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Bull-Dogging Diazinon

When Val Connor tested the rain that had collected in pie pans she'd scattered around the Central Valley last January, she found enough diazinon to kill an aquatic organism. Connor's agency, the Central Valley Regional Board, has been tracking the pervasiveness of this widely used farm and garden pesticide in rivers and runoff for several years. Last year Connor conducted some extensive urban studies that showed year-round diazinon movement from city yards and verges into waterways. Other Board studies, meanwhile, have documented waterborne pesticide pulses emanating from stone fruit and nut orchards along the Sacramento and American Rivers. But the high diazinon levels found in Connor's crude pie pan experiment suggest the pesticide may also be being translocated between cities and orchards over the airways.

As the diazinon trail soars skyward, the Board is in hot pursuit. In fact Connor recently asked the U.S. Geological Survey's Mike Majewski to get her some hard data this winter by sampling the skies for the pesticide at two sites - one in an a orchard area and one in the city.

"We're going to correlate diazinon concentrations in air and rain with wind speed and direction," says Majewski. The study will be expanded to five sites in its second year.

Majewski's study should yield new points on a map of diazinon's aerial and aquatic travels that is so wide-reaching it has regulators worried. The pesticide has turned up in the Bay-Delta's major rivers, in creeks as far apart as Hayward's San Lorenzo and San Joaquin's Orestimba, and even in municipal sewer water. Because diazinon can be toxic to aquatic organisms, the State Water Board began talks with the Department of Pesticide Regulation about the possible need for control. The department, in turn, asked Cal Fish & Game to do a hazard assessment - a draft of which is already making the rounds. The assessment process, according to Fish & Game's Mary Menconi, uses available data to come up with a recommended numerical level for the protection of aquatic life. No agency has set such a level to date; indeed the only aquatic diazinon guideline on the books is the National Academy of Science's 0.009 parts per billion (ppb). While Menconi would not disclose what that the level suggested in her assessment will be, she says "We're very confident about our numbers. We had a lot of good quality data to base them on."

Menconi's assessment has no regulatory clout; it's just a bureaucratic building block. Indeed the Department of Pesticide Regulation's John Sanders says his agency's current focus is on solving the problem through education and voluntary activities on the part of growers. To this end, Saunders is currently overseeing studies of several specific BMPs for orchards - among them the planting of vegetative strips to filter and trap the diazinon and the application of polyacrylymide gels that absorb the pesticide and bind to the soil. Both could theoretically keep diazinon from being mobilized by runoff.

Sander's agency is also actively monitoring the presence of 15-20 pesticides in the Sacramento, Russian, Salinas and Merced Rivers, and a new Geological Survey study may give them an interesting clue when it comes to diazinon. Peak storm runoff usually means peak pesticide levels, but not so in the case of diazinon. In a new Survey study of Orestimba Creek, a minor western tributary of the San Joaquin River, diazinon levels crested with the first flush of storm runoff and then plummetted.

"What this tells us is that if you're looking for diazinon in these western tributaries and take a sample when the flow is highest, you'd probably see very little," says the Survey's Neil Dubrovsky. What this also suggests, by extension, is that farmers and regulators facing the need to stanch contaminated runoff from this area may not need to manage the entire flow, just the first flush off the fields.

In Dubrovsky's study, that "first flush" contained 3.8 ppb of diazinon. He speculates that the reason concentrations dropped to 0.7 ppb within five hours, and to 0.14 ppb within 24 hours, was a combination of decreasing concentration in runoff from valley orchards and increasing runoff from the more pristine portion of the watershed. This first flush clue is in turn helping the agencies understand why they saw a double diazinon peak in last year's studies of San Joaquin River pesticide pulses. That first peak may have been the rapid response runoff from fine grained soils along the western tributaries, the second from sandier, more runoff-retentive areas in the eastern San Joaquin Valley.

To keep diazinon on fields long enough for it to break down into "harmless" constituents, CIBA - one of diazinon's three manufacturers - recommends containing runoff by building berms or temporarily closing off drainage ditches. CIBA's Greg Faust says his company is handing out slide kits and brochures on good home and yard stewardship practices, conducting research on ways to better remove diazinon from sewage wastewater and meeting with farmers to identity control mechanisms that will work with their cultural practices.

"Targeting diazinon, making it the culprit, could worsen our problems by encouraging use of other, more toxic products," says Faust. "We're better off educating farmers and householders."

Contact: Val Connor (916)255-3000; Neil Dubrovsky (916)978-4648; Greg Faust (910)632-2685; Mike Majewski (916)978-4633 ext. 345; Mary Menconi (916)355-0290; John Sanders (916)324- 4100. 2/93 & 6/93 & 6/94

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