Effects of water-soluble chitosan on Hylotelephium spectabile and soybean growth, as well as Cd uptake and phytoextraction efficiency in a co-planting cultivation system.

Intercropping a Cd-accumulator with economically valuable crops is common in slightly or moderately Cd-polluted farmland soils. A field experiment was conducted to evaluate the effects of water-soluble chitosan (WSC) on the growth and Cd uptake of the Cd-accumulator Hylotelephium spectabile and soybean (Glycine max) during a co-cultivation in Cd-contaminated agricultural soil (WSC, 0 and 10 g·m-2). The results indicated that soybean yields were highest in response to the intercropping and WSC treatment. The results from the field trials generally showed that intercropping and WSC treatments significantly decreased Cd concentrations in inedible parts of soybean by 42.9-72.1% (except for stems), in the meantime, increased 95.8%-334.6% in shoot and root tissues of H. spectabile compared with the control (p < 0.05). The data revealed that Cd uptake was highest for H. spectabile during the intercropping and WSC treatment. The application of WSC in the intercropping system significantly increased the uptake of Cd by H. spectabile, but not by soybean. The findings of this study suggest that combining an intercropping system with a WSC treatment may be better for remediating Cd-contaminated soils than other methods involving the growth of a single hyperaccumulator.

This paper clearly focused on the accumulation and uptake of Cd in the system of intercropping of Cd-accumulator (Hylotelephium spectable) and soybean (Glycine max) grown in Cd-polluted farmland soils supplied with water-soluble chitosan (WSC) under field conditions. Some studies mainly focused on active agent to promote remediation efficiency of (hyper) accumulators. This study indicated that combining the intercropping system with WSC may be better for remediating Cd-contaminated soils than the methods involving a single hyperaccumulator.

Comparison among soil additives for enhancing Pteris vittata L.: Phytoremediation of As-contaminated soil.

Pot experiments were conducted to assess the effects of monoammonium phosphate (NH4H2PO4) and citric acid (CA) on the arsenic uptake of Chinese brake fern (Pteris vittata L. in two typical arsenic-contaminated soils i.e. fluvo-aquic and brown) from Jiyuan (JY) City and Baoding (BD) City in Northern China. NH4H2PO4 improved the biomass of P. vittata, whereas CA exerted no significant influence. NH4H2PO4 and CA both increased the arsenic uptake of P. vittata by 6.08 and 2.72 times, respectively, in fluvo-aquic soil and 4.20 and 2.52 times, respectively, in brown soil. Moreover, CA, but not NH4H2PO4, promoted the transfer of arsenic from the root to the frond. NH4H2PO4 and CA increased Olsen's arsenic contents in the soils and promoted the transformation of residual arsenic and crystalline Fe/Al oxide-bound arsenic to nonspecifically and specifically sorbed arsenic. This study proved that P. vittata can be used in Northern China. Applying NH4H2PO4 and CA can enhance the effectiveness of P. vittata in the phytoremediation of arsenic-contaminated soils.

[A Comparison of Arsenic Speciation in 13 Pteris vittata L. Populations].

Synchrotron radiation X-ray absorption near edge structure was employed to study the arsenic (As) speciation in 13 Pteris vittata L. populations collected from 7 provinces, cities, and autonomous regions in China. As in roots of P. vittata was mainly combined with oxygen (O), with a small amount of As combined with glutathione (GSH). Populations from Hunan and Guangxi provinces showed higher percentages of As-GSH in soots. As in roots of P. vittata was predominated with As(V), with the percentage of As(V) to the total As being 59.6±0.6%~83.8±3.8%. The As(V) percentage was in the order of HN5HN3>HN1>TW>CQ>AH>FJ>HN5>HN2>GX2>GX3>HN4>GX1, within the range of 2.4%~12.9%. Different from that in roots, As in shoots was predominated with As(III), with no As(V) detected. The disclosure of As speciation in the roots and shoots of P. vittata contributes to the future research on As accumulation mechanism.

Evaluation of Field Portable X-Ray Fluorescence Performance for the Analysis of Ni in Soil.

