Interaction of Nanoparticles with Algae-Bacteria Consortia: Effect on Growth Parameters and Toxicity Due to Long-Term...

Due to the increasing concentration of the mixture of nanoparticles in the aquatic system, the interaction of nanoparticles with algae-bacteria consortia has increased immensely, leading to toxicity. The present study investigated the effect of long-term exposure (35 days) of CuO and ZnO nanoparticles (NPs) on the growth of consortia of Scenedesmus obliquus and Escherichia coli in BG-11 medium. The effects of NP concentrations (0, 0.1 mg/L, 1 mg/L, 10 mg/L, and 100 mg/L) on consortia at a ratio of algae to bacteria (100:1) were studied. At an environmentally- relevant NP concentration of 0.1 mg/L, the order of reduction in chlorophyll a (or chlorophyll b or biomass) was found to be: CuO alone > ZnO NPs > mixture of NPs. Overall, the exposure of algae-bacteria consortia to the 0.1 mg/L mixture of NPs resulted in a lesser effect on the growth and biomass production than that due to exposure to one type of NPs. After 35 days, the increase in lipid content for the combination of nanoparticles was estimated to be 0.74 ± 1.38%, 1.28 ± 1.33%, 2.68 ± 1.73%, and 4.51 ± 2.11%, respectively. At the environmentally-relevant 0.1 mg/L concentration, the order of toxicity, based on the reduction in growth parameters (e.g., chlorophyll), was consistently observed as: CuO NPs > ZnO NPs > Mixture of NPs. The primary hypothesis of mechanisms, as supported by the data, is that the NPs heteroaggregate which in turn reduces the overall bioavailability of the toxic components to the microbial consortia over the long-term exposure period.