Internal Electric Field Facilitates Facet-Dependent Photocatalytic Cl- Utilization on BiOCl in High-Salinity Wastewater for Ammonium Removal.

High Cl- concentration in saline wastewater (e.g., landfill leachate) limits wastewater purification. Catalytic Cl- conversion into reactive chlorine species (RCS) arises as a sustainable strategy, making the salinity profitable for efficient wastewater treatment. Herein, aiming to reveal the structure-property relationship in Cl- utilization, bismuth oxychloride (BiOCl) photocatalysts with coexposed {001} and {110} facets are synthesized. With an increasing {001} ratio, the RCS production efficiency increases from 75.64 to 96.89 µg L-1 min-1. Mechanism investigation demonstrates the fast release of lattice Cl- as an RCS and the compensation of ambient Cl-. Correlation analysis between the internal electric field (IEF, parallel to [001]) and normalized efficiency on {110} (kRCS/S{110}, perpendicular to [001]) displays a coefficient of 0.86, validating that the promoted carrier dynamics eventually affects Cl- conversion on the open layered structure. The BiOCl photocatalyst is well behaved in ammonium (NH4+-N) degradation ranging from 20 to 800 mg N L-1 with different chlorinity (3-12 g L-1 NaCl). The sustainable Cl- conversion into RCS also realizes 85.4% of NH4+-N removal in the treatment of realistic landfill leachate (662 mg of N L-1 NH4+-N). The structure-property relationship provides insights into the design of efficient catalysts for environment remediation using ambient Cl-.

Dose-dependent inhibitory effects of glyphosate on invasive Pomacea canaliculata reproductive and developmental growth under oxidative deposition.

Glyphosate (GLY) is the most widely used herbicide worldwide, and its effects on animals and plants have attracted increasing attention. In this study, we explored the following: (1) the effects of multigenerational chronic exposure to GLY and H2O2, alone or in combination, on the egg hatching rate and individual morphology of Pomacea canaliculata; and (2) the effects of short-term chronic exposure to GLY and H2O2, alone or in combination, on the reproductive system of P. canaliculata. The results showed that H2O2 and GLY exposure had distinct inhibitory effects on the hatching rate and individual growth indices with a substantial dose effect, and the F1 generation had the lowest resistance. In addition, with the prolongation of exposure time, the ovarian tissue was damaged, and the fecundity decreased; however, the snails could still lay eggs. In conclusion, these results suggest that P. canaliculata can tolerate low concentrations of pollution and in addition to drug dosage, the control should focus on two time points, the juvenile and early stage of spawning.

Behaviors of Organic Ligands and Phosphate during Biochar-Driven Nitrate Adsorption in the Presence of Low-Molecular-Weight Organic Acids.

A batch experiment was conducted to examine the behavior of nitrate, organic ligands, and phosphate in the co-presence of biochar and three common low-molecular-weight organic acids (LMWOAs). The results show that citrate, oxalate, and malate ions competed with nitrate ion for the available adsorption sites on the biochar surfaces. The removal rate of LMWOA ligands by the biochar via adsorption grew with increasing solution pH. The adsorbed divalent organic ligands created negatively charged sites to allow binding of cationic metal nitrate complexes. A higher degree of biochar surface protonation does not necessarily enhance nitrate adsorption. More acidic conditions formed under a higher dose of LMWOAs tended to make organic ligands predominantly in monovalent forms and failed to create negatively charged sites to bind cationic metal nitrate complexes. This could adversely affect nitrate removal efficiency in the investigated systems. LMWOAs caused significant release of phosphate from the biochar. The phosphate in the malic acid treatment tended to decrease over time, while the opposite was observed in the citric- and oxalic-acid treatments. This was caused by re-immobilization of phosphate in the former due to the marked increase in solution pH over time.

Role of passivators for Cd alleviation in rice-water spinach intercropping system.

