Copper in drinking water, Nebraska, 1994

In 1993, the levels of copper (Cu) in much of Nebraska's drinking water exceeded the U.S. Environmental Protection Agency's (EPA) action level of 1.3 mg/L. To determine the association of copper with gastrointestinal (GI) illness in August 1994 the authors interviewed persons living in households with 1993 Cu levels > 3 mg/L (51 households), 2-3 mg/L (54 households), and < 1.3 mg/L (43 households). Cases were defined as persons who had experienced the rapid onset of vomiting or nausea with abdominal pain during the preceding two weeks. To validate their exposure index, the authors immediately resampled drinking water in the households of 25 cases and 27 controls matched for age. Reassessment in December 1994 of the exposure and case status of the original cohort showed no association between copper in drinking water in 1993 and case status in 1994. The risk of GI illness seemed no greater with Cu > 3 mg/L (RR = 1.03; 95% CI = 0.43, 2.49) or 2-3 mg/L (RR = 0.50; 95% CI = 0.18, 1.41) than with Cu < 1.3 mg/L. The 1993 Cu concentrations could not be reproduced in August 1994; resampling in December 1994 again showed no association between GI illness and Cu exposure (RR > 1.3-2.9 mg/L, < or = 1.3 mg/L = 0.25, 95% CI = 0.10, 0.64, and RR > or = 3.0 mg/L, < or = 1.3 mg/L = 0.36, 95% CI = 0.09, 1.49).