with only 19 of 40 (47%) case-control studies reporting higher concentrations of heavy metals in blood, urine, hair, brain or teeth of children with ASD compared with controls.Regarding the third category of studies investigating potential genetic susceptibilities to toxicants, 10 unique studies examined polymorphisms in genes associated with increased susceptibilities to toxicants, with 8 studies reporting that such polymorphisms were more common in ASD individuals (or their mothers, 1 study) compared with controls (one study examined multiple polymorphisms). Genes implicated in these studies included paraoxonase (PON1, three of five studies), glutathione S-transferase (GSTM1 and GSTP1, three of four studies), δ-aminolevulinic acid dehydratase (one study), SLC11A3 (one study) and the metal regulatory transcription factor 1 (one of two studies). The findings of this review suggest that the etiology of ASD may involve, at least in a subset of children, complex interactions between genetic factors and certain environmental toxicants that may act synergistically or in parallel during critical periods of neurodevelopment, in a manner that increases the likelihood of developing ASD. Additional high-quality epidemiological studies concerning environmental toxicants and ASD are warranted to confirm and clarify many of these findings.
[Rossignol DA, Genuis SJ, Frye RE. 2014. Transl Psychiatry. 4:e360.]
- Does perinatal exposure to endocrine disruptors induce autism spectrum and attention deficit hyperactivity disorders? Review.
This study provides an overview of studies on perinatal exposure in humans to endocrine disrupting chemicals (EDCs) in relation to autism spectrum (ASD) and attention deficit hyperactivity (ADHD) disorders. Positive associations were found for ASD in relation to exposure to all chemicals investigated, which included hazardous air pollutants, pesticides and bisphenol A (BPA). Increased risks of ADHD or positive associations were found for exposure to polychlorinated biphenyls (PCBs), dialkyl phosphate (DAP) and chlorpyrifos. BPA, polybrominated diphenylethers (PBDEs) and low molecular weight (LMW) phthalates were positively associated with externalizing behaviour. Five of 17 studies did not find any association between exposure and ADHD. Perinatal exposure to EDCs appears to be associated with the occurrence of ASD as well as ADHD. Disruption of thyroid hormone function and gamma-aminobutyric acid (GABA)ergic mechanisms may offer an explanation for the observed relations; though, conclusive evidence in humans is limited.
[de Cock M, Maas YG, van de Bor M. 2012. Acta Paediatr. 101(8):811-8]
- Tipping the Balance of Autism Risk: Potential Mechanisms Linking Pesticides and Autism
Autism spectrum disorders (ASDs) have been increasing in many parts of the world and a portion of cases are attributable to environmental exposures. Conclusive replicated findings have yet to appear on any specific exposure; however, mounting evidence suggests gestational pesticides exposures are strong candidates.Authors review and discuss previous research related to autism risk, developmental effects of early pesticide exposure, and basic biological mechanisms by which pesticides may induce or exacerbate pathophysiological features of autism. In experimental and observational research, certain pesticides may be capable of inducing core features of autism, but little is known about the timing or dose, or which of various mechanisms is sufficient to induce this condition. In animal studies, authors encourage more research on gene × environment interactions, as well as experimental exposure to mixtures of compounds. Similarly, epidemiologic studies in humans with exceptionally high exposures can identify which pesticide classes are of greatest concern, and studies focused on gene × environment are needed to determine if there are susceptible subpopulations at greater risk from pesticide exposures.
[Shelton, J.F., Hertz-Picciotto, I. and Pessah, I.H. 2012. Environ Health Persp. 120 (7): 944-951.]
- A macroepigenetic approach to identify factors responsible for the autism epidemic in the United States
The demand for special education services continues to rise in disability categories associated with pervasive developmental disorders. Neurodevelopment can be adversely impacted when gene expression is altered by dietary transcription factors, such as zinc insufficiency or deficiency, or by exposure to toxic substances found in our environment, such as mercury or organophosphate pesticides. Gene expression patterns differ geographically between populations and within populations. Gene variants of paraoxonase-1 are associated with autism in North America, but not in Italy, indicating regional specificity in gene-environment interactions. In the current review, authors utilize a novel macroepigenetic approach to compare variations in diet and toxic substance exposure between these two geographical populations to determine the likely factors responsible for the autism epidemic in the United States.
