Growing applications of nanoagrichemicals have resulted in their increasing accumulation in agricultural soils, which could modify soil properties and affect soil health. A greenhouse pot trial was conducted to determine the effects of three metallic nanoagrichemicals on several fundamental chemical properties of a rice paddy soil, including zinc oxide nanoparticles (ZnO NPs) and copper oxide nanoparticles (CuO NPs) at 100 mg/kg, and silicon oxide nanoparticles (SiO₂ NPs) at 500 mg/kg, as well as their bulk and ionic counterparts. The investigated soil amendments displayed significant and distinctive impact on the examined soil chemical properties relevant to agricultural production, including soil pH, redox potential, soil organic carbon (SOC), cation exchange capacity (CEC), and plant available As. For example, all amendments increased the bulk soil pH at day 47 to some extent, but the increase was substantially higher for SiO₃²⁻ (37.7%) than other amendments (5.8%–13.7%). Soil Eh was elevated markedly at day 47 after the addition of soil amendments in both the bulk soil (45.9%–74.4%) and rice rhizosphere soil (20.3%–68.9%). CuO NPs and Cu²⁺ generally exhibited greater impact on soil chemical properties than other agrichemicals. Significantly different responses to soil amendments were observed between bulk and rhizosphere soils, suggesting the essential role of plants in affecting soil properties and their responses to environmental disturbance. Overall, our results confirmed that the tested amendments could have remarkable impacts on the fundamental chemical properties of rice paddy soils.

Heavy metal contamination has been threatening the health of human beings. To decrease the bio-toxicity of heavy metals, a thiol-functionalized nano-silica (SiO₂-SH) was adopted to remediate the soil contaminated by lead (Pb), cadmium (Cd) and copper (Cu). The remediation effect of SiO₂-SH on contaminated soils was investigated by the uptake of the heavy metals into lettuce and pakchoi in pot experiment. The bio-toxicity of the SiO₂-SH was evaluated, and its immobilization mechanisms were proposed by the fraction distribution of Cd, Pb and Cu. It was found that the SiO₂-SH can significantly reduce the uptake of Cd, Pb, Cu into pakchoi by 92.02%, 68.03%, 76.34% and into lettuce by 89.81%, 43.41%, 5.76%, respectively. The chemical species analyses of Cd, Pb, Cu indicate SiO₂-SH can transform the heavy metal in acid soluble states into reducible fraction and oxidizable fraction, thereby inhibiting the extraction of heavy metals into soil solution. The concentrations of microbial biomass carbon, organic matter, and cation exchange capacity of the soil increased while the soil bulk density decreased after remediation. Those changes demonstrate that SiO₂-SH not only has no bio-toxic impact on the soil environment but also improves the soil environment, which proves the prepared SiO₂-SH is environmental-friendly. The SiO₂-SH could be a promising amendment for heavy metal contaminated soils.

Plastic polymers are widely used in various applications and are thus prevalent in the environment. Over time, these polymers are slowly degraded into nano- and micro-scale particles. In this study, the free-living nematode, Caenorhabditis elegans, was exposed to polystyrene particles of two different sizes (42 and 530 nm) in both liquid and soil media. The number of offspring significantly (p < 0.05) decreased at polystyrene concentrations of 100 mg/L and 10 mg/kg in liquid and soil media, respectively. In soil media, but not liquid media, C. elegans was more sensitive to the larger particles (530 nm) than the smaller particles (42 nm), and the median effective concentration (EC₅₀) values of the 42 and 530 nm-sized particles were found to be > 100 and 14.23 (8.91–22.72) mg/kg, respectively. We performed the same toxicity bioassay on five different field-soil samples with different physicochemical properties and found that the size-dependent effects were intensified in clay-rich soil samples. A principal component analysis showed that the bulk density, cation exchange capacity, clay content, and sand content were the dominant factors influencing the toxicity of the 530 nm-sized polystyrene particles. Therefore, we conclude that the soil composition has a significant effect on the toxicity induced by these 530 nm-sized polystyrene particles.

