Potassium trifluorozincate

Endpoint summary

Additional information

Stability/degradation:

Due to the fact that potassium trifluorozincate is an inorganic substance, only abiotic degradation can be considered. A hydrolysis test was performed as part of a solubility study at varying pH. Although the study was not performed according to GLP criteria or guideline, the results are considered adequate for assessment. In this study, the mol ratio of K-, Zn- and F-ions in solution under acidic and neutral conditions was close to the theoretical ratio of 1:1:3 indicating that full dissociation and no hydrolysis occurs. In alkaline environment, a large amount of fluoride ions was found in solution compared to dissolved zinc. This indicates that at pH 9 hydrolysis of KZnF3 occurs through exchange of fluoride against hydroxyl groups under precipitation of zinc -oxides, -hydroxides and -hydroxyfluorides. Based on the difference between solubility at pH 6 and pH 9, as a gross estimation, hydrolysis at pH 9 is approximately 39 %.

Bioaccumulation:

Bioaccumulation of potassium trifluorozincate is not to be expected as the substance dissociates rapidly into zinc and fluoride. Data is available on uptake of zinc (EU-RAR, 2008) and fluoride ions. For zinc, the majority of BCF values for pelagic species, both invertebrates and fish, lie between 100 and 1.000 (the highest BCF reported in fish is 2.000). BCF values for fish are generally lower than those for invertebrates. In benthic invertebrates such as crabs, oysters and insect larvae, BCFs values in the range between 10.000 and 100.000 have been reported. For aquatic plants BCF values generally range from <100 to 50.000. It should be noted that these values were taken from reviews, which usually do not report whether the BCFs are based on fresh weight or dry weight of the organisms, whether or not the values have been corrected for the background concentration of zinc in the organisms and which exposure concentrations were used. In spite of these limitations, it is concluded that zinc is concentrated by aquatic organisms from the surrounding water, and that the degree of concentration is species-dependent, varying from insignificant in fish and most invertebrates to highly significant in algae and benthic organisms. However, in view of the decreasing BCF values with increasing trophic level in the food web it is concluded that biomagnification is of little significance for zinc.

In the case of fluoride, in aquatic organisms it accumulates primarily in the exoskeleton of crustacea and in the bones of fish. No fluoride accumulation was reported in edible tissues. In fish, BCF-values of 53-58 (d.w.) and <2 (w.w.) were found. In aquatic invertebrates BCF values based on whole body fluoride content are found to be <1 (d.w.). The highest reported BCF-value for Mollusca and aquatic macrophyta were 3.2 and 7.5 (w.w.), respectively. In an experimental marine ecosystem with fish, crustaceans and plants, mild accumulation was noted in all species. The highest value, a BCF of 149 was seen in fish. BCF values for crustacea ranged from 27 -62. In consumption fish, fluoride concentrations of up to 30 mg fluoride/kg were found. Based on all these data, it may be concluded that significant bioaccumulation of fluoride is unlikely to occur.

Adsorption/desorption:

Adsorption of potassium trifluorozincate to soil is not to be expected as the substance dissociates rapidly into various ions. The following information is available on bioaccumulation of zinc and fluoride ions. For zinc a Kp value of 110000 L/kg is determined for suspended matter-water, a Kp value of 73000 L/kg for sediment-water and a Kp value of 158.5 L/kg for soil-water.

For the sorption characteristics of fluoride only qualitataive data are available. Altogether, the immobile character of fluoride in soil is likely to be due mainly to formation ofcomplexes with aluminium, iron or calcium and dependent on the pH and the availability of these counter ions. Although some true adsorption processes are described (e.g. displacement of hydroxide from clay surfaces) these processes are probably of lesser significance. For pragmatic reasons, for environmental exposure assessment a Koc is calculated based on a log Kow of -1 in EUSES (in the EU-RAR for hydrogen fluoride a log Kow of -1.4 is suggested). When using the QSAR for non-hydrophobics (default QSAR), a Koc of 3.16 is determined.