CONTAMINANT MEASUREMENTS ON SOIL CORES AND LACUSTRINE SEDIMENT CORES AS A METHOD FOR DETERMINING LONG-TERM AVERAGE FLUX OF CONTAMINANTS FROM ROAD RUNOFF

Road runoff is a significant source of pollution, and the number of vehicles on roads steadily rises. Current methods for determining the flux of road runoff contaminants rely on short-term estimation methods such as the collection of road-wash samples during storm events or flow weighted composite samples. It is extremely difficult with these methods to obtain accurate estimates of average annual fluxes due to the highly variable nature of the fluxes on short time scales. We propose that the analysis of sediment cores from lakes receiving large amounts of road runoff should provide a better estimation of long-term average road runoff fluxes for particle-reactive contaminants.

Here we present radionuclide, XRF, and ICP-MS data based on seven soil cores and eleven lacustrine sediment cores collected from Van Cortlandt Park, located in the northern part of New York City. The park lake has been receiving direct runoff from three major highways for several decades. Sediment cores were dated using Cs-137 and Pb-210. Radionuclide inventories of the cores compared to the expected atmospheric fallout indicate focusing factors between 0.4 and 2.1 for the different coring sites. Soil cores from the surrounding area are used to account for the integrated atmospheric deposition of contaminants over the last several decades. The locations of the sediment cores provide adequate spatial coverage of Van Cortlandt Park Lake, with evidence of varying deposition rates and degrees of sediment mixing.

We have found that contaminant trace-metals in the lake sediment can be primarily attributed to highway runoff: 1) temporal trends of Pb in the sediments are consistent with the use of leaded gasoline in the US; 2) temporal trends of Zn and Cd are consistent with traffic increase over the last few decades and relatively recent removal of Cd from US manufactured tires; 3) the average radionuclide-normalized contaminant Pb inventory for the lake cores is more than 3 times the average for the soil cores (20 g/m^2). After obtaining historical traffic data and the surface area of the highways that drain into the lake, we should then be able to estimate annual fluxes of Pb and other metals (including platinum group elements associated with catalytic converter use) coming from the highways for the last several decades.