Contamination of cadmium (Cd) in paddy soil is a serious environmental problem threatening food safety in some parts of southern China, where rice grain Cd concentration often exceeds the Chinese ...limit (0.2 mg kg−1). We tested the effect of CaCO3 liming combined with growing low Cd cultivars on Cd accumulation in rice grain in 2-year field trials. A liming model was used to predict the doses of lime required. Lime (2.25–7.5 t ha−1) was applied in 2016 only and the effect monitored in both 2016 and 2017. Soil pH was increased from the initial 5.5 to the target value 6.5 by 7.5 t ha−1 CaCO3. Liming greatly reduced CaCl2-extractable Cd in the rhizospheric soil. Grain Cd concentration in the control exceeded the limit by 2–5 times. Liming at 7.5 t ha−1 decreased grain Cd concentration by 70–80% in both seasons without affecting grain yield. Grain Cd concentration was below the limit in the 7.5 t ha−1 liming treatment in both seasons. Grain Cd concentration correlated closely with CaCl2-extractable Cd in rhizospheric soil at the grain maturing stage. Seasonal difference in grain Cd concentration was attributed to the soil water status at the grain maturing stage. Liming had no significant effect on grain arsenic concentration or speciation. A single application of CaCO3 to raise soil pH to 6.5, combined with low Cd cultivars and delayed drainage of paddy water during late grain filling stage, was highly effective at reducing Cd accumulation in rice grain.
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•High phytoavailability of Cd in a moderately contaminated paddy soil.•Rice Cd concentration in the control exceeded the Chinese limit by 2–5 times.•Liming with 7.5 t ha−1 CaCO3 decreased grain Cd concentration by 70–80%.•Liming combined low Cd cultivars and delayed drainage was highly effective.
Arsenic (As) is an environmental and food chain contaminant. Excessive accumulation of As, particularly inorganic arsenic (As(i)), in rice (Oryza sativa) poses a potential health risk to populations ...with high rice consumption. Rice is efficient at As accumulation owing to flooded paddy cultivation that leads to arsenite mobilization, and the inadvertent yet efficient uptake of arsenite through the silicon transport pathway. Iron, phosphorus, sulfur, and silicon interact strongly with As during its route from soil to plants. Plants take up arsenate through the phosphate transporters, and arsenite and undissociated methylated As species through the nodulin 26-like intrinsic (NIP) aquaporin channels. Arsenate is readily reduced to arsenite in planta, which is detoxified by complexation with thiol-rich peptides such as phytochelatins and/or vacuolar sequestration. A range of mitigation methods, from agronomic measures and plant breeding to genetic modification, may be employed to reduce As uptake by food crops.
China faces great challenges in protecting its soil from contamination caused by rapid industrialization and urbanization over the last three decades. Recent nationwide surveys show that 16% of the ...soil samples, 19% for the agricultural soils, are contaminated based on China’s soil environmental quality limits, mainly with heavy metals and metalloids. Comparisons with other regions of the world show that the current status of soil contamination, based on the total contaminant concentrations, is not worse in China. However, the concentrations of some heavy metals in Chinese soils appear to be increasing at much greater rates. Exceedance of the contaminant limits in food crops is widespread in some areas, especially southern China, due to elevated inputs of contaminants, acidic nature of the soil and crop species or cultivars prone to heavy metal accumulation. Minimizing the transfer of contaminants from soil to the food chain is a top priority. A number of options are proposed, including identification of the sources of contaminants to agricultural systems, minimization of contaminant inputs, reduction of heavy metal phytoavailability in soil with liming or other immobilizing materials, selection and breeding of low accumulating crop cultivars, adoption of appropriate water and fertilizer management, bioremediation, and change of land use to grow nonfood crops. Implementation of these strategies requires not only technological advances, but also social-economic evaluation and effective enforcement of environmental protection law.
Deficiencies of micronutrients, including essential trace elements, affect up to 3 billion people worldwide. The dietary availability of trace elements is determined largely by their soil ...concentrations. Until now, the mechanisms governing soil concentrations have been evaluated in small-scale studies, which identify soil physicochemical properties as governing variables. However, global concentrations of trace elements and the factors controlling their distributions are virtually unknown. We used 33,241 soil data points to model recent (1980–1999) global distributions of Selenium (Se), an essential trace element that is required for humans.Worldwide, up to one in seven people have been estimated to have low dietary Se intake. Contrary to small-scale studies, soil Se concentrations were dominated by climate–soil interactions. Using moderate climate-change scenarios for 2080–2099, we predicted that changes in climate and soil organic carbon content will lead to overall decreased soil Se concentrations, particularly in agricultural areas; these decreases could increase the prevalence of Se deficiency. The importance of climate–soil interactions to Se distributions suggests that other trace elements with similar retentionmechanismswill be similarly affected by climate change.
This article is a Commentary on González‐Fontes (226: 1228–1230), Lewis (2020a, 226: 1231), Wimmer et al. (226: 1232–1237), Lewis (2020b, 226: 1238–1239)
Mineral binding is a major mechanism for soil carbon (C) stabilization, and mineral availability for C binding critically affects C storage. Yet, the mechanisms regulating mineral availability are ...poorly understood. Here, we showed that organic amendments in three long-term (23, 154, and 170 yrs, respectively) field experiments significantly increased mineral availability, particularly of short-range-ordered (SRO) phases. Two microcosm studies demonstrated that the presence of roots significantly increased mineral availability and promoted the formation of SRO phases. Mineral transformation experiments and isotopic labeling experiments provided direct evidence that citric acid, a major component of root exudates, promoted the formation of SRO minerals, and that SRO minerals acted as "nuclei" for C retention. Together, these findings indicate that soil organic amendments initialize a positive feedback loop by increasing mineral availability and promoting the formation of SRO minerals for further C binding, thereby possibly serving as a management tool for enhancing carbon storage in soils.
