Movement and retention of propanil N-(3,4-dichlorophenyl)propanamide in a paddy-riverine wetland system in Sri lanka

Abstract

Propanil N-(3,4,-dichlorophenyl)propanamide is commonly used as a post-emergent herbicide in paddy rice cultivation in Sri Lanka. This study examined propanil concentrations in paddy soil and water, in water and substrate of adjacent wetlands receiving runoff from the paddy and in tissues of two wetland macrophytes common in those wetlands. Field sampling was carried out during the wet season of 1993–1994 and the 1994 dry season. Propanil was detected in paddy soil and in paddy and wetland water samples as late as 14 days after treatment (DAT). It was not detected in the wetland substrate, but relatively high concentrations were found in leaf and stem tissues of the edible plants Ipomoea aquatica and Limnocharis flava 52 DAT in the wet season, but it was not detectable by 132 DAT. Tissue concentrations during the dry season were less consistent. This accumulation and retention by macrophytes may be important factors in reducing propanil concentrations in the wetland water below levels shown to be acutely toxic to other wetland biota. But, propanil so retained may pose a danger to humans who gather and eat these wetland plants regularly and who may, over several months, accumulate sufficient propanil to be harmful to their health.