[Dufault, R., W.J. Lukiw, R. Crider, R. Schnoll, D. Wallinga and R. Deth. 2012. Clinical Epigenetics. 4(1):6]
- A Research Strategy to Discover the Environmental Causes of Autism and Neurodevelopmental Disabilities
This editorial explores the ongoing research, both genetic and environmental studies,to identify the potentially preventable causes of neuro-develop-mental disorders (NDDs). Genetic research has demonstrated that austism spectrum disorder (ASD) and certain other NDDs have a strong hereditary component. Exploration of the environmental causes of autism and other NDDs has been catalyzed by growing recognition of the exquisite sensitivity of the developing human brain to toxic chemicals. This susceptibility is greatest during unique “windows of vulnerability” that open only in embryonic and fetal life and have no later counter-part. Additional prospective studies have linked loss of cognition (IQ), dyslexia, and ADHD to lead, methyl-mercury, organophosphate insecticides, organo-chlorine insecticides, polychlorinated biphenyls, arsenic and others.A major unanswered question is whether there are still undiscovered environ-mental causes of autism or other NDDs among the thousands of chemicals currently in wide use in the United States. The significance of early chemical exposures for children’s health is not yet fully understood. A great concern is that a large number of the chemicals in widest use have not undergone even minimal assessment of potential toxicity, and only about 20% have been screened for potential toxicity during early development. Unless studies specifically examine develop-mental consequences of early exposures to untested chemicals, sub-clinical dysfunction caused by these exposures can go unrecognized for years.
[Landrigan P.J., Lambertini,L and Birnbaum,
Environ Health Perspect. 120(7): a258-a260]
Rise in Autism and the Role of Age at Diagnosis.
Study found that a seven- to eight-fold increase in the number children born
in California with autism since 1990. These results suggest that research
should shift from genetics to the host of chemicals and infectious microbes
in the environment that are likely at the root of changes in the neurodevelopment
of California’s children, including pesticides and household chemicals.
[Hertz-Picciotto, I. and Delwiche, L. 2009. Epidemiology:20(1) - pp 84-90
Pesticide Use in Relation to Autism
A population-based study looking at how genes
and environmental factors interact shows that pet shampoos containing insecticides
may trigger autism spectrum disorders (ASD). The study findings, presented
at the International Meeting for Autism Research, show that mothers of children
with an ASD are twice as likely to have used an insecticidal pet shampoo during
the prenatal and/or postnatal period when compared to mothers of healthy children.
The strongest association was during the second trimester of pregnancy.
[Hertz-Picciotto, et al. Oral Presentation
at the International Meeting for Autism Research (ORAL 2899). London, England,
May 15, 2008)]
Transient in utero hypothyroxinemia related to maternal flavonoid ingestion
during pregnancy and to other environmental antithyroid agents
Author suggests that substances that interfere
with thyroidal activity may produce morphological brain changes leading to
autism. Environmental contaminants interfere with thyroid function including
60% of all herbicides, in particular 2,4-D, acetochlor, aminotriazole, amitrole,
bromoxynil, pendamethalin, mancozeb, and thioureas. The current surge of autism
could be related to transient maternal hypothyroxinemia resulting from dietary
and/or environmental exposure to antithyroid agents.
[Román, G, C. 2007. Journal of the Neurological
Sciences; 262(1-2), pp 15-26]
Residence Near Agricultural Pesticide Applications and Autism Spectrum Disorders
Among Children in the California Central Valley.
Study shows that children born to mothers living near agricultural fields
where organochlorine pesticides, specifically endosulfan and dicofol, were
applied during their first trimester of pregnancy were six times more likely
to have children that develop autism spectrum disorders (ASDs). compared to
mothers who did not live near the fields.
[Roberts, E, M. et al. 2007. Environ Health Perspect 115:1482-1489. doi:10.1289/ehp.10168]
- Neurodevelopmental effects in children associated with exposure to organophosphate pesticides: a systematic review.
The aim of the present article is to synthesize reported evidence over the last decade on organophosphate (OP) exposure and neurodevelopmental effects in children. The eligibility criteria considered were studies assessing exposure to OP pesticides and neurodevelopmental effects in children from birth to 18 years of age, published between 2002 and 2012 in English or Spanish. All but one of the 27 studies evaluated showed some negative effects of pesticides on neurobehavioral development. A positive dose-response relationship between OP exposure and neurodevelopmental outcomes was found in all but one of the 12 studies that assessed dose-response. In the ten longitudinal studies that assessed prenatal exposure to OPs, cognitive deficits (related to working memory) were found in children at age 7 years, behavioral deficits (related to attention) seen mainly in toddlers, and motor deficits (abnormal reflexes) seen mainly in neonates. Evidence of neurological deficits associated with exposure to OP pesticides in children is growing. The studies reviewed collectively support the hypothesis that exposure to OP pesticides induces neurotoxic effects. Further research is needed to understand effects associated with exposure in critical windows of development.
[Muñoz-Quezada MT, Lucero BA, Barr DB, et al. 2013. Neurotoxicology. 39:158-68]
- Effects of early life permethrin exposure on spatial working memory and on monoamine levels in different brain areas of pre-senescent rats.
Pesticide exposure during brain development could represent an important risk factor for the onset of neurodegenerative diseases. The present study was designed to characterize the cognitive deficits in the animal model. When during late adulthood permethrin (PERM) treated rats were tested for spatial working memory performances in a T-maze-rewarded alternation task they took longer to choose for the correct arm in comparison to age matched controls. No differences between groups were found in anxiety-like state, locomotor activity, feeding behavior and spatial orientation task. Findings showing a selective effect of PERM treatment on the T-maze task point to an involvement of frontal cortico-striatal circuitry rather than to a role for the hippocampus.
