FRAGILE ecosystems like the Arctic could face many more years of contamination from PCBs, despite international treaties banning their use. That is the conclusion of a study into the fate of polychlorinated biphenyls manufactured worldwide during much of the 20th century.
An estimated 1.3 million tonnes of PCBs were made between the 1930s and 1990s around the world for use in the manufacture of pesticides, lubricants and plastics. But an investigation funded by the European Union to determine the fate of these hormone mimics has failed to locate most of them. 鈥淲e think we can account for perhaps 30 per cent, absorbed by soils, coastal sediments or the deep ocean,鈥� says Kevin Jones, an environmental scientist at the University of Lancaster. 鈥淏ut the rest is a mystery.鈥�
Jones teamed up with scientists at the Norwegian Institute for Air Research in Kjeller and analysed soil samples from 208 sites around the world. They calculate that only around 21,000 tonnes of PCBs persist in soils worldwide. This means hundreds of thousands of tonnes of the chemical are missing 鈥� probably sitting in factories or lingering in old electrical equipment, says Jones. 鈥淪ome has degraded naturally, but we think the majority is still waiting to enter the environment,鈥� he adds.
Advertisement
If the missing PCBs turn up, it could prove particularly disastrous for Arctic countries. Once released into the environment, PCBs evaporate and travel on the winds to cold countries where they condense out in the cold air. The process, dubbed 鈥済lobal distillation鈥�, has caused PCBs to accumulate in Arctic ecosystems, and in particular in the body fat of mammals, such as polar bears, whales and even humans. The birth of hermaphrodite polar bear cubs has been blamed on the chemical (New 杏吧原创, 31 May 1997, p 24).
While most industrialised countries stopped producing PCBs in the 1970s, 90 countries gathered in Stockholm in 2001 to sign a treaty banning the substances. But Jones鈥檚 study shows that contamination could continue for a long time yet. 鈥淲e still find that urban air contains more PCBs than rural air, so we must conclude that the chemicals are still being released into the environment,鈥� says Jones. 鈥淭he bad news is that there seem to be a great deal more PCBs than anyone thought that have not entered the environment yet.鈥�
The good news is that Jones鈥檚 study, which is published in the journal Environmental Pollution (vol 121, p 75), also shows that agricultural and forest soils are good at absorbing PCBs, providing some protection for Arctic countries. Soils in temperate lands have captured most of the PCBs released into the environment until now, says Jones.