Global pollution of mercury (Hg) threatens ecosystem and human health. We measured total Hg (THg) and monomethylmercury (MMHg) concentrations in filter-feeding blackfly (Simulium spp.) larvae in the inflows and the outflows of six boreal lakes with no Hg point source pollution. THg in the larvae ranged from 0.03 to 0.31 mg kg⁻¹ dw and MMHg between 0.02 and 0.25 mg kg⁻¹ dw. The proportion of MMHg in the larvae was 74 ± 0.16% and ranged from 43 to 98% of THg, the highest proportions being comparable to those typically found in aquatic predatory insects and fish. We compared the larvae MMHg concentrations to river water quality, catchment land-use, and to size-adjusted lake pike THg data. Two of the investigated catchments have been affected by a multimetal biomine since 2008 and were characterized by higher conductivity and higher urban land-use activity. Larvae THg and MMHg concentrations were higher in the lake inflows than in outflows and associated with water conductivity and catchment land-use activity. Lake pike THg concentrations were highly correlated to lake outflow blackfly larvae MMHg concentrations. Our data illustrate that blackfly larvae take up high percentage of THg that is MMHg, which in turn is available for higher consumers in aquatic and terrestrial food webs.

The removal of Hg from contaminated aquatic media is of major importance, taking into consideration the highly toxic character of the element. One of the most promising water treatment technologies is adsorption by low cost adsorbents, such as activated carbon produced by agricultural byproducts. In this study, activated carbon in granular form (GAC) was produced using pistachio shells from Aegina Island (Greece). Two main GAC products have been synthesized. The first one was chemically activated using ZnCl₂. The second one was further treated with Na₂S in order to introduce S atoms on the functional groups. The effectiveness of synthesized GAC products for Hg removal was evaluated by conducting batch equilibrium and kinetic experiments. It was found that sulfurization was able to increase by a factor of more than 2 the adsorptive capacity of activated carbon. Namely the maximum adsorption capacity was 73 mg/g for the simple GAC and increased up to 166 mg/g for the S-modified product. The kinetics of adsorption was described with almost equivalent precision using the pseudo-first and the pseudo-second order models, a behavior which is often observed in adsorption experiments, depending on the experimental conditions. The value of activation energy EA was found to be negative (− 18.8 kJ/mol) in the case of simple GAC and positive (8.27 kJ/mol), in the case of S-modified GAC, suggesting that Hg adsorption on the modified carbon follows a different mechanism, closer to chemisorption processes.

In present work, mustard straw, an abundantly available agricultural residue in various parts of globe, is used to prepare a low-cost activated carbon by chemical activation using phosphoric acid. Response surface methodology is employed for optimization of adsorption of methylene blue dye onto mustard straw-activated carbon (MSAC). Central composite design is employed to evaluate the effect of three production variables namely activation temperature (400–800 °C), activation time (60–120 min), and impregnation ratio (2–7), on adsorption capacities of activated carbon to maximize methylene blue dye removal from its aqueous solution. Among the three process variables, activation time showed prominent effect on the response whereas the effect of activation temperature was relatively less significant on adsorption capacity of MB. The optimum conditions obtained for MSAC are activation temperature, 768 °C; activation time, 60 min; and impregnation ratio, 4.2, which leads to 198 mg g⁻¹ adsorption capacity of methylene blue. The model predicted and experimental value for response were highly comparable. Characterization of MSAC was done using several analytical techniques such as Fourier transform infrared spectroscopy and field emission scanning electron microscopy techniques, and reusability up to five adsorption-desorption cycles was tested. The results showed that MSAC obtained has highly porous structure comparable with activated carbon obtained from other biomass feed stocks.