As a rapid, in-situ analysis method, Field portable X-ray fluorescence spectrometry (FP-XRF) can be widely applied in soil heavy metals analysis field. Whereas, some factors may affect FP-XRF performance and restrict the application. Studies have proved that FP-XRF has poorer performance when the concentration of target element is low, and soil moisture and particle size will affect FP-XRF performance. But few studies have been conducted in depth. This study took an example of Ni, demonstrated the relationship between Ni concentration and FP-XRF performance on accuracy and precision, and gave a critical value. Effects of soil moisture and particle size on accuracy and precision also had been compared. Results show that, FP-XRF performance is related to Ni concentration and the critical value is 400 mg x kg(-1). Relative standard deviation (RSD) and relative uncertainty decrease while the Ni concentration is below 400 mg x kg(-1), hence FP-XRF performance improves with increasing Ni concentration in this range; RSD and relative uncertainty change little while the Ni concentration is above 400 mg x kg(-1), hence FP-XRF performance does not have correlation with Ni concentration any more. For in-situ analysis, the relative uncertainty contributed by soil moisture is 3.77%, and the relative certainty contributed by particle size is 0.56%. Effect of soil moisture is evidently more serious than particle size both on accuracy and precision.

Improvement of salinity in sewage sludge compost prior to its utilization as nursery substrate.

UNLABELLED: Soluble salts are enriched in sewage sludge compost because of their inherent derivation. Accordingly, the content of soluble salt in sludge compost is usually much higher than most seedlings can tolerate. To determine whether sludge compost is suitable for use as a nursery substrate, some experiments were conducted. Reduction of the electrical conductivity (EC) value could improve seed germination in saturated extract from sludge compost. In addition, water elution and mixing dilution with raw soil were all shown to be able to alleviate saline inhibition on seed germination and seedling growth, including stem diameter, seedling height, and above-ground weight. Overall, salinity is a crucial problem when sewage sludge compost is reused as a nursery substrate, and some effective and convenient approaches to reduce salt should be served prior to its reuse. IMPLICATIONS: Sewage sludge after being composted is usually reused as organic fertilizer or plant substrate. However, salt is the main problem during its reclamation. What is the highest salt level the seedling can tolerate? Which types of salts are effective in salinity of sludge-amended substrate? Meanwhile, can the salinity be reduced through water elution or soil mixing dilution? This paper is the first to investigate the salinity and its reduction of sewage sludge compost prior to its use in the development of nursery substrate.

[Species, Habitat Characteristics, and Screening Suggestions of Cadmium Hyperaccumulators in China].

Phytoremediation, as a green and effective in-situ remediation technology for heavy metal-contaminated soil, has attracted the attention of Chinese scholars and has resulted in a series of achievements over the past 20 years. In this study, the species characteristics, distribution of field discovery sites in various vegetation zones, habitat characteristics, habitat geological characteristics, and geochemistry of cadmium (Cd) of the Cd hyperaccumulators in China reported in the relevant literature from the past 20 years (from 2002 to 2021) were summarized by searching for related keywords. Finally, suggestions were proposed for the screening of new Cd hyperaccumulators. The results showed that a total of 45 species of Cd hyperaccumulators in China have been reported so far. In terms of plant species, they belonged to 22 families and 36 genera, among which Compositae with 14 species was the most abundant. There were 25 species discovered through the field investigation, which were mainly distributed in the subtropical broadleaf evergreen forest region of southern China. Additionally, the Cd hyperaccumulators discovered by field surveys were mainly found in high Cd-concentrated soils surrounding lead-zinc mines. In conclusion, abundant plant resources, high concentrations of heavy metal soils, and long-term domestication jointly promoted the formation of hyperaccumulators. Therefore, the region with these three points could be considered a high probability region for the presence of hyperaccumulators, and the screening of hyperaccumulators could be carried out around this. We proposed that the screening of new hyperaccumulators can be carried out through the following six steps:the identification and investigation of high probability areas, the enrichment capability test, the enrichment capability test in low concentration levels, the enrichment capability test between different ecotypes, the succession of enrichment capability, and the test of remediation proficiency.

[Main Control Factors of Cadmium Content in Rice in Carbonate Rock Region of Guangxi Based on the DGT Technique].

