also plays an important role in chemical concentrations, and this factor is ignored in calculating the ERL and ERM. When using these values for screening contaminated sediment, it is likely that the ERL will be exceeded more often when the sediment contains a larger proportion of fine-grained material. This is due to the inverse relationship between chemical concentration and particle size. Due to sediment concentrations being measured on a dry weight basis, other geochemical factors of sediment that may also influence contaminant bioavailibility are not considered. Another consideration is that effects to wildlife and humans from bioaccumulation are not considered in ERL and ERM measurements. Furthermore, Vidal and Bay noted that the use of ERMs when DDT is present resulted in a less accurate predictive level. The authors suggested that this provides evidence that other methods could prove more protective in cases where mixtures of organics are present. References Concentration indicators Toxicology