Potassium isopentyl dithiocarbonate

Short-term toxicity to fish

Description of key information

The 96-hour LC50 (mortality) to fish (Salmo salar) is 10 - 100 mg/L in a semi-static freshwater system in accordance with OECD 302 under GLP.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

10 mg/L

Additional information

No acute toxicity studies are available for the target substance. As the target substance is an analogue to the substances called xanthates, and the acute toxicity study results are available for these structural analogue substances this data was used to evaluate the acute toxicity to fish of the target substance. The read-across justifications are presented in Annex of the CSR.

All together six studies are available on acute toxicity of analogue substances potassium amyl xanthate (PAX) or potassium isobutyl xanthate (PIBX) to fish. One of them has been conducted in compliance with standard test methods, and three more have been reported with sufficient details to be scientifically acceptable (Klimisch 2).

The most recent study of Hoecst (1987c) determined acute toxicity of a read-across substance potassium isobutyl xanthate to fish (Danio rerio, former name Brachydanio rerio) in a static test in accordance with OECD 203 under GLP. The 96-h LC50 (mortality) was 10 - 100 mg/L. The results of this study was selected as a key value for CSA since it was conducted according to guidelines and considered as the most reliable study to be used for classification and labeling purposes.

The supporting study of Bertills et al. (1986) assessed acute toxicity of four xanthates to yearlings of atlantic salmon (Salmo salar) in a semi-static freshwater system, with daily renewal of test solutions. The arithmetic mean of the 96-h LC50 for a read-across substance PAX was 11 mg/L at 15 ^oC and pH 7.0. The study also observed that xanthates increased considerably toxicity of lead and cadmium to fish, and the accumulation rate of lead in fish liver.

Two older supporting studies of Fuerstenau et al. (1974) and Webb et al. (1976) were conducted on a series of xanthates with rainbow trout (Oncorhyncuss mykiss, former name Salmo gairdneri). Both studies were assessed to have restrictions in the reported methods and statistics, even if they were published in peer viewed publications, The obtained the 96-h LC50 values for different commercial grades of the read-across substance PAX were within the range of 18 to 80 mg/L fitting well in the result of the key study (10 - 100 mg/L).

Furstenau et al. (1974) reported an increase in breathing movements of the fish, which caused an increase in the volume of test solution to pass over the gill surfaces. Two possible toxicity mechanisms were proposed: 1) absorption through the lamellae and reaction with hemoglobin, or 2) adsorption on the gill surfaces resulting in interference with gas exchange. Increase of temperature from 12 to 16 and 20 ^oC was found to increase the acute aquatic toxicity. The findings could be linked with the synergistic toxic effect of xanthates with metals reported by Bertills et al. (1986).

Hawley (1977) reports several reviews on acute toxicity data of (older) short term bioassays. The 96-h median tolerance level of the minor constituent potassium amyl xanthate on freshwater fish Pimephales promelas was 1.8 - 180 mg/L and on Nothopsis atherinoides 10 - 100 mg/L. As the details on the materials, methods and study results were not reported, the results were rated as not reliable (Klimisch 3).

As the substance decomposes in water, the supporting studies on acute toxicity of the most critical degradation products were used in the exposure assessment. The 96-h LC50 of pentan-1-ol to Pimephales promelas is 452 mg/L,and the 96-h LC50 of carbon disulphide to Poecilia reticulata is 4 mg/L.

In conclusion, the lowest and the most relaible key value the 96-h LC50 of 10 mg/L was selected for CSA based on the result of Hoechst (1987c) on read across substance potassium isobutyl xanthate (PIBX).