Confounds with use of commercial products in toxicity research - Deltamethrin

What is it about?

The major problem with this paper is the inability to determine the chemical agent, or agents, responsible for the alterations in cytochrome P450 expression in offspring. The authors conclude multiple times in the paper that deltamethrin caused these effects. For example: “The present data indicating alterations in the expression of xenobiotic metabolizing CYPs during development following prenatal exposure to deltamethrin may be of significance as the CYP enzymes are not only involved in the neurobehavioral toxicity of deltamethrin but have a role in regulating the levels of ligands that modulate growth, differentiation, and neuroendocrine functions”. There is a serious problem with these conclusions: the pregnant dams were not solely exposed to deltamethrin. The authors exposed the pregnant rats to Decis 2.8% EC®, an emulsion that contains 2.8% technical grade deltamethrin and 97.2% unknown “inerts”. Roussel-Uclaf, the original manufacturer of Decis 2.8% EC®, suggests using the following formulation for an emulsifiable concentrate: 88% xylene, 1% butyl hydroxytoluene, 4% calcium phenylsulfonate, 4% polyglycolic ether of tributylphenol, and 2.8% technical grade deltamethrin (Fulconis, 1982).

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Why is it important?

The use of commercial mixtures of pesticides in toxicology studies is not an issue here. The problem is that without knowledge of the “inerts” in the commercial formulation or comparison to an “inerts" only control group, no conclusions can be made about any one constituent of the commercial mixture. This issue has been raised previously concerning developmental exposures to pyrethroids (Shafer et al., 2005). We beseech both authors and editorial boards to be cognizant of this issue in the future. Concluding that the effects reported in this paper are restricted to deltamethrin exposure is not supported by the data.