Plant and microbial response in constructed wetland treating tetracycline antibiotic polluted water: Evaluating the effects of microplastic size and concentration.

Microplastics (MPs) and antibiotics are novel water pollutants that have attracted increasing attention. Constructed wetlands (CWs) are widely applied treating various types of polluted water. How these two new pollutants affect plants and microorganisms in CWs, especially deciphering the unknown roles of MPs size and concentration, is of great essential. Here, five CW treatments with submerged macrophyte Myriophyllum aquaticum were established to treat oxytetracycline (OTC) antibiotic-polluted water. The effects of polystyrene (PS) nanoplastics (NPs) (700 nm) and MPs (90-110 µm) on plant and microbial communities at 10 µg/L and 1 mg/L, respectively, were systematically evaluated. PS reduced the nitrogen and phosphorus removal efficiencies and inhibited OTC removal. Low doses (10 µg/L) of NPs and high doses (1 mg/L) of MPs had the greatest effects on plant and microbial responses. The overall effect of MPs was greater than that of NPs. Compared with high NPs concentration (1 mg/L), low concentrations (10 µg/L) had higher catalase (CAT), superoxide dismutase (SOD), and malondialdehyde (MDA) content. However, the activity and content of MPs at low concentrations (10 µg/L) were lower than those at high concentrations (1 mg/L). The coexistence of OTC and MPs/NPs decreased the microbial diversity and abundance. Low doses of NPs and high doses of MPs decreased the relative abundance of Abditibacteriota, Deinococccota, and Zixibacteria. Redundancy and network analyses revealed a strong correlation between pollutant removal and plant and microbial responses. NH4+-N and OTC removal was positively and negatively correlated with CAT, SOD, and MDA content, respectively. MDA positively correlated to chlorophyll content, whereas SOD showed a negative correlation with Chloroflexi. This study highlighted the scale effect of MPs in wastewater treatment via CWs. It enhances our understanding of the response of plants and microorganisms to the remediation of water co-polluted with MPs and antibiotics.

Effects of polyurethane microplastics combined with cadmium on maize growth and cadmium accumulation under different long-term fertilisation histories.

Agricultural production uses different types of fertilisation treatments, typically employing the combined application of organic fertiliser (OF) or organic-inorganic fertiliser (OIF) to improve soil quality. When coupled with cadmium (Cd), microplastics (MPs) affect plant growth and Cd accumulation in soils treated with different fertilisers. This study systematically examined the effects of polyurethane (PU) MPs coupled with Cd on the growth characteristics, root metabolite characteristics, rhizosphere bacterial community structure, and Cd bioavailability of maize under different long-term fertilisation treatments and soil types (red/cinnamon soil). The combined effects of PU MPs and Cd on maize growth differed across fertilisation treatments. Under OF, maize plants accumulated more Cd than under OIF. The accumulation of Cd in maize plants in red soil was twice that in cinnamon soil. Under OF, PU MPs promoted Cd activation by decreasing the soil pH, while root metabolites promoted Cd adsorption sites by synthesising specific amino acids, degrading aromatic compounds, and synthesising pantothenic acid and coenzyme A. Under OF, PU MPs can lower the soil pH to promote the activation of cadmium, while root metabolites promote root growth and increase cadmium adsorption sites by synthesizing specific amino acids, degrading aromatic compounds, and synthesizing pantothenic acid and coenzyme A, hereby promoting root Cd absorption. Under OIF, PU MPs act by influencing the biosynthesis of amino acids in root metabolites, enriching energy metabolism pathways, promoting the transport and translocation of mineral nutrients, thereby amplifying the "toxic effects" of Cd. This study provides new insights into the risk assessment of PU MPs and Cd coupling under different fertilisation treatments, and suggests that the prevention and control of combined PU MPs and Cd pollution in red soil under OF treatment should receive more attention in the future.

Urban pipeline rainwater runoff is an important pathway for land-based microplastics transport to inland surface water: A case study in Beijing.

Microplastics (MPs) as new environmental pollutants are receiving increasing attention worldwide. Urban rainwater runoff plays an important role in facilitating the migration of land-based MPs to surface water. Previous research has focused predominantly on aquatic ecosystems, whereas research on this migration pathway and the characteristics of MPs in rainwater pipelines draining from different land-use types is still lacking. This study investigated the abundance and characteristics of MPs in rainfall and pipeline rainwater runoff from main roads, office complexes, an agricultural experiment station, and residential areas during different rainfall periods in Haidian District, Beijing, China. Microplastic abundance in pipeline rainwater runoff ranged from 1.6 to 29.6 items L-1, of which 0.7 to 6.0 items L-1 were derived from rainfalls, accounting for 24.0 % to 77.4 % of the total. Microplastic abundances in rainfall and pipeline rainwater runoff decreased significantly as rainfall events progressed. The proportions of MPs < 1 mm in rainfall (38.0 %) and rainwater runoff (44.5 %) were the largest. Average MPs abundance was the highest in rainwater runoff from the main road area and lowest in the office area (p < 0.05). The abundance of polyester fibers in rainwater runoff from the residential area was significantly higher than that in other areas, while the main road area had the highest abundance of films (p < 0.05). Overall, 72 % of MPs in rainfall were fibers, and most were composed of polyester, while the MPs in rainwater runoff were mainly fragments (41.2 %) and fibers (35.3 %) composed mainly of polypropylene, polyethylene, and polyester. This study shows that urban pipeline rainwater runoff is one of the main pathways for land-based MPs transport to surface waters, and provides a scientific reference for preventing and controlling MPs entering water bodies through rainwater pipelines.

