This study considered the temporal variations in rainfall and water level patterns as governing factors, which influence the geochemical process of coastal aquifer around Pondicherry, South India. Rainfall and water level data were collected from 2006 to 2016, which showed that the amount of rainfall from 2006 to 2011 was higher than that of 2011 to 2016. To understand the geochemical process governing groundwater, samples were collected during 2006 (n = 54), followed by 2011 (n = 93), and during 2016 (n = 63) as part of continuous observation. The major ions and stable isotopes (δ¹⁸O and δD) were analyzed in the samples to determine the geochemical variations. The predominant types were noted as Na-HCO₃ and Na-Cl; Ca-HCO₃ and Ca-Mg-Cl; and Na-Cl and Ca-Mg-Cl in 2006, 2011, and 2016, respectively. Saturation states of sulfate and carbonate minerals were compared for the study periods and it indicates that the saturation index (SI) values were increased from 2006 to 2011, but decreased from 2011 to 2016. PHREEQC inverse modeling revealed the predominance for the dissolution and leaching of carbonate minerals during increased rainy periods, and the increase of halite saturation during lesser rainfall period. AQUACHEM mixing studies suggested that geochemical signatures of 2006 and 2011 were preserved in samples of 2016 in different proportions. Considering the major factors, the main processes prevailing in the study area were inferred to be dissolution and leaching during 2006~2011 years and seawater intrusion along with ion exchange during 2011~2016 years. In all these periods of study, anthropogenic impact was also identified in the groundwater samples. Hence, this study revealed that the rainfall and water level gave a significant variation in the geochemical process of groundwater in the coastal aquifer system.

Three sequential extraction procedures (SEPs), modified Tessier, modified BCR, and CIEMAT, were compared for mercury fractionation in polluted soils. With satisfactory total mercury recovery, the modified Tessier and modified BCR SEPs were comparable with each other in terms of extraction efficiency in equivalent mercury fractions, whereas both SEPs were not as efficient as the CIEMAT SEP. However, the CIEMAT SEP might underestimate the oxidizable mercury fractions due to the humic and fulvic complexes instead of the organic matter of the other two SEPs. For mercury bioavailability identification, based on Pearson correlation analysis, all fractions in each SEP were significantly correlated with mercury uptake in Ipomoea aquatica, causing difficulty in comparison. Partial correlation analysis indicated that the mobile mercury fractions extracted by the first step in all three SEPs had a positive correlation with mercury uptake by plant, while mercury bound to organic matter extracted by both modified Tessier and modified BCR SEPs presented negative correlation with mercury uptake by plant which was in contrast to CIEMAT SEP. Meanwhile, clearly positive correlations between mercury fractions extracted by the former three steps of CIEMAT SEP and mercury uptake in Ipomoea aquatica were observed, demonstrating that CIEMAT SEP provided more accurate results related to Hg bioavailability than did the other two SEPs.

Silver nanoparticles (AgNPs) were synthesized by incubating the mixture of AgNO₃ solution and whole-cell aqueous extracts (WCAEs) of Neochloris oleoabundans under light conditions. By conducting single-factor and multi-factor optimization, the effects of parameters including AgNO₃ concentration, pH, and extraction time were quantitatively evaluated. The optimal conditions in terms of AgNP yield were found to be 0.8 mM AgNO₃, pH 5, and 9-h extraction. The AgNPs thus synthesized were quasi-spherical with a mean particle diameter of 16.63 nm and exhibited decent uniformity as well as antibacterial activities, which may facilitate AgNP biosynthesis’s application in the near future.

This study reveals the efficient bio-sorption of Cr(VI) species from simulated wastewater using raw (RSV), acid-activated (PSV) and chelated-activated (PSV-C) Sterculia villosa Roxb. shells. Batch optimization experiments were carried out for determining the optimal pH, dosage of bio-sorbent, initial Cr(VI) concentration and incubation temperature. Physico-chemical alterations in the bio-sorbents prior and following bio-sorption of Cr(VI) species were characterized. Equilibrated experimental data at different temperatures was evaluated as a function of time for understanding the isotherm, kinetics and thermodynamics of the bio-sorption process. Sorption rates for all the bio-sorbents (RSV, PSV and PSV-C) alternately fitted to the Langmuir isotherm model and Langmuir maximum adsorption capacity for RSV, PSV and PSV-C were found to be 57.78, 163.51 and 188.68 mg/g, respectively. Cr(VI) sorption by these bio-sorbents followed pseudo-second–order kinetics. Thermodynamic studies suggest endothermic interaction and increased degree of randomness between the bio-sorbents and Cr(VI) species. Regeneration of the bio-sorbents following sorption–desorption revealed that it can be reused and recycled for several times for Cr(VI) removal from wastewater. Graphical abstract

