Evaluation of potential impacts of perchlorate in the Colorado River on the Salton Sea,California

Ammonium perchlorate, a component of rocket fuel, entered Lake Mead through drainage and shallow groundwater in the Las Vegas Valley, Nevada, and is now found in the lower Colorado River from Lake Mead to the international boundary with Mexico. Perchlorate is a threat to human health through reduction of thyroid hormone production. Perchlorate has been found in water throughout the lower Colorado system and in crops in the California’s Imperial Valley, as well as in several other states, but it has not previously been included in investigations of the Salton Sea. Because perchlorate behaves conservatively in the Colorado River, it was postulated that it could be accumulating at high levels along with other salts in the Salton Sea. Results show that perchlorate is not accumulating in the Sea, although it is present in tributaries to the Sea at levels similar to those found in the Colorado River. Bacterial reduction of perchlorate is the most likely explanation for the observed results. The U.S. Government’s right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged. Guest editor: S. H. Hurlbert The Salton Sea Centennial Symposium. Proceedings of a Symposium Celebrating a Century of Symbiosis Among Agriculture, Wildlife and People, 1905–2005, held in San Diego, California, USA, March 2005     

Limitations to Natural Bioremediation of Perchlorate in a Contaminated Site

Perchlorate (ClO₄^-) has been detected in many drinking water supplies in the United States, including the Las Vegas Wash and Lake Mead, Nevada. These locations are highly contaminated and contribute perchlorate to Lake Mead and the Colorado River system. Essential elements for perchlorate bioremediation at these locations were examined, including the presence of perchlorate-reducing bacteria (PRB), sufficient electron donors, occurrence of competing electron acceptors, and ability of PRB to utilize a variety of electron donors. Enumeration of PRB was performed anoxically using most probable number (MPN). Values ranged from ≤20 to 230 PRB/100 ml or ≤20 to ≥ 1.6× 10⁵ PRB/g for Lake Mead water samples and Las Vegas Wash sediments, respectively. 16S rRNA sequences revealed that isolates were γ -proteobacteria, Aeromonas, Dechlorosoma, Rahnella and Shewanella. A screening of potential electron donors using BIOLOG^TM demonstrated that all isolates were capable of metabolic versatility. Measurements of total organic carbon (TOC), nitrate and dissolved oxygen (DO) indicated limited presence of electron donor at all sites, whereas the electron acceptors varied throughout the Wash and Lake Mead. The persistence of perchlorate in the sites is attributed to lack of available electron donor and/or the presence of competing electron acceptors. A location has been identified where perchlorate biodegradation could be implemented thereby halting the transport of perchlorate to Lake Mead and the Colorado River.     

Limitations to Natural Bioremediation of Perchlorate in a Contaminated Site

Perchlorate (ClO₄ ^?) has been detected in many drinking water supplies in the United States, including the Las Vegas Wash and Lake Mead, Nevada. These locations are highly contaminated and contribute perchlorate to Lake Mead and the Colorado River system. Essential elements for perchlorate bioremediation at these locations were examined, including the presence of perchlorate-reducing bacteria (PRB), sufficient electron donors, occurrence of competing electron acceptors, and ability of PRB to utilize a variety of electron donors. Enumeration of PRB was performed anoxically using most probable number (MPN). Values ranged from ≤20 to 230 PRB/100 ml or ≤20 to ≥ 1.6× 10⁵ PRB/g for Lake Mead water samples and Las Vegas Wash sediments, respectively. 16S rRNA sequences revealed that isolates were γ -proteobacteria, Aeromonas, Dechlorosoma, Rahnella and Shewanella. A screening of potential electron donors using BIOLOG^TM demonstrated that all isolates were capable of metabolic versatility. Measurements of total organic carbon (TOC), nitrate and dissolved oxygen (DO) indicated limited presence of electron donor at all sites, whereas the electron acceptors varied throughout the Wash and Lake Mead. The persistence of perchlorate in the sites is attributed to lack of available electron donor and/or the presence of competing electron acceptors. A location has been identified where perchlorate biodegradation could be implemented thereby halting the transport of perchlorate to Lake Mead and the Colorado River.     

