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Toxicity to soil microorganisms

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Key value for chemical safety assessment

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In accordance with Column 2 of REACH Annex X, there is no need to further investigate the effects of this substance in a toxicity to terrestrial microorganisms study because, as indicated in guidance R.7.11.6 (ECHA 2017), the quantitative chemical safety assessment (conducted according to Annex I of REACH) indicates that the Risk Characterisation Ratio is below 1, therefore the risk is already adequately controlled and further testing is not justifiable. The substance is involatile and highly adsorbing and low toxicity was observed in short-term terrestrial tests and short- and long-term aquatic tests; therefore, there is no reason to expect effects in the terrestrial compartment that were not expressed in the aquatic compartment. While aquatic microorganisms effect data are not taken into account in deriving the freshwater PNEC value, it is notable that the data on microorganisms indicate a lack of effects up to 200 mg/L, which is 20 times higher than the long-term algal NOEC of ≥10 mg active acid/L. Based on the long-term aquatic data set, the most sensitive trophic level is algae. Due to its high adsorption and low toxicity to aquatic organisms, DTPMP was assigned to soil hazard category 3 (R.7c Section R.7.11.6, ECHA 2017) and a PNECscreen was conducted, based on the equilibrium partitioning method (PEC * 10 / PNECscreen). Testing for toxicity to terrestrial organisms has been carried out with one trophic level, earthworms (consumers). PNECsoil has been derived using both the equilibrium partitioning method and measured terrestrial ecotoxicity data and the most conservative value (PNECsoil based on measured terrestrial ecotoxicity data) has been used for PNECsoil. As the terrestrial RCRs based on this PNEC are < 1, no further toxicity testing of soil organisms is currently considered to be necessary. The phosphonate ligand binds strongly and irreversibly to various minerals present in soil and so bioavailability to soil organisms is extremely limited. The PNEC calculated using measured data has been derived for the purpose of conducting a chemical safety assessment, and the risk characterisation ratios are below 1. Details on how the PNEC and the risk characterisation ratio have been derived can be found in IUCLID Section 6.0 and Chapters 9 and 10 of the Chemical Safety Report, respectively. See also the endpoint summary for additional considerations on the toxicity to micro-organisms from aquatic data.