Soil pollution with cadmium (Cd) has posed a threat to our food safety. And rice consumption is the main source of Cd intake in China. Rice intercropping with water spinach is an efficient way for crop production and phytoremediation in Cd-contaminated soil. However, few people work on the Cd remediation by a combination of the passivation and intercropping. In this study, two passivators (the Si-Ca-Mg ameliorant and the Fe-modified biochar with microbial inoculants) were used in the monoculture and intercropping systems to evaluate the potential of co-effect of passivators and cropping systems on the plant growth and Cd phytoremediation. Results showed that the highest rice biomass and rice yield were presented in the intercropping system with the passivator additions, however, relatively lower biomass was showed in water spinach due to the competition with rice. And more Cd accumulated in water spinach while lower Cd in that of different rice parts. The intercropping system with the addition of the Si-Ca-Mg ameliorant and the microbial Fe-modified biochar significantly reduced the Cd contents in brown rice by 58.86% and 63.83%, while notably enhanced the Cd accumulation of water spinach by 32.0% and 22.0%, compared with the monoculture without passivation, respectively. This probably due to the increased pH, the lowered Cd availability in soil, and the reduced TF and BCF values in rice plants with passivator applications. Collectively, this study indicated that rice-water spinach intercropping, especially with the passivator additions, may function as an effective way for Cd remediation and guarantee rice grain safety.

Biochar-driven reduction of As(V) and Cr(VI): Effects of pyrolysis temperature and low-molecular-weight organic acids.

Batch experiments were conducted to examine the differential effects of biochar pyrolysis temperature and low-molecular-weight organic acids on the reduction of As(V) and Cr(VI) driven by Pennisetum hydridum biochar. The results showed that pyrolysis temperature significantly affected the reducing strength of the biochar. Biochar produced at 500 °C had a stronger electron-donating capacity than did the biochars produced at 300 and 700 °C. In the co-presence of the biochar and a low-molecular-weight organic acid, arsenic and chromium behaved differently. Oxalic acid and malic acid tended to have better effects on enhancing biochar-driven Cr(VI) reduction, as compared to citric acid while the opposite was observed for biochar-driven As(V) reduction. Biochar produced at 300 °C was more favourable for Cr(VI) reduction, as compared to the higher-temperature biochars while the opposite was observed for As(V) reduction in the presence of low-molecular-weight organic acids. This may make the lower-temperature biochar ideal for remediating contaminated soils containing both As(V) and Cr(VI) since it could maximize Cr(VI) reduction while minimizing As(V) reduction.

Yield advantage and cadmium decreasing of rice in intercropping with water spinach under moisture management.

Rice (Oryza sativa L.) intercropping with water spinach (Ipomoea aquatica Forsk) is an effective agricultural practice for safe crop production and for phytoremediation in cadmium-contaminated soil. A field and pot experiment were conducted to investigate the growth and cadmium absorption of rice intercropped with water spinach under different moisture management schemes (continuous flooding, interval flooding, and 75% field capacity). In the field experiment, the concentration of Cd in the grain of rice was significantly lower in the intercropping system than that permitted by the National Food Safety Standard of China (GB 2762-2017). Furthermore, the land equivalent ratio (1.42) was higher in the rice-water spinach intercropping system, indicating a significant advantage of the intercropping system in yield. At the same time, the bio-concentration amount (BCA) of Cd of rice and water spinach in intercropping system significantly increased by 17.99% and 31.98%, respectively (P＜0.05). However, the metal removal equivalent ratio (MRER) of Cd was 1.34, which showed the intercropping system of rice-water spinach had advantage in Cd removal. In the pot experiment, the total iron plaque concentration on the root surface of rice and the pH of the rhizosphere soil were higher under continuous flooding (TCF) than under the control conditions (75% field capacity, TCK), which could significantly decrease the available Cd in the rhizosphere soil and the accumulation of Cd in rice organs. So, this study demonstrated that iron plaque can obstruct and decrease the Cd absorbed by rice in a rice-water spinach intercropping system combined with water management. The intercropping rice with water spinach can achieve the goal of remediation while producing for farmland contaminated by Cd.

