Derivation and validation of thresholds of cadmium, chromium, lead, mercury and arsenic for safe rice production in paddy soil.

Cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg) and arsenic (As) are potent toxicants to human health via dietary intake. It is imperative to establish accurate soil thresholds based on soil-plant transfer models and food safety standards for safe agricultural production. This study takes rice genotypes and soil properties into account to derive soil thresholds for five heavy metal(loid)s using the bioconcentration factors (BCF) and species sensitivity distribution (SSD) based on the food safety standard. The BCF generated from two paddy soils was calculated to investigate the sensitivity of heavy metal accumulation in nine rice cultivars in a greenhouse pot experiment. Then, empirical soil-plant transfer models were developed from a middle-sensitivity rice cultivar (Denong 2000, one selected from nine rice) grown in nineteen paddy soils with various soil properties under a proper exogenously metal(loid)s concentration gradient. After normalization, hazardous concentrations from the fifth percentile (HC5) were calculated from the SSD curves, and the derived soil thresholds were obtained from HC5 prediction models that based on the combination of pH and organic carbon (OC) or cation exchange capacity (CEC). The soil Cd threshold derived based on pH and organic carbon (pH < 7.5, OC ≥ 20 g kg-1) was 1.3-fold of those only considering pH, whereas the Pb threshold (pH > 6, CEC ≥ 20 cmolc kg-1) was 3.1 times lower than the current threshold. The derived thresholds for five elements were validated to be reliable through literature data and field experiments. The results suggested that deriving soil heavy metal(loid)s threshold using SSD method and local food safety standards is feasible and also applicable to other crops as well as other regions with potential health risks of toxic elements contamination in agricultural production.

Lung Cancer Risk and Low (≤50 µg/L) Drinking Water Arsenic Levels for US Counties (2009⁻2013)-A Negative Association.

While epidemiologic studies clearly demonstrate drinking water with high levels of arsenic as a significant risk factor for lung cancer, the evidence at low levels (≤50 µg/L) is uncertain. Therefore, we have conducted an ecological analysis of recent lung cancer incidence for US counties with a groundwater supply of.

Use of mode of action data to inform a dose-response assessment for bladder cancer following exposure to inorganic arsenic.

In the recent National Research Council report on conducting a dose-response assessment for inorganic arsenic, the committee remarked that mode of action data should be used, to the extent possible, to extrapolate below the observed range for epidemiological studies to inform the shape of the dose-response curve. Recent in vitro mode of action studies focused on understanding the development of bladder cancer following exposure to inorganic arsenic provide data to inform the dose-response curve. These in vitro data, combined with results of bladder cancer epidemiology studies, inform the dose-response curve in the low-dose region, and include values for both pharmacokinetic and pharmacodynamic variability. Integration of these data provides evidence of a range of concentrations of arsenic for which no effect on the bladder would be expected. Specifically, integration of these results suggest that arsenic exposures in the range of 7-43 ppb in drinking water are exceedingly unlikely to elicit changes leading to key events in the development of cancer or noncancer effects in bladder tissue. These findings are consistent with the lack of evidence for bladder cancer following chronic ingestion of arsenic water concentrations <100 ppb in epidemiological studies.

A baseline study of levels of mercury, arsenic, cadmium and lead in Northeast Arctic cod (Gadus morhua) from different parts of the Barents Sea.

This study is one of several baseline studies that will provide basic and reliable information about the content of undesirable substances in important species of fish caught in Norwegian waters. Concentrations of metals in the muscle and liver of more than 800 Northeast Arctic cod caught at 32 sites in the Barents Sea are reported. The highest concentration of both mercury in the muscle and cadmium in the liver was found in cod caught in the western part of the Barents Sea, while the highest concentration of total arsenic was found in cod from the eastern part. The arsenic concentrations varied greatly among individual fish, ranging from 0.3 to 170 mg kg(-1) wet weight in the muscle. Such high levels of total arsenic have never previously been reported in any fish, and the primary factor for these high concentrations is likely to be the shrimp in the cod diet.

Development of a certified reference material (NMIJ CRM 7531-a) for the determination of trace cadmium and other elements in brown rice flour.

