Harikumar Puthenveedu Sadasivan Pillai

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that are of global concern due to their environmental persistence, bioaccumulation potential, and adverse ecological and human health impacts. This study presents the first comprehensive baseline assessment of the distribution, sources, and risks of the indicator PCBs in the Ashtamudi Wetland listed in Ramsar, a tropical estuarine ecosystem on the southwest coast of India. Surface sediment and water samples were analyzed for six indicator PCB congeners (PCB-28, 52, 101, 138, 153 and 180). Total PCB concentrations in sediments ranged from 0.20 to 2.99 µg/kg dry weight, with a mean of 0.70 ± 0.65 µg/kg dw, indicating moderate contamination compared to global coastal environments. The congener distribution followed the order: hexa-CBs > tri-CBs > penta-CBs > tetra-CBs > hepta-CBs. Elevated concentrations near urban and industrial discharge zones indicate localized anthropogenic sources. Multivariate statistical analyzes, including Cluster Analysis and Positive Matrix Factorization (PMF), identified three primary contributors: Aroclor-type mixtures, open waste burning, and legacy e-waste contamination. The ecological risk assessment showed low potential for adverse effects, while the human health risk assessment revealed no unacceptable non-carcinogenic or carcinogenic risks through sediment ingestion or dermal contact. Because only six congeners were analyzed, the findings reflect a conservative estimate of overall PCB contamination. The study underscores the importance of integrated monitoring through chemical analysis, source allocation, and risk assessment to manage persistent pollutants in ecologically sensitive wetland ecosystems.

Bimetallic nanoparticles (BNPs) have been used as a new line of defence against heavy metal contamination among several types of nanoparticles (NPs) due to their enhanced, synergistic activity. In this study, we investigated the adsorption behaviour of porous (styrene–divinylbenzene)/CuNi bimetallic nanocomposite (P(St-DVB)/CuNi BNC) in a continuous flow fixed-bed column and its ability to remove Pb (II), Cd (II), and Zn (II) ions from aqueous solutions. We examined how the initial metal concentration, flow rate, and bed height affected the adsorption characteristics. Experimental results confirmed that the adsorption capacity increased with increase in influent metal concentration and bed height and decreased with increase in flow rate. The breakthrough and the column kinetic parameters were successfully predicted with three mathematical models: Thomas, Yoon–Nelson, and Adams–Bohart models. Both Thomas and Yoon–Nelson models showed good agreement with the experimental results for all the operating conditions. Successful desorption of heavy metals from the P(St-DVB)/CuNi BNC was performed using 0.5 M NaOH solution, and it showed good reusability of the adsorbent during four adsorption–desorption cycles. The results show that P(St-DVB)/CuNi BNC are effective and low-cost adsorbents, and they can be used in real-time large-scale industrial water treatment processes for the removal of heavy metals.

Wetlands are one of the most important ecosystems on earth, which help sustain life, yet they are reported to be at the receiving end of the high rate of pollution. The state of Kerala on the southwest coast of India is bestowed with several wetlands including Ramsar sites. Although the larger wetlands have been extensively studied, smaller or local wetlands have often been neglected; however, the environmental problems will be first reflected in the small wetlands. In this study, the ecological risk assessment of core sediments of one such site, the Biyyam wetland, a wetland of national importance, is reported for the first time. Sediment core samples were collected from four different stations of Biyyam wetland, and concentrations of heavy metals such as Ni, Zn, Mn, Cu, Cd, and Pb were determined. Statistical analysis indicated that correlation among different metals differed with respect to stations, but the percentage of organic matter showed a positive correlation with the concentration of the metals. The mean concentrations of Ni, Pb, and Cd exceeded the global average shale value. The quality of the sediments was assessed based on numeric Sediment Quality Guidelines. The degree of Contamination, Pollution Load Index, Enrichment Factor, Geoaccumulation Index, Ecological Risk Index, Toxic Unit, and Toxic Risk Index were used to evaluate the ecotoxicity of the heavy metals in the sediment core samples. The results inferred serious anthropogenic pollution in the wetland, and Cd was reported as the prominent metal contributing to heavy metal toxicity and ecological risk in the study area, which may in long run be toxic to the aquatic ecosystem.

Currently, bimetallic nanoparticles, composed of two different metal elements, have drawn great interest in drinking water treatment among various types of nanoparticles. Bimetallic nanoparticles have a greater surface area which increases their adsorption power as compared to those of monometallic nanoparticles. In the present study, we investigated the sorption behaviour of CuNi bimetallic nanoparticle and its ability to remove Cd²⁺, Pb²⁺ and Zn²⁺ions from aqueous solutions. The structural and chemical analysis of synthesised nanoparticle was determined using Scanning Electron microscopy (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectra (EDS), powder X-ray diffraction (PXRD) and surface area studies. Batch mode adsorption studies were conducted and various physico-chemical parameters such as contact time, pH, initial metal ion concentration, and adsorbent dosage level were studied. The result revealed that the adsorption of heavy metals follows the order: Zn²⁺>Pb²⁺>Cd²⁺. The percentage removal of all ions were strongly dependent on the pH and the removal efficiency is enhanced in higher pH values. The optimum pH for the removal of cadmium was 9, and for the removal of zinc and lead, it was 7. The optimum dose of adsorbent for the removal of zinc was 0.4 g, and the dose of adsorbent for the removal of lead and cadmium was 0.5 g. The adsorption isotherms were described by Freundlich and Langmuir isotherm models. Pseudo-first and second-order models were used to evaluate the mechanism of adsorption, and the results showed that the adsorption reaction was fitted very well to the Langmuir isotherm model and the pseudo-first-order kinetic model. In addition, the synthesised CuNi bimetallic nanoparticle showed a high efficiency in adsorption than Cu nanoparticle. This may be due to the increased surface area of the bimetallic nanoparticle as compared to their monometallic counterpart and the synergic effect between the two metals. The results illustrated that the synthesised nanoparticle can be used as an efficient sorbent for the removal of heavy metals from aqueous solutions.