Many chemicals (e.g. hydrocarbons, DDT and PCBs) are released into the ocean as part of maritime traffic, industrial activities, agricultural activities and urban activities or accumulate in the ocean (e.g.: plastic debris). Cetaceans seem to be particularly sensitive and have significant levels of mercury and lead. Although the effects of these pollutants have still to be studied in depth, their effects on cetaceans are dangerous, even deadly: weakened immune system (and thus overexposure to diseases), effects on hormones, poisoning of the newborns, running aground, etc.
Best known of these chemical pollutions is hydrocarbon pollution. This pollution causes serious diseases. It can also lead to beaching. For example, 745 cetaceans were running aground after the 2010 oil spill in the Gulf of Mexico. It is however necessary to be aware that the beaching caused by this pollution is only a small percentage of dead animals (perhaps 2%) and the total number of victims is much higher.