Understanding how essential and toxic elements are distributed in cereal grains is a key to improving the nutritional quality of cereal-based products. The main objective of this work was to characterize the distribution of Cd and of nutrients (notably Cu, Fe, Mn, P, S and Zn) in the durum wheat grain. Laser ablation inductively coupled mass spectrometry and synchrotron micro X-ray fluorescence were used for micro-scale mapping of Cd and nutrients. A dissection approach was used to quantitatively assess the distribution of Cd and nutrients among grain tissues. Micro X-ray absorption near-edge spectroscopy was used to identify the Cd chemical environment in the crease. Cadmium distribution was characterized by strong accumulation in the crease and by non-negligible dissemination in the endosperm. Inside the crease, Cd accumulated most in the pigment strand where it was mainly associated with sulfur ligands. High-resolution maps highlighted very specific accumulation areas of some nutrients in the germ, for instance Mo in the root cortex primordia and Cu in the scutellum. Cadmium loading into the grain appears to be highly restricted. In the grain, Cd co-localized with several nutrients, notably Mn and Zn, which challenges the idea of selectively removing Cd-enriched fractions by dedicated milling process.

International audience | 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 metal contamination in the Bohai Sea (China) has been the focus of many studies, but most of them only focused on local pollution levels and thus lacked high spatial resolution for the whole sea. In this study, heavy metals (i.e., As, Cr, Cu, Cd, Pb, Zn, and Fe) in surface sediments were analyzed to assess the spatio-temporal pollution conditions of the Bohai Sea, an important coastal environment consisting of Bohai Bay, Laizhou Bay, and Liaodong Bay. The results indicated that the heavy metal concentration in the sediments was in the range of 6.43–32.18 mg/kg for As, 14.90–58.07 mg/kg for Cr, 3.90–27.19 mg/kg for Cu, 0.04–0.27 mg/kg for Cd, 11.09–30.95 mg/kg for Pb, 18.76–65.58 mg/kg for Zn, and 0.78%–2.55% for Fe. The distribution of heavy metals revealed that the concentrations were relatively low in Laizhou Bay, very high in the northwest coastal region of the Bohai Sea, and decreased from near-shore to off-shore areas. Moreover, both the enrichment factor and geo-accumulation index demonstrated that there was no contamination to be found for Cr, Cu, Zn in the region and a slight to moderate pollution of As, Cd, and Pb. Cd and As presented considerable potential ecological risk as a result of their high toxicity. The potential ecological risk index (RI) suggested that a third of the areas (northwest coastal area of the Bohai Sea) has moderate ecological risk. The risk area was generally decreased as offshore distance increased, which suggested that the contamination and risk of heavy metals are influenced by anthropogenic activities.

The accumulation of cadmium (Cd) in rice grains is closely associated with the content of mineral nutrients and amino acid metabolism, but the causal link among them is unclear. Profiles of amino acids (AAs) and quantities of essential nutrients in grains from early and late rice cultivars grown at four sites with different Cd levels were analyzed in the present study. Hazard quotients (HQs) for consumers by intake of rice from late cultivars were much higher than that from early cultivars at sites with soil Cd content of 0.25, 0.61 and 0.84 mg kg⁻¹. Cadmium accumulation in grains resulted in a sharp reduction of total essential AAs and non-essential AAs in both early and late rice cultivars. High-Cd-accumulating (HCA) cultivars had significantly higher level of glutamate (Glu) than low-Cd-accumulating (LCA) cultivars when rice Cd content was less than 0.20 mg kg⁻¹. However, Glu level in grains dramatically declined with the accumulation of Cd, which subsequently leaded to the reduction of other AAs. Cadmium content was well predicted by five amino acids (i.e., Glu, Alanine, Phenylalanine, Glycine and Threonine) or four essential elements (Ca, Fe, Mn and Zn) when rice Cd was less than 0.80 mg kg⁻¹. Amino acids played more important roles than nutrients in Cd accumulation. When Cd content was in the range of 0.40–1.16 mg kg⁻¹, the Mn content in rice increased significantly with the increase of Cd content, while the Glu content dropped down synchronously. Remarkably, the ratio between Mn and Glu displayed the highest direct path coefficient on Cd accumulation than any single cation or amino acid. These results indicate that high capacity in synthesizing Glu and concentrating Mn is the determinant factor for Cd accumulation in rice grains, and abundant Glu in aleurone layer may alleviate Cd toxicity by forming Glu-Cd complex.

Amendment with sewage sludge or biosolids can increase soil fertility but may also transfer biosolid-borne pollutants to the soil and the possible effects on the soil ecosystem are poorly understood, especially long-term effects. A long-term experiment was therefore established to assess the effects of repeated applications of different types of biosolids (fresh domestic, dried domestic and fresh industrial sludges) in field conditions. Nine years of sludge application led to changes in soil chemical and biological properties and generally contributed little to soil nutrient status. However, soil concentrations of potentially toxic elements (PTEs) were elevated by amendment, especially with industrial biosolids. Soil fauna are usually used to decipher the underlying effects of biosolid applications on the soil ecosystem. Here, collembolans (50.9%), nematodes (41.6%) and enchytraeid worms (7.50%) were collected and differentiated into different ecological and trophic groups and their body lengths and PTE concentrations in the body tissues were investigated. The animals showed different responses to the biosolids at population and individual levels. There were substantial changes in epigeic collembolan communities and bacterivorous nematodes increased significantly after biosolid amendment. Biosolid-borne PTEs were major factors and Redundancy (RDA) analysis indicates that collembolan communities were strongly influenced by zinc (Zn). The three groups of soil animals showed similar trends in accumulation of PTEs in the sequence cadmium (Cd) > Zn > copper (Cu), and the bioaccumulation factor (BAF) values of the PTEs were significantly higher in the industrial sludge treatment than in other two treatments with a similar trend of decreasing body length of nematodes. The results indicate that it is potentially risky to use industrial biosolids in the long term, and different species and ecological groups of collembolans and different trophic groups of nematodes should be examined when assessing soil health.