A Comparative Toxicological Assessment of Perchlorate and Thiocyanate Based on Competitive Inhibition of Iodide Uptake as the Common Mode of Action

Thiocyanate and perchlorate are known to competitively inhibit thyroidal iodide uptake at the sodium-iodide symporter. Estimates of their relative potencies have recently been refined; thiocyanate is 15 times less potent than perchlorate on a serum concentration basis. Numerous studies have been published relating serum thiocyanate concentrations (or surrogate measures) with thyroid function in various populations including pregnant women and neonates in regions with varying degrees of iodine deficiency. Fifteen published studies were located that relate serum thiocyanate concentrations with thyroid function. In the absence of severe iodine deficiency or iodine excess, adverse thyroidal effects occur with chronic serum thiocyanate concentrations ≥ 200 μ mol/L whereas non-adverse effects are observed with concentrations in the range of 65–85 μ mol/L. No adverse or non-adverse effects are observed at serum concentrations below 50 μ mol/L, even among sensitive subpopulations. Recently, studies relating serum perchlorate concentrations with perchlorate dose have become available, thus making it possible to predict the perchlorate dose associated with a serum perchlorate concentration. Serum thiocyanate concentrations found to induce non-adverse or adverse thyroid effects can thereby be used to predict the perchlorate concentration and thus the perchlorate dose that would be expected to induce similar effects. To place a perspective on environmental perchlorate exposure, a serum thiocyanate concentration of 50 μ mol/L is equivalent to a serum perchlorate concentration of 3.3 μ mol/L in terms of iodine uptake inhibition. This serum perchlorate concentration would require a perchlorate dose of 0.27 mg/kg-day, or a drinking water equivalent level of 9 mg/L using standard default assumptions of a 70 kg adult drinking 2 liters of water daily.     

A Dietary Risk Assessment for Indigenous Consumption of Natural Salt Deposits in the Darhad Valley,Northern Mongolia

The nomadic herding population of the Darhad Valley, in northern Mongolia, collects and utilizes a salt precipitate, called hujir, which develops at the saline system, Tohi. This culturally important indigenous dietary supplement is consumed daily as an ingredient in a salty milk-tea and because of its essential micro- and macronutrients it is a beneficial and necessary part of their daily diet. Despite its benefits, there are increasing health concerns among the Darhad people as a result of consuming hujir. Therefore, we conducted a dietary risk assessment. Consumption rates were obtained from interviews with nomadic herders of the valley and a chronic exposure assessment was completed using chemical analyses on hujir samples. A combination of chronic toxicity threshold values, dietary reference intake recommendations, and drinking water guidelines were used to estimate dietary risks related to hujir consumption. Exposures to arsenic, fluoride, and nitrate were as high as 33, 1.2, and 1.3 times the chronic oral reference dose, respectively. Exposures to antimony, arsenic, and lead were 1.7, 19, and 14 times the drinking water guidelines, respectively. Given these results, additional studies are needed to better understand possible health effects associated with hujir consumption in the Darhad population, especially for arsenic.     

Backwash intensity and frequency impact the microbial community structure and function in a fixed-bed biofilm reactor

Linkages among bioreactor operation and performance and microbial community structure were investigated for a fixed-bed biofilm system designed to remove perchlorate from drinking water. Perchlorate removal was monitored to evaluate reactor performance during and after the frequency and intensity of the backwash procedure were changed, while the microbial community structure was studied using clone libraries and quantitative PCR targeting the 16S rRNA gene. When backwash frequency was increased from once per month to once per day, perchlorate removal initially deteriorated and then recovered, and the relative abundance of perchlorate-reducing bacteria (PRB) initially increased and then decreased. This apparent discrepancy suggested that bacterial populations other than PRB played an indirect role in perchlorate removal, likely by consuming dissolved oxygen, a competing electron acceptor. When backwash intensity was increased, the reactor gradually lost its ability to remove perchlorate, and concurrently the relative abundance of PRB decreased. The results indicated that changes in reactor operation had a profound impact on reactor performance through altering the microbial community structure. Backwashing is an important yet poorly characterized procedure when operating fixed-bed biofilm reactors. Compared to backwash intensity, changes in backwash frequency exerted less disturbance on the microbial community in the current study. If this finding can be confirmed in future work, backwash frequency may serve as the primary parameter when optimizing backwash procedures.     

