[en] The Mediterranean coastal seafloor is littered with man-made objects and materials, including a variety of ammunition in many areas. In addition, sediments in ports, harbors and marinas are contaminated with elevated concentrations of chemicals used as biocides in antifouling paints. In order to reach a satisfactory level of environmental security of the coastal sea areas, fast neutron activation analysis with detection of associated alpha particles and energy dispersive X-ray fluorescence, both in laboratory and inside an autonomous underwater vehicle for in-situ measurements, has been used for the characterization of the objects on the seafloor. Measurements have shown that gamma ray spectra are able to distinguish threat material from the surrounding material. Analysis of more than 700 coastal sea sediment samples has resulted in concentration distribution maps indicating the locations of 'hot spots', which might interfere with threat material identification.