A bioassessment approach for mid-continent great rivers: the Upper Mississippi, Missouri, and Ohio (USA).

The objectives of the Environmental Monitoring and Assessment Program for Great River Ecosystems (EMAP-GRE) are to (1) develop and demonstrate, in collaboration with states, an assessment program yielding spatially unbiased estimates of the condition of mid-continent great rivers; (2) evaluate environmental indicators for assessing great rivers; and (3) assess the current condition of selected great river resources. The purpose of this paper is to describe EMAP-GRE using examples based on data collected in 2004-2006 with emphasis on an approach to determining reference conditions. EMAP-GRE includes the Upper Mississippi River, the Missouri River, and the Ohio River. Indicators include biotic assemblages (fish, macroinvertebrates, plankton, algae), water chemistry, and aquatic and riparian physical habitat. Reference strata (river reaches for which a single reference expectation is appropriate) were determined by ordination of the fish assemblage and examination of spatial variation in environmental variables. Least disturbed condition of fish assemblages for reference strata was determined by empirical modeling in which we related fish assemblage metrics to a multimetric stressor gradient. We inferred least disturbed condition from the y-intercept, the predicted condition when stress was least. Thresholds for dividing the resource into management-relevant condition classes for biotic indicators were derived using predicted least disturbed condition to set the upper bound on the least disturbed condition class. Also discussed are the outputs of EMAP-GRE, including the assessment document, multimetric indices of condition, and unbiased data supporting state and tribal Clean Water Act reporting, adaptive management, and river restoration.

A physiologically based toxicokinetic model for dermal absorption of organic chemicals by fish.

A physiologically based toxicokinetic model was developed to describe dermal absorption of waterborne organic chemicals by fish. The skin was modeled as a discrete compartment into which compounds diffuse as a function of chemical permeability and the concentration gradient. The model includes a countercurrent description of chemical flux at fish gills and was used to simulate dermal-only exposures, during which the gills act as a route of elimination. The model was evaluated by exposing adult rainbow trout and channel catfish to hexachloroethane (HCE), pentachloroethane (PCE), and 1,1,2,2-tetrachloroethane (TCE). Skin permeability coefficients were obtained by fitting model simulations to measured arterial blood data. Permeability coefficients increased with the number of chlorine substituent groups, but not in the manner expected from a directly proportional relationship between dermal permeability and skin:water chemical partitioning. An evaluation of rate limitations on dermal flux in both trout and catfish suggested that chemical absorption was limited more by diffusion across the skin than by blood flow to the skin. Modeling results from a hypothetical combined dermal and branchial exposure indicate that dermal uptake could contribute from 1.6% (TCE) to 3.5% (HCE) of initial uptake in trout. Dermal uptake rates in catfish are even higher than those in trout and could contribute from 7.1% (TCE) to 8.3% (PCE) of initial uptake in a combined exposure.