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Microplastics in oral healthcare products (OHPs) and their environmental health risks and mitigation measures

The environmental input of microplastics from personal care products has received significant attention; however, less focus has been paid to oral healthcare products. The present study assessed the occurrence of microplastics in commercially available oral healthcare products such as toothbrushes, toothpastes, toothpowder, mouthwash, dental floss, and mouth freshener spray that have a pan-India distribution. The extracted microplastics were quantified and characterised using a microscope and ATR-FTIR. All products showed microplastic contamination, where toothbrushes showed the maximum particles (30–120 particles/brush) and mouth freshener sprays (0.2–3.5 particles/ml) had the least abundance. Fragments, fibres, beads, and films were the various shapes of microplastics observed, where fragments (60%) were dominant. Various colours such as pink, green, blue, yellow, black, and colourless were observed, where colourless (40%) particles were dominant. Microplastics were categorized into three sizes: <0.1 mm (63%), 0.1–0.3 mm (35%), and >0.3 mm (2%). Four major types of polymers, such as polyethylene (52%), polyamide (30%), polyethylene terephthalate (15%), and polybutylene terephthalate (3%), were identified. Risk assessment studies such as Daily Microplastics Emission (DME), Annual Microplastics Exposure (AME), and Polymer Hazard Index (PHI) were carried out. The DME projection for India was the highest for mouthwash (74 billion particles/day) and the least for mouth freshener sprays (0.36 billion particles/day). The AME projection for an individual was the highest in toothbrushes (48,910 particles ind.−1 yr.−1) and the least in mouth freshener sprays (111 particles ind.−1 yr.−1). PHI shows that the identified polymers fall under the low-to high-risk categories. This study forecasts the community health risks linked to microplastics in oral healthcare products and suggests mitigation strategies. It has the potential to shape environmental policy development in response.

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Importance of Seasonally Evolving Near‐Surface Salinity Stratification on Mixed Layer Heat Budget During Summer Monsoon Intraseasonal Oscillation in the Northern Bay of Bengal in 2019

AbstractThe discharge of freshwater from major rivers into the northern Bay of Bengal (BoB) increases dramatically during the summer monsoon season, reaching a peak in August–September, and there is a corresponding increase in the vertical salinity gradient in the upper ocean. Here we study the impact of seasonally evolving near‐surface salinity stratification on the response of ocean mixed layer temperature (MLT) to Summer Monsoon Intraseasonal Oscillations (MISO), using accurate surface fluxes and high vertical resolution (∼2 m) hydrographic measurements from a mooring in the northern BoB (17.8°N, 89.5°E) during June–September 2019. Prominent MLT warming and cooling with a range of 1.5°C is observed between suppressed (clear skies, calm winds) and active (cloudy, windy) phases of MISO convection. However, the intraseasonal MLT response to the active phase of a late‐season MISO event is minimal compared to MISO events in early summer. We infer this is primarily due to the much smaller contribution from oceanic vertical processes (∼6 Wm−2) in late summer 2019, compared to their role in early summer (−15 to −55 Wm−2). During the active phase of the MISO event of late summer 2019, the combined effect of reduced entrainment and weak vertical temperature gradients associated with a barrier layer inhibits near‐surface cooling. Conversely, the near‐surface salinity stratification and the barrier layer are weak during MISO events in the early summer of 2019—these hydrographic conditions lead to enhanced MLT cooling in response to MISO, apparently through a freer turbulent exchange of cool thermocline water with the surface layer.

