CATALYTIC converters, which were designed to clean up car exhausts, are
polluting the environment. Italian and French researchers have found heavy
metals from the devices in remote regions of Greenland. 鈥淭he fact that we found
the metals in Greenland means that it鈥檚 a global problem. It鈥檚 not just close to
the cities or the highways,鈥� says chemist Carlo Barbante of the University of
Venice.
Seth Dunn of the Worldwatch Institute, an environmental watchdog based in
Washington DC, agrees. 鈥淭hey have broken new ground,鈥� he says. 鈥淭he implications
could be very significant in terms of human health.鈥� For instance, workers
involved in refining platinum, one of the metals used in catalytic converters,
are known to suffer from higher than normal levels of severe asthma.
The US, Canada and Japan introduced cars with catalytic converters in the
mid-1970s. Europe followed in the early 1990s. In these devices platinum,
palladium and rhodium catalyse reactions that convert hydrocarbons, carbon
monoxide, and nitrogen oxides into less noxious emissions. A recent European
Commission study found that exhausts from fast-moving cars erode catalytic
converters, ejecting microscopic particles containing the metals.
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To assess the global impact of these particles, Barbante and his colleagues
went to central Greenland and extracted ice and snow cores dating from 1969 to
1988 and from 1991 to 1995. They also took samples from the Greenland Ice Core
Project, dating back nearly 7500 years.
They found that metal concentrations in the snow have been rising steadily
since 1976. Rhodium levels are already 120 times higher than in the
7500-year-old ice. Palladium and platinum levels have increased 80 and 40-fold
respectively. The ratio of platinum to rhodium in the snow from the mid-1990s
resembled the ratio in car exhausts from another study. This suggests that most
of the increased platinum and rhodium comes from catalytic converters, Barbante
says.
According to the European Commission study, concentrations of these metals in
urban air are still too low to create a significant health risk. But the metals,
especially palladium, can accumulate in plants and animals, and enter the food
chain. Researchers have found that the freshwater crustacean, Asellus
aquaticus, absorbs palladium from sediment. 鈥淲e know palladium gets off the
catalytic particle and is transferred into the biological system, but we don鈥檛
know how,鈥� says environmental chemist Greg Morrison of Chalmers University of
Technology in Gothenburg, Sweden.
However, Kym Jarvis, an environmental geochemist at Kingston University in
Kingston upon Thames, and her colleagues have discovered that palladium is
soluble in a dilute acid solution. 鈥淭he high solubility of palladium suggests
that, once it reaches the road surface, it would be in a form that can be more
readily absorbed by vegetation, or which can go into the watercourse,鈥� she says.
Both Jarvis鈥檚 and Barbante鈥檚 findings will appear in future issues of the
journal Environmental Science and Technology.