Soil heavy metal pollution, especially lead (Pb) and arsenic (As), is a global issue that requires urgent attention. In the present study, phosphate-modified ferric-based material (PFM) was used to remedy Pb and As co-contaminated soil. The remediation potential of PFM on Pb and As co-contaminated soil was studied by static culture experiments, and the effect on maize (Zea mays L.) seedling growth was studied using pot experiments. The results showed that the bioavailability of Pb and As in the soil and their accumulation in the seedlings were reduced when PFM was added to the soil. At 2–6 wt% PFM, the remediation rates of Pb and As reached 57%–82% and 62%–76%, respectively, and their accumulation in the seedlings decreased by 27.8%–68% and 55.6%–70%. The optimal amount of PFM was 4 wt% of the soil. There was a linear correlation between the amount of DTPA-extractable Pb or NaHCO₃-extractable As in the soil and the amount of Pb or As accumulated by the seedlings. The correlation coefficients of Pb and As reached 0.7690–0.8166 and 0.9982–0.9779. Seedling growth was also promoted. Compared with the controls, the seedling emergence rate increased by 1.4%–4%, plant height increased by 4.1%–12.4%, plant weight increased by 29.6%–37%, and the root length increased by 5%–52%. In summary, PFM offers an environmentally friendly approach with excellent potential for the remediation of Pb and As co-contaminated soil.

The effluents of municipal wastewater treatment plant (WWTP) contain excessive nitrogen and phosphorus compared with the concentration in rivers or lakes. To reduce the pollutant load placed on aqueous environments, constructed wetland (CW) technology has been widely applied to advanced wastewater treatment. Packing substrates in CW could remove various pollutants. Steel slag, yellow earth, kaolin, volcanic rock, anthracite, and ceramsite could effectively remove phosphorus (P); volcanic rock, ceramsite, zeolite, yellow earth, manganese sand, and activated carbon have an affinity for ammonia nitrogen (NH₄⁺-N). After 24 h reactions with the WWTP standard 1B synthetic wastewater, four packing substrates, i.e., volcanic rock and anthracite (1:1), volcanic rock and yellow earth (2:1), zeolite and yellow earth (2:1), and manganese sand and activated carbon (1:3), could remove over 56% and 30% of NH₄⁺-N and phosphorus respectively. In addition, anthracite and volcanic rock (1:3), anthracite and activated carbon (1:40), anthracite and manganese sand (1:5), and anthracite and zeolite (1:4) effectively purified NH₄⁺-N and phosphorus in secondary WWTP effluent, with removal efficiency exceeding 39% and 27%, respectively. A sequential experiment was performed to optimize packing substrates ratios in CW with volcanic rock and anthracite, ceramsite and yellow earth, and manganese sand and activated carbon. When the quantity of the substrate was doubled, most packing substrates adsorb more than 50% phosphorus and NH₄⁺-N of the standard 1B WWTP synthetic wastewater. Considering the removal efficiency of packing substrates on phosphorus and NH₄⁺-N, it is suggested that manganese sand and activated carbon (1:3), volcanic rock and anthracite (2:1), and yellow earth are appropriate substrates for CW in WWTP effluent advanced treatment.

Nutrient retention is an important process in lake nutrient cycling of lakes and can mitigate lake eutrophication. However, little is known about temporal lake nutrient retention efficiency and it varies due to changes in hydrological, ecological, and nutrient inputs to lake waters. Quantitative information about seasonal lake N and P retention is critical for developing strategies to reduce eutrophication in lake systems. This study investigated TN and TP retention efficiencies and retention masses using water and mass balance calculations, and statistically analyzed the seasonal variability of nutrient retention in Lake Chaohu, China, from 2014 to 2018. Lake Chaohu experienced large amounts of external loads inputs (23.2 g N m⁻² year⁻¹ and 1.3 g P m⁻² year⁻¹), and approximately 58% TN and 48% TP were retained annually. The lake acted more as a sink for N than for P. The mean annual TP retention efficiency decreased (P < 0.05) over the study period, indicating that TP retention capacity was gradually exceeded. Seasonal variability of TN and TP retention efficiency was high and ranged from − 18.7 to 144.1% and from − 58.8 to 170.7%, respectively, over the five study years. The internal P loads over the study period were equivalent to roughly 9% of the total external loads. The annual nutrient retention efficiency of TN and TP increased with hydraulic residence time, while water temperature was an essential factor for the contrasting seasonal variation patterns of TN and TP retention efficiencies.

