Toxic metal enrichment characteristics and sources of arid urban surface soil in Yinchuan City, China

To investigate the environmental quality of the urban surface soil in Yinchuan City, the capital of Ningxia Hui Autonomous Region （Ningxia）, China, we sampled surface soil and measured the concentrations of 8 toxic metals （Pb, Cr, Cu, Zn, Co, Bi, Ni and V） using X-ray fluorescence spectrometry. The enrichment characteristics and sources of these toxic metals in the soil were analyzed by the enrichment factor （EF） and multivariate statistical analysis. The results showed that the mean concentrations of these toxic metals in the soil samples were 25.0, 109.1, 16.8, 26.0, 37.2, 2.7, 25.3 and 59.9 mg/kg for Pb, Cr, Cu, Zn, Co, Bi, Ni and V, respectively, which were 1.2, 1.8, 0.8, 0.4, 3.2, 8.7, 0.7 and 0.8 times of the corresponding background values of Ningxia soil, respectively. The variations of Pb, Zn, Co, Bi and Ni concentrations in the surface soil of Yinchuan were larger than those of the other metals. Our results also showed that the toxic metals investigated in the soil had different enrichment levels. Both Co and Bi were significantly enriched, whereas Cr was only moderately enriched in the soil. There was a deficiency or minimal enrichment of the other toxic metals in the soil. Source analysis results based on the concentration, enrichment characteristics and multivariate statistical analysis indicated that Cr, V and Ni originated from a combination of fossil fuel combustion, traffic pollution and natural occurrence. Pb, Cu and Zn were predominantly derived from natural and traffic sources, while Co and Bi primarily originated from construction sources.

Potentially toxic metal concentration,spatial distribution,and health risk assessment in drinking groundwater resources of southeast Iran

In this study, the concentration and spatial distribution of potentially toxic metals(PTMs), including arsenic(As), cadmium(Cd), chromium(Cr), lead(Pb), copper(Cu), iron(Fe), manganese(Mn), and magnesium(Mg) in 23 wells and drinking groundwater distribution networks of Rafsanjan, located in southeast Iran were evaluated. Moreover, the assessment of carcinogenic and non-carcinogenic risks was estimated by Monte Carlo simulation(MCS). The results showed that the concentrations of As and Pb in more than 99% and 23.46% of the study area, respectively, were higher than the maximum concentration level(10 μg/L). The mean concentration of other metals, including Cd, Cr, Cu, Fe, Mg, and Mn in all drinking water resources was within the WHO standard level. The mean hazard quotient(HQ) for As in the age group of children was 9.246 and adults 2.972, indicating high non-carcinogenic risk of As in the study area. The lifetime cancer risk(LTCR) of As was 1.36 E-3 for adults and 1.52 E-2 for children, indicating high non-carcinogenic risk of As. The level of HQ and LTCR for Pb in both age groups was in the acceptable range. The results of sensitivity analysis showed that the most effective variables were pollutant concentration and body weight(BW), respectively. Finally, it can be concluded that exposure to PTMs, especially As through drinking water in the study area can have significant effects on people’s health living in the area;therefore, it is necessary to treat and remove As from groundwater resources before drinking or using for domestic purpose.

Variations in Toxic Metal Levels of Two Fish Species, Pomatomus saltatrix and Dicentrarchus labrax, and Risk Estimation for Children

The concentrations of five toxic metals were monthly determined in two fish species,obtained from fish markets in Turkey during 2010—2011.For the determinations,AAS and ICP-AES were used.The obtained lead concentrations for all studied Pomatomus saltatrix(mean 635μg·kg-1)and Dicentrarchus labrax(mean 463μg·kg-1)samples were found to be significantly higher than the maximum allowances concentration(MAC)of 300μg·kg-1.Mean chromium(324μg·kg-1)and Cu(940μg·kg-1)concentrations in Pomatomus saltatrix were higher than in Dicentrarchus labrax(268μg Cr·kg-1 and 600μg Cu·kg-1)while Ni in Pomatomus saltatrix(216μg·kg-1)was lower in Dicentrarchus labrax(291μg·kg-1).The estimated non-carcinogenic and carcinogenic health risks by the Target Hazard Quotient and target carcinogenic risk indicate that there are no sytemic effects,and the risk of developing cancer over a human lifetime is between 2~9in 1 000 000.

