An investigation of Arsenic in biological samples from unexposed volunteers in the UK
This thesis describes studies on the analysis of arsenic (As) in human biological samples, mainly urine but also hair and fingernails using inductively coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectrometry (GF-AAS). The relationship between ethnicity and arsenic metabolism was investigated for the first time for a population in the United Kingdom. This investigation has been carried out through comparative analysis of arsenic in human urine, hair and fingernails in volunteers from three different ethnic groups (Whites, Asians and Somali Black-Africans) who are only exposed to background levels of arsenic. Results obtained with 63 volunteers showed ethnic differences in urinary arsenic excretion as well as differences in arsenic levels in fingernail samples. The averages of total arsenic levels for the Somali Black-Africans (urine 7.2 µg/g creatinine; fingernails 723 µg/kg) are significantly (P< 0.05) different from both the Asians (urine 20.6 µg/g creatinine; fingernails 153.9 µg/kg) and Whites (urine 24.5 µg/g creatinine; fingernails 177.0 µg/kg). The Somali group also shows a higher percentage (50%) of dimethylarsinate (DMA) and a lower percentage (48%) of arsenobetaine (AB), compared to Asians (16% DMA and 83% AB) and Whites (22% DMA and 77% AB). The effect of fasting on urinary arsenic species distribution was also investigated by monitoring urine samples from 29 Ramadan fasting volunteers, with each volunteer providing a sample at the beginning (RF1) and at the end (RF2) of an approximately 12 hours fast. The results obtained showed the frequency of MA detection for RF2 was 12 and 2-fold higher than for the non-fasting and RF1 groups, respectively. This suggests fasting may alter the pattern of arsenic metabolism and excretion. However, there was no significant difference (P> 0.05) in the average of total level of arsenic for RF1 (18.3 µg/g creatinine) and RF2 (17.7 µg/g creatinine). A relationship between excretion of arsenic and selenium in individuals exposed to background levels of arsenic and selenium was investigated through analysis of urine samples from 93 volunteers from Leicester, UK. A positive correlation between arsenic and selenium was found and the As:Se ratio was 0.7 ± 0.4. The intra-individual variation of As:Se ratio does not alter significantly over time, as determined by monitoring urine samples from a volunteer over a period of one year. Furthermore, within a single day, with urine samples collected at the beginning and after a 12-hour fast, the As:Se ratio was found to be similar (0.7 ± 0.5). These findings suggest a close relationship between these two metalloids, the biological significance of which needs to be explored in the future.
Arsenic, selenium, biological samples, unexposed, GF-AAS, ICP-MS, Whites, Asians, Somali, Black-Africans, fasting, Ramadan, urine, hair, fingernail, arsenobetaine (AB), dimethylarsinate (DMA), Methylarsonate (MA)
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