Role of climate and geography in arsenic mobility and risk at an artisanal mining site in an urbanized semi-arid environment.

Ultra-enriched arsenic (As) concentrations >30% occur at an abandoned artisanal mine in an urban park in San Diego, California, presenting a complex risk to the public. This study uses geochemistry in consideration with climate and geography to evaluate As transport away from the mine. Sediment As concentrations reach 2320 mg/kg (483 times background crustal concentrations; n = 73) along drainage pathways and sequential extraction experiments indicate As overwhelmingly partitions into the least mobile phase (mean 83% As in residual fraction; n = 30); there is little redistribution of As from primary minerals into secondary or dissolved phases - a potentially positive outcome for managing the risk - despite the sediments being exposed to a century of weathering. Dissolved As transport does occur, with intermittent rain events producing As up to 272 µg/L in runoff. Both sediment and water As decrease to background concentrations within 1,000 m of the mines, influenced by the encroaching urbanization, and the semi-arid climate which limits weathering and transport. Similar patterns of As migration downgradient of abandoned mines occur at other mining sites in arid and semi-arid regions; however, off-site As transport at other sites extends far greater distances. This study indicates that a combination of geochemistry, geomorphology, climate, and urbanization can work together to retard the surface transport of As from artisanal and un-remediated mine sites; and helps inform environmental management at this site and others like it.

Groundwater Chemistry and Blood Pressure: A Cross-Sectional Study in Bangladesh.

Background: We assessed the association of groundwater chemicals with systolic blood pressure (SBP) and diastolic blood pressure (DBP). Methods: Blood pressure data for ≥35-year-olds were from the Bangladesh Demographic and Health Survey in 2011. Groundwater chemicals in 3534 well water samples from Bangladesh were measured by the British Geological Survey (BGS) in 1998-1999. Participants who reported groundwater as their primary source of drinking water were assigned chemical measures from the nearest BGS well. Survey-adjusted linear regression methods were used to assess the association of each groundwater chemical with the log-transformed blood pressure of the participants. Models were adjusted for age, sex, body mass index, smoking status, geographical region, household wealth, rural or urban residence, and educational attainment, and further adjusted for all other groundwater chemicals. Results: One standard deviation (SD) increase in groundwater magnesium was associated with a 0.992 (95% confidence interval (CI): 0.986, 0.998) geometric mean ratio (GMR) of SBP and a 0.991 (95% CI: 0.985, 0.996) GMR of DBP when adjusted for covariates except groundwater chemicals. When additionally adjusted for groundwater chemicals, one SD increase in groundwater magnesium was associated with a 0.984 (95% CI: 0.972, 0.997) GMR of SBP and a 0.990 (95% CI: 0.979, 1.000) GMR of DBP. However, associations were attenuated following Bonferroni-correction for multiple chemical comparisons in the full-adjusted model. Groundwater concentrations of calcium, potassium, silicon, sulfate, barium, zinc, manganese, and iron were not associated with SBP or DBP in the full-adjusted models. Conclusions: Groundwater magnesium had a weak association with lower SBP and DBP of the participants.

The source of naturally occurring arsenic in a coastal sand aquifer of eastern Australia.

The discovery of dissolved arsenic in a coastal aquifer used extensively for human consumption has led to widespread concern for its potential occurrence in other sandy coastal environments in eastern Australia. The development of an aquifer specific geomorphic model (herein) suggests that arsenic is regionally derived from erosion of arsenic-rich stibnite (Sb(2)S(3)) mineralisation present in the hinterland. Fluvial processes have transported the eroded material over time to deposit an aquifer lithology elevated in arsenic. Minor arsenic contribution to groundwater is derived from mineralised bedrock below the unconsolidated aquifer. An association with arsenic and pyrite has been observed in the aquifer in small discrete arsenian pyrite clusters rather than actual acid sulfate soil horizons. This association is likely to influence arsenic distribution in the aquifer, but is not the dominant control on arsenic occurrence. Arsenic association with marine clays is considered a function of their increased adsorptive capacity for arsenic and not solely on the influence of sea level inundation of the aquifer sediments during the Quaternary Period. These findings have implications for, but are not limited to, coastal aquifers. Rather, any aquifer containing sediments derived from mineralised provenances may be at risk of natural arsenic contamination. Groundwater resource surveys should thus incorporate a review of the aquifer source provenance when assessing the likely risk of natural arsenic occurrence in an aquifer.