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Toxicity to aquatic algae and cyanobacteria

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Description of key information

NOEC for freshwater algae = 44.8 mg/L.  

Key value for chemical safety assessment

EC50 for freshwater algae:
73 mg/L
EC10 or NOEC for freshwater algae:
44.8 mg/L

Additional information

There is a 2005 good quality "key study" for a 99.8% pure benzenesulfonic acid (CAS No. 98-11-3). It followed OECD Guideline 201 and was done under GLP with analytical confirmation and a reference substance. The 72h-EC50 for Selenastrum capricornutum was 70 mg/L active ingredient based on biomass inhibition. The 72h-EC50 was 73 mg/L for growth rate inhibition. The reported 72h-NOEC was 44.8 mg/L. Both values are based on measured test substance. It appears 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 for the 5 exposures

Hydrotropes

For read-across purposes, there are three guideline algal toxicity studies for the hydrotropes (i. e., the salt form of the aromatic sulphonic acids) and all three studies indicate toxicity in the same range as for the acid form.

The key study is a 1993 USEPA Guideline study - EPA OTS 797.1500 - Algal Toxicity. The study was not conducted with GLP requirements but considerable detail is available. The freshwater Selenastrum sp. was exposed to a range of nominal concentrations of the test substance, sodium xylene sulphonate (CAS No 1300-72-7). The 96-hour EC50 was 230 mg/L active substance based on cell density (with a 95% CL of 47-1200 mg/L). There was an apparent dose response and the 96-hour NOEC was 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 a 1994 EPA Guideline study (EPA OTS 797.1500) of calcium xylene sulphonate (CAS No 28088-63-3) conducted under GLP requirements and with analytical confirmation reports a 96h-EC50 of 758 mg/L active substance (with a 95% confidence limit of 592-924 mg/L) and a NOEC of 240 mg/L based on growth rate of Selenastrum sp.

The 3rd study is a 1995 EU Guideline study (EU C.3 Algal Inhibition Test) of sodium toluene sulphonate (CAS No 657-84-1 that is similar to CAS No 12068-03-3) conducted under GLP requirements and with analytical confirmation reports a 72h-EbC50 of 150 mg/L active substance based on cell density and a 72h-ErC50 of 310 mg/L based on specific growth rate of Scenedesmus sp. The 72h-NOEC is 40 mg/L active substance based on biomass.