Mercury allowed intake

Large increases in mercury levels in water can be caused by industrial and agricultural use and waste releases. The health risk from mercury is greater from mercury in hsh than simply from water-borne mercury. Mercury poisoning may be acute, in large doses, or chronic, from lower doses taken over an extended time period. The maximum amount of mercury allowed in drinking water by the standard is 0.002 mg/L of water. That level is 13% of the total allowable daily dietary intake of mercury. 

Pharmacokinetics has played a crucial and somewhat unusual role in the assessment of health risks from methylmercury. Some of the epidemiology studies of this fish contaminant involved the measurement of mercury levels in the hair of pregnant women, and subsequent measurements of health outcomes in their offspring (Chapter 4). Various sets of pharmacokinetic data allowed estimation of the level of methylmercury intake through fish consumption (its only source) that gave rise to the measured levels in hair. In this way it was possible to identify the dose-response relationship in terms of intake, not hair level. Once the dose-response relationship was established in this way, the EPA was able to follow its usual procedure for establishing an RfD (which is 0.1 ag/(kg b.w. day)). 

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 ... 

When the recommended daily allowance (RDA) for calcium is not met by the diet is (particularly in women), supplementation in the form of calcium salts is recommended. Calcium salts vary widely in calcium content by weight, calcium gluconate has 9%, calcium lactate has 13%, and calcium carbonate has 40% calcium. Absorption of calcium from salts may vary calcium carbonate is the most poorly absorbed. Bone meal and dolomite are not recommended sources of calcium, since they may contain lead, arsenic, mercury, and other toxic metals. A potential complication of excessive calcium intake is formation of urinary tract stones this risk may be reduced by ample fluid intake. 

The previous considerations are illustrative of the need to remediate underwater chemical ordnance disposal sites. Explosive ordnance also presents a problem. Whereas most types of ordnance will loose their explosive capability once water enters the shell casing through corrosion, the pollution is still a factor. Fuses often contain fulminate of mercury. Nitrogen compounds are present in all of the various explosive fillers, and nitrogen is a major water pollutant for inland lakes. As is the case with chemical agents, many explosive chemicals could be disastrous if allowed to enter drinking water aquifers, seafood, or water system intakes. 

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