Effect of Agricultural Organic Inputs on Nanoplastics Transport in Saturated Goethite-Coated Porous Media: Particle Size Selectivity and Role of Dissolved Organic Matter.

The transport of nanoplastics (NPs) through porous media is influenced by dissolved organic matter (DOM) released from agricultural organic inputs. Here, cotransport of NPs with three types of DOM (biocharDOM (BCDOM), wheat strawDOM (WSDOM), and swine manureDOM (SMDOM)) was investigated in saturated goethite (GT)-coated sand columns. The results showed that codeposition of 50 nm NPs (50NPs) with DOM occurred due to the formation of a GT-DOM-50NPs complex, while DOM loaded on GT-coated sand and 400 nm NPs (400NPs) aided 400NPs transport due to electrostatic repulsion. According to the quantum chemical calculation, humic acid and cellulose played a significant role in 50NPs retardation. Owing to its high concentration, moderate humification index (HIX), and cellulose content, SMDOM exhibited the highest retardation of 50NPs transport and promoting effect on 400NPs transport. Owing to a high HIX, the effect of BCDOM on the mobility of 400NPs was higher than that of WSDOM. However, high cellulose content in WSDOM caused it to exhibit a 50NPs retardation ability that was similar to that of BCDOM. Our results highlight the particle size selectivity and significant influence of DOM type on the transport of NPs and elucidate their quantum and colloidal chemical-interface mechanisms in a typical agricultural environment.

Spatial distribution of phthalate esters and the associated response of enzyme activities and microbial community composition in typical plastic-shed vegetable soils in China.

The widespread use of phthalate esters (PAEs) in plastic products has made them ubiquitous in environment. In this study, 93 soil samples were collected in 31 plastic-sheds from one of China's largest vegetable production bases, Shouguang City, Shandong Province, to investigate the pollution characteristics and composition of PAEs in soils. Eleven PAEs were detected in the soil samples with the total concentration of 756-1590 µg kg-1 dry soil. Di (2-ethylhexyl) phthalate (DEHP), bis (2-n-butoxyethyl) phthalate (DBEP), di-isobutyl phthalate (DiBP) and di-n-butyl phthalate (DBP) were the main pollutants with the highest concentrations. Moreover, soil properties, including pH, total organic carbon (TOC), soil enzyme activities, and soil microbial community characteristics, were monitored to explore the associated formation mechanisms. The concentration of PAEs in the plastic-shed vegetable soils was regionalized and the contamination degree in different regions was related to soil microbial characteristics and soil enzyme activities. Phthalate ester is positively correlated with catalase and sucrase, and negatively correlated with dehydrogenase and urease. Furthermore, some tolerant and sensitive bacteria were selected, which possibly could be used as potential indicators of PAE contamination in soil. Dimethyl phthalate (DMP) and DBP also had greater effects on the soil microbial community than other PAEs. The results will provide essential data and support the control of PAEs in plastic-shed vegetable soils in China.

Resolving natural organic matter and nanoplastics in binary or ternary systems via UV-Vis analysis.

Nanoplastics (NPs) and natural organic matter (NOM) are ubiquitous and usually present simultaneously in the environment. Both NPs and NOM can be adsorbed to minerals such as iron-(hydr)oxides, with such interactions being important for controlling their fate in the environment. However, the quantification of NPs and NOM in mixtures remains challenging even under controlled conditions in laboratory studies. In this research, a UV-Vis method was established to quantify concentrations of NOM, such as humic acid (HA) and fulvic acid (FA), and polystyrene NPs (PSNPs) in mixtures. In addition, both original NOM samples and those recovered following adsorptive fractionation using an iron oxide (goethite, α-FeOOH) were mixed separately with PSNPs and their concentrations were further calculated via the developed UV-Vis method. The UV-Vis method performed well (recovery of 100 ± 16 %) with original NOM and PSNPs system at detection limits of 20.8 and 7.4 mgC L-1, respectively. Particularly, for original FA and PSNPs systems with carboxylic groups (PSNPs-COOH, 200 nm), a similar recovery rate could be obtained at detection limits of only 2.5 and 1.9 mgC L-1, respectively. For fractionated NOM and PSNPs systems, detection limits (31.2 mgC L-1 and 27.5 mgC L-1, respectively) are increased to reach the same accuracy. Furthermore, the UV-Vis method can be used to estimate the proportion of HA that is adsorbed to PSNPs. The relative errors are < 13.7 % when the mass ratios of PSNPs and HA was between 1.6:1 and 8:1 and HA concentration was higher than 4.6 mgC L-1. This method developed can be applied to future laboratory research to investigate the interaction between NOM, NPs, and minerals.

