HOW MUCH OIL HAS BEEN COMPLETELY DEGRADED BY MARINE ORGANISMS?
There are no data available from the scientific literature or the National Incident Command on
rates of decomposition or weathering of oil released from the BP spill. Because so much oil
exists as micro-droplets in deep, very cold ocean waters, it is difficult to infer decomposition
rates from studies of previous spills occurring closer to the surface. However, several scientific
studies are currently underway to directly address this critical need.
We asked our scientific experts to estimate, as best they could, the percentage of subsurface oil
that has degraded. They suggested a range of between 5% (see Figure 3) and 10% (see Figure 2).
Given that estimate, we calculated that between 168,000 and 319,000 barrels have been removed
from the Gulf through degradation. This is equivalent to 4-8% of the total oil released into the
water.
However, it is important to realize that the degradation of crude oil by marine organisms mostly
entails short-chain hydrocarbons—not the more toxic, polycyclic aromatic hydrocarbons
(PAHs). Mass balance calculations, such as we are doing here, do not reflect this preferential
decomposition. The most toxic components of crude oil are the least likely to be naturally
degraded.