The carbon recovery from organic space waste by supercritical water oxidation (SCWO) was studied to support resource recovery in a regenerative life support system. Resource recovery is of utmost importance in such systems which only have a limited total amount of mass. However, the practical waste treatment strategies for solid space wastes employed today are only storing and disposal without further recovery. This work assesses the performance of SCWO at recovering organic wastes as CO₂ and water, to discuss the superiority of SCWO over most present strategies, and to evaluate the different SCWO reactor systems for space application. Experiments were carried out with a batch and a continuous reactor at different reaction conditions. The liquid and gas products distribution were analyzed to understand the conversion of organics in SCWO. Up to 97% and 93% of the feed carbon were recovered as CO₂ in the continuous and the batch reactor, respectively. Residual carbon was mostly found as soluble organics in the effluent. Compared with the batch reactor, the continuous reactor system demonstrated a ten times higher capacity within the same reactor volume, while the batch reactor system was capable of handling feeds that contained particulate matter though suffering from poor heat integration (hence low-energy efficiency) and inter-batch variability. It was concluded that SCWO could be a promising technology to treat solid wastes for space applications. A continuous reactor would be more suitable for a regenerative life support system.

This work investigates the feasibility of co-mechanochemical treatment of oil-contaminated drill cuttings (OCDC), circulation fluidized bed combustion (CFBC) fly ash, and quicklime to prepare non-sintered lightweight aggregates (NSLWAs). The NSLWAs with high cylinder compressive strength and low water absorption could be obtained under the condition of optimal water addition and appropriate steam-curing temperature, as well as steam-curing time. Co-mechanochemical treatment could enhance the pozzolanic reactivity of CFBC fly ash effectively, which is beneficial to the strength development of NSLWAs. Moreover, co-mechanochemical treatment also can degrade the petroleum hydrocarbon of OCDC, greatly reducing the leaching concentrations of total petroleum hydrocarbons (TPH) of NSLWAs. The final leaching concentrations of TPH are much lower than the requirements of Chinese National Standard GB 31571–2015. Graphical abstract

Heavy metal pollution is a global ecological safety issue, especially in crops, where it directly threatens regional ecological security and human health. Selecting scientific evaluation methods is an important prerequisite for understanding the distribution of heavy metals in a region. To evaluate the distribution characteristics of arsenic (As), cadmium (Cd), copper (Cu), and zinc (Zn) in farmland soil–rice system in Doumen District of Zhuhai City, Pearl River Delta, we analyzed the high geological background area and heavy metal contents in soil by inverse distance–weighted interpolation and single-factor pollution index. Bioconcentration factor (BCF) was used to study the migration and accumulation characteristics of heavy metals. Then, the soil–rice system was evaluated comprehensively with a novel evaluation method, i.e., the influence index of comprehensive quality (IICQ). Results showed that As, Cd, Cu, and Zn in the soil of the study area followed normal distribution. Cd and Cu were the main pollutants whose point contamination rates were 50% and 22.86%, respectively. A total of 2.86% of the soil were contaminated by As, and no Zn contamination was observed in the soil. At the same time, As and Cd in rice were partially polluted, and the Cu and Zn were not polluted. The order of bioaccumulation coefficient was Cd > Zn > Cu > As, and no evident enrichment was observed. According to the impact index of IICQ to evaluate the pollution of heavy metals in the soil–rice system, 96.98% of the soil in study area was in a state of moderate, heavy, and extreme pollution, which were concentrated in the northern and central parts of the study area. The soil–rice system in the high geological background area was in a subhealthy state. A total of 90.69% of the soil were polluted, but the rice met the national food safety standards.