Effect of microplastics on the degradation of tetracycline in a soil microbial electric field.

The degradation of organic pollutants and the adsorption of organic pollutants onto microplastics (MPs) in the environment have recently been intensively studied, but the effects of biocurrents, which are widespread in various soil environments, on the environmental behavior of MPs and antibiotic pollutants have not been reported. In this study, it was found that polylactic acid (PLA) and polyvinyl chloride (PVC) MPs accelerated the mineralization of humic substances in microbial electrochemical systems (MESs). After tetracycline (TC) was introduced into the MESs, the internal resistance of the soil MESs decreased. Additionally, the presence of MPs enhanced the charge output of the soil MESs by 40% (PLA+TC) and 18% (PVC+TC) compared with a control group without MPs (424 C). The loss in MP mass decreased after TC was added, suggesting a promotion of TC degradation rather than MP degradation for charge output. MPs altered the distribution of the highest occupied molecular orbitals and lowest unoccupied molecular orbitals of TC molecules and reduced the energy barrier for the TC hydrolysis reaction. The microbial community of the plastisphere exhibited a greater ability to degrade xenobiotics than the soil microbial community, indicating that MPs were hotspots for TC degradation. This study provides the first glimpse into the influence of MPs on the degradation of TC in MESs, laying a theoretical and methodological foundation for the systematic evaluation of the potential risks of environmental pollutants in the future.

Microplastics degradation stimulated by in-situ bioelectric field in agricultural soils.

Bioelectric field is a stimulated force to degrade xenobiotic pollutants in soils. However, the effect of bioelectric field on microplastics (MPs) aging is unclear. The degradation behavior of polyvinyl chloride (PVC), polyethylene (PE) and polylactic acid (PLA) was investigated in an agricultural soil microbial electrochemical system in which bioelectric field was generated in-situ by native microbes. Based on the density function theory, the energy gaps between the highest and the lowest occupied molecular orbitals of the three polymers with periodic structure were 4.20, 7.24 and 10.09 eV respectively, and further decreased under the electric field, indicating the higher hydrolysis potential of PLA. Meanwhile, the mass loss of PLA in the closed-circuit group (CC) was the highest on day 120, reaching 8.94%, which was 3.01-3.54 times of that without bioelectric field stimulation. This was mainly due to the enrichment of plastic-degrading bacteria and a robust co-occurrence network as the deterministic assembly process, e.g., the abundance of potential plastic-degrading bacteria on the surface of PLA and PVC in the CC increased by 1.92 and 1.30 times, respectively, compared to the open-circuit group. In terms of functional genes, the xenobiotic biodegradation and metabolism capacity of plasticsphere in the CC were stronger than that in soil, and determined by the bioaccessibility of soil nitrogen and carbon. Overall, this study explored the promoting effect of bioelectric field on the degradation of MPs and reveled the mechanism from quantum chemical calculations and microbial community analysis, which provides a novel perception to the in-situ degradation of MPs.

Effects of selected functional groups on nanoplastics transport in saturated media under diethylhexyl phthalate co-contamination conditions.

