Occurrence, distribution and sources of phthalates and petroleum hydrocarbons in tropical estuarine sediments (Mandovi and Ashtamudi) of western Peninsular India.

The present study provides baseline information on the concentration levels, distribution characteristics and pollution sources of environmental contaminants, such as phthalic acid esters (PAEs or phthalates) and petroleum hydrocarbons in surface sediments of the tropical estuaries (Mandovi and Ashtamudi) from western Peninsular India. Total PAEs (∑5PAEs), hopanes, steranes and diasteranes concentrations from Ashtamudi estuary ranged from 7.77 to 1478.2 ng/g, n.d.-363.2 ng/g, n.d.-121.5 ng/g and n.d.-116.6 ng/g, respectively. Likewise, PAEs (∑6PAEs), steranes and diasteranes concentrations from Mandovi estuary ranged from 60.1 to 271.9 ng/g, 2.33-40.1 ng/g and 2.28-23.0 ng/g, respectively. The PAEs comprising di-isobutyl phthalate (DIBP), dibutyl phthalate (DBP), an isomer peak for DBP, di(2-ethylhexyl) phthalate (DEHP), di-isononyl phthalate were dominant in Ashtamudi estuary sediments, while PAEs including diethyl phthalate, DIBP, DBP and its isomer, DEHP, di(2-ethylhexyl) terephthalate were detected in the Mandovi sediment samples. The results of this study show an insignificant correlation of TOC with PAEs, and indicates that the varying spatial distributions of the PAEs in both the estuaries can be the result of discharge sources. The higher concentration of PAE congeners was noticed in Ashtamudi, a Ramsar wetland site, that can be attributed to land-based plastic waste. The petroleum biomarkers were abundantly present in Mandovi estuary due to anthropogenic activities such as boating and spillage from oil tankers. The findings of the present study will serve as a reference point for future investigation of organic contaminants in Indian estuaries, and calls for attention towards implementing effective measures in controlling the pervasion of the PAEs and petroleum biomarkers.

Apportioning sedimentary organic matter sources and its degradation state: Inferences based on aliphatic hydrocarbons, amino acids and δ15N.

The sources and state of sedimentary organic matter (SOM) in fresh water aquatic systems are important to understand the carbon cycling in terrestrial environments. The composition of organic matter in the lake sediments demonstrates the physical and chemical condition of the lake ecosystems. However, the systematic and structured investigations focussed on to understand the source and fate of organic matters within eutrophic lakes is still far from clear. The present study is focusing on the implications of amino acids (AA), aliphatic hydrocarbons and bulk geochemical (C/N, δ15N) proxies to understand the distribution, sources and state of sedimentary organic matter in Ahansar Lake from Kashmir valley, India. The relatively low C/N ratios along with high AA contents indicate enhanced aquatic productivity in the lake system. Likewise, the dominance of the mid-chain monomethyl alkanes (MMAs), highly branched isoprenoids (HBIs), botryococcenes, steroids and triterpenoids suggest OM sourced from periphyton remains. Furthermore, the presence of C27, C28 and C29 diagenetically altered steroids also reflects a major algal contribution. The spatial variability of Paq demonstrates their applicability as a proxy for the contribution of aquatic vegetation. The ratio of individual amino acids (oxic/anoxic ratio) and low Pr/Ph (pristane/phytane) values indicate anoxic nature of the current depositional environment. This also leads to significant organic matter preservation as revealed by amino acid indices (e.g., degradation index - DI and reactivity index - RI). These data collectively demonstrate the systematic investigation and comprehensive understanding of source of sedimentary organic matters and respective depositional condition via multiple indicators. Overall, understanding the OM molecular composition and its spatial heterogeneity in a lake system is important to better constrain the fate of organic carbon, and assess the pollution risks as well as adopt relevant management strategies.

Atmospheric deposition of microplastics in an urban conglomerate near to the foothills of Indian Himalayas: Investigating the quantity, chemical character, possible sources and transport mechanisms.

The global apprehension regarding the ubiquitous presence of microplastics (MPs) and their associated health risks underscore a significant challenge. However, our understanding on the occurrence and characteristics of this emerging class of pollutants in the different environmental compartments remains limited. For instance, despite housing approximately 20-25% of the global population, the evidence of the atmospheric MPs in Indian Subcontinent is exceedingly rare. Hence, we for the first-time present data on the depositional flux, chemical composition, morphological features of the atmospheric MPs collected from the foothills of Indian Himalayas. The total number of MPs for the collected samples ranged from 65 to 752 particles, with an average of 317 ± 171 particles count. The average flux of atmospheric MPs was 2256 ± 1221 particles/m2/day and varied significantly from 462 particles/m2/day to 5346 particles/m2/day. The highest deposition (5346 particles/m2/day) of atmospheric MPs was recorded during the 3rd week of sampling, coinciding with the Diwali festival. Based on the visual characteristics, we determined that the size of MPs ranged from 67 to 2320 µm, with a predominant presence of smaller particles (<1200 µm), primarily composed of fragments and films/sheets. Raman spectroscopy indicated that the analyzed MPs were mainly composed of 4 different polymer types, including PE (46.8 ± 7.2 %), PP (20.9 ± 7.4 %), PS (15.6 ± 3.8 %) and PET (16.7 ± 9.9 %). We further highlighted the extent to which climate variables control the deposition of atmospheric MPs in this urban conglomerate located in the foothills of Himalayas. Our Lagrangian parcel tracking approach showed that the greater frequencies are of local origin and clustered near to the studied region. We also speculate that atmospheric microplastics can be transported along the westerly winds. Though we did not observe any significant relation (p > 0.05) between meteorological parameters and the quantity of atmospheric MPs.

