Biomagnification Factor

Compare paired predator/prey wet-weight and lipid-normalized concentration ratios; feeding ecology and steady state are not inferred.

Description

Compare paired predator and prey concentrations on wet-weight and lipid-normalized bases.

A biomagnification factor compares a chemical concentration in a predator with that in its prey. Lipid normalization changes the comparison from concentration per wet tissue mass to concentration per lipid mass, which can matter when lipid content differs.^[1]

This tool returns both ratios for each supplied predator–prey pair. Wet concentrations must use the same mass-per-wet-mass unit, and lipid fractions must be expressed from 0 to 1: 10% is 0.1.

The ratios are dimensionless. A value greater than one describes a higher predator concentration on the chosen basis, but the arithmetic alone does not establish trophic causation, steady state, or the suitability of lipid normalization for the chemical.

When to use Biomagnification Factor

Use it to compare matched predator and prey observations or show how different lipid fractions affect the interpretation of an observed wet-weight ratio.

How to use Biomagnification Factor and interpret its calculation

Enter aligned, nonempty predatorWetConcentrations and preyWetConcentrations lists. Predator values may be zero; prey values must be positive.
Enter aligned predatorLipidFractions and preyLipidFractions, each greater than zero and no greater than one.
Run the tool and read wetWeightRatios and lipidNormalizedRatios in pair order. Keep tissue, chemical, sampling, and matching information alongside the result.

wet ratio = Cpredator/Cprey; lipid ratio = (Cpredator/fpredator)/(Cprey/fprey) = wet ratio × fprey/fpredator

Both lipid fractions describe the same wet-mass basis as their paired concentration measurements.

The implementation calculates each wet ratio first, then rescales by the prey-to-predator lipid-fraction ratio. It does not normalize a whole food web or combine ratios across pairs.

json

{
  "input": {
    "predatorWetConcentrations": [
      2,
      4
    ],
    "preyWetConcentrations": [
      1,
      2
    ],
    "predatorLipidFractions": [
      0.2,
      0.2
    ],
    "preyLipidFractions": [
      0.1,
      0.1
    ]
  },
  "output": {
    "wetWeightRatios": [
      2,
      2
    ],
    "lipidNormalizedRatios": [
      1,
      1
    ]
  }
}

Equal predator and prey lipid fractions leave the ratio unchanged. Zero predator concentration returns zero for both ratios. Zero prey concentration or zero lipid fraction is rejected; nondetect handling must therefore be chosen separately.

Limitations and assumptions

The tool does not establish that a sampled organism is the relevant prey, account for multiple dietary sources, adjust for trophic-level distance, or validate lipid normalization.

No growth correction, temporal matching, measurement uncertainty, detection-limit model, or statistical test is performed. Ratios from different tissues or incompatible concentration units are not made comparable automatically.

Alternative or Complementary methods

Use a TMF regression for a trend across several trophic levels. For a water-exposure kinetic concentration factor, use uptake and elimination rates rather than a predator–prey concentration ratio.

References

Test No. 305: Bioaccumulation in Fish: Aqueous and Dietary Exposure (2012) — Organisation for Economic Co-operation and Development

Similar or alternative tools

Trophic Magnification Factor
Fit a normalized concentration trend across supplied trophic levels.
Bioconcentration Factor
Compute kinetic factors from uptake, elimination, and growth-dilution rates.