The production and degradation of plastic remains can result in nanoplastics (NPs) formation. However, insufficient information regarding the environmental behaviors of NPs impedes comprehensive assessment of their significant threats. In this study, the transport behavior of unmodified NPs (PSNPs), carboxyl-modified NPs (PSNPs-COOH), and amino-modified NPs (PSNPs-NH2) was investigated using column experiments in the presence and absence of goethite (GT) and diethylhexyl phthalate (DEHP). Quantum chemical computation was performed to reveal the transport mechanisms. The results showed that GT decreased the transport of NPs and the presence of DEHP decreased it further. Van der Waals forces and small electrostatic interactions coexisted between the PSNPs and GT and caused deposition. Ligand exchange caused greater deposition of PSNPs-COOH on GT-coated sand than that of PSNPs. Although hydrogen bonding existed between the DEHP and NPs with functional groups, an increase in the positive charge and chemical heterogeneity of the collector was the main reason for DEHP promoting the deposition of NPs. Because of low absolute negative zeta potential values, PSNPs-NH2 was sensitive to chemical heterogeneity, and thus fully deposited (over 96.9%) in GT and GT-DEHP-coated columns. Generally, the deposition of NPs due to chemical heterogeneity was more significant than that due to the formation of chemical bonds and van der Waals, electrostatic, and hydrogen interactions. Our results highlight that the surface charge and functional groups significantly influence the transport behaviors of NPs and elucidate the fate of NPs in the terrestrial environment.

Insights into behavior and mechanism of tetracycline adsorption on virgin and soil-exposed microplastics.

Microplastics (MPs), as vectors of pollutants, have attracted extensive attention because of their environmental effects. However, the adsorption behavior and antibiotic mechanism of environmentally exposed MPs is limited. Here, the adsorption of tetracycline (TC) onto virgin and soil-exposed polylactic acid (PLA), polyvinyl chloride (PVC) and polyethylene (PE) MPs showed that the adsorption capacity of MPs for TC increased after soil exposure, and PLA showed the strongest increase. Soil exposure increased the time to reach equilibrium, and the adsorption rate was controlled by both intraparticle diffusion and membrane diffusion. The isothermal adsorption results of soil-exposed PE and PLA indicated that TC adsorbed on heterogeneous surfaces was affected by the physicochemical adsorption process. The equilibrium absorption capacity of MPs for TC increased by 88% (PLA), 26% (PVC) and 15% (PE) after soil exposure. Soil dissolved organic matter promoted the desorption of TC from MPs, and TC speciation changed with pH. Soil-exposed MPs have the potential to promote TC degradation in solution without the addition of biological inhibitors. Moreover, density functional theory calculations verified that PE and PVC adsorbed TC through physical interactions, while hydrogen bonds were formed on PLA with TC. These results clarified the behavior and mechanisms of TC adsorption on virgin and soil-exposed MPs, which can help in the risk assessment of concomitant pollution of MPs and antibiotics.

Comparative study on the pollution status of organochlorine pesticides (OCPs) and bacterial community diversity and structure between plastic shed and open-field soils from northern China.

The pollution status of organochlorine pesticides (OCPs) and microbial community in plastic shed and open-field soils may be different due to the significant variations in environmental factors between the two cultivation modes. However, the differences remain unclear. We conducted a regional-scale survey to investigate the pollution level, distribution, and sources of 20 OCPs, and to evaluate the soil physicochemical properties and bacterial community in soils from plastic shed and open-field locating the north areas of China. We found that levels of total OCPs in the plastic shed soils were significantly higher than those in the nearby open-field soils. Most of these OCPs were attributed to historical application, except for dichlorodiphenyltrichloroethanes (DDTs) due to the fresh input along with dicofol application. Soil pH (for both cultivation modes) and total organic carbon (TOC) content (only for plastic sheds) were significantly correlated with the total OCP concentrations. Additionally, microbial diversity and richness were generally lower in plastic shed soils than in nearby open-field soils for each region. The bacterial community variation among different regions might be principally determined by the soil type. Soil pH had the greatest impact on the microbial community across all plastic shed and open-field samples. These results provide a better understanding of the environmental impact and ecological risk of OCPs in soils with different cultivation modes.