Effect of soluble calcium on enhancing nitrate retention by biochar.

Batch experiments were conducted to test the hypothesis that nitrate (NO3-) could be immobilized by biochar via adsorption of CaNO3+ to the negatively charged biochar surfaces. The results show that addition of soluble Ca in both aqueous and soil systems enabled NO3- retention by the biochar material. Increase in the added Ca enhanced the retention rate and the optimal NO3- retention was gained at a Ca/NO3 molar ratio of 2 for the aqueous system. For the soil system, the Ca/NO3 molar ratio required to attain the optimal NO3- retention was much greater due to competition of other soil-borne ligands and soil colloids for the available Ca. At the same level of added Ca, the amount of NO3- being retained tended to increase with increasing dose of the biochar. More NO3- was retained in the soil system than in the aqueous system at the same dosage level of biochar due to additional adsorption of CaNO3+ by negatively changed soil organic and inorganic colloids. The findings obtained from this study have implications for developing effective methods for reducing NO3- leaching from soils.

Effect of rainwater-borne hydrogen peroxide on manure-derived Cu and Zn speciation distribution and bioavailability in rice-soil system.

Pot experiment was conducted to examine the effects of rainwater-borne hydrogen peroxide (H2O2) on transformation of Cu, Zn from pig manure in soils and its resulting impacts on the growth of Cu and Zn uptake by a rice plant. Results showed that the exogenous application of H2O2 significantly improved the rice biomass and yield. Addition of H2O2 into the soils led to reduced uptake of soil-borne Cu and Zn by the rice plants and this had a significant effect on reducing the accumulation of Zn in rice grains. It was indicated that the increased pH in soil might play important role in reducing Cu and Zn content in rice. Furthermore, Cu and Zn content in exchangeable form and carbonate bounded form dramatically decreased in soil, on the contrary, the organic combination state increased significantly in H2O2 treatment. The findings point to a potential research direction that rainwater-borne H2O2 in nature may help to change morphology of heavy metals in natural soil environments, but further study is still needed to explore the related mechanisms in Cu and Zn in manures and paddy rice field receiving rainwater-borne H2O2.

Biochar and crushed straw additions affect cadmium absorption in cassava-peanut intercropping system.

Cassava (Manihot esculenta Crantz) intercropped with peanut (Arachis hypogaea) has good complementary effects in time and space. In the field plot test, the land equivalent ratio (LER) of cassava-peanut intercropping system was 1.43, showing obvious intercropping yield advantage. Compared with monocropping, Cd contents in the roots of cassava and seeds of peanut were significantly reduced by 20.00% and 31.67%, respectively (p < 0.05). Under the unit area of hectare, compared with monocropping of cassava and peanut, the bioconcentration amount (BCA) of Cd in the intercropping system increased significantly by 24.98% and 25.59%, respectively (p < 0.05), and the metal removal equivalent ratio (MRER) of Cd was 1.25, indicating that the intercropping pattern had advantage in Cd removal. In the cement pool plot test, compared with the control, cassava intercropped with peanut under biochar and crushed straw additions did not only enhance the available nutrients and organic matter contents in rhizosphere soil but also promoted the crop growth and increased the content of chlorophyll (SPAD values) of plant leaves. The peanut seeds biomass under biochar and straw additions were significantly increased by 112.34% and 59.38% (p < 0.05), respectively, while the cassava roots biomass under biochar addition was significantly increased by 63.54% (p < 0.05). Applying biochar significantly decreased the content of Cd which extracted by diethylenetriaminepentaacetic acid (DTPA-Cd) in soil and reduced Cd uptake as well as translocation into plant tissues. The BCA of Cd of cassava under biochar addition decreased significantly by 53.87% in maturity stage (p < 0.05), thus reduced the ecological risk of Cd to crops and was of great significance to produce high quality and safe agricultural products. Besides, the crushed straw enhanced the biomass of crops, reduced Cd content in all tissues and maintained Cd uptake in the intercropping system. Therefore, it can realize the integration of ecological remediation and economic benefit of two energy plants in Cd contaminated soil after applied crushed straw in cassava-peanut intercropping system.