In order to explore the main controlling factors of Cd enrichment in rice under a geological high background in the Guangxi carbonate rock area, this study was based on rice grain-root soil samples from the carbonate rock areas in the southwest and north of Guangxi. Combined with diffusive gradients in thin films technology (DGT), the relationship between soil pH, organic matter, cation exchange capacity (CEC), DGT-Cd, and ω(rice-Cd)-BCF value in rice grains was analyzed and discussed. The main factors were determined by principal component analysis, and a quantitative model was established. The results showed that the average value of ω(soil-Cd) was 0.975 mg·kg-1, and the over-standard rate was 33.33%; the average value of ω(rice-Cd) was 0.020 mg·kg-1, and the average BCF value was 0.038, and the over-standard rate of Cd content in rice grains was 4.2%. The content of Cd in paddy soil was high, but bioavailability was low in the study area. The BCF value of rice grains in the study area was significantly negatively correlated with soil pH and cation exchange capacity at the level of 0.01, positively correlated with DGT-CD at the level of 0.01, and negatively correlated with organic matter at the level of 0.05. The results of principal component analysis showed that the total amount of Cd in the soil, pH, and DGT-Cd were the main factors affecting the accumulation of Cd in rice in the Guangxi carbonate rock area. Taking the total amount of Cd in the soil, pH, and DGT-Cd as variables, the fitting equation of BCF value of rice grains in the Guangxi carbonate rock region was established, and the determination coefficient of the model was 0.717, which could better predict the content of Cd in rice grains in this region.

[Distribution Characteristics and Risk Assessment of Heavy Metal Pollution in Farmland Soils and Crops in Luancheng, Shijiazhuang City].

In order to explore the distribution characteristics of heavy metal contamination of farmland soil surrounding Luancheng town, Shijiazhuang City, Henan province, the concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in the surface soil and crops were determined and assessed. The principal components were also analyzed for source apportionment. The heavy metal concentrations in crops were further detected, and the non-carcinogenic health risks in the study area were evaluated using the probabilistic risk assessment method, as to provide a theoretical basis for the treatment, prevention, and control of heavy metal pollution in farmland soil in Luancheng. According to the results, ω(Cd), ω(Cr), ω(Cu), ω(Pb), and ω(Zn) in the soils were 0.06-1.08, 22.14-473.47, 12.83-150.74, 10.75-577.72, and 62.23-652.78 mg·kg-1, which exceeded the standard with over-standard rates reaching 1.83%, 1.22%, 0.61%, 0.61%, and 1.22%, respectively. Further, Cd and Pb were transported into crops, in which Cd concentrations exceeded the standard in some corn samples, and Cd and Pb concentrations exceeded the standard in some wheat samples. The total non-carcinogenic health risks (TTHQ) to the human body caused by the consumption of heavy metals in corn grown in the study area were all less than 1, with no obvious negative effects, and TTHQ was higher than 1 in wheat, increasing the likelihood of negative impacts on the human body. With the influence of the distribution of pollution-related enterprises in the industrial zone, heavy metal concentrations were higher in the south, west, and middle directions of the study area. Among them, the study area soil was slightly contaminated by Cd (Level 1). Cd and Hg had a slight potential ecological risk (Level 2), whereas other heavy metals had low potential ecological risk (Level 1). In general, most of the surface cultivated soil was not obviously polluted by heavy metals in the study area. According to the PMF results and survey, we speculated that soil heavy metals mainly came from soil parent material (52.05%), artificial pollution sources (historical sewage irrigation and industrial manufacture) (32.98%), and atmospheric deposition (14.97%). To summarize, the study area should be divided into a priority protection category and safe utilization category. The input of pollution sources should be strictly controlled for the priority protection category, and alternative planting, rotating, and fallow should be implemented for the safe utilization category to reduce the risk of standard-exceeding agricultural products.

Microbial succession and degradation during kitchen waste biodrying, highlighting the thermophilic phase.

Biodrying in conjunction with compound stone amendment was used to treat kitchen waste, which improved biodrying. After 16 days, the pile moisture content decreased from 68.8% to 23.0%. Lignin, cellulose and hemicellulose concentrations decreased from 104.6 mg g-1 d.b., 322.9 mg g-1 d.b. and 155.9 mg g-1 d.b., respectively, to 74.0 mg g-1 d.b., 224.8 mg g-1 d.b. and 134.5 mg g-1 d.b., respectively. The Shannon index for bacteria increased from 2.5 to 3.1, while for fungi, it decreased from 4.6 to 0.6. The relative abundances of Amino Acid Metabolism and Carbohydrate Metabolism exceeded 7%. The thermophilic phase during the process inactivated the pathogenic microorganisms, increased the bacterial diversity, decreased the fungal diversity, and potentially improved the metabolism of nutrients, including amino acids, carbohydrates, lipids and vitamins. The biomarker analysis and predicated protein sequences provide genetic evidence to elucidate why the thermophilic phase is the peak time for nutrient metabolism.

