A multidisciplinary study of human exposure to arsenic and other trace elements.
Arsenic (As) is a carcinogenic agent that is present in varying levels in environmental matrices including water and food. Long term As exposure can lead to skin lesions, peripheral neuropathy, diabetes, renal system effects and cardiovascular diseases. Bio-monitoring of human urine, toenail, serum and cerebrospinal fluid was carried out in this thesis to assess the exposure to arsenic and other trace elements. A multidisciplinary approach based on Inductively Coupled Plasma Mass Spectrometry (ICP-MS), HPLC-ICP-MS and Proton-Nuclear Magnetic Resonance Spectroscopy (1H-NMR) in conjunction with a questionnaire based survey was employed. The impact of rice consumption (a well-known vector of arsenic in the general population) on human urinary As levels was assessed. Results obtained show that the Bangladeshi (UK-B) community in the United Kingdom, who consume ca. 30-fold more rice than the white Caucasians (UK-C), are exposed to a higher level of arsenic. ICP-MS and HPLC-ICP-MS revealed a significant increase in dimethylarsinic acid (DMA) and inorganic arsenic (iAs) species in UK-B compared to UK-C, while cationic compounds were lower in UK-B than in UK-C. DMA and iAs levels in the Bangladeshis were positively correlated to rice consumption. Rice is likely to be responsible for the increase in levels of DMA and iAs in urine of UK-B. The link between this and the disproportional occurrence of diabetes and cardiovascular diseases (CVD) in UK-B needs to be investigated. Another important finding of this study is that the DMA to monomethyl arsenic (MA) ratio, which is often used as an indication of arsenic methylation capacity, should be applied with caution in populations consuming large quantities of rice because variation in the quantity and type of rice eaten may alter the urinary DMA levels and thereby the DMA/MA ratio. Urinary arsenic, selenium, copper and zinc were monitored for a group of Bangladeshis, Pakistanis, Indians and Caucasians living in the UK. The most striking finding was the increase in urinary copper in the UK-B group compared to other ethnicities and to reference values reported for the general UK population. Among the possible reasons for this could include dietary exposure via ethnic food consumption or a change in copper metabolism in the Bangladeshis. High serum copper levels have been correlated to CVD in the US population. In this context, further work is recommended to investigate if there is a relationship between urinary copper and the disproportionately high incidence of CVD in UK Bangladeshis. An approach based on 1H-NMR was used to detect changes in human urinary metabolomic profile as a function of As exposure through different routes. For this, the urine of UK-B, UK-C and a group residing in Bangladesh (BD-B) were monitored. The effects of other factors were explored, including arsenic urinary profile, chewing pan, ethnicity, rice consumption, selenium and diabetes. The three populations show distinctive metabolomic profiles. Urinary arsenic speciation was used in evaluating the effects of arsenic on the metabolomic profile for the UK group. This revealed that the %DMA positively correlates to %N,N-dymethylglycine, %alanine and %betaine. Comparative analysis of the 1H NMR spectra revealed that the BD-B urinary profiles were depleted in the number and quantity of metabolites. Visible signs of lower protein intake and undernourishment emerged from the urinary metabolomic profile of BD-B including a 2.5 decrease in creatinine levels compared to UK-B. Urinary creatinine and the metabolomic profile provide evidence for undernourishment in the BD-B population group that was not evident from previous studies on dietary protein intake in this population performed using food frequency questionnaires. Public health officials might consider also using bio-monitoring studies for nutrient intake rather than solely relying on estimations from food frequency questionnaires. The results reveal the complexity of the subject and pave the way for future studies, highlighting the need for awareness about diet and other specific confounding factors. Multiple Sclerosis (MS) is considered a multifactorial disease and its cause remains unknown. A case-control study on a MS cluster from the volcanic region of Mt. Etna (a natural emitter of geogenic trace elements in the environment) was undertaken. Urine and toenails were monitored for trace elements along with food consumption and life-style habits. Levels of a range of trace elements were reported for the first time for a population living in the Mt. Etna region. No significant differences were found in trace element levels in urine and toenails of MS patients and controls. However, urinary levels of nickel, manganese and selenium were higher than those reported in the literature for the general population from Italy, Germany and the UK. These findings and observations might suggest a role for nickel in the pathology of MS. However, larger studies on the possible role of nickel on MS, and trace elements in general, should be performed. Cerebrospinal fluid (CSF) and some serum from MS patients and controls from the Mt. Etna region were also monitored in this study using ICP-MS. There were significant differences in the trace elemental profile of CSF of MS volunteers and controls, including an increase in arsenic and zinc in the CSF of MS patients. Lead, aluminium, cadmium and molybdenum were significantly increased in the CSF of MS patients as well. In contrast, selenium was lower in MS patients compared to controls. The enrichment of certain trace elements in the CSF of MS patients could be the result of an impairment of the blood brain barrier and tight junction disruption due to MS and its progression, resulting in serum protein leakage and trace elements across the blood–brain barrier. Studies are necessary in the future to identify the chemical species present in the CSF and also determine their role in biological processes including their harmful effects on the brain.
- PhD