Biodegradation of petroleum tar in contaminated sediments of the Eastern Mediterranean shores and associated microbial dynamics.

The Eastern Mediterranean coasts were impacted by several oil spills over the past two decades where tar residues were encountered on the shoreline. The majority of research on marine tar residues has focused on tar formation, chemical composition, transport, and fingerprinting to trace petroleum oil spills. Only a few studies have assessed the biodegradation of tar in the marine environment, and no studies have examined the evolution of the associated microbial communities. This research evaluated the biodegradation of tar residues in contaminated beach sediments of the Eastern Mediterranean coast of Lebanon. Biodegradation experiments were conducted in laboratory microcosms over a period of 56 days at 18°C and 28°C. Tar removal throughout the incubation period was monitored by the measurement of residual IMPORTANCE: The planned oil and gas extraction activities of the Eastern Mediterranean coasts increase the risk of potential oil spills and threaten the Mediterranean shoreline with devastating impacts. A recent oil spill has resulted in huge amounts of tar residues washing up along the Lebanese southern coastline, affecting Nature Reserve shores known to be a nesting ground for several species of endangered turtles. The majority of research conducted on marine tar residues has studied tar formation, distribution and prevalence, chemical composition and tracing, transport mechanisms, as well as human and ecological effects. The biodegradation of spilled petroleum tar in aquatic media and the associated microbial dynamics are still poorly addressed in the literature. This study contributes to the state of knowledge and current scarce literature on petroleum tar biodegradation in marine environments and provides guidelines to spill responders for an effective bioremediation response plan to address future potential tar contamination.