Recent laboratory research at the University of Alaska Fairbanks, with funding assistance from the Bureau of Ocean Energy Management, suggests that some oil spilled on an Arctic beach would likely evaporate quite quickly, but that biodegradation of the oil would be relatively slow.
Depending on how sandy a beach is, wave and tidal action may remove much of the oil. Longer chained hydrocarbons would tend to persist in the beach and would be relatively difficult to remove.
A report on the research says that the researchers conducted experiments in two laboratory settings using beach material from Barrow, on the northern coast of Alaska.
In the first setting, the beach material was placed in jars and soaked in water at two salinity levels to simulate beach conditions. Nutrient from fertilizer was also placed in each jar. Different amounts of crude oil were put into different jars. Some jars were then held at a temperature of 20 degrees Celsius (68 degrees Fahrenheit) for six weeks, while other jars were kept at 3 C (37 F) for nine weeks. As a measure of biodegradation of the oil, the scientists measured the amount of carbon dioxide emitted. Volatile hydrocarbon material released from the oil was also measured. The scientists measured the amount of crude oil remaining in the sediments after the experiments, and they estimated the quantity of microbes in the sediments.
In the second setting, beach sediments, together with crude oil, were put into columns constructed from PVC piping, and water was flushed through the material every 12 hours over durations ranging from three to 18 days, to simulate tidal action. Solid or liquid fertilizer was added to some columns as a nutrient. As before, experiments were conducted at temperatures of 3 degrees and 20 degrees Celsius. Released carbon dioxide and volatile material were measured, and after experiment completion, samples from different levels of the column were analyzed.
Experimental results
The experiments using the jars showed that, although higher levels of oil degradation to carbon dioxide took place at the higher temperature, less than 10 percent of the oil biodegraded at either temperature level. However, at both temperatures about 40 percent of the oil evaporated, with most of this vaporization happening during the first week. Increasing the amount of oil in the sediment increased the amount of vaporization but reduced the percentage of the oil vaporized. On average after six weeks about 70 percent of the original oil remained in the sediment.
In the PVC column experiments the water flush moved the oil through the sediment, with only background levels of hydrocarbon left in pebbly sediments after 18 days. Considerably higher hydrocarbon levels remained in sandy gravel. On the other hand, over time, biodegradation in sandy gravel exceeded that in the pebbly material. And oil degradation over 18 days was higher in the higher temperature experiments. Fertilizer had little impact on the degradation.
Key findings
The researchers concluded that within a few weeks about 40 percent of the spilled oil would disappear from the beach sediment, mostly from evaporation, with the ambient temperature having little impact on this outcome. Relatively little biodegradation would take place during this period, although more biodegradation would be likely over longer timeframes. Bioremediation through nutrient application is unlikely to have much impact. The longer chain hydrocarbons that tend to remain in the sediments would be more difficult to remove.
In situations where a beach is subject to tidal and wave actions, most of the hydrocarbons would wash out of the pebbly sediments within an 18-day period. Oil in sandy sediments, on the other hand, would be much more resistant to this type of washout. And, in general, sandy beaches would be much more difficult to clean up than pebbly beaches, the researchers concluded.
This story originally appeared in Petroleum News and has been republished with permission.