A: There are many chemicals in our environment that can mimic the natural estrogen that animals make to regulate their sexual development and reproductive systems. These include detergent additives, synthetic estrogens found in birth control pills and estrogen replacement therapy drugs, plastics additives, some pesticides, and livestock hormones. Many of these are common household materials, and they end up in our wastewater and sewage. Sewage treatment plants also receive natural human estrogen that is excreted. Conventional water and sewage treatment doesn?t remove them efficiently, and so they end up being discharged into our rivers and other surface waters. Livestock hormones can leach from large animal operations directly into surface waters. Estrogen and estrogen mimics have been measured in sewage treatment plant effluent and in their receiving waters throughout the industrialized world."