Decomposition of long-chain petroleum hydrocarbons by Fenton-like processes: Effects of ferrous iron source, salinity and temperature.

Batch experiments were conducted to examine the effects of ferrous iron source, soil salinity and temperature on degradation of long-chain petroleum hydrocarbons by Fenton-like processes. The results show that over 70%, 50% and 25% of aliphatic C16-C21, C21-C35 and C35-C40, respectively, was eliminated at a H2O2 dose of 1.5%. The decomposition rate of petroleum hydrocarbons was similar to each other for ferrous sulfate and magnetite while the capacity of pyrite to trigger Fenton-driven decomposition of long-chain aliphatic petroleum hydrocarbons was weaker, as compared to ferrous sulfate and magnetite. The decomposition rate of aromatic hydrocarbons decreased with increasing length of carbon chain in the ferrous sulfate and magnetite systems, but the opposite was observed in the pyrite system. The effect of Fenton-like process on degradation of long-chain petroleum hydrocarbons was enhanced by increased temperature. At a temperature of 60 °C, the enhancement of Fenton process outweighed the adverse effects from potential loss of H2O2 due to elevated temperature. The use of magnetite as a source of ferrous iron was likely to prevent consumption of Fe2+ by complexation with chloride ion from occurring and consequently effectively eliminated the inhibitory effect of salinity on Fenton reaction.

Comparison of Cd subcellular distribution and Cd detoxification between low/high Cd-accumulative rice cultivars and sea rice.

Salt-tolerant rice cultivar (sea rice) is a research hotspot worldwide due to its high yield in high salinity soil. However, knowledge regarding the cadmium (Cd) effects on the growth of sea rice is limited. To determine the short-term and long-term impact of Cd stress, relatively low/high Cd-accumulative rice cultivars and sea rice were grown to compare their growth responses to Cd stress over time. The results showed that sea rice presented the highest Cd concentrations in the root, stem, and leaves under 32-days of Cd stress. Cd stress shortened and thickened the rice root, and decreased the proportion of root diameters in the 0-0.2 mm range. Cd stress remarkably increased the Cd and Fe concentration in dithionite-citrate-bicarbonate (DCB) extracts, and the DCB-Cd and DCB-Fe concentrations were the highest in sea rice. The subcellular distribution of Cd in the rice roots indicated that Cd accumulated the most in the soluble fraction and cell wall. The contents of pectin and hemicellulose 2 in the root cell wall of the low-Cd accumulative rice variety CL755 were higher than those in MXZ and sea rice. Collectively, this work provides a general understanding of the Cd effects on sea rice growth and indicates that sea rice has a relatively high Cd accumulation compared with the other two rice cultivars. However, the specifically-related mechanism remains to be further studied.

Fenton process-affected transformation of roxarsone in paddy rice soils: Effects on plant growth and arsenic accumulation in rice grain.

Batch and greenhouse experiments were conducted to examine the effects of Fenton process on transformation of roxarsone in soils and its resulting impacts on the growth of and As uptake by a rice plant cultivar. The results show that addition of Fenton reagent markedly accelerated the degradation of roxarsone and produced arsenite, which was otherwise absent in the soil without added Fenton reagent. Methylation of arsenate was also enhanced by Fenton process in the earlier part of the experiment due to abundant supply of arsenate from Roxarsone degradation. Overall, addition of Fenton reagent resulted in the predominant presence of arsenate in the soils. Fenton process significantly improved the growth of rice in the maturity stage of the first crop, The concentration of methylated As species in the rice plant tissues among the different growth stages was highly variable. Addition of Fenton reagent into the soils led to reduced uptake of soil-borne As by the rice plants and this had a significant effect on reducing the accumulation of As in rice grains. The findings have implications for understanding As biogeochemistry in paddy rice field receiving rainwater-borne H2O2 and for development of mitigation strategies to reduce accumulation of As in rice grains.

