Inoculation of cadmium-tolerant bacteria to regulate microbial activity and key bacterial population in cadmium-contaminated soils during bioremediation.

The perennial ryegrass Lolium perenne can be used in conjunction with cadmium (Cd)-tolerant bacteria such as Cdq4-2 (Enterococcus spp.) for bioremediation of Cd-contaminated soil. In this study, a theoretical basis was provided to increase the efficiency of L. perenne remediation of Cd-contaminated soil using microorganisms to maintain the stability of the soil microbiome. The experimental design involved three treatment groups: CK (soil without Cd addition) as the control, 20 mg·kg-1 Cd-contaminated soil, and 20 mg·kg-1 Cd-contaminated soil + Cdq4-2, all planted with L. perenne. The soil was collected on day 60 to determine the soil microbial activity and bacterial community structure and to analyze the correlation between soil variables, the bacterial community, available Cd content in the soil, Cd accumulation, and L. perenne growth. The soil microbial activity and bacterial community diversity decreased under Cd stress, and the soil microbial community composition was changed; while inoculation with Cdq4-2 significantly increased soil basal respiration and the activities of urease, invertase, and fluorescein diacetate (FDA) hydrolase by 83.65%, 79.72%, 19.88%, and 96.15% respectively; and the stability of the community structure was also enhanced. The Actinobacteriota biomass, the amount of available Cd, and the above- and belowground Cd content of L. perenne were significantly negatively correlated with the total phosphorus, total potassium, and pH. The activity of urease, invertase, and FDA hydrolase were significantly positively correlated with the biomasses of Acidobacteriota and L. perenne and significantly negatively correlated with the Chloroflexi biomass. Further, the available soil Cd content and the above- and belowground Cd levels of L. perenne were significantly positively correlated with the Actinobacteriota biomass and significantly negatively correlated with the Gemmatimonadetes biomass. Overall, inoculating Cd-tolerant bacteria improved the microbial activity, diversity, and abundance, and changed the microbial community composition, facilitating the remediation of Cd-contaminated soil by L. perenne.

Does phytoextraction with Sedum plumbizincicola increase cadmium leaching from polluted agricultural soil?

Sedum plumbizincicola is a cadmium (Cd) and zinc hyperaccumulator that can activate Cd by rhizosphere acidification. However, there is little understanding of the Cd leaching risk from polluted soil during phytoextraction process. Here, pot and column experiments were conducted to monitor soil Cd leaching characteristics under different rainfall simulation conditions during S. plumbizincicola phytoextraction. Soil Cd leaching increased significantly with increasing simulated rainfall intensity. Compared with normal rainfall (NR), weak rainfall (WR) resulted in a 34.3% decrease in Cd uptake by S. plumbizincicola and also led to a 68.7% decline in Cd leaching. In contrast, Cd leaching under heavy rainfall (HR) was 2.12 times that of NR in the presence of S. plumbizincicola. After two successive growing periods, phytoextraction resulted in a 53.5-66.4% decline in the amount of soil Cd leached compared with controls in which S. plumbizincicola was absent. Even compared with maize cropping as a control, S. plumbizincicola did not instigate a significant increase in Cd leaching. The contribution of Cd leaching loss to the decline in soil total Cd concentration was negligible after phytoextraction in the pot experiment. Overall, the results contribute to our understanding of soil Cd leaching risk by phytoextraction with S. plumbizincicola.

Repeated phytoextraction by hyperaccumulator Sedum plumbizincicola is an important remediation technology to remove Cd from contaminated soils. At the same time, Sedum plumbizincicola can also activate soil Cd by rhizosphere acidification. However, studies on the leaching risk of soil activated Cd during the phytoextraction process are very few. This study looked at the effects of Sedum plumbizincicola growth on soil Cd leaching with the changes in rainfall simulation and plant type. Results showed that repeated phytoextraction with Sedum plumbizincicola did not increase Cd leaching from contaminated soil.

Elevated CO2 and nitrogen addition enhance the symbiosis and functions of rhizosphere microorganisms under cadmium exposure.