A certified reference material (CRM) for trace cadmium and other elements in brown rice flour was developed at the National Metrology Institute of Japan (NMIJ). The CRM was provided as a dry powder after drying and frozen pulverization of fresh brown rice obtained from a Japanese domestic market. Characterization of the property value for each element was carried out exclusively by NMIJ with at least two independent analytical methods, including inductively coupled plasma mass spectrometry (ICP-MS), ICP high-resolution mass spectrometry, isotope-dilution ICP-MS, ICP optical emission spectrometry, and graphite-furnace atomic-absorption spectrometry. Property values were provided for six elements (Mn, Fe, Cu, Zn, As, and Cd). The concentration range of the property values was from 0.280 mg kg(-1) of As to 31.8 mg kg(-1) of Zn. The combined relative standard uncertainties of the property values were estimated by considering the uncertainties of the homogeneity, characterization, difference among analytical methods, dry-mass correction factor, and calibration standard. The range of the relative combined standard uncertainties was from 1.1% of Zn to 1.6% of As.

Arsenic in tube well water in Bangladesh: health and economic impacts and implications for arsenic mitigation.

A national drinking water quality survey conducted in 2009 furnished data that were used to make an updated estimate of chronic arsenic exposure in Bangladesh. About 20 million and 45 million people were found to be exposed to concentrations above the national standard of 50 µg/L and the World Health Organization's guideline value of 10 µg/L, respectively. From the updated exposure data and all-cause mortality hazard ratios based on local epidemiological studies, it was estimated that arsenic exposures to concentrations > 50 µg/L and 10-50 µg/L account for an annual 24,000 and perhaps as many as 19,000 adult deaths in the country, respectively. Exposure varies widely in the 64 districts; among adults, arsenic-related deaths account for 0-15% of all deaths. An arsenic-related mortality rate of 1 in every 16 adult deaths could represent an economic burden of 13 billion United States dollars (US$) in lost productivity alone over the next 20 years. Arsenic mitigation should follow a two-tiered approach: (i) prioritizing provision of safe water to an estimated 5 million people exposed to > 200 µg/L arsenic, and (ii) building local arsenic testing capacity. The effectiveness of such an approach was demonstrated during the United Nations Children's Fund 2006-2011 country programme, which provided safe water to arsenic-contaminated areas at a cost of US$ 11 per capita. National scale-up of such an approach would cost a few hundred million US dollars but would improve the health and productivity of the population, especially in future generations.

An updated inhalation unit risk factor for arsenic and inorganic arsenic compounds based on a combined analysis of epidemiology studies.

The United States Environmental Protection Agency (USEPA) developed an inhalation unit risk factor (URF) of 4.3E-03 per µg/m(3) for arsenic in 1984 for excess lung cancer mortality based on epidemiological studies of workers at two smelters: the Asarco smelter in Tacoma, Washington and the Anaconda smelter in Montana. Since the USEPA assessment, new studies have been published and exposure estimates were updated at the Asarco and Anaconda smelters and additional years of follow-up evaluated. The Texas Commission on Environmental Quality (TCEQ) has developed an inhalation URF for lung cancer mortality from exposures to arsenic and inorganic arsenic compounds based on a newer epidemiology study of Swedish workers and the updates of the Asarco and Anaconda epidemiology studies. Using a combined analysis approach, the TCEQ weighted the individual URFs from these three epidemiology cohort studies, to calculate a final inhalation URF of 1.5E-04 per µg/m(3). In addition, the TCEQ also conducted a sensitivity analysis, in which they calculated a URF based on a type of meta-analysis, and these results compared well with the results of the combined analysis. The no significant concentration level (i.e., air concentration at 1 in 100,000 excess lung cancer mortality) is 0.067µg/m(3). This value will be used to evaluate ambient air monitoring data so the general public in Texas is protected against adverse health effects from chronic exposure to arsenic.

Genotoxic potential of arsenic at its reference dose.