A novel amino-functionalized hydrochar material (referred to NH₂–HCs) was prepared and used as the soil amendment to immobilize multi-contaminated soils for the first time. The results showed that the application of NH₂–HCs significantly improved (P < 0.05) soil properties (i.e., pH value, cation exchange capacity and organic content). By introduction of NH₂–HCs, the contaminated soil showed the highest value of 96.2%, 52.2% and 15.5% reductions in Cu, Pb and Cd bioavailable concentrations and the leaching toxicity of Cu, Pb and Cd were remarkably reduced by 98.1%, 31.3% and 30.4%, respectively. Most of exchangeable Cu, Pb and Cd reduced were transformed into its less available forms of oxidizable and residual fractions. Potential ecological risk assessment indicated that the element Cd accounted for the most of total risks in NH₂–HCs amended soils. The mechanism study indicated that surface complexation, chemical chelating and cation-pi interaction of NH₂–HCs played a vital role in the immobilization of heavy metals. Pot experiments further verified that the application of NH₂–HCs significantly improved plant growth and reduced metal accumulations. The present study offered a novel approach to prepare amino-functionalized hydrochars with great potential as the green and alternative amendments for efficiently immobilizing heavy metals in multi-contaminated soil.

In China, the cadmium (Cd) levels in paddy fields have increased, which has led to the excessive uptake of Cd into rice grains. In this study, we determined the physicochemical properties of soil samples, including the pH, soil organic matter (SOM) content, cation exchange capacity (CEC), and total Cd content (Cdsoil) in order to establish a quadratic discriminant analysis (QDA) model for assessing the risk of Cd in rice and to calculate its prior probability. Decision tree and logistic regression models were also established for comparison. The results showed that the accuracy rate was 74% with QDA, which was significantly higher than that obtained using the decision tree (67%) and logistic regression (68%) models. The correlation coefficients between the soil pH and the other three factors (CEC, SOM, and Cdsoil) were higher in the inaccurate set than the accurate set, whereas the correlation coefficients were smaller in the inaccurate set than the accurate set.

Multigenerational tests provide a comprehensive assessment of the long-term toxicity of pollutants. Here, the multigenerational effects of soil metal contamination on Folsomia candida were investigated over five generations (generations 1–5: F1–F5). Nine soils with varying physicochemical properties and degrees of metal pollution were studied. The selected endpoints were survival, reproduction, body size and body metal concentrations. F. candida was cultured only up to the fifth generation with high reproduction in contaminated acid soils where reproduction was at least 5 times that in neutral soils and 20 times that in calcareous soils. Correlation analysis indicated that soil pH (68.9% contribution) and cation exchange capacity (CEC, 15.4% contribution) were more important factors than pollution level affecting the reproduction of F. candida. No significant difference was observed in adult survival or adult length over five generations. The highest collembolan body Cd concentrations in soils A1-A3 were 3.15, 2.93 and 3.23 times those in F1, with similar results for body Pb. A similar trend in reproduction and juvenile length was observed with an initial decrease (p < 0.05) and then an increase (p < 0.05) over the generations in each acid soil; the opposite trend occurred in the changes in body cadmium (Cd) and lead (Pb) concentrations which increased initially (p < 0.05) and then decreased (p < 0.05) compared to the original concentrations of the first generation. The results indicate that F. candida can adapt to soil metal stress during multigenerational exposure and the adaption energy may be related to a tradeoff between reproduction or growth of juveniles and the detoxification of metals accumulated in the body. Soil properties, especially pH and CEC, had a substantial influence on the long-term survival of the collembolan in the metal-polluted soils.

In situ remediation technology applied aims to not only decrease cadmium (Cd) and arsenic (As) uptake by rice but also improve soil health and rice quality in contaminated paddy soils. Here the effects of a combined amendment, consisting of limestone, iron powder, silicon fertilizer, and calcium-magnesium-phosphate fertilizer, with three application rates (0, 450, and 900 g m⁻²) on soil health, rice root system, and brown rice quality were compared in moderately versus highly Cd and As co-contaminated paddy fields. After the amendment application, soil pH, cation exchange capacity, four kinds of soil enzyme activities increased (sucrase, urease, acid phosphatase, and catalase), and concentrations of leached Cd/As decreased, as measured by the DTPA (diethylene triamine pentaacetic acid) and TCLP (toxicity characteristic leaching procedure). Changes in the above soil indicators promoted soil health. In both fields, the dithionite-citrate-bicarbonate (DCB)-Fe and DCB-Mn concentration in iron plaque increased and root length became longer. Changes in the above root system indicators reduced the root system's absorption of Cd and As but increased that of nutrients. Under 900 g m⁻² treatment, the Cd concentration in brown rice of two sites decreased by 55.8% and 28.9%, likewise inorganic As (iAs) decreased by 50.0% and 21.1%, whereas essential amino acids increased by 20.4% and 20.0%, respectively. Furthermore, the Cd and iAs concentrations in brown rice were <0.2 mg kg⁻¹ (maximum contaminant level of Cd and iAs in the Chinese National Food Safety Standards GB2762-2017 for brown rice) under the 900 g m⁻² in the moderately contaminated field. These results suggest the combined amendment can improve soil health and brown rice quality in the moderately and highly Cd- and As-co-contaminated paddy soils, offering potential eco-friendly and efficient remediation material for applications in such polluted paddy soils.

