CONTRIBUTION OF ZOOPLANKTON TO DISAPPEARANCE OF ORGANOPHOSPHORUS INSECTICIDES IN ENVIRONMENTAL WATER

Organophosphorus insecticide-tolerance and degrading abilities of five zooplankton species, including Sinocalanus tenellus a dominant specie s in Lake Shinjiko and Oithona davisae a dominant species in Lake Naka noumi, and rate constants for disappearances of insecticides in enviro nmental water were examined. The contribution of zooplankton to disapp earance of insecticides in environmental water was evaluated as the ra tio of insecticide disappearance rate caused by zooplankton to the dis appearance rate in lake water. The tolerance of S. tenellus and O. dav isae to phenthoate and diazinon was lower than the tolerance to other tested insecticides, such as cyanophos, salithion, malathion, fenitrot hion and dichlofenthion. Disappearance of malathion and dichlofenthion from sterilized lakes water and artificial brackishwater in the prese nce of zooplankton were faster than those of other chemicals. R Malath ion-degrading activity of zooplankton was high and the activity for di chlofenthion was low. The insecticide-degrading abilities depended on insecticide types. The maximum contributions of zooplankton to disappe arances of several insecticides in Lake Shinjiko were estimated as fol lows: 0.4% for fenitrothion, 8.1% for malathion and 3.4%, for salithio n in spring, and 0.6% for fenitrothion, 4.6% for cyanophos and 0.8% fo r diazinon in autumn. The maximum contributions of zooplankton to disa ppearance of several insecticides in Lake Nakanoumi were estimated as follows: 0.1% for fenitrothion, 0.7% for malathion and 1.9% for salith ion in spring, and 0.1% for fenitrothion, 2.7% for cyanophos and 1.2% for diazinon in autumn.