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Toxicity to soil microorganisms

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Description of key information

No toxicity data are currently available for soil microorganisms. The terrestrial chemical safety assessment has been conducted using the Equilibrium Partitioning Method based on the aquatic data set.

Key value for chemical safety assessment

Additional information

In accordance with Column 2 of REACH Annex IX, there is no need to further investigate the effects of this substance in a soil microorganism study because:

• The substance is involatile and highly adsorbing and low toxicity was observed in the available pelagic organism and aquatic microorganism tests, and there is no reason to expect effects in the terrestrial compartment that were not expressed in the aquatic compartment. 

• Based on the aquatic data set, the most sensitive relevant trophic level is algae.

• The soil hazard category 3 has been derived for the substance. According to the screening assessment for soil hazard category 3, the PNECsoil has been calculated from PNECfreshwater on the basis of the equilibrium partitioning method and a confirmatory long-term toxicity to terrestrial organisms has been proposed for the ATMP category. The risk characterisation ratio (RCR) based on PNECsoil derived from the equilibrium partitioning method is <1.

• The phosphonate ligand binds strongly and irreversibly to various minerals present in soil and so bioavailability to soil organisms is extremely limited.


The terrestrial chemical safety assessment has been conducted using the Equilibrium Partitioning method (EQPM).

It is recognised that the aquatic PNEC used in the EQPM does not consider any indicator for effects in aquatic microorganisms. However, a number of non-standard studies are available giving evidence that ATMP has no inhibitory effect on micro-organisms at concentrations up to ca. 200 mg/L. A study of seven Swiss WWTPs in 1996 shows a maximum concentration of ATMP in WWTP untreated influent of ca. 0.8 µmol/L, equivalent to ca. 0.26 mg/L. These studies demonstrate the low toxicity of ATMP and its salts to micro-organisms. See Section 6.1.7 for further details.

These results show a lesser level of effect to that observed in the lowest reliable short-term aquatic toxicity study with invertebrates, where a 48-h EC50  value of 94 mg active acid/L with Acartia tonsa  was determined (Zeneca, 1995).

The data on long-term ecotoxicity to fish and invertebrates also suggest that aquatic microorganisms are comparatively less sensitive, where the lowest reliable long-term toxicity NOEC value was observed with fish at 23 mg active acid/L (ABC, 1980).

Therefore it is unlikely that the PNECterrestrial based on aquatic ecotoxicity test results would not be protective for terrestrial microorganisms.

The chemical safety assessment using EQPM does not suggest any unacceptable risks for the terrestrial compartment.