Vegetable gardens are increasingly common in urban areas and can provide numerous societal benefits; however, contamination with potential toxic elements (PTEs) due to urbanization and ...industrialization is cause for concern. The present study aimed to assess the source of contamination and pollution levels in urban garden soils, as well as the health risks for adults and children consuming vegetables grown in such environments. Various types of vegetable samples and their corresponding soils from 26 community gardens were collected throughout Chengdu City in southwestern China. The results showed that leafy vegetables, particularly lettuce leaves and Chinese cabbage, had relatively higher levels of Cd (0.04 mg/kg FW) and Pb (0.05 mg/kg FW), while higher levels of As (0.07 mg/kg FW), Cr (0.07 mg/kg FW), and Hg (0.003 mg/kg FW) were found in amaranths, tomatoes, and Houttuynia cordatas, respectively. The pollution indices revealed that the vegetable purplish soils were relatively more polluted by Cd and As, and the concentrations of these metals in vegetables were correlated with their concentrations in the soils. Principal component analysis grouped the PTEs in two dimensions that cumulatively explained 62.3% of their variation, and hierarchical clustering identified two distinct clusters indicating that Cr originated from a unique source. The health risk assessment revealed that exposure to As and Cd induced the greatest non-carcinogenic risk, whereas Cr was most likely to cause cancer risks. Furthermore, contaminated vegetable consumption was riskier for children than adults. The critical factors contributing to PTE contamination in vegetable gardens were determined to be vegetable species, total soil element content, soil pH, and soil organic matter content. Overall, Cr and As pollution present the greatest concern, and community health care services must enact more effective regulatory and preventative measures for urban gardens in terms of PTEs.
Phyllosphere-associated microorganisms affect host plant's nutrients availability, its growth and ecological functions. Tobacco leaves provide a wide-area habitat for microbial life. Previous studies ...have mainly focused on phyllosphere microbiota at one time point of tobacco growth process, but more is unknown about dynamic changes in phyllospheric microbial composition from earlier to the late stage of plant development. In the current study, we had determined the bacterial and fungal communities succession of tobacco growth stages (i.e., seedling, squaring, and maturing) by using both 16S rRNA sequencing for bacterial and ITS sequencing for fungi. Our results demonstrated that among tobacco growth stages, the phyllospheric bacterial communities went through more distinct succession than the fungal communities did. Proteobacteria and Actinobacteria exerted the most influence in tobacco development from seedling to squaring stages. At maturing stage, Proteobacteria and Actinobacteria dominance was gradually replaced by Firmicutes and Bacteroidetes. Network analysis revealed that Proteobacteria, as the core phyllospheric microbia, played essential role in stabilizing the whole bacterial network during tobacco development, and consequently rendered it to more profound ecological functions. During tobacco development, the contents of leaf sugar, nicotine, nitrogen and potassium were significantly correlated with either bacterial or fungal communities, and these abiotic factors accounted for 39.3 and 51.5% of the total variation, respectively. We overall evinced that the development of tobacco phyllosphere is accompanied by variant dynamics of phyllospheric microbial community.
Trace element contamination in Chinese herbal medicines has been recognized as a potential health concern for consumers. To assess the health risk to the herb-consuming population, nine trace ...elements (Cu, Cd, Cr, Mo, Ni, Pb, Sr, Zn, and As) were investigated based on their concentrations in three common medicinal plants (
Astragalus membranaceus
,
Codonopsis tangshen
, and
Paris polyphylla
var. c
hinensis
) and soils from unpolluted and polluted areas in the Sichuan Province, China. The results showed that the metal content differed significantly in medicinal plants and soils from unpolluted versus polluted areas. No significant differences in metal accumulation were observed for these CHMs grown in either unpolluted or polluted areas. Evaluation of the health risk index suggested that soil ingestion and medicated diet represented the dominant exposure routes, indicating that trace metal(loids) in local soil might pose potential risks through soil-food chain transfer. Hazard quotient values for
AM
(1.473) and
CT
(1.357) were higher than the standard value (HQ > 1), whereas the hazard indices for
PC
,
AM
, and
CT
were 13.18, 14.33, and 14.01 times higher than the safe limit (HI > 1) in the polluted area, indicating non-cancer-related health hazards. Ingestion of soil was responsible for 36.39 to 91.06% of the total cancer risk and medicated diet accounted for 6.35 to 62.71%, compared with inhalation and dermal contact, suggesting carcinogenic health risks in herbs from polluted soils. In this study, Pb showed relatively higher non-carcinogenic risks, while Cr and Ni posed the highest cancer risks. Therefore, we propose more effective measures, which should be considered for Cr, Ni, and Pb remediation in soil to reduce their pollution in the studied areas.
