Incidence of heavy metal contamination in water supplies in northern Mexico.

Contaminants in drinking water present public health risks. The objective of this study was to analyze water samples taken from wells or storage tanks, direct sources for domestic water in Northern Mexico, for the presence of lead (Pb), copper (Cu), cadmium (Cd), arsenic (As), and mercury (Hg). The samples were analyzed by atomic absorption coupled with a hydride generator or a graphite furnace. High levels of Pb (0.05-0.12 ppm) were found in Hermosillo, Guaymas, and Nacozari. Forty-three percent of the samples in Sonora exceeded the action level (0.015 ppm) established by the EPA for Pb. For As, 8.92% exceeded the limit with a range of 0.002-0.305 ppm. Several studies have indicated a possible link between As and fluoride (F) in drinking water. This study showed a positive correlation between F and As (r = 0.53, P = 0.01, and n = 116). One location in Hermosillo had 7.36 ppm of F and 0.117 ppm of As, 3.5 times the recommended F levels in drinking water and 2 times higher than the level permitted for As. Hg contamination was found in 42% of the samples. Based on the results of this study, it appears that As, Hg, and Pb contamination in the drinking water for some areas of the state of Sonora is a major concern.