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In two separate studies, U.S. Geological Survey (USGS) scientists demonstrated that hormones such as estrogen can biodegrade in stream and groundwater environments. This is an important finding because the science, regulatory, and environmental communities have concerns about the environmental fate of endocrine-disrupting chemicals, such as hormones, in the human wastewaters discharged to the environment from wastewater treatment plants and domestic septic systems. The natural female sex hormone17ß-estradiol (estrogen) is made in the human body, and is an important chemical messenger related to female sexual development and reproduction. When concentrated in the environment by the disposal of treated wastewaters there is concern that elevated levels of 17ß-estradiol and other estrogenic chemicals can cause feminization of fish and wildlife exposed to the chemicals. Even though hormones are generally present in the environment near wastewater releases to streams and groundwater, they tend to absorb to sediment and/or degrade during transport.
USGS scientists published the results of a study in Environmental Science and Technology that demonstrated there is a significant potential for the biodegradation of three hormones, estrone, 17ß-estradiol, and testosterone, in the bottom sediments of streams that received wastewater from sewage treatment plants (Bradley and others, 2009). Laboratory experiments showed that all three compounds were efficiently degraded in surface water sediments under conditions where oxygen is present.
USGS scientists documented in Environmental Science and Technology that 17ß-estradiol biodegrades in the groundwater of a sandy aquifer on Cape Cod, Massachusetts, contaminated with wastewater from a sewage treatment plant (Barber and others, 2009). The scientists tested the ability of 17ß-estradiol to be transported in groundwater by injecting a solution of non-degrading tracer (bromide) and 17ß-estradiol into the subsurface. The resulting subsurface plume or cloud of tracer was allowed to move naturally with the groundwater. As the plume drifted it was monitored via multilevel samplers (see diagram). The results showed that the subsurface movement of 17ß-estradiol was retarded (reduced) when compared to bromide. Laboratory degradation experiments confirmed that the 17B-estradiol was being degraded by naturally occurring bacteria.
The results of these two studies indicate that biodegradation may give surface water and groundwater environments a natural capacity to reduce the levels of hormones in impacted streams and groundwater and reduce the potential impacts on fish and wildlife.
In addition to 17ß-estradiol, the scientists also discovered that an antibiotic (sulfamethoxazole) is resistant to biodegradation in subsurface environments and a common detergent degradation product (4-nonylphenol) is biodegradable but to a lesser extent than 17ß-estradiol. In a subsurface tracer test the antibiotic sulfamethoxazole was transported at almost the same rate as bromide (the conservative non-absorbing tracer). In addition, the researchers found sulfamethoxazole throughout most of an existing subsurface wastewater plume at the Cape Cod Toxic Substances Hydrology Program Research Site, Massachusetts. The occurrence of sulfamethoxazole in the contamination plume that is kilometers long and decades old is further evidence that sulfamethoxazole is resistant to natural attenuation in subsurface environments. Previous studies on Cape Cod have shown that free-living bacteria and organic-wastewater contaminants occur in the same wells where sulfamethoxazole was detected. This result indicates that subsurface bacteria have been exposed to antimicrobial compounds for decades. The scientists also conjecture that sulfamethoxazole may be a useful tracer or indicator of subsurface contamination by wastewater from sewage treatment plants.
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