Effect of fasting on the pattern of urinary arsenic excretion.

Millions of people in some of the poorest regions of the world are exposed to high levels of arsenic through drinking contaminated water. It has been reported that development of cancer caused by arsenic exposure in such populations is dependent on dietary and nutritional factors which can modulate arsenic metabolism. Many people in arsenic exposed regions of Bangladesh and India practice fasting for at least one month every year when they refrain from consumption of food and fluid during daylight hours. How such practices may modulate arsenic metabolism has not been previously investigated. This study investigated this issue by determining total arsenic and its species in urine samples from a group of 29 unexposed volunteers at the beginning of the fasting and at the end of approximately 12 h of fasting period. Inductively coupled plasma mass spectrometry (ICP-MS) and high performance liquid chromatography (HPLC) coupled with ICP-MS was used to measure the total arsenic and arsenic speciation in the urine samples, respectively. The mean total levels of arsenic at the beginning of fasting (18.3 microg g(-1) creatinine) and at the end of approximately 12 h of fasting (17.7 microg g(-1) creatinine) did not differ significantly (p > 0.05). However, the percentages of urinary arsenic as the methylated arsenic species methylarsonate (MA) were found to be significantly different (p < 0.05) and this species was observed more frequently at the end of fasting, although its overall concentration was similar. There were no significant differences (p > 0.05) in both the concentrations and percentages of other urinary arsenic species detected, namely arsenobetaine (AB) and dimethylarsinate (DMA). Arsenite (As(III)) and arsenate (As(V)) were also analyzed, but were not detected. We conclude that fasting for a period of 12 h results in a significant increase in the percentage of urinary arsenic as MA, and its frequency of detection in the volunteers at the end of the fasting period is almost nine fold higher. This suggests that metabolism of arsenic is altered by fasting.

Understanding arsenic metabolism through a comparative study of arsenic levels in the urine, hair and fingernails of healthy volunteers from three unexposed ethnic groups in the United Kingdom.

Very little is known about arsenic (As) metabolism in healthy populations that are not exposed to high concentrations of As in their food or water. Here we present a study with healthy volunteers from three different ethnic groups, residing in Leicester, UK, which reveals statistically significant differences in the levels of total As in urine and fingernail samples. Urine (n = 63), hair (n = 36) and fingernail (n = 36) samples from Asians, Somali Black-Africans and Whites were analysed using inductively coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectroscopy (GF-AAS). The results clearly show that the total concentrations of As in urine and fingernail samples of a Somali Black-African population (urine 7.2 microg/g creatinine; fingernails 723.1 microg/kg) are significantly (P < 0.05) different from the Asian (urine 24.5 microg/g creatinine; fingernails 153.9 microg/kg) and White groups (urine 20.9 microg/g creatinine; fingernails 177.0 microg/kg). The chemical speciation of As in the urine of the three groups was also measured using high performance liquid chromatography coupled to ICP-MS. This showed that the proportion of the total urinary As present as dimethylarsenate (DMA) was higher for the Somali Black-African group (50%) compared to the Asians (16%) and Whites (22%). However, there was no significant difference (P > 0.05) in the level of As in the hair samples from these three groups; Somali Black-Africans (116.0 microg/kg), Asians (117.4 microg/kg) and Whites (141.2 microg/kg). Significantly different levels of total As in fingernail and urine and a higher percentage of urinary DMA in the Somali Black-Africans are suggestive of a different pattern of As metabolism in this ethnic group.