Pesticide residues in spray aircraft tank rinses and aircraft exterior washes

Concentrations of the agricultural pesticides pydrin, lorsban, comite, kelthane, orthene and phosdin and some breakdown products were determined in samples of the tank rinsates and exterior washes of 2 spray aircraft after 9 different applications. Pesticides residues analysed in the first tank rinse ranged from 0.947 per cent (lorsban) to 11.70 per cent (pydrin) of the initial tank mix concentration. After the third tank rinse the residue percentage of pydrin was 0.016-0.0435 per cent. The kelthane tank mix and tank rinse contained approximately 0.28 and 0.5 per cent (w/w total kelthane) of p,p'-DDT and p,p'-DDE, respectively and orthene contained approximately 6 per cent (w/w) of its hydrolysis product dimethyl phosphorothioate in the tank mix and 8 per cent in the tank rinse. Regression equations for pesticides residues in the tank rinsates indicated that rinsing efficiency was not related to the nature of the compound or the initial tank mix concentration. Spraying rinse water to the treated field was an acceptable disposable method after calculation of the number of rinses required to reduce concentrations to subtoxic levels. Concentrations of pydrin and lorsban in exterior washes were 0.008 and 0.05 mg per litre, respectively and disposal directly to waterways could produce persistent, localized toxic residues.