The densely populated Greater Cairo (GC) region suffers from severe air quality issues caused by high levels of anthropogenic activities, such as motorized traffic, industries, and agricultural biomass burning events, along with natural sources of particulate matter, such as wind erosion of arid surfaces. Surface-measured concentrations of particulate matter (PM₁₀), sulfur dioxide (SO₂), and ozone (O₃) and its precursor’s gases (nitrogen dioxide, NO₂; carbon monoxide, CO) were obtained for the GC region. The PM₁₀ concentrations were found to exceed remarkably the Egyptian guidelines (150 μg/m³). These high levels of PM₁₀ were recorded throughout 68% of the period of measurement in some industrial areas (El-Kolaly). The measured data of pollutants were used for both the evaluation of environmental pollution levels and the validation of the online-integrated regional climate chemistry model “RegCM-CHEM4.” Calculation of the bias between the model results and the measured data was used to evaluate the model performance in order to assess its ability in reproducing the chemical species over the area. The model was found to reproduce the seasonal cycle of the pollutants successfully, but with a large underestimation of the PM₁₀ values. Validation of the RegCM-CHEM4 indicated that the emission inventories of mobile sources and anthropogenic activities need to be improved especially with respect to local and regional activities in order to enhance air quality simulations over the GC region.

This study aims to examine the convergence hypothesis of per capita carbon dioxide emission and its component such as coal, oil, and gas in the case of 53 countries covering the period of 1980 to 2016. In particular, we study whether countries are moving toward a common steady-state equilibrium condition in the per capita carbon emission or converging into different groups. To do so, this study used Phillips and Sul (Econometrica 75(6): 1771–1855, 2007, J Appl Econ 24(7): 1153–1185, 2009) technique. Our results show no evidence of convergence for full sample. However, our results support the evidence of two club convergence of total emission, emission from gas and petroleum consumption, while three clubs are noticed in case of per capita carbon dioxide emission from coal use. This invalidates the equality rule of participation of each country in climate change policy. Further, similar results emerge in case of total emission and petroleum where club 1 consists of mostly developed countries while club 2 has a large number of developing countries. Interestingly, we do not find any divergence behavior across all countries in the sample. We find that natural gas is the major component to drive the total carbon emission convergence in case of our sample countries.

Few studies have examined the effects of environmental concentrations of benzene, toluene, ethylbenzene, and xylene (BTEX) on the hematologic system of residents near a petrochemical complex. This study evaluated the potential effects of blood BTEX concentrations on the hematologic parameters of residents in a community near a petrochemical complex (contaminated group) and another community free of known petrochemical pollution (control group). Volunteer residents were randomly recruited. Each participant completed a questionnaire and donated blood samples to evaluate blood BTEX concentrations and hematologic parameters. We found the mean concentrations of blood BTEX of the contaminated group were 1.2 to 6.7 times higher than the control group. Multiple hematologic parameters of participants were significantly different between the two study groups. Inverse associations were found for ln-transformed blood benzene concentrations with mean corpuscular hemoglobin concentration (MCHC) (β = − 2.75) and platelet counts (β = −8.18). Several weaker associations were also observed between other compounds and multiple hematologic parameters. Our results suggest that the residents living near petrochemical complexes have higher blood BTEX concentrations. Furthermore, the increased blood BTEX levels in residents are associated with the reduction in RBC counts, hemoglobin concentration, hematocrit, MCHC, and platelet counts. This study provided particularly important information for the health risk assessment of residents living near petrochemical complexes.

