Bioaccumulation of Pollutants

Bioaccumulation refers to the gradual build-up over a period of time of a chemical in an organism's body. When an organism absorbs a substance - in this case, a pollutant - from a medium such as water, that pollutant is then distributed throughout the organism's system. Predators that consume these organisms can receive the pollutants as well. The phenomena can cause significant environmental health risks. A variety of different pollutants commonly cause problems with bioaccumulation.

Pesticides

• A pesticide refers to any substance that people, often farmers looking to protect crops, spray on large portions of land to remove pests, typically insects and weeds. But the chemicals are often toxic, and rain can wash pesticides into creeks and other water sources, which eventually find their way into rivers, estuaries and the ocean. In these places, tiny organisms such as phytoplankton can consume the pollutant, which bioaccumulates up the food chain as small fish eat the phytoplankton and the pollutant, followed by the big fish who eat the small fish, and finally a human or animal that eats the big fish. One popular bug-killing pesticide, dichlorodiphenyltrichloroethane (DDT), caused pollution problems prior to 1972 before it was banned, when rain washed the spray into creeks, contaminating predatory birds such as eagles and pelicans that ate contaminated fish. The pollutant resulted in eggshells that were too thin and led to premature death of baby birds.

Emissions

• Industrial smokestacks and automobiles can pollute the air with their emissions. This air pollution rises initially, but eventually it returns to earth in the form of rainfall, where organisms can absorb the pollutants into their systems and eventually spread them to other species.

PCBs

• Polychlorinated biphenyls (PCBs) are used in capacitors, transformers, hydraulic fluids, adhesives and other products. They can cause skin disorders, liver dysfunction, tumors and reproductive disorders. PCBs can leak into the water and soil and bluefish and striped bass often absorb the pollutant, making them toxic for human consumption.

Mercury

• Mercury is a toxic metal that can cause mercury poisoning, a sometimes deadly illness that usually causes impairment in vision, speech and hearing as well as a lack of coordination. Mercury may bioaccumulate in the environment when it seeps into the soil and water supply. Microscopic organisms such as bacteria and phytoplankton absorb the mercury, leading to bioaccumulation over a wide swath of species.