Soil microbes are fundamental to ecosystem health and productivity. How soil microbial communities are influenced by elevated atmospheric carbon dioxide (eCO2) concentration and nitrogen (N) deposition under heavy metal pollution remains uncertain, despite global exposure of terrestrial ecosystems to eCO2, high N deposition and heavy metal stress. Here, we conducted a four year's open-top chamber experiment to assess the effects of soil cadmium (Cd) treatment (10 kg hm-2 year-1) alone and combined treatments of Cd with eCO2 concentration (700 ppm) and/or N addition (100 kg hm-2 year-1) on tree growth and rhizosphere microbial community. Relative to Cd treatment alone, eCO2 concentration in Cd contaminated soil increased the complexity of microbial networks, including the number links, average degree and positive/negative ratios. The combined effect of eCO2 and N addition in Cd contaminated soil not only increased the complexity of microbial networks, but also enhanced the abundance of microbial urealysis related UreC and nitrifying related amoA1 and amoA2, and the richness of arbuscular mycorrhiza fungi (AMF), thereby improving the symbiotic functions between microorganisms and plants. Results from correlation analysis and structural equation model (SEM) further demonstrated that eCO2 concentration and N addition acted on functions and networks differently. Elevated CO2 positively regulated microbial networks and functions through phosphorus (P) and Cd concentration in roots, while N addition affected microbial functions through soil available N and soil organic carbon (SOC) concentration and microbial network through soil Cd concentration. Overall, our findings highlight that eCO2 concentration and N addition make microbial communities towards ecosystem health that may mitigate Cd stress, and provide new insights into the microbiology supporting phytoremediation for Cd contaminated sites in current and future global change scenarios.

Effects of mercapto-palygorskite application on cadmium accumulation of soil aggregates at different depths in Cd-contaminated alkaline farmland.

Mercapto-palygorskite (MP) is a novel immobilization material for cadmium (Cd) pollution, but the immobilization mechanism on alkaline Cd contaminated soil is not completely clear. In this paper, field experiment was carried out to study the effect of MP on the transfer of Cd in aggregates at different depth, the contribution of soil aggregates to the reduction of Cd in bulk soil and the immobilization mechanism of MP. The results showed that MP had no significant influence on the total Cd content, soil aggregates distribution, pH value, CEC value and enzyme activities no matter at any depth. At the depth of 0-20 cm, MP significantly reduced the DTPA-Cd in bulk soil by 60.7%, and increased the GWD and R0.25 value. Similarly, the content of DTPA-Cd in the soil aggregates was deceased by 40.2-63.6%, the OM, DOC, available Fe, Mn and S in soil aggregates were significantly increased by 15.0-19.1%, 19.2-41.7%, 24.7-41.2% and 12.5-35.1% respectively. The Cd fraction of aggregates, especially exchangeable Cd (EXE-Cd) and bound to Fe/Mn oxide Cd (OX-Cd), was reduced by 5.4-28.1% and increased by 22.3-50.4%. In addition, MP had different effects on the GSF value of soil aggregates, but there was a downward trend for AFX value at 0-20 cm soil depth. MP almost had no significant influence on the above indexes at the depth of 20-40 cm and 40-60 cm, but except the Cd fraction, the GSF and AFX value in individual aggregates. Small aggregates (<1 mm) and large aggregates (>1 mm) contributed 59.1% and 22% to the reduction of Cd in bulk soil. Partial Least Structural Equation Model (PL-SEM) revealed that S promoted the production of available Fe, Mn, OM and DOC, while the content of DOC inhibited the formation of EXE-Cd and the available Fe and Mn boosted the production of OX-Cd.

Bacterial seed endophyte and abiotic factors influence cadmium accumulation in rice (Oryza sativa) along the Yangtze River area.

