Evaluation of Arsenic Uptake by Marine Sediments

Abstract

After World War I and through the end of World War II, the United States military dumped unused chemical warfare munitions (CWM) into coastal waters off Oahu. A number of studies are currently researching how the condition of CWM and effect environmental quality in the marine environment. Lewisite, an arsenic-rich compound, is found in CWM and hydrolyses in water, allowing arsenic to seep into the marine environment. To supplement current ongoing studies, controlled laboratory batch reactor experiments evaluated the potential mobility of arsenic (As) derived from seadisposed lewisite in the marine environment. Sediment cores obtained from the CWM sites were evaluated for their ability to absorb and retain arsenic. Sediment-water suspension experiments, with different As concentrations (5 µM, 10 µM, and 20 µM) and species added (As(III) and As(V)), have been run from one minute to 7 days and experiment sediment samples were analyzed by ICPMS to determine As content. Arsenic uptake onto sediments continued over time but the relative or absolute uptake at the end of the experiment does not necessarily increase with increasing As spike concentrations. The uptake of As(V) was also greater over time (as compared to experiments with an equivalent concentration of As(III). It was concluded that over the 7 day experiment duration, none of the experiments reached equilibrium, therefore suggesting that As adsorption on the sediments at the CWM sites is much less than anticipated, and the amount of As going into the surrounding water is greater than expected. The calculations of As that is added to sediment and seawater, based on the experimental data, concludes that the impact on the environment is minimal.