Appendix 1-10: Summary of Diazinon Monitoring Data

2. Surface Water

1. USGS NAWQA Surface Water Data (1992 – 2014)

Surface water data from the USGS NAWQA program were obtained on December 30, 2014 (USGS, 2015). A total of 30,297 water samples across 2,206 sites throughout the United States were analyzed for diazinon between 1993 and 2014. There were 8,313 detections (27% of samples) of diazinon in the United States and concentrations ranged from not detectable to 3.8 µg/L. Forty-six states had detections of diazinon in surface water. After 2004, the highest detected concentration was 0.359 µg/L. The long term method detection level is 0.003 µg/L (Gilliom et al., 2007). As expected, higher numbers of samples collected within a given state tended to correspond with higher maximum concentrations detected (Figure B 1-10.1). Eleven states⁵ had detections at 0.9 µg/L or greater and 34 states had detections above 0.1 µg/L (Table B 1-10.4). Detections above 0.1 µg/L occurred in creeks and storm drains, as well as in major rivers.

Figure B 1-10.1. Number of surface water samples analyzed for diazinon in each state and the maximum diazinon concentration in surface water detected in that state

A total of 1,499 surface water samples across sites throughout the United States were analyzed for diazoxon between 2002 and 2014. Detections occurred in 2004 in California and Texas. Concentrations ranged from not detected to 0.06 µg/L with the highest detection occurring in 2004. The limit of quantitation ranged from 0.006 to 0.045 µg/L based on the range of less than values reported in the dataset. Diazinon and diazoxon were analyzed in these samples and the ratio of the concentration of the oxon to the diazinon concentration ranged from 0.11 to 0.25.