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Spatial variability in plankton metabolic balance in the tropical Indian Ocean during spring intermonsoon

The tropical Indian Ocean consists of three basins, namely the Arabian Sea (AS), Bay of Bengal (BoB) and Southern Indian Ocean (SIO), with relatively nutrient-rich waters in the former two basins. It is hypothesized that the excess carbon produced in the northern Indian Ocean may support heterotrophic carbon demand in the SIO. In order to test this hypothesis, deck incubation experiments were conducted during the spring intermonsoon under the aegis of the Indian-GEOTRACES program. Nutrients in the mixed layer were low in the SIO compared to AS and BoB due to strong thermal stratification in the former region. Dominant net autotrophy was noticed in the AS whereas net heterotrophy in the BoB and SIO. High community respiration (CR) was observed in the BoB which may be supported by riverine organic carbon, whereas in situ produced and advected excess carbon from the northern Indian Ocean may support in AS and SIO respectively. Net community production (NCP) displayed an inverse (linear) relationship with temperature (salinity) in the euphotic zone in the BoB and SIO suggesting that stratification driven by river discharge and equatorial currents, respectively, reduced nutrients inputs through vertical mixing in the upper ocean resulting in the formation of the strong net heterotrophy and contrast to this was found in the AS due to increase in primary production due to nitrogen fixation. The euphotic zone integrated nutrients displayed a linear relationship with NCP and Gross Primary Production (GPP) indicating that the availability of nutrients controlled the plankton metabolic rates in the tropical Indian Ocean. The threshold of GPP for plankton metabolic balance in the tropical Indian Ocean (1.9 mmol O2 m−3 d−1) was close to that of the global mean (2.2 mmol O2 m−3 d−1). The slope of the log-log relationship between GPP and CR was 0.5 and it is close to that of the global mean value of 0.60.

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Natural opening of a new inlet in Chilika Lagoon: A cause and impact analysis

Natural opening of inlet(s) is very common along the shorefront of Chilika Lagoon. Inlet openings in most of the cases have been triggered due to the narrow spit width and cyclonic storm/ depression (CS/D). Wave height and energy get further enhanced when the CS/D occurs concurrently with a full moon/ new moon with a lag/lead of 2–3 days. This has happened many times in the past. Recently, a new inlet was opened on 13th July 2022 due to deep depression (DD) over the northwestern Bay of Bengal from 09th to 12th July 2022. A cyclonic circulation prevailed over the northwest and adjoining west-central Bay of Bengal off the south Odisha-north Andhra Pradesh coast in lower and mid-tropospheric levels tilting southwestwards with height. Wave heights during the pre and post-inlet opening period spanning over one month suggest the peak wave condition coinciding with the period of the inlet opening. Geomorphological conditions of the spit before and after the inlet opening were monitored. Results indicate fast expansion of inlet width due to erosion of the spit on both sides of the inlet and the tidal incursion into the lagoon predominantly during the full-moon day/new moon day. After the opening of a narrow inlet of width 246 m on 13 July 2022, it was doubled within a month. Shoreline analysis using Sentinel 2A imagery for pre- and post-inlet opening was carried out and validated with observations. Oceanographic conditions near the new inlet were simulated and monitored by deploying a Seaguard RCM current meter with a pressure and temperature sensor. This study assessed the reasons for the inlet opening and monitored the geomorphological changes after the inlet opening. More importantly, the impact of the new inlet on lagoon ecosystem was assessed, which has severe implications for the management of the lagoon ecosystem.

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Modern sedimentation on the eastern continental shelf of India: Assessing the provenance and sediment dispersal pattern

