Mechanistic Understanding toward the Maternal Transfer of Nanoplastics in <i>Daphnia magna</i>
ACS Nano2023
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Scientists traced exactly how nanoplastics transfer from mother water fleas (Daphnia magna) to their offspring, identifying two distinct pathways: direct entry through the brood chamber opening and internal transfer through the ovaries. The nanoplastics accumulated in eggs and embryos, confirming that plastic particles can pass between generations. This maternal transfer mechanism raises concerns about how nanoplastics might affect reproduction and early development across species, including potentially in humans.
Nanoplastics induce transgenerational toxicity to aquatic organisms, but the specific pathways for the maternal transfer of nanoplastics remain unclear. Herein, laser scanning confocal microscopy (LSCM) observations identified the specific pathways on the maternal transfer of polystyrene (PS) nanoplastics (25 nm) in <i>Daphnia magna</i>. <i>In vivo</i> and <i>in vitro</i> experiments showed that PS nanoplastics could enter the brood chamber through its opening and then be internalized to eggs and embryos using LSCM imaging (pathway I). In addition, PS nanoplastics were observed in the oocytes of the ovary, demonstrating gut-ovary-oocyte transfer (pathway II). Furthermore, label-free hyperspectral imaging was used to detect the distribution of nanoplastics in the embryos and ovary of <i>Daphnia</i>, again confirming the maternal transfer of nanoplastics through the two pathways mentioned above. The contribution from pathway I (88%) was much higher than pathway II (12%) based on nanoflow cytometry quantification. In addition, maternal transfer in <i>Daphnia</i> depended on the particle size of PS nanoplastics, as demonstrated by using LSCM and hyperspectral imaging. Unlike 25 nm nanoplastics, 50 nm PS nanoplastics could enter the brood chamber and the eggs/embryos (pathway I), but were not detected in the ovary (pathway II); 100 nm PS nanoplastics were difficult to be internalized by eggs/embryos and could not enter the ovary either. These findings provide insight into the maternal transfer mechanisms of nanoplastics in <i>Daphnia</i>, and are critical for better understanding the transgenerational toxicity of aquatic organisms.