information on causes of biological impairment for the State 303d listing process. Analysis of 
existing State, REMAP, and EMAP monitoring databases ('www .epa.eov/einap/) and aquatic 
toxicity databases (AQUIRE, PHYTOTOX; www .epa.eov/ecQtox/ ) with associated exposure 
data will be coordinated across Divisions to derive diagnostic indicators to predict cause of 
impairment based on aquatic community composition. Examples of multivariate tools that can 
be applied to suggest causal hypotheses include nonmetric dimensional scaling (NMDS) 
ordinations to identify environmental gradients associated with gradients in community 
composition (Beals 1984), indicator analysis (Dufrene and Legendre 1997), discriminant function 
analysis relating environmental factors with species presence/absence (Scheller et al. 1998), and 
redundancy analysis to partition variance among multiple potential causal factors (Richards et al. 
1993). 
To address water column toxicity, EPA has developed TIE methods (Mount and Anderson- 
Camahan 1988, 1989; Burkhard and Ankley 1989; Mount 1989; Ankley et al. 1991; Norberg- 
King et al. 1991,1992; Durban et al. 1993; Mount and Norberg-King 1993; Burgess et al. 1996; 
Ho et al. 2002), which are a battery of physical/chemical manipulations coupled with toxicity 
tests. By determining which physical/chemical manipulation affect toxicity of the samples, the 
general characteristics of the causative chemical(s) can be determined. With this knowledge, 
appropriate analysis techniques and in some cases, in combination with additional sample 
fractionation techniques, are used to obtain a list of the tentative chemical(s) in the sample. With 
this information, toxicity tests using the suspected chemical(s) would be performed to establish 
the effect level for these chemicals in the water samples of interest and in reference waters using 
the TIE organisms. Successful TIEs occur when the concentrations of the suspected chemicals at 
the affect endpoint agree among the water samples and reference waters. 
For toxicity in sediments, substantial progress has been made to date for a number chemical 
classes and manipulations for whole sediments and sediment pore waters (Ankley and 
Schubauer-Berigan 1995, Besser et al. 1998, Ho et al. 1999, Leonard et al. 1999, Burgess et al. 
2000). With the successful development of solid-phase sediment TIE methods, field validation 
of interstitial water and whole sediment TIE methods is needed After development of the whole 
sediment and interstitial waters TIE methods, field validation of the methodologies are required 
to determine if the causes of toxicity identified by TIE represent the source of toxicity at the field 
site. Field validation will involve the TIE analysis of sediments with impaired benthic 
communities from both fresh and marine sites, and ideally, the causes of impairment for these 
sediments would not be some other stressor (e.g., suspended and bedded sediment or degraded 
habitat). Once a suspected toxicant is identified, field sediments and organisms would be 
analyzed. The final step in the validation process would be to reproduce the same community 
signature observed in the field, within laboratory-controlled situations by introducing the 
suspected toxicant into clean sediments in a mesocosm. The field validation effort will also 
allow the evaluation of benthic community signatures and toxicant relationships. If useful 
relationships can be developed, a library of chemical stressor-benthic community responses 
would be developed to complement relationships derived fi-om toxicity databases above, and this 
library would be developed on a water body class scale. Field validation will also permit the 
evaluation of toxicant/stressor and biological indices relationships for benthic communities. 
Specifically, a collaborative effort between MED and AED will seek to link cause and effect 
relationships observed in the laboratory to field effects using micro/mesocosm simulations. 
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