Encl. (1) TO COMDTINST 16478.12
If there were a total of 100 entries in each of the data sets, then the PEL would define
the lower limit of a range of concentrations within which there would be, on average 50
entries from the BEDS and 15 entries from the NBEDS. This is predicted to be the case
because the PEL is calculated as the geometric mean of the 50(th) percentile of the effects
data set and the 85(th) percentile of the NBEDS. The geometric means is used to account
for uncertainty in the distributions of the data sets. The PEL Levels for mercury and lead
are 1.4 ppm and 160 ppm, respectively.
The range of concentrations that could, potentially be associated with biological effects
(i.e., possible effects range) is bounded on the lower end by the NOEL andon the upper end
by the PEL. Within the range, adverse biological effects are possible, however, it is
difficult to reliably predict the occurrence, nature, and/or severity of these effects.
Site-specific conditions are likely to control the expression of toxic effects at these
locations.
Strengths of Sediment Quality Assessment Guidelines
The WEA is supported by a comprehensive database on the biological effects of sediment-
associated contaminants. It provides a compelling rational for placing a high degree of
confidence on the resultant guidelines. By considering matching sediment chemistry and
biological effects data from studies conducted in the field, the influence of mixtures of
chemicals in sediments is incorporated from studies conducted in the resultant SQAGs. A
large number of data were conducted from studies conducted in the southeastern United
States (including Florida). Therefore, the resulting guidelines are probably most
appropriate for implementation in Florida.
In addition, the procedure considers both BEDS and NBEDS for each chemical constituent, and
does not rely heavily on individual data points. Thus, outliers do not carry much weight
in the overall guidelines derivation process.
Weaknesses of the Sediment Quality Assessment Guidelines
Many of the weaknesses of the NSTPA also plaque the WEA. For instance, it is not possible
to express the guidelines in terms of the factors that influence the bioavailability of
these contaminants. The reason is that there is little comprehensive information with
which to reliably predict the bioavailability of sediment-associated contaminants.
In addition, the method does not fully support the quantitative evaluation of cause and
effect relationships between contaminant concentrations and biological responses. A wide
variety of factors other than concentrations of the contaminant under consideration could
have influenced the actual response observed in any situation. Only limited data exists on
the chronic responses of marine and estuarine organisms to sediment-based contaminants.
This should be recognized as a limitation to the approach.
However, the results of the evaluation indicate the SQAGs developed using the approach
procedure outlined here are likely to be appropriate tools for conducting assessments of
sediment quality in Florida. However, care should be exercised in applying these
guidelines.
Summary
The chart below summarizes the National Status and Trends guidelines as
well as the SQAG guidelines:
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