Distribution of chemical warfare agent, energetics, and metals in sediments at a deep-water discarded military munitions site

There is a strong need to understand the behavior of chemical warfare agent (CWA) at underwater discarded military munitions (DMM) sites to determine the potential threat to human health or the environment, yet few studies have been conducted at sites in excess of 250 m, the depth at which most U.S. chemical munitions were disposed. As part of the Hawai’i Undersea Military Munitions Assessment (HUMMA), sediments adjacent to chemical and conventional DMM at depths of 400–650 m were sampled using human occupied vehicles (HOVs) in order to quantify the distribution of CWA, energetics, and select metals. Sites in the same general area, with no munitions within 50 m in any direction were sampled as a control. Sulfur mustard (HD) and its degradation product 1,4-dithiane were detected at each CWA DMM site, as well as a single sample with the HD degradation product 1,4-thioxane. An energetic compound was detected in sediment to a limited extent at one CWA DMM site. Metals common in munitions casings (i.e., Fe, Cu, and Pb) showed similar trends at the regional and site-wide scales, likely reflecting changes in marine sediment deposition and composition. This study shows HD and its degradation products can persist in the deep-marine environment for decades following munitions disposal.