Predicted Atrazine Concentrations in the Great Lakes: Implications for Biological Effects

Atrazine is an herbicide used extensively throughout the Midwest corn belt, including the agricultural regions within the Great Lakes basin watershed. Measurements of atrazine concentrations in the Great Lakes are few, however, so knowledge of its current concentrations, persistence, and trends in this ecosystem is limited. A dynamic annual time step model was used to predict atrazine concentrations over time in the Great Lakes based on varied atrazine loading rates to the lakes (“most-likely” and “high” loading conditions). Four degradation scenarios were evaluated: no degradation, and atrazine degradation with half-lives of 2 years, 5 years, and 10 years. Predicted steady-state concentrations for all of the scenarios and all the Great Lakes ranged from 0.0024 to 0.88 μg/L. The number of years until steady-state conditions were achieved ranged from 4 to over 400 years. The most-likely loading rate and two-year half-life scenario had the lowest concentrations (0.0024 to 0.13 μg/L) and the fewest years (4 to 13 years) to achieve steady-state conditions. Available monitored atrazine concentrations in the Great Lakes are very similar to the most-likely loading rate and 2-year half-life scenario predicted values. Monitored and predicted concentrations in the Great Lakes indicate atrazine does not currently pose a toxicological risk to humans or aquatic organisms, and under current and expected lower loading rates should remain well below criteria values.