Biomonitoring of glyphosate and aminomethylphosphonic acid: Current insights and future perspectives.

Glyphosate is one of the most widely used herbicides globally, raising concerns about its potential impact on human health. Biomonitoring studies play a crucial role in assessing human exposure to glyphosate and providing valuable insights into its distribution and metabolism in the body. This review aims to summarize the current trends and future perspectives in biomonitoring of glyphosate and its major degradation product of aminomethylphosphonic acid (AMPA). A comprehensive literature search was conducted, focusing on studies published between January 2000 and December 2022. The findings demonstrated that glyphosate and AMPA have been reported in different human specimens with urine as the dominance. Sample pretreatment techniques of solid-phase and liquid-liquid extractions coupled with liquid/gas chromatography-tandem mass spectrometry have achieved matrix elimination and accurate analysis. We also examined and compared the exposure characteristics of these compounds among different regions and various populations, with significantly higher levels of glyphosate and AMPA observed in Asian populations and among occupational groups. The median urinary concentration of glyphosate in children was 0.54 ng/mL, which was relatively higher than those in women (0.28 ng/mL) and adults (0.12 ng/mL). It is worth noting that children may exhibit increased susceptibility to glyphosate exposure or have different exposure patterns compared to women and adults. A number of important perspectives were proposed in order to further facilitate the understanding of health effects of glyphosate and AMPA, which include, but are not limited to, method standardization, combined exposure assessment, attention for vulnerable populations, long-term exposure effects and risk communication and public awareness.

Factors affecting N2O fluxes from heavy metal-contaminated mangrove soils in a subtropical estuary.

A 1-year field monitoring program was carried out to observe seasonal variation in N2O fluxes at two typical mangrove wetlands in a subtropical estuary. The soils in the island-type mangrove wetland had a higher level of heavy metal(loid) contamination and a lower level of salinity compared to the small bay-type mangrove wetland. While there was a high level of similarity in the seasonal variation pattern of N2O fluxes between the two investigated sites with both being significantly higher in summer than in other seasons, the average of N2O fluxes in the island-type mangrove wetland was 7.19 µg·m-2·h-1， which tended to be lower compared to the small bay-type mangrove wetland (15.63 µg·m-2·h-1). Overall, N2O flux was closely related to soil-borne heavy metal(loid)s, showing a trend to decrease with increasing concentration of these heavy metal(loid)s. The N2O fluxes increased with decreasing abundance of either denitrifiers or nitrifiers. But the opposite was observed for the anammox bacteria present in the soils. The anammox bacteria were more sensitive to heavy metal(loid) stress but more tolerated high salinity encountered in the investigated soils compared to the denitrifiers or nitrifiers. It appears that anammox reactions mediated by anammox bacteria played a key role in affecting the spatial variation in N2O fluxes from the mangrove soils in the study area. And an increased level of ammonium in soils tended to promote the activity of anammox bacteria and consequently enhanced N2O emission from the mangrove soils.

Rainwater input reduces greenhouse gas emission and arsenic uptake in paddy rice systems.

This work aimed to test the hypothesis that rainwater-borne hydrogen peroxide (H2O2) can affect arsenic uptake by rice plants and emission of greenhouse gases in paddy rice systems. A mesocosm rice plant growth experiment, in conjunction with rainwater monitoring, was conducted to examine the effects of rainwater input on functional groups of soil microorganisms related to transformation of arsenic, carbon and nitrogen as well as various arsenic species in the soil and plant systems. The fluxes of methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) were measured during selected rainfall events. The results showed that rainwater-borne H2O2 effectively reacted with Fe2+ present in paddy soil to trigger a Fenton-like reaction to produce •OH. Both H2O2 and •OH inhibited As(V)-reducing microbes but promoted As(III)-oxidizing microbes, leading to a net increase in arsenate-As that is less phytoavailable compared to arsenite-As. This impeded uptake of soil-borne As by the rice plant roots, and consequently reduced the accumulation of As in the rice grains. The input of H2O2 into the soil caused more inhibition to methanogens than to methane-oxidizing microbes, resulting in a reduction in CH4 flux. The microbes mediating the transformation of inorganic nitrogen were also under oxidative stresses upon exposure to the rainwater-derived H2O2. And the limited conversion of NO3- to NO played a crucial role in reducing N2O emission from the paddy soils. The results also indicated that the rainwater-borne H2O2 could significantly affect other biogeochemical processes that shape the wider ecosystems, which is worth further investigations.

