Breaking from tradition: establishing more realistic sediment quality guidelines.

Sediment quality guidelines vary wildly across nations. The approaches to derive these guidelines range from crude percentile rankings of total concentrations of single chemicals to theoretical approaches that are driven by biological available effect levels. This results in a range of orders of magnitude for "safe" or threshold levels by chemical. Even the more scientifically advanced approaches using theoretical approaches are problematic in that they do not consider chemical mixtures, alternate routes of exposure, and other ligands that limit bioavailability. In the end, all that matters is that desirable resident biota are protected and with no significant ecological impacts. Complicating this determination is the role of habitat, flow, sedimentation, and nutrients-all of which are common in human-dominated waterways. A possible effective way forward is to consider the common, relevant stressors that may influence biotic communities associated with sediments. This approach would consider relevant sensitive species in terms of their ecological context and dominant exposure pathway (considering habitat, overlying water, sediment, periphyton, and hyporheos). In addition, the sum of water column (and pore water) and sediment probable effect concentration vs probable no effect concentrations ratios would be summed and considered for mixtures. Since this non-scientific mixture effect assessment may be overly conservative, in situ caged toxicity tests with benthic and water column organisms exposed to sediments, pore waters, and overlying water would be conducted for field validations along with comparisons of indigenous biota to BioCriteria.