Adsorption of Toxic Metals and Control of Mosquitos-borne Disease by Lysinibacillus sphaericus:Dual Benefits for Health and Environment

Objective Assessment of the bacterium L. sphaericus as a dual-action candidate for biological control of mosquito-borne diseases and bioremediation of toxic metals. Methods Larvae of the mosquito, C quinquefasciatus, were first evaluated for metal tolerance and then exposed to 5 ppm cadmium, chromium, arsenic, and lead in assays together with seven strains of L. sphaericus. A probit regression analysis was used to estimate the LCso of Cd, Cr, As, and Pb to C. quinquefosciatus. An analysis of covariance and multifactorial ANOVA examined the metal biosorption and larvicidal properties of the seven strains of L. sphaericus. Results We found that L. sphaericus adsorbed the toxic metal ions and was toxic against mosquito larvae. The L. sphoericus strain 111（3）7 resulted in a larvae mortality of over 80% for all the tested metals. This strain also exhibited the capacity to adsorb 76% of arsenic, 32% of lead, 25% of chromium, and 7% of cadmium. Conclusion This study found combined metal adsorption and larval toxicity associated with three strains of L. sphaericus [111（3）7, OT4b.31, and CBAM5]. This suggests that a combination of these strains shows strong dual potential for biological control of mosquitos in heavy metal-contaminated areas and remediate the heavy metal contamination as well.

Treatment of tunnel wash waters-experiments with organic sorbent materials. PartⅡ: Removal of toxic metals

In the first part of the article, the column and the bag experiments concerning removal of polycyclic aromatic hydrocarbons (PAHs) and nonpolar oil (NPO) from tunnel wash waters using organic sorbent materials have been described. This part presents the results of removal of toxic metals. The metals of concern (Al, As, Cd, Cr, Cu, Fe, Pb, Mo, Ni, and Zn) were selected based on the priority toxicant pollutants defined in surface water quality criteria. Concentrations of these metals in the collected effluent...

Assessment of Exposure to Toxic Metals through Food with Reference to Some Towns in Russia

In big countries, nutrition profiles and foodstuffs chemical contamination may differ significantly between different regions and even between areas within a region. Thus one should assess toxic exposure through food on not only national but also local level. We have developed and distributed a personal questionnaire for estimating average daily consumption of 44 types of foodstuffs, and for 12 of them-the percentage contribution of the main sources of supply. Depending on data analysis results, we choose the most important foodstuffs for determining their chemical contamination. We tested this approach in 7 industrial towns and found differences among them, as well as among children and adults, with regard to toxic exposure through food. People with a relatively high income consume more milk, cheese, meat, fish, poultry and fruit but less bread and potatoes than those with medium or low income. About 80% of consumed potatoes are grown locally and thus depend on each area＇s contamination. Although daily intakes of toxicants do not exceed WHO tolerable levels, their contribution to the total environmentally dependent dose is important. The approach developed by us can be used in epidemiological and risk assessment studies when they are performed on regional or local level.

Sorption of Pb(II), Cd(II), and Ni(II) Toxic Metal Ions by Alginate-Bentonite

The sorption of Pb(II), Cd(II), and Ni(II) toxic metal ions from aqueous solution by composite alginate-bentonite and alginate was investigated. The affinity and sorption capacity of the toxic metal ions for both type of samples were evaluated. The Langmuir maximum sorption capacity for each toxic metal ion increased for alginate-bentonite as compared to alginate. However, affinity for toxic metal ion remained unchanged for both alginate-bentonite and alginate in the order of Pb(II) > Cd(II) > Ni(II). Alginate-bentonite also shortens the duration required for complete sorption. Elementary mapping analysis depicts the gradient diffusion of toxic metal ions into the centre of alginate-bentonite beads indicated that sorption was contributed by surface adsorption and diffusion.

