Ecotoxicity of a mixture of nanoparticles on algal species Scendesmus obliquus in OECD growth media, wastewater, and pond water.

The possible impact of ZnO and CuO nanoparticles (NPs) (individually and in binary mixture) was investigated using the freshwater microalgae, Scenedesmus obliquus. The present study shows the effect of nanoparticles on algae in OECD growth media, wastewater, and pond water during a 96-h toxicity test. At 0.1 mg/L concentration of the mixture of NPs, the reduction in the chlorophyll a content was 13.61 ± 1.34% (OECD media), 28.83 ± 1.85% (wastewater), and 31.81 ± 2.23% (pond water). Values of reduction in biomass were observed to be 42.13 ± 1.38, 39.96 ± 1.03, and 33.10 ± 1.29% for OECD media, wastewater, and pond water, respectively. The highest increase in lipid values was observed in the case of pond water (6.3 ± 1.31%). A significant increase in the value of EPS-generated protein was observed in the wastewater sample. EPS-generated carbohydrate values were increased in OECD media but decreased in the wastewater matrix. The transmission electron microscope images showed structural damage to algae cells due to the exposure to a mixture of nanoparticles at higher concentrations. Fourier transform infrared analysis showed an addition of bonds and differences in the peak and its intensity during exposure to high concentrations of NPs. Overall, this study gives fundamental insights into the interaction and toxicity of a mixture of NPs to algal species in different water matrices.

Effect of long-term exposure of mixture of ZnO and CuO nanoparticles on Scenedesmus obliquus.

The present study investigated the possible toxic effect of ZnO and CuO nanoparticles (NPs) on freshwater microalgae, Scenedesmus obliquus at environmentally- relevant nanoparticle concentration (1 mg/L) and high concentration (10 mg/L) in BG-11 medium under white light LED-illumination over 35 days. The effect of time on the stability of media, nanoparticles, and their relation to toxicity to algae was also studied. The transmission electron microscopy indicated structural damage to algae due to the presence of a mixture of nanoparticles (at 10 mg/L). FTIR (Fourier Transform infrared) analysis of a sample containing a mixture of nanoparticles showed an addition of bonds and a difference in the peak location and its intensity values. The inhibition time for biomass was observed between 14 days and 21 days at 10 mg/L NPs. At 1 mg/L, the order of toxicity of NPs to algae was found to be: CuO NPs (highest toxicity) > ZnO NPs>ZnO + CuO NPs (least toxicity). During exposure of algae cells to a mixture of NPs at 10 mg/L NP concentration, a smaller value of metal deposition was observed than that during exposure to individual NPs. Antagonistic toxic effects of two NPs on dry cell weight of algae was observed at both concentration levels. Future work is needed to understand the steps involved in toxicity due to mixture of NPs to algae so that environmental exposures of algae to NPs can be managed and minimized.

Quantitative Assessment of Microbial Pathogens and Indicators of Wastewater Treatment Performance for Safe and Sustainable Water Reuse in India.

Currently, there is no data on the molecular quantification of microbial indicators of recycled water quality in India. In this study, multiple microbial pathogens and indicators of water quality were evaluated at three wastewater treatment plants located in two Indian cities (New Delhi and Jaipur) to determine the treatment performance and suitability of recycled water for safe and sustainable reuse applications. Real-time polymerase chain reaction (PCR) was used for the rapid evaluation of six human pathogens and six microbial indicators of fecal contamination. Among the microbial indicators, pepper mild mottle virus (PMMoV), F+RNA-GII bacteriophage, Bacteroides thetaiotamicron, and four human pathogens (Norovirus genogroups I & II, Giardia, and Campylobacter coli) were detected in all of the influent samples analyzed. This work suggests that the raw influents contain lower levels of noroviruses and adenoviruses and higher levels of Giardia compared to those reported from other geographic regions. Overall, the efficacy of the removal of microbial targets was over 93% in the final effluent samples, which is consistent with reports from across the world. PMMoV and Giardia were identified as the best microbial targets, from the microbial indicators spanning across bacteria, bacteriophages, DNA/RNA viruses, and protozoan parasites, by which to evaluate treatment performance and recycled water quality in Indian settings, as they were consistently present at high concentrations in untreated wastewater both within and across the sites. Also, they showed a strong correlation with other microbial agents in both the raw influent and in the final effluent. These findings provide valuable insights into the use of culture-independent molecular indicators that can be used to assess the microbial quality of recycled water in Indian settings. IMPORTANCE Wastewater treatment plants (WWTPs) have rapidly increased in India during the last decade. Nonetheless, there are only a few labs in India that can perform culture-based screening for microbial quality. In the last 2 years of the pandemic, India has witnessed a sharp increase in molecular biology labs. Therefore, it is evident that culture-independent real-time PCR will be increasingly used for the assessment of microbial indicators/pathogens in wastewater, especially in resource-limited settings. There is no data available on the molecular quantitation of microbial indicators from India. There is an urgent need to understand and evaluate the performance of widely used microbial indicators via molecular quantitation in Indian WWTPs. Our findings lay the groundwork for the molecular quantitation of microbial indicators in WWTPs in India. We have screened for 12 microbial targets (indicators and human pathogens) and have identified pepper mild mottle virus (PMMoV) and Giardia as the best molecular microbiological indicators in Indian settings.