Sete Cidades Lake (São Miguel Island, Portugal) is subdivided into two interconnected branches: the Green Lake and Blue Lake. The lake has an area and maximum depth of 4.39 km² and 29.5 m (Blue Lake), respectively, with evidence of eutrophication, particularly in the northern area of the Green Lake. In this study, we conducted a sampling survey during January 2017 to measure CO₂ fluxes from the lake using a floating accumulation chamber. We also produced two hydrogeochemical profiles for each of the lake’s branches. A total of 1760 CO₂ flux measurements were taken along the lake’s surface. The lake water was relatively cold (14.0 °C on average) and weakly mineralised (average electrical conductivity of 116 μS cm⁻¹) with a neutral pH (7.7 on average). The relative composition of major ions occurred in the following decreasing order: Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ for cations and Cl⁻ > HCO₃⁻ > SO₄²⁻ for anions. The lake water was mainly the Na–Cl type due to sea salt input from seawater spraying. CO₂ fluxes ranged from 0.3 to 17.2 g m⁻² d⁻¹ and from 2.1 to 17.9 g m⁻² d⁻¹ for the Blue and Green Lakes, respectively. Highest CO₂ degassing occurred in areas dominated by macrophytes and algal blooms. The measured values suggest that the CO₂ was predominantly biogenically sourced, which was further supported by the δ¹³C isotopic data. The estimated total CO₂ emissions varied between 5.8 t d⁻¹ (Green Lake; area = 0.81 km²) and 24.9 t d⁻¹ (Blue Lake; area = 3.58 km²). This study further elucidates the lake’s trophic and chemical pollution status and has major implications for lacustrine CO₂ emissions to the atmosphere. Our study also provides a reference for understanding potential future variations in volcanic activity.

The determination of both stable nitrogen (δ¹⁵N–NO₃⁻) and stable oxygen (δ¹⁸O–NO₃⁻) isotopic signatures of nitrate in PM₂.₅ has shown potential for an approach of assessing the sources and oxidation pathways of atmospheric NOx (NO+NO₂). In the present study, daily PM₂.₅ samples were collected in the megacity of Beijing, China during the winter of 2017–2018, and this new approach was used to reveal the origin and oxidation pathways of atmospheric NOx. Specifically, the potential of field δ¹⁵N–NO₃⁻ signatures for determining the NOx oxidation chemistry was explored. Positive correlations between δ¹⁸O–NO₃⁻ and δ¹⁵N–NO₃⁻ were observed (with R² between 0.51 and 0.66, p < 0.01), and the underlying environmental significance was discussed. The results showed that the pathway-specific contributions to NO₃⁻ formation were approximately 45.3% from the OH pathway, 46.5% from N₂O₅ hydrolysis, and 8.2% from the NO₃+HC channel based on the δ¹⁸O-δ¹⁵N space of NO₃⁻. The overall nitrogen isotopic fractionation factor (εN) from NOx to NO₃⁻ on a daily scale, under winter conditions, was approximately +16.1‰±1.8‰ (consistent with previous reports). Two independent approaches were used to simulate the daily and monthly ambient NOx mixtures (δ¹⁵N-NOx), respectively. Results indicated that the monthly mean values of δ¹⁵N-NOx compared well based on the two approaches, with values of −5.5‰ ± 2.6‰, −2.7‰ ± 1.9‰, and −3.2‰ ± 2.2‰ for November, December, and January (2017–2018), respectively. The uncertainty was in the order of 5%, 5‰ and 5.2‰ for the pathway-specific contributions, the εN, and δ¹⁵N-NOx, respectively. Results also indicated that vehicular exhaust was the key contributor to the wintertime atmospheric NOx in Beijing (2017–2018). Our advanced isotopic perspective will support the future assessment of the origin and oxidation of urban atmospheric NOx.

