Trophic transfer of differently functionalized zinc oxide nanoparticles from crustaceans (Daphnia magna) to zebrafish (Danio rerio)

• Surface functionalization of ZnO NP affected uptake and depuration rates in D. magna.
• Zn content after exposure to functionalized ZnO NP differed from ZnCl2 and ZnO bulk.
• Trophic transfer of functionalized ZnO NP was observed from D. magna to D. rerio.

The potential uptake and trophic transfer of nanoparticles (NP) is not well understood so far and for ZnO NP the data presented in peer-reviewed literature is limited. In this paper the influence of surface functionalization on the uptake and depuration behavior of ZnO NP, ZnO-OH NP and ZnO-octyl NP in D. magna was studied. Bulk ZnO particles (≤5 μm) and ZnCl2 were used as references for uptake of particles and dissolved species of Zn, respectively. Furthermore, the trophic transfer of ZnO NP and ZnO-octyl NP from daphnids (Daphnia magna) to zebra fish (Danio rerio) was studied. For ZnO NP and ZnO-octyl NP fast uptakes in D. magna were observed, whereas no measurable uptake took place for ZnO-OH NP. Lower body burden of ZnCl2 was found compared to both ZnO NP and ZnO-octyl. Contrary, the body burden for bulk ZnO was higher than that of ZnO NP but lower than ZnO-octyl. The higher body burdens found for functionalized ZnO-octyl NP than for non-functionalized ZnO NP showed that that the functionalization of the NP has a high influence on the uptake and depuration behavior. Though no mortality was observed, the resulting body burdens were 9.6 times (ZnO NP) and 47 times (ZnO-octyl NP) higher than toxic levels reported for zinc in D. magna. Consequently, the zinc recovered in the animals was not solely due to soluble zinc, but agglomerates/aggregates of ZnO NP or ZnO-octyl NP contributed to the body burdens. The trophic transfer study showed uptake of both ZnO NP and ZnO-octyl NP reaching more than tenfold higher levels than those obtained through aqueous exposure in other studies. This study contributes to expand the available data on uptake behavior of differently functionalized ZnO NP in D. magna and the potential trophic transfer from zooplankton to fish.