Transport of Heavy Metals between Soil and Rice in the Jiulong River River Basin

Diet is one of the main pathways for heavy metals to enter the human body,so studying the content of heavy metals in agricultural products and evaluating them is of great significance.When farmland soil is contaminated with heavy metals,the heavy metals accumulated in the soil will be absorbed by the roots of rice plants growing on it,and will migrate and transform between different tissues and organs of rice plants.There is a significant correlation between heavy metal pollution in soil and the content of heavy metals in rice.The migration and enrichment of heavy metals in the agricultural soil rice system is a complex process that is influenced by many factors,such as the physical and chemical properties of the soil,the content and occurrence forms of heavy metals in the soil,and the physiological characteristics of rice plants.In actual field environments,these influencing factors have significant spatial differences and are relatively complex.Therefore,it is necessary to conduct practical analysis of the various influencing factors in actual field environments.Based on actual data analysis,studying the heavy metal content in rice and the characteristics of heavy metal accumulation and migration in rice plants is of great significance for improving the food safety of rice.

Distribution and Migration of Heavy Metals in Undisturbed Forest Soils:A High Resolution Sampling Method

The vertical distribution and migration of Cu,Zn,Pb,and Cd in two forest soil profiles near an industrial emission source were investigated using a high resolution sampling method together with reference element Ti.One-meter soil profile was sectioned horizontally at 2 cm intervals in the first 40 cm,5 cm intervals in the next 40 cm,and 10 cm intervals in the last 20 cm.The migration distance and rate of heavy metals in the soil profiles were calculated according to their relative concentrations in the profiles,as calibrated by the reference element Ti.The enrichment of heavy metals appeared in the uppermost layer of the forest soil,and the soil heavy metal concentrations decreased down the profile until reaching their background values.The calculated average migration rates of Cd,Cu,Pb,and Zn were 0.70,0.33,0.37,and 0.76 cm year-1,respectively,which were comparable to other methods.A simulation model was proposed,which could well describe the distribution of Cu,Zn,Pb,and Cd in natural forest soils.

Migration and accumulation of heavy metals in disturbed landscapes in developing ore deposits, East Kazakhstan

This paper studied the contents of heavy metals and their accumulation in the disturbed landscapes in ore deposits of East Kazakhstan. A total of 14 sites were examined in Zyrynovsky and Tishinsk deposits and Ridder town, and 50 soil samples were taken. Results indicated that the contents of heavy metals in the soil reached the maximum permissible concentration. Emissions of the zinc plant negatively affected the soil of nearby territories. In the remediated areas, a high concentration of heavy metals was observed at a depth where the bulk soil borders the rock. Accumulation of heavy metals on the surface of the remediated areas occurred due to biological accumulation in the plant. Plants transmitted heavy elements through the root system to the upper vegetative organs, making them accumulate in the upper layers of the soil. The heavy metals migrated and accumulated from the lower layers to the surface layers of the soil. The absence of soil meso-fauna resulted in the contamination of soil by heavy metals. The analysis of water samples, taken from the waste storages and the waste waters with heavy metals in the Zyryanovsk deposit and Ridder town, revealed severe water contamination.

Harmful evaluation of heavy metals from soil layer to the groundwater: Take the Jilin Hunchun Basin as an example

The continuous enrichment of heavy metals in soils has caused potential harm to groundwater.Quantitative methods to evaluate the harm of heavy metals in soil to groundwater are lacked in previous studies.Based on the theory of groundwater circulation and solid-liquid equilibrium,a simple and easy-touse flux model of soil heavy metals migrating to groundwater is constructed.Based on groundwater environmental capacity,an innovative method for evaluating the harm of heavy metals in soil to groundwater is proposed,which has been applied in Hunchun Basin,Jilin Province,China.The results show that the fluxes of soil heavy metals into groundwater in the study area are Zn,Cu,As,Pb,Cd,Ni,and Hg in descending order.The content of heavy metals in groundwater(As,Hg,Cu,Pb,Zn,Ni,and Cd)in most areas has not risen to the threshold of environmental capacity within 10 years.The harm levels of soil heavy metals to groundwater in the most townships soils are at the moderate level or below.This evaluation method can quantify the flux of soil heavy metals into groundwater simply and quickly,determine the residual capacity of groundwater to heavy metals,evaluate the harm level of soil heavy metals to groundwater,provide support for relevant departments to carry out environmental protection of soil and groundwater,and provide a reference to carry out similar studies for related scholars.

