Earthworm Soil Avoidance Bioassay

Test Substance

Test Setup

Concentration 1.0× EC50

Soil moisture 25% w/w

Test speed 1.2 h/s

ISO 17512-1 Result

Elapsed time

0.0 / 48 h

Worms: control | test

10 | 10

Avoidance A%0%

Test running…

How it works

This reproduces the logic of the ISO 17512-1 earthworm (Eisenia fetida) avoidance bioassay: worms are released into a chamber split into a clean control half and a contaminated test half, and after 48 hours the fraction that fled the contaminated side scores the soil's toxicity.

A(%) = ((C - T) / N) × 100

C = worms ending in control soil
T = worms ending in test (contaminated) soil
N = C + T (total worms)

A < 50%   → soil not classified as harmful
50% ≤ A < 80% → measurable avoidance response
A ≥ 80%   → soil MUST be classified as harmful (ISO 17512-1)

Each worm follows a correlated random walk with a repulsion term proportional to how far the local, moisture-adjusted concentration exceeds that compound's avoidance EC50:

C_eff = C_nominal × sqrt(moisture / 25%)
repulsion = k × max(0, C_eff − EC50)

Higher moisture raises contaminant bioavailability (and worm mobility), so the same nominal concentration produces a stronger avoidance response in wetter soil. Cadmium, chlorpyrifos and diesel TPH each carry a different literature-typical EC50, so the same concentration multiplier means very different real-world mg/kg exposure between them.

Control soil Contaminated soil Earthworm

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