A method for the analysis of six thyroid hormones in thyroid gland by liquid chromatography–tandem mass spectrometry

Perchlorate can competitively inhibit iodide uptake by the thyroid gland (TG) via the sodium/iodide symporter, consequently reducing the production of thyroid hormones (THs). Until recently, the effects of perchlorate on TH homeostasis are being examined through measurement of serum levels of TH, by immunoassay (IA)-based methods. IA methods are fast, but for TH analysis, they are compromised by the lack of adequate specificity. Therefore, selective and sensitive methods for the analysis of THs in TG are needed, for assessment of the effects of perchlorate on TH homeostasis. In this study, we developed a method for the analysis of six THs: l-thyroxine (T₄), 3,3′,5-triiodo-l-thyronine (T₃), 3,3′,5′-triiodo-l-thyronine (rT₃), 3,5-diiodo-l-thyronine (3,5-T₂), 3,3′-diiodo-l-thyronine (3,3′-T₂), and 3-iodo-l-thyronine (3-T₁) in TG, using liquid chromatography (LC)–tandem mass spectrometry (MS/MS). TGs used in this study were from rats that had been placed on either iodide-deficient diet or iodide-sufficient diet, and that had either been provided with perchlorate in drinking water (10 mg/kg/day) or control water. TGs were extracted by pronase digestion and then analyzed by LC–MS/MS. The instrumental calibration range for each TH ranged from 1 to 200 ng/ml and showed a high linearity (r > 0.99). The method quantification limits (LOQs) were determined to be 0.25 ng/mg TG for 3-T₁; 0.33 ng/mg TG for 3,3′- and 3,5-T₂; and 0.52 ng/mg TG for rT₃, T₃, and T₄. Rats were placed on an iodide-deficient or -sufficient diet for 2.5 months, and for the last 2 weeks of that period were provided either perchlorate (10 mg/kg/day) in drinking water or control water. Iodide deficiency and perchlorate administration both reduced TG stores of rT₃, T₃, and T₄. In iodide-deficient rats, perchlorate exacerbated the reduction in levels of THs in TG. With the advances in analytical methodology, the use of LC–MS/MS for measurement of hormone levels in TG will allow more comprehensive evaluations of the hypothalamic-pituitary–thyroid axis.     

Neonatal thyroid-stimulating hormone level and perchlorate in drinking water

BACKGROUND: The effect of perchlorate in drinking water on neonatal blood thyroid-stimulating hormone (thyrotropin; TSH) levels was examined for Las Vegas and Reno, Nevada. METHODS: The neonatal blood TSH levels in Las Vegas (with up to 15 microg/L (ppb) perchlorate in drinking water) and in Reno (with no perchlorate detected in the drinking water) from December 1998 to October 1999 were analyzed and compared. The study samples were from newborns in their first month of life (excluding the first day of life) with birth weights of 2, 500-4,500 g. A multivariate analysis of logarithmically transformed TSH levels was used to compare the mean TSH levels between Las Vegas and Reno newborns, with age and sex being controlled as potential confounders. RESULTS: This study of neonatal TSH levels in the first month of life found no effect from living in the areas with environmental perchlorate exposures of 相似文献   

Rats retain chromium in tissues following chronic ingestion of drinking water containing hexavalent chromium

Humans have sometimes been exposed to as much as 10 ppm Cr(VI) in drinking water from contaminated wells. The risks to these individuals are not well understood because the digestive tract reduces some of the Cr(VI) to the less bioavailable Cr(III) prior to absorption, and the disposition of the remaining Cr(VI) has not been well studied. We determined tissue Cr concentrations in rats after chronic ingestion of Cr(VI) in drinking water at concentrations relevant to human exposure levels. Adult male and female Fischer 344 rats consumed ad libitum 0, 0.5, 3, or 10 ppm Cr(VI) as K₂CrO₄ in drinking water for 44 wk. Rats then were given deionized water 4–6 d prior to sample collection. Females given 3 or 10 ppm Cr(VI) consumed more Cr(VI) per unit of body weight than did males. Bone Cr concentrations were significantly elevated in rats that drink 10 ppm Cr(VI). Renal Cr concentrations were significantly elevated in male rats that drink 3 or 10 ppm Cr(VI) and in female rats dosed with 10 ppm Cr(VI). Female rats had elevated liver Cr concentrations after drinking 3 or 10 ppm Cr(VI). Testicular Cr concentrations were slightly elevated in rats that drank 10 ppm Cr(VI). Brain, ovarian, and whole-blood Cr concentrations were below detection limits in all exposure groups. Although tissue Cr accumulation may have resulted from absorption of Cr(III), it is poorly absorbed. Therefore, the increased tissue retention may also have resulted, in part, from increased absorption of Cr(VI) and its subsequent uptake from the systemic circulation.     

