Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2006
Publication Date: 12/22/2006
Citation: Potter, T.L., Mohamed, M.A., Ali, H. 2007. Solid-Phase Extraction Combined with High-Performance Liquid Chromatography-Atmospheric Pressure Chemical Ionization-Mass Spectrometry Analysis of Pesticides in Water: Method Performance and Application in a Reconnaissance Survey of Residues in Drinking Water in Greater Cairo (Egypt). Journal of Agricultural and Food Chemistry. 55:204-210. Interpretive Summary: Pesticides are a diverse group of chemicals whose use helps farmers provide a safe and secure supply of food and fiber at relatively low cost. While potential benefits are substantial pesticide use may have adverse impacts. One of the most serious is due to runoff and drainage in landscapes where pesticides are applied. This may carry residues into drinking water supplies and threaten aquatic ecosystem health. Thus systematic water quality monitoring is often needed. In this study we demonstrated that use of a common laboratory technique, solid-phase extraction (SPE), prior to shipment of samples to testing laboratories can facilitate implementation of monitoring programs. The work was a collaborative effort between research groups working in Egypt and the USA. Water samples were collected in Egypt where they were processed by SPE. The SPE cartridges were then shipped to the USA where they were eluted and analyzed. The study permitted the first rigorous assessment of the potential for pesticides to contaminate the Nile River and water supplies used by the >16,000,000 residents of Greater Cairo. Residues were detected; however concentrations were well below established water quality thresholds. Results showed that water quality risks of intensive pesticide use for crop production in the region does not appear to present significant risks to human health and environment. Simultaneous implementation of a rigorous quality assurance program showed that SPE when used in this way effectively preserved sample integrity. In addition shipping costs were modest and sample handing logistics greatly simplified. Study results raise the possibility of use of SPE to extract samples at remote sites in the USA or internationally. This will make pesticide monitoring in settings that otherwise would not be feasible.
Technical Abstract: The portability, ease of use, and potential to enhance analyte stability makes solid-phase extraction (SPE) an attractive technique for extracting water samples collected for pesticide residue analysis prior to their shipment to analytical laboratories. The technique is especially valuable when samples are collected at remote sites and internationally since SPE shipping costs are modest and handling logistics are simplified. In this study the feasibility of using SPE to monitor pesticides residues in drinking water supplies in Egypt was demonstrated. Quantitative recovery and high reproducibility (average = 93%; RSD = 23%) of a structurally diverse mixture of 27 current-use pesticides was demonstrated through analysis of matrix spikes prepared in the field, SPE, SPE cartridge shipment to the USA, and analysis of extracts by HPLC-APCI-MS. Simultaneous analysis of unspiked samples permitted conduct of reconnaissance survey of pesticides in raw and filtered drinking water in Greater Cairo where water is supplied by withdrawals from the Nile River. Four active ingredients (atrazine, diazinon, malathion, and tribufos) and one degradate, DEA, were detected and confirmed in one or more samples. Residue levels in all cases were below drinking water and “harm to aquatic-life” water quality thresholds indicating risks are relatively small; however the scale and scope of the study was small. Further monitoring is needed to define spatial and temporal variation in residue concentrations that may occur.