Evaluation of evidence that the organophosphorus insecticide chlorpyrifos is a potential persistent organic pollutant (POP) or persistent, bioaccumulative, and toxic (PBT)

A number of chemicals, including several organochlorine pesticides, have been identified as persistent organic pollutants (POPs). Here, the properties of chlorpyrifos (CPY; CAS No. 2921-88-2) and its active metabolite, chlorpyrifos oxon (CPYO; CAS No. 5598-15-2), are assessed relative to criteria for classification of compounds as persistent, bioaccumulative, and toxic substances (PBTs). The manufacture and use of POPs are regulated at the global level by the Stockholm Convention (SC) and the UN-ECE POP Protocol. Properties that result in a chemical being classified as a POP, along with long-range transport (LRT), while understood in a generic way, often vary among jurisdictions. Under the SC, POPs are identified by a combination of bulk (intensive) properties, including persistence and biomagnification, and an extensive property, hazard. While it is known that CPY is inherently hazardous, what is important is the aggregate potential for exposure in various environmental matrices. Instead of classifying chemicals as PBT based solely on a few simple, numeric criteria, it is suggested that an overall weight of evidence (WoE) approach, which can also consider the unique properties of the substance, be applied. While CPY and its transformation products are not currently being evaluated as POPs under the SC, CPY is widely used globally and some have suggested that its properties should be evaluated in the context of the SC, especially in locations remote from application. In Europe, all pesticides are being evaluated for properties that contribute to persistence, bioaccumulation, and toxicity under the aegis of EC Regulation No. 1107/2009: ‘Concerning the Placing of Plant Protection Products on the Market.’ The properties that contribute to the P, LRT, B, and T of CPY were reviewed, and a WoE approach that included an evaluation of the strength of the evidence and the relevance of the data to the classification of CPY and CPYO as POPs or PBTs was applied. While toxic under the simple classification system used in EC Regulation No. 1107/2009, based on its intensive properties and results of monitoring and simulation modeling, it was concluded that there is no justification for classifying CPY or its metabolite, CPYO, as a POP or PBT.