Indigenous populations of economically important bivalve molluscs were used as monitors for detecting and quantifying environmental PNAH, including 11 compounds classified as carcinogens, 11 EPA Priority Pollutants and 11 Toxic Pollutants. Baseline levels of PNAH were determined during a two-year period for mussels (Mytilus edulis), clams (Mytilus arenaria and T. capax) and oysters (C. gigas) from different sites, ranging from relatively pristine to moderately polluted, in Yaquina, Coos and Tillamook Bays, Oregon. Total concentrations of 15 unsubstituted PNAH were 30 to 60 micrograms/kg in shellfish from uncontaminated waters to greater than 1000 micrograms/kg in those from sites classified as contaminated. A major effort was made to determine and evaluate certain relationships between PNAH and their concentrations in shellfish. Studies were conducted to: determine the effects of depuration of PNAH concentrations; identify seasonal differences in PNAH concentrations; and measure BAP uptake and elimination. Preliminary studies indicated that mussels may possess a limited ability to metabolize BAP. Multiple regression and multiple correction techniques were used to identify and evaluate interrelationships between PNAH. Certain relationships may be useful for predictive purposes in evaluating environmental PNAH. The data from these studies indicate that it may be possible to identify and measure significant variables to assess total PNAH.