Pesticide mixes: when 1 + 1 does not equal 2

Dec 11, 2008

Laetz, CA, DH Baldwin, TK Collier, V Herbert, JD Stark and NL Scholz.  2008.  The synergistic toxicity of pesticide mixtures: implications for risk assessment and the conservation of endangered Pacific salmonEnvironmental Health Perspectives doi: 10.1289/ehp.0800096.

A mix of two pesticides had greater toxic effects on exposed salmon than would be expected from one separately, adding to concerns that health risks from pesticides are underestimated.

Risk assessment tests determine how dangerous chemicals are and if they should be regulated. They are usually done one compound at a time. However, most pesticide exposures in the natural world involve multiple chemicals that interact with each other and with living things.

In this study, scientists in Washington state looked at the effects of organophosphate and carbamate pesticides on juvenile coho salmon.

The fish were treated with several different combinations of the two pesticides. The activity of a brain enzyme called acetylcholine esterase (AChE) was measured to assess the total toxic effect.  Pesticides target this enzyme to cause neurological damage.

Many of the combinations caused greater toxicity than was predicted mathematically using data generated from individual chemical exposure tests.  Results like these with phthalates have just led the National Resesarch Council to recommend to the EPA that it change its risk assessment methods to reflect cumulative exposure to chemicals.

Agencies that develop regulations for pesticide use generally rely on data from studies using single chemicals.  The new data provide more evidence that standards that rely on results from single chemical tests may greatly underestimate the actual risk of exposure to multiple pesticide pollutants.