Reproductive outcomes in a population exposed long-term to inorganic selenium via drinking water

Exposure to a high selenium environment in Punjab, India: Biomarkers and health conditions

Seleniferous areas have been identified and described in many parts of the world. Despite the interest in selenium as a trace element of considerable toxicologic and nutritional relevance, however, only a few studies have been carried out on human health effects of such high selenium environments. We collected blood, hair and nail samples from 680 adult volunteers (267 men and 413 women) living in seven villages located in the seleniferous area of Punjab, India. We measured selenium levels in these specimens. We also administered a questionnaire to collect information about diet and other lifestyle characteristics, to identify the sources of selenium exposure and to correlate it with a number of health conditions. Serum and hair selenium contents were highly correlated, while the association of these biomarkers with nail selenium content was weaker. Serum selenium showed limited association with consumption of locally produced foods, while pulses and vegetables, along with cereals and pulses, were associated to higher hair and nail selenium contents, respectively. Association of a number of adverse health endpoints with serum and hair selenium was stronger than for nail selenium contents. Such endpoints included higher prevalence of nausea and vomiting, bad breath, worm infestation, breathlessness exert and bad breath, chest pain, hair and nail abnormalities and loss, garlic odor, edema, spontaneous abortion, and overall selenosis. In contrast, we gathered no evidence of dermatitis or loss of appetite in residents most exposed to selenium. Overall, and despite some statistical imprecision in effect estimates, these results confirm the occurrence of adverse health effects in subjects exposed to high levels of environmental selenium. Nail selenium contents may be less adequate to reflect and monitor such overexposure, compared with blood and hair levels.

Metal(loid)s in Cucurbita pepo in a Uranium Mining Impacted Area in Northwestern New Mexico, USA

More than 500 unreclaimed mines and associated waste sites exist on the Navajo Nation reservation as a result of uranium (U) mining from the 1940s through the 1980s. For this study, the impact of U-mine waste on a common, locally grown crop food was examined. The goal of this site-specific study was to determine metal(loid) concentration levels of arsenic (As), cadmium (Cd), cesium (Cs), molybdenum (Mo), lead (Pb), thorium (Th), U, vanadium (V) and selenium (Se) in Cucurbita pepo Linnaeus (squash), irrigation water, and soil using inductively coupled plasma-mass spectrometry. The concentrations of metal(loid)s were greatest in roots > leaves > edible fruit (p < 0.05), respectively. There were significant differences between metal(loid)s in squash crop plot usage (<5 years versus >30 years) for V (p = 0.001), As (p < 0.001), U (p = 0.002), Cs (p = 0.012), Th (p = 0.040), Mo (p = 0.047), and Cd (p = 0.042). Lead and Cd crop irrigation water concentrations exceeded the United States Environmental Protection Agency (USEPA) Maximum Contaminant Levels for drinking water for those metals. Edible squash concentration levels were 0.116 mg/kg of As, 0.248 mg/kg of Pb, 0.020 mg/kg of Cd, and 0.006 mg/kg of U. Calculated human ingestion of edible squash did not exceed Provisional Tolerable Weekly Intake or Tolerable Upper Limit levels from intake based solely on squash consumption. There does not appear to be a food-ingestion risk from metal(loid)s solely from consumption of squash. Safer access and emphasis on consuming regulated water was highlighted. Food intake recommendations were provided. Continued monitoring, surveillance, and further research are recommended.

Environmental Selenium and Human Health: an Update

PURPOSE OF REVIEW

Selenium, a trace element, is ubiquitous in the environment. The main source of human exposure is diet. Despite its nutritional benefits, it is one of the most toxic naturally occurring elements. Selenium deficiency and overexposure have been associated with adverse health effects. Its level of toxicity may depend on its chemical form, as inorganic and organic species have distinct biological properties.

RECENT FINDINGS

Nonexperimental and experimental studies have generated insufficient evidence for a role of selenium deficiency in human disease, with the exception of Keshan disease, a cardiomyopathy. Conversely, recent randomized trials have indicated that selenium overexposure is positively associated with type 2 diabetes and high-grade prostate cancer. In addition, a natural experiment has suggested an association between overexposure to inorganic hexavalent selenium and two neurodegenerative diseases, amyotrophic lateral sclerosis and Parkinson's disease. Risk assessments should be revised to incorporate the results of studies demonstrating toxic effects of selenium. Additional observational studies and secondary analyses of completed randomized trials are needed to address the uncertainties regarding the health risks of selenium exposure.

A comprehensive review on environmental transformation of selenium: recent advances and research perspectives

Selenium (Se) is an important micronutrient and essential trace element for both humans and animals, which exist in the environment ubiquitously. Selenium deficiency is an important issue worldwide, with various reported cases of its deficiency. Low selenium contents in some specific terrestrial environments have resulted in its deficiency in humans. However, high levels of selenium in the geochemical environment may have harmful influences and can cause a severe toxicity to living things. Due to its extremely narrow deficiency and toxicity limits, selenium is becoming a serious matter of discussion for the scientists who deals with selenium-related environmental and health issues. Based on available relevant literature, this review provides a comprehensive data about Se sources, levels, production and factors affecting selenium bioavailability/speciation in soil, characteristics of Se, biogeochemical cycling, deficiency and toxicity, and its environmental transformation to know the Se distribution in the environment. Further research should focus on thoroughly understanding the concentration, speciation, Se cycling in the environment and food chain to effectively utilize Se resources, remediate Se deficiency/toxicity, and evaluate the Se states and eco-effects on human health.

