SOLID-PHASE EXTRACTION AND GC-MS TECHNIQUES FOR THE CONFIRMATION OF CHLORPYRIFOS CONTAMINATION OF SURFACE-WATER SUPPLIES

Chlorpyrifos, hyl-O-[3,5,6-trichloro-2-pyridyl]-phosporothioate, is an organophosphorus insecticide which is used in Saskatchewan to protect crops from aphids, armyworms, cutworms, diamondback moths, grasshoppe rs, and wheat midges. It is the active ingredient in the insectide for mulations known as Dursban and Lorsban. Like other organophosphorus in secticides, chlorpyrifos primarily affects the human nervous system by inhibiting the function of the cholinesterase enzyme. In addition to the central nervous system, the cardiovascular and respiratory systems are also impacted by exposure to chlorpyrifos. Application of chlorpy rifos to crops may be performed using either ground or aerial spraying equipment. In a recent incident in rural Saskatchewan, a landowner cl aimed that his surface water supply (a dugout) had been contaminated d uring aerial spraying of his neighbor's crops. Upon inquiry, the claim ant discovered that the material sprayed contained the formulation Lor sban. Since this water supply was utilized for drinking purposes (both human and animal), the landowner requested that his water be tested f or contamination. Solid phase extraction disks consisting of an inert membrance impregnated with adsorbents such as octadecylsilane (C18), o ctylsilane (CX), and styrene-divinylbenzene (SDB) have recently replac ed liquid-liquid partitioning procedures in numerous analytical method s. Applications to the determination of pesticides in water samples in clude chlorinated acid herbicides (Hodgeson 1994), triazine herbicides (Brouwer 1990), organochlorine insecticides (Tang 1993; Hendriks 1993 ), and organophophorus pesticides (Lacorte 1993). SPE disks have been used for the trace enrichment of various pesticides from river and sea water samples (Barcelo 1993; Durand 1992; Durand 1993). Beltran(1993) compared SPE disks and cartridges for use in extracting organochlorine and organophosphorus pesticides from ground water samples. Chiron and Barcelo (1993) used SPE disks coupled with on-line HPLC analysis for the determination of pesticides in drinking water. In a recent study, SPE disks were used to extract organochlorine and organophosphorus pes ticides from water samples with subsequent elution using supercritical fluid extraction (Barnabus 1994). Our laboratory has routinely used s olid phase extraction techniques combined with GC-MS detection for the determination of a variety of pesticides in ground and surface water samples. The methodology used for the analysis of a series of chlorina ted phenoxyacid herbicides was adapted for use in determining chlorpyr ifos (Thompson and Morphy 1995).