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Toxicity to microorganisms

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No study data is available for the test substance. Effects on microorganisms were studied using the read across substance boric acid (CAS No 10043-35-3). In a weight of evidence approach the toxicity of the read across substance was evaluated.

WoE (publication; Guhl, 2000; boric acid)
Opercularia birmarginata was used by Guhl (2000) in order to estimate the toxicity of boric acid. An electronic cell counter (Coulter) is used for quantitative determination of the protozoa inoculated and of the multiplication of protozoan cells within the test cultures after addition of a suitable electrolyte. If cell counts in the test cultures are 5% below the average of the counts in reference cultures free of toxic influence this may be considered as an initial inhibition of protozoan cell multiplication by a pollutant and thus serve for determining the toxicity threshold (TGK) for that particular pollutant.

Up to 10 mg B/L no effect was observed on the organisms. Up to 20 mg/L only deformations were observed but at a concentration higher or equal to 20 mg B/L effects relative to the colony were observed.

WoE (overview of public references (1976 -2001); focus on boron)
Effects of boric acid on micro-organisms was estimated using the standardized OECD 209 method, Hanstvelt and Schoonmade (2001) reported 24% inhibition at 175 mg B/L, and an EC10 can be calculated from their data as 58 mg B/L. A NOEC was reported by the study authors of 17.5 mg B/L, but was not determined via any statistical means. Actually there was 4% inhibition at this exposure, so it is an EC4, thus more stringent than intended by the OECD 209 protocol. An EC10 value was calculated by linear regression from the data which showed a good fit (R2= 0.863) with a value of 58.0 mg B/L. This study complies with GLP practice, is rated as highly reliable in quality, and is consistent with earlier tests of activated sludge, however they were not published.
Gerike et al.(1976), using an earlier version of the OECD activated sludge method reported LOEC and NOEC of 120 and 20 mg B/L, respectively. Guhl (1992, 2000) reported activated sludge LOEC and NOEC of 50 and 20 mg B/L, respectively.
Other reports include tests of the microbe, Pseudomonas putida, with NOEC values ranging from 7.6 to 1040 mg B/L. However, these study reports are of varying reliability. The geometric mean value of the Henkel studies is 50.8 mg B/L (EC10 values of 340 and 7.6 mg B/L).

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