The largest U.S. sources of mercury contamination are coal-fired power plants. In addition, exposure can result from skin contact during use in the workplace (dental, health services, chemical and other industries that use mercury.) The nervous system is very sensitive to all forms of mercury. Fetuses, infants and young children are especially vulnerable. Effects on brain functioning may result in irritability, tremors, loss of vision or hearing and memory problems. Exposure to high levels of metallic, inorganic, or organic mercury can permanently damage the brain, kidneys and developing fetus. Fetal effects from poisoning can lead to learning disabilities.