High Levels of Platinum and Palladium Found in Boston Harbor Sediments
Likely Sources Industry and Automobile Catalytic Converters
The first systematic study of the influence of human activity on platinum and palladium concentrations in an urban coastal system show high levels of these metals. Scientists at the Woods Hole Oceanographic Institution (WHOI) and their colleagues found platinum and palladium concentrations in recent surface sediments in Boston Harbor up to five times local pre-industrial sediment concentrations. While the levels do not exceed those found in environments where metals naturally concentrate, such as manganese nodules in the deep sea, the levels are significantly higher than those found in pre-industrial Massachusetts Bay sediment. The researchers say the most likely source of these enrichments is the use of automobile catalytic converters, as well as some waste from the chemical, jewelry, electrical, medical and dental industries entering the Harbor through the sewage system.
"Our estimates of platinum (Pt) and palladium (Pd) fluxes show a large discrepancy between those associated with sludge and effluent release into the Harbor and those determined from sediment concentrations," Caroline Tuit of WHOI's Geology and Geophysics Department said of the study. Tuit says the discrepancy suggests there is an additional source of the metals, most likely their release from automobile catalytic converters. Catalytic converters account for 60% and 40%, respectively, of the total U.S. Pt and Pd demand. Pt and Pd release from catalytic converters, primarily as small metal particles, has led to documented enrichment of Pt and Pd in road dust. Tuit and her colleagues say the Pt and Pd could be reaching the Harbor through street sewers and combined sewage overflows unimpeded by the sewage treatment system. The widespread use of catalytic converters also suggests that these enrichments are likely to be common in urban coastal environments.
Tuit is a graduate student in the MIT/Woods Hole Oceanographic Institution's Joint Program. Other authors of the study, published in the American Chemical Society's Journal of Environmental Science & Technology are Tuit's advisor, Gregory Ravizza, an Associate Scientist in WHOI's Geology and Geophysics Department, and Michael Bothner of the US Geological Survey in Woods Hole.
Unlike other metals influenced by human activity, such as lead and mercury, the chemical behavior and possible toxicity of platinum and palladium in the marine environment is largely unknown. The bulk concentration data presented in this study indicate that some portion of these metals may be chemically mobile. Simple platinum compounds, among them the cancer drug cisplatin, are capable of diffusing into the cell membrane, binding to cell DNA and preventing cell replication. They produce serious side effects and their palladium analogues are generally too toxic to use.
"To our knowledge, no one knows the chemical form of Pt and Pd in the environment," Tuit says. "Toxicity studies on these metals were conducted at levels much higher than those seen in these sediments, but given the widespread dispersal of Pt and Pd to the environment and the potential for accumulation within marine organisms, known as bioaccumulation, there may be long term toxicological and ecological effects. At this point, we simply do not have the data to determine whether these levels are dangerous."
There has been little research on Pt and Pd release into the environment in the US. Most of the studies have been done in Europe, and nearly all have focused on the accumulation of these two metals in road dust and terrestrial environments. European studies show that Pt is bioaccumulated by freshwater isopods (small crustaceans) and that Pt is toxic to some marine bacteria. The work by Tuit and her colleagues represents the first systematic study of the release of these two toxic elements into the marine environment. About 120 samples collected from the seafloor in Massachusetts Bay and from Boston Harbor itself were used in the study. Funding was provided by a joint funding agreement between the Massachusetts Regional Water Resources Authority (MWRA) and the US Geological Survey (USGS), and by a Mellon Independent Study Award from the Woods Hole Oceanographic Institution.
While catalytic converters have been dramatically successful in reducing automobile emissions and preserving the atmosphere, their use has led to the widespread release of potentially hazardous metals. "Trying to stay on top of these sorts of changes in our environment is an important part of our efforts to anticipate adverse human impacts," Tuit says. "It is also part of good environmental stewardship."
Additional information about Woods Hole Oceanographic Institution can be found on the World Wide Web at: http://www.whoi.edu (general WHOI information)