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Aims: Atmospheric trace metal deposition is an important source in agricultural soils and crops, but a large knowledge gap exists between foliar and root uptake of wet/dry deposition. We aim to distinguish the contribution of dry and wet-deposited trace metals to rice plant via foliar and root uptake and to investigate their accumulations during the full growth season. Methods: We performed an atmospheric exposure experiment using customized open top chambers (OTCs) to distinguish the impacts of wet and dry deposition contribution to foliar and root uptake and their mobility in soils. The foliar uptake and then translocation was hypothesized the major pathway of trace metal accumulation in rice grains. Results: Foliar uptake of wet- and dry-deposited Cu, Zn, and Pb played an important role in their accumulations in rice plant, contributing to 44–47%, 23–25%, and 35–37% in rice grains, respectively. The leaf Cu, Zn, and Pb accumulated from atmospheric deposition can be transported upward to rice grains but nodes seem to restrict them downward translocation. Rice leaves cannot directly take up atmospheric As and the deposited As can only accumulate in rice through the root uptake. The trace metals showed high mobility in atmospheric deposition, which significantly increase the bioavailable trace metal fractions in surface soils and soil solutions. Conclusions: This study provides a new insight of similar or even higher contributions of foliar uptake than root uptake of trace metals from atmospheric deposition and that reducing the accumulation of atmospheric trace metals due to deposition on leaves can effectively decrease the accumulation of trace metals in crops. [ABSTRACT FROM AUTHOR]

Phytoextraction is a promising technology for remediating heavy metal-contaminated soil. Continuously screening potential plants is important for enhancing the efficiency of remediation. In this study, fourteen local native plant species and four cultivated plant species, along with their paired soils, were collected from around a copper smelter. The characteristics of soil pollution were evaluated using contaminant factors (CF) and a geoaccumulation index (Igeo). The phytoextraction potential of plants was investigated using the translocation factor (TF) and bioconcentration factor (BCF). The soils around the smelter were very acidic, with a mean pH of 5.01. The CF for copper and cadmium were 8.67–32.3 and 5.45–44.2, and the Igeo values for copper and cadmium were 2.43–4.43 and −0.12–2.29, respectively, indicating that the level of soil contamination was moderate to severe. The copper concentrations in the root (357 mg/kg), shoot (219 mg/kg), and leaf (269 mg/kg) of Elsholtzia splendens Nakai were higher than that in the other species. The cadmium in the shoot (32.2 mg/kg) and leaf (18.5 mg/kg) of Sedum plumbizincicola was the highest, and Phytolacca acinosa Roxb. had the highest cadmium level (20 mg/kg) in the root. Soil total and CaCl2-extractable copper and cadmium were positively correlated with copper and cadmium in the plant roots, respectively. The results of TF and BCF for copper and cadmium suggested that the accumulation and translocation capacities for cadmium were higher than those of copper in the eighteen plant species. Although not all plants met the criteria of being hyperaccumulators, Sedum plumbizincicola, Mosla chinensis Maxim, and Elsholtzia splendens Nakai showed the most potential as candidates for the phytoextraction of copper and cadmium contaminated soils, as indicated by their TF and BCF values. [ABSTRACT FROM AUTHOR]

Fly ash (FA) is promising for environmental remediation, but how to modify the FA with high remediation efficiency through an environmentally friendly and low-cost modification method is scare. A modified FA (MFA) was prepared through a one-step hydrothermal modification with Ca(OH)2 and KH2PO4. Results indicated that irregular agglomerates occurred on the surface of the MFA and that the specific surface area increased by 1.94 times compared to that of FA. Compared to FA, glassy compositions in MFA were destroyed and amorphous Si/Al and alkaline aluminosilicate gels were formed. The soil application of 0.2–0.6% MFA significantly increased soil pH by 0.23–0.86 units compared to FA and decreased available lead (Pb) and copper (Cu) by 25–97.1% and 13.5–75%, respectively. MFA significantly decreased exchangeable Pb and Cu by 12.5–32% and 11.4–35.2%, respectively, compared to FA. This may be due to the high pH and specific surface area of MFA, which promoted to the formation of amorphous Si/Al, metal–phosphate precipitation, and complexation with functional groups. In addition, MFA slightly increased the biomass of shoots and roots and decreased the uptake of Pb and Cu by ryegrass. This study provides a new modification method for the utilization of FA in the heavy metal-contaminated soils. [ABSTRACT FROM AUTHOR]