Ecological indicators have widespread appeal to scientists, environmental managers, and the general public. Remote sensing is unique in its capability to record variety of spatio-temporal information on land surface with complete coverage, especially with regard to larger spatial scales, which has been proven to be an effective data source to create indicators to rapidly identify regional eco-environment. In this paper, a new index, remote sensing based ecological index (RSEI) based on the pressure-state-response (PSR) framework, was applied to assess regional ecological changes in Fuzhou City of Fujian Province, southeastern China, using Landsat ETM+/OLI/TIRS images. Taking the advantages of being totally free of artificial interference in the calculation using principal components analysis (PCA) to assign weights of each variable, the RSEI can assess the regional ecological status more objectively and easily. The effectivity of the new index was validated by four approaches, including point-based, classification-based, correlation-based, and urban-rural-gradient-based comparisons. The case study showed that Fuzhou has witnessed ecological improvement during the study period, with the value of RSEI increasing from 0.663 in 2000 to 0.675 in 2016. Spatial variation analysis showed that the poor level of RSEI distributed mostly in the central urban areas, and the ecological degradation was attributed to the fast expansion of the built-up area, characterized by increasing greatly in the value of the normalized differential built up and soil index (NDBSI) in such areas.

Nitrosamines (NAms) are potent genotoxic and carcinogenic but widely detected in drinking water. This study aimed to investigate the occurrence of major types of NAms in drinking water in Shaoxing, China, and to conduct multi-pathway probabilistic cancer risk (CR) assessment to residents based on age-dependent adjustment Chinese exposure factors. Results showed that concentrations of NAms in water varied from not detected (ND) to dozens of nanograms per liter level. N-Nitrosodimethylamine (NDMA) was detected most frequently (93.06%), followed by N-nitrosodiethylamine (NDEA) (64.08%)—with the highest cancer risk among NAms. The CR of NAms came mainly through the oral exposure pathway. The 95th percentile of the total CR of five major NAms was 1.06 × 10⁻⁴, exceeding the maximum acceptable lifetime CR (1 × 10⁻⁴) recommended by US EPA. Exposure to NDEA contributed the highest to the total CR. The CR of the five NAms through ingestion was 2.5 times higher using the Chinese exposure factors than that of the Americans. The most important variables related to CRs were concentrations of NAms in drinking water, exposure duration, drinking water ingestion rate, and exposure time during bathing. Our findings suggest the urgent need to develop and enforce effective regulatory policies to control the contamination of NAms in drinking water in China. Graphical abstract

The Thymus vulgaris (T. vulgaris) has been used in foods for the flavor, aroma, and preservation and in folk medicines. The objective of the present work was to determine the antioxidant and protective effects of T. vulgaris extract against lead (Pb)-intoxicated rats. A thirty-two male Sprague-Dawley were randomly assigned into 4 equal groups and treated for six weeks as follows: group I (GP-I), served as negative control; GP-II, -III, and -IV received either Pb acetate in drinking water (500 mg/L), T. vulgaris extract (500 mg/kg/day) by oral gavage or Pb acetate with T. vulgaris extract, respectively. Blood samples were collected at the end of the study week 6 to measure the hepatic and renal biochemical markers, complete blood count alongside the serum levels of interleukin (IL)-1β, IL-6, IL-10, tumor necrosis (TNF)-α, and interferon (IFN)-γ. Additionally, liver and kidney tissue specimens were collected for histopathology as well as to measure the antioxidant-reduced glutathione (GSH), glutathione peroxidase (GPx), catalase (CAT), and superoxide dismutase (SOD) alongside the lipid peroxidation marker, malonaldehyde (MDA). The results indicated that Pb toxicity increased the serum levels of IL-1β, IL-6, and TNF-α, whereas IL-10 and IFN-γ were reduced. The results showed disturbed liver and renal functions; increased serum levels of ALT, AST, ALP, total bilirubin, creatinine, and urea; and decreased total protein, albumin, and calcium. The GSH, Gpx, and CAT levels were significantly decreased in the Pb-administrated group, while MDA was increased. However, regarding the hepatorenal markers, those animals treated with T. vulgaris alone did not induce any significant changes. Moreover, the combined treatment with T. vulgaris extract together with Pb showed significant improvement in Pb-induced toxicity in all the tested parameters compared to the negative control group. We investigated the potential protective effects of the medicinal plant T. vulgaris in vivo, since there are no publications that address the potential protective effect of this leaf extract against Pb-induced hepatorenal toxicity. Our studies concluded that the T. vulgaris extract reduces Pb overload in hepatorenal tissues, and that this has a potential immunomodulatory role, antioxidant activity, and a protective effect against Pb toxicity.