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Significant amounts of fluoride are found in the abstracted groundwater of San Luis Potosí. This groundwater withdrawal induces a cold, low-fluoride flow as well as deeper thermal fluoride-rich flow in various proportions. Flow mixing takes place depending on the abstraction regime, local hydrogeology, and borehole construction design and operation. Fluoride concentrations (≈3.7 mg l−1) could become higher still, in time and space, if the input of regional fluoride-rich water to the abstraction boreholes is enhanced. It is suggested that by controlling the abstraction well-head water temperature at 28-30 °C, a pumped water mixture with a fluoride content close to the maximum drinking water standard of 1.5 mg l−1 will be produced. Further, new boreholes and those already operating could take advantage of fluoride solubility controls to reduce the F concentration in the abstracted water by considering lithology and borehole construction design in order to regulate groundwater flow conditions.

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No abstract

We analysed the relationship between free 2,5-hexanedione (2,5-HD) and total 2,5-HD in the urine of 87 workers exposed to n-hexane and other solvents (hexane isomers, acetone and toluene), in relation to different working conditions. The concentration of free 2,5-HD in urine of workers exposed to n-hexane was about 12% of total urinary 2,5-HD. The most significant correlation (r = 0.936) was that of total 2,5-HD in urine with environmental n-hexane and exhaled air. With equal exposure to n-hexane, the concentrations in urine of free and total 2,5-HD increased when cutaneous absorption was involved (gloves not used), during the working week and with co-exposure to acetone. An analysis of the relationship between combined exposure to acetone and urinary concentrations of the various forms of 2,5-HD suggests that acetone might influence the toxicokinetics of n-hexane, increasing the proportion of free 2,5-HD.