Different Types Of Heavy Metals Research Articles

Effects and Mechanisms of Different Types of Biochar on Heavy Metal Passivation during Sludge Composting.

The effects and mechanisms of the different types of biochar on heavy metal passivation are still not fully understood. This study compared the effects of three types of biochar on heavy metal passivation during sludge composting. Compared with composting without biochar, rice husk biochar was most effective for the passivation of Zn and Pb, with increased passivation rates of 1.90% and 20.43%, respectively. In contrast, sludge biochar was the most effective for the passivation of Cr and Hg, with increased passivation rates of 28.30% and 3.09%, respectively. Coconut shell biochar showed the best performance for the passivation of Cu, Ni, As, and Cd, and was enriched with micropore structures, which possibly led to the adsorption and reaction of heavy metals, organic matter, and microorganisms. The improved passivation effect of the rice husk and sludge biochar on heavy metals can be attributed to the improved humification of organic matter. This study suggests that specific types of biochar should be considered for the passivation of different types of heavy metals for practical applications.

Investigating the distribution of microplastics in soils from e-waste dismantling sites and their adsorption of heavy metals.

Microplastics are characterized by strong hydrophobicity, large specific surface area. In addition to the pollutant they contain, the heavy metals adsorbed on the surface of microplastics can migrate or be transformed with them into the environmental medium, which is potentially harmful to humans. The distribution characteristics of microplastics in contaminated soil at the e-waste dismantling site were studied. The study investigated the adsorption characteristics of polyvinyl chloride (PVC), polypropylene (PP) and acrylonitrile-butadiene-styrene (ABS) on copper (Cu), zinc (Zn) and lead (Pb). It analysed the influence of various factors on the adsorption process of heavy metals, the adsorption law of microplastics on some of the heavy metals in the environment, and the risk of heavy metal release from microplastics to soil. The results showed that ABS and PP were the main microplastics in the contaminated soil. Among them, black, white and transparent microplastics accounted for 89.91%. The shape of microplastics is mainly granular, and microplastics with a particle size of 1-2 mm accounted for the largest proportion. Further studies showed that plastic particles made of ABS, PP and PVC also have the adsorption capacity for different types of heavy metals in soil, and the trends of adsorption capacity are: PP>PVC>ABS. When PP does not reach adsorption equilibrium in the adsorption process, the smaller the particle size and the more added amount, the greater the adsorption capacity. This is because the smaller the particle size of the microplastic is, the more adsorption points it can provide, increasing its ability to adsorb heavy metal ions.

Do You Know What You Drink? Comparative Research on the Contents of Radioisotopes and Heavy Metals in Different Types of Tea from Various Parts of the World.

The aim of this study was to assess the potential health risks of radioactive elements and heavy metals ingested through the consumption of various types of tea imported to the Polish market (black, green, red, oolong and white). The concentrations [Bq/kg] of radionuclides (40K, 137Cs, 226Ra, 210Pb and 228Th) in tea leaves before and after brewing were measured using γ-ray spectrometry with high-purity germanium (HPGe). The concentrations [mg/kg] of the studied elements (Fe, Cr, Cu, Mo, Al, Mn, Ni, P, V, Cd and Pb) were determined using a microwave-induced plasma optical emission spectrometer (MIP-OES). The results presented here will help to expand the database of heavy metals and radioactivity in teas. With regard to the potential health risk, the percentage of leaching of individual elements in different types of tea infusions was determined, and the assessment of the consumption risk was estimated. Since the calculated exposure factors, namely the HQ (Hazard Quotient) and THQ (Target Hazard Quotient), do not exceed critical levels, teas can still be considered health-beneficial products (most of the radionuclides as well as elements remain in the leaves (65-80%) after brewing).