Phosphorus-inactivating agents (PIAs) as geoengineering tools in lakes have been investigated extensively, but PIA resuspension in the photic layer occurs frequently in shallow lakes and little is known about the influence of algae on PIA performance. Our results proved that algae increased the dissolved oxygen, pH and dissolved organic carbon concentration substantially. In the absence of sediment, lanthanum modified zeolite (LMZ) as a representative PIA and algae could deplete dissolved inorganic phosphorus (DIP) from water but the former was faster than the latter. When LMZ and algae coexisted, the amount of phosphorus that was captured by LMZ was 3.1 times greater than that taken up by algae. An increase in pH or dissolved organic carbon increased the zero-equilibrium phosphorus concentration (EPC₀) of the sediment but LMZ addition could lower the EPC₀ and reduce the risk of phosphorus release during the algal blooming season. In the presence of sediment, LMZ reduced the DIP concentration more rapidly and yielded a lower final DIP concentration compared with algae. In conclusion, the influence of algae on the performance of LMZ by (i) taking up DIP to reduce the availability of DIP and convert DIP into a releasable phosphorus form and (ii) increasing the pH and dissolved organic carbon concentration to hinder the adsorption ability of DIP were recognized. The LMZ performed well, even in the presence of algae.

Dissolved organic matter (DOM) and dissolved ions are two integral parameters to affect the environmental fate of As in different ways. Numerous studies chose surrogate of DOM, humic substances (HSs), to investigate the As complexation behavior. However, microbial secretion (protein and polysaccharide) was also considered for a great proportion in surface aquatic system, and its effect was still not fully understood. The present research distinguished the As complexation behavior with different DOM components (HSs, protein, polysaccharide and synthetic organic matter) in natural and simulated water samples. The results indicated that different DOM components exhibited various binding capacities for As. HSs showed the strongest affinity for As, followed by long-chain compounds (polysaccharide and synthetic organic matter) and proteins. In water source, HSs were probably the primary parameter for As complexation. In eutrophic water system, however, polysaccharide maybe the main DOM component to bind As. Cationic bridge function was prone to occur in the presence of HSs, but not observed in the presence of protein. PO₄³⁻ competed for binding sites with As, consequently decreasing the As complexation with all the DOM components. The research implied that a comprehensive and meticulous analyses of DOM fractions and coexist ions are the prerequisite to understanding the behavior of As (or other pollutants) in different natural aquatic systems.

Plastic pollution in the world's ocean is one of the major environmental challenges that affects the society today, due to their persistence at sea, adverse consequences to marine life and being potentially harmful to human health. Rivers are now widely recognized as being the major input source of land-based plastic waste into the seas. Despite their key role in plastic transportation, riverine plastic pollution research is still in its infancy and plastic sources, hot-spots and degradation processes in riverine systems are to date poorly understood. In this contribution, we introduce a novel concept of following the aging of polypropylene based post-consumer goods placed in known trapping and mobility zones of macroplastics on a fluvial point bar, which was determined through repeated field surveys of macroplastic densities on this bar. As a proof-of-concept, we followed the degradation of 5 identical plastic butter tubs in 5 different locations on a riverbank and significant differences in the aging of the tubs were observed. The degree of aging of the tubs can to some extent be correlated to their proximity to the main river channel, exposure to natural conditions, such as solar radiation, and its storage time on land.

Cadmium (Cd) and lead (Pb) are ubiquitously present in surface soils, due to anthropogenic activities, causing threat to ecological and human health because of their carcinogenic nature. They accumulate in large quantities in the environment and affect negatively soil microbiota, plants, animals, and humans. For the cleanup of Cd/Pb polluted soils, different plant species have been studied. Many plants have shown the potential to hyperaccumulate Cd/Pb in their above-ground tissues. These plants decrease soil pH by root exudation or by releasing H⁺ ions, and this, in turn, increases the bioavailability of Cd/Pb for plant uptake. Different environmental processes related to soil organic matter, microorganisms, pH, genetic modifications, and various soil-borne chelating agents affect the potential of phytoremediation technology. Review papers trying to identify a single factor influencing the phytoremediation of heavy metals are available in the literature. However, an integrated approach dealing with different factors involved in the remediation of both metals is scarcely discussed. The main focus of this review is to discuss the phytoextraction technique for Cd/Pb removal from contaminated sites along with detoxification mechanisms. Further, the challenges in the Cd/Pb phytoextraction and different options available to cope with these challenges are also discussed. The update on the relevant findings on the use of microorganisms and amendments in enhancing the Cd/Pb phytoextraction is also provided. Finally, the areas to be explored in future research for the removal of Cd/Pb by integrated strategies have been discussed.