Non-Destructive Detection and Evaluation of Heavy Metal Pollution in Tailings Reservoir

Heavy metal pollution is a negative effect generated in the process of utilizing non-ferrous mineral. Studies about heavy metal migration detection are very important. A new method for rapid detection of heavy metal migration based on ground penetrating radar (GPR) was provided. Comparative tests were studied from field to lab with GPR and X-ray fluorescence analysis (XRF). A tailings reservoir in the Xiangjiang River basin at Hunan Province was taken as experimental site. The downward transfer rule of heavy metal migration was confirmed through tests on systematically arranged survey lines and sampling points in tailings site. Results showed: 1) Through GPR image recognition, tailings reservoir had 3 layers. Reclaimed soil layer (the first layer) and tailings layer (the second layer) had a clear interface. However, tailings layer (the second layer) and subsoil layer (the third layer) had an obscure interface on radar images. It was concluded that heavy metal component had migrated downwards. 2) Chemical component analysis verified image recognition conclusions. Concentrations of As, Cd and Pb were significantly out of limit, while concentration of Cr was under limit according to analysis results on samples from different depths. 3) Pollution degree was evaluated. Downward migration was the main form of heavy metal migration in tailings site, upward migration occurred through adsorption at the same time.

Vitrification of MSWI Fly Ash by Thermal Plasma Melting and Fate of Heavy Metals

Municipal solid waste incinerator （MSWI） fly ash with high basicity （about 1.68） was vitrified in a thermal plasma melting furnace system. Through the thermal plasma treatment, the vitrified product （slag） with amorphous dark glassy structure was obtained, and the leachability of hazardous metals in slag was significantly reduced. Meanwhile, it was found that the cooling rate affects significantly the immobility of heavy metals in slag. The mass distribution of heavy metals （Zn, Cd, Cr, Pb, As, Hg） was investigated in residual products （slag, secondary residues and flue gas）, in order to analyze the behavior of heavy metals in thermal plasma atmosphere. Heavy metal species with low boiling points accounting for the major fraction of their input-mass were adsorbed in secondary residues by pollution abatement devices, while those with high boiling points tended to be encapsulated in slag.

Migration of Heavy Metal Elements in Reclaimed Irrigation Water-Soil-Plant System and Potential Risk to Human Health

[Objectives]To study the impact of heavy metal pollution of soil and plants during the process of reclaimed water for irrigation of green land in arid areas and the potential health risks to humans during use.[Methods]Taking Zhongwei City in Ningxia,a typical arid area,as the research area,the irrigation water,soil and green grass in the reclaimed water irrigation region and the original green water irrigation region were sampled,the heavy elements Hg,As,Zn,Pb,Cd,Cr were detected,and the Nemerow method,biological absorption coefficient,and health risk assessment were employed to evaluate the degree of soil pollution,plant absorption capacity,and human health risks.[Results]Compared with the original green water,the Hg,Cd,and Cr pollution of the reclaimed water irrigated green land was higher,the As,Zn,Pb pollution was lower,and the content of Hg and Cd was higher than the environmental background values of soil in Ningxia;the Cr content exceeded the risk intervention values of the first type of land in the Soil Environmental Quality—Risk Control Standard for Soil Contamination of Development Land(GB 36600-2018).Compared with the original green water irrigation region,it is found that the reclaimed water irrigation reduced the heavy metal pollution of the soil to a certain extent.The heavy metal content of tall fescue grass(Festuca arundinacea)in the reclaimed water irrigation region was Zn,Cr,Pb,As,Cd,and Hg from high to low;the order of the biological absorption coefficient was Cd>As>Zn>Pb>Hg>Cr;irrigation water exerted a certain effect on the content of heavy metals in plants and the biological absorption coefficient through the soil.Using the health risk assessment method recommended by Environmental Protection Agency of the United States of America(USEPA),it was found that the reclaimed water has the highest risk through the inhalation route,and the occupational population has a higher risk of skin contact with soil and plants.[Conclusions]This study is intended to provide data support and theoretical basis for the environmental safety risk research of the application of reclaimed water in arid areas to urban greening.

Migration and transfer of chromium in soil-vegetable system and associated health risks in vicinity of ferro-alloy manufactory

Study was carried out to analyze the distribution and migration patterns,soil-to-plant transfer and potential health risks of chromium in soil-vegetable system in areas near a ferro-alloy manufactory in Hunan province.The results show that soils near sewer outlet,sewer channel and in control area are averaged 2 239.5,995.33 and 104.9 mg/kg,respectively.The total Cr has a relative accumulation in soil depth of 200-400 mm near the sewer outlet,mainly enriches in the surface layer（0-200 mm） near the sewer channel and decreases gradually in unpolluted soils.The differential concentration level of enrichment between layers is little.The results also indicate that the three vegetables of celery,lettuce and Chinese cabbage are able to convert the potentially toxic Cr（Ⅵ） species into the non-toxic Cr（Ⅲ） species,and the chromium contents in the edible parts of the vegetables are averaged 11.95 mg/kg.The transfer factors of the three vegetables follow the order：Chinese cabbage lettuce celery.The estimated total daily intake of chromium substantially exceeds the dietary allowable value,which may pose health risks to local population.

