Bioconcentration factor (BCF)

A BCF test exposes fish or similar animals to a steady concentration of the chemical in water until tissue levels level off, then divides the tissue concentration by the water concentration. The result is a plain ratio, so a BCF of many hundreds means the animal concentrates the chemical many hundreds of times above the water level.

BCF isolates uptake from water through gills and skin. It leaves out the food route, so it can understate real-world accumulation for substances that pass up the food chain. A related measure, the bioaccumulation factor, includes all exposure routes and usually reflects field conditions better.

Measured BCF values are preferred, but testing is costly, so estimates from LogKow are common. The supplier's SDS may therefore list a calculated value, a measured one, or a statement that no data are available. Regulations such as REACH use BCF thresholds to help decide if a substance is bioaccumulative, and the actual cutoffs are in the regulation rather than the SDS.

A BCF is useful for comparing substances, not for predicting exact levels in a lake. Different species, temperatures and fat content give different results, and the figure should be read with persistence and toxicity.