Optical space division multiplexed heavy metals reflective sensors array coated with polyaniline/graphite nanofibers nanocomposite

Globally, water contamination with different types of heavy metals is a vital issue as it becomes poisonous and is considered a serious threat to human health. Three reflective standard single mode optical fiber (SSMF) sensors are developed for lead ions (Pb(II)) detection as a pollutant in water. The three SSMFs are etched with 40 µm diameter after that tapered with 13, 20, and 30 µm final diameter to produce an etched-tapered SSMF (ETSSMF). A nanocomposite of polyaniline/graphite nanofibers (PANI/GNF) nanocomposites is deposited on the three sensors to enhance their sensitivity towards the lead ions. Nanocomposite is investigated using SEM and a microscope. The three sensors are space division multiplexed using a 100 m length 4-core SMF for remote monitoring and measurements for remote monitoring for a wide geographical area coverage. The ETSSMF sensors exhibit response times of 84, 107, and 121 s and recovery times of 74, 81, and 87 s, respectively. The sensor with a smaller diameter shows a stronger response and higher sensitivity than the others. The sensors are linear and selective towards lead ions. The developed system can support the ability of real-time monitoring via the Internet from any place.

Heavy metal pollution is more conducive to the independent invasion of Solidago canadensis L. than the co-invasion of two Asteraceae invasive plants

Allelopathy is one of the primary factors that affects the successful invasion of invasive plants. Two invasive plants can often co-invade the same habitat. However, increasing amounts of heavy metal contamination can alter the independent allelopathy and co-allelopathy of two invasive plants that co-invade the same habitat. However, research on the co-allelopathy of two invasive plants treated with different types of heavy metals is limited. This study aimed to analyze the independent allelopathy and co-allelopathy of the two Asteraceae invasive plants horseweed (Conyza canadensis [L.] Cronq.) and Canadian goldenrod (Solidago canadensis L.) on the seed germination and seedling growth of the horticultural Asteraceae species lettuce (Lactuca sativa L.) treated with different types of heavy metals, including the independent contamination with copper (Cu), the independent contamination of lead (Pb), and the co-contamination of Cu and Pb. The aqueous extract of S. canadensis leaves triggers stronger allelopathy than that of C. canadensis. There is an antagonistic effect for the co-allelopathy of the two Asteraceae invasive plants compared with their independent allelopathy. Both types of heavy metals can significantly intensify the independent allelopathy of S. canadensis and the co-allelopathy of two Asteraceae invasive plants but weaken the independent allelopathy of C. canadensis. Thus, the increase in heavy metal contamination can favor the independent invasion of S. canadensis and the co-invasion of two Asteraceae invasive plants by intensified allelopathy. The intensity of influence of co-allelopathy of both invasive plants was lower than that of the independent allelopathy of S. canadensis treated with heavy metals. Thus, heavy metal contamination is more conducive to the independent invasion of S. canadensis than the co-invasion of the two Asteraceae invasive plants.

Bioaccumulation and ecological risk assessment of heavy metal contamination in various mangrove species of Kannur District, Kerala, India

The present investigation measures the concentration of heavy metals in different types of mangroves collected from the banks of the Peruvamba river, Payyanur region, Kannur District. The mangrove species viz. Acanthus illicifolius, Aegiceras corniculatum, Avicennia officinalis, Excoecaria agallocha, and Rhizophora mucronata are selected for the study and the concentrations of heavy metals such as Cd, Hg, Pb, Cu, Mn, Zn, Co, and Fe in the plant samples as well as in the soil samples were measured using Inductive Coupled Plasma-Mass Spectrometer. The concentration of Mn and Zn was relatively high in the soil. The concentration of Mn was higher in mangroves. The higher value of the transfer factor for Cd, Hg, Pb, and Fe of Aegiceras corniculatum denotes its suitability for heavy metal phytoremediation. The result of this systematic investigation is presented and discussed in this manuscript.

