After the World War II, approx. 40.000 tonnes of chemical munitions containing about 13.000 tonnes of chemical warfare agents (CWAs) were dumped in the Baltic Sea [1]. As the artillery shells, aircraft bombs and containers are corroding, the contents are leaking into the environment contaminating the surrounding sediments but also spreading far beyond the dumpsite boundaries [2]. Thus, the necessity of investigations on the impact of chemical warfare on biota, such as inorganic arsenic and organo-arsenic compounds, is increasing. Among the dumped CWAs are the vesicant mustard gas (Bis(2-chloroethyl)sulfide), the tear gas chloroacetophenone (2-Chloro-1-phenylethanone) as well as the irritants Clark I (Diphenylarsinechloride) and Adamsite (10-Chloro-5-hydrophenarsazine(10)) [3]. Persistent contaminations at dumping sites are mostly related to arsenic containing compounds [2]. Thus, arsenic containing CWAs have been chosen as model CWAs in the present study. Here, we present the first approach to investigate biological effects of CWA mixtures on the health of blue mussels (M. trossulus) under laboratory conditions. The evaluation of the health status was based on a great array of biomarkers encompassing immunocompetence, oxidative stress defence and pathological alterations in different tissues. Chemical analysis of tissue and water samples facilitated an integrated assessment.