Microbial Precipitation of Arsenic Sulfides in Andean Salt Flats

An abiotic origin has traditionally been assumed for the arsenic minerals realgar and orpiment associated with thermal springs. Microbial precipitation of arsenic, however, has been studied in pure cultures and the isotopic composition of arsenic sulfides associated with some borate deposits suggests a biotic origin for those minerals. The aim of the present study is to demonstrate the role of bacterial arsenic precipitation in the biogeochemical cycle of arsenic in such borate deposits. For this purpose both enrichment and pure cultures were obtained from the natural arsenic minerals and the composition and isotopic signatures of the arsenic sulfide minerals precipitated by the cultures and those associated with boron deposits from an Andean salt flat in northern Chile were compared. Based on the microbiological and chemical evidence gathered, it is concluded that bacteria contributed to the formation of the arsenic minerals. This interpretation is based on the consistent association of a variety of features that strongly indicate microbial involvement in the precipitation process. These include: (1) enrichment and isolation of cultures with arsenic precipitation capacity from arsenic mineral samples, (2) high numbers of arsenic-precipitating bacteria in the Andean minerals and brines, (3) chemical and mineralogical properties of precipitates experimentally formed under biotic and abiotic conditions, (4) similarities in stoichiometry between natural and laboratory obtained minerals, and (5) the consistent depletion in δ³⁴S values for natural versus laboratory obtained sulfides. Thus, microbial precipitation of arsenic sulfides is a geochemically relevant metabolism.     

The influence of Trisenox on actin organization in HL-60 cells

The aim of this study was to show the influence of Trisenox (arsenic trioxide, ATO) on cytoplasmic and nuclear F-actin organization in HL-60 human leukemia cell line. Changes in localization were determined with the use of fluorescence microscopy and flow cytometry. Alterations, in both cytoplasmic and nuclear actin, were observed in cells exposed to ATO. F-actin network underwent accumulation and formed aggregates, that were very often placed under the cell membrane in whole cells and at the periphery of isolated nuclei. Addition of ATO also induced apoptosis and a decrease in G2 phase cells. These results suggest the influence of actin on the formation of apoptotic bodies and also participation of this protein in apoptotic alterations within nuclei, i.e. chromatin reorganization.     

Arsenic exposure and cancer risk reduction with local ordinance requiring whole-house dual-tank water treatment systems

Arsenic, a known human carcinogen, occurs naturally in groundwater in New Jersey and many other states and countries. A number of municipalities in the Piedmont, Highlands, and Valley and Ridge Physiographic Provinces of New Jersey have a high proportion of wells that exceed the New Jersey maximum contaminant level (MCL) of 5 µg/L. Hopewell Township, located in Mercer County and the Piedmont Province, has a progressive local ordinance which requires the installation of dual-tank, point-of-entry treatment systems on affected wells. This provided a unique study opportunity. Of the 55 homes with dual-tank POE treatment systems recruited into this study, 51 homes (93%) had arsenic levels under the MCL at the kitchen sink, regardless of years in service and/or maintenance schedule adherence. Based on the study participants’ water consumption and arsenic concentrations, we estimate that Hopewell's arsenic water treatment ordinance, requiring POE dual-tank arsenic treatment, reduced the incidence of excess lifetime (70-year) bladder and lung cancers from 121 (1.7 cancer cases/year) to 16 (0.2 cancer cases/year) preventing 105 lifetime cancer cases (1.5 cases/year). Because the high risk of cancer from arsenic can be mitigated with effective arsenic water treatment systems, this ordinance should be considered a model for other municipalities.     

Arsenic in Seafood: Speciation Issues for Human Health Risk Assessment

Major sources of arsenic exposure for humans are foods, particularly aquatic organisms, which are called seafood in this report. Although seafood contains a variety of arsenicals, including inorganic arsenic, which is toxic and carcinogenic, and arsenobetaine, which is considered nontoxic, the arsenic content of seafood commonly is reported only as total arsenic. A goal of this literature survey is to determine if generalizable values can be derived for the percentage of total arsenic in seafood that is inorganic arsenic. Generalizable values for percent inorganic arsenic are needed for use as default values in U.S. human health risk assessments of seafood from arsenic-contaminated sites. Data from the worldwide literature indicate the percent of inorganic arsenic in marine/estuarine finfish does not exceed 7.3% and in shellfish can reach 25% in organisms from presumably uncontaminated areas, with few data available for freshwater organisms. However, percentages can be much higher in organisms from contaminated areas and in seaweed. U.S. site-specific data for marine/estuarine finfish and shellfish are similar to the worldwide data, and for freshwater finfish indicate that the average percent inorganic arsenic is generally < 10%, but ranges up to nearly 30%. Derivation of nationwide defaults for percent inorganic arsenic in fish, shellfish, and seaweed collected from arsenic-contaminated areas in the United States is not supported by the surveyed literature.     

