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Endocrine Disrupting Chemicals May Target Fish Hearts

(Beyond Pesticides, February 5, 2014) According to a new study published in Environmental Health Perspectives, chemical contaminants in waterways that mimic estrogen -endocrine disruptors- target developing heart valves in fish and impair the growth of fish hearts. The study illustrates that these hormone-mimicking compounds, which include some pesticides, pharmaceuticals, and other household chemicals often found in sewage effluent and runoff that flows into waterways, are being linked to mounting science that show serious human and environmental adverse effects.

Researchers from the Fish Health Branch of the U.S. GeoDigital StillCameralogical Survey (USGS) and the Carnegie Institution for Science exposed zebrafish embryos to water from 19 sites in the Susquehanna, Delaware, Allegheny and Shenandoah watersheds. Water from 16 of the sites triggered proteins in the fish that were estrogen receptors, indicating that the rivers contained endocrine disrupting chemicals. These receptors are attached to DNA, which turn genes on and off. While such activity is common in the liver, this is the first experiment to show estrogenic activity in heart valves.

“This tells us that endocrine-disrupting chemicals could lead to improper heart development. We were quite surprised, since this is something that others hadn’t observed before,” said study co-author Luke Iwanowicz, PhD, and research biologist with the U.S. Geological Survey based in West Virginia.

In the study, “Transgenic Zebrafish Reveal Tissue-Specific Differences in Estrogen Signaling in Response to Environmental Water Samples,” most of the water samples activated estrogen receptors in both the heart valves and the liver, but when the river water was more diluted, five of the samples activated receptors only in the heart valves. According to the authors, endocrine disrupting chemicals often do not act in a typical way, but can have health effects at low doses and no effects or different effects at high doses.  Previous research supports the growing importance of understanding low dose exposures, and one 2012 report in particular documents extensive scientific research on the low dose effects of endocrine disruptors.

The researchers, however, did not analyze the specific chemical makeup of the river water and so these heart valve findings are not linked to any specific chemical. However, the presence of endocrine disrupting contaminants in U.S. waterways is well-documented. The USGS identified contaminants, including pesticides in the Potomac River which flows through downtown Washington, DC, that could be responsible for the alarming discovery of “intersex fish”- male fish producing eggs. The suspected chemicals include: atrazine, a common herbicide used in agriculture and on lawns that is already linked to sexual abnormalities in frogs; insecticides chlorpyrifos and endosulfan; the herbicide metolachlor; and two chemicals used to add fragrance to perfumes, soaps and other products, tonalide and galaxolide. Similarly, the antibacterial pesticide triclosan, also an endocrine disruptor and frequently detected in several U.S. waterways, was shown to hinder muscle contractions at a cellular level, slow swimming in fish, and reduce muscular strength in mice. In similar experiments triclosan was found to impair the ability of isolated heart muscle cells and skeletal muscle fibers to contract.

In wildlife and humans, endocrine disrupting effects include direct effects on traditional endocrine glands, their hormones and receptors such as estrogens, anti-androgens, and thyroid hormones, as well as signaling cascades that affect many of the body’s systems, including reproductive function and fetal development, the nervous system and behavior, the immune and metabolic systems, the liver, bones and many other organs, glands and tissues. Hundreds of scientific articles have been published across the globe demonstrating how a broad selection of chemicals can interfere with the normal development at extremely low levels of exposure. Scientists discovered effects for some widely used chemicals at concentrations thousands of times less than federal “safe” levels of exposure derived through traditional toxicological tests.

A 2012 study from a group of renowned endocrinologists finds that even low doses of endocrine disrupting chemicals can cause certain human disorders, highlighting various epidemiological studies that show that environmental exposures to endocrine disrupting chemicals are associated with human diseases and disabilities. The authors of the new study conclude that the effects of low doses cannot be predicted by the effects observed at high doses, and therefore recommend fundamental changes in chemical testing and safety determination to protect human health. The U.S. Environmental Protection Agency (EPA) is tasked with evaluating chemicals for their endocrine disrupting potential, but is still in the process of finalizing a screening protocol, decades after the agency was tasked to do so. According to the agency, it would be another decade before their protocol is up and ready.

In the meantime, endocrine disrupting chemicals continue to contaminate sewage effluent and runoff that flows into waterways adversely impacting fish, amphibians and other wildlife, and eventually the human public. A 2013 UN report, considered the most comprehensive report on endocrine disruption in humans to date, highlights some association between exposure to endocrine disruptors and health problems, including the potential for such chemicals to contribute to the development of non-descended testes in young males, breast cancer in women, prostate cancer in men, developmental effects on the nervous system in children, attention deficit /hyperactivity in children  and thyroid cancer. Beyond Pesticides’ Pesticide-Induced Disease Database features a wealth of studies that have linked pesticide exposures to adverse impacts on the endocrine system. These studies explore outcomes and mechanisms for several health effect endpoints including cancer, developmental and learning disorders, Parkinson’s disease, reproductive health.

For more on endocrine disrupting chemicals, download Beyond Pesticides’ Endocrine Disruption brochure (bi-fold), or read Beyond Pesticides article, Pesticides That Disrupt Endocrine System Still Unregulated by EPA.

All unattributed positions and opinions in this piece are those of Beyond Pesticides.

Source: Environmental Health News


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