Photodegradation of bisphenol A (BPA) in coastal aquaculture waters: Influencing factors, products, and pathways.

Bisphenol A (BPA), an endocrine-disrupting contaminant, is ubiquitous in the environment due to its presence in plastics, wastewater, and agricultural runoff. This study investigated the photodegradation behavior of BPA in coastal aquaculture waters near Qingdao, China. Lower salinity promoted BPA photodegradation, while higher salinity has an inhibitory effect, suggesting slower degradation in seawater compared to ultrapure water. Triplet-excited dissolved organic matter (3DOM*) was identified as the primary mediator of BPA degradation, with additional contributions from hydroxyl radicals (•OH), singlet oxygen (1O2), and halogen radicals (HRS). Alepocephalidae aquaculture water exhibited the fastest degradation rate, likely due to its high DOM and nitrate/nitrite (NO3-/NO2-) content, which are sources of 3DOM* and •OH. A positive correlation existed between NO3-/NO2- concentration and the BPA degradation rate. Ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) analysis identified the primary BPA photodegradation products, formed mainly through oxidative degradation, hydroxyl substitution, nitration, and chlorination pathways. Elucidating these photodegradation mechanisms provides valuable insights into the environmental fate and potential ecological risks of BPA in aquaculture environments. This knowledge can inform strategies for marine environmental protection and the development of sustainable practices.

Seaweeds as a major source of dietary microplastics exposure in East Asia.

Microplastics (MPs) occurrence in marine ecosystems is well known, but their accumulation in seaweeds and subsequent human exposure remain understudied. This research quantifies MPs presence in two commonly consumed seaweeds, kelp (Saccharina japonica) and nori (Pyropia yezoensis), in East Asia, revealing widespread contamination dominated by microfibers (<500 µm). Based on dietary patterns, human uptake through seaweed consumption was estimated and quantified. Notably, Chinese people consume an estimated 17,034 MPs/person/year through seaweed consumption, representing 13.1% of their total annual MPs intake. This seaweeds-derived exposure surpasses all other dietary sources, contributing up to 45.5% of overall MPs intake. The highest intake was in South Korea, followed by North Korea, China, and Japan. This research identifies seaweeds as a major, previously overlooked route of dietary MPs exposure. These findings are crucial for comprehensive risk assessments of seaweed consumption and the development of mitigation strategies, particularly for populations in East Asian countries.

Co-exposure of microplastics and polychlorinated biphenyls strongly influenced the cycling processes of typical biogenic elements in anoxic soil.

The co-exposure of microplastics (MPs) and polychlorinated biphenyls (PCBs) in soil is inevitable, but their combined effect on cycles of typical biogenic elements (e.g. C, N, Fe, S) is still unclear. And the co-exposure of MPs and PCBs caused more severe effects than single exposure to pollution. Therefore, in this study, a 255-day anaerobic incubation experiment was conducted by adding polyethylene microplastics (PE MPs, including 30 ± 10 µm and 500 µm) and PCB138. The presence of PE MPs inhibited the PCB138 degradation. Also, PE MPs addition (1%, w/w) enhanced the methanogenesis, Fe(Ⅲ) reduction, and sulfate reduction while inhibited nitrate reduction and the biodegradation of PCB138. And PCB138 addition (10 mg·kg-1) promoted the methanogenesis and Fe(Ⅲ) reduction, but inhibited sulfate reduction and nitrate reduction. Strikingly, the presence of PE MPs significantly reduced the impact of PCB138 on the soil redox processes. The abundance changes of special microbial communities, including Anaeromyxobate, Geobacter, Bacillus, Desulfitobacterium, Thermodesulfovibrio, Metanobacterium, etc., were consistent with the changes in soil redox processes, revealing that the effect of PE MPs and/or PCB138 on the cycle of typical biogenic elements was mainly achieved by altering the functional microorganisms. This study improves the knowledge of studies on the impact of MPs and combined organic pollutants to soil redox processes, which is greatly important to the stabilization and balance of biogeochemical cycling in ecology.

