PAHs from fossil fuels and their impact on oysters

Petroleum, coal and gas are used in enormous quantities to provide the energy for modern civilizations. This consumption releases numerous hazardous organic substances that are either directly present in fossil fuels or may be generated in chemical reactions. The most toxic products are polycyclic aromatic hydrocarbons (PAHs), cresols and phenols. There is growing evidence indicating that PAHs are carcinogens and cause abnormalities in most invertebrate and vertebrate species. The anthropogenic sources of PAHs and the contamination of estuaries and marine environments will be reviewed in this chapter. Oil spills, coal tar, creosote, motor vehicle exhaust, industrial processes and run-off from urban environments are significant sources of contamination. This chapter describes the pathways of these compounds into aquatic environments. Quantitative studies reveal the extent of contamination of aquatic environments caused by PAHs. Monitoring programs use oysters and bivalves as sentinel organisms because they bioaccumulate PAHs. These studies show that the oyster's environment may be contaminated by a variety of external factors. In addition, oyster farms use tar-treated and creosote-treated timber which also contaminates the environment. In this chapter data is provided from a study of PAHs in Sydney rock oysters and Pacific oysters in Port Stephens, Australia. The concentration of total PAHs was 500-2,500 mg/kg in the sediment on the butt of creosote-treated posts and only 30 mg/kg for sediment on the butt of tar treated posts. Also, wild oysters that grow on creosote-treated posts had high levels of phenols and P AHs. Bioassays with contaminated sediments demonstrated that bioaccumulation of PAHs by oysters can be about 50,000 times higher than that of the PAHs in water. PAHs are relatively stable compounds with long residence times. The clean-up of aquatic environments where oysters are grown may remove the primary source of contamination, and improve the visual aesthetics. However, this process can cause disturbance and dispersal of contaminated sediments, so there is a dilemma for farmers and administrators. This may impact on the health of workers, consumers and aquatic organisms. PAHs have been reported to cause histopathological lesions in oysters and detrimental effects on the immune system. Hence, there needs to be an improved awareness of the risks posed by PAHs. The research reviewed in this chapter strongly suggests the need for improved management strategies to minimize the risks from PAHs.