[Nasuti C, Carloni M, Fedeli D, et al. 2013. Toxicology. 303:162-8]
- Prenatal p,p´-DDE exposure and neurodevelopment among children 3.5-5 years of age.
The results of previous studies suggest that prenatal exposure to bis[p-chlorophenyl]-1,1,1-trichloroethane (DDT) and to its main metabolite, 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene (DDE), impairs psychomotor development during the first year of life. However, information about the persistence of this association at later ages is limited. Authors assessed the association of prenatal DDE exposure with child neurodevelopment at 42-60 months of age. Study report McCarthy Scales of Children's Abilities for 203 children at 42, 48, 54, and 60 months of age. Maternal DDE serum levels were available for at least one trimester of pregnancy
After adjustment, a doubling of DDE during the third trimester of pregnancy was associated with statistically significant reductions of -1.37, -0.88, -0.84, and -0.80 points in the general cognitive index, quantitative, verbal, and memory components respectively. The association between prenatal DDE and the quantitative component was weaker at 42 months than at older ages. No significant statistical interactions with sex or breastfeeding were observed. Findings support the hypothesis that prenatal DDE impairs early child neurodevelopment; the potential for adverse effects on development should be considered when using DDT for malaria control.
[Torres-Sánchez L, Schnaas L, Rothenberg SJ, et al. 2013. Environ Health Perspect. 121(2):263-8]
- Cognitive, visual, and motor development of 7-month-old Guadeloupean infants exposed to chlordecone.
The insecticide chlordecone was extensively used in the French West Indies to control banana root borer. Its persistence in soils has led to the widespread pollution of the environment, and human beings are still exposed to this chemical. Chlordecone has been shown to impair neurological and behavioural functions in rodents when exposed gestationally or neonatally.The aim of the study was to evaluate the impact of prenatal and postnatal exposure to chlordecone on the cognitive, visual, and motor development of 7-month-old infants from Guadeloupe. Infants were tested at 7 months. Visual recognition memory and processing speed were assessed. Samples of cord blood and breast milk at 3 months were analyzed for chlordecone concentrations. Postnatal exposure was determined through breast feeding and frequency of contaminated food consumption by the infants. Cord chlordecone concentrations in tertiles were associated with reduced novelty preference on the FTII in the highly exposed group. Postnatal exposure through contaminated food consumption was marginally related to reduced novelty preference and longer processing speed. Detectable levels of chlordecone in cord blood were associated with higher risk of obtaining low scores on the fine motor development scale.These results suggest that pre- and postnatal low chronic exposure to chlordecone is associated with negative effects on cognitive and motor development during infancy.
[Dallaire R, Muckle G, Rouget F, et al. 2012. Environ Res. 118:79-85]
- Does the home environment and the sex of the child modify the adverse effects of prenatal exposure to chlorpyrifos on child working memory?
In the current paper, the authors expanded the previous work on CPF to investigate how additional biological and social environmental factors might create or explain differential neurodevelopmental susceptibility, focusing on main and moderating effects of the quality of the home environment (HOME) and child sex. The study evaluate how the quality of the home environment (specifically, parental nurturance and environmental stimulation) and child sex interact with the adverse effects of prenatal CPF exposure on working memory at child age 7years. Results found a borderline significant interaction between prenatal exposure to CPF and child sex suggesting males experience a greater decrement in working memory than females following prenatal CPF exposure. In addition, a borderline interaction between parental nurturance and child sex was detected suggesting that, in terms of working memory, males benefit more from a nurturing environment than females. This is the first investigation into factors that may inform an intervention strategy to reduce or reverse the cognitive deficits resulting from prenatal CPF exposure.
[Horton, M.K., L.G. Kahn, F. Perera, D.B. Barr and V. Rauh. 2012.
Neurotoxicology and Teratology. 34(5):534-41]
- In-utero exposure to dichlorodiphenyltrichloroethane and cognitive development among infants and school-aged children.
DDT continues to be used for control of infectious diseases in several countries. In-utero exposure to DDT and DDE has been associated with developmental and cognitive impairment among children. This study examined this association of in-utero DDT and DDE exposure with infant and child neurodevelopment was examined in 1100 subjects in the Collaborative Perinatal Project, a prospective birth cohort enrolling pregnant women from 12 study centers in the United States from 1959 to 1965. Maternal DDT and DDE concentrations were measured in archived serum specimens. Infant mental and motor development was assessed at age 8 months using the Bayley Scales of Infant Development, and child cognitive development was assessed at age 7 years, using the Wechsler Intelligence Scale for Children. Although levels of DDT and DDE were relatively high in this population, neither were related to Mental or Psychomotor Development scores on the Bayley Scales nor to Full-Scale Intelligence Quotient at 7 years of age. Categorical analyses showed no evidence of dose- response for either maternal DDT or DDE, and estimates of the association between continuous measures of exposure and neurodevelopment were indistinguishable from 0. Adverse associations were not observed between maternal serum DDT and DDE concentrations and offspring neurodevelopment at 8 months or 7 years in this cohort.
