Sediment-based evidence of platinum concentration changes in an urban lake near Boston, Massachusetts.

Emission from automobile catalysts has resulted in elevated platinum concentration in the urban and roadside environment. The work presented here investigates the chronological record of platinum in sediments from the Upper Mystic Lake near Boston, MA, and aims at providing a better understanding of the environmental platinum cycle. Sediment cores were collected by freeze-coring and dated using 210Pb activities, laminations, and depth profiles of elements with a well-known history. Platinum concentrations were determined by quadrupole ICP-MS. While platinum concentration remained relatively low and steady from 1870 to 1975 (<5 ng g(-1)), the time of automobile catalyst introduction is followed by a sharp concentration increase, reaching a plateau in 1992 with 29.2 ng g(-1). Platinum deposition likewise remains low with 0.8 microg m(-2) yr(-1) before 1975, increases from 1975 to 1990, and then remains relatively constant throughout the 1990s with a deposition rate of 7.2 microg m(-2) yr(-1). The average size for Pt-containing particles was estimated to be 17 microm, corresponding to the deposition of approximately 14,000 particles m(-2) yr(-1).