Combined effects of artificial sweetener acesulfame on the uptake of Cd in rice (Oryza sativa L.)

Ryegrass uptake behavior and forage risk assessment after exposing to soil with combined polycyclic aromatic hydrocarbons and cadmium

Internalization of chemicals and the forage risks of ryegrass under the combined exposure to PAHs and Cd at environmental concentrations were studied here. The effect of soil pH was also concerned due to the widely occurred soil acidification and general alkali remediation for acidification soil. Unexpectedly, as same as the acid-treated group (pH 6.77), the alkali-treatment (pH 8.83) increased Cd uptake compared with original soil pH group (pH 7.92) for the reason of CdOH+ and CdHCO3+ formed in alkali-treated group. Co-exposure to PAHs induced more oxidative stress than Cd exposure alone due to PAHs aggregated in young root regions, such as root tips, and consequently, affecting the expression of Cd-transporters, destroying the basic structure of plant cells, inhibiting the energy supply for the transporters, even triggering programmed cell death, and finally resulting in decreased Cd uptake. Even under environmental concentrations, combined exposure caused potential risks derived from both PAHs and Cd. Especially, ryegrass grown in alkali-treated soil experienced an increased forage risks despite the soil meeting the national standards for Cd at safe levels. These comprehensive results reveal the mechanism of PAHs inhibiting Cd uptake, improve the understanding of bioavailability of Cd based on different forms, provide a theoretical basis to formulate the safety criteria, and guide the application of actual soil management.

Prioritizing ecological restoration in hydrologically sensitive areas to improve groundwater quality

Greening is the optimal way to mitigate climate change and water quality degradation caused by agricultural expansion and rapid urbanization. However, the ideal sites to plant trees or grass to achieve a win-win solution between the environment and the economy remain unknown. Here, we performed a nationwide survey on groundwater nutrients (nitrate nitrogen, ammonia nitrogen, dissolved reactive phosphorus) and heavy metals (vanadium, chromium, manganese, iron, cobalt, nickel, copper, arsenic, strontium, molybdenum, cadmium, and lead) in China, and combined it with the global/national soil property database and machine learning (random forest) methods to explore the linkages between land use within hydrologically sensitive areas (HSAs) and groundwater quality from the perspective of hydrological connectivity. We found that HSAs occupy approximately 20 % of the total land area and are hotspots for transferring nutrients and heavy metals from the land surface to the saturated zone. In particular, the proportion of natural lands within HSAs significantly contributes 8.0 % of the variability in groundwater nutrients and heavy metals in China (p < 0.01), which is equivalent to their contribution (8.8 %) at the regional scale (radius = 4 km, area = 50 km2). Increasing the proportion of natural lands within HSAs improves groundwater quality, as indicated by the significant reduction in the concentrations of nitrate nitrogen, manganese, arsenic, strontium, and molybdenum (p < 0.05). These new findings suggest that prioritizing ecological restoration in HSAs is conducive to achieving the harmony between the environment (improving groundwater quality) and economy (reducing investment in area management).

Effect of biochar application on rice, wheat, and corn seedlings in hydroponic culture

In recent years, biochar has attracted considerable attention for soil quality improvement and carbon sequestration due to its unique physicochemical properties. However, the mechanism by which biochar application negatively affects the growth of crop seedlings has not been fully investigated. In this study, a hydroponic experiment was conducted to evaluate the response of rice, wheat, and corn seedlings to biochar application (CK, 0 g/L; BC1, 0.5 g/L; and BC2, 1.0 g/L). Compared with the CK treatment, the BC1 and BC2 treatments decreased the fresh shoot and root weights of rice and corn seedlings (P < 0.05), but there was no significant effect on wheat seedlings (P > 0.05). For the contents of nutrient elements in seedlings, both BC1 and BC2 treatments hindered the roots from absorbing Fe and Cu and increased the uptake of Ca and Mn. Compared with the CK treatment, the translocation factor (TF) values of Ca, Mn, and Zn were significantly decreased especially in rice seedlings (35.3%-36.8%, 68.7%-76.5%, and 29.8%-22.0%, respectively) under the BC1 and BC2 treatments, while only Mn was significantly decreased in wheat and corn seedlings (P < 0.05). Transmission electron microscope (TEM) analysis of root cross-sections showed that nano-sized biochar particles (10∼23 nm) were found in the root cells under BC2 treatment conditions. Our findings reveal that a large amount of biochar application can reduce nutrient absorption and translocation, and hinder rice, wheat, and corn seedlings, particularly rice seedling, in hydroponic system.

