RMP News Volume 2, Issue 1

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Regional Monitoring News, Winter 1995-96

Contents

Flea Killers in the Estuary
Central San's Experience with Diazionon and Chlorpyrifos
Annual Report Review Summary
Annual Meeting Summary
Steering Committee Meeting Summary
RMP Database Web Page
SINBAD
Administrative Civil Liabilities
RMP Program Participants
Staff Profile: Rainer Hoenicke
Calendar
Announcements

Flea Killers in the Estuary

by Jay Davis, San Francisco Estuary Institute

Of all the contaminants measured in the RMP, the organophosphate pesticides
are perhaps the most likely to be causing toxicity in Bay-Delta biota.
Some of the most popular pesticides in current usage, including diazinon,
chlorpyrifos (Dursban), and malathion, are classified as organophosphates.
This article provides some general background information on organophosphates
and a specific description of diazinon, one of the organophosphates
of greatest concern in the Estuary. 

Characteristics of Organophosphates

The term organophosphate refers to the chemical structure of these
pesticides, which centers around a phosphorus atom. The key properties
of organophosphates that account for their popularity are their potency
toward insects and their limited persistence in the environment. 

Organophosphates owe their toxicity primarily to their inhibition
of acetylcholinesterase, an enzyme that degrades the neurotransmitter
molecule acetylcholine. Animals exposed to toxic quantities of organophosphates
suffer from excessive stimulation of their nerve cells due to the
lack of acetylcholine degradation. Chemicals with this mode of action
can be extremely potent, as exemplified by the nerve gases used
in chemical warfare. A few milligrams of Sarin, an extremely potent
nerve gas, can kill a human (Sarin was the chemical used in the
recent fatal terrorist attack in a Japanese subway). Although organophosphate
pesticides are hundreds of times less toxic than Sarin, humans are
susceptible to organophosphate toxicity, but the primary concern
with regard to human exposure is for people who might be exposed
directly to pesticide residues (such as pesticide applicators and
farm workers). Organophosphates in...