Organic Selenium Supplementation Increases Mercury Excretion and

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Organic Selenium Supplementation Increases Mercury Excretion and Decreases Oxidative Damage in Long-Term Mercury-Exposed Residents from Wanshan, China Yu-Feng Li,† Zeqin Dong,§ Chunying Chen,‡,* Bai Li,† Yuxi Gao,† Liya Qu,§ Tianchen Wang,∥ Xin Fu,⊥ Yuliang Zhao,† and Zhifang Chai† †

Multidiscipline Initiative Center and CAS Key Laboratory of Nuclear Analytical Techniques, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China ‡ National Center for Nanoscience and Technology, Beijing 100190, China § Guizhou Institute of Environmental Science and Designing, Guiyang 550002, China ∥ The Third Hospital of Peking University, Beijing 100191, China ⊥ Uppsala University, Uppsala SE-751 05, Sweden S Supporting Information *

ABSTRACT: Due to a long history of extensive mercury mining and smelting activities, local residents in Wanshan, China, are suffering from elevated mercury exposure. The objective of the present study was to study the effects of oral supplementation with selenium-enriched yeast in these long-term mercury-exposed populations. One hundred and three volunteers from Wanshan area were recruited and 53 of them were supplemented with 100 μg of organic selenium daily as selenium-enriched yeast while 50 of them were supplemented with the nonselenium-enriched yeast for 3 months. The effects of selenium supplementation on urinary mercury, selenium, and oxidative stress-related biomarkers including malondialdehyde and 8hydroxy-2-deoxyguanosine were assessed. This 3-month selenium supplementation trial indicated that organic selenium supplementation could increase mercury excretion and decrease urinary malondialdehyde and 8hydroxy-2-deoxyguanosine levels in local residents.

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1.5 ng/mL).5 Due to the elevated Hg exposure, health problems such as digestive dysfunction, hypomnesia, sleeping problems, and tremors were observed in these occupationally exposed persons.6 Therefore, it was urgently necessary to find ways to restore their health. Although chelating drugs, such as sulfur-containing dimercaptopropanesulfonic acid (DMPS) have been used in the clinical treatment of Hg poisoning, these drugs are more suitable for acute Hg poisoning since the strong chelating abilities of these drugs can cause drastic loss of other essential elements, such as Cu and Zn.7 The mercury issue in Wanshan, Guizhou had drawn great attention to the scientific and administrative communities. However, more attentions were paid to the acute Hg intoxication in the working places while less to the health impacts to long-term passively Hg-exposed local residents. There are about 15 000 residents around Wanshan Hg mine site alone.8 Our studies revealed that local residents were posed

INTRODUCTION As a well-known highly hazardous element, mercury (Hg) can induce toxic effects to kidneys, lungs, and nervous tissues, and has been linked to a number of human health diseases likes myocardial infarction, and even autism.1 The town of Wanshan in Northeastern Guizhou province was one of the largest Hgmining areas in China, and its Hg mining and smelting activities can be traced back to Qin Dynasty (c.a. 220 BC). Extensive large-scale production of Hg lasted for more than 50 years before the official closure of the mercury mine in 2001. Because of the long history of Hg mining and smelting activities, the average atmospheric Hg concentration in this area was elevated by 2−4 orders of magnitude compared to the values observed in pristine areas in Europe and North America, which was 1.5− 2 ng/m3.2 It has been found that the local soil, water, cereals, vegetables, and domestic animals raised by local residents showed elevated Hg levels.2−4 For some occupationally Hg exposed persons, the Hg concentration in serum samples (38.5 ± 61.5 ng/mL) was approximately 40 times higher than that in the normal population (0.9 ± 0.3 ng/mL) and the Hg concentration in urine samples (86.8 ± 65.2 ng/mL) was almost 75 times higher than that in a normal population (1.2 ± © 2012 American Chemical Society

Received: Revised: Accepted: Published: 11313

September 8, 2010 September 25, 2012 September 25, 2012 October 3, 2012 dx.doi.org/10.1021/es302241v | Environ. Sci. Technol. 2012, 46, 11313−11318