This paper investigated the organic matter removal in waste stabilization ponds (WSP) based on ten full-scale wastewater treatment plants (WWTP) located in Rio Grande do Norte, Northeast Brazil. Although many systems are operating at high organic loading rates, in some cases, over 1000 kg BOD₅ ha⁻¹ d⁻¹, the ponds promoted satisfactory removals of biochemical oxygen demand (BOD₅) and chemical oxygen demand (COD). The first-order removal rates (k) for BOD₅ and COD were obtained by assuming the ideal hydraulic patterns of completely mixed and plug-flow models. The k values proved to be a function of physical and operational parameters that affect fluid movement in a pond. The increase in the organic loading rate caused an increase in first-order removal rates. Moreover, increasing the ratio between hydraulic retention time (HRT) and depth (H) led to a reduction in k values. This information can be adapted into predictive models to be applied in WSP designs with similar characteristics. In comparison with the empirical equations reported in the literature, these models lead to removal rates more appropriate to the local reality.

There is evidence that water-soluble fraction (WSF) from fuel oil/diesel mixture affects marine microbiota. In order to establish a sequence of WSF effects during microalgal growth, this work aimed to monitor Dunaliella tertiolecta exposed to WSF during 15 days. Three different pigments (chlorophyll a, lutein, and β-carotene) and four metabolites (protein, lipids, fatty acids, and phenols) were studied, and FTIR spectroscopy was used to determine the biomolecular transitions of lipids and their accumulation. The results show that D. tertiolecta triggered a physiological and biochemical response with changes in growth rate, pigments, phenols, lipids, and proteins of the microalga, although fatty acid profile was unaltered. For all the biochemical parameters altered, there were significant differences with the controls. At the end of the assay, exposed D. tertiolecta showed similar values with the control on all the compounds analyzed, except lipids. FTIR absorbance showed an increase in unsaturated acyl chains within the exposed microalgae, giving support for a possible uptake of hydrocarbons from WSF. Variation in pigments and phenol contents is presented as an integrated antioxidant response to the stress imposed by WSF. Overall, this research provides information about the effects of WSF on D. tertiolecta, and the ability of this microalga to recover after long-term exposure to the water-soluble fraction of fuel oil/diesel.

To determine the dynamic change characteristics of NO₃–N in a rural–urban ecotone channel, five tracer tests were conducted in the Dongda Channel in the suburbs of Changchuan city, Jilin province, China, from October 2016 to April 2017. NaBr was used as conservative tracer and KNO₃ served as an added nutritive salt. The kinetic features of NO₃–N were simulated via the addition of tracers and by employing the spiralling curve characterization approach and the Michaelis–Menten (M–M) equation. The average absorption length of NO₃⁻–N background concentration (Sw₋ₐₘb) is 199 m, which is much less than the discharge channel length (2.5 km), thereby suggesting that the channel has a strong NO₃–N retention potential. Moreover, the M–M equation fits well the kinetic features of NO₃–N adsorption. The average maximum absorption rate and subsaturation constant are 631 μg (m² s)⁻¹ and 1.46 mg L⁻¹, respectively. The correlation analysis reveals that Sw₋ₐₘb and NO₃⁻–N absorption rates (NO₃–Nₐₘb) are significantly negatively correlated whereas the absorption rates of NO₃⁻–N background concentration (Uₐₘb) and NO₃–Nₐₘb are significantly positively correlated. The other spiralling indices show faint correlations with the background concentration of NO₃–N. Meanwhile, the hydrological factors slightly influence NO₃–N retention, but the geomorphic features of the channel, including (width residual) Фw and (cross-sectional area residual) ФA, have significant correlations with most spiralling indices, thereby highlighting the relatively important roles of geomorphic features in NO₃–N retention.

China has become the largest carbon-emitting country in the world since 2007. To achieve national environmental goals by 2030, the carbon emissions per unit of gross domestic product (GDP) will need to fall to 60–65% of 2005 levels. Such a dramatic decrease presents a challenge for a nation in adjusting its energy source and usage, but via monitoring of reductions, greater understanding can be gained of how carbon emitters are responding to national goals. We analyzed the change in carbon emissions from China’s fossil energy consumption from population, per capita GDP, energy efficiency improvements and energy structure using a Kaya identity model and Logarithmic Mean Divisia Index (LMDI) factor decomposition method from 2006 to 2018. Results suggest that trends in carbon emissions from 2006 to 2018 can be broken down into four periods: a rapid increase period during 2006–2011, a slowdown increase period during 2011–2014, a consecutive decline period during 2014–2016 and a rebound during 2017–2018. Trends in carbon emissions were greatly affected by per capita GDP and energy efficiency. While per capita GDP increased carbon emissions, energy efficiency had a countering effect on carbon emissions. Our results suggests that China’s measures in the past decade to reduce carbon emissions (i.e. carrying out carbon emissions trading on a fixed basis, readjusting the economic structure, optimizing the energy structure, improving energy efficiency and increasing forest carbon sinks) have helped to reduce carbon emissions. However, China should continue to actively respond to climate change while striving to achieve of economic sustainable development and social progress.