[Jusko TA, Klebanoff MA, Brock JW, Longnecker MP. 2012. Epidemiology. 23(5):689-98]
- Prenatal exposure to organochlorine compounds and neuropsychological development up to two years of life.
Polychlorinated biphenyls (PCB), hexachlorobenzene (HCB), and dichlorodiphenyl dichloroethylene (pp'DDE) are persistent, bioaccumulative, and toxic environmental pollutants with potential neurotoxic effects. Despite a growing body of studies investigating the health effects associated with these compounds, their specific effects on early neuropsychological development remain unclear. Study investigated such neuropsychological effects in a population-based birth cohort based in three regions in Spain (Sabadell, Gipuzkoa, and Valencia) derived from the INMA [Environment and Childhood] Project. The main analyses in this report were based on 1391 mother-child pairs with complete information on maternal levels of organochlorine compounds and child neuropsychological assessment (Bayley Scales of Infant Development) at age 14 months. Data found that prenatal PCB exposure, particularly to congeners 138 and 153, resulted in impairment of psychomotor development, but found no evidence for effects on cognitive development. Prenatal exposure to pp'DDE or HCB was not associated with early neuropsychological development. The negative effects of exposure to PCBs on early psychomotor development suggest that the potential neurotoxic effects of these compounds may be evident even at low doses.
[Forns J, Lertxundi N, Aranbarri A, Murcia M, et al. 2012. Environ Int. 45:72-7]
- Brain anomalies in children exposed prenatally to a common organophosphate pesticide
Study investigated associations between chlorpyrifos (CPF) exposure and brain morphology using magnetic resonance imaging in 40 children selected from a nonclinical, representative community-based cohort. High CPF exposure was associated with enlargement of superior temporal, posterior middle temporal, and inferior postcentral gyri bilaterally, and enlarged superior frontal gyrus, gyrus rectus, cuneus, and precuneus along the mesial wall of the right hemisphere. A significant exposure × IQ interaction was derived from CPF disruption of normal IQ associations with surface measures in low-exposure children. In preliminary analyses, high-exposure children did not show expected sex differences in the right inferior parietal lobule and superior marginal gyrus, and displayed reversal of sex differences in the right mesial superior frontal gyrus, consistent with disruption by CPF of normal behavioral sexual dimorphisms reported in animal models. High-exposure children also showed frontal and parietal cortical thinning, and an inverse dose–response relationship between CPF and cortical thickness.
[Rauh, V. A., F. P. Perera, M. K. Horton, R. M. Whyatt, et al. 2012. PNAS.109 (20): 7871-6.]
- Prenatal Exposure to Organophosphates, Paraoxonase 1, and Cognitive Development in Childhood
Researchers examine the relationship between biomarkers of organophosphate exposure, PON1, and cognitive development at ages 12 and 24 months, and 6 to 9 years in this Mount Sinai Children’s Environmental Health Study. Prenatal exposurel was associated with a decrement in mental development at 12 months among blacks and Hispanics. In later childhood, increasing pesticide metabolites were associated with decrements in perceptual reasoning, with a monotonic trend consistent with greater decrements with increasing prenatal exposure. Findings suggest that prenatal exposure to organophosphates negatively impacts cognitive development, particularly perceptual reasoning, with evidence of effects beginning at 12 months and continuing through early childhood.
[Engel SM, Wetmur J, Chen J, Zhu C, Barr DB, Canfield RL, et al. 2011. Environ Health Perspect :-. doi:10.1289/ehp.1003183]
- 7-Year Neurodevelopmental Scores and Prenatal Exposure to Chlorpyrifos, a Common Agricultural Pesticide
This is a longitudinal birth cohort study of inner-city mothers and children (Columbia Center for Children’s Environmental Health) to estimate the relationship between prenatal chlorpyrifos (CPF) exposure and neurodevelopment among cohort children at age 7 years. 265 children were sampled and researchers measured prenatal CPF exposure using umbilical cord blood plasma (picograms/gram plasma), and 7-year neurodevelopment. On average, for each standard deviation increase in exposure (4.61 pg/g), Full-Scale IQ declined by 1.4%, and Working Memory declined by 2.8%. These findings are important in light of continued widespread use of CPF in agricultural settings and possible longer-term educational implications of early cognitive deficits.
[Rauh V, Arunajadai S, Horton M, Perera F, Hoepner L, Barr DB, et al. 2011. Environ Health Perspect. doi:10.1289/ehp.1003160]
- Prenatal Exposure to Organophosphate Pesticides and IQ in 7-Year Old Children
Study conducted a birth-cohort study (CHAMACOS) among predominantly Latino farmworker families from an agricultural community in California and assessed exposure to OP pesticides by measuring dialkyl phosphate (DAP) metabolites in urine collected during pregnancy and from children at age 6 months and 1, 2, 3½ and 5 years. Averaged maternal DAP concentrations were associated with poorer scores for Working Memory, Processing Speed, Verbal Comprehension, Perceptual Reasoning, and Full Scale IQ. Children in the highest quintile of maternal DAP concentrations had an average deficit of 7.0 IQ-points compared with those in the lowest quintile.
