Very minute amounts of some heavy metals and carcinogenic chemicals occur in waters of the state, usually at concentrations too low to be measured by current technology. Some of these chemicals can accumulate in fish through the food chain. Levels of these chemicals found in fish usually do not cause problems to their survival or reproduction, however they may represent a health concern when we eat those fish. The department collects data needed to determine which chemicals are occurring in fish, the concentrations of chemicals in fish, and how these vary by fish species, location, and over time.

The department's Water Quality Monitoring Section (WQMS) staff collects 100 to 200 fish tissue samples from streams and lakes across Missouri each year. Some samples are collected from long-term monitoring sites, some of which have been monitored since the 1970s. Data from these sites is used primarily to assess ecological risk and long-term trends. Other sites are sampled for three to five years and provide data to assess the health risk to people who eat fish from these areas. All fish tissue data also contributes to overall water quality assessment work.

WQMS staff collects fish for analysis using specialized equipment that passes electricity through the water temporarily paralyzing fish near the electrical field. When paralyzed by the electrical field, most fish rise close to the water’s surface where staff can capture them with dip nets. Fish regain control of their muscles within seconds after the electric current ceases and swim away unharmed.

WQMS staff processes the collected fish the same day. The tissue samples are frozen until they are submitted to a contract lab to be analyzed for mercury, cadmium, lead, selenium and organic compounds, such as pesticides and polychlorinated biphenyls (PCBs).

For more information on human health concerns with eating fish please visit the Missouri Department of Health and Senior Services’ Missouri Fish Advisory website.