(Beyond Pesticides, September 29, 2009) A new study reveals that children exposed to agricultural pesticides applied near their home have up to twice the risk of developing the most common form of childhood leukemia, according to the Northern California Cancer Center (NCCC). The study, â€śResidential proximity to agricultural pesticide applications and childhood acute lymphoblastic leukemia,â€ť published in the October issue of Environmental Research, used a unique California database to reveal an elevated risk in acute lymphoblastic leukemia (ALL) among children living near applications of certain categories of pesticides used in agriculture.
The study, led by Rudolph Rull, Ph.D., shows an elevated risk of ALL associated with moderate exposure, but not high exposure, to pesticides classified as organophosphates (odds ratio (OR) 1.6), chlorophenoxy herbicides (OR 2.0), and triazines (OR 1.9), and with agricultural pesticides used as insecticides (OR 1.5) or fumigants (OR 1.7).
California is one of the few states in the country that requires active reporting of pesticide applications, including time, place, and the type and amount of pesticide used. For this study, researchers were able to link childrenâ€™s entire residential histories from birth to the time of case diagnosis to this pesticide-use reporting database and identify agricultural pesticides that were applied within one-half mile of each residence.
The innovative use of residential histories allowed the researchers to look at different time periods of exposure, such as the childâ€™s lifetime or first year of life, while accounting for changing addresses during childhood. The University of California, Berkeley, collected the residential histories from 213 children diagnosed with ALL and 268 children without leukemia enrolled in the Northern California Childhood Leukemia Study. The scientists selected over 100 of the most commonly used pesticide active ingredients to examine from over 600 used on crops between 1990 and 2002, the time period of the study. The childrenâ€™s lifetime exposure to these ingredients is ranked into three levels: low, moderate, and high.
The researchers identified over 600 different pesticide active ingredients applied near residences during the study period. A total of 118 of those were selected for the study due to their frequent use and if the chemical is listed as one of the following:
â€˘ Probable or possible carcinogen identified on US EPAâ€™s List of Chemicals Evaluated for Carcinogenic Potential, the International Agency for Research on Cancer (IARC), or the US National Toxicology Program (NTP);
â€˘ Developmental or reproductive toxicant as defined by the State of California Proposition 65 Chemicals Known to Cause Developmental or Reproductive Harm;
â€˘ Neurologic cholinesterase inhibitors as designated by California Department of Pesticide Regulation;
â€˘ Suspected genotoxins on the basis of at least two positive results in genetic toxicity assays; or,
â€˘ Suspected endocrine disruptors listed by Dr. Colborn, Illinois EPA or the Keith List (1997).
Organophosphates are a family of insecticides that are derived from World War II nerve agents. They are cholinesterase inhibitors, meaning that they bind irreversibly to the active site of an essential enzyme for normal nerve impulse transmission, acetylcholine esterase (AchE), inactivating the enzyme. Examples of the 22 organophosphate pesticides the study identified include chlorpyrifos, diazinon, malathion, and trichlorfon.
â€śThese initial findings suggest that there may be a specific agent or set of agents that can increase the risk of this disease among children,â€ť said Dr. Rull.
A recent study, published in the August 2009 issue of the journal Therapeutic Drug Monitoring, â€śPediatric Acute Lymphoblastic Leukemia and Exposure to Pesticides,â€ť by researchers at the Lombardi Comprehensive Cancer Center at Georgetown University, also found an association between organophosphate pesticide exposure and development of childhood ALL, a cancer that develops most commonly between three and seven years of age.
In addition, according to Beyond Pesticidesâ€™ research on childhood ALL link to pesticide exposure, several previous studies show an increased risk. A partial list of such studies follows.
â€˘ Looking at residential proximity to agricultural pesticides, a population-based case-control study of early childhood cancer, ages 0-4 years, in California finds an elevated risk for leukemia associated with probable and possible carcinogen use and with nearby agricultural applications of organochlorines and organophosphates during pregnancy (metam sodium OR 2.05 and dicofol OR 1.83).
â€˘ A study of household pesticide exposure and childhood acute leukemia finds an increased risk for maternal home insecticide use during pregnancy (OR 1.8) and during childhood (OR 1.7), and with garden insecticide use (OR 2.4) and fungicide use (OR 2.25) during childhood. Pyrethroid and lindane lice shampoo treatment is also associated with childhood acute leukemia (OR 1.9). The majority of the childhood cancers were acute lymphocytic leukemia.
â€˘ A California study shows childrenâ€™s exposure to insecticide use is associated with a five-fold increase in childhood ALL (OR 5.0).
â€˘ A population-based case-control study of childhood ALL finds an increased risk for homeowner use of indoor insecticides and garden and interior plant pesticides, in particular with use during pregnancy and among carriers of the CYP1A1m1 and CYP1a1m2 gene mutations.
â€˘ Children with Downâ€™s syndrome have about a 20-fold increased risk for developing leukemia. A case-control study of acute leukemia in children with Downâ€™s syndrome finds a positive association for acute lymphoblastic leukemia and maternal exposure to professional pest exterminations (OR 2.25) and to any pesticide (OR 2.18).
â€˘ A hospital-based case-control study in Italy finds a positive association with paternal work as a farmer and childhood ALL.
â€˘ A population based case-control study in China of childhood leukemia cases finds an association between ALL and maternal occupational exposure to pesticides (OR 3.5).
Beyond Pesticides supports organic agriculture as effecting good land stewardship and a reduction in hazardous chemical exposures for workers on the farm. The pesticide reform movement, citing pesticide problems associated with chemical agriculture, from groundwater contamination and runoff to drift, views organic as the solution to a serious public health and environmental threat. Organic agriculture embodies an ecological approach to farming that does not rely on or permit toxic pesticides, chemical fertilizers, genetically modified organisms, antibiotics, sewage sludge, or irradiation. Instead of using these harmful products and practices, organic agriculture utilizes techniques such as cover cropping, crop rotation, and composting to produce healthy soil, prevent pest and disease problems, and grow healthy food and fiber.
Looking for information on specific pesticides? Find data on more than 80 pesticides commonly used in the U.S. in the Pesticide Gateway. Beyond Pesticides created this database tool to provide decision and policy makers, practitioners and activists with easier access to current and historical information on pesticide hazards and safe pest management, drawing on and linking to numerous sources and organizations that include information related to pesticide science, policy and activism.