Cadmium (Cd) contamination in rice (Oryza sativa) is particularly problematic due to its high risk to human health. Investigating the hidden roles of seed endophytes of rice in influencing Cd accumulation is essential to comprehensively understand the effects of biotic and abiotic factors to food security. Here, the content of Cd in soils and rice (Huanghuazhan) seeds from 19 sites along the Yangtze River exhibited considerable differences. From a biotic perspective, we observed the dominant endophytic bacteria, Stenotrophomonas (7.25 %), contribute to Cd control of rice (below 0.2 mg kg-1). Partial Least Squares (PLS) analysis further suggested that Enterobacteriaceae (15.48 %), altitude and pH were found to be the strong variables that might reduce the Cd uptake of rice. In contrast, Cytophagaceae (0.58 %), latitude and mean annual air pressure had the opposite effect. In pot experiments, after respectively inoculating the isolated endophytic bacteria Stenotrophomonas T4 and Enterobacter R1, N1 (f_Enterobacteriaceae), the Cd contents in shoot decreased by 47.6 %, 21.9 % and 33.0 % compared to controls. The distribution of Cd resistant genes (e.g., czcABC, nccAB, cznA) of Stenotrophomonas, Enterobacteriaceaea and Cytophagaceae further suggested their distinct manners in influencing the Cd uptake of rice. Overall, this study provides new insights into the food security threatened by globally widespread Cd pollution.

Effects of Cadmium on Physiochemistry and Bioactive Substances of Muskmelon (Cucumis melo L.).

Muskmelon pedicel is the fruit stalk of muskmelon and one of the traditional Chinese medicines, which can be used to treat jaundice, diabetes and neuropathy. However, in recent years, agricultural soil heavy metal cadmium (Cd) pollution has become serious, coupled with the imperfect sales management of herbal medicine, increasing the potential health risk of contaminated herbal medicine in the human body. In this paper, the comprehensive quality of contaminated muskmelon was tested. The results showed that Cd stress significantly inhibited the growth of muskmelon plants, reduced the anthocyanin and chlorophyll contents, and increased the fruit size and sweetness of muskmelon. In addition, heavy metal Cd can also cause oxidative stress in plants, resulting in a series of changes in antioxidant enzyme activities. In the experimental group, the content of polyphenols and saponins increased by 27.02% and 23.92%, respectively, after high-concentration Cd treatment, which may be a mechanism of plant resistance to stress. This paper reveals that the content of bioactive substances in Chinese herbal medicine is high, but the harm in heavy metals cannot be underestimated, which should be paid attention to by relevant departments.

[Planning of ecologically suitable areas for Ligusticum chuanxiong under background of soil cadmium pollution].

Chuanxiong Rhizoma is a traditional Chinese medicinal material mainly produced in Sichuan and Chongqing of China. In recent years, the cadmium content in Chuanxiong Rhizoma produced in most of the genuine producing areas has exceeded the standard, which makes Chuanxiong Rhizoma difficult to be exported. To solve the problem of excessive cadmium content in soil, this study employed the MaxEnt model to simulate the potential geographic distribution of Ligusticum chuanxiong and evaluate important environmental factors, and re-plan its ecologically suitable areas based on the mineral distribution characteristics and soil cadmium pollution status. The results showed that the places suitable for L. chuanxiong growing covered an area of 335 523.69 km~2, mainly in central and eastern Sichuan, southern Shaanxi and most parts of Chongqing. Among them, the highly suitable areas of L. chuanxiong were mainly concentrated in Chengdu, Ya'an, Deyang, and Mianyang. Solar radiation, annual precipitation, and annual range of temperature were evaluated as important variables affecting the distribution of L. chuanxiong, with the contribution rates of 62.3%, 13.3%, and 6.8%, respectively. In addition, Qionglai county, Chongqing county, Mianyang city(Youxian district and Fucheng district), Qingchuan county, and Xinjin county were classified into the first-class ecologically suitable zone, covering a total area of 2 768.87 km~2. The se-cond-class ecologically suitable zone was even wider, involving such counties as Tongjiang county, Renshou county, Jianyang county, and Nanjiang county, and the total area reached 43 616.92 km~2. The re-planning of the ecologically suitable areas for L. chuanxiong has provided strong data support for the cultivation and resource development of L. chuanxiong and also new ideas for solving the problem of excessive cadmium content in L. chuanxiong.

The combined use of arbuscular mycorrhizal fungi, biochar and nitrogen fertilizer is most beneficial to cultivate Cichorium intybus L. in Cd-contaminated soil.

