TRIPHENYLTIN AND ITS DEGRADATION PRODUCTS IN FOLIAGE AND SOILS FROM SPRAYED PECAN ORCHARDS AND IN FISH FROM ADJACENT PONDS

摘要

Triphenyltin (TPT) is a fungicide used on a variety of crops throughout the world. In this study, pecan orchards in central Georgia (USA) previously sprayed with commercial TPT hydroxide mixtures were found to have TPT concentrations of 8.5 to 37 μg/g dry weight in foliage and 1.2 to 12 μg/g dry weight in soil. Total phenyltin concentrations (monophenyltin [MPT] + diphenyltin [DPT] + TPT) in foliage and soils immediately after application were up to 72 and 26 μg/g dry weight, respectively. Besides TPT, DPT and MPT were present in the leaves and soils, with MPT generally the predominant compound. The proportion of MPT to TPT in pecan leaves increased with time after spraying, which was indicative of photolytic degradation of TPT. Microbial degradation of radiolableled TPT in soil or sediment samples was slow, with only 5% degraded during a 14-d incubation period. Triphenyltin was absent from the subsurface soils (2 to 15 cm depth) even though it had been sprayed eight to 10 times a year at a rate of 850 g/ha for the past 10 years. In an orchard where the last spraying was carried out approx. 2 years ago, TPT was absent, but MPT was present at approximately the same concentration as recently sprayed orchards. Fish (blue gill, largemouth bass, and channel catfish) from a pond near a recently sprayed pecan orchard had TPT as well as DPT and MPT. The predominate phenyltin in all fish was MPT, with 22 μg/g wet weight in the liver of catfish. Radiolabeled TPT was only slowly metabolized by the fathead minnow, with 2% of the TPT metabolized to DPT after 6 d of exposure via water. Photodegradation appears to be the major factor affecting the fate of TPT in soils.