Species Transformation of Trace Elements and Their Distribution Prediction in Dyestuff Residue Incineration

The release of heavy metals from the combustion of hazardous wastes is an environmental issue of in-creasing concern.The species transformation characteristics of toxic heavy metals and their distribution are consid-ered to be a complex problem of mechanism.The behavior of hazardous dyestuff residue is investigated in a tubular furnace under the general condition of hazardous waste pyrolysis and gasfication.Data interpretation has been aided by parallel theoretical study based on a thermodynamic equilibrium model based on the principle of Gibbs free en-ergy minimization.The results show that Ni,Zn,Mn,and Cr are more enriched in dyestuff residue incineration than other heavy metals(Hg,As,and Se)subjected to volatilization.The thermodynamic model calculation is used for explaining the experiment data at 800℃ and analyzing species transformation of heavy metals.These results of species transformation are used to predict the distribution and emission characteristics of trace elements.Although most trace element predictions are validated by the measurements,cautions are in order due to the complexity of incineration systems.

Study on Deliver Analysis Method of Heavy Metal Elements during Cigarette Smoking

[Objective] The deliver amount and deliver rate of heavy metal elements during smoking were studied, which could provide a reference for reducing the damage of cigarette products. [Method] Two pretreatment methodsof microwave di- gestion and acid extraction were used to process the ash content, the total particu- late matter of mainstream smoke （TPM） and cigarette filter. Detection results of heavy metal elements were compared by the two methods. [Result] The microwave digestion method was better than acid solution extraction method on analysis of TPM, but presented disadvantages on analysis of ash and filter. Meanwhile, the migration amount and rate were studied and resultsshowed that most heavy metal elements were escaped along with sidestream smoke between 66.89% and 95.48%, and almost all Hg escaped through sidestream smoke. Other heavy metal elements, except Hg, were separately found in ash, TPM and filter. Cr, Ni, As and Se were mostly residual in ash, followed by TPM, and filter had the least, while Cd and Pb were just in the reverse order. Normally, 5% or less heavy metal elements were transferred to TPM, only a small part of which could reach 5%-10%. [Conclusion] Most of the heavy metal elements are taken by sidestream smoke, ash and filter, while the migration amounts to mainstream smoke are extremely low.

Surface reaction of Bacillus cereus biomass and its biosorption for lead and copper ions

In this study, the surface chemical functional groups of Bacillus cereus biomass were identified by Fourier transform infrared （FTIR） analytical technique. It had been shown that the B. cereus cells mainly contained carboxyl, hydroxyl, phosphate, amino and amide functional groups. The potentiometric titration was conducted to explain the surface acid-base properties of aqueous B. cereus biomass. The computer program FITEQL 4.0 was used to perform the model calculations. The optimization results indicated that three sitesthree pKas model, which assumed the cell surface to have three distinct types of surface organic functional groups based on the IR analysis results, simulated the experimental results very well. Moreover, batch adsorption experiments were performed to investigate biosorption behavior of Cu（Ⅱ） and Pb（Ⅱ） ions onto the biomass. Obviously, the adsorption equilibrium data for the two ions were reasonably described by typical Langmuir isotherm.

Effects of organic acids on heavy metal release or immobilization in contaminated soil

In order to explicit the environmental activity of heavy metals affected by different organic acids in soil,a batch incubation experiment was explored to investigate the influence of high relative molecular mass organic acid(HMWOA)(humic acid and fulvic acid)and low relative molecular mass organic acid(LMWOA)(threonic acid and oxalic acid)on the release or immobilization of Pb,Cu and Cd in soils.Results showed that LMWOA,especially threonic acid,had a good performance in the release of Pb,Cu and Cd from soils,and decrease in the fractions of HOAc-extractable,reducible and oxidable Pb,Cu and Cd.Conversely,HMWOA,especially humic acid,decreased the release of Pb,Cu and Cd,while it increased the fractions of HOAc-extractable,reducible and oxidable Pb,Cu and Cd,indicating that HMWOA can immobilize heavy metals.The release of Pb,Cu and Cd caused by LMWOA was attributed to the dissociation of soil organic matter and amorphous iron oxides since the total organic carbon and the water-soluble iron increased.The immobilization of Pb,Cu and Cd by HMWOA was attributed to the adsorption onto HMWOA followed by amorphous iron since HMWOA resulted in a significant decrease of zeta potential and an increase of amorphous iron oxide.It can be concluded that LMWOA has a potential application in soil washing remediation,while HMWOA can be used in the immobilization remediation for heavy metals contaminated soils.

