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CLP Annex I · Table 4.1.3

M-factor Calculator

Derive the multiplying factor for aquatic-toxic substances under CLP Annex I Table 4.1.3. Works for acute L(E)C50 and chronic NOEC, with the rapidly-degradable shift.

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How to read this from the SDS

Everything you need is in the aquatic toxicity data for the substance, not the mixture.

The value
Section 12 Ecological information, aquatic toxicity. There are usually up to three results: fish LC50, Daphnia EC50 and algae ErC50. Enter the single lowest (most sensitive) value, since that is the one that drives the M-factor. The algae value is often the least toxic, so it is usually ignored.
Acute or chronic
Use Acute with an L(E)C50. Switch to Chronic only if you are working from a NOEC (chronic) value.
Rapidly degradable
Section 12 Persistence and degradability. Tick the box only for chronic, and only if the SDS says the substance is readily biodegradable. It shifts the bands one decade.

Note the M-factor may already be stated outright in Section 3 or in the Annex VI harmonised entry. If so, use that value directly; this tool is for deriving it when only the raw toxicity numbers are given.

Example — prallethrin Fish LC50 0.012, Daphnia EC50 0.0062, algae ErC50 4.5 mg/L. The lowest is 0.0062, which sits in the 0.001–0.01 band, so M = 100.

Enter the toxicity value as a positive number in milligrams per litre.

Enter a value to derive the M-factor.

What it covers

Acute and chronic

One tool covers both acute L(E)C50 and chronic NOEC derivations. Same formula, different starting band.

Degradability shift

A single checkbox applies the one-decade shift for rapidly degradable substances on the chronic side.

Band shown

The result tells you which Table 4.1.3 band your value falls into, so the verdict is auditable.

CLP Annex I Table 4.1.3 — multiplying factors

For each order of magnitude beyond the highest band, the M-factor multiplies by 10. The three columns start one decade apart: acute L(E)C50 begins at 0.1–1 mg/L, chronic NOEC for not rapidly degradable substances one decade lower, and chronic NOEC for rapidly degradable substances one decade lower again.

Band (mg/L) Acute — L(E)C50 Chronic NOEC — not rapidly degradable Chronic NOEC — rapidly degradable
0.1 to 11——
0.01 to 0.1101—
0.001 to 0.01100101
0.0001 to 0.001100010010
0.00001 to 0.0001100001000100
further decades×10 per decade×10 per decade×10 per decade
How to use the M-factor
  1. 01Identify the most sensitive aquatic endpoint for the substance (L(E)C50 for acute, NOEC for chronic).
  2. 02Use this calculator to derive M.
  3. 03In the mixture summation method, multiply the component's concentration by M before applying the Aquatic Acute 1 (≥25%) and Aquatic Chronic 1-4 cut-offs.
  4. 04Record both the value and the M-factor in your classification dossier for traceability.

Frequently asked questions

What is an M-factor for?
Substances classified Aquatic Acute 1 or Aquatic Chronic 1 receive an M-factor that amplifies their concentration in the mixture summation method. The more toxic the substance (lower L(E)C50 or NOEC), the higher the M, so it triggers mixture classification at a lower concentration.

When does the rapidly-degradable shift apply?
Only for chronic NOEC. Rapidly degradable substances clear the water column faster, so the same NOEC poses less long-term risk. Chronic NOEC bands already sit one decade below the acute L(E)C50 bands (M=1 at 0.01–0.1 mg/L), and ticking rapidly degradable shifts them a further decade, so the M=1 band drops to 0.001–0.01 mg/L.

What defines rapidly degradable?
CLP Annex I §4.1.2.9.5: an organic substance is rapidly degradable if it meets the OECD ready-biodegradability criteria, or shows >70% DOC removal / >60% theoretical O2 demand within 28 days, or shows BOD5/COD ≥ 0.5, or other equivalent evidence. Check Section 12 of the SDS or a REACH dossier for the assessment.

Does this replace a full aquatic-tox classification?
No. The M-factor is one input to the mixture summation method. The full classification also weighs bioaccumulation, the choice of acute or chronic data, summation across components, and the additivity formula for components without an M. NextSDS automates the full process.

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Disclaimer: Provided as an aid for understanding CLP Annex I Table 4.1.3. Always verify M-factor derivations against the current regulatory text and your supplier-provided data, and consult a qualified chemical safety adviser when in doubt.