Health issues harmful effects

Numerous toxicity tests, including some using primates (see, e.g., Ji et al. 1988), have been reported and their results have firmly testified that REE is, within normal range, convincingly safe . A special issue of the Journal of the Chinese Rare Earth Society, published in September, 1985, reported thirteen experimental studies of REE toxicity, from which it was concluded (Ji 1985) that the possible harmful effect of trace rare earths used in agriculture on human health was almost non-existent . 

CDDs and the structurally related CDFs and dioxin-like PCBs are of concern to ATSDR because of the potential of these chemicals to harm health at relatively low doses. As discussed in Section 2.5, many of the toxic effects of these compounds appear to be mediated by a common mechanism, and CDDs frequently occur with CDFs in the environment. Therefore, due to the common mechanism of toxicity, total toxicity of a CDD/CDF mixture probably results from the added contribution (not necessarily linear) of both classes of chemicals. Because of this, the complex issue of appropriate methodology for quantitatively assessing health risks of CDDs and CDFs is currently being evaluated by ATSDR. Additional information on toxic interactions between CDDs and CDFs, as well as PCBs, would facilitate health risk assessment of this class of chemicals. 

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