Sediment and water phase toxicity and UV-activation of six chemicals used in military explosives

Abstract

Explosives used in ammunition have been dumped in both lakes and oceans before the potential environmental effects of these chemicals were understood. Growing environmental concern in society and in the Swedish military resulted in a project dealing with the aquatic toxicology of explosives. The aim of the present study was to assess the hazard of six explosives by determining the acute sediment and water phase toxicity for two crustaceans ( Daphnia magna and Nitocra spinipes). Detoxification during storage was used as an indication of degradability (hydrolysis and biodegradation). The effect of ultraviolet light on the toxicity of these compounds was determined by post-exposure to ultraviolet light and determination of toxicity enhancement. The explosives were picric acid, trinitrotoluene, (2,4-dinitrotoluene), hexahydro-1,3,5-trinitro-1,3,5-trazine, nitroguanidine, and pentyl. The stabilising agent diphenylamine was tested in the same way. For the major explosive, trinitrotoluene, the water-phase EC/LC 50s were between 5 and 20 mg l −1 and the toxicity was not significantly affected by storage of test solutions for 30 days, indicating hydrolytic stability. The toxicity was not affected by addition of sediment, indicating that trinitrotoluene was not bound appreciably to sediment, but toxicity decreased after storage for 30 days in the presence of sediment, indicating biological degradation or slow adsorption of the chemical. The toxicity of the other explosives was similar or lower than for trinitrotoluene, but the stabilising agent diphenylamine was slightly more toxic with EC/LC 50s between 0.5 and 5 mg l −1. Photoinduced toxicity by ultraviolet light is known for many chemicals including polycyclic aromatic hydrocarbons and trinitrotoluene. The latter was confirmed in this study and especially for degraded trinitrotoluene. 2,4-Dinitrotoluene, which is one degradation product of trinitrotoluene was also activated by ultraviolet light. The toxicity of diphenylamine decreased after storage in water (hydrolysis) and with sediment (biodegradation), but both diphenylamine and its degradation products exhibited photoinduced toxicity.