ACCUMULATION OF MERCURY IN FISH FROM THE GRAND RIVER, NEAR GALLATIN MISSOURI

Of the various foods human beings are able to consume, fish, in particular, serve as a major source of omega-3-fatty acids, which are essential in protecting people against heart disease and other illnesses. However, global mercury pollution and the bioaccumulation of methylmercury (MeHg) into marine food chains has led to both national and state consumption advisories for fish species. Those living along the Missouri and Mississippi River are advised not to eat more than one serving of flathead (Pylodicits olivarus), blue (Ictalurus furcatus) or channel (Pylodicti olivaris) catfish greater than 17 inches in length per week.

In 2014 we reported the MeHg in a sample containing 36 channel catfish, 6 flathead catfish and 13 freshwater drum (Aplodinotus grunniens) collected from the Grand River (a Missouri River tributary) in August 2013, near the town of Gallatin. MeHg concentrations (ng/g wet weight) varied from 109-482 in freshwater drum, from 99-343 in flathead catfish and from 50-305 in channel catfish in 2013.

This year we have sampled long nose gar (Lepisosteus osseus), flathead catfish (Pylodictis olivaris), and channel catfish (Ictalurus punctatus), which were collected near the town of Gallatin in August 2014. Fish lengths and weights were recorded and muscle samples frozen for determination of total mercury on a Teledyne Leeman Labs Hydra IIC Hg Analyzer. Fish lengths varied as follows: channel catfish 12- 23 in., flathead catfish 23-34.5 in., longnose gar 18-28 in.. MeHg concentrations (ng/g wet weight) varied from 56-199 in channel catfish, from 122-483 in longnose gar and from 307-544 in flathead catfish.

Fish species at higher trophic levels are expected to contain greater levels of MeHg because of increased bioaccumulation. Based on the dietary habits of these species, we expect long nose gar and flathead catfish, which consume primarily fish, to have the highest levels of MeHg. Channel catfish are omnivores and were expected to have slightly lowered levels of MeHg. We expected freshwater drum, which mainly prey on aquatic insects and small fish, to have the lowest levels of MeHg but as reported last year, which was not the case. In conclusion, eating fish provides several pertinent nutritional benefits, but care must be taken in size selection and how frequently it is consumed.