Adoption of crop residue amendments has been increasingly recommended as an effective management practice for mitigating greenhouse gas emissions while enhancing soil fertility, thereby increasing ...crop production. However, the effect of biochar and straw on nitrous oxide (N2O) and methane (CH4) emissions in soils of differing pH remains poorly understood. Three treatments (control (i.e., no amendment), maize straw, and biochar derived from maize straw) were therefore established separately in soils with different pH levels, classified as follows: acidic, neutral, and alkaline. N2O and CH4 were investigated using a static chamber–gas chromatography system during 57 days of a mesocosm study. The results showed that cumulative N2O emissions were significantly higher in acidic soils than in other experimental soils, with the values ranging from 7.48 to 11.3 kg N ha−1, while CH4 fluxes ranged from 0.060 to 0.089 kg C ha−1, with inconclusive results. However, a weak negative correlation was observed between log N2O and log NO3-N in acidic soil with either biochar or straw, while the same parameters with CH4 showed a moderate negative correlation, suggesting a likelihood that these amendments could mitigate GHGs as a result of the NO3-N increase in acidic soils. It is also possible, given the alkaline nature of the biochar, that incorporation had a significant buffer effect on soil acidity, effectively increasing soil pH by >0.5 pH units. Our findings suggest that for the rates of application for biochar and straw used in this study, the magnitude of reductions in the emissions of N2O and CH4 are dependent in part on initial soil pH.
•Phytoplankton was identified as the dominant source of the SPN.•No distinctly spatial and seasonal variations in the source apportionment of SPN.•Strong assimilation process of nitrate and ...degradation of SSN were revealed.
Globally, the large rivers export amounts of particulate nitrogen (PN) to the ocean, and studying the source and biogeochemical processes of the PN in the large river is important to regional/global N budget and cycle. However, the source apportionments and transformations of the PN along the Yangtze River remain unclear. Here, the elemental and isotopic compositions (N%, δ15N and δ13C value) of suspended particulate N (SPN) and surface sediment N (SSN) were determined in the wet and dry seasons along the Yangtze River, to investigate the seasonal and spatial variation in sources apportionments and transformations of the PN. In the wet season, the δ15N and PN content (%) of SPN increased from the headwater stream (2.3 ± 3.9 ‰ and 0.12 ± 0.04 %, respectively) to the lower stream (6.8 ± 2.4 ‰ and 0.47 ± 0.41 %, respectively) due to the imported anthropogenic N into the downriver section, while there was no significant change in the dry season. There were no distinctly spatial and seasonal variations in the source apportionment of SPN. Phytoplankton was identified as the dominant source of the SPN (42.3–56.9 %), which is probably the result of reducing soil erosion, reservoir construction, rapid urbanization and development of freshwater aquaculture. Terrestrial soil was the major source of SSN (34.5–49.8 %). Furthermore, the significant relationship between the δ15N-SPN values and NO3− concentrations, as well as the lower δ15N-SPN value compared to that of δ15N-NO3−, indicated a strong assimilation process of nitrate during phytoplankton growth. Meanwhile, most of the SSN showed lower C and N concentrations and higher δ13C and δ15N values, compared to those of the SPN samples at the corresponding sampling sites, which might be due to the SSN degradation. Our findings provided valuable information for the N cycle in the Yangtze River and underlined the importance of phytoplankton in the PN inputs.
