Sampling and analysis of airborne residues of paraquat in treated cotton field environments

Abstract

A method was developed for the analysis of paraquat residues in airborne particulate matter collected by filtration or impaction. The method is based on extraction of paraquat with 6N hydrochloric acid, transfer of residue to saturated ammonium bicarbonate solution, and reduction of the resulting residue with alkaline sodium borohydride to a mixture of two tertiary amines with subsequent determination by nitrogen-selective gas chromatography (GLC). Recoveries ranged from 74 to 96% for filters spiked at 0.05 microgram and above; the limit of detection is approximately 0.5 ng/m3 for high volume air samples. Paraquat concentrations measured in the air downwind from two commercial applications to cotton during spraying fell regularly from extrapolated interval-average values of 4.31 and 10.7 microgram/m3 at the 1 m downwind edge of the two fields to less than 50 ng/m3 at approximately 400 m downwind. Downwind samples taken 2 to 4 hr after spraying contained 1 to 10% as much paraquat as those during spraying, and by 5 to 7 hr no paraquat was detectable in the downwind air. Paraquat was also found in the airborne particulate matter during mechanical harvesting of one of the fields, the maximum interval-average values being 1,245 and 516 ng/m3 just outside and inside an open cab, respectively. The analytical findings for paraquat are compared with those for S,S,S-tributylphosphorotrithioate (DEF), a component of the harvest aid mixture employed, and discussed in terms of occupational exposure, potential hazard, and recommended occupational practices.