The brackish water clam, Villorita cyprinoides var. cochinensis, was exposed to an oil refinery effluent at 8, 16 and 24 ppt salinities. Significant fluctuations in total hemocyte counts were observed in those exposed to the effluents at 16 and 24 ppt salinities. The significant drop in the total counts at 16 ppt has been attributed to cell injury and cell death, while increase in the total counts at 24 ppt has been attributed more to trans-migration of hemocytes from hemocyte reservoir than to hemocyte proliferation under stressed condition. Since the internal defense mechanisms in molluscs are primarily cellular in nature, fluctuations in total hemocyte counts could theoretically affect the efficiency of immune system in them.

Water pollution is an undesirable physical, chemical, and biological change in the environment caused largely due to anthropogenic activities such as industrialization and urbanization, which have detrimental effects. The main cause of water pollution is the discharge of solid and/or liquid waste products containing pollutants on to the land surface or into water bodies. The larger volume of discharged waste is in the form of effluents from industries. The effluents discharged from petrochemical industries contain mostly petroleum hydrocarbons such as oil, grease, and other petroleum fractions. Acute and insidious environmental problems are associated with the presence of petroleum hydrocarbons in the estuarine environment. Major changes are brought about in the physiology of estuarine organisms, and in the estuarine ecology. These changes may persist for days to years.

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