Thursday, July 24, 2014

Bioaccumulation and Biomagnification

Heavy metals (mercury, lead, cadmium), pesticides and herbicides (such as DDT) and endocrine-disrupting chemicals (PCB’s and BPA’s) do not readily biodegrade. These are fat-soluble substances that are stored in organisms and are not quickly broken down by bacteria or other decomposers. Bioaccumulation is the process by which persistent pollutants accumulate in the fatty tissues of organisms. These pollutants are absorbed at a greater rate than they are released and therefore build up within the individual organism. Biomagnification is the process by which persistent pollutants increase in concentration up a food chain. So secondary and tertiary consumers have higher concentrations than producers and primary consumers.

This phenomena has been observed with DDT, causing the thinning of eggshells in raptors, such as the threatened Peregrine Falcon. Rachel Carson, a marine biologist and conservationist,  made the American public aware of the environmental problems caused by synthetic pesticides, such as DDT, in her famous book, “Silent Spring”. DDT is now prohibited in most developed countries.

Mercury has been shown to bioaccumulate in marine food webs, affecting higher order consumers, such as dolphins, sharks and swordfish. As such, Food Standards of Australia and New Zealand recommend that the intake of certain types of fish is limited.

Content Courtesy : vceenviroscience