Organochlorine concentrations declined during 1987-2002 in western Mediterranean bottlenose dolphins, a coastal top predator.

We collected blubber samples from bottlenose dolphins stranded on Spain's Mediterranean coasts over a 25-year period (1978-2002). Samples were analyzed to determine time trends in levels of: HCB (hexachlorobenzene), PCB (polychlorinated biphenyls) and tDDT (dichlorodiphenyltrichloroethane and its metabolites). Overall, levels were high relative to other areas. This reflects both the ubiquity of organochlorine pollution in the western Mediterranean and the sampled species' coastal habit. There was a significant decline over the study period in the concentrations of all the compounds analyzed. However, the DDE/tDDT, which is indicative of DDT ageing, significantly increased. This suggests there has been no significant use of HCB, DDT or PCB in the region for a long time. It also indicates that the pollutant loads in the environment are gradually being reduced; either by degradation or by migration of the compounds to other regions. A comparison with dolphin species that have an oceanic distribution suggests that PCB decline at a comparable pace in coastal and offshore water bodies. However, the decline of tDDT is faster near the coast.