California, January 18, 2005 (ENS): A University
of California researcher has found that many widely
used pesticides pose previously uncalculated toxic risks
due to the differing biological reactions of their isomers
in the environment. Isomers are molecules with the same
chemical formula but in which the atoms are arranged
Jay Gan, a professor of environmental chemistry at the
University of California-Riverside has found that this
group of pesticides, although chemically identical,
have very different biological and environmental impacts
between their two, or more, isomers.
He says this fact may have implications for risk assessment
and research and development directions of new products.
Currently about 25 percent of pesticides - including
organophosphates and synthetic pyrethroids - fall into
this classification and this ratio is expected to increase
as new products are being introduced into the market.
Gan and his colleagues at UC Riverside examined five
common insecticides, including organophosphates, such
as profenofos, and synthetic pyrethroids, such as permethrin.
For all these compounds, one of the isomers was consistently
over 10 times more toxic than the other to Ceriodaphia,
a small crustacean often used to assess water toxicity.
The researchers also found that a specific isomer lingered
longer in the environment than the other, making one
form of permethrin almost twice as prevalent in sediment
or runoff water. This means that the environmental impact
of these pesticides may depend on the behavior of a
particular isomer instead of the whole compound, the
Gan’s findings add weight to the argument that
when assessing risk regulators should consider whether
a product is a compound with more than one isomer, and
that the chemical industry should pursue the value of
producing single isomer products instead of mixed isomer
By using pesticides with just the active isomer, farmers
will likely achieve the same degree of pest control
at a much-reduced rate of chemical use, Gan concludes.
This will have environmental benefits as much less chemical
is introduced into the environment.
The findings were published in a paper titled "Enantioselectivity
in Environmental Safety of Current Chiral Insecticides"
in last week’s online edition of the Proceedings
of the National Academy of Sciences. Gan published the
paper in cooperation with a team of UCR colleagues including
Daniel Schlenk, professor of aquatic ecotoxicology;
Soil Physics Professor, William A. Jury; and visiting
professor Weiping Liu.