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Reliable acute toxicity data for the three trophic levels (algae, invertebrates and fish) are available together with data on microorganism toxicity. Due to the caustic property of the submission substance adjustment of pH to physiological values is a prerequisite for meaningful results (considered in all studies but acute fish toxicity with the active ingredient BHMT, see below).

Algae proved to be the most sensitive trophic level. The available algae study performed with the submission substance according to internationally accepted guidelines and GLP included also chemical analysis of main constituents concentrations of the test item. A decline of test item concentration in the test media throughout the test period of 72 hours was observed. This decline was inversely correlated to test item concentration and restricted to the constituent BHMT while the other constituent, HMD, was demonstrated to be relatively stable throughout the experiment. Based on time weighted mean measured concentrations growth rate related 72 h EC10 and EC50 values of 1.0 mg test item/L (IC95% = 0.65-1.38) and 9.3 mg test item/L (IC95% = 7.9-12), respectively, were determined. The decline in BHMT concentrations is assumed to be caused by adsorption to algae, a common phenomenon in the algae test.


Separate acute tests on fish are available for the constituents of the submission substance, HMD and BHMT. The study on HMD (according to OECD 203, reliability category 2) with fathead minnow (Pimephales promelas) resulted in a LC50 (96 h) of 1825 mg/L (95%IC = 1237-2461 mg/L; Probit analysis). No effects were observed up to a nominal concentration of 1000 mg/L. The study on BHMT with Golden ide (Leuciscus idus melanotus) was performed similar to OECD 203 (48 hour exposure, compliant to GLP, reliability category 2). A LC50 (48 h) of 76 mg/L was determined and at 58 mg/L no mortality occurred. Sub-lethal effects were generally not observed. In this study, the alkaline properties of the test item were not taken into account and toxicity due to alkaline pH is likely. Thus, inherent toxicity of the test item is probably considerably lower and observed toxicity values may be taken as worst case and most probably overestimate toxicity of the test item. However even taking the LC50 of 76 mg/L determined for BHMT as worst case toxicity value for the submission substance, fish proves to be the least sensitive species in acute tests.


For invertebrates a reliable key study is available for the submission substance testing acute immobilization of Daphnia magna according to OECD 202 (compliant to GLP, reliability category 1). Test item main constituents concentrations were analytically verified and proved to be stable throughout the duration of the experiment. For the submission substance, an EC50 (48 h) of nominal 17 mg/L (95% CL of 11 - 29 mg test item/L) was determined, the NOEC (48 h) was 10 mg test item/L. This is supported by an unreliable (reliability category 3 due to poor documentation) acute study on Daphnia magna reporting an EC50 (immobilization, 24h) of 35 mg/Lfor the submission substance.


Microorganism toxicity in regard to sewage treatment plants, microorganism toxicity was assessed in a reliable activated sludge respiration inhibition study with the submission substance performed according to the new OECD 209 guideline and compliant to GLP. An EC50 (3 h) of 335 mg/L (95% CL of 267 - 432 mg test item/L) and an EC10 (3 h) of 12 mg/L (95% CL of 6.4 - 18 mg test item/L) were determined.  


No data on sediment toxicity are available for the submission substance. The toxicity potential towards sediment organisms is assessed via equilibrium partitioning (EPM method).