Bioconcentration

Bioconcentration is the accumulation of a substance in an aquatic organism through direct uptake from the surrounding water. Unlike the concept of bioaccumulation of the recording path is disregarded in the diet. The bioconcentration and the derived bioconcentration factor (BCF ) are important test parameters in ecotoxicology. The inclusion in the body of a fish or other aquatic organism is via the gills or other permeable body surfaces that are highly permeable especially in soft-bodied organisms for many lipophilic substances.

The term bioconcentration is used for both the dynamic process of the gradual concentration of the substance in the organism, as well as for the characterization of the respective instantaneous or the end state ( equilibrium state ). If the concentration in the water back, the bioconcentration reduced in the organism usually according to a first stronger and weaker later running exponential curve. Depending on the lipid solubility of the compound and size of the organism, the decrease but will run at different speeds and sometimes only partially. Depending on the lipid solubility of a compound, it may take a longer time to reach the Gleichgewichszustandes. The time required can be estimated using the following equation.

(hours)

Consequently, it takes on a connection with an octanol - water partition coefficient ( KOW ) of 4 around five days to achieve the equilibrium state, at a KOW of 6, however, as early as nine months.

Bioconcentration factor ( BCF)

The bioconcentration compared to the water can be characterized as bioconcentration. This is a dimensionless number that represents the ratio of the concentrations in the organism as compared to water. The kinetics of uptake or decrease speed of bioconcentration and thus also of the BCF corresponds to the kinetics of the one-, two-or multi - compartment models.

In ecological fish tests the BCF is defined as the ratio between the concentration of the test substance in the test fish ( cf) to the concentration in the test water ( cw):

,

Where the value is measured under equilibrium conditions, ie, when the corresponding uptake rate by diffusion across body surfaces equal to the rate of elimination ( excretion, outward diffusion or degradation).

The BCF of a substance can be calculated except in animal experiments also approximately from the KOW value.

Compounds with a BCF of> 2000 l / kg and > 5000 l / kg in aquatic species meet the criteria for PBT part or vPvB substances under REACH.

Bioconcentration compared to bioaccumulation and biomagnification

In studies with aquatic organisms, the bioconcentration is often regarded as only one of two possible seen recording and accumulation paths that contribute to the overall bioaccumulation, because in addition to the direct uptake from the water is the dietary intake mitzuberücksichtigen ( biomagnification ). This conceptual division is, however, often difficult to detect in practice, because the different routes of exposure often run simultaneously in the body and bioaccumulation is in a complex dynamic equilibrium between this recording and the various forms of elimination ( degradation or excretion of the substance from the body). In addition, especially for small soft-bodied aquatic organisms (as they are often used for testing purposes ) and lipophilic substances the bioconcentration of faster and thus more significant uptake mechanism compared to biomagnify.