Nonpoint source (NPS) water pollution regulations are environmental regulations that restrict or limit water pollution from diffuse or nonpoint effluent sources such as polluted runoff from agricultural areas in a river catchments or wind-borne debris blowing out to sea. In the United States, governments have taken a number of legal and regulatory approaches to controlling NPS effluent. Nonpoint water pollution sources include, for example, leakage from underground storage tanks, storm water runoff, atmospheric deposition of contaminants, and golf course, agricultural, and forestry runoff. Nonpoint sources are the most significant single source of water pollution in the United States, accounting for almost half of all water pollution, and agricultural runoff is the single largest source of nonpoint source water pollution. This water pollution has a number of detrimental effects on human health and the environment. Unlike point source pollution, nonpoint source pollution arises from numerous and diverse sources, making identification, monitoring, and regulation more complex. Basis for controls and regulations The basis for nonpoint source pollution regulation is the negative direct and indirect effects on both human health and the environment caused by the pollutants in NPS effluent. Human health Human health is most directly affected when polluted water is ingested into the body. Nonpoint source pollution can often have toxic contaminants and chemicals present in the water. Additionally, there can be both bacteria and viruses (aka pathogens) found in the water. Toxic contaminants and chemicals Effluent from nonpoint sources may include toxic contaminates and chemical compounds including heavy metals like lead, mercury, zinc, and cadmium, organics like polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs), and other substances resistant to breakdown. There are many health effects associated with many of these toxic substances. Lead – can cause damage to the nervous connections as well as blood and brain disorders. Specific diseases include nephropathy, colic-like abdominal pains, and anemia. Mercury – Studies have shown effects such as chronic effects including tremors, impaired cognitive skills, and sleep disturbances. Acute exposure has shown to cause chest pain, dyspnea, cough, hemoptysis, impairment of pulmonary function, and evidence of damage to the lung tissue. Zinc – The U.S. Food and Drug Administration (FDA) has stated that zinc damages nerve receptors in the nose, which can cause loss of the sense of smell. Additionally, zinc toxicosis can occur in high doses of zinc. Cadmium – Exposure to cadmium-containing substances can result initially in metal fume fever