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Ecotoxicological information

Short-term toxicity to fish

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Description of key information

The value of 770 mg (NH4)2S2O3/L for the fish C. variegatus is put forward for the environmental classification of ammonium thiosulfate.	Expressed as S2O32-, SO32- or S, this value becomes 583, 831 or 333.2 mg/L, respectively.

Key value for chemical safety assessment

LC50 for freshwater fish:
831 mg/L

Additional information

Three acute fish toxicity study that evaluated the effects of a thiosulfate substances were identified (BASF, 1982). Tested fish species were the trout Salma gairdneri, the sheepshead minnow Cyprinodon variegatus and the bluegill Lepomis macrochirus.

 

 

Substance

 

Test organism

LC50

(mg test item/L)

Reference

(NH4)S2O3

Salmo gairdneri

770

Springborn Bionomics, 1986a

(NH4)S2O3

Cyprinodon variegatus

510

Springborn Bionomics, 1986b

(NH4)S2O3

Lepomis macrochirus

>1000

Springborn Laboratories, 1994

 

The result obtained with C. variegatus (96h-LC50 of >1000 mg/L) is questionable as 100% survival was reported for fish that lived in complete anaerobic water for 72h. Therefore the reported effects data in this study are disregarded for hazard and risk assessment purposes.

The two remaining LC50 values of 770 mg/L and >1000 mg/L are considered reliable, and the lowest value of 770 mg/L is put forward as key value for this endpoint.

 

 

In the test with S. gairdneri a concentration of 600 mg/L resulted in 0% mortality after 96h, but 100% mortality was noted after 24h for fish exposed to 1000 mg/L ammonium thiosulfate. At an exposure concentration of 600 mg/L, however, some fish were lethargic and exhibited (partial) loss of equilibrium. pH remained stable throughout the test, regardless of the administered test concentration (pH: 6.7 – 7.4 ). Oxygen levels, however, decreased over time, and this decrease became more distinct at higher test concentration. O2-levels in the control dropped from 8.8 to 6.8 mg/L during the 96h exposure period; at 600 mg (NH4)2S2O3/L, however, the oxygen levels went from 9.0 to 3.4 mg/L. This observation suggests that recorded effects may be related (partially) to decreased O2 levels in the test medium.

 

The value of 770 mg (NH4)2S2O3/L for the fish C. variegatus is put forward for the environmental classification of ammonium thiosulfate. Expressed as S2O32-, SO32-or S, this value becomes 583, 831 or 333.2 mg/L, respectively.