[Bouchard MF, Chevrier J et al. 2011. Environ Health Perspect :-. doi:10.1289/ehp.1003185]
- Trends in the Prevalence of Developmental Disabilities in US Children, 1997–2008
A new report by the American Academy of Pediatrics reveals that roughly one in six children in the U.S. have developmental disabilities, particularly those that are linked to environmental exposure, which showcases the need for stricter policies to reduce the use of pesticides and other toxic chemicals. The study is based on National Health Interview Surveys of children aged 3 to 17 years over the 12-year period of 1997-2008. Results show that boys have a higher prevalence overall and for a number of select disabilities compared with girls. Prevalence of any developmental disability increased from 12.84% to 15.04% over 12 years. Autism, attention deficit hyperactivity disorder, and other developmental delays increased, whereas hearing loss showed a significant decline. These trends were found in all of the sociodemographic subgroups, except for autism in non-Hispanic black children. Daily News
[Boyle, C. et al 2011. American Academy of Pediatrics, (doi: 10.1542/peds.2010-2989]
- Impact of Prenatal Exposure to Piperonyl Butoxide and Permethrin on 36-Month Neurodevelopment
Research published February 7, 2011 in the online edition of the journal Peditatrics shows that children more highly exposed to pyrethroid insecticides and piperonyl butoxide (PBO), a synergist added to increase the potency of pyrethroids, are three times as likely to have a mental delay compared to children with lower levels. The study measured exposure to pesticides using maternal and umbilical cord plasma samples and in personal air samples, collected using backpack air monitors during pregnancy. Children were then tested for cognitive and motor development (using the Bayley Scales of Infant Development) at three years of age. Children with the highest prenatal exposures scored about 4 points lower on the test. That’s about the same intelligence loss caused by lead, Philip Landrigan, MD, a pediatrics professor and environmental health expert at New York’s Mount Sinai School of Medicine, told USA Today. Pyrethroid pesticides kill bugs by “being toxic to the developing brain,” Dr. Landrigan says. The results are “very believable and should be taken seriously.”
[Horton, et al. 2011. Pediatrics, Online February 7, 2011 (doi:10.1542/peds.2010-0133)]
Deficits and Increased Blood Pressure in School-Age Children Prenatally Exposed
Prenatal exposure to pesticides at levels that do not cause adverse health
effects in the mother can lead to delayed brain developmental in the child.
A definite negative effect was found in children, whose mother had been exposed
to pesticides during pregnancy. The effect was the strongest for motor coordination,
spatial performance and visual memory. Children were 1.5 to 2 years behind
in the development of these functions, which is a very marked shift at age
6-to-8 years, where brain development is particularly rapid. The researchers
also found increased blood pressure, likely a result of adverse effect on
brain nuclei responsible for regulation of cardiovascular functions.
[Harari, R. et al. 2010. Environ Health Perspect, 118:890–896]
- PON1 and Neurodevelopment in Children from the CHAMACOS Study Exposed to Organophosphate Pesticides in Utero
Paraoxonase 1 (PON1) detoxifies oxon derivatives of some organophosphate (OP) pesticides, and its genetic polymorphisms influence enzyme activity and quantity.Study ained to determine whether PON1 genotypes and enzyme measurements were associated with child neurobehavioral development and whether PON1 modified the association of in utero exposure to OPs (as assessed by maternal DAPs) and neurobehavior.Children with the PON1−108T allele had poorer MDI scores and somewhat poorer PDI scores. Children were less likely to display PDD when they or their mothers had higher ARYase activity and when their mothers had higher POase activity.Study concludes PON1 was associated with child neurobehavioral development, but additional research is needed to confirm whether it modifies the relation with in utero OP exposure.
[Eskenazi B., K. Huen, A. Marks, K.G.Harley, A. Bradman, D.B. Barr, et al. 2010.
Environ Health Perspect. 118: 1775-1781]
Exposure and Urban Residential Environment Characteristics as Determinants
of Early Childhood Neurodevelopment
Study found that high concentrations of chlorpyrifos in umbilical cord blood
(>6.17 pg/g) corresponds to a 6.5 point decrease in the Psychomotor Development
Index, and a 3.3 point decrease in the Mental development index in 3 year
olds.The study examined neighborhood characteristics such as poverty levels
and dilapidated housing, factors that are also linked to lower test scores.
Researchers were able to conclude that neighborhood characteristics and chlorpyrifos
exposure were independently associated with children’s neurodevelopment.
[Lovasi , G. et al. 2010. Am J Public Health. AJPH.2009.168419v1]
Disrupted: How Toxic Chemicals May Affect How We Think and Who We Are
First-ever biomonitoring report identifying toxic chemical pollution in people
from the learning and developmental disability community. Report examines
61 toxic chemicals present in project participants in the context of rising
rates of autism, attention-deficit hyperactivity disorder, and other learning
and developmental disabilities.