Microbial degradation in the co-composting of pig manure and biogas residue using a recyclable cement-based synthetic amendment.

This research investigated a synthetic amendment to improve composting and resource recycling of pig manure and biogas residue. We further examined whether adding a synthetic amendment impacts the microbial ecosystem in the composted materials. Three mixing ratios were used to investigate composting performance: no synthetic amendment (T0), 5% synthetic amendment (T1), and 10% synthetic amendment (T2) (T1 and T2 were measured as a wet weight ratio). There were no significant differences in the fundamental characteristics between composting products in T0 and T1. The moisture content of composting material in T0, T1, and T2 significantly decreased from a baseline of approximately 65% to 35.5%, 37.3%, and 55.9%, respectively. Meanwhile, the germination index significantly increased to 111.6%, 155.6%, and 62.3%, respectively. When an optimal proportion of synthetic amendment was added, T1 showed high degree of humification, lignocellulase activities, and effective biodegradation. Firmicutes, Actinobacteria, Proteobacteria, and Bacteroidetes were the dominant bacteria, while Ascomycota and Basidiomycota were the dominant fungi in all treatment groups. Amino sugar and nucleotide sugar metabolism, glycolysis, starch, and sucrose metabolism were among the primary pathways in predicted functions. The synthetic amendment can generate a mature composting product and can be reused or recycled to conserve resources.

[Spatial Distribution and Risk Assessment of Heavy Metal Pollution in Farmland Soils Surrounding a Typical Industrial Area of Henan Province].

In order to fully explore the spatial distribution of soil heavy metal contaminants in farmland soil surrounding a typical industrial area in Dakuai town, Xinxiang city, Henan Province, the concentrations of As, Cd, Cr, Cu, Ni, Pb, and Zn in the surface soil and within the soil profile were determined and assessed. The principal components were also analyzed for source apportionment to provide a theoretical basis for the control and prevention of heavy metal pollution. According to the results, the soils in the study area are severely contaminated by Cd and Cu and moderated contaminated by As due to the battery manufacture and Cu (e.g., pipe and wire) processing. The concentrations of Cd, Cu, and As in soils were (2.56±1.23) mg·kg-1, (205.58±157.49) mg·kg-1, and (15.27±4.14) mg·kg-1, respectively, which exceeds standards by 100%, 89.44%, and 3.40%, respectively. Accounting for the influence of pollution sources, terrain, runoff erosion, and prevailing wind direction, all heavy metal concentrations were higher in the south direction, lower in the north direction. The concentrations of Cd and Cu in soil profile samples decreased with depth, with highest concentrations at the surface, indicating the strong effect of industrial activities. Arsenic concentrations varied little with soil depth due to its strong migration ability in alkaline soil, again suggesting an industrial source. Among them, the soil of study area was severely contaminated by Cd and Cu (Level 5). Cd poses a severe potential ecological risk (Level 5) and Cu poses a medium risk (Level 2) in the study soils, while other heavy metals show low potential ecological risk (Level 1). The order of the risk identified was Cd > Cu > Ni > As > Pb > Cr > Zn. In addition, the combined potential ecological risk of heavy metals in the target area is severe. The principal component analysis showed that the high As, Cd, and Cu contents are mainly derived from industrial areas. Therefore, it is urgent to remediate Cd and Cu soil contamination in this area and implement precautions to limit As contamination.

[Cd Accumulation Characteristics in Different Populations of Hylotelephium spectabile Under Salt Stress].

A pot experiment was conducted to investigate the growth response and Cd accumulation characteristics among different populations of Hylotelephium spectabile in Cd-contaminated cinnamon soil (2.22 mg·kg-1) with the addition of different concentrations of NaCl. Results showed that the biomasses and Cd concentrations of H. spectabile showed significant differences among different populations under Cd alone or Cd-salt combined stress. Moreover, salt stress aggravated the growth inhibition of H. spectabile and the Cd concentrations in different H. spectabile populations showed a declining trend, which may be related to the salt-derived pH increase leading to a decrease in Cd bioavailability. In addition, the growth and Cd absorption responses of H. spectabile under salt stress were significantly different in the different populations. The shoot biomasses of the LN population were significantly higher than in other populations under different treatment, and showed no significant decrease with the addition of 1% NaCl when compared with the control treatment and the tolerance index remained 0.91. At the same time, the shoot Cd concentration of the LN population was significantly higher than in other populations under different treatments. The result may be attributed to the Cd accumulation and detoxification mechanisms in LN are prior than other populations that may also have important physiological mechanisms for tolerance of salt stress. In summary, although Cd uptake in H. spectabile decreased with salt stress, there were significant differences among different populations. LN populations accumulated 84.4 µg·plant-1 Cd in shoots with 2% NaCl addition, which was 48.4%-89.3% higher than in other populations. Therefore, H. spectabile, especially LN populations, is a good candidate for phytoremediation of Cd-contaminated saline soil.