The mineral concentrations in cereals are important for human health, especially for individuals who consume a cereal subsistence diet. A number of elements, such as zinc, are required within the ...diet, while some elements are toxic to humans, for example arsenic. In this study we carry out genome-wide association (GWA) mapping of grain concentrations of arsenic, copper, molybdenum and zinc in brown rice using an established rice diversity panel of ~300 accessions and 36.9 k single nucleotide polymorphisms (SNPs). The study was performed across five environments: one field site in Bangladesh, one in China and two in the US, with one of the US sites repeated over two years. GWA mapping on the whole dataset and on separate subpopulations of rice revealed a large number of loci significantly associated with variation in grain arsenic, copper, molybdenum and zinc. Seventeen of these loci were detected in data obtained from grain cultivated in more than one field location, and six co-localise with previously identified quantitative trait loci. Additionally, a number of candidate genes for the uptake or transport of these elements were located near significantly associated SNPs (within 200 kb, the estimated global linkage disequilibrium previously employed in this rice panel). This analysis highlights a number of genomic regions and candidate genes for further analysis as well as the challenges faced when mapping environmentally-variable traits in a highly genetically structured diversity panel.
Arsenic (As) accumulation in rice (Oryza sativa) may pose a significant health risk to consumers. Plants take up different As species using various pathways. Here, we investigated the contribution of ...the phosphate (Pi) transport pathway to As accumulation in rice grown hydroponically or under flooded soil conditions. In hydroponic experiments, a rice mutant defective in OsPHFl (for phosphate transporter traffic facilitator1) lost much of the ability to take up Pi and arsenate and to transport them from roots to shoots, whereas transgenic rice overexpressing either the Pi transporter OsPhtl;8 (OsPT8) or the transcription factor OsPHR2 (for phosphate starvation response2) had enhanced abilities of Pi and arsenate uptake and translocation. OsPT8 was found to have a high affinity for both Pi and arsenate, and its overexpression increased the maximum influx by 3-to 5-fold. In arsenate-treated plants, both arsenate and arsenite were detected in the xylem sap, with the proportion of the latter increasing with the exposure time. Under the flooded soil conditions, the phfl mutant took up less Pi whereas the overexpression lines took up more Pi. But there were no similar effects on As accumulation and distribution. Rice grain contained predominantly dimethylarsinic acid and arsenite, with arsenate being a minor species. These results suggest that the Pi transport pathway contributed little to As uptake and transport to grain in rice plants grown in flooded soil. Transgenic approaches to enhance Pi acquisition from paddy soil through the overexpression of Pi transporters may not increase As accumulation in rice grain.
The Park Grass experiment (PGE) in the UK has been ongoing since 1856. Its purpose is to study the response of biological communities to the long-term treatments and associated changes in soil ...parameters, particularly soil pH. In this study, soil samples were collected across pH gradient (pH 3.6–7) and a range of fertilizers (nitrogen as ammonium sulfate, nitrogen as sodium nitrate, phosphorous) to evaluate the effects nutrients have on soil parameters and microbial community structure. Illumina 16S ribosomal RNA (rRNA) amplicon sequencing was used to determine the relative abundances and diversity of bacterial and archaeal taxa. Relationships between treatments, measured soil parameters, and microbial communities were evaluated. Clostridium, Bacteroides, Bradyrhizobium, Mycobacterium, Ruminococcus, Paenibacillus, and Rhodoplanes were the most abundant genera found at the PGE. The main soil parameter that determined microbial composition, diversity, and biomass in the PGE soil was pH. The most probable mechanism of the pH impact on microbial community may include mediation of nutrient availability in the soil. Addition of nitrogen to the PGE plots as ammonium sulfate decreases soil pH through increased nitrification, which causes buildup of soil carbon, and hence increases C/N ratio. Plant species richness and plant productivity did not reveal significant relationships with microbial diversity; however, plant species richness was positively correlated with soil microbial biomass. Plants responded to the nitrogen treatments with an increase in productivity and a decrease in the species richness.
•Archived biosolids from australia and UK from 1950 to 2016 analyzed for 7 plastics.•Increasing concentrations over time of PP, PS, PET, PMMA, PVC and PE.•Prior to the 1990s, leakage of plastics into ...biosolids was limited except for PS.•Leakage from 1990s driven by increased production and consumption of PE, PET, PVC.•Concentrations of plastics closely correlate with production and consumption.
Plastics are ubiquitous contaminants that leak into the environment from multiple pathways including the use of treated sewage sludge (biosolids). Seven common plastics (polymers) were quantified in the solid fraction of archived biosolids samples from Australia and the United Kingdom from between 1950 and 2016. Six plastics were detected, with increasing concentrations observed over time for each plastic. Biosolids plastic concentrations correlated with plastic production estimates, implying a potential link between plastics production, consumption and leakage into the environment. Prior to the 1990s, the leakage of plastics into biosolids was limited except for polystyrene. Increased leakage was observed from the 1990s onwards; potentially driven by increased consumption of polyethylene, polyethylene terephthalate and polyvinyl chloride. We show that looking back in time along specific plastic pollution pathways may help unravel the potential sources of plastics leakage into the environment and provide quantitative evidence to support the development of source control interventions or regulations.
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