Long-term effects of zinc oxide nanoparticles on the autumn phytoplankton of the Black Sea

Abstract

The widespread use of zinc oxide nanoparticles (ZnO NPs) in human economic activity makes the issue of assessing their impact on the environment relevant. In the presented work, the effects of ZnO NPs (10-60 μg/L) on Black Sea phytoplankton during long-term cultivation (17 days) under experimental microcosm conditions were studied. A dose-dependent effect of nanoparticle impact on the growth and functional state of phytoplankton of the Black Sea was established. The addition of ZnO NPs led to inhibition of growth, photosynthetic activity, and a decrease in the species diversity of phytoplankton. At 10 and 20 μg/L ZnO NPs, the community abundance maintained a positive trend. However, suppression of the growth rate and a decrease in the final algal abundance to 60 and 21% of control values were noted. At the same time, a decrease in the abundance of mass planktonic species, an increase in the contribution of bentho-planktonic forms, and a change in the size structure of the algocenosis toward the predominance of small-celled species were observed. At 30 and 60 μg/L ZnO NPs, at the initial stage of the experiment, the development of acute toxic stress, suppression of photosynthetic activity and cell division, and a decrease in community abundance were noted. However, further cultivation of the microcosms under these conditions led to the recovery of community growth due to the restructuring of the species structure with subsequent dominance of a small number of tolerant species (mainly bentho-planktonic forms of diatoms, coccolithophores Emiliania huxleyi) capable of withstanding a high level of toxic load. Thus, the phytoplankton community is capable of restoring its abundance and photosynthetic activity after acute toxic stress. However, the ability of the community to survive under conditions of chronic contamination is achieved at the cost of simplification of its structure, which leads to a loss of stability and self-regulation and, in the long term, reduces the production potential of the ecosystem.