Polyaspartic acid assisted-phytoremediation of cadmium-contaminated farmland: Phytoextraction efficiency, soil quality, and rhizosphere microbial community.

Cadmium is highly toxic and one of the most dangerous metal pollutants in soil, and poses a serious threat to human health through soil-crop-food chain transmission. Polyaspartic acid (PASP) is a biodegradable additive that is environment-friendly compared to traditional chelating agents. Current studies have explored its effect on auxiliary phytoextraction at a laboratory scale; however, the method is still rarely reported at the field scale. Therefore, this study used two ecotypes of Pennisetum sinese in a field experiment for 3 years in Jiaoxi Township, Liuyang City, Hunan Province, China, to understand the effect of PASP on the phytoremediation of Cd-contaminated soil and soil quality through long-term field studies. Moreover, because the soil microbial community responds well to the phytoremediation effect of heavy metal (including Cd)-contaminated soil, the changes in rhizosphere soil microbial community diversity and composition were analyzed. After 2 years of PASP-enhanced phytoremediation, the PASP application increased the total Cd reduction in soil by 237 % and 255 %, and the soil DTPA-extractable Cd content decreased to 0.092 and 0.087 mg kg-1. When the application of PASP ceased in the third year, the two ecotypes of P. sinese obtained after harvest could achieve feed safety. Our study showed that the application of PASP could significantly increase the Cd extraction capacity and shoot biomass of P. sinese, and maintain soil health by optimizing the composition and structure of rhizosphere bacterial communities. The rhizosphere bacterial community structure was improved and dominated by Acidobacteriota, Proteobacteria, and Chloroflexi at the phylum level, and the increased abundance of Acetobacter, Enterobacter, Pseudomonas, and Stenotrophomonas at the genus level may promote heavy metal detoxification in soil, plant growth, and phytoremediation. Long-term field monitoring demonstrated that the low-cost and eco-friendly features of PASP made it a good candidate for enhancing phytoextraction efficiency and regulating soil microbial communities for remediation.

Contribution of free hydroxyl radical to the formation of micro(nano)plastics and release of additives during polyethylene degradation in water.

The omnipresence of secondary microplastics (MPs) in aquatic ecosystems has become an increasingly alarming public health concern. Hydrogen peroxide (H2O2) is an important oxidant in nature and the most stable reactive oxygen species occurred in natural water. In order to explore the contribution of free ˙OH generated from H2O2-driven Fenton-like reactions on the degradation of polyethylene (PE) and generation of micro- and nano-scale plastics in water, a batch experiment was conducted over a period of 620 days in water treated with micromolar H2O2. The incorporation of H2O2 in water induced the formation of flake-like micro(nano)-sized particles due to intensified oxidative degradation of PE films. The presence of ˙OH significantly enhanced the generation of both micro- and nano-scale plastics exhibiting a higher proportion of particles in the range of 200-500 nm compared to the Control. Total organic carbon in the H2O2 treated solution was nearly 174-fold higher than that of the Control indicating a substantial liberation of organic compounds due to the oxidative degradation of native carbon chain of PE and subsequent decomposition of its additives. The highly toxic butylated hydroxytoluene detected from the gas chromatography-mass spectrometry (GC-MS) analysis implied the toxicological behavior of secondary micro(nano)plastics influenced by the oxidation and decomposition processes The findings from this study further expand our understanding of the role of ˙OH in degrading PE micro-scale plastics into nanoparticles as an implication of naturally occurring H2O2 in aquatic environments. In the future, further attention should be drawn to the underlying mechanisms of H2O2-driven in-situ Fenton reaction mediated by natural environmental conditions targeting the alternation of light and darkness on the oxidative degradation of plastics.

