The Chemical Culprits in Great Lakes fish

from Up to the Gills Report by Environmental Defence, July 2007

Mercury
Exposure to mercury is known to cause damage to the central nervous system, act as a reproductive toxin, and cause cancer. Mercury is considered a toxic substance under the Canada Environmental Protection Act and is listed as a chemical for virtual elimination in the Great Lakes Water Quality Agreement, yet it continues to be released across Ontario and the Great Lakes States into the air, land and water. Some mercury occurs naturally in the environment, but the major sources of mercury pollution are emissions from coal-fired power plants, mining, incineration and manufacturing. In lake sediments, mercury is converted into highly toxic methylmercury, which can bioaccumulate in the fatty tissue of living organisms, particularly fish living in polluted waters. Fish and other seafood, with methylmercury concentrations 10 to 100 times greater than other food, are the main sources of methylmercury in the human diet.

Dioxins and Furans
Dioxins and furans are byproducts of industrial processes, particularly incineration. Seventeen of the 210 different dioxins and furans are considered toxic enough to warrant fish consumption advisories. These chemicals can have adverse effects on the liver, skin, immune system, and nervous system, and can cause certain types of cancers. Dioxins and furans can travel long distances, and accumulate and remain in animal body fat for long periods of time, so fish, other meats and milk have higher levels than fruits, vegetables and grains. Dioxins and furans are among a small number of chemicals targeted for “virtual elimination” by the United States and Canada, but the compounds continue to be released into the water, air and soil of the Great Lakes basin.

PCBs
First manufactured in 1929, Polychlorinated Biphenyls (PCBs) have been used as ingredients in a number of industrial processes, including manufacture of coolants and lubricants. PCBs were first detected in the Great Lakes in 1966. Although a North American ban on manufacturing and importing PCBs was put in place in 1977, they continue to be permitted for use in older industrial machinery and processes. PCBs are listed as a chemical for virtual elimination under the Great Lakes Water Quality Agreement, and are particularly persistent because they are stored in the bodies of humans and animals for long periods. They can cause skin ailments, numbness in limbs, muscle spasms, chronic bronchitis, nervous system problems, and cancer. In the Great Lake basin, recent studies indicate fish consumption remains the major cause of PCB exposure.

Pesticides
Pesticide exposure is linked to non-Hodgkin's lymphoma, leukemia, neurological problems, reproductive abnormalities, immunotoxicity and cancer. Children are at particular risk from pesticides because they are more vulnerable to the effects and have greater exposure to the chemicals. While some municipalities around the Great Lakes have instituted bans on cosmetic pesticide use, there is still widespread use in the Great Lakes basin for domestic, commercial and agricultural purposes. Toxaphene is an insecticide heavily used in the United States until it was banned in 1990 that has historically triggered significant fish advisories in Lake Ontario, Lake Huron and Lake Superior.