DDT and PCB reduction in the western Mediterranean from 1987 to 2002, as shown by levels in striped dolphins (Stenella coeruleoalba)

Temporal trends in DDT and PCB contamination were recorded in the offshore waters of the western Mediterranean Sea during 1987–2002 using striped dolphins (Stenella coeruleoalba) as indicators. Despite the fact that the use of DDT and PCB was banned at the end of the 1970s–early 1980s, dolphins were still found to carry moderate to high levels of these chemicals in their tissues, reflecting their ubiquity and environmental persistence. Concentrations of both groups of compounds have slowly decreased, although the decline in PCB has been steeper than that of DDT. Consequently, the tDDT/PCB ratio increased significantly. Indices of metabolisation of both DDT and PCB substantiated progressive aging of pollutant loads and degradation, suggesting that the offshore marine environment has not been exposed to significant releases of these contaminants in recent years. This all indicates a decline in organochlorine pollution in oceanic waters which is consistent, albeit not always, with trends observed in coastal surveys. Dolphins and other top predators are thus confirmed as useful indicators to assess long-term trends of pollutants in oceanic ecosystems and large water masses.