[Safety Assessment of Rice Planting in Soil Cadmium Geological Anomaly Areas in Southwest Guangxi].

To evaluate the safety of rice planting in cadmium geological anomaly areas, 41 natural soil, 479 paddy soil, and 432 rice samples were collected in southwestern Guangxi. The contents of Cd, Cu, Ni, and Zn and soil physical and chemical properties were measured. The single factor pollution index method (Pi) was used to evaluate the degree of contamination of the sample, and correlation analysis were used to explore the main factors affecting the heavy metal content in rice. The results showed that ① soil pH of the paddy field was 6.8; the organic matter content was 39.00 g·kg-1; the risk screening value was based on the soil environmental quality standards for soil pollution risk control and control of agricultural land (GB 15618-2018), the exceeding standard rates of Cd, Cu, Ni, and Zn in soil were 60.75%, 2.09%, 0.83%, and 1.88%. ② The over-standard rates of Cd and Ni in rice were 9.03% and 4.39%, respectively. Considering straw as raw material for feed and organic fertilizer, the corresponding over-standard rates of Cd were 6.94% and 1.16%. ③ Correlation analysis showed that soil pH, organic matter, total heavy metal, and available content were the main factors affecting the content of heavy metals in rice. Cd and Ni in the study area all exhibited certain over-standard phenomena, and the low-accumulation rice varieties could be planted to reduce heavy metal content in rice.

Adding a recyclable amendment to facilitate sewage sludge biodrying and reduce costs.

Finding an economical amendment, available in a steady supply, is needed to support the biodrying industrialization. This research developed a recyclable biodrying amendment (RBA) to condition the biodrying of sewage sludge. The pilot-scale treatment (TR), which included the addition of equivalent weights of RBA and sawdust as amendments, resulted in a higher pile temperature and longer thermophilic phase compared to the control (TC), which used only sawdust as an amendment. The final moisture content levels were below 50% with both TR and TC. The heat use efficiency for water evaporation was 72.2% and 73.0% in TR and TC, respectively. The activity of α-amylase and cellulose 1,4-ß-cellobiosidase increased during the thermophilic phase, while the activity of endo-1,4-ß-glucanase and endo-1,4-ß-xylanase decreased during the thermophilic phase with both TR and TC. The fourier-transform infrared spectra indicated that adding the RBA resulted in good biodegradability of the lipids, proteins, and polysaccharides. The humic acid to fulvic acid ratio in TR and TC increased from 0.33 (TR) and 0.35 (TC) on day 0-0.46 (TR) and 0.45 (TC) on day 21, indicating the humification process. The RBA recovery rate was 95.6% and can be reused. These findings highlight that adding RBA showed satisfactory biodrying performance, reduced the amendment cost, and the biodrying product could be incinerated without energy deficit.

[Effect of Nutrient Regulation and Control on Cd Accumulation Efficiency of Hylotelephium spectabile Under Field Conditions].

A field experiment with an orthogonally designed experiment L9(34) was designed to investigate the effect of different N, P, and K levels on plant growth and Cd uptake by Hylotelephium spectabile. The results showed that the biomass of H. spectabile significantly increased with the N application rate. The highest dry weight in the shoot occurred in the treatments with a high level of N (337.5 kg ·hm-2), which was 0.86-2.00 times higher than the value with no fertilizer treatment. The addition of K contributed to promoting the Cd absorption of H. spectabile, while no effect was observed when N and P were added. Consequently, NPK fertilizers contribute to increasing the Cd uptake of H. spectabile, and the N and K fertilizer play important role in plant growth and Cd absorption respectively. Moreover, the effect of fertilizers on Cd uptake of H. spectabile was in the order of N > K > P, which indicated that N fertilizer was the main factor for promoting the Cd phytoextraction efficiency of H. spectabile by increasing the biomass. Therefore, the application of high levels of N combined with moderate levels of P and K will be an effective approach to improve the Cd phytoremediation efficiency of H. spectabile by promoting its growth, and the Cd uptake can be increased by a factor of 0.9-2.2 compared to no fertilizer treatment condition.

