Potassium isopentyl dithiocarbonate

Endpoint summary

Additional information

Purity of the target substance (potassium isoamyl xanthate; PIAX) is 84 %. It contains also 11% of another analogue xanthate potassium amyl xanthate (PAX) as a minor constituent. Therefore, the read-across data on PAX was used in the weight of evidence approach to evaluate the biodegradation of the target substance. In addition, as the xanhates have a similar degradation behaviour, data on other analogue substances were used for this endpoint, as there were no results available for PIAX. The read-across justifications are presented in Annex I of the CSR.

Ready biodegradability of n-amyl xanthate (PAX) was screened in a study conducted according to ISO 7827, corresponding to OECD Guideline 301 A. 74 % of the substance was degraded in 8 days, indicating ready biodegradability of the test substance PAX. The findings suggest slightly slower biodegradation rate for PIAX having a branched alkyl chain. Biodegradability of another analogue substance potassium isobutyl xanthate (PIBX) was assessed in a modified Zahn-Wellens test (OECD 302 B). As 75 % of the substance was degraded in 5 days, the result suggests that PIBX is inherently biodegradable under favorable laboratory conditions. Carbon disulphide, monothiocarbonate and dixanthogen were found to accumulate in the test system of the standard biodegradability screening tests reviewed.

The major dissolved degradation products 3-methylbutan-1-ol and pentan-1-ol are readily biodegradable.

At higher temperature (30 ˚C) and at pH 9, the biodegradation studies of xanthates by the microbes isolated from tailings lagoon had presented the most promising results with Pseudomonas putida and P. stutzeri up to xanthate concentration of 10 mg/l (Lam 1999). Higher xanthate concentrations (> 20 mg/l) and presence of cyanide compounds inhibited the microbial activity of tailings lagoon microbes. However, the biodegradation is not expected to be relevant degradation process in the tailings pond.

 

In conclusion, potassium isoamyl xanthate is considered inherently biodegradable based on the available information. Xanthates have been found to be biodegradable in ready biodegradability test and in inherent biodegradability test indicating that the substance is not persistent. However, based on the knowledge of the degradation at the relevant environmental conditions, the degradation cannot be considered to be rapid. This is based on the reported half-lives and the fact that biodegradation is not expected as an important process in the tailings ponds. The substance is not fully mineralized but rapidly degraded to less degradable degradation products and this has to be considered in the assessment. In addition, some of the degradation products are more toxic to aquatic organisms (e.g hydrogen sulphide) than the parent substance.