Widespread environmental contamination from relic munitions in the southwestern Baltic Sea

Relic munitions from warfare and intentional dumping contaminate coastal waters worldwide, with an estimated 300,000 tons in the German Baltic Sea alone. These contain toxic conventional explosive chemicals, including 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitro-1,3,5-triazinane (RDX), and 1,3-dinitrobenzene (DNB). Corrosion of metal munition housings in seawater releases these munition chemicals (MCs) to the marine environment. The current study performed detailed environmental sampling throughout German waters of the southwest Baltic Sea in 2017 and 2018, and measured MCs in water, suspended particles, and sediments. At least one MC was detected in nearly every water sample, from sub-pmol/L up to several thousand pmol/L. Most MC were in the dissolved phase, not on suspended particles, and MC content in sediments was patchy and generally low. TNT levels were especially high in Kiel Bay, whereas RDX and DNB concentrations were highest in Lübeck Bay, likely reflecting regional differences in munitions types. A TNT module was developed and implemented in the General Estuarine Transport Model (GETM), incorporating TNT input to the water column by dissolution and removal by microbial degradation/transformation. Simulated TNT distributions matched observed environmental patterns well, indicating good parametrization of the primary controls. Dissolved concentrations of the target MCs were generally far below acute or chronic toxicity levels for aquatic organisms, but the highest observed concentrations approached toxic levels, especially for DNB. The inventory of dissolved MC in the study region was approximately 3000 kg, implying that current contamination levels can be sustained continuously for over 800 years by existing munitions on the seafloor.