probably correct. However, in the field, where these guidelines are applied for regulatory 
applications, equilibrium conditions may not always be present. Examples of non-equilibrium 
conditions include seasonal changes in the benthic environment resulting in changes in A VS 
levels (Leonard et al. 1993), storm events and dredging operations under which sediments 
become suspended into the water column (Karickhoff and Morris 1985a,b, Calvo et al. 1991, 
Simpson et al. 1998, Latimer et al. 1999, Bonnet et al. 2000), and the presence of unusual 
binding phases in the water column and benthos (e.g., soot carbon) (Gustafsson and Gschwend, 
1997). The occurrence of conditions resulting in non-equilibrium may alter how well guidelines 
function and cause under-protective situations as well as introducing unacceptable uncertainty. 
Non-equilibrium, along with the importance of dietary uptake, is one of the greatest remaining 
sources of uncertainty in the development of criteria for non-bioaccumulative compounds. 
The over-all objective of this project is to perform research allowing the Agency to better 
understand the importance of non-equilibrium conditions and have greater confidence in the use 
of aquatic guidelines under field conditions. The research will focus on three predominant areas 
which may result in non-equilibrium: seasonality, sediment suspension, and unusual binding 
phases. Seasonality affects nearly every environmental setting and therefore its impacts on the 
effectiveness of aquatic guidelines must be understood. Sediment suspension occurs under a 
variety of environmental situations ranging from storms to dredging, and signifies a potential 
source of toxic chemicals to most coastal systems. Unusual binding phases are a recently 
recognized source of variability to the application of aquatic guidelines but nonetheless may 
represent a significant source of error to existing regulatory values. Another critical component 
of this research will be to complete an evaluation of how well current guidelines predict adverse 
effects in field sediments. This information will be very useful in designing studies to assess the 
effects of non-equilibrium conditions on guidelines development and application. Although this 
work focuses on non-equilibrium in the sediment, the issues explored also have consequences for 
the water column, via the sediment-water interface, and for other sources of heterogeneity in the 
sediment as well. 
Scientific Approach 
Seasonality 
Seasonality is especially important in relation to metals in sediment. Currently there are no 
published EPA guidelines for metals in sediment, but ESGs for metals are under development. 
These guidelines use A VS and interstitial water to predict biological effects. These methods 
have been demonstrated to be very useful in predicting biological effects in laboratory 
experiments and in a limited number of field experiments. The current draft guidelines do not 
explicitly consider the effects of seasonality on AVS and metal bioavailability. However, it is 
known that AVS varies with season and depth as a function of seasonality (Leonard et al. 1993); 
therefore, it is possible that metal bioavailability will correspondingly vary. If metal 
bioavailability varies significantly over an annual cycle, decisions based on the comparison of 
sediment guidelines with measured chemistry taken at one time of year may not be appropriate 
for other times of the year. Research in this section will seek to quantify the magnitude of 
fluctuation of metal bioavailability as a function of season. 
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