Effect of exogenous Ca on the physiology and growth indicators of pakchoi under foliar and root fluorine stress.

Fluorine (F) is not an essential element for vegetation and excessive F can be phytotoxic to plant growth, which can cause fluorosis to human beings by ingesting F-contaminated plant. Although there have been some studies focusing on the toxicity of F to plants and the retarding effect of Ca to F-stress plant, atmospheric F contamination to vegetation and the role of the application of foliar Ca are scantly reported. This study investigated several biochemical parameters to evaluate F toxicity under both F-exposure (root and leaf F-exposure) and the remedial effects of foliar Ca. The results showed that F concentration of pakchoi leaves was correlated with exogenous F level positively in both foliar and root F-exposure series, and F concentration of pakchoi roots was only changed under root F-exposure treatments. Ca supplement (0.5 g/L and 1 g/L) significantly decreased plant F concentration. Both F-exposure treatments caused lipid peroxidation in plants and exogenous Ca alleviated the toxicity of F to pakchoi. Meanwhile, chlorophyll-a concentration was decreased by foliar and root F, whereas chlorophyll-b concentration was only affected by foliar F, and chlorophyll-a concentration could be elevated by exogenous Ca but chlorophyll-b could not. It was concluded that both atmospheric and root F can impair pakchoi growth and disturb photosynthesis, and foliar Ca showed an ameliorative effect to F toxicity of pakchoi through alleviating chlorophyll decomposition, increasing protein content and alleviating oxidative damage.

Multiple heavy metal distribution and microbial community characteristics of vanadium-titanium magnetite tailing profiles under different management modes.

Vanadium-titanium (V-Ti) magnetite tailings have caused great concern due to their safety hazards and environmental risks. However, the microbial community structure and the key geochemical factors of V-Ti magnetite tailing profiles under different management modes remain unclear. Therefore, we investigated the heavy metal distribution and the microbial community structure of the soils and tailings at varied depths of V-Ti magnetite tailing profiles with and without soil coverage. The results indicated that the topsoil covering measures retarded the acidification of tailings during stockpiling. However, As, Mn, and V in tailings have the ability to migrate to the overlying soil. Based on 16S rRNA gene amplicon sequencing, Proteobacteria was the dominant genus in the topsoil-covered tailings, whereas the most abundant genus in the exposed tailings was Betaproteobacteria. Furthermore, Rhodobacter, Hydrogenophaga, Novosphingobium, and Geobacter enriched in tailings may potentially contribute to V(V) biotransformation and the development of mine bioreremediation technologies. RDA and Spearman correlation analysis showed that pH, EC, Cd, Mn, Pb, and V were the main influencing factors regulating microbial community composition. Overall, this study provides insights for evaluating the soil covering management mode and the engineering applications of microbial technologies to manage V-Ti magnetite tailings.

Transfer characteristic of fluorine from atmospheric dry deposition, fertilizers, pesticides, and phosphogypsum into soil.

Fluorine (F) is widely dispersed in the environment and frequently used in industry and agriculture with a high migration ability. Thus, it is essential to understand the leaching characteristic of F in soil from industry and agriculture sources. Several sources of F pollutants in soil, including fertilizers, pesticides, phosphogypsum, and atmospheric deposition, were selected to investigate leaching characteristics of F in soil by leaching experiments. The addition of phosphate fertilizer and compound fertilizer (N:P:K = 20:10:15) enhanced the leachability of F in soil and the proportion of F leached out from soil treated by these fertilizers were 0.25% and 0.24%, respectively. However, unanticipated lower leachability of F appeared in compound fertilizer (N:P:K = 17:17:17), nitrogen fertilizer, dipterex, fluoroglycofen, fluopimomide, simulative dry deposition (YF3), and phosphogypsum loaded soils compared with additive-absent treatment. Although phosphogysum had a high F concentration, minimum proportion of F released (0.18%) was observed in phosphogypsum-coverd soil. The amounts of F leaching-out from surface soils (0-25 cm) treated with nitrogen fertilizer decreased 1.03 kg ha-1 comparing with blank control. Soil with phosphate fertilizer leached 5.47 kg F ha-1 a year, having the highest environment risk to deeper soil and groundwater. However, phosphogypsum and dry deposition of airbone F chemical had few effects on F leaching in soil. F-containing materials from agricultural process may leach more F from surface soils than industrial sources.

Agricultural activities impact on soil and sediment fluorine and perfluorinated compounds in an endemic fluorosis area.

Perfluorinated compounds (PFCs) are organo-fluorine compounds which have been identified at significant levels in soils due to their widespread usage in industrial and commercial applications. However, few studies are available regarding the occurrence of PFCs in the environment of endemic fluorosis areas. To address the issue, soils collected from an endemic fluorosis area of southwestern China were analyzed for the distribution of fluorine and 21 kinds of PFCs. The average water-soluble fluorine concentration in cultivated soil (4.87 mg kg-1) was significantly higher than that in uncultivated soil (3.15 mg kg-1), which mainly ascribed to the utilization of fluorine-enriched fertilizers during agricultural practices. Concentrations of ΣPFCs in all soils ranged from 0.508 to 6.83 ng g-1, with an average of 2.81 ng g-1, dominated by perfluorononanoic acid (PFNA) and perfluorooctanoic acid (PFOA). Highest ΣPFCs was found in the soil samples collected from cropland with intensive agricultural activities. Long-chain PFCs, including four perfluoroalkylcarboxylic acids (PFCAs, C ≥ 8) and one perfluoroalkylsulfonic acids (PFSAs) (perfluorooctane sulfonate (PFOS), C8), exhibited high levels in soils, probably due to their higher hydrophobicity and lower water-solubility than short-chain PFCs. While in sediments, short-chain PFCAs were the dominant compounds. Based on correlation analysis, the relationship between total fluorine and PFCs was insignificant, and soil organic matter was a relevant factor affecting PFCs distribution in soils. This study is expected to present a more comprehensive information about fluorine contamination under the influence of agricultural activities in an endemic fluorosis area.

Distribution and superposed health risk assessment of fluorine co-effect in phosphorous chemical industrial and agricultural sources.

The industrial and agricultural activities based on phosphorous can increase the F content in the surrounding area, causing a widespread adverse effect on the organisms. However, the current information on the superposed health risk posed by the multi-exposure to the F contamination in an area jointly affected by agricultural and industrial activities (DA) is limited. Herein, the F distribution in multi-environmental media and the exposure risk to humans by ingestion, inhalation, and dermal contact pathways are studied in an DA. The content of soil water-soluble fluorine (WF) was higher in the DA than in the area individually affected by agricultural activities (SA). This indicated a superposed contribution of the industrial and agricultural activities to increase the F toxicity in the soil. The correlation of the soil pH and the organic matter content with the soil WF concentration in DA suggested an inter-relationship between the soil physicochemical properties and the toxicity of F in the soil by industrial and agricultural activities. Irrigation water was not a major anthropogenic source of the cropland soil F. The large variation in F concentration in the crops (101.8-195.6%) might have originated from the discrepancies in the soil F content and air F concentration. The air F pollution (0.6-1.6 µg dm-2 d-1) in the area particularly influenced by intensive industrial activities should be important. The exposure of residents to F was mainly from the ingestion of F-enriched crops. The higher exposure of adults to F than that of children could be attributed to more industrial and agricultural outdoor activities, larger exposure area of the skin, and more daily ingestion of F-enriched food by adults. Overall, present insights into the distribution of and the multi-exposure to F may be beneficial for decreasing the adverse F effects on the residents in DAs worldwide.