Fate of 14C-chlorpyrifos in the tropical estuarine environment

The distribution and fate of 14C-chlorpyrifos were investigated in microcosms simulating the conditions of the tropical estuarine environment of North Vietnam. The microcosms containing brackish water, sediment, clams (Meretrix meretrix) and green algae (Gracilaria verucosa) from the Red River estuary, were maintained for 30 days. The results show that chlorpyrifos released into the water was rapidly adsorbed onto sediment. However, only 1-2% of the initial amount of 14C-chlorpyrifos could be detected in the sediment by the end of the experiment. The accumulation of chlorpyrifos in fauna and flora attained, respectively, a maximum of 5.8% and 2.2% of the initial activity observed at days 3 and 2 after application. The compound 3,4,5-trichloro-2pyridinol (TCP) was the major transformation product of chlorpyrifos found in the microcosm. TCP accumulated in the clam's soft tissues, and, 3 days after application, reached a maximum of 0.5% of the total 14C-activity. The balance of the 14C-activity at the end of the experiment suggests that the main loss of the insecticide from the system was through volatilisation of chlorpyrifos and escape to the atmosphere. The persistence half-time of the compound in the aquatic microcosms was computed at 5 days.