Chlorpyrifos

Chlorpyrifos
Benjah-bmm27 · Public domain · source
Name	Chlorpyrifos
Othernames	O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate
Cas number	2921-88-2
Formula	C9H11Cl3NO3PS
Molar mass	350.59 g·mol−1
Appearance	amber liquid
Density	1.4 g·cm−3
Melting point	−60 °C
Boiling point	502 °C (decomposes)

Chlorpyrifos is an organophosphate insecticide first introduced in the 1960s and widely used for control of insect pests on crops and in structural pest control. It belongs to a class of organophosphates derived from earlier nerve agents and replaced many organochlorine pesticides due to perceived lower persistence; however, concerns about neurotoxicity, developmental effects, and environmental persistence have led to extensive scientific, regulatory, and legal debate. Major manufacturers and regulatory bodies have been central to its production, study, and governance.

Chemistry and Properties

Chlorpyrifos is chemically O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate; its structure features a phosphoryl sulfur bound to a 3,5,6-trichloropyridinyl moiety, producing physicochemical properties used in formulation by firms linked to Dow Chemical Company, Bayer AG, Syngenta, Corteva and industrial chemical suppliers. The compound’s molecular weight, lipophilicity, and vapor pressure determine behavior described in analytical chemistry literature from American Chemical Society and instrumentation standards at U.S. Environmental Protection Agency and European Food Safety Authority laboratories. Spectroscopic signatures are catalogued in repositories maintained by National Institute of Standards and Technology, and standard methods for extraction and quantification employ gas chromatography–mass spectrometry consistent with protocols from Food and Agriculture Organization and World Health Organization guidance.

Mechanism of Action and Toxicokinetics

As an organophosphate, chlorpyrifos exerts acute toxicity primarily via inhibition of acetylcholinesterase (AChE) at cholinergic synapses, a mechanism historically studied alongside early work on nerve agents at institutions such as Porton Down, Johns Hopkins University, Harvard University, Columbia University, and Massachusetts Institute of Technology. The parent compound is bioactivated by hepatic cytochrome P450 enzymes (notably CYP2B6 and CYP3A4 as characterized in studies from National Institutes of Health), producing chlorpyrifos-oxon, the more potent AChE inhibitor; detoxification pathways include dearylation and hydrolysis mediated by paraoxonase 1 (PON1), an enzyme studied in populations by researchers at Centers for Disease Control and Prevention, University of California, Berkeley, and University of Michigan. Toxicokinetic parameters—absorption, distribution, metabolism, and excretion—have been quantified in animal models at National Toxicology Program and in human biomonitoring studies associated with Mount Sinai Health System and Columbia University Irving Medical Center.

Agricultural and Non-Agricultural Uses

Chlorpyrifos has been applied to a broad range of crops including corn, soybean, cotton, almond, apple, and citrus commodities, with product registrations historically managed via submissions to agencies such as U.S. Environmental Protection Agency, Health Canada, European Chemicals Agency and national ministries of agriculture like those in Brazil and India. Non-agricultural uses included structural pest control in buildings, termite treatments, and vector control, with commercial formulations produced by multinational agrochemical companies including DowDuPont and distributors servicing markets through channels allied with United Nations pesticide conventions. Label use patterns, application rates, and pre-harvest intervals are documented in extension publications from land-grant institutions such as Iowa State University, University of California Cooperative Extension, and University of Florida IFAS.

Environmental Fate and Ecotoxicology

Environmental fate studies conducted at government laboratories including U.S. Geological Survey, Environment and Climate Change Canada, and research universities such as Rutgers University have shown chlorpyrifos binds to soils, undergoes microbial degradation and photolysis, and can volatilize and undergo long-range transport under certain conditions. Environmental monitoring around agricultural regions documented residues in surface water and sediment, with ecotoxicology data demonstrating high toxicity to aquatic invertebrates, pollinators such as Apis mellifera studied by International Union for Conservation of Nature-linked programs, and vertebrates including birds and fish assessed by U.S. Fish and Wildlife Service and European Food Safety Authority. Bioaccumulation and sublethal effects on behavior and reproduction have been reported in studies associated with Smithsonian Institution, Scripps Institution of Oceanography, and conservation groups like World Wildlife Fund.

Human Health Effects and Epidemiology

Epidemiological research from cohorts at institutions such as Columbia University, University of California, Berkeley, Mount Sinai, Harvard School of Public Health, and University of Washington has investigated associations between chlorpyrifos exposure and neurodevelopmental outcomes, including cognitive, behavioral, and motor deficits in children exposed prenatally or during early life. Occupational studies of applicators and agricultural workers documented acute cholinergic poisoning episodes reported to Centers for Disease Control and Prevention and national poison control centers, while biomonitoring by National Health and Nutrition Examination Survey and research consortia identified biomarkers of exposure and variation in susceptibility tied to PON1 polymorphisms studied at National Human Genome Research Institute. Case reports from hospitals affiliated with Johns Hopkins Hospital and St. Michael's Hospital detailed severe poisoning, and systematic reviews in journals affiliated with The Lancet and Environmental Health Perspectives synthesized evidence on developmental toxicity.

Regulation, Risk Assessment, and Legal Actions

Regulatory reviews and risk assessments by U.S. Environmental Protection Agency, European Food Safety Authority, Health Canada, and national agencies in Australia and Japan have led to restrictions, cancellations, or continued conditional registrations based on differing interpretations of hazard and exposure data. Litigation involving manufacturers reached courts in United States District Court venues, with settlements and enforcement actions involving state attorneys general offices in jurisdictions such as California and New York; international regulatory actions referenced multilateral frameworks including Rotterdam Convention discussions and national policy debates in India and Brazil. Scientific advisory panels convened by National Academies of Sciences, Engineering, and Medicine and reviews in publications associated with World Health Organization have influenced policy trajectories and ongoing monitoring programs.

Category:Pesticides