Pesticide concentrations in wetlands on the Lake Traverse Reservation, South and North Dakota, July 2006

During July 2006, water samples were collected from selected Lake Traverse wetlands within the historic Reservation boundary in northeastern South Dakota and southeastern North Dakota as part of a reconnaissance-level assessment by the U.S. Geological Survey (USGS) and Sisseton-Wahpeton Oyate (SWO) Sioux Tribe. Eighteen wetlands were sampled by the SWO and USGS personnel after primary pesticide application occurred on the Lake Traverse Reservation. Samples were analyzed for 61 pesticide compounds. In addition, the samples were analyzed for physical properties that might help further characterize the water quality of the wetlands.

During July 2006, water samples were collected from 18 wetlands and were analyzed for 61 widely used pesticide compounds. Pesticides were detected in 17 of the 18 sampled wetlands. In the 17 wetlands in which pesticides weredetected, the number of pesticides detected ranged from two to eight. Of the 61 pesticides for which the samples were analyzed, 51 pesticides were not detected in any of the wetland samples. Ten pesticides were detected in water samples from at least one of the wetlands at small concentrations. Atrazine and de-ethyl atrazine were detected in samples from 17 of the 18 wetlands. The minimum, maximum, and median concentrations of dissolved atrazine detected were 0.007, 0.12, and 0.064 microgram per liter (?g/L), respectively. Two pesticides (picloram and simazine) were detected in only one wetland each. None of the pesticide concentrations exceeded any U.S. Environmental Protection Agency Maximum Contaminant Levels for drinking water, and concentrations were much less than levels considered toxic for humans or aquatic species.