We assessed Cichorium intybus L. (chicory) growth, nutrients and Cd uptake in the presence of arbuscular mycorrhizal fungi (AMF), biochar (BC) and nitrogen (N) fertilizer applications in experimental pot studies. Mycorrhizal colonization was improved by BC addition but not N addition. However, in the presence of AMF, BC and N had positive effects on shoot biomass and plants grown in the presence of all 3 components yielded the highest levels of shoot biomass compared to pair-wise combinations or individual components singly added. AMF inoculation also increased root biomass and this effect was apparent in the combinations that included AMF without BC. Fungal inoculation also led to increased contents of phosphorus (P), magnesium (Mg) and copper (Cu) in both chicory shoots and roots and potassium (K) and manganese (Mn) in roots. Moreover, in the presence of BC, AMF inoculation evidently enhanced the shoot Ca content. In contrast, the presence of AMF inhibited plant Cd absorption and BC addition further inhibited root Cd concentration following the AMF inoculation. Applying N fertilizer alone increased Cd transfering from soil to plants. However, when combined with use of AMF and BC, Cd toxicity to plants was reduced. This study demonstrated that AMF inoculation combined with BC and N fertilizer could improve chicory growth, nutrient absorption and reduction of Cd uptake in Cd-contaminated soil.

The combined effects of elevated atmospheric CO2 and cadmium exposure on flavonoids in the leaves of Robinia pseudoacacia L. seedlings.

Flavonoids participate in several plant processes such as growth and physiological protection in adverse environments. In this study, we investigated the combined effects of eCO2 and cadmium (Cd)-contaminated soils on the total flavonoid and monomer contents in the leaves of Robinia pseudoacacia L. seedlings. Elevated CO2, Cd, and eCO2+ Cd increased the total flavonoids in the leaves relative to the control, and eCO2 mostly increased (p < 0.05) the total flavonoid content under Cd exposure. Elevated CO2 increased (p < 0.05) robinin, rutin, and acacetin contents in the leaves of 45-day seedlings and decreased (p < 0.05) the content of robinin and acacetin at 90 and 135 d under Cd exposure except for robinin at day 45 under Cd1 and acacetin on day 135 under Cd1. Quercetin content decreased (p < 0.05) under the combined conditions relative to Cd alone. Kaempferol in the leaves was only detected under eCO2 on day 135. The responses of total chlorophyll, total soluble sugars, starch, C, N, S, and the C/N ratio in the leaves to eCO2 significantly affected the synthesis of total flavonoids and monomers under Cd exposure. Overall, rutin was more sensitive to eCO2+ Cd than the other flavonoids. Cadmium, CO2, and time had significant interactive effects on the synthesis of flavonoids in the leaves of R. pseudoacacia L. seedlings. Elevated CO2 may improve the protection and defense system of seedlings grown in Cd-contaminated soils by promoting the synthesis of total flavonoids, although robinin, rutin, quercetin, and acacetin yields may reduce with time. Additionally, increased Cd in the leaves suggested that eCO2 could improve the phytoremediation of Cd-contaminated soils.

Effects of Pseudomonas TCd-1 on rice (Oryza sativa) cadmium uptake, rhizosphere soils enzyme activities and cadmium bioavailability under cadmium contamination.

