The Coastal Resource Coordinator's Bioassessment Manual

HAZMAT 93-1–Bioaccumulation
CHAPTER 4
BIOACCUMULATION
INTRODUCTION
Bioaccumulation is the net result when the uptake of a chemical by a biological organism
exceeds the depuration of the chemical from the organism. Uptake may occur directly from
the air, water, soil, or sediment via absorption or indirectly through the ingestion of food
containing the chemical. Bioconcentration is the process by which a chemical is directly
taken up (by absorption only) from water and is accumulated to levels greater than those
found in the surrounding water. Biomagnification is the increase in tissue concentrations
of a bioaccumulated chemical as the chemical passes up through two or more trophic levels.
A chemical is usually considered capable of being biomagnified if concentrations of the
chemical increase by more than an order of magnitude at each step up the food chain.
DDTs, polychlorinated biphenyls (PCBs) and mercury are among the few chemicals for
which there is evidence of biomagnification.
Bioaccumulation studies take many forms. They may simply involve the measurement
of tissue residues in indigenous organisms, or they may involve the measurement of tissue
residues in test organisms exposed to contaminated environmental media (water or
sediment) for a specific length of time. This exposure may be accomplished either by
transplanting the test organisms to a contaminated area or by exposing them in a laboratory.
The results of these types of studies are generally reported as the concentration of the
chemical per unit weight of the organism (body burden) or some component of the
organism.
Another type of bioaccumulation study uses artificial organisms (e.g., lipid bags). These
artificial organisms are exposed to contaminated water or sediments for a specific length of
time and then the concentration of the chemical(s) of concern in the lipid are measured.
Since artificial organisms only take up chemicals through absorption, they only measure the
potential for bioconcentration of the chemical(s). In studies with artificial or real organisms
when the only route of uptake is through absorption (not through ingestion) the results are
often reported as a unitless bioconcentration factor (BCF). The BCF relates the
concentration of a chemical in an organism (real or artificial) or component of an organism
to the average concentration found in the surrounding water.
4-1 November 1992