At the same time, fish may be contaminated by environmental pollutants, most notably methylmercury. Coal fired power plants are the most significant source of mercury that enters the ocean. Methylmercury is toxic to the nervous system, especially the developing brain. Because of the health risks for babies associated with methylmercury exposure, the United States Food and Drug Administration and Environmental Protection Agency have recommended that women of childbearing age, pregnant women, and breastfeeding mothers limit their intake of fish, and avoid all consumption of some types of fish higher in mercury (shark, swordfish, king mackerel, or tile fish). About 10% of all US women of childbearing age, and a higher percent of women who are older, Asian, or live near the coasts, have mercury levels above recommended limits. Current federal guidelines do not recommend a specific mercury limit for non-pregnant adults, but some evidence also suggests that mercury can increase risks for heart disease and neurological problems in adulthood.