Samples collected each year during spring-quarterly and summer-event sampling were analyzed for pesticides; thereby yielding data for four samples per site. The analytical schedule for pesticides included 41 pesticides and 23 metabolites, or breakdown products (appendix 3). Of the 41 pesticides, 21 were detected in at least one sample. Of the 23 metabolites, 9 were detected in at least one sample. Two pesticides were detected in every sample: atrazine (along with its metabolite 2-chloro-4-isopropylamino-6-amino-s-triazine) and metolachlor. Concentrations of all three constituents were generally higher in stream samples than harbor samples. Atrazine concentrations at stream sites ranged from 0.014 µg/L at Honey Creek to 0.95 µg/L at Root River at Grange Avenue, while concentrations at harbor sites ranged from 0.039 µg/L at the Northern Outside Harbor Breakwall Lake site to 0.11 µg/L at the Middle Mid-Harbor Milwaukee Outer Harbor site. 2-Chloro-4-isopropylamino-6-amino-s-triazine (deethylatrazine) concentrations at stream sites ranged from 0.006 µg/L at Honey Creek to 0.128 µg/L at Root River at Grange Avenue, while concentrations at harbor sites ranged from 0.013 µg/L at the Northern Outside Harbor Breakwall Lake site to 0.037 µg/L at the Middle Mid-Harbor Milwaukee Outer Harbor site. Metolachlor concentrations at stream sites ranged from 0.014 µg/L at Honey Creek to 0.488 µg/L at Little Menomonee River, while concentrations at harbor sites ranged from 0.008 µg/L at the Northern Outside Harbor Breakwall Lake and Middle Outside Harbor Breakwall Lake sites to 0.02 µg/L at the Middle Mid-Harbor Milwaukee Outer Harbor site. The presence of atrazine, deethylatrazine, and metalochlor in every sample is typical, as these pesticides are among the most heavily used and their presence in streams across the Nation has been well-documented (Gilliom and others, 2006).

Generally, concentrations of pesticides were low. The highest concentration observed was in a sample from Little Menomonee River (7.86 µg/L of simazine). In that same sample, no other pesticides were present in unusually high concentrations. Remaining samples ranged in concentration from below detection to 2.9 µg/L (bromacil, also at Little Menomonee River). These concentrations were typical of samples collected at fixed intervals and during normal flow conditions. Modern pesticides have moderate to high water solubility and relatively short half-lives. As a result, stream pesticides concentrations are generally highest following rainfall events producing notable runoff, with an enhanced effect when rainfall events occur shortly after pesticide application (Graczyk and others, 1997 and 1999). Selected pesticides will be discussed further in the wastewater compound section, where pesticides are divided into herbicide and insecticide classes.

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