Arsenic, a hazardous metalloid, is found in more than 245 minerals and more than 25 different As compounds have been identified in biological samples. This high number of compounds was identified despite the fact that scientists have focused mostly on the water-soluble fraction. An international research group now found arsenic in lipids from fish oil. The discovery of arsenic in oil from capelin (Mallotus villosus), a North Atlantic fish in the smelt family, and the prospect that it could also be present in other fatty fish, could have important implications for human health and the ocean environment.