Bioconcentration Factor (BCF) Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 10/10/2026
The bioconcentration factor (BCF) is calculated with concentration in the organism (mg/kg) ÷ concentration in water (mg/L), at equilibrium. A concentration of 600 mg/kg for 0.1 mg/L gives a BCF of 6000 L/kg, considered very bioaccumulative under European regulatory thresholds (REACH).
Explanation
The bioconcentration factor (BCF) measures the tendency of a chemical substance present in water to accumulate in the tissues of an aquatic organism (fish, mollusk) exposed only through the water, at the equilibrium between uptake and elimination of the substance. A high BCF means the substance accumulates strongly in the organism relative to its concentration in the surrounding water, a concerning phenomenon for persistent toxic substances, which can then concentrate throughout the food chain — a risk that is even more serious for an ecosystem already low in species, see our Shannon diversity index calculator to assess that diversity. EU REACH regulation uses this factor to classify chemical substances: a BCF above 2000 L/kg qualifies a substance as "bioaccumulative," and a BCF above 5000 L/kg as "very bioaccumulative," two thresholds that trigger stricter regulatory obligations for manufacturers and importers of these substances. BCF differs from two related concepts: the bioaccumulation factor (BAF), which additionally includes exposure through diet (not just surrounding water, making it generally a more realistic estimate for real ecosystems), and the biomagnification factor (BMF), which compares a predator's concentration to its prey's along the food chain rather than an organism to its direct aquatic environment. This calculator covers only the BCF, the simplest of the three and the most commonly measured in the lab under controlled conditions. In fish, accumulation can also affect reproduction: see our gonadosomatic index calculator for an indicator of reproductive investment.
Example: a very bioaccumulative substance
Inputs
Concentration in the organism: 600 mg/kg. Concentration in water: 0.1 mg/L.
Calculation
BCF = 600 ÷ 0.1 = 6000 L/kg, above the 5000 L/kg threshold used by REACH regulation to classify a substance as very bioaccumulative.
Result
This substance is classified as very bioaccumulative under EU regulatory thresholds.
Frequently asked questions
Why is BCF expressed in L/kg?
Because it results from dividing a concentration in mg per kg of tissue (mg/kg) by a concentration in mg per liter of water (mg/L): the mg cancel out in the calculation, leaving a kg⁻¹ × L ratio, i.e. L/kg. This unit, while it may seem abstract at first, simply reflects how many liters of water would contain the same mass of substance as is actually concentrated in one kilogram of the organism's tissue.
What's the difference between BCF and BAF?
BCF (bioconcentration factor) only considers exposure through surrounding water, typically measured in the lab under controlled conditions. BAF (bioaccumulation factor) additionally includes exposure through diet (prey consumed by the organism), generally making it a more representative estimate of what actually happens in a natural ecosystem, where exposure is never limited to water alone.
Why do the 2000 and 5000 L/kg thresholds matter?
Because they correspond to the official criteria used by EU REACH chemical regulation to classify a substance as bioaccumulative or very bioaccumulative, two classifications that trigger stricter regulatory requirements (more extensive risk assessments, possible use restrictions) for manufacturers and importers of the substance concerned.