This study investigates the asymmetric effects of economic growth, energy use, and financial development, on carbon dioxide emissions in Saudi Arabia, from 1971 to 2014, using the nonlinear autoregressive distributed lag (NARDL) model. Prior to the application of the model, the integration proprieties of the variables were examined employing the recently RALS-LM (Residual Augmented Least squares—Lagrange Multiplier) unit root test, with two endogenous structural breaks. The main finding is that there exists an asymmetric cointegration relationship among the variables. In the long-run, both positive and negative shocks in economic growth rise emissions, but the effect of positive shocks is larger. In addition, both positive shocks in energy consumption and negative shocks in financial development surge CO₂ emissions. In the short-run, the increasing economic growth is being made at the expense of the polluted environment. In contrast, any decrease in the economic growth would contribute to the improvement of environmental quality. Furthermore, positive shocks on energy consumption surges CO₂ emissions and positive shocks in financial development reduces emissions. The asymmetric causality test of Hatemi-J (2012) suggests that economic growth (positive shocks) causes carbon dioxide emissions. At the same time, CO₂ emissions (positive shocks) cause energy consumption. However, no significant causal relationship is found between financial development and CO₂ emissions. In light of these findings, some policy implications are recommended.

We found an error in the materials and methods section. Since our team used two methodsfor anesthesia in rats and the anesthesia method used in this paper was 3.5% chloralhydrate anesthesia, we mistakenly wrote the anesthetic as 3% sodium pentobarbital.

The ecological consequences of military spending is a hugely neglected area, and a veil of mystery surrounds this topic. The environmental threats posed by militaries remain insufficiently investigated in the name of national security. Prompted by the internal and external conflicts and prolonged military dictatorships, the Pakistani military assumes a role that goes beyond that of a traditional army. The current study addresses this significant gap in the literature by investigating the impacts of military spending on economic growth and the ecological footprint in Pakistan from 1971 to 2016 using the combined cointegration test and the bootstrap causality test. The findings of the study unveil a positive impact of military spending on the ecological footprint, while a negative impact on economic growth. The outcomes of the bootstrap causality test of Hacker and Hatemi-J (2012) highlight that economic growth Granger causes military spending, while causality runs from military spending to the ecological footprint. Energy consumption contributes to the ecological footprint and economic growth, whereas education expenditures do not influence economic growth and the environment in the long run. Further, the findings suggest a U-shaped link between GDP and footprint in Pakistan. The authorities should focus on resolving external and internal conflicts, on a priority basis, and reduce military spending to improve economic growth and the environment.

Urbanized rivers flowing through polluted megacities receive substantial amount of carbon from domestic sewage and industrial effluents which can significantly alter the air-water CO₂ flux rates. In this regard, we quantified the partial pressure of CO₂ in the surface water (pCO₂(water)), air-water CO₂ fluxes, and associated biogeochemical parameters in the Hooghly River, India, flowing through two of the most polluted cities of the country, Kolkata and Howrah, over a complete annual cycle during spring tidal phase (SP) and neap tidal phase (NP). This urbanized part of Hooghly River was always supersaturated with CO₂ having an annual mean pCO₂(water) and air-water CO₂ flux of ~ 3800 μatm and ~ 49 mol C m⁻² year⁻¹, respectively. Significant seasonal variability was observed for both pCO₂(water) and air-water CO₂ flux (pre-monsoon, 3038 ± 539 μatm and 5049 ± 964 μmol m⁻² h⁻¹; monsoon, 4609 ± 711 μatm and 7918 ± 1400 μmol m⁻² h⁻¹; post-monsoon, 2558 ± 258 μatm and 4048 ± 759 μmol m⁻² h⁻¹, respectively). Monthly mean pH and total alkalinity varied from 7.482 to 8.099 and from 2437 to 4136 μmol kg⁻¹, respectively, over the annual cycle. pCO₂(water) showed significant positive correlation with turbidity and negative correlation with electrical conductivity and gross primary productivity (GPP). High water discharge could have facilitated high turbidity, especially during the monsoon season, which led to depletion in GPP and enhancement in pCO₂(water) which in turn led to very high CO₂ effluxes. The CO₂ efflux rate in this urbanized riverine stretch was substantially higher than that observed in previous studies carried out in the less urbanized estuarine stretch of Hooghly. This indicates that the presence of highly urbanized and polluted metropolis potentially enhanced the pCO₂(water) and CO₂ effluxes of this river. Similar observations were made recently in some Asian and Australian urban rivers.