Microbial remediation is a promising technique to reduce Cd accumulation in rice (Oryza sativa). In present study, a set of pot experiments were conducted to evaluate the effects of Cd-tolerate Pseudomonas TCd-1 inoculation on rice Cd uptake, soil enzyme activities and Cd bioavailability in the rhizosphere soils under Cd contaminated conditions. The results showed that at the ripening stage, with the inoculation of TCd-1, Cd contents in root, culm, leaf, hull and brown rice significantly reduced by 60.7%, 47.7%, 50.6%, 58.1% and 47.9%, respectively, and the cadmium bioconcentration factor (BCF) of rice lowered by 66.2% under 5 mg kg-1 Cd treatment. At the meantime, in the rhizosphere soils, pH increased by 0.05, the contents of exchangeable Cd (EX-Cd) and Fe-Mn oxides (OX-Cd) increased by 107.8% and 33.5%, whereas organic matter (OM-Cd) and residual (Res-Cd) decreased by 31.9% and 60.0%, respectively. The activity of acid phosphatase (ACP) increased by 28.3%, catalase (CAT), saccharase (SUC) activity decreased by 28.5% and 26.0%. Similarly, the Cd contents in root, culm, leaf, hull and brown rice reduced by 42.1%, 42.5%, 58.0%, 50.3%, and 68.8%, respectively, and the BCF lowered by 57.1%, under 10 mg kg-1 Cd treatment. Simultaneously, the soil pH increased by 0.06, the activities of CAT, SUC, urease (URE), ACP decreased by 26.4%, 34.6%, 63.8% and 15.3%, respectively. Furthermore, the correlation analysis showed that the inoculation of TCd-1 changed the correlation between rice Cd content and the biomass of roots, leaves, soil pH, CAT, PPO, URE activities, OM-Cd in rhizosphere soils. It suggested that Pseudomonas TCd-1 effectively reduced Cd uptake and Cd accumulation in rice was closely linked to the changes of soil pH, enzyme activities and Cd availability.

The combinations of sulfur and molybdenum fertilizations improved antioxidant capacity of grazing Guizhou semi-fine wool sheep under copper and cadmium stress.

Mineral development and metal smelting are the main sources of heavy metal pollution, and copper (Cu) and cadmium (Cd) are the most serious mineral elements in heavy metal pollution. Food chain is the main channel for Cu and Cd to enter human body. Excessive accumulation of Cu and Cd can lead to a variety of diseases and threaten human health. Therefore, it is urgent to repair Cu and Cd-contaminated soil. Previous several studies found that sulfur (S) and molybdenum (Mo) had the effect of alleviating the decrease of antioxidant capacity caused by heavy metal poisoning. To investigate the co-combinations of S and Mo fertilizations on antioxidant capacity of grazing Guizhou semi-fine wool sheep in Cu and Cd-contaminated meadow, and explore the control methods of co-pollutions of Cu and Cd in natural pastures, fertilizing and grazing experiments were carried out in the Wumeng Prairie in the northwest of Guizhou Province, Southwest China. 24 hm2 Cu and Cd-polluted meadows were fenced, and were randomly divided into four groups with 3 replications per group and 2 hm2 per replication. The tested groups included the control group (no fertilizer) and the three treatment groups, applied 40 kg S + 1 kg Mo, 80 kg S + 2 kg Mo, and 120 kg S + 3 kg Mo per hectare for group I, group II, and group III, respectively. 72 healthy Guizhou semi-fine wool sheep (one year old, 33.9 ± 1.2 kg) were randomly assigned to the tested pastures with 18 sheep per group. The grazing experiment lasted for 60 days. The results showed that the contents of Mn, Zn, Mo, and S in herbage in fertilized pastures were higher than that in the control group (P < 0.05). The content of Cu in herbage in fertilized pastures was lower than that in the control group (P < 0.05). The contents of Mn, Zn, Mo, and S in serum of grazing Guizhou semi-fine wool sheep were higher than that in the control group (P < 0.05). The content of Cu in serum of grazing Guizhou semi-fine wool sheep was lower than that in the control group (P < 0.05). The levels of blood Hb, RBC, and PCV, and the activities of serum SOD, GSH-Px, T-AOC, CAT, and Cp in group Ⅲ were higher than that in the control group, group Ⅰ, and group Ⅱ (P < 0.05). The MDA content of sheep in group Ⅲ was lower than that in the other treatment sheep (P < 0.05). In summary, the combinations of S and Mo fertilizers influenced the mineral contents in herbage and serum of grazing Guizhou semi-fine wool sheep. The combinations of 120 kg S + 3 kg Mo fertilizer reduced the toxicity and improved antioxidant capacity of grazing Guizhou semi-fine wool sheep in Cu and Cd-polluted grasslands.

Compost application increases the ecological dose values in a non-calcareous agricultural soil contaminated with cadmium.