Aluminum speciation in natural waters: measurement using Donnan membrane technique and modeling using NICA-Donnan.

The study of Al speciation is of interest for the assessment of soil and water quality. For the measurement of "free" aluminum (Al3+), a recently developed Donnan membrane technique was tested by measuring Al3+ in aluminum-fluoride solutions and gibbsite suspensions. It shows that the Donnan membrane technique can measure free Al3+ reliably up to 10(-9) M and the equilibration takes 3-4 days. Next, Al binding to humic acid (HA) purified from a forest soil was measured using either the Donnan membrane technique or gibbsite suspension. Results were compared with those predicted with the non-ideal consistent competitive adsorption (NICA)-Donnan model. The predictions using the generic parameters without fitting were in reasonable agreement with the measured data. Finally, the Donnan membrane technique was used to determine Al binding to dissolved organic matter (DOM) in the solutions of 24 soil samples at pH interval of 3-7. Measurements agree well with the predictions using the NICA-Donnan model assuming 30% of DOM is HA and 30% is fulvic acid. With this model, the effects of pH and DOM changes on the concentration of Al in 81 soil solutions were predicted reasonably without adjustment of model parameters. The comparison between the results of analysis and the modeling provides a mutual validation for the two methods.

Determination of free Zn2+ concentration in synthetic and natural samples with AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) and DMT (Donnan Membrane Technique).

The determination of free Zn(2+) ion concentration is a key in the study of environmental systems like river water and soils, due to its impact on bioavailability and toxicity. AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) and DMT (Donnan Membrane Technique) are emerging techniques suited for the determination of free heavy metal concentrations, especially in the case of Zn(2+), given that there is no commercial Ion Selective Electrode. In this work, both techniques have been applied to synthetic samples (containing Zn and NTA) and natural samples (Rhine river water and soils), showing good agreement. pH fluctuations in DMT and N(2)/CO(2) purging system used in AGNES did not affect considerably the measurements done in Rhine river water and soil samples. Results of DMT in situ of Rhine river water are comparable to those of AGNES in the lab. The comparison of this work provides a cross-validation for both techniques.

Effects of lability of metal complex on free ion measurement using DMT.

Very low concentrations of free metal ion in natural samples can be measured using the Donnan membrane technique (DMT) based on ion transport kinetics. In this paper, the possible effects of slow dissociation of metal complexes on the interpretation of kinetic DMT are investigated both theoretically and experimentally. The expressions of the lability parameter, Lgrangian , were derived for DMT. Analysis of new experimental studies using synthetic solution containing NTA as the ligand and Cu(2+) ions shows that when the ionic strength is low (

Measuring free metal ion concentrations in multicomponent solutions using the Donnan membrane technique.

Among speciation techniques that are able to measure free metal ion concentrations, the Donnan membrane technique (DMT) has the advantage that it can measure many different free metal ion concentrations simultaneously in a multicomponent sample. Even though the DMT has been applied to several systems, like surface waters, soil solutions, and manure slurry, basic features and calibrations with model calculations of the laboratory and field DMT have not been done sufficiently yet. Therefore, we tested the application of the DMT on metal complexation with several synthetic and natural ligands and the applicability of the dynamic mode of the DMT. The results show that there is a high agreement between the calculated and measured free metal ion concentrations in solutions containing synthetic (nitriloacetic acid, diglycolic acid) and natural organic ligands (fulvic acid, humic acid) at various pH values. Both the laboratory DMT and the field DMT give very similar results. In a solution containing labile ligands, equilibrium time is smaller than in a donor solution containing inert ligands or no ligands. Moreover, when labile ligands are present in the donor solution, a dynamic procedure can be used to decrease equilibrium time. This procedure cannot be applied when no ligands or only inert ligands are present.