[Gonzalez, S. et al. 2010. The Learning and Developmental Disabilities Initiative]
Airborne Polycyclic Aromatic Hydrocarbon Exposure and Child IQ at Age 5 Years.
A mother’s exposure to urban air pollutants known as polycyclic aromatic
hydrocarbons (PAHs) can adversely affect a child’s intelligence quotient
or IQ. The Study found that children exposed to high levels of PAHs in New
York City had full scale and verbal IQ scores that were 4.31 and 4.67 points
lower than those of less exposed children.
[Perera, F. et al. 2009. Pediatrics, DOI: 10.1542/peds.2008-3506]
- Influence of Glutathione S-Transferase Polymorphisms on Cognitive Functioning Effects Induced by p,p’-DDT among Preschoolers
Study used data from 326 children assessed in a prospective population-based birth cohort at the age of 4 years. In that study, the McCarthy Scales of Children's Abilities were administrated by psychologists, organochlorine compounds were measured in cord serum, and genotyping was conducted for the coding variant Ile105Val from GSTP1 and for null alleles from GSTM1 and GSTT1. This study used linear regression models to measure the association between organochlorines and neurodevelopmental scores by GST polymorphisms. p,p'-DDT cord serum concentration was inversely associated with general cognitive, memory, quantitative, and verbal skills, as well as executive function and working memory, in children who had any GSTP1 Val-105 allele. GSTP1 polymorphisms and prenatal p,p'-DDT exposure showed a statistically significant interaction for general cognitive skills, quantitative skills, executive function, and working memory. There were no significant associations between p,p'-DDT and cognitive functioning at 4 years of age according to GSTM1 and GSTT1 polymorphisms. Results indicate that children with GSTP1 Val-105 allele were at higher risk of the adverse cognitive functioning effects of prenatal p,p'-DDT exposure.
[Morales E, Sunyer J, Castro-Giner F, Estivill X, et al. 2008. Environ Health Perspect. 116(11):1581-5.]
- Neonatal Exposure to Low Doses of Diazinon: Long-Term Effects on Neural Cell Development and Acetylcholine Systems
Researchers gave diazinon (DZN) to newborn rats on postnatal days 1-4, using doses (0.5 or 2 mg/kg) spanning the threshold for barely detectable cholinesterase inhibition, then evaluated the lasting effects on indices of neural cell number and size, and on functional markers of acetylcholine (ACh) synapses (choline acetyltransferase, presynaptic high-affinity choline transporter, nicotinic cholinergic receptors) in a variety of brain regions. DZN exposure produced a significant overall increase in cell-packing density in adolescence and adulthood, suggestive of neuronal loss and reactive gliosis; however, some regions (temporal/occipital cortex, striatum) showed evidence of net cell loss, reflecting a greater sensitivity to neurotoxic effects of DZN. Deficits were seen in ACh markers in cerebrocortical areas and the hippocampus, regions enriched in ACh projections. In contrast, there were no significant effects in the midbrain, the major locus for ACh cell bodies.These results indicate that developmental exposures to apparently nontoxic doses of DZN compromise neural cell development and alter ACh synaptic function in adolescence and adulthood. The patterns seen here differ substantially from those seen in earlier work with chlorpyrifos, reinforcing the concept that the various organophosphates have fundamentally different effects on the developmental trajectories of specific neurotransmitter systems, unrelated to their shared action as cholinesterase inhibitors.
[Slotkin TA, Bodwell BE, Levin ED, Seidler FJ.2008. Environ Health Perspect. 116(3):340-8]
Organochlorine Exposure and Measures of Behavior in Infancy Using the Neonatal
Behavioral Assessment Scale (NBAS)
Findings provide evidence for an association between low-level prenatal PCB
and DDE exposures and poor attention in early infancy.
[Sagiv SK, et al. 2008. Environ Health Perspect 116:666-673. doi:10.1289/ehp.10553]
- In Utero p,p’-DDE Exposure and Infant Neurodevelopment: A Perinatal Cohort in Mexico
The goal of this study was to assess the prenatal DDE exposure window and its effect on the psychomotor development index (PDI) and mental development index (MDI) during the first year of life. Authors recruited 244 children whose pregnancies and deliveries were uncomplicated, and whose mothers were monitored throughout the pregnancy. Participating mothers were not occupationally exposed to DDT (dichlorodiphenyltrichloroethane) but were residents of a zone in Mexico with endemic malaria. Third-trimester DDE level was significantly higher than the level at baseline, first, and second trimesters, but the differences never exceeded 20%. Only DDE levels during the first trimester of pregnancy were associated with a significant reduction in PDI. DDE was not associated with MDI.
A critical window of exposure to DDE in utero may be the first trimester of the pregnancy, and psychomotor development is a target of this compound. Residues of DDT metabolites may present a risk of developmental delay for years after termination of DDT use.
