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1.14 Bioaccumulation and Biomagnification (Sec 5.3 pg 120-125)
We know that energy and matter move up the food chain – pollutants also move up the food chain from one trophic level to the next!
If pollutants aren’t degraded, they can build-up & become concentrated in the tissues of organisms; the build-up of chemical substances in organisms is known as bioaccumulation.
Biomagnification is a related process that causes higher and higher concentrations of pollutants to accumulate in organisms that are higher in the food change (Fig.1&2p.121-2).
note that even small concentrations introduced low enough on the food chain can have huge effects on carnivores (parts per million = ‘ppm’; parts per billion = ‘ppb’)
Pesticides (chemicals used to control organisms humans consider ‘pests’) often bioaccumulate in consumers. • DDT is a ‘famous’ example – it was widely used in the 50’s and 60’s to control pests (mosquitoes) carrying malaria. DDT (now banned in Canada) is soluble in fat but not water, and so accumulates in the fatty tissues of consumers, and is not released through urine or sweat.
DDT remains in the environment for a very long time – even tiny amounts have big effects. • studies have shown that DDT interferes with the deposition of calcium that makes eggs laid by female birds of prey hard enough to survive, leading to reduced reproduction. • Pesticides also bioaccumulate in secondary consumers (e.g. blue herons), and humans too.
Heavy metals (a group of dense metal elements found in the middle of the periodic table) can be part of toxic wastes from industrial processes, and can be very harmful to organisms in the environment (see and understand Table 1 p.123)
Endocrine-disrupting compounds (EDCs),including DDT & PCBs, are a group of particularly concerning chemicals that bioaccumulate – they either mimic or disrupt the regular function of certain hormones in organisms that control important processes like reproduction. • Some EDCs mimic estrogen and have negative impacts on animals.