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.

Bending rules for animal propulsion.

Animal propulsors such as wings and fins bend during motion and these bending patterns are believed to contribute to the high efficiency of animal movements compared with those of man-made designs. However, efforts to implement flexible designs have been met with contradictory performance results. Consequently, there is no clear understanding of the role played by propulsor flexibility or, more fundamentally, how flexible propulsors should be designed for optimal performance.