Rumen liquid can effectively degrade lignocellulosic biomass, in which rumen microorganisms play an important role. In this study, transformation of bacterial community structure in rumen liquid anaerobic digestion of rice straw was explored. Results showed that rice straw was efficiently hydrolyzed and acidified, and the degradation efficiency of cellulose, hemicellulose and lignin reached 46.2%, 60.4%, and 12.9%, respectively. The concentration of soluble chemical oxygen demand (SCOD) and total volatile fatty acid (VFA) reached 12.9 and 8.04 g L⁻¹. The high-throughput sequencing results showed that structure of rumen bacterial community significantly changed in anaerobic digestion. The Shannon diversity index showed that rumen bacterial diversity decreased by 32.8% on the 5th day of anaerobic digestion. The relative abundance of Prevotella and Fibrobacter significantly increased, while Ruminococcus significantly decreased at the genus level. The Spearman correlation heatmap showed that pH and VFA were the critical factors affecting the rumen bacterial community structure. The function prediction found that rumen bacteria mainly functioned in carbohydrate transport and metabolism, which might contain a large number of lignocellulose degrading enzyme genes. These studies are conducive to the better application of rumen microorganisms in the degradation of lignocellulosic biomass.

To characterize the emissions of polycyclic aromatic hydrocarbons (PAHs) from residential biomass burning and coal combustion in field environments, smoke samples were collected from the combustion of six types of biomass in heated kangs and four types of coal in traditional stoves and semi-gasifier stoves. The emission factors (EFs) of the total PAH were in the range of 84.5–344 mg/kg for biomass burning, with lower EFs for biomass with higher densities, and in the range of 38.0–206 mg/kg for coal combustion, with lower EFs for coals with higher maturity. Moreover, EFs were lower from high-density biomass fuels (wood trunk, 84.5 ± 11.3 mg/kg) than low-maturity coals (bituminous coal, 206 ± 16.5 mg/kg). Parent, oxygenated, alkylated, and nitrated PAHs accounted for 81.1%, 12.6%, 6.2%, and 0.1%, respectively, of the total-PAH EFs from biomass burning, and 84.7%, 13.8%, 1.4%, and 0.1%, respectively, of the total-PAH EFs from coal combustion. PAH source profiles differed negligibly between biomass fuels but differed significantly between bituminous coal and anthracite coal fuels. The characteristic species of sources were phenanthrene, 9-fluorenone, and 2-nitrobiphenyl for biomass burning, and were phenanthrene, benzo[ghi]perylene, 1,4-naphthoquinone, and 2-nitrobiphenyl for coal combustion. The ratios of benzo[b]fluoranthene/(benzo[b]fluoranthene + benzo[k]fluoranthene) were 0.40–0.45 for biomass burning and 0.89–0.91 for coal combustion, and these significantly different values constitute unique markers for distinguishing these fuels in source apportionment. Benzo[a]pyrene-equivalent factor emissions were 2.79–11.3 mg/kg for biomass and 7.49–41.9 mg/kg for coal, where parent PAHs contributed 92.0%–95.1% from biomass burning and 98.6%–98.8% from coal combustion. Total-PAH emissions from residential heating were 1552 t across Shaanxi province, to which wheat straw (445 t) in biomass burning and bituminous coal (438 t) in coal combustion were the highest contributors. Results from this study provide crucial knowledge for the source identification of PAHs as well as for the design of abatement strategies against pollutant emissions.

