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Arsenic (As) is a toxic trace element with many sources, including hydrocarbons such as oil, natural gas, oil sands, and oil- and gas-bearing shales. Arsenic from these hydrocarbon sources can be released to the environment through human activities of hydrocarbon production, storage, transportation and use. In addition, accidental release of hydrocarbons to aquifers with naturally occurring (geogenic) As can induce mobilization of As to groundwater through biogeochemical reactions triggered by hydrocarbon biodegradation. In this paper, we review the occurrence of As in different hydrocarbons and the release of As from these sources into the environment. We also examine the occurrence of As in wastes from hydrocarbon production, including produced water and sludge. Last, we discuss the potential for As release related to waste management, including accidental or intentional releases, and recycling and reuse of these wastes. ; U.S. Geological Survey Toxic Substances Hydrology ProgramUnited States Geological Survey ; Published version ; We gratefully acknowledge Adam Mumford for assistance with data compilation on produced waters and Denise Akob for creating Fig. 1. We also appreciate insightful comments from two anonymous reviewers and Bill Orem of the U.S. Geological Survey. This work was supported by the U.S. Geological Survey Toxic Substances Hydrology Program. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. ; Public domain authored by a U.S. government employee

This paper describes a mixed flow reactor experiment and associated data analysis scheme that are well suited for studying the chemical and physical processes that occur in limestone drains used to treat acid mine drainage (AMD). The experiment simulates the slowly evolving, near steady state, reactions that form coatings on limestone. The resulting coatings can be recovered for analysis of their structure and composition. Analysis of the time evolution of the composition of the effluent solutions is used to isolate and understand key factors that affect limestone drain performance. The experiment investigated reactions between acidic aluminum sulfate solutions and calcite. The aluminum sulfate feed solutions contained 0.002-0.01 molal (32-329 mg/kg) Al and had pH values ranging from 3.7 to 4.2. At the beginning each experiment, the rate of H+ consumption by reaction with the calcite was fast causing a distinct increase of the effluent pH. The pH increase caused some of the dissolved Al to precipitate as a coating on the calcite surfaces. The coating blocked the transfer of ions to and from the calcite causing the reaction rates to be limited by ion diffusion through the coating. The continued growth of the coating caused it to become an increasingly effective barrier to ion transport, which caused the neutralization rate to slow and the effluent solution pH to decline toward that of the feed solution. Powder X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) suggested that the coatings were mostly poorly crystalline gibbsite. Effluent solutions were analyzed to determine pH along with Al, Ca and S concentrations. The coating thickness at each sample time was estimated from the amount of Al lost from the solution since the beginning of the experiment. This thickness and the Ca and H+ fluxes were used to find the apparent H+ diffusion coefficient in the coatings. ; Department of Geosciences at Virginia Tech; College of Science at Virginia Tech; Graduate School at Virginia Tech ; Palomino-Ore thanks the Fulbright program for the opportunity to study in the USA and the Department of Geosciences, the College of Science and the Graduate School at Virginia Tech for financial support. We thank F. Marc Michel for manufacturing the reactor used in this study. We thank Neil Johnson for help with the XRD, Qing Tang for help with the SEM, and Athena Tilley for ICP OES analyses. We greatly appreciate helpful reviews by Charles Cravotta, Kate Campbell, and Jane Hammarstrom. ; Public domain authored by a U.S. government employee