Bioaccumulation of hydrocarbons
The incorporation of even minimal quantities of hydrocarbons
in the tissue of a marine organism, through uptake of dissolved fractions
across the gills or skin or direct ingestion of the pollutant, can affect
its predators. If the pollutant is not broken down in the course of the
organism’s metabolic processes, it can become increasingly concentrated
all the way along the food chain. This is the phenomenon of bioaccumulation
of chemicals through the food chain until they reach considerably higher
concentrations than those found in the water.
At every link in the food chain, organisms consume around 10 kg of matter from the level below to produce 1 kg of their own living matter. If a contaminant passes from one level to another without being broken down, its concentration in the living matter multiplies nearly ten times at each link in the chain. Organisms at the top of the chain can therefore be exposed to very high concentrations of a product which did not affect the organisms further down the chain and can be detrimental to their health.
Hydrocarbon bioaccumulation is often put forward as a major concern when an oil spill occurs. It has never been definitively proven in the case of oil spills, a subject which was broached in a French study, published under the title “Marées noires et environnement” (black tides and the environment), which is discussed in detail in the final chapter. This lack of proof does not imply that the risk does not exist. Fortunately however, many of the components of oil and petroleum products are biodegradable at some level of the food chain. Only the rarer, high molecular weight PAHs tend to have a significant bioaccumulation potential as far as the highest levels of the food chain. Therefore bioaccumulation, if indeed it occurs, is generally of a sufficiently low level to be masked by other clearer phenomena in the incidence of an oil spill.