Effects of pollution by petroleum hydrocarbons on the bivalve venus verrucosa

Abstract

Benthic fauna inhabiting shallow coastal waters are often exposed to chronic low levels of petroleum hydrocarbons (PHC) especially in specific areas in the Mediterranean. To help in assessing any environmental impact of such exposure, a number of biological responses of the bivalve, Venus verrucosa have been investigated in the laboratory. Water-accommodated fractions (WAF) or chemical dispersions of Kuwait crude oil have been used in these studies. Acute toxicity studies indicated that exposure to levels of WAF varying from 820 to 300 µg 1- 1 produced 80% mortality within 96 to 144h. Both short-term exposure to chemically dispersed PHC (initial concentrations ranging from 30 to 10 mg 1 -1 > and long-term exposure ta WAF < 150d to 100 µg 1-1 caused changes in rates of respiration , feeding, and excretion. This resulted in a decrease in scope for growth and oxygen ta nitrogen ratio and to a reduction in somatic growth and body condition indices in the long-term experiment. Changes in gill retention efficiencies for particles less than 6 µm in diameter and in various gill ciliary systems were recorded. Most PHC accumulated in the digestive gland where digestive cells were found to be reduced in height and had reduced lysosomal stability. Short-term exposure to higher concentrations produced more drastic cellular responses in other organs. The animal was although these induced to greater exposure. altered although no repeated stimuli was not affected. unable to detect and avoid PHC changes in valve activities leading Siphonal reactions to light were change in their habituation to detected. Burrowing activitists were not affected. By using different stress indices spanning several levels of biological organisation of Venus verrucosa it was possible to provide an integrated view of this species response to PHC and to conclude that such exposure would present a potential threat to its populations in the field.