Assessing Septic System Discharge to Lakes

PROJECT OVERVIEW
Pharmaceuticals, hormones, and other contaminants of emerging concern are increasingly being found in surface waters in Minnesota, including the state's lakes. Recent research surveying Minnesota lakes found that the most frequent occurrence of these chemicals was in lakes with a high density of septic systems. In river ecosystems some of these chemicals have been known to cause extinction of forage fish species and abnormal sexual development in other fish species, such as bass and walleye. However, little is known about how these compounds affect fish populations in lake ecosystems. Researchers from the U.S. Geological Survey, St. Cloud State University, and the Minnesota Department of Health will cooperatively use this appropriation to help assess which of these chemicals are most frequently present in lakes with high septic system concentration and determine whether native fish populations are being affected. Part of this appropriation will help pay for specialized equipment to study these chemical compounds, expanding the capability of the research laboratory at the Department of Health.

OVERALL PROJECT OUTCOME AND RESULTS
The current study (1) sampled 20 Minnesota lakes that receive groundwater under the potential influence of septic systems to determine the occurrence of pharmaceutically active compounds (PhACs) and endocrine active compounds (EACs), (2) assessed watershed and groundwater characteristics that may contribute to the frequency of PhAC and EAC detections, (3) assessed the histo-pathology of actively spawning bluegill sunfish for biomarkers of EAC exposure to compounds in the near-shore zone of four target lakes, and (4) enhanced EAC analytical capabilities at the Minnesota Department of Health (MDH) through the purchase of new analytical equipment. Study lakes were chosen based on depth to water table, septic system density regardless of functionality, bluegill nesting habitat, and groundwater temperature surveys in the near-shore zone. Lake water or lake-sediment pore water (water stored between sediment particles,contained within the lake-bed sediment) samples were collected and analyzed for a broad suite of 179 PhACs, EACs, and other waste compounds. All surface water samples and over three quarters of pore water samples had at least one compound detected. Overall, 43 of 69 (62%) waste compounds and 5 of 110 (4%) pharmaceuticals were detected in all samples. Twelve known or suspected endocrine active compounds were detected in at least one lake. On average, the prevalence of detections normalized to the number of compounds tested was three to four times higher in near-shore lake water than in near-shore pore water. Actively spawning male bluegill sunfish were collected from reference and groundwater discharge sites in four lakes. Pathologies were more common in fish collected at near-shore sites when compared to fish collected across entire lakes in the 2008 statewide study. The greater abundance of indicators of adverse biological impact suggests that a lake-wide sampling of fish will underestimate the impact of contaminant exposure to fish during reproductively important life stages.

PROJECT RESULTS USE AND DISSEMINATION
Information from this project has been disseminated to scientific audiences via presentations at Minnesota Water Resources and Midwest Groundwater Conferences.