The effects of soil pH variations induced by submergence/drainage and biochar application on soil cadmium (Cd) availability to different rice (Oryza sativa L.) varieties are not well understood. This ...study aims to investigate the possible reasons for available Cd(II) reduction in paddy soil as influenced by biochar and to determine Cd(II) absorption and translocation rates in different parts of various rice varieties. A pot experiment in a greenhouse using four japonica and four indica rice varieties was conducted in Cd(II) contaminated paddy soil with peanut straw biochar. The results indicated that the submerging led to an increase in soil pH due to the consumption of protons (H+) by the reduction reactions of iron/manganese (Fe/Mn) oxides and sulfate (SO42−) and thus the decrease in soil available Cd(II) contents. However, the drainage decreased soil pH due to the release of protons during the oxidation of Fe2+, Mn2+, and S2− and thus the increase in soil available Cd(II) contents. Application of the biochar increased soil pH during soil submerging and inhibited the decline in soil pH during soil drainage, and thus decreased soil available Cd(II) contents under both submerging and drainage conditions. The indica rice varieties absorbed more Cd(II) in their roots and accumulated higher amounts of Cd(II) in their shoots and grains than the japonica rice varieties. The Cd(II) sensitive varieties exhibited a greater absorption and translocation rate of Cd(II) compared to the tolerant varieties of both indica and japonica rice. Biochar inhibited the absorption and accumulation of Cd(II) in the rice varieties, which ultimately lowered the Cd(II) contents in rice grains below the national food safety limit (0.2 mg kg−1). Overall, planting japonica rice varieties in Cd(II) polluted paddy soils combined with the use of biochar can effectively reduce Cd(II) content in rice grains which protects human health against Cd(II) toxicity.
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•Redox reactions were responsible for soil pH change in submergence/drainage alteration.•Biochar inhibited soil pH decline and reduced available soil Cd(II) during drainage.•Indica rice varieties absorbed more Cd(II) from soils than japonica rice varieties.•Cd(II)-sensitive rice varieties absorbed more Cd(II) than tolerant rice varieties.•Biochar decreased Cd(II) contents in the roots, shoots and grains of rice varieties.
•Soil aggregate stability was determined by wetting and wet-shaking pre-treatment.•Wet-shaking had the highest impacts on aggregate stability decrease than wetting.•ASI reduction caused by ...wet-shaking was negatively correlated with elevation.•CEC was the key internal factor in surface soil aggregate stability.
Soil aggregate stability is a key indicator of soil quality and susceptibility to water erosion. The water level fluctuation zone (WLFZ) of Three Gorges Reservoir (TGR) experiences hydraulic disturbances induced by rainfall, reservoir wave, and water-level fluctuation. Soil aggregate in this region has a unique mechanism of disintegration different from other terrestrial soils. The traditional methods of soil aggregate stability measurement cannot reveal the complex external factors of the soil in the WLFZ. In the present study, an attempt has been made to establish an approach mimicking the real situation in the WLFZ to deeply understand the effects of water movement and periodical wetting on soil aggregate stability in the WLFZ. The soil samples from different elevations were allowed to stay under wetting and wet-shaking conditions for 3 and 81 min, followed by a quantitative separation of disintegrated aggregates by wet-sieving. The mean differences between wetting and wet-shaking for the mean weight diameter (ΔMWD) were highly significant at all elevations for 81 min. Contrary, both treatments applied within a short time period disintegrated aggregates at the same magnitude. Additional to slaking, the kinetic energy applied to soil has induced a mechanical breakdown as a result of water movement. The difference of aggregate stability index (ASI) was highly significant among the elevations p < 0.001 and strongly significant between lower and upper elevations. The Cation Exchange Capacity (CEC) was the most predominant factor determining the stability of soil aggregates with r2 = 0.61, 0.65, 0.69 (p < 0.05) and r2 = 0.71, 0.7, 0.77 (p < 0.05) for ASI, GMD and MWD recorded after wetting and wet-shaking, respectively. Crucially, understanding different effects between arising impacts of water level fluctuations and periodical inundations on soil aggregate stability is a promise for future studies in areas experiencing similar conditions.
