Baltic Sea is a very specific water body. Its geographical situation, geological development, hydrological features and physical drivers, make it very susceptible to pollutants, including arsenic contamination. Baltic Sea is surrounded by nine countries with different industrialization levels, affecting the riverine outflow and surface runoff into the sea. Some parts of the Baltic Sea are characterized with highly elevated arsenic concentrations resulting from the anthropogenic activity on land. There is also a significant inner source of arsenic in the Baltic – arsenic containing Chemical Warfare Agents (CWA) from chemical munitions dumped after the World War II and remaining on the sea bottom.