Effects of Septic Seepage in Minnesota Lakes on Resident Fish Species

The potential of On-site Wastewater Treatment Systems (OWTSs) being a non-point source of contaminants into lake systems is a growing concern. Since many lakes are down gradient of OWTSs, the septic seepage easily contacts surrounding groundwater and enters the shallow waters though the hydrological process.It is also in these shallow areas that many native fish species spawn. Five study lakes were established that included two septic-influenced sites and two reference sites each. Water sampling throughout the early spring and summer established the presence and absence of Contaminants of Emerging Concerns (CECs) at each respective site. Adult male sunfish were collected off their spawning beds between May and July to explore the effects of these contaminants on the native fish species. The fish were euthanized and sampled for blood and internal organs. To explore the effects of these contaminants on the larval fathead minnow, a 21-day static renewal exposure was completed using groundwater collected from the same septic influenced and reference sites in each study lake. Following the 21-day exposures, larvae underwent behavioral testing that included the analysis of predator avoidance as well as feeding performance. Two CEC mixtures were also created from the water chemistry results to replicate seepage from different OWTSs. Adult sunfish and fathead minnows were exposed to these mixtures at a range of concentrations for a 21-day period. Larval fathead minnows were also exposed to these mixtures at the same concentrations. Laboratory exposures assessed the same endpoints as the resident male sunfish and larval groundwater exposures to observe if the same pathologies and behaviors would occur. The assessment of biological endpoints in resident sunfish and laboratory exposed sunfish and fathead minnows provides a rich data matrix to test the hypothesis that septic seepage causes adverse health effects in resident fish populations in northern lakes