Praseodymium trichloride

Endpoint summary

Description of key information

All available existing information on the toxicity of praseodymium trichloride to aquatic organisms is presented in this dossier. Only one Klimisch 1 study is available, i.e. the acute toxicity study in Daphnia magna, resulting in a 48-h EC50 of 2.4 mg PrCl3/L (Ablitt, 2018). This study would lead to classification for the aquatic environment as Chronic 2. So far, rare earth salts such as rare earth chlorides and rare earth nitrates typically have been classified as Acute 1 and Chronic 1. Therefore, it was decided to also take into account the study of Bazin (1997), which investigated the acute toxicity of praseodymium trinitrate to Oncorhynchus mykiss (not included in the dossier though since not a required endpoint for An VII and no data available for praseodymium trichloride itself). This study reported an LC50 of 0.71 mg Pr(NO3)3/L after a 96-h exposure to praseodymium nitrate. The results cannot be considered entirely reliable as the test concentrations were not analytically verified and as precipitation may have occurred, which could have led to an underestimation of toxicity. When recalculated to PrCl3, an LC50 of 0.54 mg PrCl3/L would be obtained for fish. Although toxicity to fish might have been underestimated in this study, this LC50 would lead to a classification for the aquatic environment as Acute 1 and Chronic 1, which is a more severe classification compared to the classification that would be obtained based on the reliable data for praseodymium trichloride only. Based on the precautionary principle, and considering the weight of evidence for all rare earth chlorides and nitrates tested so far, it was considered appropriate to assign the classification of Aquatic Acute 1 and Aquatic Chronic 1 to praseodymium trichloride.