Sewage sludge contains Ag₂S-NPs causing NP exposure of soil fauna when sludge is applied as soil amendment. Earthworm bioturbation is an important process affecting many soil functions. Bioturbation may be affected by the presence of Ag₂S-NPs, but the earthworm activity itself may also influence the displacement of these NPs that otherwise show little transport in the soil. The aim of this study was to determine effects of Ag₂S-NPs on earthworm bioturbation and effect of this bioturbation on the vertical distribution of Ag₂S-NPs. Columns (12 cm) of a sandy loamy soil with and without Lumbricus rubellus were prepared with and without 10 mg Ag kg⁻¹, applied as Ag₂S-NPs in the top 2 cm of the soil, while artificial rainwater was applied at ∼1.2 mm day⁻¹. The soil columns were sampled at three depths weekly for 28 days and leachate collected from the bottom. Total Ag measurements showed more displacement of Ag to deeper soil layers in the columns with earthworms. The application of rain only did not significantly affect Ag transport in the soil. No Ag was detected in column leachates. X-ray tomography showed that changes in macro porosity and pore size distribution as a result of bioturbation were not different between columns with and without Ag₂S-NPs. Earthworm activity was therefore not affected by Ag₂S-NPs at the used exposure concentration. Ag concentrations along the columns and the earthworm density allowed the calculation of the bioturbation rate. The effect on the Ag transport in the soil shows that earthworm burrowing activity is a relevant process that must be taken into account when studying the fate of nanoparticles in soils.

The dissipation of famoxadone as well as the behaviour of its metabolites in environmental samples such as water and soil is a major concern. In this study, the dissipation of the target compound in both matrices was carried out applying an analytical method based on ultra-high performance liquid chromatography coupled to Orbitrap mass spectrometry (UHPLC-Orbitrap-MS). The dissipation of famoxadone was monitored over a period of 100 days after the plant protection product, Equation Pro®, was administered to the target matrices. This study was performed at two doses, normal and double in the case of soils and fivefold instead of double dose in water. The concentration of famoxadone steadily decreased during the monitoring period in both matrices. Half-life (DT₅₀) values were lower than 30 days in most cases except for loam soils, for which it was 35 days. Therefore, persistence of this pesticide in both matrices was low. Famoxadone metabolites such as IN-KF015 ((5RS)-5-methyl-5-(4-phenoxyphenyl)-1,3- oxazolidine-2,4-dione) and IN-JS940 ((2RS)-2-hydroxy-2-(4- phenoxyphenyl)propanoic acid) were detected in both matrices and their concentration increased while the concentration of the parent compound decreased. Metabolite IN-JS940 was the compound detected at highest concentration for both matrices. In water the maximum concentration was 20% of the initial famoxadone content and in soils it was 50% of initial famoxadone content. In addition, another metabolite, IN-MN467 ((5RS)-5-methyl-3-[(2-nitrophenyl)amino]- 5-(4-phenoxyphenyl)-1,3-oxazolidine-2,4-dione), was detected in soils, following the same behaviour as the other metabolites. These results provided ample information about the behaviour of metabolites and the necessity of knowing their toxicity in both matrices in order to detect possible risks for living beings.

It has been proposed that non-protein thiols and organic acids play a major role in cadmium phytoavailability and distribution in plants. In the Cd-hyperaccumulator Solanum nigrum and non-accumulator Solanum melongena, the role of these organic ligands in the accumulation and detoxification mechanisms of Cd are debated. In this study, we used X-ray absorption spectroscopy to investigate Cd speciation in these plants (roots, stem, leaves) and in the soils used for their culture to unravel the plants responses to Cd exposure. The results show that Cd in the 100 mg kg⁻¹ Cd-doped clayey loam soil is sorbed onto iron oxyhydroxides. In both S. nigrum and S. melongena, Cd in roots and fresh leaves is mainly bound to thiol ligands, with a small contribution of inorganic S ligands in S. nigrum leaves. We interpret the Cd binding to sulfur ligands as detoxification mechanisms, possibly involving the sequestration of Cd complexed with glutathione or phytochelatins in the plant vacuoles. In the stems, results show an increase binding of Cd to –O ligands (>50% for S. nigrum). We suggest that Cd is partly complexed by organic acids for transportation in the sap.

The fate of organic pollutants in the environment, especially the formation and stability of non-extractable (i.e., bound) residues (NERs) determines their environmental risk. Using ¹⁴C-tracers, we studied the fate of the carcinogen phenanthrene in active or sterilized oxic loamy soil in the absence and presence of the geophagous earthworm Metaphire guillelmi and characterized the NERs derived from phenanthrene. After incubation of ¹⁴C-phenanthrene in active soil for 28 days, 40 ± 3.1% of the initial amount was mineralized and 70.1 ± 1.9% was converted to NERs. Most of the NERs (>92%) were bound to soil humin. Silylation of the humin-bound residues released 45.3 ± 5.3% of these residues, which indicated that they were physically entrapped, whereas the remainder of the residues were chemically bound or biogenic. By contrast, in sterilized soil, only 43.4 ± 12.6% of the phenanthrene was converted to NERs and all of these residues were completely released upon silylation, which underlines the essential role of microbial activity in NER formation. The presence of M. guillelmi in active soil significantly inhibited phenanthrene mineralization (24.4 ± 2.6% mineralized), but NER formation was not significantly affected. Only a small amount of phenanthrene-derived residues (1.9–5.3% of the initial amount) accumulated in the earthworm body. When humin-bound residues were mixed with fresh soil, 33.9% (humin recovered from active soils) and 12.4% (humin recovered from sterilized soils) of the residues were mineralized after 75 days of incubation, respectively, which indicated a high bioavailability of NERs, albeit lower than the initial addition of phenanthrene. Our results indicated that many phenanthrene-derived NERs, especially those physically entrapped, are still bioavailable and may pose a toxic threat to soil organisms.

