Sediment Suspension 
As noted above, sediment suspension is a natural and anthropogenic process that results in the 
release of contaminants into the water column. Research has demonstrated this geochemical 
phenomena (e.g., Latimer et al. 1999, Cantwell et al. in prep.) but little study has investigated the 
biological effects of sediment suspension and contaminant release on benthic oiganisms. This 
section of the project will perform studies to assess the magnitude of contaminant release and 
effects under realistic environmental scenarios. 
Initially, resuspension and benthic flux experiments will be performed under controlled 
(laboratory) conditions in order to determine the significance of specific variables in the 
remobilization of contaminants from sediments. In this phase, toxicity tests will be perfcxmed to 
measure adverse effects. Resusp^sion of contaminated field sediments will be performed at a 
number of energy levels and time scales which are representative of estuarine conditions, with 
continuous monitoring of chemical changes to the sediment and overlying water. Additional 
experiments will take place resuspending sediments and monitoring longer term (1-6 month) 
fluxes and chemical changes to the sediment. Once a better understanding of the variables 
influencing stressor availability is gained, field-based experiments will be conducted. 
Unusual Binding Phases 
Currently, ESGs for metals and organic chemicals are based on the concentrations of the binding 
phases A VS and organic carbon, respectively, in the benthos. In recent years, it has been 
speculated and observed that other binding phases may also influence the bioavailability of 
metals and organic chemicals. For example, organic carbon has been speculated to affect metal 
bioavailability beyond the influence of AVS (DiToro et al. 2002). Further, while the 
bioavailability of organic chemicals like pesticides and PCBs are well predicted using organic 
carbon (EPA 2000b, Burgess et al. 2000), the behavior of PAHs vary widely (Gustafsson and 
Gschwend 1997). Unusual binding phases like soot carbon have been proposed to explain these 
discrepancies (Gustafsson and Gschwend 1997). 
To address the significance of unusual binding phases, research will be conducted to assess the 
relative importance of these phases as compared to AVS and organic carbon as currently applied 
by Agency guidelines. The draft ESGs for both metals and PAHs contain adjustments for 
unusual binding phases but these adjustments are crude and based on limited scientific 
information (EPA 2000a,d). Consequently, research will be performed to expand and/or improve 
the current adjustments factors to ultimately reduce the variability in regulatory guidelines these 
unusual binding phases introduce when used in the field. 
Field Validation of Aquatic Guidelines 
It is prudent to field validate the existing aquatic guidelines as this provides a way to determine 
their effectiveness. One efficient way to do this is to use the guidelines along with our increased 
understanding of the effects of contaminants in dynamic and variable sediments to predict the 
toxicity of sediments collected in large data bases for which concurrent chemistry and toxicity 
data are available, such as the EMAP and NOAA Status and Trends data bases. Numerous 
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