Soil cadmium (Cd) pollution resulting from anthropogenic activities has become a major concern for microbial and biochemical functions that are critical for soil quality and ecosystem sustainability. Organic amendments can reduce Cd toxicity to the microbial community and enzymatic activity in Cd-polluted soils and thus would increase the ecological dose (ED) values. However, there has been less focus on the effect of organic amendments on microbial and biochemical responses to Cd toxicity in non-calcareous soils using the concept ED. The aim of this study was to assess the impact of compost application on microbial activity, microbial biomass, turnover rates of carbon and nitrogen, and enzymatic activities as the key ecological functions in a non-calcareous soil spiked with different Cd concentrations (0-200 mg kg-1). Results showed that soil amendment with compost decreased Cd availability by 48-76%, depending on the total soil Cd content. The application of compost reduced the negative influence of Cd eco-toxicity on most soil microbial and biochemical functions by 20-122%, depending on the Cd level and the assay itself. The ED values, derived from the sigmoidal dose-response and kinetic models, were 1.10- to 2.24-fold higher in the compost-amended soils than the unamended control soils at all Cd levels. In conclusion, the potential risks associated with high levels of Cd pollution can be alleviated for microbial and biochemical indicators of soil quality/health with application of 2500 kg ha-1 compost as a cost-effective source of organic matter to non-calcareous soils. The findings would have some useful implications for organic matter-limited non-calcareous soils polluted with Cd.

Influences of rice straw biochar and organic manure on forage soybean nutrient and Cd uptake.

This pot experiment aimed to investigate the influence of rice straw biochar (BC 0, 1, and 3%, w/w) and organic manure (OM 0, 1, and 2%, w/w) addition on the growth, nutrient and cadmium (Cd) uptake of forage soybean in 10 mg Cd kg-1 contaminated soils. Compared with non-biochar treatments, biochar decreased shoot biomass, height and nitrogen (N) contents. Organic manure markedly increased the shoot biomass, shoot phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) concentration, and root N, P, Ca contents without biochar addition treatments, while in the case of 3% biochar, there were no significant effects on N, K, Ca, and Mg contents of shoot and root among organic manure treatments. In comparison with other treatments, the minimum Cd content of shoots and roots both occurred in the treatment of BC3%+OM2%, while shoot Cd content reached the maximum value in OM2% treatment. Thus, these results suggested that organic manure addition can elevate forage soybean yield and nutrient content, while biochar had no positive effects. High biochar (3%) addition in combination with highest dose of organic manure (2%) can decline the Cd content of soybean and contribute to the agricultural product safety.

Research progress and mechanism of nanomaterials-mediated in-situ remediation of cadmium-contaminated soil: A critical review.

Cadmium contamination of soil is a global issue and in-situ remediation technology as a promising mitigation strategy has attracted more and more attention. Many nanomaterials have been applied for the in-situ remediation of cadmium-contaminated soil due to their excellent properties of the nano-scale size effect. In this work, recent research progress of various nanomaterials, including carbon nanomaterials, metal-based nanomaterials and nano mineral materials, in the removal of cadmium and in-situ remediation of cadmium-contaminated soil were systematically discussed. Additional emphases were particularly laid on both laboratory and field restoration effects. Moreover, the factors which can affect the stability of cadmium, main interaction mechanisms between nanomaterials and cadmium in the soil, and potential future research direction were also provided. Therefore, it is believed that this work will ultimately contribute to the myriad of environmental cleanup advances, and further improve human health and sustainable development.

Geochemical transfer of cadmium in river sediments near a lead-zinc smelter.

Cadmium (Cd) is a highly toxic element and non-essential to human. Herein, the source and fate of Cd were examined in a typical sediment profile from the North River, South China, which was affected by the massive Pb-Zn smelting activities for decades. An exceptionally high enrichment of Cd, 107-441 mg/kg, was observed across the whole profile. Approximately 50-75% of Cd was retained in the weak acid soluble fraction. Risk assessment based on geoaccumulation index (Igeo), potential ecological risk index (Eri), bioavailable metal index (BMI) and toxic risk index (TRI) further indicated an extremely strong degree of potential ecological pollution and high toxic risks. The mineralogical composition of particles from the sediment profile exhibited the presence of pyrite, magnetite, wurtzite and greenockite. This further confirmed that Cd was migrated from smelting slags to the North River basin and enriched in sediment profile. Sediment Cd speciation analysis also implied a possible transformation of Cd from metal oxides in smelting slags to adsorbed phases and carbonates, which enhances the bioavailability of Cd. The findings indicate proper countermeasures or remediation approaches should be promptly taken towards high ecological risks of Cd arising from the depth profile extending nearly 1 m, due to lead-zinc smelting related activities.