[Tolerance Mechanism and Cadmium Enrichment Abilities in Two Brassica napus L. Cultivars].

A hydroponic experiment was conducted to explore the differences in growth status and Cd accumulation characteristics of two Brassica napus L. cultivars (QY-1 and SYH) under different concentrations of cadmium (Cd) stress (0, 2, and 5 mg·L-1). The Cd subcellular compartmentalization and antioxidant enzyme activities were determined to elucidate the intrinsic mechanism of the differences in the Cd accumulation capacity between the two cultivars of Brassica napus L. Furthermore, field trials were conducted to further verify the differences in phytoremediation of the two cultivars. Results show that neither of the cultivars exhibited obvious growth inhibition under Cd stress. Under the 2 mg·L-1 Cd condition, there were no significant differences in shoot Cd concentrations between the two cultivars. Under 5 mg·L-1 Cd condition, however, the Cd concentrations in both shoot and root of SYH were significantly higher than that of QY-1, which increased by 32.05% and 99.57%, respectively. In addition, the bioconcentration factor (BCF) of the root in SYH is significantly higher than that of QY-1. The subcellular Cd distribution in leaves of the two cultivars of Brassica napus L. showed that, with an increase of Cd stress, Cd concentrations of heat stable protein (HSP) and metal-rich granule (MRG) fractions in leaves significantly increased by 143.69% and 118.91% for QY-1, and by 63.34% and 118.91% for SYH. Thus, the segregation of Cd in HSP and MRG, which was reported to be biological detoxified metal fractions (BDM), might play an important role in the detoxification of Brassica napus L. at a subcellular level under Cd stress. Moreover, the distribution of Cd in the cellular debris fraction might be another important factor contributing to the differences in Cd accumulation of the two Brassica napus L. cultivars, which was 4.41 times higher in SYH than in QY-1 under Cd stress. The results of the antioxidant enzyme activities of two Brassica napus L. cultivars showed that, under the 5 mg·L-1 Cd condition, the antioxidant enzyme system may represent an important detoxification mechanism for QY-1 to cope with stress induced by high concentrations of Cd, while SYH is more effective in reducing the toxicity of Cd by separation of Cd into BDM fractions. The results of the field trial confirmed that the Cd concentrations in the above- and underground parts of SYH were 2.34 and 1.43 times higher than in QY-1, respectively. Therefore, SYH possess a higher Cd phytoextraction capacity than QY-1, and might be a good candidate for the remediation of moderate and mildly Cd-contaminated farmland.

[Cd Content Characteristics and Ecological Risk Assessment of Paddy Soil in High Cadmium Anomaly Area of Guangxi].

To investigate the levels of heavy metal Cd in paddy soils in high cadmium anomaly areas in Guangxi, and to assess their potential ecological risks to the environment. Through preliminary screening and detailed investigation, 912 pieces of soil samples from high-cadmium abnormal area were collected in multiple batches to determine the soil Cd content. The single-factor pollution index method and potential risk index method were used to control the Cd pollution degree of paddy soil. Potential risks were evaluated. The results showed that:① The average Cd values of natural soil, paddy soil, and dryland soil in the initial screening were 0.915, 0.591, and 0.593 mg·kg-1, respectively. ② In the detailed investigation, the soil pH is 4.6-8.7, which is between acidic and weakly alkaline. If the Soil Environmental Quality Standard (GB 15618-2018) is used as the evaluation standard, the Cd of the soil sample in Pingguo County, Tiandong County, Long'an County, and Liucheng County is seriously exceeded, and the soil sample in the paddy field of Rongshui Country is not polluted. Based on the soil baseline value, the Cd in the soil samples of Tiandong County, Liucheng County, and Rongshui County were non-polluting. In the paddy soils of Tianyang County, Pingguo County, Tianxian County, Daxin County, Long'an County, and Rong'an County, the proportion of Cd in mild to moderate pollution was 4.2%, 3.7%, 14.9%, 2.6%, 7.1%, and 1.4%, respectively. ③ Cd in paddy soils of nine counties and cities presents different levels of potential ecological risks. The soil Cd of some paddy fields in Tiandeng County, Daxin County, and Long'an County was at a high ecological risk ratio of 4.3%, 2.6%, and 2.4%. The soil Cd of Tianyang County, Pingguo County, Rong'an County, and Liucheng County was medium-Middle and high potential risks. Tiandong County and Rongshui County are at low potential ecological risks. In conclusion, the overall Cd in the paddy soil of the study area is high, which may affect the safe planting of rice in the long-term. It will eventually pose a health threat to local residents and should be taken care of. It is recommended to carry out research on soil cadmium bioavailability and rice cadmium accumulation in the study area in order to assess its ecological risk and health risk more scientifically and reasonably.