The Differential Antagonistic Ability of Curcumin against Cytotoxicity and Genotoxicity Induced by Distinct Heavy Metals

Widespread heavy metal pollution has aroused severe health risks worldwide. Curcumin has been reported to play a wide-spectrum protective role for various heavy metals. However, the specificity and difference in the antagonistic ability of curcumin against distinct types of heavy metals are still largely unknown. Here, using cadmium (Cd), arsenic (As), lead (Pb), and nickel (Ni) as the typical heavy metals, we systematically compared the detoxification efficiency of curcumin on the cytotoxicity and genotoxicity elicited by different heavy metals under the same experimental conditions. Curcumin was proved to have a significant discrepant antagonistic capacity when counteracting the adverse effect of different heavy metals. Stronger protective effects of curcumin emerged when antagonizing the toxicity of Cd and As, rather than Pb and Ni. Curcumin exhibits a better detoxification ability against heavy metal-induced genotoxicity than cytotoxicity. Mechanistically, inhibiting the oxidative stress elicited by heavy metals and reducing the bioaccumulation of metal ions both contributed to the detoxification of curcumin against all the tested heavy metals. Our results illustrated that curcumin shows prominent detoxification specificity against different types of heavy metals and toxic endpoints, which provides a new clue for the better and targeted application of curcumin in heavy metal detoxification.

Comparative Study of the Presence of Heavy Metals in Edible Vegetable Oils

Currently, the processes of obtaining and producing food as well as consumption habits give rise to new challenges for food safety. The presence of heavy metals in edible vegetable oils has harmful effects for humans. In this study, the scientific literature which reports the presence of heavy metals in different types of vegetable oils was analysed. More than 25 heavy metals are evaluated in 35 different oils from 24 countries. The widely studied metals are Cd, Pb, Cu, and Fe in olive oil, sunflower oil, rapeseed oil, and corn oils, mainly in Brazil, Turkey, China, Iran, and India. Likewise, the presence of Antimony (Sb) as a product of migration from PET containers to edible vegetable oils is a topic of great interest in recent years. Additionally, the different analytical techniques used for this purpose and the standards are analysed. This study highlights the main findings and challenges in this research field.

Association of blood cadmium and metabolic syndrome: a cross-sectional analysis of National Health and Nutrition Examination Survey 2017-2020.

Previous findings have reported the role of different types of heavy metals in cardiometabolic diseases. In the present research, we aim to evaluate the association between blood cadmium levels and Metabolic Syndrome (MetS) based on the large-sample NHANES data. Public availably data from NHANES 2017-2020 cycle was obtained. Participants were divided into MetS and non-MetS groups according to waist circumference (WC), triglyceride (TG), high-density lipoprotein (HDL), blood pressure (BP) and fasting plasma glucose (FPG) levels based on the National Cholesterol Education Program (NCEP) criteria. Student's t test, Mann-Whitney U test, and Chi-square test were performed for univariate analysis. Multivariate logistic analysis was performed to explore the relationship between blood cadmium and MetS and research findings were presented in forest plot. We also investigated the association of blood cadmium and MetS in subgroups stratified by age, gender and race. Population with MetS had significantly higher levels of blood [0.30 (0.18-0.54) vs. 0.24 (0.15-0.46) ug/L, p < 0.001] and urinary cadmium levels [0.29 (0.17-0.52) vs. 0.20 (0.09-0.42) ug/L, p < 0.001] compared with those without MetS. Higher blood cadmium concentrations were also observed in participants with elevated WC (0.28 vs. 023 ug/L, p < 0.001], TG (0.28 vs. 0.26 ug/L, p = 0.029), BP (0.33 vs. 0.23 ug/L, p < 0.001) and FPG (0.29 vs. 0.24 ug/L, p < 0.001) compared with those with normal metabolic parameters. Multivariate logistic regression showed that one-unit increasement of blood cadmium was associated with 1.25 times higher prevalence ratios for MetS after adjusting potential confounders (95% CI: 1.06-1.48, p = 0.0083). The associations between serum cadmium concentrations and MetS components were then evaluated, and the results showed higher blood cadmium levels were associated with higher risk for elevated TG, low HDL and elevated BP when treated as continuous variable. When treated as categorical variable, only BP was found positively associated with blood cadmium. Stratified multiple logistic regression analysis indicated that the positive association between blood cadmium and MetS remained significant in subjects less than 60years old and female subgroup. In conclusion, the cross-sectional survey suggested the positive association between blood cadmium levels and risk for MetS, prospective research need to be conducted for further evaluation of the causal relationship between blood cadmium and MetS.

