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Demon Diazinon
Scientists up and down the Estuary are finding the same toxic ingredient in urban stormwater, and it ain't anything "esoteric" like heavy metals from auto brake linings, according to toxicologist Steve Hansen. It's the common garden pesticide diazinon. Hansen's found it in Hayward's San Lorenzo Creek in runoff from residential areas. And the Central Valley Regional Board's Val Connor has found it in City of Sacramento stormwater - enough to kill 100% of the Ceriodaphnia (water fleas) in bioassays within 24 hours.
"Here's a situation where you have high levels of toxicity that can easily harm aquatic life in streams and that can just as easily be controlled," says Hansen. "It's pretty obvious what we should do about it. Looking for more esoteric sources of toxicity may not be where it's at."
Hansen's found diazinon toxicity in both dry and wet weather samples. Connor decided to follow his lead but take testing several steps further. First, she wanted to find out how typical her results were. Tests on Stockton, Yuba City and Tracy runoff confirmed the pervasiveness of the pesticide. Second, Connor added piperonyl butoxide (PBO), which inhibits the toxic reaction of water fleas to diazinon and other metabolically activated organophosphate pesticides, to her samples. When the fleas die in PBO-treated samples, which they did in samples from several of Connor's test sites, an additional (and as yet unidentified) toxicant may be present.
The next step, now that diazinon has been shown to be a major urban pollutant, is to track down the source. Though Connor's tests were on city stormwater, Central Valley orchards and farms also use diazinon sprays. "We stuck glass pans out to collect rainwater and wind-blown debris and detected diazinon, which could be from urban or non-urban sources," says Connor. Next year she plans more sophisticated air sampling.
Contact: Val Connor (916)255-3111 or Steve Hansen (510)687-5400
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