Perchlorate Chemistry: Implications for Analysis and Remediation

Since the discovery of perchlorate in the ground and surface waters of several western states, there has been increasing interest in the health effects resulting from chronic exposure to low (parts per billion [ppb]) levels. With this concern has come a need to investigate technologies that might be used to remediate contaminated sites or to treat contaminated water to make it safe for drinking. Possible technologies include physical separation (precipitation, anion exchange, reverse osmosis, and electrodialysis), chemical and electrochemical reduction, and biological or biochemical reduction. A fairly unique combination of chemical and physical properties of perchlorate poses challenges to its analysis and reduction in the environment or in drinking water. The implications of these properties are discussed in terms of remediative or treatment strategies. Recent developments are also covered.     

Pharmaceutical Contaminants in Potable Water: Potential Concerns for Pregnant Women and Children

There has been increasing concern of late over measurable levels of pharmaceutical contaminants in drinking water. Because most data on water contaminants pertains to aquatic organisms, we wished to assess the risk of these contaminants to human health at currently reported levels. Unlike most other chemicals, there are large amounts of information for the effects of most pharmaceuticals to humans and the current model uses the clinical dose required to cause biological effects as an endpoint to assess risks for pregnant women, children, and the healthy adult population. Twenty-six drugs have been detected in water systems worldwide: 7 in drinking water, 16 in ground water and post-treatment effluent, and 3 in both. Current water treatment practices, clearly, do not always remove pharmaceutical residues. Although healthy adults are unlikely to be adversely affected at the levels of exposure reported, children were shown to have up to eightfold higher risk and may be exposed to several drugs that are contraindicated or not established for safe use in pediatric medicine. The time taken to ingest a single clinically used dose was 3.4–34,000 years. In addition, pregnant women may be exposed to several drugs that are teratogenic (range of % single doses ingested over 36 weeks was 0.0006–12.6%) and in the post-natal period to drugs that are not recommended during breastfeeding. Albeit at low levels, the exposure of pregnant women and children to contraindicated drugs through drinking water is of concern. Further research in this area should focus on integrated ecological and human health consequences of long-term, low-level exposure to pharmaceutical contaminants, particularly in pregnancy and childhood.     

Radiation-induced bystander effects in the Atlantic salmon (salmo salar L.) following mixed exposure to copper and aluminum combined with low-dose gamma radiation

Very little is known about the combined effects of low doses of heavy metals and radiation. However, such “multiple stressor” exposure is the reality in the environment. In the work reported in this paper, fish were exposed to cobalt 60 gamma irradiation with or without copper or aluminum in the water. Doses of radiation ranged from 4 to 75 mGy delivered over 48 or 6 h. Copper doses ranged from 10 to 80 μg/L for the same time period. The aluminum dose was 250 μg/L. Gills and skin were removed from the fish after exposure and explanted in tissue culture flasks for investigation of bystander effects of the exposures using a stress signal reporter assay, which has been demonstrated to be a sensitive indicator of homeostatic perturbations in cells. The results show complex synergistic interactions of radiation and copper. Gills on the whole produce more toxic bystander signals than skin, but the additivity scores show highly variable results which depend on dose and time of exposure. The impacts of low doses of copper and low doses of radiation are greater than additive, medium levels of copper alone have a similar level of effect of bystander signal toxicity to the low dose. The addition of radiation stress, however, produces clear protective effects in the reporters treated with skin-derived medium. Gill-derived medium from the same fish did not show protective effects. Radiation exposure in the presence of 80 μg/L led to highly variable results, which due to animal variation were not significantly different from the effect of copper alone. The results are stressor type, stressor concentration and time dependent. Clearly co-exposure to radiation and heavy metals does not always lead to simple additive effects.     