The Predominant Sources of Heavy Metals in Different Types of Fugitive Dust Determined by Principal Component Analysis (PCA) and Positive Matrix Factorization (PMF) Modeling in Southeast Hubei: A Typical Mining and Metallurgy Area in Central China.

To develop accurate air pollution control policies, it is necessary to determine the sources of different types of fugitive dust in mining and metallurgy areas. A method integrating principal component analysis and a positive matrix factorization model was used to identify the potential sources of heavy metals (HMs) in five different types of fugitive dust. The results showed accumulation of Mn, Fe, and Cu can be caused by natural geological processes, which contributed 38.55% of HMs. The Ni and Co can be released from multiple transport pathways and accumulated through local deposition, which contributed 29.27%. Mining-related activities contributed 20.11% of the HMs and showed a relatively high accumulation of As, Sn, Zn, and Cr, while traffic-related emissions contributed the rest of the HMs and were responsible for the enrichment in Pb and Cd. The co-applied source-identification models improved the precision of the identification of sources, which revealed that the local geological background and mining-related activities were mainly responsible for the accumulation of HMs in the area. The findings can help the government develop targeted control strategies for HM dispersion efficiency.

Micro-computed tomography for analysis of heavy metal accumulation in the opercula

Micro-computed tomography (micro-CT) provides numerous opportunities in biomedical research. It allows the examination of samples in a non-destructive manner and visualization of the inner structures of various biological and nonbiological objects. This study was conducted to evaluate the potential of micro-CT scanner in the assessment of heavy metal accumulation in the opercula. The samples were taken from Prussian carp (Carassius gibelio) exposed to waterborne Cd (4.0 mg/L), Zn (4.0 mg/L), and the mixture of these two metals (4.0 mg Cd/L and 4.0 mg Zn/L) for 28 days. Heavy metal concentrations were determined using atomic absorption spectrometry. The results demonstrated higher concentrations of Cd and Zn in the treatment group opercula samples compared with the control group opercula samples. A simple micro-CT scan was performed to verify whether heavy metal accumulation could be determined in the reconstructed images. The results showed that micro-CT is potentially a powerful tool for metal accumulation detection. Moreover, it allowed visualization of the examined samples, revealing regions of heavy metal accumulation and providing the opportunity to compare samples exposed to different types of heavy metals.

Health Risk Assessment of Heavy Metals in Raw and Packed Milk from the Areas of Rawalpindi and Islamabad: A comparative study

Abstract: Milk is a complex of biomolecules and is a good source of proteins, fats, sugars, vitamins and minerals. Various types of milk available in the market are solid and liquid milk. Solid milk is available in the form of formula milk and liquid milk is raw and packed milk (branded milk) like GM1, OL2, Dp3, T4, H5, Mp6, DO7 and N8. Milk having different additive components like “micronutrients, vitamin and minerals” play a vital role in our daily life therefore it is by kids, adults and elders all over the world. The chemical composition of raw milk not only focuses on its components, but also the treatment, in the case of quality of the raw materials, packing, storage and conditions are very important. Cow milk is one of the major resources contaminated with different heavy metal atoms. Different samples of milk (raw and packed) were collected from diverse zone of Islamabad. The packed milk like GM1, OL2, Dp3, T4, H5, Mp6, DO7 and N8 were collected from different shops of Rawalpindi and Islamabad. Result showed the presence of different types of heavy metals in milk samples. The level of zinc in the raw milk samples was high in the Islamabad city as compared to Rawalpindi. The sequence of heavy metals present in fresh milk were detected as Zn&gt; Cu&gt; Cr&gt; Pb and Cu. In packed milk, level of Chromium was different across the world.&#x0D;

Alkali-activated binders based on incinerator bottom ash combined with limestone-calcined clay or fly ash