Populations of plants and animals, including humans, living in close proximity to abandoned uranium mine sites are vulnerable to uranium exposure through drainage into nearby waterways, soil accumulation, and blowing dust from surface soils. Little is known about how the environmental impact of uranium exposure alters the health of human populations in proximity to mine sites, so we used developmental zebrafish (Danio rerio) to investigate uranium toxicity. Fish are a sensitive target for modeling uranium toxicity, and previous studies report altered reproductive capacity, enhanced DNA damage, and gene expression changes in fish exposed to uranium. In our study, dechorionated zebrafish embryos were exposed to a concentration range of uranyl acetate (UA) from 0 to 3000 μg/L for body burden measurements and developmental toxicity assessments. Uranium was taken up in a concentration-dependent manner by 48 and 120 h post fertilization (hpf)-zebrafish without evidence of bioaccumulation. Exposure to UA was not associated with teratogenic outcomes or 24 hpf behavioral effects, but larvae at 120 hpf exhibited a significant hypoactive photomotor response associated with exposure to 3 μg/L UA which suggested potential neurotoxicity. To our knowledge, this is the first time that uranium has been associated with behavioral effects in an aquatic organism. These results were compared to potential metal co-contaminants using the same exposure paradigm. Similar to uranium exposure, lead, cadmium, and iron significantly altered neurobehavioral outcomes in 120-hpf zebrafish without inducing significant teratogenicity. Our study informs concerns about the potential impacts of developmental exposure to uranium on childhood neurobehavioral outcomes. This work also sets the stage for future, environmentally relevant metal mixture studies. Summary Uranium exposure to developing zebrafish causes hypoactive larval swimming behavior similar to the effect of other commonly occurring metals in uranium mine sites. This is the first time that uranium exposure has been associated with altered neurobehavioral effects in any aquatic organism.

Initial Cadmium (Cd) isotope fractionation studies in cereals ascribed the retention of Cd and its light isotopes to the binding of Cd to sulfur (S). To better understand the relation of Cd binding to S and Cd isotope fractionation in soils and plants, we combined isotope and XAS speciation analyses in soil-rice systems that were rich in Cd and S. The systems included distinct water management (flooded vs. non-flooded) and rice accessions with (excluder) and without (non-excluder) functional membrane transporter OsHMA3 that transports Cd into root vacuoles. Initially, 13% of Cd in the soil was bound to S. Through soil flooding, the proportion of Cd bound to S increased to 100%. Soil flooding enriched the rice plants towards heavy isotopes (δ¹¹⁴/¹¹⁰Cd = −0.37 to −0.39%) compared to the plants that grew on non-flooded soils (δ¹¹⁴/¹¹⁰Cd = −0.45 to −0.56%) suggesting that preferentially light Cd isotopes precipitated into Cd sulfides. Isotope compositions in CaCl₂ root extracts indicated that the root surface contributed to the isotope shift between soil and plant during soil flooding. In rice roots, Cd was fully bound to S in all treatments. The roots in the excluder rice strongly retained Cd and its lights isotopes while heavy isotopes were transported to the shoots (Δ¹¹⁴/¹¹⁰Cdₛₕₒₒₜ₋ᵣₒₒₜ 0.16–0.19‰). The non-excluder rice accumulated Cd in shoots and the apparent difference in isotope composition between roots and shoots was smaller than that of the excluder rice (Δ¹¹⁴/¹¹⁰Cdₛₕₒₒₜ₋ᵣₒₒₜ −0.02 to 0.08‰). We ascribe the retention of light Cd isotopes in the roots of the excluder rice to the membrane transport of Cd by OsHMA3 and/or chelating Cd–S complexes in the vacuole. Cd–S was the major binding form in flooded soils and rice roots and partly contributed to the immobilization of Cd and its light isotopes in soil-rice systems.