The long term vertical and horizontal mobility of mercury (Hg) in soils of agricultural areas of a historically contaminated Italian National Relevance Site (SIN Brescia-Caffaro) was investigated. The contamination resulted from the continuous discharge of Hg in irrigation waters by an industrial plant (Caffaro S.p.A), equipped with a mercury-cell chlor-alkali process. The contamination levels with depth ranged from about 20 mg/kg dry weight (d.w.) of soil in the top (plow) layer to less than 0.1 mg/kg d.w. at 1 m depth. The concentrations varied also spatially, up to one order of magnitude within the same field and showing a decreasing trend from the Hg source (i.e., irrigation ditches). The concentration profiles and gradients measured were explained considering Hg loading, soil properties, such as the texture, organic carbon content, pH and cation exchange capacity. A Selective Sequential Extraction (SSE) was also applied on soil samples from an ad hoc greenhouse experiment to investigate the role of different plant species in influencing Hg speciation in soils. Although most of the extracted Hg was included in scarcely mobile or immobile forms, some plant species (i.e., alfalfa) showed to importantly increase the soluble and exchangeable fractions with respect to the unplanted control soils, thus affecting mobility and potential bioavailability of Hg.

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.

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.

Heavy metals contamination in agricultural soil has become a worldwide problem, and soil characteristics modulate metal availability in soils. Four field experiments were conducted simultaneously to evaluate concentration and distribution of cadmium (Cd) and lead (Pb) in 39 oilseed rape cultivars at four agricultural locations with different contamination levels of Cd and Pb, as well as the influence of soil characteristics together with soil total and bioavailable Cd and Pb concentration on metal transfer from soil to oilseed rape. Shoot concentrations of Cd and Pb in oilseed rape cultivars ranged from 0.09 to 3.18 and from 0.01 to 10.5 mg kg⁻¹ across four sites. For most cultivars, Cd concentration in root or shoot were higher than pod and lowest in seed, while the highest Pb concentration was observed in root followed by shoot and seed. Stepwise multiple linear regression analysis allows for a better estimation of Cd and Pb concentration in oilseed rape while taking soil properties into consideration. The results demonstrated that Cd and Pb concentration in oilseed rape were correlated with soil organic matter (OM), cation exchange capacity (CEC), available phosphorus (AP), available potassium (AK), sand, soil total and available Cd and Pb concentration, and R² varied from 0.993 to 0.999 (P < 0.05). The Cd and Pb levels found in oilseed rape indicated its phytoextraction potential for Cd and Pb co-contaminated agricultural soils in winter without stopping agricultural activities.

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.

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.

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.

The potential environmental risk associated with nutrient surplus after switching from rice monoculture (RM) to rice–crayfish rotation (RCR) was assessed in the Jianghan Plains in China. Nutrient surplus was achieved by surveying 32 RM and 69 RCR and determining their nutrient inputs and outputs, and the soil nutrient status for different soil properties were recorded for 0–23 years. The annual average input of N, P₂O₅, and K₂O in RCR was 536, 185, and 253 kg ha⁻¹, respectively, wherein fertilizer and feed accounted for the major fraction of the total nutrient input. For instance, they accounted 58% and 18% of N, 74% and 24% of P₂O₅, and 70% and 30% of K₂O, respectively. The annual apparent surplus of N, P₂O₅, and K₂O was 397, 145, and 225 kg ha⁻¹, respectively, leading to low apparent nutrient use efficiency. Consequently, compared with RM, the total N and soil readily oxidized organic carbon in the upper soil surface (0–20 cm) for the RCR field significantly increased by 0.42–0.96 g kg⁻¹ and 1.63–3.19 g kg⁻¹, respectively. The available N, Olsen P, and exchangeable K of the RCR in the upper soil layer also increased significantly. In the RCR system, a significant positive linear relationship between the apparent accumulated nutrient surplus of N, P, and K elements and the total N, Olsen P, and exchangeable K present in the 0–60 cm soil profile was observed. In RCR, the soil pH in 0–60 cm soil profile and cation exchange capacity in the 0–20 cm soil layer increased as the cultivation time progressed. Nutrient accumulation in the soil not only enhanced soil fertility but also negatively influenced the environment. Therefore, several measures (e.g., new fertilization technologies, new fertilizer, legislation approaches for nutrient surplus, and technical training) should be adopted to control the nutrient surplus.

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.

Calcium peroxide (CaO₂) has been proven to oxidize various organic pollutants when they exist as a single class of compounds. However, there is a lack of research on the potential of unactivated CaO₂ to treat mixed chlorinated organic pollutants in soils. This study examined the potential of CaO₂ in treating soils co-contaminated with p-dichlorobenzene (p-DCB) and p-chloromethane cresol (PCMC). The effects of CaO₂ dosage and treatment duration on the rate of degradation were investigated. Furthermore, the collateral effects of the treatment on treated soil characteristics were studied. The result showed that unactivated CaO₂ could oxidize mixed chlorinated organic compounds in wet soils. More than 69% of the pollutants in the wet soil were mineralized following 21 days of treatment with 3% (w/w) CaO₂. The hydroxyl radicals played a significant role in the degradation process among the other decomposition products of hydrogen peroxide. Following the oxidation process, the treated soil pH was increased due to the formation of calcium hydroxide. Soil organic matter, cation exchange capacity, soil organic carbon, total nitrogen, and certain soil enzyme activities of the treated soil were decreased. However, the collateral effects of the system on electrical conductivity, available phosphorus, and particle size distribution of the treated soil were not significant. Likewise, since no significant release of heavy metals was seen in the treated soil matrix, the likelihood of metal ions as co-pollutants after treatment was low. Therefore, CaO₂ can be a better alternative for treating industrial sites co-contaminated with chlorinated organic compounds.