Persistent pollutants have a tendency to accumulate in the tissues of plants and animals, and to biomagnify through the food web. When a pollutant biomagnifies, it increases in concentration in tissues as it moves through the food chain, from algae or sediments to shellfish to fish to fish-eating birds and mammals. The current list of 15 Great Waters pollutants of concern consists chiefly of air toxics. Nitrogen compounds such as nitrogen oxides and ammonia are also pollutants of concern. In estuaries and coastal waters, excess nitrogen can cause excessive algal growth.
Excess algae can also decrease light available to submerged aquatic vegetation or to corals.
EPA released the first and second Reports to Congress in 1994 and 1997. Determining the relative contributions of local, regional, national, and global sources of atmospheric deposition to specific waterbodies is complex, requiring careful monitoring, modeling and other analysis. The contribution of atmospheric deposition to overall pollutant loadings varies by pollutant and location. The pollutants of concern are associated with damage to many organs in humans and animals, including the liver, kidneys, nervous system, endocrine system, reproductive organs and immunological system. At current levels of contamination, pollutants of concern in the Great Waters pose potentially the greatest health risks to individuals who consume fish from contaminated waters.