Context: Wastewater treatment plants (WWTP) clean up dirty water that is flushed and drained from homes, businesses and industry. Generally, solids and organic matter are removed, and the water is oxygenated before it is returned to a water system. The main purpose of treating sewage is to control disease by removing bacteria, but these plants do not necessarily take out all the pollutants.
In some cities, the facilities also treat yard and street runoff that is collected through storm sewers. WWTPs can become overloaded when excess water enters a plant following a large rainstorm, hurricane or during other severe weather. In these cases, the capacity to treat water is exceeded and untreated sewage and runoff is released directly into lakes and streams. The overflows often result in beach closings and restrictions on fishing and shellfish harvesting.
Concern is growing about WWTPs releasing chemicals with biological activity -- including nutrients, personal care products, estrogenic compounds and pharmaceuticals -- into the environment. (Daughton 2007; Khetan and Collins 2007; USEPA 2004).
Estrogens are a group of chemically similar steroid hormones that are responsible for guiding development of feminine traits and sexual characteristics in females. Males also need estrogens although at much lower levels. The three major natural hormones are estradiol (most potent), estrone and estriol. All vertebrate animals make estrogens but in differing amounts depending on the species.
Many pharmaceuticals contain synthetic estrogens alone or in combination with other synthetic or natural hormones. Ethynylestradiol, for example, is manufactured and used in birth control pills as an oral contraception. Physicians prescribe other xenoestrogens to protect against osteoporosis and treat menopause symptoms, breast cancer and prostate cancer.
Some compounds found in household products, pesticides and industrial chemicals can act like estrogens. These estrogenic compounds include bisphenol A, DDT and detergent components (nonylphenol and octylphenol).
Estrogen hormones are moderately hydrophobic (don't mix readily with water) and weakly adsorb to sediment and soil. WWTP remove most of the estrogens but some hormones can pass through treatment plants intact, ending up in the environment and possibly in drinking water.
Importantly -- and rarely discussed -- is that the majority of the hormones removed in the WWTP process bind to the solid sludge, which can be spread on fields as fertilizer, buried or burned. Little is known about where these hormones end up. No one knows if estrogens and estrogenic chemicals from the treated or untreated sewage water and sludge are environmental health concerns for people. Effects on the reproductive development and behavior of sheep, however, have been reported.
Adverse effects of WWTP effluent on fish living downstream of the plants is well documented. Field and laboratory studies have shown altered development and reproduction in fish exposed to effluent discharge. In one study, the synthetic estrogen ethynylestradiol was associated with the collapse of a fish population living in an experimental lake treated with the hormone.
Recycled wastewater often becomes drinking water. Public water systems use surface water from lakes and rivers and groundwater pumped from shallow and deep aquifers. Also, some WWTP effluent is pressure injected into aquifers, which are supposed to be geologically separated from drinking water aquifers. In communities with particularly scarce drinking water resources, treated effluent from WWTPs constitutes part of the source water for humans. |
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What did they do? The research team obtained four sediment cores from two sites on the River Ouse in the UK in 2004 and 2005. One was a freshwater sampling site at Ditchling, and the second was an estuarine sampling site at Lewes. Labadie et al. wanted to determine the extent estrone, estradiol and ethynylestradiol were being transported vertically through sediment under waters receiving effluent from waste water treatment plants (WWTP).
The Ditchling site is 200 meters downstream of a small treatment plant. The river's stratified sediment is composed of clay with an overlying layer of sand/silt. Estrogen concentrations in overlying surface waters at both sites were predicted using the Georeferenced Regional Exposure Assessment Tool for European Rivers (GREAT-ER 1.0). The model predicted Ditchling would have the highest water estrogen concentrations.
The Lewes is 5 kilometers downstream of the nearest WWTP. The estuarine sediment is composed of clay, and the predicted water estrogen concentrations were lower than the Ditchling site.
Each sediment core was examined for estrogenic substances using the YES assay and liquid chromatography combined with mass spectrometry (LC-MS). YES, the Yeast Estrogen Screen assay, uses genetically engineered yeast containing the human estrogen receptor which, which activated, produces a signal that is easily and reliably measured. When the recombinant yeast are exposed to an estrogen, they change color. LC-MS was used to quantify the amounts of estrone, estradiol and ethinylestradiol in the sediment cores.
The ages of the core sediments were dated using radioisotope methods. Standard techniques were used to determine total organic carbon, particle size distribution and shear strength, water content and other physical characteristics.
What did they find? Estrogens, and in particular estrone, were transported vertically in sediments at both sites. Estrogenic activity and estrone concentrations were greatest below surface at the sand/silt and clay interface at the Ditchling site.
As can be seen in the figure to the right, estrone levels were approximately 28.8 parts per billion (ppb) between 10 and 18 cm below ground, which was about 9 times higher than the surface sediment concentration of approximately 3.3 ppb. |
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The Ditchling site was closest to the WWTP and was predicted to have higher water estrogen concentrations. YES and LC-MS, the two methods of measuring sediment estrogens, were in good agreement. Estrone was detected down to a depth of approximately 20 cm and the sediment age was determined to be at least 120 years old.
In contrast, estrone concentrations at the Lewes site steadily decreased with depth. This was probably due to the clay-rich nature of the Lewes site. Estrone was detected in the core down to 12 cm in sediment that was at least 120 years old.
The YES and LC-MS estrogen measurements did not agree. Independent of depth, less than 35% of the estrogenicity detected by YES could be attributed to estrone, estradiol and ethynylestradiol suggesting that approximately 65% was due to other estrogenic substances in the Lewes sediment.
What does it mean? Estrogens and estrogenic compounds released into the environment with wastewater effluent can migrate out of the water and down into riverbed sediments. The findings are important because they demonstrates that hormones and chemicals can reach and may contaminate shallow groundwater. People can be exposed to the pollutants by drinking the water or irrigating with it.
This is the first field evidence that estrogens from WWTP's can move down into the sediment under effluent receiving waters. The results challenge prior beliefs about the life and transport of estrogenic substances. One is that estrogen concentrations in WWTP effluent are so low they are of little ecological consequence. Another is that estrogens are rendered harmless either by dilution in large water bodies or by clinging to suspended particles.
Estrogen movement through the water bottom depended on if it was sand or clay. In this study, estrogens traveled through sediment, especially the sandy sediment, to at least 20 cm. It is not known how deep estrogens would go if the sediment was mostly sand, as is found in Florida and other geologically similar areas.
Other unknown estrogenic substances from the sewage effluent appear to be moving through clay sediment. Although they were not identified, these compounds may include surfactants, for example nonylphenol and octylphenol, which are ubiquitous components of industrial and residential detergents.
It is both fair and important to realize that the current WWTP technology was not designed to remove nutrients, estrogenic compounds, pharmaceuticals and personal care products. It is fair, because the outdated wastewater treatment methods should not shoulder the blame; it is important, because it is clear that current technologies are creating risks of unknown magnitude for public health. |
