Tar balls (TBs) are dark-coloured, sticky blob of oil residue that forms when crude oil floats in aquatic environment. TBs are usually coin sized, but in some cases they are as big as tennis ball. Sea currents and waves sweep them onshore in some stretches of coastline, depending on the beach orientation to the waves, etc. TBs are a serious threat for tourists and the seafood sector, in addition to being a source of marine pollution.
The possible oil-spill sources in the Arabian Sea are offshore oil fields located off Mumbai-Gujarat coast; clandestine release of tanker ballast, along the International Tanker Route; and discharge from the refineries, industries, power plants, ports along the Gulf of Kachchh and the Gulf of Khambhat. There are also many offshore oil fields, including Bombay High oil fields, where oil spill can occur.
The lighter components (methane, hexane, and octane) evaporate fast during photo-oxidation once the crude oil is discharged at sea. Direct and indirect photolysis can occur in the aromatic and unsaturated fractions of hydrocarbons. Microbes may also breakdown the residue, allowing it to dissolve in water and leave the crude behind, which then mixes with seawater to form a thick, sticky tar. When tar is rolled over the waves, it coagulates into balls that penetrate the intertidal zone and are deposited on beaches, causing environmental damage.
According to a 2015 study published in Total Environment, oil seepage in the Bombay High oil fields could possibly contribute to TBs throughout a 650-km stretch of coast stretching from Gujarat to Goa. If oil is dumped into the sea in April, according to a research based on computer simulations of oil-slick trajectories, the remnant will go southeast. Under the influence of the southwest wind direction and the ocean circulation generated by the winds, it would reach the Goa coast by May.
The leaching of Polycyclic Aromatic Hydrocarbons (PAHs) into the marine environment when oil slicks float over time can have negative effects on marine life. Because certain compounds contained in TBs, such as fluorine, naphthalene, and acenaphthene, are cacogenic, these compounds are added to genetic materials and induce genetic diseases in marine species as a result of long-term exposure. PAHs are more likely to affect sessile animals with limited mobility (mollusks, crabs, shellfish, and shrimps). There is enough data to suggest that PAHs such as benzo(a)pyrene and chrysene, even at extremely low concentrations, are linked to an increased cancer risk as well as other negative health impacts such immune suppression and congenital defects. Consuming contaminated sea food like oysters, clams, and shrimp people are exposed to the PAHs and pathogens, which may increase the risk of cancer.
PAHs can render fish and shellfish dangerous for human consumption even if no deadly effects are evident. Constant exposure to oil-related contamination in the coastal environment can have serious long-term ecological implications, leading to the extinction or impairment of some species.
