title: Review of the toxicology of chlorpyrifos with an emphasis on human exposure and neurodevelopment.
abstract: This review examines the large body of toxicological and epidemiological information on human exposures to chlorpyrifos, with an emphasis on the controversial potential for chlorpyrifos to induce neurodevelopmental effects at low doses. The results of this review demonstrate that the use of urinary 3,5,6-trichlorpyridinol (TCPy), a metabolite of chlorpyrifos as a biomarker of nonoccupational exposure is problematic and may overestimate nonoccupational exposures to chlorpyrifos by 10-to 20-fold because of the widespread presence of both TCPy and chlorpyrifos-methyl in the food supply. Current "background" (nonoccupational) levels of exposure to chlorpyrifos are several orders of magnitude lower than those required to inhibit plasma cholinesterase activity, which is a more sensitive target than nervous system cholinesterase. However, several in vitro studies have identified putative neurodevelopmental mechanisms that are altered at concentrations of chlorpyrifos below those that inhibit cholinesterases. Although one human cohort study reported an association between maternal and cord blood chlorpyrifos levels and several measures of neurodevelopment, two other cohort studies that utilized urinary TCPy as a surrogate for chlorpyrifos exposure did not demonstrate an association. Although the weight of the scientific evidence demonstrates that current levels of chlorpyrifos exposure will not have any adverse effects on neurodevelopment that might result from inhibition of nervous system cholinesterases, several recent studies propose alternative mechanisms. Thus, further in vivo investigation on neurodevelopment in an appropriate animal model is needed; additional epidemiological studies may be warranted if a suitable, chlorpyrifos-exposed cohort can be identified and more rigorous measures of exposure are utilized.
authors: Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, Washington, USA.
authors: David L
authors: DL
authors: Eaton
authors: Robert B
authors: RB
authors: Daroff
authors: Herman
authors: H
authors: Autrup
authors: James
authors: J
authors: Bridges
authors: Patricia
authors: P
authors: Buffler
authors: Lucio G
authors: LG
authors: Costa
authors: Joseph
authors: J
authors: Coyle
authors: Guy
authors: G
authors: McKhann
authors: William C
authors: WC
authors: Mobley
authors: Lynn
authors: L
authors: Nadel
authors: Diether
authors: D
authors: Neubert
authors: Rolf
authors: R
authors: Schulte-Hermann
authors: Peter S
authors: PS
authors: Spencer
mesh_terms: D000367:Age Factors; D000818:Animals; D004390:Chlorpyrifos / Q000493:pharmacokinetics / Q000494:pharmacology / Q000633:toxicity*; D002800:Cholinesterase Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology / Q000633:toxicity*; D004781:Environmental Exposure / Q000009:adverse effects*; D004785:Environmental Pollutants / Q000493:pharmacokinetics / Q000494:pharmacology / Q000633:toxicity*; D006801:Humans; D007306:Insecticides / Q000493:pharmacokinetics / Q000494:pharmacology / Q000633:toxicity*; D009420:Nervous System / Q000187:drug effects* / Q000196:embryology / Q000254:growth & development
chemical_list: D002800:Cholinesterase Inhibitors; D004785:Environmental Pollutants; D007306:Insecticides; D004390:Chlorpyrifos