Superfund Research Program
Toxicity and Mobilization of PAHs and Chromium in Soils and Sediments (ARRA Funded)
Project Leader: Dominic M. Di Toro (University of Delaware)
Grant Number: P42ES010344
Funding Period: 2009-2011
Project Summary (2009-2011)
The two overall goals of this project are:
- To develop methods to predict the chronic eco-toxicity of single and mixtures of PAHs in the water column, sediments and soils; and
- To build an integrated framework to quantify both the exposure and toxicity of chromium in sediments.
For PAHs, Dr. Di Toro will extend a previously developed model - the target lipid model (TLM) for predicting the acute aquatic toxicity of single and PAH mixtures in water column and sediment exposures - a method that is now in use by the US EPA - to predict the onset of sub-lethal effects from chronic exposures. The currently available method relies on an acute to chronic ratio that has a large uncertainty and no mechanistic basis. In addition Dr. Di Toro's research group will expand the model to include a wider class of more polar compounds that are also found at Superfund sites. Initially exposures to water column organism will be examined, followed by sediment, and finally soil dwelling organisms. There is at present no mechanistic model for establishing soil PAH Superfund guidelines. The prediction of toxicity of the divalent metal cations (Cd, Cu, Ni, Pb, Zn) to sediment dwelling organisms is now possible using the SEM-AVS method that was developed with support from previous SBRP projects. This method is also currently being used by US EPA to set sediment quality benchmarks.
The second overall goal is to extend this method to chrome (Cr). The complication is that, unlike the aforementioned metals, Cr exists in two oxidation states: Cr(lll) and Cr(VI), with widely different chemistries. It is known that in the presence of acid volatile suphide (AVS), Cr(VI) is reduced to Cr(lll) which is very insoluble and not toxic in the normal pH ranges found in sediment. However, Cr(VI), which can exist in the aerobic zone of sediments, is quite soluble and toxic. The second goal is to build a model that can predict the extent to which Cr(lll) is transformed to Cr(VI) in sediments so as to predict its toxicity. There is at present no mechanistic model for establishing Cr sediment criteria for Superfund sites.
Scientifically sound criteria that are protective of human and ecosystem health are a critical component of sound risk based management of Superfund sites. Our project proposes to continue our development of such criteria for PAHs and chrome. These criteria will be of immediate use to Superfund regulators that are charged with making cleanup and other decisions that directly affect the level of risk.