Subj: Need for Toxicity Testing in Diazinon Monitoring and TMDL Development
Date: 11/3/1999 1:15:28 PM Central Standard Time
From: Gfredlee
To: [email protected]
To: [email protected], [email protected]
CC: [email protected]

November 3, 1999

Subject: Need for Toxicity Testing in Diazinon Monitoring Program

At the last Sacramento/Feather River OP Pesticide Management Strategy Focus Group meeting, issues were raised about the need to conduct toxicity testing as part of the diazinon monitoring. I wish again to emphasize the importance of focusing the control of diazinon on the control of toxicity and not on diazinon concentrations. While it is my assessment that, at least with respect to the Sacramento/Feather River dormant spray associated aquatic life toxicity measured thus far, diazinon is the constituent responsible for this toxicity, there is need to verify this on some samples that will be collected this winter as part of this monitoring program. Further, there is need to continue to verify this each year, as diazinon is phased out and new pesticides are introduced.

The toxicity testing should include an assessment of the total toxicity, and if there is toxicity, how much of the toxicity is due to OP pesticides through conducting a dilution series with or without PBO.

If there are questions on this comment, please contact me.

G. Fred Lee

Reference as: "Lee, G.F., 'Need for Toxicity Testing in Diazinon Monitoring and TMDL Development,' G. Fred Lee & Associates, November (1999)."