Mercury consumed in the diet accumulates in the bodies of organisms. When an organism consumes mercury-contaminated food it is not broken down in the digestive system and it moves easily from the gut to the circulatory system where it is distributed throughout the body and binds to muscle tissue.
For many organisms, the rate at which mercury is excreted is very slow and much lower than the rate of intake. This contributes to an increasing concentration of mercury in the tissues of organisms at successively higher levels in the food chain. Top predators such as fish-eating largemouth bass or fish-eating birds can have concentrations of mercury that are millions of times the concentration of mercury in the water. This is why we can drink water from rivers and lakes (the water has very low, almost undetectable mercury concentrations), but top predatory fish can be hazardous to our health (they have very high concentrations of mercury relative to the water).
To examine how mercury biomagnifies in Caddo Lake, scientists determined mercury concentrations in different organisms in the lake’s food chain. Mercury increased in organisms as a function of their position in the food chain. Organisms at the bottom of the food web like snails and mussels that feed on algae had the lowest concentrations of mercury. Largemouth bass and spotted gar that feed on fish had the highest concentrations of mercury.
Sources of Information
- Chumchal, M.M., T.R. Rainwater, S.C. Osborn, A.P. Roberts, M.T. Abel, G.P. Cobb, P.N. Smith, and F.C. Bailey. 2011. Mercury speciation and biomagnification in the food web of Caddo Lake (TX/LA, USA), a subtropical freshwater ecosystem. Environmental Toxicology and Chemistry 30: 1153–1162.
For more information about our mercury research, go to our Aquatic Ecology Lab website.