Cadmium (Cd) contamination is a big challenge for managing food supply and safety around the world. Reduction of the bioaccumulation of cadmium (Cd) in wheat is an important way to minimize Cd hazards to human health. This study compared and highlighted the effects of soil and foliar applications of Zn on Cd accumulation and toxicity in cultivars with high Cd accumulation (high-Cd wheat) and low Cd accumulation (low-Cd wheat). Both foliar and soil Zn applications provided effective strategies for reducing wheat grain Cd concentrations in the high-Cd wheat by 26–49% and 25–52%, respectively, and these also significantly reduced the concentrations in wheat stems and leaves. Foliar and soil Zn applications significantly reduced Cd in leaves and stems of the low-Cd wheat but had no effects on grain Cd. Both soil and foliar Zn applications significantly alleviated Cd toxicity by regulation of Cd transport genes, as reflected by the increased grain yield and antioxidant enzyme activity in the wheat tissues. Gene expression in response to zinc application differed in the two wheat cultivars. Down-regulation of the influx transporter (TaNramp5) and upregulation of the efflux transporters (TaTM20 and TaHMA3) in the high-Cd wheat may have contributed to the Zn-dependent Cd alleviation and enhanced its tolerance to Cd toxicity. Additionally, foliar Zn applications down-regulated the leaf TaHMA2 expression that reduced root Cd translocation to shoots, while soil Zn applications down-regulated the root TaLCT1 expression, which contributed to the reduction of root Cd concentrations. Soil (99 kg ZnSO₄·7H₂O ha⁻¹) and foliar (0.36 kg ZnSO₄·7H₂O ha⁻¹) Zn applications can effectively decrease the Cd in grains and guarantee food safety and yield, simultaneously. The presented results provide a new insight into the mechanisms of, and strategies for, using Zn for the Cd reduction in wheat.

Cattle-derived biochar (CB), which is derived from industrial pyrolysis of cattle carcasses in harmless treatment plants, is a naturally occurring mineral form of carbonate-bearing hydroxyapatite (CHAP) with a small amount of elemental carbon. CB has 4.02% of carbonate content, which falls under the B-type substitution of CHAP. In this work, the Cd(II) sorption capacity of CB was determined to be 0.82 mmol/g, with 97.6% of the Cd(II) uptake contributing to CHAP and only 2.36% of the Cd(II) uptake contributing to the elemental carbon component. The calculation and linear combination fitting (LCF) of Cd L₃-edge X-ray absorption near-edge structure (XANES) analysis indicated that the contributions of Cd(II) species to CB presented the following order: ion exchange (57.6%–61.0%) > precipitation (24.4%–29.9%) > surface complexation (12.5%–13.4%). The depth dependent X-ray photoelectron spectroscopy (XPS) showed the presence of ion exchange, which is accompanied by intraparticle diffusion. LCF of XANES and Rietveld analysis of X-ray diffraction (XRD) demonstrated that Cd(II) was precipitated in the form of Cd₅H₂(PO₄)₄·4H₂O on the CB surface. Furthermore, the precipitate was directly observed and identified by scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS). Consequently, we revealed the intricate binding mechanism of Cd(II) to CHAP-rich CB and confirmed the importance of surface precipitation.

Technologies for cleaner production of rice in cadmium (Cd) contaminated field are being explored worldwide. In order to investigate the inhibition mechanism of phosphate on Cd transport in soil-plant system, controlled experiments were performed in this study. Experimental results showed that Cd levels in roots, flag leaves, rachises and grains of rice plants (Oryza sativa L.) were significantly reduced by supplement of 0.5–2.5 g kg⁻¹ calcium magnesium phosphate fertilizer (CMP). Path coefficient analysis revealed that phosphorous had significant negative direct effect on Cd, but positive indirect effect on essential and non-essential amino acids. Applying 2.5 g kg⁻¹ CMP made the Cd concentration decreased by 45.7% while free essential and non-essential amino acids increased by 28.0–28.6% in grains. Levels of the branched-chain amino acids in grains were much higher than other essential amino acids, and increased with the amount of CMP fertilization. After application of CMP, pH of soil solution and thickness of the iron plaque around roots increased significantly. Spectra from X-ray photoelectron spectrometer (XPS) showed that content of N, P and Fe increased apparently, C, O and Ca had no change, while S decreased by 74.2% in roots after application of 2.5 g kg⁻¹ CMP. Meanwhile, Cd concentration in protoplasts of root cells decreased by 39.5–80.1% with the increase of CMP. These results indicate that application of CMP can effectively inhibit Cd accumulation in root protoplasts by promoting iron plaque formation on the root surface, reduce Cd concentration and increase free amino acids in rice grains.