Research Product

Oysters, Crassostrea virginica, were reared from juveniles (27 mm mean height) to sexual maturity in flowing sea water chronically polluted with low levels (3.0 ppb, µg/l, or less) of DDT, toxaphene and parathion. The study was performed in two phases over a period of 2 years, the insecticides being administered as a mixture during the first phase and separately in the second phase of the experiment. The weights of oysters grown in a mixture (1.0 ppb each of DDT, toxaphene and parathion) of the three insecticides were significantly less (a=0.05) than control oysters after 9 months. This loss of weight was about 10% of the total body weight (including shell) of the oysters. Weights and heights of separate groups of oysters reared in sea water containing about 1.0 ppb of either DDT, toxaphene or parathion were not statistically different from controls. Oysters reared in the pesticide mixture had tissue changes associated with kidney, visceral ganglion, gills, digestive tubules and tissues beneath the gut. A mycelial fungus was also present, indicating a breakdown in the oyster's natural defense against this parasite. Eggs and spermatozoa removed from the oysters developed into 24-hour trochophore larvae. The oysters accumulated relatively high levels of DDT and toxaphene but eliminated them during a 3-month depuration period.