Copper rates, and carcass dressing percentages. Chronic copper toxicity does not normally occur in humans because of transport systems that regulate absorption and excretion. Autosomal recessive mutations in copper transport proteins can disable these systems, leading to Wilson's disease with copper accumulation and cirrhosis of the liver in persons who have inherited two defective genes. Elevated copper levels have also been linked to worsening symptoms of Alzheimer's disease. In the US, the Occupational Safety and Health Administration (OSHA) has designated a permissible exposure limit (PEL) for copper dust and fumes in the workplace as a time-weighted average (TWA) of 1 mg/m.
Lead and Copper Rule necessarily representative of the lead corrosion potential in a particular water/pipe system, nor did they measure the amount of lead to which customers were exposed. In the second half of the twentieth century, concern was growing about what constituted a safe level of lead. The 1986 Safe Drinking Water Act amendments defined "lead-free" plumbing and prohibited the use of plumbing for public water supply that did not meet the new definition. The amendments also required EPA to set standards limiting the concentration of lead in public water systems. EPA first issued the Lead and Copper Rule on June 7, 1991.