This study investigates the feasibility of improving the properties of alkali-activated bottom ash (AABA) binders by incorporating limestone-calcined clay (LC2) or fly ash (FA) with the aim of treating and utilising bottom ash in a large-scale as a potential resource for construction materials. Experimental results revealed that increasing the substitution with LC2 or FA in the AABA binders increased both the compressive strength and the immobilization capacity of heavy metal when compared to the pure AABA binders. Given a Na2O content of 5%, the compressive strength of the AABA binder with 30% bottom ash substituted by FA was almost 200% higher than that of the pure AABA binder. However, further increase in the Na2O dosage did not necessarily lead to higher compressive strength, which was found to be controlled by the volume fraction of air voids and large pores. When greater Na2O dosages were employed, i.e., 6 % and 7 %, LC2 was found to be more useful in improving the properties of AABA binders than FA. Furthermore, the substitution of bottom ash with FA resulted in the formation of N-A-S-H gels, whereas the substitution with LC2 led to the formation of more C-A-S-H gels. Finally, the immobilization capacity appeared to be influenced by many factors, such as hydration products, capillary pores and different types of heavy metals.

Accumulation risk and source apportionment of heavy metals in different types of farmland in a typical farming area of northern China.

The types of land used for farmland can greatly influence the source and accumulation risk of heavy metals in soil. However, the apportioning quantitatively the source of soil heavy metals has been studied insufficiently, especially in terms of different types of farmland. In this study, a total of 252 soil samples were taken from dry land, paddy fields and greenhouse fields in the Jinyuan district of Taiyuan city, China, to assess the accumulation risk of heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn). The results were then integrated, and source apportionment was evaluated by geospatial analysis, multivariate statistical analysis and positive matrix factorization (PMF). Cr, Cd and Hg were the dominant pollutants in the studied area. Accumulation risk by Cd and Cu was more severe in greenhouse fields than in dry land or paddy fields, whereas As, Hg and Pb had relatively higher accumulation in paddy fields than in dry land or greenhouse fields. Hg was derived mainly from coal combustion by atmospheric precipitation for the three types of farmland. Long-term irrigation using sewage is the main reason for the accumulation of Cu and Ni in dry land soil, Cu and Zn in paddy field soil and Zn in greenhouse soil. Cd in dry land, Cd and Pb in paddy fields and Cd, Cu, Ni and Pb in greenhouse fields were primarily added to soil through fertilization. Sewage irrigation and fertilization were the dominant sources of heavy metals for paddy field (31.3%) and greenhouse field (33.1%), respectively.

Analysis of the Spatial Distribution of Heavy Metals in Soil from a Coking Plant and Its Driving Factors

Coking plants are typical industrial pollution sites and may release heavy metals into the environment, posing a threat to human health. Scholars have discovered that different types of heavy metals are released during different coking production processes and lead to spatial differences in heavy metals. Research on the spatial distribution and driving factors of pollutants in the soil inside and outside coking plants is important for sampling design, risk assessment, pollution prevention and control, etc.. Inverse distance weight was used to analyze the spatial distribution of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn inside and outside of the coking plant. A geo-detector was used to find out the difference in the driving factors for the spatial distribution of heavy metals between soil from inside and outside the coking plant. The results showed that except As, Ni, and Zn, the overall background value rate of other heavy metals was above 50%, and the continuity of the spatial distribution of heavy metals in the soil was poor. The coefficient of variation (CV) exceeded 30%, representing a moderate variation. The average degree of CV inside the coking plant was Hg > Cd > As > Cu > Zn > Cr > Pb > Ni, and the external average degree of CV was Hg > Cu > Cd > As > Zn > Pb > Cr > Ni. An analysis of heavy metal content showed that the content of As, Cd, Cr, Pb, and Zn outside the coking plant was bigger than inside. According to geo-detector results, the physicochemical properties factors with a large contribution rate to the spatial distribution of heavy metals inside and outside the coking plant was the soil's total nitrogen, organic matter, and available medium-micro element content. Pollution source factors that contributed the most to the spatial distribution of heavy metals inside were the crude benzol and cold drum section, while the coke oven and quench section determined the outside spatial distribution of heavy metals. The q value of the strongest factor inside the coking plant was more than 0.5 while outside the coking plant it was less than 0.5. According to the interaction detector result, the interaction factors values of pollution sources and soil physicochemical properties to the inside spatial distribution of heavy metals was higher than outside. According to the distribution and geo-detector results, the strongest physicochemical properties driving factors that determined the inside and outside spatial distribution of heavy metals were relatively consistent. These factors were soil nutrient factors, which mainly influenced the availability of heavy metals. The differences in the production processes led to the difference between the inside and outside spatial distribution of heavy metals. The content of heavy metals outside the coking plant was higher than inside because the heavy metals came from various pollution sources. The driving forces for the distribution of heavy metals inside the plant were higher than outside and showed that the heavy metals inside of the plant were mainly from the coking plant. Heavy metal distribution inside the coking plant was mainly driven by the pollution source factor of the coking refining process and coking water, while heavy metal distribution outside the coking plant was mainly driven by the coking gas production process and other emission pollution source factors.