Sediments deposited on the eastern continental shelf of India are studied for texture, mineralogy and their major, trace, and rare earth elemental composition in lithogenic fraction. The objective of this study was to identify the sources, and evaluate the factors affecting the erosion and weathering in the catchment area and dispersal and deposition of sediments over the shelf region. Here, we present an extensive dataset covering the entire eastern continental shelf of India from the Ganges-Brahmaputra (G-B) basin in the north including the shelf off major peninsular Indian river basins of Mahanadi, Godavari, and Krishna up to the Kaveri basin in the southern tip.Textural and geochemical studies have shown that the lithology of the source rocks plays an important role in governing the chemistry and mineralogy of the sediments. The results show that the G-B shelf sediments are primarily derived from the Higher Himalaya Crystalline sequence (HHCS) and the Tethyan sedimentary series (TSS) exposed along the peaks and drainage divide of the Himalayas. Mahanadi shelf sediments are mainly derived from the felsic rocks belonging to Precambrian metamorphic formations of the Eastern Ghats, limestones, sandstones, and shales of the Gondwanas and recent deltaic alluvium deposits, whereas the Krishna-Godavari (K-G) sediments find a part of their source in the Deccan Basalts. The shelf sediments off River Kaveri are derived from a mixture of peninsular granitic gneisses, tonalite-trondjhemite gneisses, and charnockites. The sediment geochemistry has also allowed us in assessing the weathering patterns in the source areas. The sediments have undergone a moderate degree of weathering. Weathering intensities were found to have varied with the source area lithology.The least square regression of the geochemical data allowed us to estimate the relative contribution of each of these sources and their geographic extent. Unlike the massive offshore deposition and formation of a major Fan system (the Bengal fan), the fluvial sediment dispersal of the mighty Himalayan Rivers on the continental shelf is significant only at the G-B mouth and their contribution reduces to <50% at about 18oN. The sediment dispersal from the Godavari River is seen to extend on either side of the mouth of the river which is attributed to the reversing East India Coastal Current (EICC), which plays an important role, in the sediment transport along the central and south-central part of the east coast of India. The influence of the Mahanadi, Krishna, and Kaveri River sediments is however confined to a small area near their mouths and has a limited geographic extent of influence in the shelf region.

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Early detection of emerging persistent perfluorinated alkyl substances (PFAS) along the east coast of India

Perfluorooctanoic acid (PFOA) and Perfluorooctane sulfonate (PFOS) are resistant to breakdown and are now considered global contaminants. However, interest in these recalcitrant compounds among scientists and legislators has grown significantly in recent years. In the present study, we analyzed the level of PFOA and PFOS contamination in surface water from the coastal regions of Tamil Nadu and West Bengal. After solid phase extraction, 49 samples were analyzed by liquid chromatography coupled with mass spectrometry (LOD ≤ 1.5 ng L−1). The PFOA and PFOS present in all samples at the highest concentration were found in the Ennore coastal region (reaching a maximum of 24.8 ng L−1 and 13.9 ng L−1 in CH-6 and CH-14 respectively). Similarly, on the West Bengal coast, concentrations of PFOA ranged from <1.5 to 14.0 ng L−1 and <1.3 to 8.2 ng g−1 in water and sediment respectively. PFOS concentrations in water and sediment ranged from <1.2 to 9.0 ng L−1 and <1.2 to 7.9 ng g−1, respectively. According to the principal component analysis, the majority of the variances (65.04 %) show a positive association, which points to industrial and domestic discharges as significant point sources of these compounds. The results from this study could be used to determine and understand the levels of PFOA and PFOS contamination along the Indian Coast as well as provide baseline information for imminent monitoring investigations. The environmental occurrences of PFOA and PFOS reported in the current study would allow policymakers to take appropriate measures to safeguard coastal ecosystems or reduce the likelihood of contamination, creating a sustainable and healthy environment.

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Interaction of climate change and marine pollution in Southern India: Implications for coastal zone management practices and policies

Climate change and marine litter are inextricably linked, and their interaction manifests differently depending on the specific environmental and biological characteristics, and other human activities taking place. The negative impacts resulting from those synergistic interactions are threatening coastal and marine ecosystems and the many goods and services they provide. This is particularly pervasive in the coastal zone of the Indian subcontinent. India is already experiencing severe climate change impacts, which are projected to worsen in the future. At the same time, the country is gripped by a litter crisis that is overwhelming authorities and communities and hindering the country's sustainable development goals. The coastal environment and communities of the southern states of Kerala and Tamil Nadu are particularly vulnerable to the impacts of climate change. While these state governments and authorities are stepping up efforts to improve the management of their coastal zones, the scale and severity of these issues are mounting. Here we review the combined effects of climate change and marine litter pollution in Southern India, focusing on the Gulf of Mannar Reserve in Tamil Nadu and the Malabar Coast in Kerala. Finally, we discuss effective management options that could help improve resilience and sustainability.

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