Pesticides are widely used chemicals in the agricultural sector to control pests, diseases, and other plant pathogens. This study aimed to assess the storage conditions of pesticides, the community perception, and health risk of pesticide exposure. The study was conducted in three different zonal cities in Ethiopia, East Africa, namely Mekelle, Aksum, and Alamata. Community perception was studied in a community living near a pesticide stockpile with a cross-sectional study of 384 randomly selected households. In addition, questionnaires were administered, a field investigation was conducted, and focused group discussions with responsible bodies were held to assess storage condition. Accidental ingestion and inhalation were considered to determine average daily exposure (ADE) and incremental lifetime cancer risk (ILCR). This study reveals that all obsolete and banned hazardous pesticides were stored in one area. The storage sites were only secured with simple locks and exposed to rain, sunlight, and temperature variation. The majority of the residents perceived that pesticides pose risk to human health (46.6%), to the environment (28.4%), and to animals (25%). The association between residence proximity of respondents to the store and side effect of obsolete pesticides is statistically significant (p = 0.008). Children aged 2 years and below have higher ADE when exposed to the same concentration of contaminant via inhalation. The probability of a person developing cancer was very low with a risk value of 2.54E−08 and 1.65E−07 as a result of exposure to air containing heptachlor and dichlorodiphenyltrichloroethane (DDT), respectively.

Microplastics in marine organisms are nowadays considered a worldwide phenomenon. An action plan needs to establish to solve this marine pollutant. It requires multidisciplinary information, including the accumulation of data on microplastics in marine biota. The research of microplastic ingestion in the marine environment and organisms of Thailand is limited. As a result, this study was conducted to evaluate the accumulation of microplastics in marine fish from Thailand and to investigate whether the different foraging mechanisms of fish impact the occurrence of microplastics in their gastrointestinal tract. A total number of 361 demersal fish and 131 pelagic fish were investigated. The collected microplastics were counted according to their shape and color. Their polymer type was identified by FT-IR for the first time in fish from Thailand. Moreover, microplastics ingestion sorted by fish size was noted. The number of ingested microplastics in this study was relatively low compared to other locations. There was no significant difference in the number of microplastics ingested between demersal and pelagic fish (p = 0.132). Microplastic fibers were the dominant shape found in both demersal (82.76%) and pelagic fish (57.14%). The most common polymer type was polyamide in both demersal (55.17%) and pelagic fish (50.00%). The dominant microplastics color in both demersal and pelagic fish was red (31.03% and 28.57%, respectively). Microplastics ingestion along different fish sizes fluctuated. This study provides evidence to fill a gap of research relating to microplastic ingestion by fish from Thailand.

It is of great importance to determine the risk grades of the leakage and non-leakage cases of concentrated saltwater from an underground reservoir for the safe operation of reservoirs and environmental protection. In this paper, the model of risk evaluation for environmental pollution of an underground reservoir stored with concentrated saltwater is established. Moreover, the effects of different influencing factors on the risk grades are investigated, along with an uncertainty analysis. In addition, the risk grade of Lingxin Mining Area is calculated, which can contribute to the prevention and control of pollution in the future for that area. The results show that the water quality complexity of mine water is the most significant indicator for risk grade determination. The certainty of weak-risk grade for environmental pollution caused by an underground reservoir when there is no leakage is more than 60% in the Lingxin Mining Area, and the risk grade becomes a strong-risk grade rapidly after concentrated saltwater leakage is considered. This research can provide a theoretical basis for risk control and management of underground reservoirs storing concentrated saltwater.