Countermeasures of heavy metal pollution

This article gives a review on heavy metal pollution prevention and control,and it also discusses heavy metal pollutant discharge,prediction and evaluation of environmental impact,and pollution prevention and monitoring.

Migration and distribution characteristics of soil heavy metal(loid)s at a lead smelting site

Heavy metal(loid)s contamination is a constant issue at smelting sites.It is essential to investigate the spatial distribution and migration characteristics of heavy metal(loid)s in the soil for environmental management and remediation strategies of non-ferrous smelting sites.In this study,203 soil samples from 57 sites were collected in a typical lead smelting site.The findings demonstrated that there were significant Pb,Zn,Cd,and As contamination in soil samples.The spatial distribution of heavy metal(loid)s showed strong spatial heterogeneity,the contaminated soil areas of Pb,As,Cd,and Zn were 99.5%,98.9%,85.3%,and 72.4%,respectively.Pb,Cd,and As contamination of the soil reached a depth of 5 m,which migrated from the surface to deep soil layers.The leaching contents of Zn,Pb,and As decreased obviously in 3-4 m soil layer,but the leaching content of Cd was still high,which indicated the high migration of Cd.With the increase of depth,the proportion of acid soluble fraction of heavy metal(loid)s decreased,and the residual fraction increased.The acid soluble fraction of Cd accounted for a higher proportion,and As mainly existed in reducible and residual fractions in soil.According to the calculation of the migration factor,the migration of heavy metal(loid)s in soils were ordered as Cd>Zn>Pb>As.The outcomes are advantageous for risk reduction and site remediation for non-ferrous metal smelting sites.

The impact of particle size on the cumulative process of street dust migration

Street dust is a carrier of various pollutants widely distributed in the urban road environment, and has obvious particle size effect on environmental pollution. In this paper, the effects of particle size distribution on dust accumulation, heavy metal pollution and cleaning conditions are mainly discussed. Based on the particle size effect of street dust, the future research and control of non-point source pollution are given a breakthrough.

A review on the transformation of birnessite in the environment:Implication for the stabilization of heavy metals

Birnessite is ubiquitous in the natural environment where heavy metals are retained and easily transformed.The surface properties and structure of birnessite change with the changes in external environmental conditions,which also affects the fate of heavy metals.Clarifying the effect and mechanism of the birnessite phase transition process on heavy metals is the key to taking effective measures to prevent and control heavy metal pollution.Therefore,the four transformation pathways of birnessite are summarized first in this review.Second,the relationship between transformation pathways and environmental conditions is proposed.These relevant environmental conditions include abiotic(e.g.,co-existing ions,pH,oxygen pressure,temperature,electric field,light,aging,pressure)and biotic factors(e.g.,microorganisms,biomolecules).The phase transformation is achieved by the key intermediate of Mn(Ⅲ)through interlayer-condensation,folding,neutralizationdisproportionation,and dissolution-recrystallization mechanisms.The AOS(average oxidation state)of Mn and interlayer spacing are closely correlated with the phase transformation of birnessite.Last but not least,the mechanisms of heavy metals immobilization in the transformation process of birnessite are summed up.They involve isomorphous substitution,redox,complexation,hydration/dehydration,etc.The transformation of birnessite and its implication on heavy metals will be helpful for understanding and predicting the behavior of heavy metals and the crucial phase of manganese oxides/hydroxides in natural and engineered environments.

Modeling Heavy Metal Movement in Soil

[Objective] The migration process and feature of CdCl2 in the vertical and horizontal profiles of soil were studied by the stimulating experiment to present the theory for the treatment of significant pollution accident.[Method]The column leaching device was taken to simulate the vertical and horizontal migration of CdCl2 in the soil profile under two-phase rainfall during 16 days.The portable manual control negative pressure pump was taken to extract soil solution sample and the Cd concentration was determined by the atomic absorption spectrophotometer.[Result]During the whole experiment,the obvious horizontal and vertical migration features of CdCl2 appeared.The CdCl2 covered the whole horizontal profile in 0.5 h and the whole vertical profile in 146 hours.The relative variation rate of Cd in the different depth of bulk showed that the rapid passing time differed in the different depths.In the depth of 15,35 and 55 cm,the rapid passing time were about 48,117 and 266 h,respectively.[Conclusion]The simulating device used in this paper could well investigate the vertical and horizontal distribution and migration of contaminant.Under the condition of greater rainfall,the CdCl2 gave priority to the horizontal runoff in the surface soil,followed by the vertical migration.

