Evidence of Endocrine Disruption Unexpectedly Found in Minnesota Lakes

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Endocrine disrupting chemicals and indicators of endocrine disruption were found in several Minnesota lakes with surrounding urban, residential, agricultural, and forested land uses. The lakes do not directly receive discharges from industries or wastewater-treatment plants; however, they are used for recreation, and they receive water from widely scattered sources. The presence of both male and female characteristics is known to occur in fish exposed to chemicals that are hormonally active. Such evidence is commonly found in streams affected by point sources discharges from wastewater-treatment plants and industries. This study, conducted by a team of scientists from the U.S. Geological Survey (USGS), St. Cloud State University, and the Minnesota Pollution Control Agency, documents that endocrine disrupting chemicals and endocrine disruption in fish can occur in lakes receiving chemicals from diffuse nonpoint sources.

Lake Owasso, Minnesota is surrounded by urban land use

Lake Owasso, Minnesota, is surrounded by urban land use and has eutrophic (high nutrient concentrations in the water) conditions. Many of the fish sampled in the lake showed signs of intersex (presence of both male and female characteristics).

Indicators of Endocrine Disruption

Vitellogenin, a female egg-yolk protein not typically found in male fish, was found in several species of wild, male fish in the studied lakes. The presence of vitellogenin in male fish is commonly used as an indicator of endocrine disruption. The scientists also placed cages containing male fathead minnows in the lakes. A few of the caged male fathead minnows also produced vitellogenin after exposure to the lake water for 21 days. The scientists observed other indicators of endocrine disruption, such as male fish having female egg cells (oocytes) in their testes (commonly referred to as gonadal intersex).

Endocrine Disrupting Chemicals

Natural steroidal hormones common in wastewaters, such as 4-androstene-3, 17-dione, 17β-estradiol, and estrone, were detected at levels that have been found to cause adverse health effects. Other potential endocrine disrupting compounds, including bisphenol A (a plastic- and epoxy-manufacturing ingredient) and alkylphenols (the breakdown products of surfactants used in detergents and cleaning products), were found at concentrations similar to those found in streams downstream of wastewater treatment plant discharges.

"We were surprised to see the same types of compounds found in wastewater treatment plant discharges in these Minnesota lakes. This study illustrates a need for future research to learn more about where these chemicals are coming from and the potential effects on the fish."
-- USGS scientist Jeffrey Writer

What Does it All Mean?

The occurrence of fish with indicators of endocrine disruption along with the occurrence of endocrine disrupting chemicals in the lakes indicate that nonpoint sources of endocrine disrupting chemicals may be causing endocrine disruption in native fish. While evidence of endocrine disruption in fish was generally higher in lakes surrounded with urban land use, it was evident in lakes with other land uses as well. All of the lakes in the study are used for seasonal recreation, which also could be a source of contaminants to the lakes. Further studies are needed to determine the specific sources of the endocrine disrupting chemicals and confirm a linkage between the occurrence of these chemicals and fish endocrine disruption. The results of this study can help water-resource managers understand and assess the health of fish populations in recreational lakes.

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