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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Target Substance_OECD 201_ Selenastrum capricornutum: NOEL: 500 mg/L WAF, ErL50(72h) > 1000 mg/L.
RA_CAS68608-26-4_OECD 201_Scenedesmus subspicatus: NOEL: 100 mg/L WAF, ErL50(72h) > 100 mg/L.
RA_CAS61789-86-4_OECD 201_Scenedesmus subspicatus: NOEL: 100 mg/L WAF, ErL50(72h) > 100 mg/L.
RA_CAS115733-09-0_EPA OTS 797.1050_Selenastrum capricornutum: NOEL: 1000 mg/L WAF, ErL50(72h) > 1000 mg/L.

Key value for chemical safety assessment

EC50 for freshwater algae:
1 000 mg/L
EC10 or NOEC for freshwater algae:
500 mg/L

Additional information

General considerations

The toxicity to aquatic algae was investigated for Benzenesulfonic acid, mono-C20-24 (even)-sec-alkyl derivs., para-, sodium salts (generic name: C20-24 sodium sulfonate) and for three different analogue structures of the target substance. Since the read-across substances used belong to the same chemical group, aryl-alkyl sulfonates, the same behaviour and toxicity potential can be expected.

The sodium sulfonate read-across substance (CAS 68608-26-4) and the calcium sulfonate read-across substances (CAS 115733-09-0 and CAS 61789-86-4) were used to provide further information regarding the endpoint of toxicity to algae and cyanobacteria. Investigations concerning toxicity in marine algae were not performed. For the detailed procedure of the read-across principle and justifications, please refer to the separate Read-Across Statement attached to the Chemical Safety Report.

Experimental results -Selenastrum capricornutum

In a key study, Benzenesulfonic acid, mono-C20-24 (even)-sec-alkyl derivs., para-, sodium salts (generic name: C20 -24 sodium sulfonate) was tested at nominal concentrations of 33, 65, 130, 250, 500, and 1000 mg/L as WAF loading rates under static conditions (Boeri et al., 2000). The study was performed according to OECD Guideline 201 and US EPA (TSCA) 797.1050 with GLP compliance. No insoluble material was observed during the toxicity test. The algal population grew well, resulting in an average of 2,427,000 cells/mL in the control after 96 hours. Water quality throughout the test was within acceptable limits. No effects (size differences, unusual cell shapes, colors, flocculations, adherence of cells to test containers, or aggregation of cells) were noted during the test. The exposure of freshwater alga to the test substance resulted in an EbC50 (96h) of 720 mg/L (95% CL = 500 to >1000 mg/L) and ErC50 (96h) of >1000 mg/L. The NOEC (96h) is reported as 130 mg/L when determined using the number of cells/mL and 500 mg/L using the average specific growth rate. The EbC50 (72h) was determined as 490 mg/L (95% CL = 260 to 920 mg/L) and the ErC50 (72h) amounts to >1000 mg/L.

In another key study, the calcium sulfonate read-across substance (CAS 115733-09-0) was tested at nominal concentrations of 100, 300 and 1000 mg/L as WAF loading rates under static conditions (Ward, 1994). The study was performed according to US EPA Guideline OTS 797.1050. The algal population grew well during the test, since an average of 1,711,000 cells/mL was recorded in the control group; resulting in a doubling time of 13 h. The test vessels containing 1000 mg/L WAF were slightly cloudy at the start of the test and after 24 h exposure time. After 72 hours, biomass measurements were 80 %, 62 % and 70 % of the control at 100, 300 and 1000 mg/L WAF, respectively. At 96-hours, biomass measurements were 70 %, 66 % and 88 % of the control at 100, 300 and 1000 mg/L WAF, respectively. Based on these findings, the ErL50 (72h), ErL50(96h), EbL50(72h) as well as the EbL50(96h) value are considered to be > 1000 mg/L. The corresponding No Observed Effect Level (NOEL) amounts to 1000 mg/L WAF for each sampling period.

Experimental results -Scenedesmus subspicatus

In a key study, the sodium sulfonate read-across substance (CAS 68608-26-4) was tested at a single nominal concentration of 100 mg/L as WAF loading rate under static conditions (Mead, 2005a). The study was performed according to OECD Guideline 201 referenced as Method C.3 of Commission Directive 92/69/EEC under certificated GLP compliance. Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group, using a haemocytometer and light microscope. It was clear that neither the growth (r) nor the biomass (b) of Scenedesmus subspicatus were affected by the presence of the test material over the 72h exposure period. As final results, an EbL50 and ErL50 value of greater than 100 mg/L loading rate WAF (respectively) and a No Observed Effect Loading rate of 100 mg/L loading rate WAF were determined.

In a 72 hour key study, the cultures of the green algae (Scenedesmus subspicatus) were exposed to sulphonic acids, petroleum, calcium salts (CAS 61789 -86-4) at nominal concentrations of 0 and 100 mg/L nominal WAF loading rate under static conditions (limit test). The test was performed by Mead (2005b) in accordance with the OECD Guideline 201 (Alga, Growth Inhibition Test). The EL50 based on biomass was > 100 mg/L and the EL50 based on growth rate was > 100 mg/L. There were no compound related phytotoxic effects.