Study of Adsorption Performance of Biochar for Heavy Metals Removal

The main objective of this work is to evaluate the performance of four different types of biochars in removing heavy metals from synthetic solution. Four types of biochars are investigated in this study, namely; jazaurin, ficus, orange, and mango biochars. A pilot plant is set up to investigate the efficiency of these biochars as a filter media for synthetic solution treatment. The removal efficiency of different heavy metals is assessed by a four-column pilot plant under different parameters; mean particle size of biochars, initial metal concentration, hydraulic load, and time. Results indicate that the different types of biochars used in this study show high performance in removing the different types of heavy metals utilized (Copper (Cu), Cadmium (Cd), Lead (Pb), and Zinc(Zn)). The removal efficiencies of these heavy metals are more than 99% for all types of biochar. It is concluded that using biochars as a filter media could be an effective solution for removing heavy metals from industrial wastewater in the environmental conditions of Egypt.

Content of Heavy Metals in Different Types of Honey

The industrialization of agriculture has led to the great use of pesticides, which leads to huge global problems, such as the production of safe food that is safe for humans and the environment. By heavy metals we mean elements whose relative density is above 5 g cm-3, heavy metals can be divided into essential trace elements (Fe, Cu, Zn, Mo, Mn, Ni) and toxic elements (Pb, Cd, Cr, As, Hg ). Heavy metals are represented 25% in the soil, and the largest percentage is occupied by K, Fe, Mg, Ca, Al, Na. In addition to anthropogenic processes such as urbanization, traffic, industrialization, heavy metals can be a consequence of natural or pedogenetic processes, ie. inheritance from the parent substrate. The aim of this study was to determine the content of heavy metals Lead and Cadmium in the examined samples, to compare the obtained samples with the norms of the EU and BiH and the influence of the content of heavy metals on the quality of honey. Data collection was performed on the basis of honey analysis of four producers from the area of ​​Tuzla, Lukavac, Živinice and Bihac. The analysis was performed on February 18, 2020. to 25.02.2020. years. The analysis of the processed data was performed in the statistical program IBM SPSS.

Influence of different land use types on hydrochemistry and heavy metals in surface water in the lakeshore zone of the Caohai wetland, China

In recent years, with the expansion of the Weining county in the northeast of Caohai wetland, the construction of a new port in the north, and the large-scale development of cultivated land in the east, land use patterns in lakeshore areas have changed. These changes have affected the state of lake shores water bodies in complex ways, resulting in varying degrees of local water pollution. To explore the distribution and transformation characteristics of water chemistry and heavy metals in different areas of a water body under the influence of different land uses, especially the interactions between water chemical factors and heavy metals in different areas of a water body, this study used Circos diagrams, originally used in biological genetic analysis, to visualize these interactions. This is the first time that the Circos diagram has been applied to the analysis of environmental interactions. The results showed that there are significant differences in the distribution of water chemical factors and heavy metals in different areas of the Caohai wetland. In particular, Cd is affected by anthropogenic sources. The Cd content is higher in the NCL and UL areas, which are at greater risk from pollution. The factors controlling heavy metal levels in water bodies were different in the different regions. The NCL region was mainly affected by construction excavation ore, UL was mainly affected by man-made industrial inputs, CL was mainly affected by pesticide and fertilizer inputs, and ML and FL were mainly affected by Eh and DO. The PCA results showed that the sources of heavy metals in different types of water bodies in the lakeshore zone were both natural and anthropogenic. Therefore, controlling pollutants, reducing environmental pollution inputs to the lakeshore zone, and strengthening supervision and management near wetlands may be of great significance for handling heavy metal pollution.