Light Pollution Changes the Toxicological Effects of Cadmium on Microbial Community Structure and Function Associated with Leaf Litter Decomposition.

Artificial light at night (ALAN/A) can not only alter the behavior and communication of biological organisms, it can also interact with other stressors. Despite its widespread use and the numerous potential ecological effects, little is known about the impact of ALAN on plant litter decomposition under cadmium (Cd) pollution in aquatic ecosystems. In an indoor microcosm experiment, we tested single and combined effects of ALAN and Cd on the activities and community structure of fungi associated with plant litter. The results showed that ALAN and/or Cd can change both water and leaf litter characteristics. ALAN exposure not only altered fungal community structure and their correlations, but also increased the activities of alkaline phosphatase, ß-glucosidase, and cellobiohydrolase. The leaf litter decomposition rate was 71% higher in the A-Cd treatment than that in the N-Cd treatment, indicating that the presence of ALAN weakened the negative impact of Cd on leaf litter decomposition. These results suggested that ALAN exposure mitigated the negative effect of Cd on leaf litter decomposition, contributing to the duel effect of ALAN on leaf litter decomposition. Overall, the results expand our understanding of ALAN on the environment and highlight the contribution of ALAN to Cd toxicity in aquatic ecosystems.

Effects of exogenous sulfur on maize (Zea mays L.) growth and Cd accumulation in Cd-contaminated plastic shed soil.

Cadmium (Cd) pollution in plastic shed soils has become increasingly severe, posing a great threat to human health and social stability. Phytoremediation of cadmium pollution is an environmentally friendly and inexpensive remediation method. In this study, maize (Zea mays L.) was selected as the phytoremediation crop by a potted method, and the bioavailability of cadmium was investigated by adding exogenous elemental sulfur. The relationships among the sulfur content, maize growth, cadmium accumulation, and soil parameters were systematically studied. The results showed that, with the supplement of sulfur, the soil pH and activities of soil enzymes (urease, catalase, and sucrase) decreased gradually, and the available heavy metals (Cd, Cr, Zn, and Cu) in soil showed an upward trend. The optimal cadmium enrichment was achieved under T2 by increasing both the biomass of the maize plant and the cadmium concentration in roots and stems. However, T3 and T4 significantly inhibited the growth of maize roots and shoots, leading to a much lower plant biomass compared with that of CK (sulfur-free treatment) and T2. In addition, the cumulative cadmium was not increased because of the low accumulation of cadmium in some parts of the plant. Correlation analyses showed that the sulfur content was negatively correlated with soil pH and maize biomass (P < 0.01), and the cadmium content of whole maize was positively correlated with the dry weight of maize (P < 0.05) and the cadmium content in roots and stems (P < 0.01). In summary, to optimize cadmium phytoremediation of the plastic shed soil, an appropriate concentration of sulfur should be selected in practical applications to ensure that the biomass of the maize is maximized, and the cadmium concentration in different parts of the maize is increased or stabilized.

Trace metals in aquatic environments of a mangrove ecosystem in Nansha, Guangzhou, South China: pollution status, sources, and ecological risk assessment.

