Mercury drinking water limits

Recent studies suggest that mercury can cause an instant decrease in the sperm viability of fish at concentrations comparable to those which are permitted in drinking water (1 /rg C ). The bioconcentration of the metal to levels in the testis considerably higher than this from water containing only 1/30 of permitted levels" suggests that current legal limits are much too high. 

Until now there has been no effective technology for reducing groundwater mercury to two parts per billion, as required by the maximum contamination limit for drinking water established by the U.S. Food and Drug Administration and the U.S. EPA. 

Suppose a limit on mercury levels in drinking water needs to be set. The goal is to ensure that the RfD is not exceeded. To do this, the EPA first selects a hypothetical, average person, whose lifetime body... 

Mercury (11) is a frequent component of industrial wastewaters, remarkably toxic at concentrations higher than 0.005 mg The World Health Organization (2006) and national environmental agencies recommend a limit of 0.006 mg of inorganic mercury in drinking water. The health hazards due to the toxic effect of mercury at Minamata, Japan, and Iraq are very well known (Bockris, 1997). 

A modified reduction-aeration method to analyse mercury in environmental water samples is described. After aeration of the sample, the mercury is pre-concentrated on gold-coated sand which is then analysed by thermal desorption and cold vapour atomic absorption spectrometry (CVAAS). When applying reduction-cells of volumes up to 1 1, limits of detection as low as 1 ng.r are obtained. The method avoids matrix-effects caused by complexing agents such as Cl and 1, which interfere in the direct measurement of mercury by common CVAAS-techniques. The method was applied to dty drinking-water. Mercury levels ranging from less than 1 ng.l" to 10 ng.T were found. 

The recommended health-based limits are 0.05mgm for occupational exposure, 50pgg creatinine in urine for long-term occupational exposure to mercury vapors, and 1 pgl for exposure by drinking water (WHO report, 1980). 

The final issue that needs to be mentioned here concerns the relationship between the ADI for a chemical and its associated level in an environmental medium. The ADI is a dose, typically expressed in mg/ kg b.w./day. Consider mercury, a metal for which an RfD of 0.0003 mg/kg b.w./day has been established by EPA, based on certain forms of kidney toxicity observed in rats (these are not the only toxic effects of mercury, but they are the ones seen at the lowest doses). Suppose a limit on mercury levels in drinking water needs to be set. The goal is to ensure that the RfD is not exceeded. To do this, EPA first selects a hypothetical, average person, whose lifetime body weight averages 70 kg and who drinks the average two liters of water each day. If the RfD is 0.0003 mg/kg b.w./day, then the allowable daily mercury intake is ... 

Two studies in school children (He et al. 1994 Zhang et al. 1995) showed that over-exposure to manganese in drinking water and food was associated with poorer performance in school and on neurobehavioral tests as compared to non-exposed children. The exposed and control children in these studies were reportedly well-matched and the reports indicated that hair manganese was inversely related to performance on neurobehavioral exams and in school. However, there were several limitations in the reporting of the study, including the lack of analysis for lead or mercury, which are neurotoxins, and the lack of definitive exposure characterization. 

In 1856, J. Nessler was the first to propose an alkaline solution of mercury(II) iodide in potassium iodide as a reagent for the colorimetric determination of ammonia. It has been widely used especially in determining small amounts of ammonia in simple solutions as, for example, drinking water. It is, unfortunately, due to its limited selectivity, feasible only if all other metals except sodium and potassium are absent. 

Some heavy metals that affect human health are presented. Also their EPA regulatory limits (for drinking water) are provided. The metals that are described include arsenic, cadmium, chromium, lead, and mercury. 

The EPA s regulatory limit for mercury in drinking water is 2 parts per billion (ppb) [21]. 

Arsenic is well known because of its widespread use as a poison in criminal activity. Arsenic has also been widely used for agricultural appHcations, which include herbicides, pesticides, and wood preservatives. These applications have been reduced in recent years due to concerns about its toxicity, and the US EPA has recently reduced the acceptable limit of arsenic in drinking water. Unlike mercury and tin, organometallic forms of arsenic, such as arseno-betaine, arsenocholine, and some arsenosugars, are relatively nontoxic, while inorganic arsenic(III) (arse-nite) and arsenic(V) (arsenate) are highly toxic. 

The Safe Drinking Water Act (SDWA) sets a limit for mercury—a toxin to the central nervous system—at 0.002 mg/L. Water suppliers must periodically test their water to ensure that mercury levels do not exceed 0.002 mg/L. Suppose water became contaminated with mercury at twice the legal limit (0.004 mg/L). How much of this water would have to be consumed to ingest 0.100 g of mercury ... 

The level of mercury in the air of large cities is in the tens to units of ng/m. Natural waters contain only trace amounts of mercury. The concentration of mercury in rivers is in the region of 0.01-0.2 p.g/1 (while the permissible limit for drinking water... 

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