Environmental Science & Technology

Article

one identical-looking non-Se-enriched yeast tablet (Pharma Nord, Denmark) as the placebo group. Compliance was determined by pill counting and by measuring each participant’s serum Se level and comparing it with the mean value of the group and also to the level before Se supplementation. The treatment period was 3 months for each subject and it was started 1 week after the baseline visit. The participants were instructed to keep their dietary structure during the trial. At least 50 mL first morning void urine samples were collected in metal-free polypropylene bottles before Se supplementation (d0), and on days 15 (d15), 30 (d30), 45 (d45), 60 (d60), 75 (d75), and 90 (d90) after Se supplementation. The fresh urine samples were transported to the laboratory at 4 °C within 2 h after collection and stored at −80 °C before analyses. Hg and Se Analyses. Hg and Se in urine were analyzed by ICP-MS after simple dilution.28 Detailed information and QA/ QC can be found in the Supporting Information. Mercury chloride stock standard solution was obtained as a 1000 mg Hg/L solution (GBW 08617; National Research Centre for CRMs, Beijing, China). Se stock standard solution was obtained as a 100 mg Se/L solution (GBW(E) 080215; National Research Centre for CRMs). Working standard solutions of 0.5, 1, 2, 5, and 10 μg Hg/L and 1, 5, 10, and 50 μg Se/L were diluted daily as required. Biochemical Analyses. Urinary MDA Assay. Colorimetric determination of MDA for lipid peroxidation was based on the reaction of one molecule of the reactive aldehyde with two molecules of thiobarbituric acid at low pH (2−3) and 95−98 °C for 45 min. The pink product was extracted with n-butanol, and the absorbance at 532 and 580 nm were determined using a spectrophotometer. Urinary 8-OHdG Measurement. Urinary 8-OHdG was measured by solid-phase extraction (SPE) and HPLC with electrochemical detection as described previously.6 Detailed information was shown in the Supporting Information. Statistical Analysis. The results are expressed as geometric mean ± SE. One-way analysis of variance (ANOVA) was carried out to compare the data on different days and two-tailed paired t-tests was carried out to compare the data between the supplementation and placebo groups using the Statistical Package for Social Science (SPSS) for Windows (version 9.05; SSPS Inc., Chicago, IL). For all tests, values of P < 0.05 were considered to indicate statistical significance.

to high health threat due to Hg exposure through inhalation and the intake of local food.9,10 Besides, it is estimated that about 100 000 residents are passively exposed to Hg due to Hg mining, smelting, coal combustion, zinc smelting, and gold mining, etc in Guizhou province. Further, there are over 20 mercury clinical thermometer and sphygmomanometer companies, over 10 000 lighting producers, over 400 disposable batteries companies using Hg in their products and over 60% of the productions of Vinyl Chloride Monomer (VCM) in China are using HgCl2 as catalysts.11 If not properly protected, millions of residents around these sectors may be passively exposed to Hg, which will lead to adverse health problems. It was found that the mercury’s molecular mechanisms of toxicity involved the inhibition of selenoenzymes like glutathione peroxidase and thioredoxin reductase.12,13 A number of important selenoenzymes are involved in antioxidant defense, DNA synthesis, and reproduction.14 The protective effects of selenium (Se) against Hg toxicity have been reported for a long time.15,16 Numerous animal studies have found that taking Se simultaneously with Hg could reduce the toxicity of Hg.17−23 Increasing number of Se supplementation trials have been conducted such as in people suffering from HIV infection,24 Keshan disease,25 and arsenicosis,26 etc. Protective and beneficial effects of Se have been confirmed according to these studies. A Se supplementation trial in persons exposed to methylmercury through fish consumption found reduced pubic hair Hg level,27 which suggested reduced accumulation of Hg after Se supplementation. However, to the best of our knowledge, there has been no investigation on effects of Se supplementation in long-term Hg-exposed residents living around Hg-mining area, who are exposed mostly to inorganic and elemental Hg.4 Therefore, this study was initiated to evaluate effects of Se supplementation (as Se-enriched yeast) in residents from Wanshan Hg-mining area, China. The urinary Hg and Se levels and the levels of biomarkers for oxidative stresses including malondialdehyde (MDA) and 8-hydroxy-2deoxyguanosine (8-OHdG) before and after Se supplementation were compared. The change of urinary Hg and Se levels on different days after Se supplementation were also studied.

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EXPERIMENTAL SECTION Subjects, Study Design and Sampling. This study was approved by the Health Department of Guizhou and the Ethics Committee of Institute of High Energy Physics. Informed consents were obtained from all the participants. One hundred and seventy-seven residents aged between 18 and 65 years who were born and/or lived in a local community near the Wanshan Hg mine for over 15 years without severe diseases were recruited and medically examined. Before the start of the trial, personal dietary structure (using food frequency questionnaires) were investigated and recorded by responsible community health workers. Medical examination included measurements of height, weight, the general clinical statuses, and the urinary Hg, Se, MDA, and 8-OHdG levels. Among the 177 residents, 103 of them (52 men and 51 women), who has baseline urinary Hg level over 10 ng/mL but lower than 50 ng/mL, participated in this trial. The 103 volunteers were randomly allocated to the supplementation group or the placebo group. Fifty-three volunteers (27 men and 26 women) were supplemented with one tablet (100 μg Se/ tablet) of Se-enriched yeast (SelenoPrecise, Pharma Nord, Denmark) daily as the supplementation group, and 50 volunteers (25 men and 25 women) were supplemented with

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RESULTS Compliance with Treatment. Over the 90-day treatment with Se-enriched yeast and placebo, all the 103 participants were compliant, and missed