Abstract. Numerical sediment quality guidelines (SQGs) for
freshwater ecosystems have previously been developed using a
variety of approaches. Each approach has certain advantages
and limitations which influence their application in the sediment
quality assessment process. In an effort to focus on the
agreement among these various published SQGs, consensusbased
SQGs were developed for 28 chemicals of concern in
freshwater sediments (i.e., metals, polycyclic aromatic hydrocarbons,
polychlorinated biphenyls, and pesticides). For each
contaminant of concern, two SQGs were developed from the
published SQGs, including a threshold effect concentration
(TEC) and a probable effect concentration (PEC). The resultant
SQGs for each chemical were evaluated for reliability using
matching sediment chemistry and toxicity data from field studies
conducted throughout the United States. The results of this
evaluation indicated that most of the TECs (i.e., 21 of 28)
provide an accurate basis for predicting the absence of sediment
toxicity. Similarly, most of the PECs (i.e., 16 of 28)
provide an accurate basis for predicting sediment toxicity.
Mean PEC quotients were calculated to evaluate the combined
effects of multiple contaminants in sediment. Results of the
evaluation indicate that the incidence of toxicity is highly
correlated to the mean PEC quotient (R2 5 0.98 for 347
samples). It was concluded that the consensus-based SQGs
provide a reliable basis for assessing sediment quality conditions
in freshwater ecosystems.