Assessing Children's Exposures and Risks to Drinking Water Contaminants: A Manganese Case Study

Background: Compared to adults, children maybe more highly exposed to toxic substances in drinking water because they consume more water per unit of body weight. The U.S. Environmental Protection Agency (USEPA) has developed new guidance for selecting age groups and age-specific exposure factors for assessing children's exposures and risks to environmental contaminants. Research Aim: To demonstrate the application and importance of applying age-specific drinking water intake rates, health reference values, and exposure scenarios when assessing drinking water exposures because these approaches illustrate the potential for greater potential for adverse health effects among children. Methods: manganese, an essential nutrient and neurotoxicant, was selected as a case study and chemical of potential concern for children's health. A screening-level risk assessment was performed using age-specific drinking water intake rates and manganese concentrations from U.S. public drinking water systems. Results: When age-specific drinking water intake rates are used to calculate dose, formula-fed infants receive the highest dose of manganese from drinking water compared to all other age groups. Estimated hazard quotients suggest adverse health effects are possible. Use of USEPA's standardized childhood age groups and childhood exposure factors significantly improves the understanding of childhood exposure and risks.     

The effect of high dose oral manganese exposure on copper,iron and zinc levels in rats

Manganese is an essential dietary nutrient and trace element with important roles in mammalian development, metabolism, and antioxidant defense. In healthy individuals, gastrointestinal absorption and hepatobiliary excretion are tightly regulated to maintain systemic manganese concentrations at physiologic levels. Interactions of manganese with other essential metals following high dose ingestion are incompletely understood. We previously reported that gavage manganese exposure in rats resulted in higher tissue manganese concentrations when compared with equivalent dietary or drinking water manganese exposures. In this study, we performed follow-up evaluations to determine whether oral manganese exposure perturbs iron, copper, or zinc tissue concentrations. Rats were exposed to a control diet with 10 ppm manganese or dietary, drinking water, or gavage exposure to approximately 11.1?mg manganese/kg body weight/day for 7 or 61 exposure days. While manganese exposure affected levels of all metals, particularly in the frontal cortex and liver, copper levels were most prominently affected. This result suggests an under-appreciated effect of manganese exposure on copper homeostasis which may contribute to our understanding of the pathophysiology of manganese toxicity.     

高氯酸盐污染及修复的研究进展

戏真做高氯酸盐作为一种甲状腺干扰物质,因其高溶解度、低吸附性及其稳定性,决定了其是一种可快速扩散的持久型污染物,其环境污染问题已引起人们的高度关注。从高氯酸盐污染的危害性出发,阐述了我国可能存在的高氯酸盐污染状况,并对近年来不同介质中高氯酸盐的分析检测技术及前处理方法进行了介绍,同时对已开展的高氯酸盐动物毒理研究、在不同环境介质中的迁移转化和植物积累、及其按生物修复和非生物修复进行分类的修复方法进行了综述。最后,对进一步研究的意义和方向提出建议。     

Toxic effects of cadmium on GABA and taurine content in different brain areas of adult male rats

This work assesses the possible changes in gamma amino butyric acid (GABA) and taurine content in the hypothalamus, the median eminence and striatum after the exposure to various doses of cadmium. Cadmium chloride (CdCl2) was administered in the drinking water at the doses of 5, 10, 25, 50 or 100 ppm to adult male rats for 1 month. In the anterior hypothalamus, taurine and GABA content decreased with the dose of 10 ppm of CdCl2 only. Cadmium exposure decreased both GABA and taurine content in mediobasal hypothalamus except for the 50 ppm dose. In posterior hypothalamus GABA and taurine content was not affected by cadmium treatment. As far as the median eminence, 5 or 10 ppm of CdCl2 increased taurine concentration, and at a dose of 5 ppm enhanced GABA content. A significant decrease of GABA and taurine concentration was seen in the striatum at any dose of cadmium used. The concentration of cadmium increased in the hypothalamus and in the striatum in animals receiving CdCl2 in the drinking water at doses of 25, 50 or 100 ppm. The results indicate that cadmium globally decreased GABA and taurine content in the brain areas studied through effects that were not dose dependent.     

