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6 Risk Assessment and Management of Chemical Products
Internal exposure of aquatic organisms to a chemical can be quantified by comparing their internal concentrations to the surrounding environmental concentrations
as well as to the concentration of the chemical in their food. The bioconcentration
factor (BCF) is defined as the ratio of the concentration of a chemical in the organism and the chemical’s concentration in the surrounding water under the condition
that uptake occurs via the gills only, but not via food. This is a setting that can only
be realized in laboratory test systems; in the real environment, uptake always occurs
via gill respiration and food ingestion in combination. Next, the biomagnification
factor (BMF) is defined as the ratio of the chemical’s concentration in the organism
and in the food consumed by the organism. It describes a chemical’s ability to be
taken up via the food chain in such a way that concentrations in higher trophic levels
increase (biomagnification). Finally, the bioaccumulation factor (BAF) is defined
as the ratio of the concentration of chemical in the organism and the chemical’s
concentration in the surrounding water, but in this case—in contrast to the BCF—
with uptake of the chemical by both gill respiration and food ingestion. The BAF,
therefore, considers all exposure routes and multiple physiological processes to
describe the net resulting uptake and accumulation of a chemical in an organism. All
three factors are further defined in Appendix B.1 and also discussed in the literature
(Arnot et al., 2010) and testing standards (OECD, 2012).
6.4.2.2 Regional Exposure (Area-Related Emission Sources)
To estimate exposure on the regional or continental level, the scope of the calculations needs to be greatly expanded. After entering the environment, natural processes of transport, transformation, and accumulation affect the fate of a substance
(see Appendices B.1 and B.2 as well as Schwarzenbach et al., 2016). Estimating
exposure at this level needs to consider emission characteristics, physicochemical
properties of the chemical, and environmental conditions. These considerations can
be grouped as questions for analysis into the following dimensions:
• Compartment: Does the substance remain in the environmental compartment
into which it was emitted? Or does a significant portion move to another
compartment?
• Space: Does the substance remain in the region where it was emitted? Or is a
significant portion transported to other regions?
• Time: Is the substance significantly removed in one of the environmental
compartments by physical, chemical, or biological processes, making it no longer
available for natural cycles and biota? Or is it likely to remain environmentally
relevant because of its persistence or its transformation products?
• Accumulation: Is the substance significantly enriched in an environmental
compartment or in a food chain?
To help answer these questions, multimedia mass-balance models are used that
describe and estimate the environmental behavior of products and the resulting
6 Risk Assessment and Management of Chemical Products
Internal exposure of aquatic organisms to a chemical can be quantified by comparing their internal concentrations to the surrounding environmental concentrations
as well as to the concentration of the chemical in their food. The bioconcentration
factor (BCF) is defined as the ratio of the concentration of a chemical in the organism and the chemical’s concentration in the surrounding water under the condition
that uptake occurs via the gills only, but not via food. This is a setting that can only
be realized in laboratory test systems; in the real environment, uptake always occurs
via gill respiration and food ingestion in combination. Next, the biomagnification
factor (BMF) is defined as the ratio of the chemical’s concentration in the organism
and in the food consumed by the organism. It describes a chemical’s ability to be
taken up via the food chain in such a way that concentrations in higher trophic levels
increase (biomagnification). Finally, the bioaccumulation factor (BAF) is defined
as the ratio of the concentration of chemical in the organism and the chemical’s
concentration in the surrounding water, but in this case—in contrast to the BCF—
with uptake of the chemical by both gill respiration and food ingestion. The BAF,
therefore, considers all exposure routes and multiple physiological processes to
describe the net resulting uptake and accumulation of a chemical in an organism. All
three factors are further defined in Appendix B.1 and also discussed in the literature
(Arnot et al., 2010) and testing standards (OECD, 2012).
6.4.2.2 Regional Exposure (Area-Related Emission Sources)
To estimate exposure on the regional or continental level, the scope of the calculations needs to be greatly expanded. After entering the environment, natural processes of transport, transformation, and accumulation affect the fate of a substance
(see Appendices B.1 and B.2 as well as Schwarzenbach et al., 2016). Estimating
exposure at this level needs to consider emission characteristics, physicochemical
properties of the chemical, and environmental conditions. These considerations can
be grouped as questions for analysis into the following dimensions:
• Compartment: Does the substance remain in the environmental compartment
into which it was emitted? Or does a significant portion move to another
compartment?
• Space: Does the substance remain in the region where it was emitted? Or is a
significant portion transported to other regions?
• Time: Is the substance significantly removed in one of the environmental
compartments by physical, chemical, or biological processes, making it no longer
available for natural cycles and biota? Or is it likely to remain environmentally
relevant because of its persistence or its transformation products?
• Accumulation: Is the substance significantly enriched in an environmental
compartment or in a food chain?
To help answer these questions, multimedia mass-balance models are used that
describe and estimate the environmental behavior of products and the resulting