Pyrethroids in Creeks

by Dave Tamayo,
Pesticide Control Program Manager,

Sacramento County Stormwater Program

Way back at the end of the last century (the 1990s), the Sacramento Stormwater Quality
Partnership (or SSQP, which includes Sacramento County and the cities of Citrus
Heights, Elk Grove, Folsom, Galt, Rancho Cordova, and Sacramento) found that the
water in local creeks was contaminated with the insecticides diazinon and chlorpyrifos, at
levels toxic to the water flea Ceriodaphnia. Since then, most urban uses of these
chemicals have been phased out, only to be largely replaced in the urban marketplace
with pyrethroids. In our area, pyrethroids are widely used for ant control around
buildings, in most aerosol bug sprays, and even in combination with lawn fertilizers
(even though the target insects rarely cause problems in Sacramento lawns).

Recent studies by Professor Donald Weston of U.C. Berkeley frequently
found pyrethroids at toxic levels in urban creek sediments of the Sacramento region and the
Bay Area. Weston’s studies also indicate that urban areas, not upstream agriculture,
are the source of these chemicals in the creeks. Pyrethroids bind strongly to sediments, so
that the vast majority of them will be found in the stream bottom. This is better for animals
like Ceriodaphnia that swim and don’t interact much directly with the sediment. However,
animals that dwell on or in the stream bottom are at risk, since they are more likely to
contact the pyrethroids. Weston’s study animal, Hyallela azteca, is a sediment-dwelling
amphipod crustacean found naturally in this area, and is an important component of the aquatic
food web.

To help prevent harm to creek life, SSQP actively encourages residents and
professionals to reduce pesticide use wherever possible. In addition, the SSQP is a leader
in the effort to prod State and Federal pesticide regulators to re-evaluate pyrethroids,
and to improve the overall process for pesticide regulation. A key goal is to evaluate
pesticides more effectively so future water quality problems are avoided before pesticides
are allowed on the market. Visit the

Sacramento Storm Water Quality Partnership
for resources on avoiding pesticide use.

Our Water Our World and WaterWise are two programs supported by the
Sacramento Stormwater Partnership that provide useful information for managing pests in
Sacramento area landscapes. These programs distribute information through retail outlets
and the internet. Water Wise also provides help through the Sacramento Master
Gardeners who can answer specific questions during business hours at (916) 875-6913.
Our Water Our World provides individual assistance on pest management issues through
Ask the Expert,
which links to the Bio-Integral Resource Center ( The University of
California Statewide Integrated Pest Management Program has abundant information on IPM
for landscapes, especially in its Pest Notes, and Turf sections.

This article originally appeared in our Winter 2007 Newsletter

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