[Torres-Sánchez, L, Rothenberg,S, Schnaas, L, et al. 2007. Environ Health Perspect. 115(3): 435–439.]
Exposure and Stunting as Independent Predictors of Neurobehavioral Deficits
in Ecuadorian School Children
Children in Ecuador whose mothers were exposed to pesticides while pregnant
have diminished ability to copy geometric figures as part of a standardized
Stanford-Binet test as compared to a control group, according to the epidemiological
study. Adjusted regression analysis indicates that the exposed children experience
a developmental delay on this aptitude of four years. The researchers also
concluded that prenatal pesticide exposure may add to the already deleterious
effects of malnutrition.
[Grandjean, P. et al. 2006. Pediatrics, 117(3) pp. e546-e556]
of Prenatal Chlorpyrifos Exposure on Neurodevelopment in the First 3 Years
of Life Among Inner-City Children
A 2006 study linked the insecticide chlorpyrifos, which is used on some fruits
and vegetables, with delays in learning rates, reduced physical coordination,
and behavioral problems in children.
[Rauh, V. et al. 2006. Pediatrics, 118(6) pp. e1845-e1859 ]
- In Utero Exposure to Dichlorodiphenyltrichloroethane (DDT) and Dichlorodiphenyldichloroethylene (DDE) and Neurodevelopment Among Young Mexican American Children
Study investigated the relationship between prenatal exposure to dichlorodiphenyltrichloroethane (DDT) and dichlorodiphenyldichloroethylene (DDE) and neurodevelopment of Mexican farm-workers' children in California. Participants from the Center for the Health Assessment of Mothers and Children of Salinas study, a birth cohort study, included 360 singletons with maternal serum measures of p,p'-DDT, o,p'-DDT, and p,p'-DDE. Psychomotor development and mental development were assessed with the Bayley Scales of Infant Development at 6, 12, and 24 months. Results found a approximately 2-point decrease in Psychomotor Developmental Index scores with each 10-fold increase in p,p'-DDT levels at 6 and 12 months (but not 24 months) and p,p'-DDE levels at 6 months only. We found no association with mental development at 6 months but a 2- to 3-point decrease in Mental Developmental Index scores for p,p'-DDT and o,p'-DDT at 12 and 24 months, corresponding to 7- to 10-point decreases across the exposure range. Even when mothers had substantial exposure, breastfeeding was usually associated positively with Bayley scale scores. Prenatal exposure to DDT, and to a lesser extent DDE, was associated with neurodevelopmental delays during early childhood, although breastfeeding was found to be beneficial even among women with high levels of exposure. Countries considering the use of DDT should weigh its benefit in eradicating malaria against the negative associations found in this first report on DDT and human neurodevelopment.
[Eskenazi B, Marks AR, Bradman A, Fenster L, et al. 2006. Pediatrics.118(1):233-41.]
- Developmental neurotoxicity of industrial chemicals.
Neurodevelopmental disorders such as autism, attention deficit disorder, mental retardation, and cerebral palsy are common, costly, and can cause lifelong disability. Their causes are mostly unknown. A few industrial chemicals (eg, lead, methylmercury, polychlorinated biphenyls [PCBs], arsenic, and toluene) are recognised causes of neurodevelopmental disorders and subclinical brain dysfunction. Exposure to these chemicals during early fetal development can cause brain injury at doses much lower than those affecting adult brain function. Recognition of these risks has led to evidence-based programmes of prevention, such as elimination of lead additives in petrol. Although these prevention campaigns are highly successful, most were initiated only after substantial delays. Another 200 chemicals are known to cause clinical neurotoxic effects in adults. Despite an absence of systematic testing, many additional chemicals have been shown to be neurotoxic in laboratory models. The toxic effects of such chemicals in the developing human brain are not known and they are not regulated to protect children. The two main impediments to prevention of neurodevelopmental deficits of chemical origin are the great gaps in testing chemicals for developmental neurotoxicity and the high level of proof required for regulation. New, precautionary approaches that recognise the unique vulnerability of the developing brain are needed for testing and control of chemicals.
[Grandjean P and Landrigan PJ.2006. Lancet.368(9553):2167-78]
- Developmental neurotoxicity of pyrethroid insecticides: critical review and future research needs.
Pyrethroid insecticides have been used for more than 40 years and account for 25% of the worldwide insecticide market. Although their acute neurotoxicity to adults has been well characterized, information regarding the potential developmental neurotoxicity of this class of compounds is limited. There is a large age dependence to the acute toxicity of pyrethroids in which neonatal rats are at least an order of magnitude more sensitive than adults to two pyrethroids. There is no information on age-dependent toxicity for most pyrethroids. In the present review authors examine the scientific data related to potential for age-dependent and developmental neurotoxicity of pyrethroids. As a basis for understanding this neurotoxicity, authors discuss the heterogeneity and ontogeny of voltage-sensitive sodium channels, a primary neuronal target of pyrethroids. Authors also summarize 22 studies of the developmental neurotoxicity of pyrethroids and review the strengths and limitations of these studies. These studies examined numerous end points, with changes in motor activity and muscarinic acetylcholine receptor density the most common. Many of the developmental neurotoxicity studies suffer from inadequate study design, problematic statistical analyses, use of formulated products, and/or inadequate controls. These factors confound interpretation of results. To better understand the potential for developmental exposure to pyrethroids to cause neurotoxicity, additional, well-designed and well-executed developmental neurotoxicity studies are needed. These studies should employ state-of-the-science methods to promote a greater understanding of the mode of action of pyrethroids in the developing nervous system.
