A Multidisciplinary Approach to Evaluate the Effects of Contaminants of Emerging Concern on Natural Freshwater and Brackish Water Phytoplankton Communities

SIMPLE SUMMARY: Zinc oxide nanoparticles (ZnO NPs) and potassium dichromate (K(2)Cr(2)O(7)) are two contaminants of emerging concern (CECs; chemicals not commonly monitored in the environment but has the potential to enter the environment and cause known or suspected adverse ecological and/or human health effects). On this path, phytoplankton species, because of their photosynthetic activity, are vital for providing oxygen, and environmental impacts on such organisms can disrupt an entire ecosystem’s integrity. Generally, ecotoxicological assays on monospecific phytoplankton cultures provide useful information about the cellular effects of toxic compounds; however, they have limited application for detecting the effects of environmental pollutants on multiple species communities like in nature. For this reason, in this study, we took for the first time an ecotoxicological (growth rate and inhibition growth rate), ecological (taxonomic identification of species and diversity in communities), and biochemical (photosynthetic pigments) approach to evaluate the effects of ZnO NPs and K(2)Cr(2)O(7) on natural freshwater and brackish water phytoplankton communities. Results show that both chemicals have negative effects on natural phytoplankton communities with an alteration of the growth rate, species composition, and photosynthetic activity. However, the exposure to ZnO 10 mg/L acts as a growth stimulant for phytoplanktonic communities. Our findings provide evidence for alterations in natural phytoplankton after exposure to such CECs. ABSTRACT: Ecotoxicological assays on monospecific phytoplankton have limited application for detecting the effects of environmental pollutants on multiple species communities. With this study, we took an ecotoxicological, ecological, and biochemical approach to evaluate the effects of two contaminants of emerging concern (zinc oxide nanoparticles, ZnO NPs, and potassium dichromate, K(2)Cr(2)O(7)) at different concentrations (K(2)Cr(2)O(7) 5.6–18–50 mg/L; ZnO NPs 10–100–300 mg/L) on natural freshwater and brackish water phytoplankton communities. Cell density and absorbance values decreased in freshwater and brackish water phytoplankton communities after exposure to ZnO NPs (100 mg/L and 300 mg/L only for freshwater), whereas growth rate was increased in both freshwater and brackish water phytoplankton communities after exposure to ZnO NPs 10 mg/L. Differently, there was no clear relationship between concentration and inhibition growth after exposure to K(2)Cr(2)O(7): the lowest cell density was recorded after exposure to 18 mg/L. Moreover, the evenness index value was lower compared to the other concentrations, indicating the growth of a few, albeit resistant species to higher K(2)Cr(2)O(7) concentrations. Generally, Bacillariophyceae and Dinoficee were prevalent in phytoplankton cultures after exposure to ZnO NPs and K(2)Cr(2)O(7). The Shannon-Wiener index was slightly higher in the negative than the positive controls, but diversity was low after all treatments in both ecotoxicological assays. The evenness index was always very close to zero, indicating the numerical predominance of one or very few species. Finally, the decrease in chlorophyll-a and pheophytin-a in both ecotoxicological assays indicated a change in photosynthetic activity. Our findings provide evidence for alterations in natural phytoplankton after exposure to emerging contaminants that can disrupt an entire ecosystem’s integrity.