Distinction between Cr and other heavy–metal–resistant bacteria involved in C/N cycling in contaminated soils of copper producing sites

For typical copper producing provinces of Heilongjiang, Henan, Inner Mongolia, Jiangxi, Shandong, Tibet, and Yunnan in China, 90 % of sampling sites were heavily polluted with multiple heavy metals. Soil heterogeneity and mutual interference of multimetals are obstacles to explore bacterial resistance pathways in contaminated field soils. Through analyses of contamination indices and bioindicators, combined with multivariate statistical models, the antioxidant enzyme activity, urease–induced precipitation of heavy metals, excretion of extracellular polymeric substances (EPS) were attributed to different types of heavy metals. Furthermore, through redundancy analysis combined with phylogenetic analysis of metal–resistant bacteria, we identified that Verrucomicrobia, Acidobacteria, and Planctomycetes secreted EPS–polysaccharides and EPS–proteins to detoxify Cr, a metal with lower concentrations and lower ecological risk as compared to other metals. The pathway was innovatively differentiated from the multimetal resistance pathways in urease and/or catalase–producing bacteria such as Proteobacteria, Firmicutes, BRC1, Bacteroidetes, Dadabacteria, Entotheonellaeota, Nitrospirae, and Gemmatimonadetes using field studies and high–throughput sequencing. Moreover, these metal–resistant bacteria were linked to C/N cycling processes of urea hydrolysis, nitrification, denitrification, EPS production, and calcite precipitation. It will provide new insight into soil bacterial resistance to multimetals in field studies.

Effects of coastal reclamation history on heavy metals in different types of wetland soils in the Pearl River Delta: Levels, sources and ecological risks

The human activity of coastal reclamation for agriculture production has caused serious environmental pollution problems and threatened the sustainable development of coastal delta area. Top soils (0–10 cm) were collected to clarify the effects of reclamation years (100y, 40y, 30y and 10y) on heavy metal pollution in reclaimed wetlands and ditch wetlands in Nansha District of the Pearl River Delta. Three parallel samples were also collected from each sampling site. As, Cd, Zn, Cu and Pb were analyzed to assess their concentration levels compared with other deltas. Geoaccumulation index, enrichment factor values, new toxicity evaluation index and principal component analysis were also used in this study. Compared with the reclaimed wetland soils, the highest concentrations of the selected elements were observed in the ditch wetland soils, with the value of Cd (1.97 ± 0.38 mg/kg), As (18.21 ± 4.61 mg/kg), Pb (68.56 ± 6.28 mg/kg), Cu (103.98 ± 23.38 mg/kg) and Zn (250.89 ± 52.35 mg/kg). Meanwhile, the elevated concentrations of heavy metals under the reclamation periods of 10y and 30y were found in two types of wetland soils except for As and Cd, which indicated that the comprehensive interactions of physical and chemical properties of soil, geographical factors, river network transportation and human activities jointly regulated the changes of heavy metal accumulation with wetland types and reclamation years. The highest potential ecological risks of Cd and Cu were observed in ditch wetlands. The sum of the toxic units were lower than 4. The contributing ratios of As (18.66 ± 3.23%) and Cd (12.97 ± 1.73%) were enhanced according to the new toxicity evaluation index compared with the ratios of As (14.70 ± 2.57%) and Cd (11.39 ± 2.35%). All the enrichment factor values of Cd, Zn and Cu exceeded 1.5, implying a large anthropogenic origin. However, the sources of As and Pb in the ditch and reclaimed wetland soils of the Pearl River Delta were generally controlled by the comprehensive effect of the natural, industrial and agricultural sources. Based on the results, key strategies including reducing the amount of pesticide and fertilizer and developing environment-friendly modern agriculture and clean production process were proposed for healthy development of the wetland ecosystems in the Pearl River Delta.