Authorities in the US state of Pennsylvania have begun an extensive sampling of chemical contaminants after the discovery of intersex fish in three of the state's major rivers.
Male fish carrying eggs were found in the Susquehanna, Delaware and Ohio river basins, a sign that the water may be tainted with chemicals, the US Geological Survey found in new research released.
Amanda Witman, a Department of Environmental Protection spokeswoman, said the agency is testing two tributaries of the Susquehanna River: Juniata River and Swatara Creek.
The USGS research said that two fish species, smallmouth bass and white sucker, were exhibiting intersex characteristics due to exposure to endocrine-disrupting chemicals - hormones and hormone-mimicking chemicals that caused the male fish to produce eggs.
"The sources of estrogenic chemicals are most likely complex mixtures from both agricultural sources, such as animal wastes, pesticides and herbicides, and human sources from wastewater treatment plant effluent and other sewage discharges," Vicki Blazer, a fish biologist and lead author of the USGS study was quoted as saying by the Los Angeles Times.
Estrogenic chemicals disrupt the endocrine system, which regulates the release of hormones such as estrogen and testosterone. This interferes with the fish's ability to reproduce.
Some of the compounds and contaminants found were new, and researchers had to develop new laboratory test procedures to measure them, Witman said.
"The results will provide a much better understanding of the kinds, distribution and concentrations of these compounds," she said.
This is not the first time intersex fish have been discovered in US rivers. Since 2006, the USGS has found similar characteristics during several surveys of bass in the Potomac River, the report said.