Bioconcentration Factor & Environmental Fate
Estimate a fish bioconcentration factor (BCF) from the octanol-water partition coefficient, classify the bioaccumulation potential, and screen against the REACH bioaccumulative (B) and very bioaccumulative (vB) thresholds that feed PBT assessment and waste decisions.
How to use this tool
Estimate how strongly a substance builds up in fish from how fat-loving it is. Use it as a first screen for whether a chemical is likely to bioaccumulate and trip REACH PBT criteria.
What to enter
- log P (log Kow): the octanol-water partition coefficient, a measure of how much a substance prefers fat over water. Higher means more fat-loving. Typical organics run about 1–6; a value of 3.5 is moderately hydrophobic. No value handy? Estimate one with the linked log P tool.
Reading the result
The headline is the estimated BCF in L/kg, roughly how many times more concentrated the substance gets in fish than in the surrounding water. It is then labelled low / moderate / bioaccumulative (B, > 2000) / very bioaccumulative (vB, > 5000), with a REACH Annex XIII flag. Treat it as an indicative screen, not a regulatory conclusion.
Worked example
A log Kow of 3.5 gives an estimated BCF of about 232 L/kg, "moderate", below the REACH B threshold.
Input
vB (very bioaccumulative): BCF > 5000
Result
BCF is roughly how many times more concentrated the substance becomes in fish than in the surrounding water. Above 2000 L/kg trips the REACH "B" flag, above 5000 "vB", but this is a log Kow screen only; a regulatory call needs a measured BCF (OECD 305) or a validated model.
Methodology
BCF is estimated from log Kow with the Veith/Mackay regression: log BCF = 0.79 × log Kow − 0.40, so BCF = 10log BCF. The result is classified as low (BCF < 100), moderate (100–2000), bioaccumulative (B, > 2000) or very bioaccumulative (vB, > 5000) per the REACH Annex XIII criteria.
Known limits
- The regression is reliable roughly for 1 ≤ log Kow ≤ 6. Superhydrophobic compounds (log Kow > ~6) show lower measured BCF than the line predicts because of reduced membrane permeation and metabolism, so high values are flagged as out-of-range.
- It ignores biotransformation, ionisation, and growth dilution. A regulatory B/vB conclusion needs a measured BCF (OECD 305) or a validated model.
- BCF is bioconcentration (water-only uptake), not BAF/BMF (dietary and trophic transfer).