Arsenic, a highly hazardous contaminant in our drinking water, accounts for various toxic effects (including cancer) in human. However, intake of arsenic @0.3 µg kg(-1)day(-1) through drinking water, containing arsenic at its guideline value or maximum contaminant limit (10 µg L(-1)), has been estimated to pose very little or no measurable risk to cancer in humans. The value also appears to be equal to the human reference dose (or index dose) of arsenic based on human skin toxicity data. The present work was a quantitative assessment of the genotoxic potential of arsenic in mice at doses equivalent to its human reference dose as well as its multiples. Significant increases in the frequencies of chromosome abnormalities in the bone marrow cells were registered over the control level upon exposure to all the doses of arsenic including its reference dose (or index dose). The assessment of arsenic genotoxicity in humans at low doses will therefore be highly instrumental in establishing a permissible limit of arsenic in drinking water.

Biomonitoring equivalents for inorganic arsenic.

This paper presents Biomonitoring Equivalents (BEs) for inorganic arsenic. Biomonitoring Equivalents (BEs) are defined as the concentration or range of concentrations of a chemical or its metabolite in a biological medium (blood, urine, or other medium) that is consistent with an existing health-based exposure guideline, and are derived by integrating available data on pharmacokinetics with existing chemical risk assessments. This study reviews available health-based exposure guidance values for arsenic based on recent evaluations from the United States Environmental Protection Agency (US EPA), US Agency for Toxic Substances and Disease Registry (ATSDR) and Health Canada (HC). BE values corresponding to the Reference Dose (RfD) or risk-specific doses for cancer endpoints from these agencies were derived based on kinetic data (urinary excretion) from controlled dosing studies in humans. The BE values presented here provide estimates of the sum of inorganic arsenic-derived urinary biomarkers (inorganic arsenic, monomethylated arsenic, and dimethylated arsenic). The BE associated with the United States Environmental Protection Agency's Reference Dose and the Agency for Toxic Substances and Disease Registry's Minimal Risk Level is 6.4 microg arsenic/L urine. The BEs associated with the various cancer risk assessments are significantly lower. These BE values may be used as screening tools for evaluation of biomonitoring data for inorganic arsenic in a public health risk context.

Preservation of As(III) and As(V) in drinking water supply samples from across the United States using EDTA and acetic acid as a means of minimizing iron-arsenic coprecipitation.

Seven different treatment/storage conditions were investigated for the preservation of the native As(III)/As(V) found in 10 drinking water supplies from across the United States. These 10 waters were chosen because they have different As(III)/As(V) distributions; six of these waters contained enough iron to produce an iron precipitate during shipment. The waters were treated and stored under specific conditions and analyzed periodically over a span of approximately 75 days. Linear least squares (LLS) was used to estimate the change in As(III) and As(V) over the study period. Point estimates for the first and last analyses days and 95% confidence bounds were calculated from the LLS. The difference in the point estimates for the first and last day were then evaluated with respect to drinking water treatment decision making. Three primary treatments were evaluated: EDTA/AcOH-treatment and AcOH treatment as well as no treatment. The effect of temperature was explored for all treatments, while the effect of aeration was evaluated for only the EDTA/AcOH treated samples. The nontreated samples experienced a 0-40% reduction in the native arsenic concentration due to the formation of Fe/As precipitates. The Fe/As precipitates were resolubilized and shown to contain elevated concentrations of As(V) relative to the native distribution. Once this Fe/As precipitate was removed from solution using a 0.45 and 0.2 microm filter, the resulting arsenic concentration (As(III) + As(V)) was relatively constant (the largest LLS slope was -1.4 x 10(-2) (ng As g water(-1)) day(-1)). The AcOH treatment eliminated the formation of the Fe/As precipitate observed in the nontreated samples. However, two of the AcOH water samples produced analytically significant changes in the As(III) concentration. The LLS slopes for these two waters were -5.7 x 10(-2) (ng As(III) g water(-1)) day(-1) and -1.0 x 10(-1) (ng As(III) g water(-1)) day(-1). This corresponds to a -4.3 ng/g and a -7.8 ng/g change in the As(III) concentration over the study period, which is a 10% shift in the native distribution. The third and final treatment was EDTA/AcOH. This treatment eliminated the Fe/As precipitate that formed in the nontreated sample. The LLS slopes were less than -7.5 x 10(-3) (ng As(III) g water(-1)) day(-1) for the above-mentioned waters, corresponding to a 0.6 ng/g change over the study period. One of the EDTA/AcOH treated waters did indicate that using the 5 degrees C storage temperature minimized the rate of conversion relative to 20 degrees C storage.