PH01 TMDL and Monitoring Programs for the San Joaquin River Basin (USA)
Exhibit Hall
8:00 AM - Thursday
(PH001) Dormant Season Pesticide Residue Monitoring of Surface Water in the Sacramento and San-Joaquin River Watersheds.
Gill, S1, Bacey, N1, Nordmark, C1, Jones, D1, Bennet, K1, Gana, C 1, Spurlock, F1, 1 California Dept. Pesticide Regulation, Sacramento, ca, USA
ABSTRACT- Dormant season applications of the organophosphorus (OP) insecticides diazinon, chlorpyrifos, and methidathion are applied to stone fruit and nut orchards in the Sacramento and San Joaquin Valleys to control over-wintering pests. Studies conducted in valley watersheds have found that dormant use OP insecticide concentrations in surface waters are responsible for acute toxicity to the water flea, Ceriodaphnia dubia. This five-year study monitored the occurrence of toxicity and the levels of diazinon, chlorpyrifos, and methidation in the Sacramento and San Joaquin River watersheds. Levels of several carbamate insecticides and pre-emergent herbicides were also monitored. The reporting limit for diazinon and chlorpyrifos was 0.04 ppb and 0.05 ppb for methidathion and the herbicides. Thirty-nine of the 197 samples were acutely toxic to C. dubia. Diazinon concentrations ranged up to 2.74 ppb with detection frequencies between 13 and 74 percent at sites in the Sacramento River watershed. Concentrations in the San Joaquin River watershed ranged up to 0.161 ppb with detection frequencies at 13 percent. Chlorpyrifos was detected once out of 560 samples taken. Methidathion was detected 15 times with concentrations ranging up to 1.74 ppb. Diuron concentrations ranged up to 8.45 ppb and detection frequencies were as high as 100 percent.
Key words: chlorpyrifos, diazinon, Ceriodaphnia, toxicity