Using this approach, the US EPA (1997a) developed SQGs that
are intended to represent chronic toxicity thresholds for various
sediment-associated contaminants, primarily nonionic organic
substances. The concentrations of these contaminants are considered
to be sufficient to cause or substantially contribute to
sediment toxicity when they exceed the EqP-based SQGs (Berry
et al. 1996). To evaluate the extent to which the consensusbased
SQGs are causally based, the PECs were compared to the
chronic toxicity thresholds that have been developed previously
using the EqP approach (see Table 2). The results of this
evaluation indicate that the consensus-based PECs are generally
comparable to the EqP-based SQGs (i.e., within a factor of
three; MacDonald et al. 1996; Smith et al. 1996). Therefore,
the consensus-based PECs also define concentrations of sediment-associated
contaminants that are sufficient to cause or
substantially contribute to sediment toxicity.