Which is least likely to speed up the rate of decomposition of oil by microorganism?
Answers
The Deepwater Horizon well was finally capped 85 days after the explosion and over that time about 780 000 cubic metres oil had escaped into the sea.
The Gulf of Mexico oil spill is different from most previous spills. In the past, most major spills have been at the surface. The Deepwater Horizon rig was drilling in seawater about 1500 metres deep, and the oil that gushed from the broken well on the sea bed was released at great depth.
A lot reached the surface, but some has probably travelled in deep water currents and it is hard to predict the effects that this might have, and how long the oil will take to decay. One of the agents of decay is microbial action, where bacteria and other microbes are able to utilise components of oil as a food source.
Crude oils vary in composition but all contain a mixture of hydrocarbons, molecules containing carbon and hydrogen only. Some hydrocarbons have ring shaped molecules, and include benzene, naphthalenes, xylenes and toluenes.
Hydrocarbon molecules containing two or more rings, are known as polycyclic aromatic hydrocarbons (PAHs), and they are highly toxic to marine organisms. Hydrocarbons made of straight chain molecules are also abundant. The longer the hydrocarbon chain the greater the viscosity - the thickness and resistance to flow).
The components of crude oil are separated by refining, and oil tankers may be carrying a refined fraction rather than crude oil.
Many marine microbes feed on oil and refined oil products, gaining energy for growth and reproduction by breaking down the hydrocarbons, using the process of respiration. These microbes are abundant where oil seeps naturally through fissures in the oceanic floor into seawater, as happens in the Gulf of Mexico.
After an accidental oil spill into open water, the numbers of oil eating microbes increase. Oxygen concentration is high in sea water close to the surface, so microbes break down oil at relatively rapid rates using aerobic respiration.
Oil eating bacteria include Alcanivorax borkumensis, which breaks down straight-chain and branched-chain hydrocarbons 1. As the oil is fragmented into droplets by wave action, Alcanivorax cluster on the surface of droplets forming a biofilm, and secrete biosurfactant which helps with ingesting the oil.