Morpholinium toluene-4-sulphonate

Toxicity to aquatic algae and cyanobacteria

Description of key information

Acutely harmful to aquatic algae.

Additional information

The test substance is soluble in water and dissociates to morpholinium and toluene-4-sulphonate. Since no studies on the toxicity of the test substance to aquatic algae are available, the assessment has been performed with the substance's dissociation products.

The toxicity of morpholine has been assessed in a study according to EPA guideline with Pseuokirchneriella subcapitata as test species [Calamari et al., 1980]. At test termination after 72 h an ErC50 of 28 mg/L (nominal) and a NOErC of 10 mg/L were determined. These results are supported by data from NITE (2008) which conducted an algae study with Pseudkirchneriella subcapitata. After a 72 hour exposure period, an ErC50 of 58 mg/L was determined.

For the assessment of toluene-4 -sulphonate there is sufficient information from the aromatic sulphonic acids category available. The key study has been conducted with the read-across substance benzenesulphonic acid according to OECD guideline 201 with the test species Selenastrum capricornutum [p-Toluenesulphonic Acid Coalition, 2005]. At test termination after 72 hours an ErC50 = 73 mg/L (measured) and a NOErC of 44.8 mg/L (measured) were determined. It appears that the pH of the test substance was responsible for the observed toxicity. The report indicates that the observed toxicity may very well have been due to the acidity of the test substance. The pH of the test medium at the two highest test concentrations (100 and 220 mg/L) was in the range of 5 and 3, respectively. The test conditions were confirmed to be valid and the measured concentrations were in the range of 90 - 110 % of the nominal concentrations.

Additionally, there are three guideline studies available that assess the toxicity of the hydrotropes (i. e., the salt form of the aromatic sulphonic acids) to aquatic algae and which all indicate toxicity in the same range as for the acid form. Stepan AG (1993) conducted a non-GLP guideline study according to US EPA requirements with the hydrotrope sodium xylene sulphonate (CAS 1300 -72 -7). The freshwater species Selenastrum capricornutum was exposed to a range of nominal concentrations of the test substance and at test termination after 96 h an EC50 of >= 230 mg/L active substance based on cell density was determined. The 96 hour NOEC was determined to be 31 mg/L. The test substance was observed to be algistatic but not algicidal at the highest concentration (1000 mg/L active substance). The 2nd study is GLP compliant and has been conducted according to US EPA OTS 797.1050 with the hydrotrope calcium xylene sulphonate (CAS 28088 -63 -6) and the algae species Selenastrum capricornutum [Ruetgers-Nease 1994]. At the end of the 96 hour exposure period an ErC50 of 758 mg/L and a NOErC of 240 mg/L has been determined. The 3rd study has been is GLP compliant and has been conducted according to EU C.3 "Algal Inhibition Test" with sodium toluene sulphonate (CAS 12068-03-3) [Sasol GmbH 1995]. At the end of the exposure period after 72 h an ErC50 of 310 mg/L active substance was determined.

Taking all available information into account it can be concluded that the test substance is acutely harmful to aquatic algae.