Fluorescent quantum dots (QDs) have great potential for in vivo biomedical imaging and diagnostic applications. However, these nanoparticles are composed of heavy metals and are very small in diameter, and their possible toxicity must therefore be considered. As yet, no studies have reported the transfer of QDs between mother and fetus. The transfer of CdTe/CdS QDs of different sizes and dosages, and with different outer capping materials, from pregnant mice to fetuses is investigated. It is shown that QDs may be transferred from female mice to their fetuses across the placental barrier. Smaller QDs are more easily transferred than larger QDs and the number of QDs transferred increases with increasing dosage. Capping with an inorganic silica shell or organic polyethylene glycol reduces QD transfer but does not eliminate it. These results suggest that the clinical utility of QDs could be limited in pregnant women.

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The wide distribution and high heterogeneity of different elements in biochars derived from diverse feedstocks make it difficult to regulate their application in soil and to evaluate the maximum potential contribution of the nutrients and trace metals as well as the potential risk of toxic metals. This study classified 20 biochars, covering six typical categories, into three clusters according to their similarity and distance on nutrients and minerals using cluster analysis. Four principle components (PC) were extracted using factor analysis to reduce dimension and clearly characterize the mineral profile of these biochars. The contribution of each group of elements in the PCs to every cluster was clarified. PC1 had a high loading for Mg, Cu, Zn, Al, and Fe; PC2 was related to N, K, and Mn; and PC3 and PC4 mainly represented P and Ca. Cluster 1 included bone dregs and eggshell biochars with PC3 and PC4 as the main contributors. Cluster 2 included waterweeds and waste paper biochars, which were close to shrimp hull and chlorella biochars, with the main contributions being from PC2 and PC4. Cluster 3 included biochars with PC1 as the main contributor. At a soil biochar amendment rate of 50 t ha, the soil nutrients were significantly elevated, whereas the rise in toxic metals was negligible compared with Class I of the China Environmental Quality Standards for Soil. Biochar can potentially supply soil nutrients and trace metals, and different cluster biochars can be applied appropriately to different soils so that excessive or deficient nutrient and metal applications can be avoided.

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