Development of a model to simulate soil heavy metals lateral migration quantity based on SWAT in Huanjiang watershed,China

Lateral transportation of soil heavy metals in rainfall events could significantly increase the scope of pollution. Therefore, it is necessary to develop a model with high accuracy to simulate the migration quantity of heavy metals. A model for heavy metal migration simulation was developed based on the SWAT(Soil and Water Assessment Tool) model. This model took into consideration the influence of soil p H value, soil particle size, runoff volume, sediment amount,concentration of water-soluble heavy metals dissolved in runoff and insoluble absorbed to the soil particles. This model was reasonable in Huanjiang watershed, Guangxi Zhuang Autonomous Region, south China, covering an area of 273 km^2. The optimal drainage area threshold was determined by analyzing the effects of watershed subdivision on the simulation results to ensure the simulation accuracy. The main conclusions of this paper were:(1) watershed subdivision could affect simulation migration quantity of heavy metals;(2) the quantity of heavy metals transported by sediment accounted for 97%–99% of the total migration quantity in the study watershed. Therefore, sediment played the most important role in heavy metal migration;(3) the optimal drainage area threshold percentage to ensure high simulation accuracy was determined to be 2.01% of the total watershed;(4) with the optimal threshold percentage, this model could simulate the migration quantity of As, Pb and Cd accurately at the total watershed and subwatershed level. The results of this paper were useful for identifying the key regions with heavy metal migration.

Heavy Metal Migration Characteristics of Co-Combustion between Sewage Sludge and High Alkaline Coal on Circulating Fluidized Bed

The migration characteristics of heavy metals in co-combustion of sewage sludge and high alkali coal in circulating fluidized bed were studied by experiments and simulations. Temperature plays a crucial role in thermodynamic equilibrium distribution and migration characteristics of heavy metals. At the temperature range of 700℃-1200℃, Hg is completely gaseous and the proportion of Pb, Ni, and Cd in the gas phase is also high. As is mainly elemental in the system, and the proportion of Cr in the solid phase is large. Zn compounds are diverse and mostly solid materials. The volatility of Cu is not strong, and it will become gaseous when the temperature exceeds 1700℃. The proportion of heavy metals in the gas phase decreases as the excess air ratio increases. In an oxygen-rich atmosphere, most of Zn and Ni are converted to oxides;Pb and Cd are converted to crystalline silicate;Cu is converted to partial aluminate;Cr compound is decomposed to form Cr_(2)O_(3);they are good for the solidification and controlling of heavy metals. The elemental Hg is converted to HgCl_(2) and the elemental As is converted to AsCl_(3). Temperature also has a great influence on the volatilization rate of heavy metals. The higher the temperature, the shorter the time they reach the maximum volatility.

Comparative study of two modeling approaches for predicting heavy metals contaminant migration from polyethylene bags

Plasto-Foam brand,medium size of 30 mm thickness(black and green)commonly used polyethylene bags for preparing foods were selected from those available in local markets.The polyethylene bag samples were crushed into pieces,ashed and then acid digested to determine the concentrations of heavy metals selected(Pb,Cr,Co and Cd)using Atomic Absorption spectrophotometer.All the polyethylene samples were tested positive for heavy metals.Concentrations of heavy metals in polyethylene bags ranged from 1080 ppm to 1725 ppm,76 ppm to 112 ppm,35 ppm to 52 ppm,18 ppm to 31 ppm for Pb,Cd,Cr and Co,respectively.Forty-eight posho(Ugali)samples were prepared and wrapped in these polyethylene bags and migration studies were carried out at 65°C and 80°C.The experimental data obtained were then compared to the modeled data using the models developed by Baner et al.,and Limm and Hollifield to determine which model was a better estimator.Model fitting was done based on Non-linear least square analysis using Microsoft EXCEL 2003.Diffusion and partition coefficients both between food and the contact material were also obtained by fitting experimental data to the model equation.The modeling approaching could best describe the experimental data of the measured contaminants.The study revealed that all polyethylene bags showed highest contaminant concentration(above USFDA limit)of Pb,Cd,Cr and Co,respectively confirming the potential health risk to individuals if continuously eat food thermally prepared in polyethylene bags.