The atmospheric deposition of copper (Cu) and cadmium (Cd) was monitored in eight sites around a Cu smelter with similar distance to verify whether tree leaf and ring can be used as bio-indicators to track spatial pollution record. Results showed that total atmospheric deposition of Cu (103–1215 mg/m2/year) and Cd (3.57–11.2 mg/m2/year) were 4.73–66.6 and 3.15–12.2 times higher than those in background site (164 mg/m2/year and 0.93 mg/m2/year). The frequencies of wind directions significantly influenced the atmospheric deposition of Cu and Cd, and the highest atmospheric deposition of Cu and Cd were at the prevalent northeastern wind (JN), and low frequency south (WJ) and north (SW) winds for the lowest deposition fluxes. Since the bioavailability of Cd was higher than that of Cu, the atmospheric deposition of Cd was more easily adsorbed by tree leaf and ring, resulting in only significant relation between atmospheric Cd deposition and Cinnamomum camphora leaves and tree ring Cd. Although tree rings cannot correctly record the atmospheric Cu and Cd deposition, higher concentrations in the indigenous tree rings than the transplanted tree rings suggested that tree rings can reflect to some extent the variations of atmospheric deposition. Generally, spatial pollution of atmospheric deposition of heavy metals cannot reflect the distribution of soil total and available metals around the smelter, and only camphor leaf and tree ring can bio-indicate Cd deposition. A major implication of these findings is that leaf and tree ring can serve for biomonitoring purposes to assess the spatial distribution of atmospheric deposition metal with high bioavailability around a pollution source with similar distance. [ABSTRACT FROM AUTHOR]

To study the remediation effect of hydroxyapatite with different particle sizes, a field in situ experiment was carried out by adding conventional hydroxyapatite (0.25 mm) and microhydroxyapatite (3 μm) and nanohydroxyapatite (40 nm) to the contaminated soil and planting Elsholtzia splendens. The distribution and migration of copper (Cu) and cadmium (Cd) in soil were investigated after 4 years. The results show that the application of three different particle sizes of hydroxyapatite significantly raise the soil pH, total phosphorus, and soil organic carbon. Moreover, the addition of hydroxyapatite can reduce the EXC fraction of Cu and Cd by 73.7%–80.1% and 20.8%–35.2%, respectively. In addition, the concentrations of Cu and Cd in >2 mm, 0.25–2 mm, 0.053–0.25 mm, and <0.053 mm aggregate are significantly increased. This improvement indicates that there are risks which may cause the increasing of total Cu and Cd in the soil where the pollution sources still exist. Furthermore, the content of soil colloid is significantly increased, and the colloidal Cu and Cd distribution percentage have been significantly increased by 49.9%–120% and 30.3%–181%. This result illustrates that the application of hydroxyapatite may greatly increase the possibility of colloid and dust migration of Cu and Cd. [ABSTRACT FROM AUTHOR]