Investigating the impact of climate change on the lake ecosystem during the late Holocene using a sedimentary record from the southern Arabian Desert, Yemen.

Lake systems respond physically, chemically, and biologically to hydro-climatic change and variability, and these responses are documented in the sediments. Individual proxies and lacustrine environments may respond to climate variations in a nonlinear way, making it difficult to determine the direction and extent of a climatic shift. Here we investigate the response of lake ecosystem to climatic and environmental changes using a suite of paleo-proxies including ostracods, chironomids, and n-alkanes distribution from paleolake 'Gayal el Bazal (Yemen)'. A previous study from this site has provided a continuous, and high-resolution dataset providing an understanding of precipitation during the last ca 1200 years, particularly during Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). However, the response of the lake ecosystem to these changing hydro-climate conditions, including water-level, salinity, and productivity, remains unknown. The n-alkanes dataset shows that during pluvial interval such as the MCA, the lake experienced an increase in nutrient input resulting in enhanced aquatic productivity. Concurrently, ostracods assemblage displays an increased abundance of swimmer species (like Bradleytriebella lineata and Fabaeomiscandona cf. breuili), suggesting an indirect response between ostracods and climate shifts. The chironomid community during the MCA interval is dominated by taxa belonging to the subfamilies of Chironomini, suggesting a warm, shallow, productive environment with macrophyte vegetation. The LIA interval is marked by increased abundance of higher-chain length n-alkanes, suggesting increased contribution from higher plants. Furthermore, ostracod distribution revealed increased abundance of non-swimmer species like Vestalenula cylindrica., which thrive under saline conditions in the lake. Changes in abundances of Tanytarsini during the LIA interval, which are associated with higher oxygen levels, suggest changes in lake productivity. As a result, the overall patterns in biological indicators reveal that their individual abundance and species/tribe distribution fluctuates in response to changes in the climate and hydrological conditions.

Pyrenedione-Catalyzed α-Olefination of Nitriles under Visible-Light Photoredox Conditions.

Herein, we report a combination of pyrenedione (PD) and KOtBu to achieve facile alcohol dehydrogenation under visible-light excitation, where aerobic oxygen is utilized as the terminal oxidant. The resulting carbonyl compound can be easily converted to vinyl nitriles in a single-pot reaction, at 60 °C in 6-8 h. This environmentally benign, organocatalytic approach has distinct advantages over transition-metal-catalyzed α-olefination of nitriles, which often operate at a significantly higher temperature for an extended reaction time.

Bioinspired Radical-Mediated Transition-Metal-Free Synthesis of N-Heterocycles under Visible Light.

A redox-active iminoquinone motif connected with π-delocalized pyrene core has been reported that can perform efficient two-electron oxidation of a class of substrates. The design of the molecule was inspired by the organic redox cofactor topaquinone (TPQ), which executes amine oxidation in the enzyme, copper amine oxidase. Easy oxidation of both primary and secondary alcohols happened in the presence of catalytic KOtBu, which could reduce the ligand backbone to its iminosemiquinonate form under photoinduced conditions. Moreover, this easy oxidation of alcohols under aerobic condition could be elegantly extended to multi-component, one-pot coupling for the synthesis of quinoline and pyrimidine. This organocatalytic approach is very mild (70 °C, 8 h) compared to a multitude of transition-metal catalysts that have been used to prepare these heterocycles. A detailed mechanistic study proves the intermediacy of the iminosemiquinonate-type radical and a critical hydrogen atom transfer step to be involved in the dehydrogenation reaction.

Distribution and characteristics of microplastics and phthalate esters from a freshwater lake system in Lesser Himalayas.

The occurrence, distribution, characterization and quantification of microplastics (MPs) and phthalic acid esters (PAEs) from the freshwater aquatic environment are not thoroughly explored in the Indian Himalayas despite concern over their adverse effects on human health and ecosystem. In this study, we have investigated the presence of MPs and PAEs in an aquatic system from Indian subcontinent. The MPs were detected in all water and sediment samples with abundances ranging from 02-64 particles/L and 15-632 particles/kg dw, respectively. The abundance of MPs, dominated by polyethylene and polystyrene, with the majority being fibres and fragments indicated that they were derived from plastic paints, boats or synthetic products. The concentrations of PAEs in the surface sediment samples varied from 06-357 ng/g dw. The most abundant PAEs in the sediments were dibutyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP), since they were present in all the samples collected from the lake basin. The relatively higher abundances of MPs and higher concentrations of PAEs were generally found in the vicinity of areas impacted by anthropogenic activities. A clear correlation between the abundance of microplastics and PAEs concentration was observed suggesting that they are closely attributed to a single source. This study also provides an alternative approach to utilize the chemical additives in plastics as markers to trace the presence and distribution of MPs in the aquatic environment.