The present study investigated the bioaccumulation and translocation of mercury (Hg) and chromium (Cr) in Yunyan 87 flue-cured tobacco (
Nicotiana tabacum
) and assessed the influence of soil pH on ...the metal uptake by plant organs at the field scale. The study was conducted in 4 different regions selected from Sichuan Province, China: Guangyuan, Luzhou, Panzhihua, and Yibin. The results revealed that Hg highly contaminated Yibin soils at 0.29 mg kg
−1
and by Cr at 147 mg kg
-1
, which is above the permissible limit. The levels of Hg in tobacco plant organs were predominantly in the order of leaves > root > stem. The overall trend for Cr contents in tobacco organs was in the order of root > leaves > stem. The results of an index of bioaccumulation (IBA) and translocation factor (TF) showed that the values observed in Panzhihua and Guangyuan tobacco leaves were generally higher, despite the low levels of soil contamination. The linear mixed model (LMM) demonstrated that the log of Hg IBA in tobacco organs was likely to decrease with soil pH increase, whereas the log of Cr IBA only decreased in the root but gradually increased in the aerial parts with soil pH increase. The total random variation in the log of metals’ IBA due to regions indicated that for Hg, 33.42% of the variation was explained by regional differences, while for Cr, only 13% was accounted. The results suggested that Yibin and Luzhou need to correct the soil acidity if they are set to reduce Hg contamination in tobacco-growing soils. Guangyuan and Panzhihua need efforts to keep the soil pH on track to avoid high contamination levels, and effective measures of soil nutrients supply are required to produce high tobacco leaf quality free from heavy metal content. The findings of this study may be used to ascertain regional differences in heavy metals, particularly Hg and Cr uptake by tobacco plant organs, and to prevent the cultivation areas contamination through soil pH monitoring.
The rapid increase in soil acidity coupled with the deleterious effects of cadmium (Cd) toxicity had led to a decline in worldwide agricultural production. Rice absorbs and accumulates Cd(II) from ...polluted paddy soils, increasing human health risks throughout the food chain. A 35-day hydroponic experiment with four
japonica
and four
indica
(two each of them tolerant and sensitive cultivars) was conducted in this study to investigate the adsorption and absorption of Cd(II) by rice roots as related with surface chemical properties of the roots. The results showed that the three chemical forms of exchangeable, complexed, and precipitated Cd(II) increased with the increase in Cd(II) concentration for all rice cultivars. The roots of
indica
rice cultivars carried more negative charges and had greater functional groups and thus adsorbed more exchangeable and complexed Cd(II) than those of
japonica
rice cultivars. This led to more absorption of Cd(II) by the roots and greater toxicity of Cd(II) to the roots of
indica
rice cultivars and more inhibition of Cd(II) stress on the growth of the roots and whole plants of
indica
rice cultivars compared with
japonica
rice cultivars, which was one of the main reasons for more declines in the biomass and length of
indica
rice roots and shoots than
japonica
rice cultivars. Cd(II) stress showed more toxicity to the sensitive rice cultivars and thus greater inhibition on the growth of the cultivars due to more exchangeable and complexed Cd(II) adsorbed by their roots induced by more negative charges and functional groups on the roots compared with tolerant rice cultivar for both
indica
and
japonica
, which resulted in greater decreases in the biomass and length of roots and shoots as well as chlorophyll contents of the sensitive cultivars than the tolerant cultivars. The roots of sensitive rice cultivars also absorbed more Cd(II) than tolerant rice cultivars due to the same reasons as above. These findings will provide useful references for the safe utilization and health risk prevention of Cd-contaminated paddy fields.
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