The desorption rate is an important factor determining cadmium (Cd) ecotoxicity and pollution remediation in soils. The pedotransfer functions (PTFs) of desorption rate coefficients of fresh Cd in soils have been developed in literature. We hypothesized that the aging of Cd pollution would alter Cd desorption process. Taking historically polluted soils as the object, this study aimed at testing the hypothesis and developing new PTFs of desorption rate coefficients for historical Cd. 15 d batch extraction experiments and 13 kinetic models were employed to define Cd desorption rate coefficients in 27 historically polluted soil samples. Compared with fresh Cd, the desorption rate coefficients of historical Cd were lower, and the break time of biphasic desorption processes was retarded to 3 d (4320 min). Different with the usual models for fresh Cd desorption (e.g. parabolic diffusion and two constant rate models), the best models to mimic the historical Cd desorption processes were the pseudo first order, logarithmic, Elovich, and simple Elovich models. The rate-limiting step controlling Cd desorption was changed from the intraparticle diffusion to the interface reaction with aging of pollution. New PTFs of desorption rate coefficients of historical Cd were established (R² ≥ 0.71). Cd desorption rate coefficients increased with organic matter and clay contents, but decreased with oxalate extractable Fe content, solution pH, cation exchange capacity, and silt content. The key soil properties influencing desorption rate coefficients were not altered by the aging of pollution. The developed PTFs could guide us to adjusting the ecotoxicity and pollution remediation of Cd in historically polluted field soils.

Soil washing using a strong chelating agent is a common practice for restoring contaminated soils, but significant soil fertility degradation and high operation costs are the major disadvantages. Washing soil with a dissolved organic matter (DOM) solution has been identified as a method that can moderate the loss of nutrients in the soil and enhance metal removal. The DOM solutions were extracted from waste sludge obtained from a local whisky distillery. Single chelating washing and chelate-DOM washing were carried out using ethylenediaminetetraacetic acid (EDTA), citric acid, and DOM solutions to remediate highly Cu-contaminated soil. Two-phase washing using 0.34 M citric acid and then 1500 mg L−1 DOM solution (pH 8.5) was found to be most favorable for the soil. With this treatment, 91% Cu was removed from the topsoil; the organic matter, cation exchange capacity, plant-available nitrogen, and available phosphate content increased by 28.1%, 103%, 17.7%, and 422%, respectively.

Soil properties, such as soil pH, soil organic matter (SOM), cation exchange capacity (CEC), are the most important factors affecting cadmium (Cd) accumulation in vegetables. In this study, we conducted big data mining of 31,342 soil and vegetable samples to examine the influence of soil properties (soil pH, SOM, CEC, Zn and Mn content) on the accumulation of Cd in root, solanaceous, and leafy vegetables in Hunan Province, China. Specifically, the Cd accumulation capability was in the following order: leafy vegetables > root vegetables > solanaceous vegetables. The soil property thresholds for safety production in vegetables were determined by establishing nonlinear models between Cd bioaccumulation factor (BCF) and the individual soil property, and were 6.5 (pH), 30.0 g/kg (SOM), 13.0 cmol/kg (CEC), 100–140 mg/kg (Zn), and 300–400 mg/kg (Mn). When soil property values were higher than the thresholds, Cd accumulation in vegetables tended to be stable. Prediction models showed that pH and soil Zn were the leading factors influencing Cd accumulation in root vegetables, explaining 87% of the variance; pH, SOM, soil Zn and Mn explained 68% of the variance in solanaceous vegetables; pH and SOM were the main contributors in leafy vegetables, explaining 65% of the variance. Further, variance partitioning analysis (VPA) revealed that the interaction effect of the corresponding key soil properties contributed mostly to BCF. Meanwhile, partial least squares (PLS) path modeling was employed to analyze the path and the interactive effects of soil properties on Cd BCF. pH and SOM were found to be the biggest two players affecting BCF in PLS-models, and the most substantial interactive influence paths of soil properties on BCF were different among the three types of vegetables.