Distribution, Genesis, and Human Health Risks of Groundwater Heavy Metals Impacted by the Typical Setting of Songnen Plain of NE China

Heavy metals pollution in groundwater and the resulting health risks have always been an environmental research hotspot. However, the available information regarding this topic and associated methods is still limited. This study collected 98 groundwater samples from a typical agricultural area of Songnen Plain in different seasons. The pollution status and sources of ten heavy metals (As, Ba, Cd, Co, Cr (VI), Cu, Fe, Mn, Ni, Pb, and Zn) were then analyzed and compared. In addition, the human health risks assessment (HHRA) model was used to calculate human health risks caused by heavy metals in groundwater. The results revealed that heavy metals were mainly distributed in the northwest of the study area and along the upper reaches of the Lalin river and that the concentrations of heavy metals were higher during the wet season than the dry season. Industrial and agricultural activities and natural leaching are the main sources, and each kind of heavy metal may have different sources. Fe and Mn are the primary pollutants, mainly caused by the native environment and agricultural activities. The exceeding standard rates are 71.74% and 61.54%, respectively based on the Class III of Quality Standard for Groundwater of China (GB/T 14848-2017). The maximum exceeding multiple are 91.45 and 32.05, respectively. The health risks of heavy metals borne by different groups of people were as follows: child > elder > young > adult. Carcinogenic heavy metals contribute to the main risks, and the largest risks sources are Cr and As. Therefore, the government should appropriately restrict the use of pesticides and fertilizers, strictly manage the discharge of enterprises, and control man-made heavy metals from the source. In addition, centralized water supply and treatment facilities shall be established to prevent the harm of native heavy metals.

Myriophyllum elatinoides: A potential candidate for the phytoremediation of water with low level boron contamination

Phytoremediation is considered to be a cost-effective strategy for removing boron (B) from polluted water. In this study, Myriophyllum elatinoides, a widespread submerged or floating macrophyte, was found to survive in 40 mg B/L. Time-dependent kinetics show that the shoot exhibits a much longer period of B uptake and a much higher maximal tissue B concentration than the root. High values of the bioconcentration factor (BCF) and translocation factor (TF) indicate that M. elatinoides is a potential hyperaccumulator of B. Transmission electron micrographs show that excess B damages the cells of M. elatinoides, and the major target organelles are the chloroplast (leaf), mitochondria (stem and root), and nucleolus (root). Energy dispersive spectroscopy (EDS) shows that B is mainly deposited in the cytoplasm and on the surface of the chloroplast of the leaf cell. In the stem and root cells, B is mainly deposited on the mitochondrial membrane and in the vacuoles, respectively. This study indicates that the mechanisms of B toxicity, tolerance, and accumulation in M. elatinoides are involved in the cellular localization of B. Future work should focus on the evaluation of the physiological and genetic mechanisms involved in B tolerance and accumulation in M. elatinoides under different conditions.

Environmentally Relevant-Level CeO2 NP with Ferrous Amendment Alters Soil Bacterial Community Compositions and Metabolite Profiles in Rice-Planted Soils

The environmental risks and benefits associated with the introduction of CeO₂ nanoparticle (NP) in agricultural soil must be carefully assessed. The ferrous ion is rich in rhizosphere soil of rice due to the reduction states underground. The aim of this study was to investigate the effects of environmentally relevant-level CeO₂ NP (25 mg·kg^-1) in the absence or presence of ferrous (30 mg·kg^-1) amendment on soil bacterial communities and soil metabolomics in rice-planted soil over 150 days. Results showed that CeO₂ NP exposure changed soil bacterial community compositions and soil metabolomics, and the above changes were further shifted with the ferrous amendment. Several functionally significant bacterial phyla containing Proteobacteria and Bacteroidetes abundances, which were associated with carbon and nitrogen cycling, were promoted after CeO₂ NP exposure with ferrous amendment. However, CeO₂ NP inhibited plant-growth-promoting rhizobacteria containing genera Bacillus and Arthrobacter irrespective of the presence or absence of ferrous. Among rhizosphere soil enzyme activities, cellulose activity was the most sensitive for CeO₂ NP exposure. NP decreased Firmicutes and increased Chloroflexi, Rokubacteria, and Thaumarchaeota abundances at the phylum level, which contributed to reduce soil cellulose activity. Additionally, CeO₂ NP positively or negatively affected soil pH, Ce accumulation in root, and rice physiological properties (root-POD, stem-POD). As a result, the above factors were related to the changes of Chloroflexi, Gemmatimonadetes, Rokubacteria, Thaumarchaeota, and Nitrospirae at the phylum level. After adding CeO₂ NP with ferrous or not, the main metabolic changes were concentrated on fluctuations in starch and sucrose metabolism, nitrogen metabolism, sulfur metabolism, propanoate metabolism, fatty acid metabolism, and urea cycle. The eight changed metabolites containing glycerol monstearate, boric acid, monopalmitin, palmitic acid, alkane, ethanol, dicarboximide, and stearic acid accounted for the separation of different treatments with CeO₂ NP exposure. Activities of soil enzymes (urease, invertase, and cellulose), pH, and soil organic matter affected dominant metabolites containing fatty acids, inorganic acid, and sugar. Network analysis showed that the influence of soil bacterial community on metabolites varied with metabolites and bacteria species. The presence of CeO₂ NP mainly promoted fatty acids (hexanoic acid, nonanoic acid) and amino acid (oxoproline) and amine (diethanolamine) concentrations, which could be from the increased Proteobacteria abundance after CeO₂ NP exposure. Phylum Proteobacteria had the most genus species containing 13 genera affecting soil metabolite profiles. These results provide valuable information for understanding the impact of environmentally relevant-level CeO₂ NP exposure on soil microbial communities and metabolites with or without ferrous, which is needed to understand the ecological risk posed by long-term CeO₂ NP exposure in rice-planted soil with rich ferrous.