[Shafer TJ, Meyer DA, Crofton KM.2005. Environ Health Perspect. 113(2):123-36.]
- In Utero Pesticide Exposure, Maternal Paraoxonase Activity, and Head Circumference.
Although the use of pesticides in inner-city homes of the United States is of considerable magnitude, little is known about the potentially adverse health effects of such exposure. Recent animal data suggest that exposure to pesticides during pregnancy and early life may impair growth and neurodevelopment in the offspring. To investigate the relationship among prenatal pesticide exposure, paraoxonase (PON1) polymorphisms and enzyme activity, and infant growth and neurodevelopment, authors conducted a prospective, multiethnic cohort study of mothers and infants delivered at Mount Sinai Hospital in New York City. In this report the effects of pesticide exposure on birth weight, length, head circumference, and gestational age among 404 births between May 1998 and May 2002 were evaluated. Pesticide exposure was assessed by a prenatal questionnaire administered to the mothers during the early third trimester as well as by analysis of maternal urinary pentachlorophenol levels and maternal metabolites of chlorpyrifos and pyrethroids. When the level of maternal PON1 activity was taken into account, maternal levels of chlorpyrifos above the limit of detection coupled with low maternal PON1 activity were associated with a significant but small reduction in head circumference. In addition, maternal PON1 levels alone, but not PON1 genetic polymorphisms, were associated with reduced head size. Because small head size has been found to be predictive of subsequent cognitive ability, these data suggest that chlorpyrifos may have a detrimental effect on fetal neurodevelopment among mothers who exhibit low PON1 activity.
[Berkowitz GS, Wetmur JG, Birman-Deych E, Obel J, et al. 2004. Environ Health Perspect.112(3):388-91.]
Development: A study on the Human Health Impacts of Pesticides
A study found a strong link between pesticide exposure and cognitive abilities
among farmers' children in India. The study revealed serious mental development
disorders that ranged from severely impaired analytical abilities, motor skills,
concentration and memory among the children in the chemical-intensive cotton
belts of India (A 2004 study reveals serious mental development disorders
that range from severely impaired analytical abilities, motor skills, concentration
and memory among the children in the chemical-intensive cotton belts of India.
[Kuruganti, K. 2003. Greenpeace. Bangalore India.]
Harms Way: Toxic Threats to Child Development.
Animal studies link pesticides in the organochlorine, organophosphate (OP),
and pyrethroid families to hyperactivity. OPs are also linked to developmental
delays, behavioral disorders and motor dysfunction in animal studies.
[Shettler, T., et al., 2000. Greater Boston Physicians for Social Responsibility:
- Pesticides and Inner-city Children: Exposures, Risks, and Prevention.
The organophosphate insecticide chlorpyrifos and certain pyrethroids are the registered pesticides most heavily applied in cities. Illegal street pesticides are also in use, including tres pasitos (a carbamate), tiza china, and methyl parathion. In New York State in 1997, the heaviest use of pesticides in all counties statewide was in the urban boroughs of Manhattan and Brooklyn. Compounding these risks of heavy exposures are children's decreased ability to detoxify and excrete pesticides and the rapid growth, development, and differentiation of their vital organ systems. These developmental immaturities create early windows of great vulnerability. Recent experimental data suggest, for example, that chlorpyrifos may be a developmental neurotoxicant and that exposure in utero may cause biochemical and functional aberrations in fetal neurons as well as deficits in the number of neurons. Certain pyrethroids exert hormonal activity that may alter early neurologic and reproductive development. Assays currently used for assessment of the toxicity of pesticides are insensitive and cannot accurately predict effects to children exposed in utero or in early postnatal life. Protection of American children, and particularly of inner-city children, against the developmental hazards of pesticides requires a comprehensive strategy that monitors patterns of pesticide use on a continuing basis, assesses children's actual exposures to pesticides, uses state-of-the-art developmental toxicity testing, and establishes societal targets for reduction of pesticide use.
[Landrigan,PJ, Claudio,L, Markowitz, SB et al. 1999. Environ Health Perspect. 107(Suppl 3): 431–437.]
Anthropological Approach to the Evaluation of Preschool Children Exposed to
Pesticides in Mexico
In a comparative study in Mexico, children exposed to pesticides demonstrated
decreases in stamina, coordination, memory, and the ability to draw familiar
[Guillette, E., et al. 1998. Environmental Health Perspectives, 106(6):347-353.]