What are Endocrine Disrupting Compounds?
EDCs are chemical compounds that disrupt the normal functioning of the endocrine system, the body’s system responsible for hormone regulation.
There are several endocrine-specific organs throughout the body that enable chemical communication between cells, these include: the hypothalamus, pituitary gland, thyroid glands, parathyroid glands, pancreas, adrenal glands, testes, and ovaries.
Many other cells throughout the body also secrete hormones, making up what is sometimes deemed the “diffuse endocrine system.
These include cells such as the myocetes in the heart atria and epithelial cells in the stomach and small intestine. All organs and bodily processes are affected by hormone signalling.
When the endocrine system is disrupted, many aberrant outcomes may occur. Some of these include: abnormal sex ratios in populations of affected organisms, abnormal sex hormone ratios in individuals, underdeveloped sex organs, feminization, courtship behaviour changes, low sperm count, and intersex.
Sources of EDCs
A variety of environmental chemicals can disrupt the endocrine systems of humans and other animals. Some common sources of endocrine disrupting compounds are:
- Detergents, herbicides (i.e., alkyphenols)
- Pesticides (i.e., lindane, dieldrin)
- Insecticides (i.e., chlordane, trichlorfon)
- Water treatment, paper manufacturing, incinerators (e.g. dioxins, CDDs)
- Cigarette smoke, auto exhaust, insulation, styrofoam (styrenes)
- Paints/epoxy resins
- PVCs/plastics
- Fungicides (i.e., atrazine, alachor)
- Flame retardants (i.e., PBB)
- Contraceptive pills (i.e., estradiol)
Poultry Litter Contains EDCs:
One source of endocrine disrupting compounds that affects organisms of the Chesapeake Bay is chicken litter applied to fields as fertilizer. The lower Eastern Shore of the Chesapeake Bay is home to some of the largest poultry production operations in the U.S. A decade ago, the lower Eastern Shore poultry industry generated approximately 1.6 billion pounds of poultry litter annually.
Based on an increase in poultry production, this estimate is believed to have substantially increased since then. Most of the litter is ultimately applied to soils on local farmlands and serves as fertilizer for ground crops. Although chicken litter is an effective fertilizer for crops, it can pose problems to aquatic organisms if it is not retained by soil and instead is able to run-off into surrounding water systems.
Thus, the primary cause for concern surrounding the use of poultry litter as fertilizer is the contamination of the aquatic environment, via agricultural runoff, through the release of steroid
hormones in the litter. When no-till practices are used, fertilizer is applied to the surface of the soil and upon heavy rain events, runs-off into drainage ditches, streams, and rivers, thereby polluting water with endocrine disrupting compounds and other toxic chemicals.
The majority of estrogens excreted by poultry are estriol, estradiol and estrone. There are also other contaminants present in poultry litter including pesticides and trace metals. Recent data indicate that, based on analyses of multiple samples, Eastern Shore poultry litter contains 17b-estradiol, as well as a variety of contaminants including current use and historic pesticides, metals and antibiotics.
The organic compounds observed in these litter samples included traces of the banned organochlorine pesticides lindane, DDT & metabolite DDE, as well as currently used pesticides including chlordane, acetachlor, metolachlor, permithrin, cyhalothrin, and atrazine, and the PAH, benz[a]anthracene.
Most of these organics were present in low ppb concentrations (ng/g) except atrazine at levels of 0.34 to 1.3 ?g/g. Also of note was the presence of the antibiotic chlortetracycline in the concentration range of 1.2-1.6 ng/g. High concentrations of several trace metals including copper (400-500 ?g/g), zinc (450-700 ?g/g), and arsenic (30-45 ?g/g) were found in the poultry litter samples as well.
Oestrogens are relatively hydrophobic (log Kow generally in the 2.6-4.0 range) and have a low solubility in water (0.8-13.3 mg/L). These characteristics tend to make oestrogen-like compounds relatively stable, resistant to microbial degradation and bioavailable to aquatic organisms, resulting in chronic exposures.
Field surveys of soils, surface and ground waters have demonstrated environmentally-significant levels of oestrogen’s surrounding agricultural areas of the lower Eastern Shore. Recent data has demonstrated that runoff from experimental agricultural plots, fertilized with poultry litter, leach hormones that act as EDCs.
These hormones are contained in surface runoff and are measured in biologically-relevant concentrations (5-85 ng/L) in receiving waters months after field litter applications.
Effects of Poultry Litter on Fish:
Recent efforts through collaborations at the University of Maryland’s Aquatic Pathobiology Laboratory have shown that poultry litter leachates can effect fish health. Exposure of fish larvae to poultry litter extracts, in concentrations seen in agricultural runoff, is associated with several abberant outcomes: (1) intersex, (2) a reduction in spermatozoa, and (3) a shift in gender ratio.
Intersex (the state of having both male and female characteristics, although not functionally) has been observed in the testes of male minnows exposed to poultry litter extracts. The degree of gonadal maturity, observed as the relative proportion of spermatozoa and spermatids, can also be
affected in association with exposure to both 17b-estradiol and environmentally-realistic concentrations of estradiol equivalents from poultry litter extracts.
USGS recently reported intersex in smallmouth bass (Micropterus dolomieu) taken from the South Branch of the Chesapeake Bay’s Potomac River. Agriculture, principally integrated poultry industry and beef cattle production, is a primary part of the Potomac headwaters regional economy.
The land that drains to the headwaters of portions of the South Branch was ranked first in terms of poultry litter production and the number of poultry houses/feedlots in sub water sheds of the Potomac. Also of recent interest are data from the Maryland Department of Natural Resources focusing on white perch and yellow perch.
There appears to be an association between altered gender ratio in these species and their residency in certain regions of the Chop tank River, the Patuxent River, the Severn River and areas of the Upper Bay.
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