In an effort to address public concerns of the long-term stability and ecological risk reduction of Cu and Cd in a farmland located at the Guixi, Jiangxi Province, China, containing ∼ 800 mg kg−1 Cu and 0.8 mg kg−1 Cd soil, were treated in situ by attapulgite, apatite, montmorillonite and lime at the rate: 10, 10, 10 and 4 g kg−1 soil, respectively. Field experiment consisted of 2 × 3-m plots arranged in a randomised complete block design with each treatment. Soil and plant samples were collected in sixth years post-treatments and analysed for Cu and Cd bioaccessibility, chemical fraction and Cu, Cd concentration in plant tissue. The results indicated that the apatite and lime treatments significantly reduced bioaccessible and exchangeable fractions Cu and Cd in the soil at sixth years post the treatments. Cu and Cd concentration in plant tissue was positively related to the bioaccessibility of Cu and Cd. The treatment used 10 g apatite kg−1 soil appeared to be most effective for overall risk reduction. The Cu and Cd stabilisation and risk reduction by the apatite treatments were accomplished by the induced transformation of labile Cu and Cu species to relatively insoluble forms. This study illustrated that in situ Cu and Cd stabilisation by apatite would be long-term and ecologically safe, which could safeguard human health and ecosystem from Cu and Cd contamination in mining areas. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HAP) can effectively decrease bioavailability of trace metals in soils, but the phosphorus (P) release risk was not fully known. In this study, the impacts of ferrihydrite (FH) on passivation of copper (Cu) and cadmium (Cd) and P release risk in soil amended by HAP were investigated under flooding conditions. Results showed that the combinations of HAP and FH increased soil pore water pH by 0.74–2.24 units and reduced phosphate by 71.1–99.5% than single HAP. Soil pore water Cu2+ and Cd2+ in HAP plus 5% FH treated soils were decreased by 96.8–98.6% and 86.6–98.6% than those of single HAP. The combinations of HAP and FH significantly decreased CaCl 2 extractable Cu and Cd by 55.9–99% and 13–72.2%, respectively. Moreover, the combinations of HAP and FH significantly decreased exchangeable Cu 47.1–91.5%, but only FH5 decreased exchangeable Cd by 69.4% than the single HAP. Amorphous iron oxide in FH treated soils was 4.06–20 times higher than control, but some of them were transformed into crystalline iron oxide after 42-d flooding incubation. The FH significantly decreased soil labile P by 42.8–78.8% in the presence of HAP and increased stable P by 23.1–33.5% than the single HAP. This study suggested that the addition of FH can not only promote the passivation of HAP on Cu and Cd in the soil, but also reduce the P release risk. Overall, this study highlighted the potential value of the combination of HAP and FH in the passivation of Cu and Cd contaminated soils. [Display omitted] • Ferrihydrite (FH) reduced soluble Cu2+ and Cd2+ in the presence of HAP. • FH reduced pore water phosphate in the presence of HAP. • FH plus HAP effectively decreased the bioavailability of Cu and Cd in soil. • FH reduced soil labile P and eutrophication risk in the presence of HAP. [ABSTRACT FROM AUTHOR]

While biochar is useful for environmental remediation, the effects of aging on the activation of endogenous trace metals in biochar remain unclear. In this study, three biochars with different concentrations of copper (Cu) and cadmium (Cd) were produced from the straws of Pennisetum sinese grown in moderately-polluted (MB), highly-polluted (HB), and clean (CB) soils. The effects of aging on biochar properties and bioavailability of endogenous Cu and Cd were investigated by Fourier-transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, Boehm titration, and chemical extraction before and after dry-wet (DW) and freeze-thaw (FT) aging. DW and FT aging increased the specific surface areas and abundance of oxygen-containing functional groups in the biochars. Aging decreased the biochar pH, degree of graphitization, and stability. The leachability of Cu and Cd were higher after FT aging than after DW aging, and the bioavailability of Cu and Cd were higher in MB and HB than those in CB. Aging increased the bioavailability of Cu in all biochars, whereas it only increased the bioavailability of Cd in MB. Aging increased the mobility of Cu and Cd by 2.31–12.2 and 0.22–1.31 times. The trends of the mobility and leachability of Cu were not consistent with those of total Cu in the biochars, while mobility and leachability of Cd and total Cd had the same trends. The activation of endogenous Cu was primary associated with the compositions of organic functional groups in the biochars. However, Cd activation was mostly related to the changes in the inorganic components and pH of the biochars. This study implies that aging can activate endogenous metals in biochars, and the potential environmental risk of a biochar should be carefully evaluated to ensure its safe and sustainable application. Image 1 • Biochars with various inherent metals were produced by straws of Pennisetum sinese. • Aging increased oxygen-containing functional groups and decreased pH of biochar. • FT aging increased leachability of copper and cadmium than that of DW aging. • Bioavailability of copper and cadmium were higher in biochar with elevated metals. [ABSTRACT FROM AUTHOR]

