Dibutyl phosphonate

Toxicity to microorganisms

Description of key information

EC₅₀ (3h, activated sludge) > 10000 mg/L (respiration rate)

Key value for chemical safety assessment

EC50 for microorganisms:

10 000 mg/L

Additional information

Evaluation of the toxicity of DBHP to microorganisms was performed using a weight of evidence approach. No experimental data on the substance itself was available, therefore, the following read-across data were taken into consideration:

- EC₅₀ (3h, activated sludge) > 10000 mg/L (read-across data on Source Chemical 01)

- EC₅₀ (3h, activated sludge) > 100 mg/L (nominal); EC₂₀ > 100 mg/L (read-across data on Source Chemical 03)

- IC₅₀ (3h, activated sludge) > 1000 mg/L (nominal) (read-across data on Source Chemical 07)

- EC₅₀ (17h, P. putida) = 4390 mg/L (nominal; growth inhibition) (read-across data on Source Chemical 09)

All four studies demonstrate no cause for concern regarding the toxicity to microorganisms to the category substances. Justification for the use of the read-across approach for the evaluation of this endpoint is provided in Section 13 of IUCLID. Based on the consensual absence of concern for toxicity to microorganisms across these studies, it is accepted that this also applies to the test item, and the EC₅₀ value of greater than 10000 mg/L is applied.

Experimental data and publications which support the very low toxicity of substances in the phosphonate diester category and their metabolites.

- Two additional studies on Source Chemical 09 demonstrated no cause for concern for toxicity to microorganisms. The first of these compared the biological growth (as measured by turbidity) of industrial sewage obtained over 16 hours demonstrated no growth inhibition at any concentration, up to the highest concentration tested (1000 mg/L). The second demonstrated very low toxicity to Pseudonomas putida measured by growth inhibition (EC₃ (16h) = 650 mg/L).

- An additional respiration inhibition study (OECD 209, but with poor documentation) was performed on Source Chemical 02 which demonstrated very low toxicity to microorganisms (EC₅₀of 4634 mg/L).

- Toxicity of Source Chemical 08 to Paramecium caudatum was also found to be very low: LC₁₀₀ (10 minutes) = 39500 mg/L; and LC₅₀ (4h) = 5800 mg/L (nominal).

- Additionally, a field study measuring soil microbial enzyme activities and soil mesofauna feeding activity performed on Source Chemical 11 (the other metabolite of the substance), demonstrated that phosphites do not harm the biocoenosis of microorganisms. The publication is not sufficiently detailed to be used for classification of toxicity to microorganisms, however, it supports the absence of toxicity to microorganisms at high doses.

Based on the consensual results, the absence of concern for toxicity of the test item to microorganisms is supported.