Algal extracellular polymeric substances (algal-EPS) for mitigating the combined toxic effects of polystyrene nanoplastics and nano-TiO2 in Chlorella sp

The continuous release of nanoparticles and nanoplastics into the marine environment necessitates the examination of their combined effects in marine organisms. Natural Organic Matter (NOM) can significantly influence the behavior of nanomaterials in the marine environment. The present study explores the effects of algal Extracellular Polymeric Substances (EPS) in reducing the combined toxic effects of three different polystyrene nanoplastics (PSNPs)- aminated (NH₂-PSNPs), carboxylated (COOH-PSNPs), and plain PSNPs - and P25 titanium dioxide nanoparticles (Nano-TiO₂) towards the marine alga, Chlorella sp. Two doses (0.25 and 2.5 mg/L) of nano-TiO₂ mixed with the PSNPs (1 mg/L) were employed. The COOH-PSNPs with 2.5 mg/L nano-TiO₂ exhibited higher growth inhibition toward algal cells. Addition of algal EPS to the mixture of NMs decreased the negative effect significantly. The mean hydrodynamic diameter increased significantly from 666 to 797 nm and 1248 to 3589 nm at concentrations 0.25 and 2.5 mg/L, respectively when the mixtures of nano-TiO₂ and COOH-PSNPs were incubated with the algal EPS. In comparison to the pristine NMs, the EPS-NMs were found to significantly reduce the superoxide and hydroxyl radical production. The results were further validated with the estimation of lipid peroxidation (LPO), esterase activity, photosynthetic efficiency, and membrane permeability in the cells. The major outcomes from this study highlight the role of algal EPS in significantly reducing the toxic impact of binary mixture of NMs in marine organisms.

Polystyrene nanoplastics diminish the toxic effects of Nano-TiO2 in marine algae Chlorella sp

Widespread usage of nano-TiO₂ in various commercial products and their consequent release into the seawater pose a severe threat to marine biota. Nanoplastics, a secondary pollutant in the marine environment, could influence adverse effects of nano-TiO₂. The main goal of the present study was to investigate the influence of the differently functionalized polystyrene nanoplastics (COOH-PSNPs, NH2-PSNPs, and Plain-PSNPs) on the acute toxic effects of P25 nano-TiO₂ in marine algae Chlorella sp. Three different concentrations of nano-TiO₂, 0.25, 0.5, and 1 mg/L, mixed with 5 mg/L of the PSNPs were employed in this study. A substantial increase was noted in mean hydrodynamic sizes of nano-TiO₂ when they were mixed with the PSNPs. This hetero-aggregation would reduce the bioavailability of the particles to the algae. The presence of the PSNPs in the mixture reduced the toxicity of nano-TiO₂ significantly. A signficant decline in the oxidative stress parameters like total ROS, superoxide (), and hydroxyl radical generation was noted for the mixture of nano-TiO₂ with the PSNPs in comparison with the pristine counterparts. The lipid peroxidation, and the antioxidant enzyme activities in the cells correlated well with the reactive species generation results. The treatments with the mixture resulted in notable enhancement in the esterase activity in the cells. The Independent Action model suggested antagonistic interactions between PSNPs and nano-TiO₂. The results from this study clearly demonstrate that nano-TiO₂ in presence of the PSNPs exerted significantly reduced cytotoxic effects in Chlorella sp, in comparison with the pristine particles.

Eco-corona formation on the nanomaterials in the aquatic systems lessens their toxic impact: A comprehensive review

Recent studies have shown that nanosized materials including plastics as a major cause of concern in the aquatic ecosystem. Fortunately, in the aquatic environment, the surface of the materials is often colonized by exudates of aquatic microorganisms (biofilm), where these materials are attached and surrounded by a secreted matrix with a sticky layer. The significance of these biofilms on the existence and beneficial implications of these pollutants has been studied in recent decades. Here we develop the concept of these pollutants as a complex matrix of polymers to which Extracellular Polymeric Substances (EPS) binds to form eco-corona modifying its density and surface charge of these particles. This review critically integrates the outstanding properties and functions of algal EPS in the aquatic environment and their dynamic interactions of early colonization on the surface of these pollutants, the impact of biofilm formation on stability, reactivity and, toxicity from the current literature. Due to the modifications of the environmental processes, EPS can have an impact on the toxicity thus special attention is focused on their behavior to decrease the toxicity of the pollutants in the aquatic environment. Although there has been an increasing number of researches in this area, further progress is needed to explore the extent to which ecological processes could be impacted, including the modifications in the behavior of aquatic pollutants. Thus, this review provides a recent perspective into the mechanisms of how eco-corona formation mitigates the toxicity of nanomaterials prevalent in aquatic ecosystems.