Iron (Fe) oxides are intimately coupled with phosphorus and closely associated with the bioavailability of potential toxic elements (PTEs) in soil. Thus, Fe oxides may influence the stabilization of PTEs in contaminated soils amended by phosphorus. To evaluate the effects of hematite (HMT) on the stabilization of PTEs, 1–5% (by weight) of HMT was added into a contaminated red soil amended with hydroxyapatite (HAP) to simulate naturally occurring Fe oxides. The stabilization efficiencies of soil copper (Cu) and cadmium (Cd) amended with HAP in soils with low, moderate, and high content of HMT were assessed after a 60-day incubation. HAP treated the soil with high rate HMT decreased the CaCl 2 -extractable and acid-soluble fractions of Cu and Cd than that of HAP alone. In particular, CaCl 2 -extactable Cu and Cd in the soil with 5% HMT amended by HAP were 91–95% and 41–68% lower than those amended with only HAP. High content of HMT in soil could decrease the concentration of labile phosphorus in the presence of HAP, but it did not increase the concentration of NaOH-extractable inorganic phosphorus (the fraction bound to Fe oxides). The concentrations of free and crystalline Fe oxides were significantly increased by adding high dosages of HMT with or without HAP. High content of HMT in soil amended by HAP reduced metal phytotoxicity and uptake by wheat shoots than the soil containing HAP without HMT. The results indicate that HMT can promote Cu and Cd stabilization while decrease labile phosphorus in red soil amended with HAP, suggesting that phosphorus-based amendments combined with Fe oxides can be used to stabilize PTEs in contaminated red soils. Image 1 • A contaminated red soil with 1–5% hematite was treated by hydroxyapatite (HAP) for 60 d. • Hematite decreased Cu and Cd bioavailability in the soil amended with HAP. • Hematite decreased soil labile phosphorus content in the presence of HAP. • Hematite promoted the reduction of wheat phytotoxicity in red soil amended with HAP. • Hematite promoted the stabilization of Cu and Cd in red soil amended with HAP. [ABSTRACT FROM AUTHOR]

• More than half of the atmospheric metal depositions presented as mobile fractions. • The newly deposited metals in soils resulted in higher bioavailable fractions. • The newly deposited metals contributed 30˜84% and 6˜41% in rice tissues. • Atmospheric deposition reactivated the metals and transported to plant tissues. Despite the global importance of atmospheric heavy metal input into agricultural soils, research has primarily focused on the amount of the depositions with limited attention given to the risk of the newly deposited heavy metals. To understand the remobilization of the newly deposited copper (Cu) and lead (Pb) from the atmosphere and explore the metals' mobility and bioavailability to rice (Oryza sativa L.), a soil transplant experiment was conducted in three areas along a gradient of atmospheric depositions. Approximately 61% of the Cu and 76% of the Pb depositions tended to be present in potentially mobile fractions. The soil retention of newly deposited Cu and Pb presented as higher mobile fractions than these in the original soil. The newly deposited Cu and Pb in soils only accounted for 0.34–8.7% and 0.07-0.29% of the total soil Cu and Pb pools, but they contributed 30–84% and 6–41% in rice tissues, respectively. A major implication of these findings is that once the heavy metal is deposited, it may be reactivated in soils and transported to aerial parts or foliar uptake into plant tissues, emphasizing the important role of the newly deposited Cu and Pb in contributing to the edible parts of crops. [ABSTRACT FROM AUTHOR]