Mangrove forests are widely located along coastlines. They have been identified to be inimitable and dynamic ecosystems. This study investigated the trace metals in mangrove water and surface sediments of Nansha, Guangzhou, China. Zn (148.42 ± 247.47 µg L-1) was the most abundant metal in waters, followed by As (82.34 ± 118.95 µg L-1), Pb (22.96 ± 120.50 µg L-1), and Ni (19.42 ± 47.84 µg L-1). In sediments, the most abundant metal was Fe (27.04 ± 1.91 g kg-1), followed by Mn (1049.04 ± 364.11 mg kg-1), Zn (566.33 ± 244.37 mg kg-1), and Cr (106.9 ± 28.51 mg kg-1). Higher contents of trace metals were detected in vicinity areas of the river mouth. The results of pollution indexes, including contamination factor, enrichment factor, and geo-accumulation index, indicated the pollution of Cd, Cu, Pb, and Zn in sediments. The Spearman correlation and cluster analysis were used to evaluate the metal sources. In water, the significant correlations among Zn and water chemical parameters (Na, Mg, K, Ca, conductivity, pH, and Cl) might indicate the natural source of Zn from the seawater. Water sampling sites in estuaries and coastal areas were clustered separately, which might indicate the influences of upstream water and the seawater, respectively. In sediments, the significant relationships among Cd, Pb, and Zn concentrations were likely to imply the emissions from industries and exploitation of the Pb-Zn mine. The occurrence of Cr and Cu in sediments can be attributed to the spills of lubricants or oil. Cd in sediments could cause serious ecological risk.

Heat-induced oxidative stress and inflammation involve in cadmium pollution history in the spleen of zebrafish.

Zebrafish were exposed to 0, 2.5 and 5 µg/L cadmium (Cd) for 10 weeks, and then each group was exposed to 26 °C(control) and 32 °C (high temperature) for 7 days. 22 indicators were compared between 26 °C and 32 °C in the spleen, including body weight, LPO and NO levels, activity levels of Cu/Zn-SOD, CAT and iNOS, MTs protein levels, and mRNA levels of Nrf2, Cu/Zn-SOD, CAT, HSF1, HSF2, HSP70, MTF-1, MTs, IL-6, IL-10, IL-1ß, TNF-α, iNOS and NF-κB. Most indicators were not significantly affected by heat in fish from no Cd pollution. However, almost all of indicators were responsive to heat in fish pre-exposed to Cd. Several indicators were sensitive to heat in fish pre-exposed to 2.5 µg/L Cd such as iNOS activities, and mRNA levels of iNOS and IL-10. Most other indicators were sensitive to heat in fish pre-exposed to 5 µg/L. The mRNA levels of HSP70 and MTF-1 were up-regulated by heat in fish pre-exposed to 0, 2.5 and 5 µg/L Cd. However, the magnitude of increase was the greatest in fish pre-exposed to 5 µg/L Cd. These differences between control and high temperature would serve as biomarkers to distinguish healthy from Cd-polluted group. The findings imply that metal pollution history should be carefully considered when screening heat biomarkers in fish.

Evaluation of cadmium transfer from soil to leafy vegetables: Influencing factors, transfer models, and indication of soil threshold contents.

Food chain contamination by soil cadmium (Cd) through leafy vegetable consumption poses a threat to human health. It is imperative to understand the relationship between Cd phytoavailability in soils and its uptake in common leafy vegetables. A large-scale field survey in Zhejiang Province, southeast China, was conducted to develop models to evaluate the Cd phytoavailability to leafy vegetables based on soil properties and to establish soil Cd thresholds based on food safety. The empirical models developed in this study explained the combined effects of soil properties and diethylenetriaminepentaacetic acid (DTPA)-extractable Cd content on Cd phytoavailability to leafy vegetables. The Cd accumulation in celery, pak choi, and amaranth was quantitatively predicted by measurement of DTPA-extractable soil Cd and soil pH, organic matter, cation exchange capacity and clay content. For predicting Cd accumulation, the DTPA-extractable Cd, pH and clay content had a major influence in lettuce; and for water spinach, the DTPA-extractable Cd, pH, and cation exchange capacity had a major influence. Soil DTPA-extractable Cd was suitable to be used as Cd thresholds in soils cultivating celery, amaranth, pak choi, lettuce, and water spinach, with values of 0.24, 0.13, 0.23, 0.32, and 0.37 mg kg-1, respectively. However, the threshold values of soil total Cd were 0.26, 0.34, and 0.83 mg kg-1 for amaranth, celery, and pak choi fields, indicating that the current soil quality standard (GB 15618-1995) for soils cultivating different types of vegetables could be overestimated or underestimated for Cd contamination and the associated risk. This study will provide a useful reference for controlling Cd contamination in common leafy vegetables and developing sustainable production of leafy vegetables.