Rapid As(III) oxidation mediated by activated carbons: Reactive species vs. direct oxidation.

Activated carbon (AC) is widely used in pollutant removal, due to its adsorption capacity, conductivity and catalytic performance. However, few studies focus on the redox activity of AC and its role in pollutant transformation. In this study, we found that AC could efficiently mediate the oxidation of As(III) and the process of As(III) oxidation was pH and oxygen concentration dependent. In general, the presence of O2 promoted As(III) oxidation at pH 3.0-9.5. Acidic and alkaline conditions favored As(III) oxidation regardless of whether there was oxygen, but the mechanisms involved were quite different when there was oxygen. At pH 3.0, reactive species (H2O2 and ·OH) were generated and accounted for As(III) oxidation; at pH 9.5, As(III) was directly oxidized by O2 (electron transfer from As(III) to O2 mediated by carbon matrix) under aerobic conditions. Pre-oxidation and cyclic experiments results indicated the ability of AC to oxidize As(III) at pH 9.5 was sustainable and recyclable. This study provided a new insight in pollutant oxidation by AC in the environment.

Hydroxyl radicals induced mineralization of organic carbon during oxygenation of ferrous mineral-organic matter associations: Adsorption versus coprecipitation.

The iron (Fe) phases have been widely proposed to preserve organic carbon (OC) via adsorption or coprecipitation pathways, however, such role of Fe phases might be largely reversed under redox-fluctuation conditions, especially for Fe(II) minerals-protected OC. In this study, we synthesized the Fe(II)-OC associations via adsorption and coprecipitation using FeCO3 and three types of low-molecular-weight organic compounds (LMWOCs) at different C/Fe molar ratios, and investigated the OC mineralization induced by hydroxyl radicals (OH) during oxygenation processes. Abundant OH can be produced upon oxygenation of FeCO3-LMWOCs associations within 96 h, giving values of 28.49-151.36 µM in adsorption and 12.63-76.41 µM in coprecipitation treatments depended on types of LMWOCs and C/Fe molar ratios. Fe(II) species in coprecipitates with hydroquinone (HQ) mainly transformed into Goethite-like phases after oxygenation, while adsorption samples induced more formation of lower-crystalline Fe phase (e.g., ferrihydrite). The surface-Fe(II) was the primary electron donors to O2, which further induced hydrogen peroxide (H2O2) formation via one- and two-electron transfer pathways. Finally, the produced OH removed 0.55-9.65 and 0.16-85.54 mg L-1 total OC in adsorption and coprecipitation treatments after oxygenation. Collectively, this study highlights that OC associated with Fe(II) minerals might be labile due to the oxidation of formed OH, and the role of Fe phases in OC sequestration may be further re-evaluated under redox fluctuation conditions.

Dibutyl phthalate release from polyvinyl chloride microplastics: Influence of plastic properties and environmental factors.

In recent years, great efforts have been made to understand the capacity of microplastics to adsorb environmental pollutants; however, relatively little is known about the ability of microplastics to release inherent additives into peripheral environments. In this study, we investigated the leaching behavior of phthalate plasticizer from polyvinyl chloride (PVC) microplastics, in aqueous solutions relevant to aquatic and soil environments. It was found that plastic properties, such as particle size, plasticizer content and aging of plastics had a great effect on the leaching of dibutyl phthalate (DnBP). Phthalate release was generally higher in smaller particles and particles with higher phthalate content. Whereas, plastic aging caused by solar irradiation could either enhance phthalate release by increasing plastic hydrophilicity or decrease the leaching by reducing readily available fractions of phthalate. Regarding environmental factors, solution pH (3-9) and ionic strength (0-0.2 M NaCl) were found to have minor effect on phthalate release, while fulvic acid (0-200 mg/L) greatly promoted the release by improving phthalate solubility and solution-plastic affinity. Interestingly, we found that more DnBP was leached out when fulvic acid and NaCl coexisted, and the results from dissolved organic carbon (DOC) and three-dimensional fluorescence spectroscopy analyzes suggested that the leaching of other fulvic acid-like additives might have played a role. These findings would be helpful for predicting the potential of microplastics to release toxic additives under different environmental conditions.