[Remediation Potential of Ageratum conyzoides L. on Cadmium Contaminated Farmland].

To evaluate the remediation potential of Ageratum conyzoides L. on cadmium (Cd) contaminated farmland soil, the Cd-containing plants and root were collected and analyzed by field investigation, original pot experiment, and field experiment. The enrichment factor and removal rate of Ageratum conyzoides L. was calculated. The results showed that the maximum Cd content in the leaves of Ageratum conyzoides L. growing in soil of different lead-zinc mines was 77.01 mg·kg-1. In the high-concentration Cd soil treatment (T2), Cd content of the above-ground of Ageratum conyzoides L. was 69.71mg·kg-1, and Cd enrichment coefficient was 6.09. In the low-concentration Cd soil treatment (T1), the enrichment characteristics of Cd (Ageratum conyzoides L.) are consistent with the enrichment characteristics of Cd under high concentration conditions. Ageratum conyzoides L. exhibits stable accumulation characteristics for Cd. In the field experiment, the average Cd content of Ageratum conyzoides L. was 21.13 mg·kg-1, and the enrichment coefficient was 6.93. The removal rate of the three planting Ageratum conyzoides L. per mu of soil using the Ageratum conyzoides L. to repair Cd contaminated soil was 13.2%-15.6%. The use of Ageratum conyzoides L. to repair Cd pollution in farmland has a good prospect for engineering application.

[Interaction of Cd and Zn Affecting the Root Morphology and Accumulation of Heavy Metals in Sedum aizoon].

A hydroponic experiment was conducted to study the interaction of Cd and Zn affecting the root morphology and accumulation of Cd and Zn in Sedum aizoon. The results show that S. aizoon exhibits a high tolerance to single stress of Cd and Zn and the concentrations of Cd and Zn in the leaf, stem, and root of S. aizoon increase as the stress levels increase. A strong phytoextraction capacity in S. aizoon was also observed for the Cd concentration in the aboveground part reaching 133.0 mg·kg-1. The combined stress of Cd and Zn has a greater effect on the growth of S. aizoon than single stress to which the root is more sensitive. The root length, surface area, root volume, and tips significantly decrease under combined stress of Cd and Zn; the effect on the tips is most significant. The low-level Zn application (10 mg·L-1) has a synergistic effect on the Cd accumulation in the shoot of S. aizoon because of the promotion of Cd translocation from root to shoot. However, the addition of Cd leads to a notable antagonism of the Zn absorption of S. aizoon. The concentration ratio of Zn and Cd also has a significant effect on the Cd uptake of S. aizoon. A high ratio promotes the Cd accumulation in the shoot, while the latter is inhibited by a low Zn/Cd ratio. Therefore, S. aizoon possesses a strong potential of Cd phytoextraction and can be applied for phytoremediation of Cd-contaminated soil, while the adjustment of the ratio of Cd and Zn in the growth medium will help to enhance the phytoremediation efficiency of S. aizoon.

Pile settlement and volume reduction measurement during forced-aeration static composting.

In this study, a settlement measurement device was used to track the settlement of different layers in composting piles, and time courses of settlement velocity, bulk density distribution, and effective bulk density were investigated. Settlement is divided into two stages: the physical compressive settlement and the mass loss settlement. At the end of the former stage, bulk density (rho') and pile height (h) follow rho'=Ah(B), where A is a fitting parameter for the initial bulk density of the composting material, and B is the compression parameter. The physical compressibilities of composting mixtures are night-soil sludge and garden refuse (1:1) >sewage sludge and cornstalks (5:4) >night-soil sludge and garden refuse (2:3) >sewage sludge and bark (1:1). Adding the proportion of bulking agent in the proper extent effectively retarded composting settlement. Bark exhibits a better supporting capability than cornstalk does as a bulking agent.