Eco-corona formation lessens the toxic effects of polystyrene nanoplastics towards marine microalgae Chlorella sp

Unabated use of nanoplastics (<1 μm) in the consumer products and their consequent release to the marine environment poses a substantial threat to the marine ecosystem. The toxic impact of the nanoplastics on marine microalgae is yet to be explored in detail, and the role of reactive oxygen species generation remains largely unclear. The algal exudates constitute a significant part of the natural organics present in the marine system that may readily adsorb over the nanoplastics to form eco-corona. In the current work a marine alga, Chlorella sp., was considered a bioindicator organism and the effects of eco-corona formation in lessening the toxic impact of the nanoplastics was analyzed. Three differently functionalized polystyrene nanoplastics (PS NPs): Aminated (NH₂-PS NPs), Carboxylated (COOH-PS NPs) and Plain nanoplastics were aged (12, 24, and 48 h) in the EPS containing medium to facilitate eco-corona formation. Decline in cell viability, membrane integrity, and photosynthetic yield were considered to be principle toxicity indicators. The role of oxidative stress as key mode of action (MOA) was studied considering generation of overall reactive oxygen species, and specific radicals (hydroxyl and superoxide) as relevant markers. The changes in antioxidant enzyme activities (superoxide dismutase, and catalase) were also measured. The results clearly indicate a significant decline in the oxidative stress and corresponding lessening of the toxic effects due to eco-corona formation on the PS NPs. The response varied with surface charge on the NPs and ageing duration. Considering the increasing importance of the nanoplastics as one of the major emerging pollutants in marine ecosystem, this study strongly suggests that the EPS mediated eco-corona formation may substantially lessen their toxic burden.

Assessing groundwater quality for drinking water supply using hybrid fuzzy-GIS-based water quality index

Groundwater is a vital source of freshwater in both urban and rural regions of the world. However, its injudicious abstraction and rapidly increasing contamination are posing a severe threat for sustainable water supply worldwide. Geographical Information System (GIS)-based groundwater quality evaluation using Groundwater Quality Index (GQI) has been proved to be a cost-effective tool for assessing groundwater quality and its variability at a larger scale. However, the conventional GQI approach is unable to deal with uncertainties involved in the assessment of environmental problems. To overcome this limitation, a novel hybrid framework integrating Fuzzy Logic with the GIS-based GQI is proposed in this study for assessing groundwater quality and its spatial variability. The proposed hybrid framework is demonstrated through a case study in a hard-rock terrain of Southern India using ten prominent groundwater-quality parameters measured during pre-monsoon and post-monsoon seasons. Two conventional GIS-based GQI models GQI-10 (using all the ten groundwater-quality parameters) and GQI-7 (using seven 'concerned/critical' groundwater-quality parameters) as well as hybrid Fuzzy-GIS-based GQI (FGQI) models (using seven critical parameters) were developed for the two seasons and the results were compared. The Trapezoidal membership functions classified the model input parameters into 'desirable', 'acceptable' and 'unacceptable' classes based on the experts' knowledge and water quality standards for drinking purposes. The concentrations of Ca²⁺, Mg²⁺, and SO₄^2- in groundwater were found within the WHO desirable limits for drinking water throughout the year, while the concentrations of seven parameters (TDS, NO₃^--N, Na⁺, Cl^-, K⁺, F^- and Hardness) exceed their permissible limits during pre-monsoon and post-monsoon seasons. A comparative evaluation of GQI models revealed that the FGQI model predicts groundwater quality better than the conventional GQI-10 and GQI-7 models. GQI modeling results suggest that the groundwater of most of eastern and southern parts (∼60% in pre-monsoon season; ∼90% in post-monsoon season) of the study area is unsuitable for drinking. Further, the groundwater quality deteriorates during post-monsoon seasons compared to pre-monsoon seasons, which indicates an increased influx of contaminants from different industries, mining areas, waste disposal sites and agricultural fields during monsoon seasons. This finding calls for the strict enforcement of regulations for proper handling of effluents from various contamination sources in the study area. It is concluded that the fuzzy logic-based decision-making approach (FGQI) is more reliable and pragmatic for groundwater-quality assessment and analysis at a larger scale. It can serve as a useful tool for the water planners and decision makers in efficiently monitoring and managing groundwater quality at watershed or basin scales.