Pyrogenic Carbon Initiated the Generation of Hydroxyl Radicals from the Oxidation of Sulfide.

Sulfide is one of the most abundant reductants in the subsurface environment, while pyrogenic carbon is a redox medium that widely exists in sulfide environment. Previous studies have found pyrogenic carbon can mediate the reductive degradation of organic pollutants under anoxic sulfide conditions; however, the scenario under oxic sulfide conditions has rarely been reported. In this study, we found that pyrogenic carbon can mediate hydroxyl radicals (•OH) generation from sulfide oxidation under dark oxic conditions. The accumulated •OH ranged from 2.07 to 101.90 µM in the presence of 5 mM Na2S and 100 mg L-1 pyrogenic carbon at pH 7.0 within 240 min. The Raman spectra and electrochemical cell experiments revealed that the carbon defects were the possible chemisorption sites for oxygen, while the graphite crystallites were responsible for the electron transfer from sulfide to O2 to generate H2O2 and •OH. Quenching experiments and degradation product identification showed that As(III) and sulfanilamide can be oxidized by the generated •OH. This research provides a new insight into the important role of pyrogenic carbon in redox reactions and dark •OH production.

Photooxidation mechanism of As(III) by straw-derived dissolved organic matter.

Straw return-to-field is a common agronomic practice that would affect the physicochemical characteristics of the paddy soil and overlying water, but few studies have focused on the possible impacts of straw return on the conversion of pollutants. In this study, the photooxidation of As(III) in aqueous solution by straw-derived dissolved organic matter (S-DOM) was investigated. The results showed that dissolved organic matter derived from wheat straw (DOMws) and rape straw (DOMrs) exhibited good spectroscopic features and could efficiently oxidize As(III) under irradiation at pH 5.0, with the kobs values of As(III) oxidation being 0.15 h-1 and 0.17 h-1 for DOMws and DOMrs, respectively. Quenching studies indicated that hydroxyl radical (OH) dominated the oxidation of As(III) for both types of dissolved organic matter (DOM), though singlet oxygen (1O2) also played a role in the DOMrs system. Since acidic conditions are favorable for the formation of OH, As(III) oxidation decreased with an increase of pH value. Additionally, the oxidation efficiency of As(III) was inhibited in the presence of NO3- (0.2-2 mM) while enhanced in the presence of Fe(III) (5-50 µM). This study is of great significance for understanding the removal/transformation behavior of pollutants in paddy fields that receive straw return.

Effect of Straw Return on Hydroxyl Radical Formation in Paddy Soil.

Straw return, as an important agricultural management measure, is receiving growing attention. Hydroxyl radical (•OH) can be produced when subsurface soil interacts with oxygen, but the effects of straw incorporation on •OH formation have rarely been evaluated. In this study, we found that straw return had a significant effect on soil properties. Soil pH and redox potential (Eh) decreased while electronic conductivity (EC) showed an increment. Dissolved organic carbon content of soil initially increased and then decreased to the same level as the control by the end of the experiment of 120 days. Moreover, Fe(II) formation was promoted by straw return under anaerobic conditions. •OH was produced in the flooded paddy soil when exposed to oxygen, which correlated well with Fe(II) content. The effect of rape (Brassica campestris L.) straw on •OH formation rate was more evident as compared to wheat (Triticum aestivum L.) straw, suggesting a potentially more profound influence of rape straw return on pollutant transformation in paddy soils.

Rapid DDTs degradation by thermally activated persulfate in soil under aerobic and anaerobic conditions: Reductive radicals vs. oxidative radicals.

