Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

more natural conditions with vertical stratification of oxygen concentrations and, hence, varying
levels of AVS. The authors concluded that important uncertainties remain in the application of
the AVS-SEM approach as a regulatory tool. Similarly, some studies suggest that AVS-SEM
measurements in the natural environment must be interpreted cautiously as AVS can be quite
variable with sediment depth and season (Van den Berg et al., 1998). Finally, Long et al. (1998)
critically compared the ability of AVS-SEM and dry weight-normalized concentrations to predict
toxicity of sediment-associated trace metals. Based on an analysis of 77 field-collected sediment
samples, Long et al. (1998) found that dry weight-normalized concentrations were equally or
slightly more accurate than AVS-SEM in predicting non-toxic and toxic results in laboratory
bioassays. Long et al. suggests that a limitation of the AVS-SEM approach is that the criteria
were not derived from field studies with mixture of toxic chemicals and thus may be less relevant
to sites comprising complex chemical mixtures. Thus, although the AVS-SEM approach for
developing sediment quality criteria is being pursued by the U.S. EPA, there is clearly not
scientific consensus on this approach, at least not for all circumstances.
Many alternative approaches for developing sediment quality guidelines are based on
empirical correlations between metal concentrations in sediment to associated biological effects,
based on sediment toxicity tests (Long et al., 1995; Ingersoll et al., 1996; MacDonald et al.,
2000). However, these guidelines are based on total metal concentrations in sediment and do not
account for the bioavailability of metals between sediments. Sediment quality guidelines
proposed for Pb from these other sources are shown in Table AX7-2.1.3.
Table AX7-2.1.3. Recommended Sediment Quality Guidelines for Lead
Source Water Type Guideline Type Conc. (mg/kg dw)
MacDonald et al. (2000) Freshwater TEC
PEC
Ingersoll et al. (1996) Freshwater ERL
ERM
Long et al. (1995) Saltwater ERL
ERM
AX7-115
35.8
128
55
99
TEC = Threshold effect concentration; PEC = Probable effect concentration; ERL = Effects range – low;
ERM = Effects range – median
46.7
218