Study Notes High Pesticide Levels in Lake Trout

A new study in the latest issue of Environmental Toxicology and Chemistry examined the biomagnification of pesticides and other contaminants in North American lakes. Stable isotope ratios were used to measure the trophic level (position in the food chain) because of the predictable fractionation of nitrogen isotopes from prey to predator.

Biomagnification is the increase in concentration of a substance, such as the pesticide dichloro-diphenyl-trichloroethane (DDT), in successively higher levels of a food chain resulting in top predators having increased tissue concentrations relative to other organisms. The lake-to-lake variability in concentrations of pesticides and PCBs (polychlorinated biphenyls, which may be found in paints, adhesives, coolants, and sealants, among other things) has so far been difficult to explain.

Significant biomagnification of some PCBs isomers and several organochlorine pesticides (OCPs) was found in the lakes studied. Lake trout represented the largest sampling pool, and they also showed the highest concentrations of certain PCBs and OCPs as a result of their trophic status. Lower concentrations were found in invertebrates, including snails, mussels, mayflies, and zooplankton.

The chemical with the highest biomagnification factor was DDE, which has been linked to cancer in humans and eggshell thinning in eagles, resulting in crushed eggs when parent eagles attempt to incubate the eggs. Not surprisingly, the highest DDE levels occurred in lakes next to large agricultural drainage basins.

Overall, a positive relationship between hydrophobicity (Kow) and biomagnification rate was observed, but biomagnification of selected PCBs and OCPs were variable across the 17 lakes in this study. Some compounds were observed to biomagnify in some lakes, but not in others. This variability suggests that factors other than the physical and chemical properties of the contaminants were influencing biomagnifications.

To read the entire study, visit

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