Persulfate (PS)-based oxidation technologies have been extensively employed for contaminant remediation, but the mechanisms of PS-mediated pollutant removal in soil under anaerobic conditions have not been fully explored. In this study, the degradation of DDTs (DDT and DDE) by thermally activated PS in a real contaminated soil was investigated. It was found that DDTs degradation could be achieved under both aerobic and anaerobic conditions, and anaerobic conditions were comparatively more efficient. Further analyses based on electron paramagnetic resonance (EPR), free radical quenching studies and degradation product identification showed that, oxidative radicals (SO4-/OH) were the major species responsible for DDTs degradation under aerobic conditions, while both reductive (persulfate radical S2O8-) and oxidative radicals were involved under anaerobic conditions. Furthermore, reductive degradation of DDT could also be observed in the presence of ethanol (EtOH) due to the formation of EtOH radical. In addition, DDT degradation was hardly affected by anions such as HCO3- and Cl- at anaerobic conditions while its degradation was greatly inhibited by these anions under aerobic conditions. This study significantly improved our knowledge of PS-mediated degradation processes of DDTs and provided new insight into soil remediation by in-situ chemical oxidation at different oxygen status.

Enhanced removal of chromium(III) for aqueous solution by EDTA modified attapulgite: Adsorption performance and mechanism.

Ethylenediaminetetraacetic acid modified attapulgite (EDTA-ATP) was developed as a novel and promising adsorbent for removal of aqueous Cr(Ш). The structure and surface properties of EDTA-ATP were characterized and the results indicated that EDTA moieties have been successfully anchored on the surface of ATP. Adsorption of Cr(III) on EDTA-ATP and aminopropyl-modified attapulgite (APTES-ATP) monotonously reduced with decreasing pH, and Cr(III) adsorption on EDTA-ATP is substantially higher than APTES-ATP in tested pH range, especially at lower pH. Presence of citric acid and gelatin had no obvious influence on Cr(III) adsorption to EDTA-ATP, but significantly reduced Cr(III) adsorption on APTES-ATP. Coexisting cations resulted in decreased Cr(III) adsorption on EDTA-ATP by competition with Cr(III) for surface-bound EDTA groups of the adsorbent. Adsorption isotherm of Cr(III) on EDTA-ATP followed the Langmuir model and the maximum adsorption capacity of the adsorbent for Cr(III) was 131.37 mg/g at 25 °C and pH 3.0. Cr(Ш) loaded adsorbent could be regenerated easily in HCl solution and the regenerated adsorbent still exhibited high adsorption capacity for Cr(III). XPS analysis confirmed that the enhanced Cr(III) adsorption on EDTA-ATP was ascribed to form the stable complexes between Cr(III) and surface-bound carboxyl and amino groups of the adsorbents.

[Effects of forest gap on tree species regeneration and diversity of mixed broadleaved Korean pine forest in Xiaoxing'an Mountains].

This paper studied the quantitative characteristics of main tree species along a forest gap gradient (gap center-near gap center-gap border) of mixed broadleaved Korean pine forest in Xiaoxing'an Mountains, as well as the effects of forest gap size on the regeneration of the tree species. In forest gap, the density of shrub species was obviously larger than that in non-gap, and the density ratio of the same shrub species in forest gap to in non-gap ranged from 1.08 to 18.15. With the increase of gap size, the regeneration density of tree seedlings increased, and that of sapling I (H > or = 1 m, DBH < or = 2 cm) and sapling II (H > or = 1 m, 2 cm < DBH < or = 5 cm) exhibited multiple peak curve. The overall regeneration density of shrubs in forest gaps varied mainly with the amounts of tree seedlings and sapling I. The mean height, mean basal diameter, species density, and individual density of trees in different locations of forest gaps were all different. From gap center to non-gap, the importance value of tree species seedlings in regeneration layer was ranked in gap center > near gap center > gap border > non-gap, the tree species evenness presented a variation of high-low-high, and the species diversity decreased in the order of early phase gap > mid phase gap > late phase gap.