Sensitivity Analysis of U.S. EPA's Estimates of Skin Cancer Risk from Inorganic Arsenic in Drinking Water

The current U.S. Environmental Protection Agency's (USEPA's) risk analysis on the Integrated Risk Information System (IRIS) for arsenic in drinking water is based on an epidemiological study of skin cancer in Taiwan. Assumptions used in the USEPA application of the multistage-Weibull model for risk estimation were varied to assess the effect on predicted risk of skin cancer to the U.S. population at arsenic concentrations of 1 to 50?µg/L in drinking water. Among the assumptions tested, the only notable change in risk estimates was a reduction when the arsenic concentration used as representative for Taiwan villages in the low range (<300?µg/L) was increased to the 75th percentile (245?µg/L) in place of the mean used in the USEPA analysis (170?µg/L), but the representative value for Taiwan villages in the high range (≥600?µg/L) was not increased simultaneously to the 75th percentile. Additionally, a simulation study was conducted using records of arsenic measurements in wells from the same period and region of Taiwan as the original study. The exposure-response curve estimated from 60 villages (60 data points) differed only marginally from the outcome when data were summarized into four data points (as in the USEPA skin cancer analysis). Briefly discussed are differences between the study area of Taiwan and the U.S. in nutritional status and consumption of inorganic arsenic in food that might bias predicted U.S. skin cancer risks.     

Tolerance of Landoltia punctata to arsenate: an evaluation of the potential use in phytoremediation programs

Abstract

Plants used in phytoremediation should accumulate and tolerate a specific pollutant. Here, we aimed at evaluating a possible arsenic (As) accumulation and mechanisms of tolerance against As-induced damage in Landoltia punctata to explore this species for phytoremediation. Plants were subjected to increasing As levels. As absorption was higher with increasing As levels. The activity of superoxide dismutase and glutathione reductase as well as anthocyanin levels increased with As levels. Catalase and peroxidase activities increased in plants subjected to As levels up to 1.0?mg L^?1 and decreased at higher levels. Due to the antioxidant system, higher levels of reactive oxygen species were restrained in plants under low levels of As. However, the levels of superoxide anion, hydrogen peroxide, and lipid peroxidation increased in response to the impaired antioxidant system induced by the highest As levels. Biomass decreased in plants exposed to As and scanning electron microscopy revealed root structural damage in the root cap of plants under 3.0?mg L^?1?As. This work highlights that L. punctata can be considered a hyperaccumulator species and has potential for As phytoremediation when levels are lower than 1.0?mg L^?1—a concentration 100-fold higher than that recommended for drinking water.

Novelty Statement: Landoltia punctata can be considered a hyperaccumulator species and has the potential for arsenic phytoremediation when levels are lower than 1.0?mg L^?1.     

Variation of Total and Speciated Arsenic in Commonly Consumed Fish and Seafood

This article compiles available data and presents an approach for predicting human intakes of inorganic arsenic (As_i), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) from marine, estuarine, and freshwater seafood when only total arsenic (As_tot) concentrations are reported. Twenty studies provided data on total arsenic (As_tot) and As_i. Mean As_i concentrations were approximately 10 to 20 ng/g wet weight (ww) in freshwater, anadromous, and marine fish, whereas crustaceans and molluscs had mean As_i concentrations of 40 to 50 ng/g ww. Thirteen studies provided data for MMA and DMA. MMA was seldom detected, whereas DMA averaged 10 ng/g ww in freshwater fish, and 45 to 95 ng/g ww in anadromous fish, marine fish, crustaceans, and molluscs. There was little correlation between As_tot concentrations and As_i concentrations; however, when only As_tot data are available to assess health risks from arsenic in seafood, these data could support conservative, upper end estimates of the percent of As_tot likely to be As_i. For marine and estuarine fish, and crustaceans and molluscs 2–3% of As_tot was As_i at the 75th percentile of the dataset. For freshwater fish As_i was 10% of As_tot at the 75th percentile. Due to the nonlinearity and low carcinogenic potency of DMA, the reported DMA concentrations should not contribute substantially to potential health risks from arsenic in seafood.     

Nrf2-dependent repression of interleukin-12 expression in human dendritic cells exposed to inorganic arsenic

Inorganic arsenic, a well-known Nrf2 inducer, exerts immunosuppressive properties. In this context, we recently reported that the differentiation of human blood monocytes into immature dendritic cells (DCs), in the presence of low and noncytotoxic concentrations of arsenic, represses the ability of DCs to release key cytokines in response to different stimulating agents. Particularly, arsenic inhibits the expression of human interleukin-12 (IL-12, also named IL-12p70), a major proinflammatory cytokine that controls the differentiation of Th1 lymphocytes. In the present study, we determined if Nrf2 could contribute to these arsenic immunotoxic effects. To this goal, human monocyte-derived DCs were first differentiated in the absence of metalloid and then pretreated with arsenic just before DC stimulation with lipopolysaccharide (LPS). Under these experimental conditions, arsenic rapidly and stably activates Nrf2 and increases the expression of Nrf2 target genes. It also significantly inhibits IL-12 expression in activated DCs, at both mRNA and protein levels. Particularly, arsenic reduces mRNA levels of IL12A and IL12B genes which encodes the p35 and p40 subunits of IL-12p70, respectively. tert-Butylhydroquinone (tBHQ), a reference Nrf2 inducer, mimics arsenic effects and potently inhibits IL-12 expression. Genetic inhibition of Nrf2 expression markedly prevents the repression of both IL12 mRNA and IL-12 protein levels triggered by arsenic and tBHQ in human LPS-stimulated DCs. In addition, arsenic significantly reduces IL-12 mRNA levels in LPS-activated bone marrow-derived DCs from Nrf2^+/+ mice but not in DCs from Nrf2^−/− mice. Finally, we show that, besides IL-12, arsenic significantly reduces the expression of IL-23, another heterodimer containing the p40 subunit. In conclusion, our study demonstrated that arsenic represses IL-12 expression in human-activated DCs by specifically stimulating Nrf2 activity.