Long-term application of organic compost is the primary contributor to microplastic pollution of soils in a wheat-maize rotation.

Microplastics (MPs) are posing new threats to soil ecosystems. Organic fertilizers are considered as an emerging contributor to MPs accumulation in agricultural soils. However, few studies have focused on the MPs fate in soils under long-term organic fertilizer application. Based on an 11-year field test with wheat-maize cropping rotation, this study investigated the characteristics of MPs in pig manure and cow manure composts, and examined the impact of long-term compost application on soil MPs accumulation, surface morphology, and distribution. The MPs contents in pig manure and cow manure composts were 3547 and 4520 items kg-1, respectively. Microplastics abundances in soils under long-term use of these two composts were 144 to 287 and 140 to 316 items kg-1, respectively, which increased significantly with increasing compost application amount and was substantially higher than that in soils without compost. Accumulated soil MPs sourced from long-term compost application were 1.73 × 108 to 7.22 × 108 items ha-1, accounting for 43.0 %-75.9 % of the total, and the contribution value doubled as the compost application rate doubled. The proportion of MPs <1 mm in composts (31.0 %) was lower when compared with that in compost-amended soils (43.8 %), and size and abundance reduced with increasing soil depth. Microplastics shapes and polymer types in composts and compost-amended soils were similar and mostly included fragments of polyethylene and polypropylene and fibers of polyethylene terephthalate. Microplastics in compost-amended soils showed complicated weathered surface morphologies, and soil mineral colloids were attached. These results demonstrate that compost-derived MPs in soils can be gradually weathered and degraded into smaller particles under long-term compost application. These findings provide key insights into the pollution level of soil MPs with organic fertilizer application and serve as a scientific basis for developing MPs mitigation measures in agricultural soils.

Microplastics promoted cadmium accumulation in maize plants by improving active cadmium and amino acid synthesis.

Combined pollution from microplastics (MPs) and cadmium (Cd) can influence soil environment and soil biota, altering plant growth and development, and Cd mobilization. We investigated the effects of polystyrene (PS) and polypropylene (PP) MPs alongside Cd on soil Cd bioavailability, rhizosphere soil metabolomics, bacterial community structure, and maize (Zea mays L.) growth in two soil types (red soil and cinnamon soil). Although the addition of PS/PP-Cd promoted Cd accumulation in maize plants overall, there were large-particle-size- and small-particle-size-dependent effects in the red soil and cinnamon soil, respectively. The difference is mainly due to the capacity of the large particle size MPs to significantly reduce soil pH, improve soil electrical conductivity (EC), promote active Cd, and intensify Cd mobilization in red soil. In contrast, small-size MPs in cinnamon soil promoted the synthesis and secretion of rhizosphere amino acids and soil metabolites, thus promoting Cd absorption by maize roots. Soil microorganisms also improved Cd bioavailability via C-related functional bacteria. Overall, our study provides novel insights on the potential effects of combined MPs and Cd pollution on soil ecology and agricultural production, enhancing our understanding of rhizosphere metabolites in different soils.

Microplastic pollution and the related ecological risks of organic composts from different raw materials.

Organic composts are considered emerging contributors to microplastics (MPs) accumulation in agricultural soils. However, MPs pollution in organic compost from different raw materials is unknown. This study investigated MPs occurrence and characteristics in 124 organic compost samples, including single feedstock (livestock manure, poultry manure, crop straw, and solid waste) and compound organic composts, and quantitatively assessed related ecological risks of MPs pollution. The highest and lowest MPs abundances were observed in solid waste (6615 items kg-1) and crop straw (1500 items kg-1) composts, respectively. Compost MPs were mainly 0.5-1 mm (39.5%), colorful polypropylene and polyethylene fragments and films, and polyethylene terephthalate fibers, and the input to farmland soils was 6.96 × 107 to 1.88 × 108 items ha-1 yr-1. Regardless of feedstock, compost-based MPs of different shapes exhibited complicated weathering morphologies and adhered to some mineral colloids. The highest and lowest MPs-induced risk indices in solid waste (H = 134.3) and crop straw (H = 8.9) composts yielded hazard levels IV (high risk) and II (low risk), respectively, due to the different abundance of polymers with diverse hazard scores. These findings provide insights into MPs pollution in organic composts and a theoretical basis for the safe production and application of compost.

Soil bacterial community and metabolism showed a more sensitive response to PBAT biodegradable mulch residues than that of LDPE mulch residues.