Uranium and Associated Heavy Metals in Ovis aries in a Mining Impacted Area in Northwestern New Mexico

The objective of this study was to determine uranium (U) and other heavy metal (HM) concentrations (As, Cd, Pb, Mo, and Se) in tissue samples collected from sheep (Ovis aries), the primary meat staple on the Navajo reservation in northwestern New Mexico. The study setting was a prime target of U mining, where more than 1100 unreclaimed abandoned U mines and structures remain. The forage and water sources for the sheep in this study were located within 3.2 km of abandoned U mines and structures. Tissue samples from sheep (n = 3), their local forage grasses (n = 24), soil (n = 24), and drinking water (n = 14) sources were collected. The samples were analyzed using Inductively Coupled Plasma-Mass Spectrometry. Results: In general, HMs concentrated more in the roots of forage compared to the above ground parts. The sheep forage samples fell below the National Research Council maximum tolerable concentration (5 mg/kg). The bioaccumulation factor ratio was >1 in several forage samples, ranging from 1.12 to 16.86 for Mo, Cd, and Se. The study findings showed that the concentrations of HMs were greatest in the liver and kidneys. Of the calculated human intake, Se Reference Dietary Intake and Mo Recommended Dietary Allowance were exceeded, but the tolerable upper limits for both were not exceeded. Food intake recommendations informed by research are needed for individuals especially those that may be more sensitive to HMs. Further study with larger sample sizes is needed to explore other impacted communities across the reservation.

The need for a reassessment of the safe upper limit of selenium in drinking water

Results of recent epidemiologic studies suggest the need to reassess the safe upper limit in drinking water of selenium, a metalloid with both toxicological and nutritional properties. Observational and experimental human studies on health effects of organic selenium compounds consumed through diet or supplements, and of inorganic selenium consumed through drinking water, have shown that human toxicity may occur at much lower levels than previously surmised. Evidence indicates that the chemical form of selenium strongly influences its toxicity, and that its biological activity may differ in different species, emphasizing the importance of the few human studies on health effects of the specific selenium compounds found in drinking water. Epidemiologic studies that investigated the effects of selenate, an inorganic selenium species commonly found in drinking water, together with evidence of toxicity of inorganic selenium at low levels in from in vitro and animal studies, indicate that health risks may occur at exposures below the current European Union and World Health Organization upper limit and guideline of 10 and 40 μg/l, respectively, and suggest reduction to 1 μg/l in order to adequately protect human health. Although few drinking waters are currently known to have selenium concentrations exceeding this level, the public health importance of this issue should not be overlooked, and further epidemiologic research is critically needed in this area.

Associations between blood metals and fecundity among women residing in New York State

Trace exposures to metals may affect female reproductive health. To assess the relation between trace concentrations of blood metals and female fecundity, 99 non-pregnant women discontinuing contraception for the purpose of becoming pregnant were prospectively followed. Participants completed a baseline interview and daily diaries until pregnant, or up to 12 menstrual cycles at risk for pregnancy; home pregnancy test kits were used. For 80 women, whole blood specimens were analyzed for arsenic, cadmium, lead, magnesium, nickel, selenium and zinc using inductively coupled plasma mass spectrometry (ICP-MS). Time to pregnancy was estimated using Cox proportional hazards models for discrete time. Metal concentrations were generally within population reference intervals. Adjusted models suggest a 51.5% increase in the probability for pregnancy per 3.60 μg/L increase in Mg (P=0.062), and a 27.7% decrease per 0.54 μg/L increase in Zn (P=0.114). Findings indicate that Mg and Zn may impact female fecundity, but in varying directions.

Rationale for a tissue-based selenium criterion for aquatic life

This paper proposes a national tissue-based criterion for the protection of aquatic life in the United States based on the growing body of selenium literature, but may be of international importance due to the raising global awareness of selenium contamination. A recent peer consultation workshop was undertaken by the US Environmental Protection Agency to address the technical issues underlying the freshwater aquatic life chronic criterion for selenium. The workshop participants discussed concerns associated with three possibilities for a new criterion: a water-based criterion, a tissue-based criterion, and a sediment-based criterion. Since the current national water quality criterion was established in 1987, several publications have reported adverse effects in fish from dietary selenium exposure with waterborne concentrations below the current criterion of 5 microg/l. Based on this literature, a water-based criterion seems unsuitable because of the propensity for selenium to bioaccumulate through the food chain to toxic dietary concentrations. There is little information to support a sediment-based criterion. A tissue-based criterion accounts for selenium's biogeochemical pathways because it integrates the route, duration, and magnitude of exposure, chemical form, metabolic transformations, and modifying biotic and abiotic factors. The convergence of laboratory and field data shows 4 microg/g to be a conservative value for a national tissue-based criterion for selenium.