Developments in microbiological risk assessment models for drinking water—a short review

Microbiological risk assessment (MRA) is the emerging method to predict the risks of infection from waterborne pathogens (e.g. rotavirus and Cryptosporidium parvum ) in the drinking water supply. The objectives of this paper are to review the appropriateness of current models, with emphasis on pathogen exposures through drinking water, and to consider the information necessary to further their development. Calculating pathogen exposures in MRA is currently limited by the fact that pathogen density data for drinking water supplies are only available for very large volume samples—much larger than imbibed daily by any consumer. To develop MRA, information is needed on how pathogens are dispersed within those large volumes at the resolution of volumes typically consumed daily by individuals. Available evidence suggests that micro-organisms, including pathogens, are clustered to some degree, even within small volumes, exposing some drinking water consumers to much higher doses than others. By assuming pathogens are randomly dispersed, current models overestimate the risk from the more infectious agents (e.g. rotaviruses) but underestimate the risk from less infectious pathogens (e.g. C. parvum ). Approaches to modelling pathogen densities in drinking water from source water data and treatment removal efficiencies require additional information on the degree to which treatment processes (e.g. filtration and coagulation) increase pathogen clustering. The missing information could be obtained from large-scale pilot plant studies.     

Uncloaking a cryptic, threatened rail with molecular markers: origins, connectivity and demography of a recently-discovered population

The threatened California Black Rail lives under dense marsh vegetation, is rarely observed, flies weakly and has a highly disjunct distribution. The largest population of rails is found in 8–10 large wetlands in San Francisco Bay (SF Bay), but a population was recently discovered in the foothills of the Sierra Nevada Mountains (Foothills), within a wetland network comprised of over 200 small marshes. Using microsatellite and mitochondrial analyses, our objectives were to determine the origins, connectivity and demography of this recently-discovered population. Analyses of individuals from the Foothills (n = 31), SF Bay (n = 31), the Imperial Valley (n = 6) and the East Coast (n = 3), combined with rigorous power evaluations, provided valuable insights into past history and current dynamics of the species in Northern California that challenge conventional wisdom about the species. The Foothills and SF Bay populations have diverged strongly from the Imperial Valley population, even more strongly than from individuals of the East Coast subspecies. The data also suggest a historical presence of the species in the Foothills. The SF Bay and Foothills populations had similar estimated effective population size over the areas sampled and appeared linked by a strongly asymmetrical migration pattern, with a greater probability of movement from the Foothills to SF Bay than vice versa. Random mating was inferred in the Foothills, but local substructure among marshes and inbreeding were detected in SF Bay, suggesting different dispersal patterns within each location. The unexpected dimensions of Black Rail demography and population structure suggested by these analyses and their potential importance for management are discussed.     

高氯酸盐胁迫对水稻生长发育和养分吸收的影响

通过土培盆栽试验,研究了0.2、2.0和4.0mmol/kg 3种浓度下高氯酸盐胁迫对两个水稻品种的生长发育和吸收主要养分元素氮、磷、钾的影响。研究发现:(1)高氯酸盐对水稻生长的抑制程度随高氯酸盐处理浓度的增高而加重,且随着处理时间的延长,水稻的受害症状也越来越明显,到分蘖期时,3个浓度组对赣糯香生长的抑制率分别为3.08%、33.39%和39.03%,对IR65598-112-2生长的抑制率分别为9.18%、21.07%和34.97%。(2)各浓度处理组(赣糯香0.2mmol/kg组除外)都显著抑制了两品种水稻的分蘖。(3)各浓度处理组水稻始穗时间都比对照组晚,其中高浓度处理组晚了1个月。(4)IR65598-112-2对高氯酸盐的胁迫表现出更早的反应和对低浓度污染物的敏感性,而赣糯香表现出相对较强的抗性。(5)高氯酸盐对水稻根部的伤害比对地上部的伤害更严重。(6)高氯酸盐处理减少了水稻各器官的生物量,降低了水稻各器官中养分元素总氮和总磷的总积累量。研究表明,高氯酸盐污染可抑制两品种水稻的生长和分蘖,延迟其发育,降低水稻对养分元素的积累,其植物毒性效应与污染物的浓度、处理的延续时间、水稻品种及不同植物器官都有关系。