Arsenic Metabolites and Methylation Capacity Among Individuals Living in a Rural Area with Endemic Arseniasis in Inner Mongolia, China

Abstract

More than 0.3 million individuals are subject to chronic exposure to arsenic via their drinking water in Inner Mongolia, China. To determine arsenic methylation capacity profiles for such individuals, concentrations of urinary arsenic metabolites were measured for 548 subjects using high-performance liquid chromatography and a hydride generator combined with inductively coupled plasma-mass spectrometry. Mean urinary concentrations of dimethylarsonic acid (DMA), monomethylarsonic acid (MMA), inorganic arsenic (iAs), and total arsenic (TAs) were 200.50, 46.71, 52.96, and 300.17 μg/L, respectively. The %iAs, %DMA, and %MMA were 15.98, 69.72, and 14.29 %. Mean urinary %iAs and %MMA were higher in males, while urinary %DMA was higher in females. There was a strong positive correlation between %iAs and %MMA, with negative correlations between %iAs and %DMA, and %iAs and %MMA. In addition, %iAs and %MMA were positively associated with total arsenic in drinking water (WAs), while %DMA was negatively related with WAs. Regression analysis indicated that the primary methylation index (PMI) and secondary methylation index (SMI) generally decreased with increasing WAs. Females had a higher arsenic methylation capacity compared to males. Younger subjects had lower primary arsenic methylation capacity. However, the secondary arsenic methylation capacity was hardly affected by age. Moreover, both primary and secondary arsenic methylation capacities were negatively related to WAs.

Urinary Arsenic in Human Samples from Areas Characterized by Natural or Anthropogenic Pollution in Italy

“…There is wide evidence demonstrating that some individuals are more susceptible to As [ 102 , 103 ], and genetic factors can also play a role in susceptibility [ 104 , 105 ]. The factors we found to be associated with the urinary profile of As are supported by the scientific literature: consumption of seafood [ 48 , 79 , 83 , 90 , 91 , 94 , 96 , 98 , 99 ], consumption of contaminated tap water [ 30 , 94 , 97 ], occupational exposure [ 87 , 96 ], and some polymorphisms [ 97 , 100 , 101 ]. We also identified some other factors, such as wine, grains, meat, and milk consumption, which make for interesting further investigations.…”

“…In Inner Mongolia, in an endemic area for As poisoning where the groundwater typically contains high As concentrations of up to 1354 μg/L, with a mean value of 173 µg/L, the mean u(iAs+MMA+DMA) concentration was 300.17 µg/L [ 30 ]. In the same area, another study found mean u(iAs+MMA+DMA) concentrations of 252.84 µg/L [ 95 ].…”

“…A study conducted in Pabna, Bangladesh, investigating factors influencing biomarkers of As exposure, reported that u(iAs+MMA+DMA) concentrations were significantly associated with As concentration in drinking water ( p < 0.001) [ 97 ]. In a study performed in inner Mongolia among inhabitants of a rural area, Wei et al, showed a positive association between As in drinking water and u(iAs+MMA+DMA) [ 30 ]. In a recent study carried out in Taranto [ 94 ], the authors reported higher median values of u(iAs+MMA+DMA) in those who drank tap water (3.6 µg/L) than those who drank bottled mineral water (2.5 µg/L).…”

“…The metabolic pathway consists in an alternation of reduction and oxidation reactions: reduction of the pentavalent form (As(V)) to form compounds such as monomethylarsonic acid (MMA(V)) and dimethylarsonic acid (DMA(V)), and oxidative methylation of (As(III)), monomethylarsonous acid (MMA(III)), and dimethylarsonous acid (DMA(III)) [ 28 , 29 ]. The metabolic pattern is considered a detoxification pattern because of the relatively low toxicity of MMA and DMA [ 30 ], therefore, As toxicity is closely related to its metabolism. Arsenic species in the trivalent state are generally considered more toxic at lower doses than the other As species [ 1 , 31 ].…”

Factors Affecting Arsenic Methylation in Arsenic-Exposed Humans: A Systematic Review and Meta-Analysis

“…Arsenic enters an organism via the respiratory tract, alimentary canal, and skin, and it is primarily metabolized in the liver [ 3 ]. The metabolic pattern has primarily been regarded as occurring through oxidative methylation [ 4 ], which was formerly considered a detoxification pattern [ 5 ]. However, monomethylarsonous acid (MMA III ) and dimethylarsonous acid (DMA III ) have recently been shown to be more poisonous than inorganic arsenic (iAs) [ 6 , 7 ].…”