Registration Dossier

Ecotoxicological information

Endpoint summary

Administrative data

Description of key information

Additional information

The following toxicity data for aquatic organisms are available for OBSH (n = nominal concentration; m = measured concentration). It should be noted that these values may reflect toxic effects of degradation products as well as the parent compound.

Short-term toxicity

Fish [Oryzias latipes]:         

LC50(96 hrs) = 74 mg/L (n)

LC50(96 hrs) > 6.6 mg/L (m)

Invertebrates [Daphnia magna]:          

EC50(48 hrs) = 15 mg/L (n)

EC50(48 hrs) = 2.9 mg/L (m)

Algae [Pseudokirchneriella subcapitata]: 

EC50(72 hrs) = 6.7 mg/L (Growth rate); (n)

EC50(72 hrs) = 2.2 mg/L (Biomass) (n)

EC50(72 hrs) = 3.0 mg/L (Growth rate) (m)

Long-term toxicity:

NOEC for freshwater fish (Oryzias latipes, Early-Life Stage Toxicity Test, 45d): 0.09 mg/L

NOEC for freshwater invertebrates (Daphnia magna, 21 d reproduction study): 2.1 mg/L

NOEC for fresh water algae (Pseudokirchnerella subcapitata, 3 d, growth rate): 0.7 mg/L

It is re-called that the hydrolysis studies showed quite short hydrolysis half-lives of 5.8 hr (pH=9), 7.9 (pH=7), 9.2 (pH=4). The pH range of the toxicity studies were in the range of 7.3 – 9.0 (except the short-fish study which was carried out at the pH-range 6.4-7.7). At these pH-ranges, a large percentage of the mother substance is degraded (>65% after 12 hours, >88% after 24 hours, >98% after 48 hours) during the test, if no water exchange has been carried out. The main degradation products from the hydrolysis have been identified to be hydrazine (CAS No. 302-01-2) and 4,4’-oxybis(benzenesulfonic acid) (SIDS Initial Assessment Profile, It is very likely that especially hydrazine has contributed to the observed toxicity. Regarding the long-term fish study, the derived NOEC is considered valid for the parent substance, i.e. the registered substance. In this study, the water exchange rate was 4 times per hour – meaning that the hydrolysis in this experiment only had a very limited impact. Thus, the NOEC determined for this long-term fish study is considered valid for the parent substance, i.e. the registered substance. This is of importance as this NOEC also determines the PNECs and classification of the substance.

Very good toxicity data for hydrazine are available in the open literature. The 96-hr LC50 of hydrazine range from 0.61 (for guppy) to 7.7 mg/L for fresh water fish and a LC50 of 3.4 mg/L has been reported for the marine fish (three-spined stickleback). The 48-hrs EC50 of hydrazine to Daphnia magna of 0.175 mg/L is reported. The 72-hrs EC50 of 0.0061 mg/L respectively a NOEC of 0.001 mg/L in Selenastrum capricornutum is reported (CERI, 2007). A long-term fish study reports a NOEC of Based on these data, a PNEC for hydrazine of 0.006 µg/L (fresh water – assessment factor 1000) respectively 0.0006 µg/L (marine water- assessment factor 10,000) can be derived. Several data on the toxicity of hydrazine to microorganism can also be found in the report. For the determination of PNEC(STP), an EC3 (pseudomonas putida, 16-hr) of 0.019 mg/L is used. The PNEC(STP) is then derived at 0.02 mg/L (assessment factor set to 1).

No literature toxicity data can be found for the other main degradation product, namely 4,4’-oxybis(benzenesulfonic acid. The below table shows toxicity data for substances with similar structure. The number given in the parenthesis is a normalized (with respect to molar mass) effect concentration



NOEC/EC10 (algae)


NOEC/EC10 (crustacean)


NOEC/EC10 (fish)

EC10/EC50 NOEC (microorganism)


Disodium oxybis(methylbenzenesulfonate)*

104 (85)

46 (m) (38)

>92 (m) (75)


>92 (m) (75)


>1000 (NOEC)

4-hydroxybenzenesulphonic acid**

73 (70)

44 (42)

>103 (98)


>500 (476)


580 (NOEC)

Benzene sulfonic acids****

73 (65)

44.8 (40)

103 (91)


>500 (0)


580 (NOEC)


230-236 (341)

31-75 (46)

>318 (472)

~30 (45)

>400 (594)


>16000 (EC10)

*Data from REACH registration dossier for substance

**Data based on read-across

***Includes Xylenesulfonic acid (sodium, ammonium, calcium, potassium salts); Toluenesulfonic acid (sodium salt and potassium); Cumenesulfonic acid (sodium salt and ammonium salt). Data from SIDS on hydrotropes (

****Includes Benzenesulphonic acid, p-cumenesulphonic acid, Toluene-4-sulphonic acid and Xylenesulphonic acid


From above, it is clearly indicated that 4,4’-oxybis(benzenesulfonic acid is not expected to be very toxic to the environment. It is also seen that - except for the acute algae, where a quite high EC50 is noted for the hydrotopes - that the effect concentrations of the three substances are on the same level. The most sensitive species appears to be algae. A PNEC value for 4,4’-oxybis(benzene sulfonic acid is then derived by applying an assessment factor of 50 respectively 500 on the lowest NOEC/EC10 of 40 mg/L. The derived PNECs for 4,4’-oxybis(benzenesulfonic acid are PNEC(Fresh water)=0.8 mg/L and PNEC(Marine water)=0.08 mg/L. It is also seen that 4,4’-oxybis(benzenesulfonic acid is not very toxic to microorganism. A PNEC(STP) of 50 mg/L is used in the risk assessment.