Biodegradable mulch film (BDM) is considered as an environmentally sustainable alternative to low density polyethylene (LDPE) mulch film. However, the low degradation rate of BDM resulted in residues in soil after service period which were similar to LDPE mulch film. Distinguishing the differential responses of crop growth, soil bacteria and metabolism to residues of BDM and LDPE mulch films is favourable for comparing the environmental toxicities of the two materials. The results indicated that emergence rate and yield of Chinese cabbage (Brassica campestris L. ssp. chinensis Makino) were significantly inhibited by two types mulch residues. BDM residues significantly decreased bacterial diversity by 1.2-2.3% through the enrichment of dominant phyla and inhibition of inferior phyla, while LDPE mulch residues not. The effects of BDM residues on soil metabolite spectrum were stronger than LDPE mulch residues with significant increase (3.9% 5.8%) in the abundance of total metabolites. Besides the pathways of metabolism, organismal systems, environmental information processing influenced by LDPE mulch resides, differential pathways including human diseases and cellular processes were also determined in soil with BDM residues. According to all the results of the present study, prior to the promotion of BDM, its influences on soil safety must be carefully investigated through critical and systematic research.

Typical microplastics in field and facility agriculture dynamically affect available cadmium in different soil types through physicochemical dynamics of carbon, iron and microbes.

Combined pollution from microplastics (MPs) and other environmental pollutants has attracted considerable attention. Few studies have investigated the effects of polyurethane (PU) and polypropylene (PP) MPs on available Cadmium(Cd) in different soil types. Here, PU and PP additions affected available Cd and reduced its concentration in soil (P > 0.05). PU and PP reduced available Cd more strongly in clay soil than that in sandy soil. PU and PP improved the soil porous structure and voids and significantly increased the Zeta potential in clay soil (P < 0.05). Dissolved organic carbon and pH in clay soil were significantly negatively correlated with available Cd after PU and PP addition, and Fe(Ⅱ) was significantly negatively correlated with available Cd in sandy soil. PU and PP addition promoted the C-C, CO32-, and C-H functional groups and FeO, FeOOH, and Fe3O4 formation and influenced the effective Cd through adsorption and precipitation. CdCO3 formation and clay mineral adsorption, and iron oxide formation, influenced the effective Cd in clay and sandy soils, respectively. PU and PP influenced the effective state of Cd by affecting bacterial communities related to carbon and iron cycles. This study is significant for assessing the environmental risks of MPs combined with heavy metals in different soils and their mechanisms.

How do controlled-release fertilizer coated microplastics dynamically affect Cd availability by regulating Fe species and DOC content in soil?

Microplastics (MPs) affect the accumulation of heavy metals by regulating the soil environment. However, studies on the dynamic effects of microplastics on the available states of heavy metals in soil are lacking. In particular, how controlled-release fertilizer coated microplastics can synergistically change the avsilable states of heavy metals in soil by affecting soil physical and chemical properties and microbial community structure is still lacking. The dynamic effect of polyurethane (PU) MPs on the effective state of soil cadmium (Cd; DGTCd), at different particle sizes and concentrations, was studied in situ by diffusive gradient in thin-films (DGT) for the first time. The bioavailability, soil chemical properties, and microbial effects of PU MPs on Cd depend on PU particle size and concentration; high-concentration (1 %) PU MPs cause a significant increase in DGT-Cd concentration. The addition of PU MPs decreased soil pH and dissolved organic carbon (DOC), while increasing the absolute zeta value, Fe(II) and Mn(II), in a manner dependent on particle size, concentration, and culture time. Correlation analysis combined with path analysis showed that PU MPs affected the effective state of Cd by changing soil properties, among which Fe(II) content and DOC were important factors controlling the activation of Cd. Meanwhile, changes in soil properties and heavy metal availability correlated significantly with microbial community composition, suggesting that PU MPs may indirectly impact heavy metal activity by affecting microorganisms and functional genes associated with C and Fe cycling. Therefore, when the concentration of PU MPs is higher than 1 %, we should strengthen ecological risk prevention and control of the compound pollution of controlled-release fertilizer coated microplastics and heavy metals in farmland soil.

[Development and evaluation of fertilizers cemented and coated with organic-inorganic materials].

Four kinds of organic-inorganic cementing and coating materials were prepared by a coating method using water as the solvent, and the corresponding cemented and coated fertilizers (B2, PS, F2, and F2F) were produced by disc pelletizer. The tests on the properties of these fertilizers showed that the granulation rate, compression strength, and film-forming rate were B2 > PS > F2 > F2F. Soil column leaching experiment showed that the curve of accumulated nitrogen-dissolving rate was the gentlest for B2. In 48 days, the accumulated nitrogen-dissolving rate was in the order of B2, 54.65% < PS, 56.16% < F2, 59.47%, < F2F, 63.12%. Field experiment showed that compared with the same application amount of NPK, all the test fertilizers had better effects on corn yield, among which, B2 was the best, with the corn yield and fertilizer use efficiency increased by 19.72% and 20.30%, respectively. The yield-increasing effect of other test fertilizers was in the order of PS > F2 > F2F.