Occurrence and possible sources of arsenic in seafloor sediments surrounding sea-disposed munitions and chemical agents near Oʻahu, Hawaiʻi

The Department of Defense disposed of conventional and chemical munitions as well as bulk containers of chemical agents in US coastal waters including those surrounding the State of Hawaiʻi. The Hawaiʻi Undersea Military Munitions Assessment has been collecting biota, water, and sediment samples from two disposal areas south of the island of Oʻahu in waters 500 to 600m deep known to have received both conventional munitions and chemical agents (specifically sulfur mustard). Unlike a number of other sea-disposed munitions investigations which used grabs or corers lowered from surface vessels, we used manned submersibles to collect the samples. Using this approach, we were able to visually identify the munitions and precisely locate our samples in relation to the munitions on the seafloor. This paper focuses on the occurrence and possible sources of arsenic found in the sediments surrounding the disposed military munitions and chemical agents. Using nonparametric multivariate statistical techniques, we looked for patterns in the chemical data obtained from these sediment samples in order to determine the possible sources of the arsenic found in these sediments. The results of the ordination technique nonmetric multidimensional scaling indicate that the arsenic is associated with terrestrial sources and not munitions. This was not altogether surprising given that: (1) the chemical agents disposed of in this area supposedly did not contain arsenic, and (2) the disposal areas studied were under terrestrial influence or served as dredge spoil disposal sites. The sediment arsenic concentrations during this investigation ranged from <1.3 to 40mg/kg-dry weight with the lower concentrations typically found around control sites and munitions (not located in dredge disposal areas) and the higher values found at dredge disposal sites (with or without munitions). During the course of our investigation we did, however, discover that mercury appears to be loosely associated with munitions. Given that mercury contamination has been seen in about 20% of the munitions and ton containers of sulfur mustard, the association of mercury with chemical agents is not totally unexpected.