This text compares and contrasts ecological risk assessment with human risk assessment. Topics discussed include: an introduction to environmental fate models and pharmacokinetic factors; documentation and critiques for the quantitative basis of uncertainty factors (UFs) in ecological risk assessment; a schema for deriving chemical-specific and species-specific maximum acceptable tissue concentration (MATs); a discussion about sediment quality criteria (SQC); and methods for deriving multi-comtaminant ecosystem MATs.