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The following toxicity data for aquatic organisms are available for p-TSH (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

These toxicity values were derived by a read-across to data for OBSH (80-51-3), for which substance 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). In static tests and 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) at the end of the test.

The main degradation products from the hydrolysis of OBSH 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, and therefore also for p-TSH. 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-hrs 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 and 21 d reproduction study on Daphnia magna of 0.016 mg/L(NOEC) (Ministry of the Environment in Japan (2016) are reported. Several values for 72-hrs EC50 in Selenastrum capricornutum ranging between of 0.006-0.19 mg/L are reported (CERI, 2007, US EPA ECOTOX(2017), Ministry of the Environment in Japan (2016) and values for NOEC of 0.001 mg/L (3d), 0.0192 (8d), 0.002 (10d) and 0.016 (3d) in Selenastrum capricornutum are reported (CERI, 2007, US EPA ECOTOX(2017), Ministry of the Environment in Japan (2016) - giving a geometric NOEC of 0.005 mg/L.

Based on these data, a PNEC for hydrazine of 0.1 µg/L (fresh water – assessment factor 50) respectively 0.01 µg/L (marine water- assessment factor 500) can be derived. Several data on the toxicity of hydrazine to microorganism can also be found. For the determination of PNEC(STP), an EC3 (pseudomonas putida, 16-hrs) of 0.019 mg/L (CERI 2007) is used. The PNEC(STP) is then derived at 0.02 mg/L (assessment factor set to 1).

The other main degradation product from hydrolysis is p-Toluenesulfonic acid. The below table shows toxicity data for the substance which is based on grouping of data with similar structure. Data are retrieved from SIDS Initial Assessment Profile for hydrotropes.

 Substance EC50(algae)  NOEC/EC10 (algae) EC50(crustacean)   NOEC/EC10 (crustacean) LC50(fish)   EC10/EC50 NOEC (microorganism)
   mg/L  mg/L  mg/L  mg/L  mg/L  mg/L
   230-236 31-75   >318 ~30   >400 >16000 (EC10) 

The PNECs for this degradation product is then set to: PNEC(fresh water) = 0.6 mg/L (assessment factor = 50), PNEC(Marine water) = 0.06 mg/L (assessment factor = 500); PNEC(STP) = 16000 mg/L (assessment factor = 1).

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.