Neonicotinoid insecticides and their metabolites: Specimens tested, analytical methods and exposure characteristics in humans.

The use of neonicotinoid insecticides (NEOs) has been rising globally due to their broad-spectrum insecticidal activity, unique mode of neurotoxic action and presumed low mammalian toxicity. Given their growing ubiquity in the environment and neurological toxicity to non-target mammals, human exposure to NEOs is flourishing and now becomes a big issue. In the present work, we demonstrated that 20 NEOs and their metabolites have been reported in different human specimens with urine, blood and hair as the dominance. Sample pretreatment techniques of solid-phase and liquid-liquid extractions coupled with high performance liquid chromatography-tandem mass spectrometry have successfully achieved matrix elimination and accurate analysis. We also discussed and compared exposure characteristics of these compounds among types of specimens and different regions. A number of important knowledge gaps were also identified in order to further facilitate the understanding of health effects of NEO insecticides, which include, but are not limited to, identification and use of neuro-related human biological samples for better elucidating neurotoxic action of NEO insecticides, adoption of advanced non-target screening analysis for a whole picture in human exposure, and expanding investigations to cover non-explored but NEO-used regions and vulnerable populations.

Generation of micro(nano)plastics and migration of plastic additives from Poly(vinyl chloride) in water under radiation-free ambient conditions.

A batch experiment was conducted to observe the liberation of micro- and nano-sized plastic particles and plastic additive-originated organic compounds from poly(vinyl chloride) under radiation-free ambient conditions. The weathering of PVC films in deionized water resulted in isolated pockets of surface erosion. Additional ●OH from Fenton reaction enhanced PVC degradation and caused cavity erosion. The detachment of plastic fragments from the PVC film surfaces was driven by autocatalyzed oxidative degradation. Over 90% of micro-sized plastic particles were <60 µm in length. The detached plastic fragments underwent intensified weathering, which involved strong dehydrochlorination and oxidative degradation. Further fragmentation of micro-sized particles into nano-sized particles was driven by oxidative degradation with complete dehydrochlorination being achieved following formation of nanoplastics. 20 organic compounds released from the PVC films into the solutions were identified. And some of them can be clearly linked to common plastic additives. In the presence of additional ●OH, the coarser nanoplastic particles (>500 nm) tended to be rapidly disintegrated into finer plastic particles (<500 nm), while the finest fraction of nanoplastics (<100 nm) could be completely decomposed and disappeared from the filtrates. The micro(nano)plastics generated from the PVC weathering were highly irregular in shape.

Biochar Is Not Durable for Remediation of Heavy Metal-Contaminated Soils Affected by Acid-Mine Drainage.

Biochar is a soil conditioner for enhancing plant growth and reducing plants' uptake of heavy metals. However, the protonation of biochar surfaces in acid soils can weaken the capacity of biochar to reduce the phytoavailability of soil-borne heavy metals over time. The aim of this study was to test this hypothesis by performing a plant-growth experiment with five harvest cycles to examine the durability of rice-straw biochar for the remediation of an acidic-mine-water-contaminated soil. The application of the biochar significantly reduced the phytoavailability of the heavy metals and inhibited the plant uptake of cationic heavy metals but not anionic Cr. The beneficial effects of the biochar were weakened with the increasing number of harvest cycles caused by the gradual protonation of the biochar surfaces, which resulted in the desorption of the adsorbed heavy metals. The weakening capacity of the biochar to reduce the heavy-metal uptake by the vegetable plants was more evident for Cu, Zn, and Pb compared to Ni and Cd. The experimental results generally confirmed the hypothesis. It was also observed that the bioaccessible amount of various metals in the edible portion of the vegetable was also reduced as a result of the biochar application.