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Oil cleanup agents do not impede natural biodegradation, research reveals

Using spill-treating agents to clean up oil spills does not significantly hinder naturally occurring oil biodegradation, according to a new study. The research, in Applied and Environmental Microbiology, provides information that will be useful in future oil spills.

Biodegradation is an incredibly important natural process when it comes to oil spill cleanup. A significant portion of the oil can be permanently removed from the contaminated area through microbial activity. On-scene coordinators and other first responders must weigh the benefits against potential risks of any response action, such as using spill-treating agents. Emergency response actions to oil spills vary widely depending on the scale of an oil spill, location and environmental conditions.

Different treating agents serve different functions. Oil dispersants break the oil into smaller droplets. Surface washing agents lift stranded oil from solid substrates. Chemical herders corral oil into a thicker slick to ease mechanical removal and can also enhance burning efficiency.

Oil dispersants are the most well-known category of spill-treating agent due to their unprecedented use during the high-profile Deepwater Horizon oil spill. Their effect on oil biodegradation has been extensively scrutinized by the scientific community. Some of the lesser-known spill-treating agents are used far more frequently than chemical dispersants, and their impacts on oil biodegradation remain unknown.

"We were able to address some of those knowledge gaps with our laboratory-based study investigating the impacts of a surface washing agent and a chemical herder on oil biodegradation," said lead study author Kiara Lech, Ph.D., a research biologist at the Center for Environmental Solutions and Emergency Response at the U.S. Environmental Protection Agency's Office of Research and Development.

In their study, Lech and colleagues exposed a community of bacteria to crude oil that was treated with two types of spill-treating agents (surface washing agent or chemical herder); they also had sets of single-agent control treatments where the microbial community was only exposed to crude oil alone or the spill-treating agents alone. They then monitored how the microbial community responded to the addition of crude oil and spill-treating agents.

The researchers observed an initial delay in oil biodegradation with the addition of the treating agents, but that inhibition was later overcome by the diverse microbial community that actively degraded the treating agents simultaneously with the crude oil. A subset of oil compounds did not degrade as extensively when treated with a surface washing agent compared to the oil-alone treatment. The researchers concluded that in the natural environment, this impact would likely be negligible but should be evaluated.

"One of the most interesting findings was how quickly and effectively the oil-degrading bacteria were able to pivot to the treating agents as a food source," Lech said. "We found striking and significant differences in the composition of the microbial communities, with certain groups of bacteria becoming more prominent depending on treatment."

Lech said that at the EPA Office of Research and Development, one of the core responsibilities is to provide regional and programmatic partners with research that supports their decision-making during an environmental emergency.

"The nagging question during an oil or other hazardous substance spill response is 'how clean is clean?' Thankfully, microbial communities are well-adapted to degrade oil, and we rely on biodegradation and other processes to whittle away at residual contamination," Lech said. "The findings presented in this study provide confidence that using these spill-treating agents will not significantly hinder naturally occurring oil biodegradation."