Movement and retention of propanil N-(3,4-dichlorophenyl)propanamide in a paddy-riverine wetland system in Sri lanka.
Propanil concentrations were studied in paddy soil and water, in water and substrate of adjacent wetlands receiving runoff from the paddy and in tissues of 2 wetland macrophytes common in those wetlands. Field sampling was carried out during the wet season of 1993-94 and the 1994 dry season in eastern Sri Lanka, following a single application of propanil at about 3.5 litres/ha. Propanil was detected in paddy soil up to 52 days after treatment (DAT) and in paddy and wetland water samples as late as 14 DAT. Propanil was not detected in the wetland substrate. Relatively high propanil concentrations (up to 0.575 mg/kg) were found in leaf and stem tissues of the edible plants Ipomoea aquatica and Limnocharis flava 52 DAT in the wet season, but propanil was not detectable by 132 DAT. Tissue concentrations during the dry season were less consistent. Propanil accumulation and retention by macrophytes may be important factors in reducing propanil concentrations in wetland water below levels shown to be acutely toxic to other wetland biota. However, propanil so retained may pose a danger to humans regularly consuming wetland plants.