Herald: Impacts of tar balls on marine ecosystem

Impacts of tar balls on marine ecosystem

16 May 2019 05:30am IST

Report by
Alvarinho Luis

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16 May 2019 05:30am IST

Report by
Alvarinho Luis

Deposition of tar balls on beaches of Goa is a common phenomenon during May to October. Tar balls or globs, which are dense accumulation of oil residues made up of hydrocarbons, have been a source of pollution on the pristine beach environment worldwide. Tar balls have two main sources: an offshore oil spill from drilling platforms or discharge of ballast from tankers (tanker-wash derived spills), barges or refineries and a natural oil seep from fissures on the ocean floor. When crude oil is released in offshore ocean, the lighter components of the oil evaporate (volatilisation) or dissolve in the water, leaving behind the heavier types of oil, like crude, which then mixes with saltwater to create a thick, sticky substance called tar. It changes its physical composition and its extent due to weathering caused by wind, waves and currents. The tar coagulates into balls and ends up on the beach offering a nasty, sticky surprise to beach goers who steps on them.

According to published research for west India coast, this problem has been monitored since 1970 under Marine Pollution (Petroleum) Monitoring Pilot Project of the Integrated Global Ocean Station System. Since the international tanker route passes closer to the west India coast, it is understood that tanker ballast discharge is the source of the tar balls. According to research published in Science of The Total Environment in 2015, the researchers tracked that the source of tar balls as tanker wash and also pointed out that the Bombay High oil fields can also contribute to tar balls along 650 km stretch of the west India coast, running from Gujarat in the north to Goa in the south. The southwesterly wind direction during May-September force the tar balls toward the coastline.

Because these tar balls end up in a variety of shapes and sizes, sea turtles may mistake them for food particles, eat them, and die from the toxic compounds attached to them. Their constituent chemicals ‘hydrocarbons’ are a threat to sensitive marine ecosystem such as molluscs and shrimps. The polycyclic aromatic hydrocarbons are associated with elevated cancer risk and other detrimental health effects such as immune-suppression and birth defects. Tiny tar balls even in small amounts can kill a fish larva - which means that oil stored in deep layers of beach sediment present a potential source of toxins to near-shore waters and groundwater. Fish, may consume smaller bits of tar, and if a hungry shark chomps down on some fish that just finished its tar ball meal, the risk of biomagnifications becomes a real risk.

In research published online in November 2011 in the journal EcoHealth, Auburn University microbiologist Cova Arias and colleagues discovered that Deep Horizon tar balls found months after the spill contained high levels of bacteria (between 5.1 million and 8.3 million colony-forming units per gram), almost 10 times the level of Vibrio vulnificus found in the surrounding sand. V. vulnificus - a naturally occurring bacterium that thrives in warm seawater is absorbed by filter-feeding oysters. It is a leading cause of seafood-borne disease fatalities.
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