Elemento traza: contaminación y valores de fondo en aguas subterráneas de San Luis Potosí, SLP, México

Abstract

lt is misleading not to distinguish between; i) bad (natural) quality water and ii) polluted water (anthropogenic effects). The concept of BACKGROUND LEVEL is proposed for the concentration anywhere in a flow system due to natural chemical reactions between the host rack and tite groundwater. lt is a direct function of rack mineralogy, hydraulic conductivity, effective porosity and flow system. In the case of some trace elements such as Zn, Li, F, B and Fe, their natural concentration in thermal waters is proportional to the salinity, especially when it is considered equivalent to the square of molar sodium concentration. This behaviour was studied in the water supply of San Luis Potosí which has an important thermal component (minimun 70% in volume). As expected, the results show that the background levels in groundwater depend on the mineralogical composition of the aquifer and on the nature of the flow system. The background level for boron is between 0.07 and 0.27mg/1 and 0.004 to 0.04mg/1 for zinc, which falls within drinking water standards; however, some of the analyzed samples are polluted. On the other hand, lithium is present from 0.01 to 0.11mgll and fluoride is bctween 0.3 and 3 .6mg/1 , both as the result of natural mineral solution. Many samples indicate that concentrations for the latter are not in excess of drinking water standards (1.5mg/l).