Atmospheric deposition of mineral dust and associated nutrients over the Equatorial Indian Ocean.

Aerosols are potential supplier of nutrients to the surface water of oceans and can impact biogeochemical processes particularly in the remote locations. The nutrient data from atmospheric supply is poorly reported from the Indian Ocean region. In this study, we present atmospheric nutrients such as reactive nitrogen species (Nitrate, Ammonium, Organic nitrogen), micro-nutrients (e.g. Fe, Mn and Cu) concentration along with mineral dust in the aerosol samples collected over meridional transect during summer (April-May 2018) and monsoon (June-July 2019) months. A significant spatial variation of dust was observed during summer (0.6-22.8 µg m-3) and monsoon (2.8-25.1 µg m-3) months with a decreasing trend from north to south. Dust as well as other nutrient species shows a general north to south decreasing trend, however, no such trend was seen in the soluble trace elements (TEs) concentration. Anthropogenic species like NH4+ and nss-K+ were found below detection limit during monsoon campaign. The fractional solubility (in percentage) of Fe, Mn and Cu were estimated by measuring their concentration in ultrapure water leach which averaged around 0.99 ± 1.12, 31.0 ± 14.9 and 31.1 ± 25.4, respectively during summer and 0.09 ± 0.08, 6.0 ± 8.9, 16.7 ± 9.6, respectively, during monsoon period. Correlation of soluble Fe with total Fe and total acidic species suggest varying dust sources is an important controlling factor for the fraction solubility of Fe with negligible contribution from the chemical processing. However, a significant correlation was observed between total acid and fractional solubility of Mn and Cu suggest role of chemical processing in enhancement of their solubility. Dry deposition flux of aeolian dust was estimated for both campaign using Al concentration and relatively higher fluxes were observed for summer (12.6 ± 8.4 mg·m-2·d-1) and monsoon (8.7 ± 8.4 mg·m-2·d-1) months as compared to model based estimates reported in the literature. Contrastingly, estimated deposition flux of soluble Fe from both campaign displays relatively lower values as compared to model based results which underscores a need for re-evaluation of biogeochemical models with real-time data.

Identification and physico-chemical characterization of microplastics in marine aerosols over the northeast Arabian Sea.

Microplastics (MPs) in the atmosphere can undergo long-range transport from emission regions to pristine terrestrial and oceanic ecosystems. Due to their inherent toxic and hazardous characteristics, MPs pose serious risks to both human well-being and the equilibrium of ecosystem. The present study outlines the comprehensive characterization, spanning physical and chemical attributes of MPs associated with atmospheric aerosols. Total suspended particulates (TSPs) were collected on a quartz fibre filter by operating a high-volume sampler for 24 h during distinct years (March, 2016 and November, 2020) at a coastal location in the northeast Arabian Sea. Subsequent to the sampling, a series of techniques were applied including density separation. The assessment and scrutiny of the MPs was carried out using stereo-zoom microscopy with supplementary validation using advanced fluorescence microscopy for enhanced precision in identification. Our comparative assessment suggests peroxide treatment followed by density separation could be a robust procedure for the definitive identification and characterization of MPs in the atmosphere. Average total abundance of MPs was found to be 1.30 ± 0.14 n/m3 in 2016 and 1.46 ± 0.12 n/m3 in 2020 with fibres, fragments and films having similar relative contributions (41 %, 31 %, 28 % in 2016 and 40 %, 35 %, 25 % in 2020). Fibres were found to be dominant morphotype followed by fragments and films over the coastal region of the Arabian Sea. In order to unravel the detailed chemical nature of these MPs, spectral analysis using µ-FTIR was carried out. The outcome of the analysis showed prevailing polymers as polyvinyl chloride and polymethyl methacrylate (50545 %) as dominant polymers followed by polyester (15 %), styrene butyl methacrylate (11 %), and polyacetal (9 %). MPs present in the vicinity of the Arabian Sea have potential to supply nutrients and toxicants, consequently can contribute to the modulation of the surface water biogeochemical processes.

Antimicrobial and dye degradation application of fungi-assisted silver nanoparticles and utilization of fungal retentate biomass for dye removal.

The present study utilized Aspergillus spp. for the synthesis of silver nanoparticles (AgNPs); the developed AgNPs were categorized using analytical techniques, that is, ultraviolet-visible (UV-vis) spectrophotometer, Zeta-potential, dynamic light scattering (DLS), and transmission electron microscopy (TEM). A sharp peak of 463 nm highlighted the synthesis of AgNPs; further Zeta-potential of -16 mV indicates stability of synthesized AgNPs. The TEM micrograph showed spherical and hexagonal shapes of synthesized AgNPs of 6-25 nm. The photocatalytic activity of fungal-mediated AgNPs was evaluated for degradation of reactive yellow dye in the concentration range of 20-100 mg L-1 . The results showed efficient degradation of dye using AgNPs in short span of time. For antibacterial activity, synthesized AgNPs, antibiotic, and AgNPs + antibiotic were tested. As per results, the zone of inhibition (ZOI) of AgNPs showed the values of 13 and 10 mm for Escherichia coli and Staphylococcus aureus, respectively. Further, the ZOI of penicillin highlighted the values of 18 and 17 mm for E. coli and S. aureus, respectively. When AgNPs and penicillin were used in combination, a clear synergistic effect was observed; the ZOI showed 0.49- and 0.36-fold increase in area against E. coli and S. aureus, respectively, in comparison with penicillin or AgNPs alone. Further, the leftover biomass (retentate biomass) was used to decolorize the reactive yellow dye at different initial concentration ranging from 20 to 100 mg L-1 . It was observed that 1 g L-1 retentate biomass (BR ) can effectively remove 82%-100% dye at 20 and 100 mg L-1 initial dye concentration. Results also indicated that with increase in initial reactive dye concentration from 20 to 100 mg L-1 , the decolorization capacity of retentate biomass (BR ) (at 0.2 g L-1 ) decreased from 79.2% to 32.3%. However, the use of AgNPs synthesized leftover fungal biomass can be a good option for up taking the additional dyes/contaminants, and also as leftover biomass can be utilized effectively, it can prove to be an excellent approach for environment safety. As the literature studies did not mentioned the further use of retentate biomass, the present study provides an excellent approach for further research on this aspect. PRACTITIONER POINTS: Synthesis of AgNPs from Aspergillus spp. and characterized with the help of a U.V-vis spectrophotometer, a zeta potential, DLS and TEM. The developed AgNPs were used for antibacterial and dye degradation activity. The left over (retentate) fungal biomass was used further for additional dye degradation activity.