Ecological and Human Health Risk Assessment of Toxic Metals in Water, Sediment and Fish from Lower Usuma Dam, Abuja, Nigeria

The study assessed the levels of some toxic metals (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) with their potential ecological and human health risks in water, African Catfish (Clarias gariepinus), Tilapia (Oreochromis spilurus niger) and sediment samples from the Lower Usuma dam FCT, Nigeria during two major seasons in a year (rainy and dry seasons). Toxic metal concentrations were determined using Atomic Absorption spectrophotometry (Cd, Cr, Cu, Ni, Pb and Zn) and Atomic Emission Spectrophotometry (for As and Hg), and the results obtained were compared with national and international standards. The ecological and human health risk indices of the toxic metals present in the samples from the Dam were evaluated and interpreted. Tilapia from the dam posed the highest but medium ecological and human health risk due to Pb concentration of up to 7.11 mg/kg;ecological risk index of 35.55 and hazard quotient of 50.78. Overall ecological and human health risks were low due to the low concentrations of other toxic metals determined. As, Cd, Cr, Cu, Hg, Ni and Zn concentrations were all below WHO limits in the LUD water;Ni and Pb were above limits in the African Catfish and Tilapia samples. The data obtained were analyzed using one-way analysis of variance (ANOVA) and significant differences accepted at p ≤ 0.05. There was no statistical difference in the concentrations of toxic metals in water but there was significant difference between the concentrations of toxic metals in the fish and sediment samples. Correlation was found to exist between toxic metals in the water, fish and sediment analyzed from the dam. The ecological and human health risks of toxic metals in Lower Usuma dam require regular checks and monitoring hence, it was recommended by the researcher, that this and similar research work be carried out annually by NESREA and also, as research work by other students of Environmental and Analytical chemistry.

Roadside dust contamination with toxic metals along industrial area in Islamabad, Pakistan

An investigation has been carried out to understand the contamination characteristics of roadside dust in the industrial area of Islamabad, Pakistan. The amounts of Si, S, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Pb,Zn, Ga, As, Se and Cd were determined from 95 roadside dust samples collected along the Islamabad industrial area using Proton Induced X-ray Emission(PIXE). The results indicated that concentrations of all elements,except Cd, in the roadside dust were significant. The results of the enrichment factor show that the elementary composition of the roadside dust could be categorized as soil elements from the crust of the earth and elements from anthropogenic pollution. The high enrichment factors imply that elements such Cr, Cu, Pb, Zn, As, Se,Cd, Ni, Co and S came from anthropogenic activities. The source of metal contamination was identified using multivariate statistical analysis. It has been concluded that Ca, Sc, Ti, V, Mn and Fe mainly originate from crustal sources; Cr, Cu, Ni, Pb, Zn and Ga are associated with point-sources from industrial pollution/traffic;and S, Cl, K, As and Se are mainly related to oil/coal combustion.

Double Burden of Malnutrition: Toxic Metals in Breast Milk May Limit the Amounts of Micronutrients Available to Infants through Breast Milk

Background: The amounts of micronutrients in the diets of infants, and the factors that influence them needs to be monitored at the population level in order to avert detrimental developmental defects that impose lifetime-limitations on an infant’s regulatory and defense systems. This study therefore, sought to evaluate if increasing levels of the toxic metals, Hg, Pb and Cd in breast milk will result in reducing amounts of the micronutrients Zn, Se and Cu in breast milk. Methods: Breast milk samples of 114 women living in two mining areas (57 women each) in Ghana, whose babies’ amounts of breast milk intake at three months postpartum, and amounts of toxic metals had previously been determined in a prospective study, were analyzed for micronutrients by a combination of acid and microwave digestion, and quantifications were by two different modes (hydrogen and helium) of Octapole Reaction System Inductively Coupled Plasma Mass Spectrometer (7500 ce. Agilent), equipped with an ASX-510 Auto-sampler (Cetac). Results: All the breast milk specimen collected contained detectable amounts of Cu, Zn, both at levels less than have been previously reported, and Se. For specimen that did not contain Pb the amount of Se ranged from about 110 to 245 ng/g of milk, however, as the amount of Pb increased, the corresponding highest detected amount of Se reduced steeply, resulting in a right-angle triangle-shaped scatter plot. Similar relationships were observed between other toxic metals and micronutrients studied. A curve fitting regression analysis showed significant quadratic and cubic relationships between the amounts of Hg and Se, as well as between Pb, As and Cu. Conclusion: The results clearly suggest a double burden of malnutrition in these mining areas, where high loads of maternal toxic metals in breast milk, related significantly with a progressive reduction in the amounts of the micronutrients Cu and Se in breast milk, potentially reducing in infants’ intake of these micronutrients.

