Interpreting Bioaccumulation Data
Evaluating the environmental consequences of contaminant bioaccumulation is
a complex technical and regulatory problem (Bridges et al. 1996).
In part, this complexity results from the fact that bioaccumulation is a
measurable phenomenon, rather than an effect. Merely identifying the presence of
a chemical substance in the tissues of an organism, for example, following a
bioaccumulation test, is not sufficient information to conclude that the
chemical will produce an adverse
effect. All chemical substances have the potential to produce adverse effects
(i.e., toxicity), including such diverse compounds as aspirin, zinc, and dioxin.
The likelihood that a chemical substance in the tissues of an organism will
produce an adverse effect is a function of the physical and chemical properties
of the substance, the concentration of the chemical in the tissues of the
organism, and the length of time the organism is exposed to the compound.
Because environmental contaminants vary so widely in their potential to produce
toxicity, contaminant-specific information must be used to reach a determination
regarding the potential for a bioaccumulated substance to produce adverse
effects.
Interpreting Bioaccumulation Data in the Dredging Program
Making regulatory decisions regarding what level of bioaccumulation is or is
not acceptable must be based on data that link a given concentration of
substance "X" with measurable biological effects, e.g., reduced survival,
growth, or reproduction. This requirement is emphasized in Section 2.3.3 of the
Ocean Testing Manual (USEPA/USACE 1991),
which states that
"To use bioaccumulation in a decision, it is necessary to predict whether
there will be a cause-and-effect relationship between the animal's presence in
dredged material and a meaningful adverse elevation of body burden...."
Bioaccumulation data are evaluated at two levels of interpretation according
to current dredged material evaluation guidance. At the first level, the amount
of bioaccumulation of a specific contaminant in dredged material-exposed
organisms is compared to a numerical effect limit, such as a Food and Drug
Administration action level or a fish advisory. If the concentration of a
contaminant in a dredged material-exposed organism exceeds a numerical limit,
there is the potential for the dredged material disposal to have an
"unacceptable adverse effect." If it does not, or there is no numerical limit, a
second level of evaluation is undertaken which involves a statistical comparison
to data collected from animals exposed to a reference sediment. If
bioaccumulation in the animals exposed to the dredged material is statistically
greater than that of animals exposed to the reference sediment, then a number of
evaluatory factors are considered to determine whether or not dredged material
disposal will result in an "unacceptable adverse effect"; this includes
consideration of the magnitude of bioaccumulation and the toxicological
significance of the bioaccumulated contaminants (USEPA/USACE 1991,
1994). The utility of current bioaccumulation interpretive guidance is
constrained by two important limitations: 1) the small number of published
numerical limits available for use in the first level of interpretation compared
to the large number of contaminants commonly present in freshwater and marine
sediments and 2) the uncertainties involved in applying the largely
qualitative/subjective evaluatory factors in the second level of interpretation.
The USACE/USEPA Environmental Residue-Effects Database (ERED) was developed
to reduce the level of uncertainty associated with interpreting bioaccumulation
data for the purpose of making regulatory decisions regarding dredged material.
Use of the ERED will improve the decision-making process by providing the basis
for making quantitative determinations regarding the likelihood for
effects.
