FLUORIDE LEVELS IN WELL-WATER FROM A CHRONIC ARSENICISM AREA OF NORTHERN MEXICO

This paper reports on the concentrations and geographical relationships between fluoride and total arsenic in 129 water wells of the Region Lagunera, Mexico, where arsenic has caused severe health effects. Fluoride concentrations ranged from less than 0.5 to 3.7 mg liter-1; 25 samples (19.4%) had levels above 1.5 mg liter-1, the current WHO and Mexican drinking water standard, whereas 45 (34.9%) had levels below 0.5 mg liter-1. The range of total arsenic concentrations was 0.008-0.624 mg liter-1 and 64 (50%) had levels above 0.050 mg liter-1, the current WHO standard. A linear regression analysis of arsenic and fluoride concentrations showed a highly positive correlation (r = 0.774), consistent with their geographical distribution. The highest concentrations of both elements were found in the northeastern part of the Region, mostly corresponding to rural areas, whereas the lowest concentrations were found in the southwestern part of the Region, as well as in the cities of Torreon in the state of Coahuila, and Gomez Palacio and Lerdo in the state of Durango. In consequence, people exposed to high arsenic concentrations are also exposed to fluoride at levels above the drinking water standard. The possibility of interactions between both elements is also discussed.