Publication Summary

Pesticides were analyzed in water and sediment samples collected from six Walla Walla River tributaries and the lower main stem during April 22-23 and June 18-19, 1996. Water samples were analyzed for 162 pesticides, or breakdown products, that include most of the compounds currently or historically used in Washington. Sediment analysis was limited to the eight chlorinated pesticides for which the Walla Walla River is listed as water quality limited (303d). Results showed relatively few instances where pesticides were a significant water quality concern.

Pesticides were analyzed in water and sediment samples collected from six Walla Walla River tributaries and the lower main stem during April 22-23 and June 18-19, 1996. Water samples were analyzed for 162 pesticides, or breakdown products, that include most of the compounds currently or historically used in Washington. Sediment analysis was limited to the eight chlorinated pesticides for which the Walla Walla River is listed as water quality limited (303d). Results showed relatively few instances where pesticides were a significant water quality concern.

Twenty-two pesticides were detected at sub-parts per billion levels in the water samples. Eighteen of these were herbicides, with 2,4,-D, bromacil, MCPA, and bromoxynil being found in 50 - 85% of the samples. Although the detection frequency of herbicides appears high compared to other parts of the state, the concentrations were several orders of magnitude below levels considered toxic to aquatic life.

Four insecticides were detected, but each only once or twice. Malathion exceeded EPA chronic water quality criteria once in Lower Mud Creek and once in Pine Creek. The concentration in Pine Creek approached the LC-50 for some invertebrate species. Diazinon was detected at non-toxic levels in Yellowhawk and Mill creeks. The historically-used insecticides aldrin and DDT exceeded state chronic standards once each in Yellowhawk and Dry Creek, respectively. Aldrin is rarely reported in state waters and the concentration, 0.11 ug/L (ppb), was high compared to the 0.0019 ug/L standard.

Low levels (generally less than 5 ug/Kg; ppb) of DDT, hexachlorobenzene, gamma BHC, and chlordane was detected in most of the sediment samples. The limited data collected indicate Yellowhawk and Dry creeks may be the largest sources of these compounds to the Walla Walla main stem. With the single exception for DDT mentioned above, none of these pesticides reached detectable levels in water.