Understanding the distribution and persistence of the fumigant dimethyl disulfide (DMDS) under different soil conditions would contribute to a more environmentally sustainable use of this gas. We determined the effects of soil type, soil moisture content and soil organic amendment rate on DMDS distribution and persistency using soil columns in the laboratory. The peak concentrations of DMDS at 60 cm soil depth in sandy loam soil, black soil and red loam soil were 1.9 μg cm⁻³, 0.77 μg cm⁻³, 0.22 μg cm⁻³, respectively. The total soil residues of DMDS in sandy loam soil, black soil and red loam soil were 0.4, 1.3 and 1.3%, respectively. The peak concentrations of DMDS at 60 cm soil depth and the total soil residues of DMDS applied decreased from 3.2 μg cm⁻³ to 0.9 μg cm⁻³ and 3.3 to 0.5% when soil moisture content increased from 6 to 18%, respectively. Incremental increases (0–5%) in organic amendment rates decreased DMDS distribution through the soils and increased soil residues. Wait periods were required of 7, 21 and 21 days after polyethylene (PE) film was removed to reduce residues sufficiently for cucumber seed germination in sandy loam soil, black soil and red loam soil with 12% moisture content and 0% organic amendment rate, respectively. However, no wait period was required for successful cucumber seed germination in sandy loam soils (Beijing) with 6, 12 or 18% moisture content or organic amendment rates of 1 or 5%, respectively, but in commercial practice 7 days delay would be prudent. Our results indicated that soil type, soil moisture content and organic amendment rates significantly affected DMDS distribution, persistency and residues in soil. Those factors should be taken into consideration by farmers when determining the appropriate dose of DMDS that will control soil pests and diseases in commercially-produced crops.

Microplastics are emerging contaminants and widely distributed in the environment. They are considered as a vector of numerous organic pollutants including antibiotics in aquatic environments and thereby influence their distribution and transport behaviors. However, the effects of microplastics on the environmental behavior of antibiotics in soils remain largely unclear. In this paper, the influence of polyamide (PA) microplastics on sorption and transport of the selected antibiotic [oxytetracycline (OTC)] in a sandy loamy soil was studied by performing batch and column experiments. Results show that PA microplastics increase the pH of reaction systems, which contributes to OTC sorption onto the tested soils. However, altering pH is not the key influencing mechanism because the overall sorption capacity decreases slightly after adding PA microplastics, which can be attributed to the dilution effect. Reduction of OTC sorption by adding microplastics promotes the migration of OTC in the tested soil, which could be demonstrated by the results of column experiments that the breakthrough of OTC occurs earlier with an increasing content of PA microplastics. According to the fitting parameters of HYDRUS−1D model, PA microplastics can affect the transport of OTC by altering the soil pore structure and dispersion coefficient. These results provide new insight into the interaction between microplastics and organic pollutants in soil environments.

Spread of antibiotic resistance genes (ARGs) poses a worldwide threat to public health and food safety. However, ARG spread by plasmid mobilization, a broad host range transfer system, in agricultural soil has received little attention. Here, we investigated the spread of chloramphenicol resistance gene (CRG) and tetracycline resistance gene (TRG) in agricultural soil by mobilization of pSUP106 under different conditions, including different concentrations of nutrients, temperatures, soil depths, rhizosphere soils, and soil types. The number of resistant bacteria isolated in non-sterilized soil from the experiments was approximately 10⁴ to 10⁷ per gram of soil, belonging to 5–10 species from four genera, including nonpathogen, opportunistic pathogen, pathogen bacteria, and gram-positive and gram-negative bacteria, depending on the experiment conditions. In sterilized soil, higher levels of nutrients and higher temperatures promoted plasmid mobilization and ARG expression. Topsoil and deep soil might not support the spread of antibiotic resistance, while ARG dissemination by plasmid mobilization was better supported by maize rhizosphere and loam soils. All these factors might change bacterial growth and the activity of bacteria and lead to the above influence. Introduction of only the donor and helper, or the donor alone also resulted in the transfer of ARGs and large numbers of antibiotic resistant bacteria (ARB), indicating that some indigenous bacteria contain the elements necessary for plasmid mobilization. Our results showed that plasmid mobilization facilitated dissemination of ARGs and ARB in soil, which led to the disturbance of indigenous bacterial communities. It is important to clear ARG dissemination routes and inhibit the spread of ARGs.

Microplastics (MPs) in soil and sediment (SS) matrices are emerging pollution hazards to ecosystems and humans. To mitigate MP pollution, suitable extractors and associated extracting solutions are required to efficiently separate MPs from SS matrices. In this study, we introduced a four-stage microplastic extractor (ME) device and investigated the fractional separation efficiencies of three extracting solutions (ultrapure water, saturated NaCl, and corn oil-in-NaCl) plus aeration, magnetic stirring, and electric stirring for three kinds of SS matrices (loam soil, sandy sediment, and muddy sediment) with four types of virgin MP pellets (acrylonitrile butadiene styrene (ABS), polycarbonate (PC), polypropylene, and polystyrene). In addition, fragments of these four types of post-consumer MPs were also tested by the ME device. The mean recovery efficiencies of these MPs in the three SS matrices were 88.3 %–100 %. Oil-in-NaCl further improved the recovery efficiencies for the denser ABS and PC up to 40 % based on NaCl extraction.