Arsenic in Drinking Water (1999) / Chapter Skim
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8 Variation in Human Sensitivity
8 Variation in Human Sensitivity
Pages 229-250
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From page 229... ...
Those and other factors contributing to variability are discussed in this chapter. Variation In Arsenic Metabolism This section discusses variations in the metabolism of inorganic arsenic in humans, especially those variations evidenced by the urinary excretion of
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From page 230... ...
However, the relative amounts of arsenic metabolites in the urine might not reflect the actual methylation efficiency in the body (i.e., the fraction of the absorbed dose that is methylated) , because the methylated metabolites are excreted in the urine more quickly than inorganic arsenic (Buchet et al.
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From page 231... ...
The variations among the laboratories were 1.3-2.7 µg/L for inorganic arsenic, 1.3-2.7 µg/L for MMA, and 5.8-11.2 µg/L for DMA in a urine sample with low arsenic concentrations; and 3.2-6.0 µg/L for inorganic arsenic, 3.5-5.5 µg/L for MMA, and 14.9-22.3 µg/L for DMA in a medium concentration sample (Crecelius and Yager 1997)
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From page 232... ...
. However, children in northern Argentina exposed to arsenic at about 200 µg/L in drinking water had a significantly higher percentage of inorganic arsenic and a lower percentage of DMA in the urine, compared with adults (49% vs.
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From page 233... ...
Also, one study of human exposure to arsenic via drinking water (up to 600 µg/L) in northeastern Taiwan indicates that women had a somewhat higher percentage of DMA and lower percentage of MMA in the urine than men (Hsu et al.
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change in the source of water, involving a decrease in arsenic concentration from 600 to 45 µg/L, resulted in a small decrease in the average proportion of inorganic arsenic (about 3 %) and in the ratio of MMA to DMA in the urine, but those changes were not related to the magnitude of the decrease in concentration of total urinary metabolites (Hopenhayn-Rich et al.
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From page 235... ...
However, in a study of adults in northeastern Taiwan, the percentage of urinary DMA increased and that of MMA decreased with increasing arsenic concentrations in the drinking water (three groups of people drinking water with 0-50, 51-300, and > 300 µg/L, respectively; Chiou et al.
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From page 236... ...
in the Urine of Individuals Exposed to Inorganic Arsenic via Drinking Water Drinking-Water Exposure Cases, U-As met , Urinary Arsenic Metabolites, % to Arsenic No. µg/L Inorganic Arsenic MMA DMA Reference Argentina, 200 µg/L, women S.A.
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From page 237... ...
µg/L Inorganic Arsenic MMA DMA Reference Mexico, 415 µg/L, adults Santa Ana 35 544 31 11 54 Del Razo et al. 1997 429-689 28-34 9.5-13 50-58 United States, 300-400 µg/L, adults California 10 161 24 18 55 Hopenhayn-Rich et al.
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From page 238... ...
Whether that is also true for humans is not known. In areas with severe arsenic-related health effects due to ingestion of drinking water with high arsenic concentrations (i.e., southwestern Taiwan and the Antofagasta region in northern Chile)
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MTHFR is a metabolic source of methyl groups. These observations obviously show that nutritional factors affecting one-carbon and methyl metabolism must be taken into account in any survey of the nutritional status of persons chronically exposed to inorganic arsenic.
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Such a health effect, however, resulting from the lack of adequate selenium to counteract arsenic excesses would be consistent with the situation in the blackfoot-disease areas of Taiwan. Selenium status there should be considered a moderator of arsenic toxicity and taken into account when the Taiwanese data are applied to populations with adequate selenium intakes.
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Nutritional Status of Populations in Taiwan As early as 1961, Yang and Blackwell reported that blackfoot-disease patients had poor nutritional status. Their report appeared before arsenic was implicated as a possible causative agent for blackfoot disease.
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From page 242... ...
Again one must emphasize that these are epidemiological data derived from questionnaires and are not measurements of sweet potato consumption or chemical analysis of sweet potato composition. There is no question that the nutritional status of persons chronically exposed to arsenic is crucial to understanding the signs and symptoms of arsenic toxicity.
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Important factors to consider in evaluating diet in this context are methionine, cysteine, vitamin B12, and folic acid, as well as essential trace elements, such as selenium and zinc. On the basis of its review of the data on the variations in human sensitivity to arsenic exposure, the subcommittee concludes the following: · Studies on human volunteers show that a low proportion of DMA in urine is associated with a low rate of methylation of ingested inorganic arsenic and a low rate of excretion of arsenic metabolites.
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From page 244... ...
Recommendations Factors influencing the susceptibility to or expression of arsenic-associated cancer and noncancer effects need to be better characterized. Particular attention should be given to the study of the extent and reasons for interindividual and intraindividual variation in arsenic metabolism, tissue accumulation, and excretion (including total and relative amounts of urinary arsenic metabolites)
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Lauwerys. 1985. Study of inorganic arsenic methylation by rat liver in vitro: Relevance for the interpretation of observations in man.
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1998a. Metabolism of inorganic arsenic in children with chronic high arsenic exposure in northern Argentina.
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1996b. Arsenic methylation patterns before and after changing from high to lower concentrations of arsenic in drinking water.
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1998. Urinary excretion of arsenic species after exposure to arsenic present in drinking water.
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1979. Metabolism of inorganic arsenic ( 74 As)
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1995. A unique metabolism of inorganic arsenic in native Andean women.
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