In aquatic toxicology, bioconcentration is the accumulation of a water-borne chemical substance in an organism exposed to the water.
The BCF is a measure of the extent of chemical sharing between an organism and the surrounding environment.
[6] BCF can simply be an observed ratio, or it can be the prediction of a partitioning model.
[6] A partitioning model is based on assumptions that chemicals partition between water and aquatic organisms as well as the idea that chemical equilibrium exists between the organisms and the aquatic environment in which it is found[6] Bioconcentration can be described by a bioconcentration factor (BCF), which is the ratio of the chemical concentration in an organism or biota to the concentration in water:[2]
[2] Bioconcentration factors can also be related to the octanol-water partition coefficient, Kow.
The octanol-water partition coefficient (Kow) is correlated with the potential for a chemical to bioaccumulate in organisms; the BCF can be predicted from log Kow, via computer programs based on structure activity relationship (SAR)[7] or through the linear equation:
[6] where ZFish is equal to the Fugacity capacity of a chemical in the fish, PFish is equal to the density of the fish (mass/length3), BCF is the partition coefficient between the fish and the water (length3/mass) and H is equal to the Henry's law constant (Length2/Time2)[6] Through the use of the PBT Profiler and using criteria set forth by the United States Environmental Protection Agency under the Toxic Substances Control Act (TSCA), a substance is considered to be not bioaccumulative if it has a BCF less than 1000, bioaccumulative if it has a BCF from 1000 to 5000[10] and very bioaccumulative if it has a BCF greater than 5,000.
[11] A bioconcentration factor greater than 1 is indicative of a hydrophobic or lipophilic chemical.
[1] Based on an assumed steady state scenario, the fate of a chemical in a system is modeled giving predicted endpoint phases and concentrations.
For a substance with a log(KOW) of 4, it thus takes approximately five days to reach effective steady state.
Fugacity is another predictive criterion for equilibrium among phases that has units of pressure.
[1] BCF can be determined from output parameters of a fugacity model and thus used to predict the fraction of chemical immediately interacting with and possibly having an effect on an organism.
[1] This is especially pertinent for conservative chemicals that are not easily metabolized into degradation products.
Biomagnification of conservative chemicals such as toxic metals can be harmful to apex predators like orca whales, osprey, and bald eagles.
[citation needed] Bioconcentration factors facilitate predicting contamination levels in an organism based on chemical concentration in surrounding water.
Fish, for example uptake chemicals via ingestion and osmotic gradients in gill lamellae.
In determining the degree at which bioconcentration occurs biological factors have to be kept in mind.
[15] k1 is the rate constant for chemical uptake from water at the respiratory surface (L*kg−1*d−1).
Because organisms are modeled as bags of fat, lipid to water ratio is a factor that needs to be considered.
[6] Size also plays a role as the surface to volume ratio influence the rate of uptake from the surrounding water.
[15] If a contaminant is ionic, the change in pH that is influenced by a change in temperature may also influence the bioavailability[1] The natural particle content as well as organic carbon content in water can affect the bioavailability.
The contaminant can bind to the particles in the water, making uptake more difficult, as well as become ingested by the organism.