Bioaccumulation and Biomagnification

Short-term exposures to crude oil fractions did not lead to mortality in mayflies, but long-term exposures did (see more here). These results may indicate that the mayflies were accruing toxins over time, a process known as bioaccumulation. During the 3 week experiment the mayflies would have the potential to continuously consume residue as they fed on organic matter within the contaminated sediment. Small doses of residue did not seem to affect the mayflies, but the accumulation of toxins over time could have led to the increased mortality.

If the mayflies accumulated a fair amount of toxins in their bodies prior to death, they would transfer those toxins to any organism that consumed them. This means that insect-eating fish such as bluegill would be consuming residue toxins even though they didn’t directly feed on sediment.

In turn, these bluegills would accumulate toxins and pass them on to their predators. Because a bluegill will eat many mayflies, it has the potential to end up with a much higher level of contaminant than any of the individual mayflies it consumed. This process is referred to as biomagnification and explains how pollutants can make their way through the aquatic food web and affect species that seem far removed from the original pollutant. (more information on Bioaccumulation and Biomagnification)

Theoretical toxin levels in select organisms as a result of biomagnification. Toxins levels will be higher in organisms nearer the top of the food web. The toxin levels in humans will depend on the quantity, size, species and origin of fish eaten.