Toxic metals and metalloids:Uptake,transport,detoxification,phytoremediation,and crop improvement for safer food

Agricultural soils are under threat of toxic metal/metalloid contamination from anthropogenic activities,leading to excessive accumulation of arsenic(As),cadmium(Cd),lead(Pb),and mercury(Hg)in food crops that poses significant risks to human health.Understanding how these toxic metals and their methylated species are taken up,translocated,and detoxified is prerequisite to developing strategies to limit their accumulation for safer food.Toxic metals are taken up and transported across different cellular compart-ments and plant tissues via various transporters for essential or beneficial nutrients,e.g.As by phosphate and silicon transporters,and Cd by manganese(Mn),zinc(Zn),and iron(Fe)transporters.These transport processes are subjected to interactions with nutrients and the regulation at the transcriptional and post-translational levels.Complexation with thiol-rich compounds,such as phytochelatins,and sequestration in the vacuoles are the common mechanisms for detoxification and for limiting their translocation.A num-ber of genes involved in toxic metal uptake,transport,and detoxification have been identified,offering tar-gets for genetic manipulation via gene editing or transgenic technologies.Natural variations in toxic metal accumulation exist within crop germplasm,and some of the quantitative trait loci underlying these variations have been cloned,paving the way for marker-assisted breeding of low metal accumulation crops.Using plants to extract and remove toxic metals from soil is also possible,but this phytoremediation approach requires metal hyperaccumulation for efficiency.Knowledge gaps and future research needs are also discussed.

Mobility of toxic metals in sediments: Assessing methods and controlling factors

Metals and metalloids（termed as metals in this article）are important constituent elements of the earth＇s crust.A number of metals,if present in excess,are toxic to organisms and therefore they are usually defined as toxic metals.

Synthesis of new superabsorbent poly(NIPAAm/AA/N-allylisatin)nanohydrogel for effective removal of As(Ⅴ) and Cd(Ⅱ) toxic metal ions

The present studies highlight the effective removal of As（V） and Cd（II） from aqueous solutions by superabsorbent poly （NIPAAm/AA/N-allylisatin） nanohydrogel. Batch removal studies were performed as a function of treatment time, initial metal ion concentration, pH, and adsorbent dose. TEM micrographs confirm the particle size distribution in the range between 5 nm and 10 rim. The simple and metal ions adsorbed nanohydrogels were characterized by FF-IR, TGA, and EDX analysis. Finally, the equilibrium removal efficiency of the nanohydrogel was analyzed according to the Langmuir and Freundlich adsorption isotherm models which showed the removal of As（V） and Cd（II） metal ions fitted to Freundlich and Langmuir isotherms, respectively. Removal efficiency order of the metal ions is As（V） 〉 Cd（II）.

Risk assessment and binding mechanisms of potentially toxic metals in sediments from different water levels in a coastal wetland

The excessive accumulation of potentially toxic metals(Pb and Cd)in coastal wetlands is among the main factors threateningwetland ecosystems.However,the effects ofwater table depth(WTD)on the risk and binding mechanisms of potentially toxic metals in sediments remain unclear.Here,sediments from different WTD obtained from a typical coastal wetland were evaluated using a newly developed strategy based on chemical extraction methods coupled with high-resolution spectroscopy.Our findings indicated that the WTD of the coastal wetland fluctuates frequently and the average enrichment factor for Pb was categorized as minor,whereas Cd enrichment was categorized as moderate.High-resolution spectroscopy techniques also demonstrated that organic functional groups and partly inorganic compounds(e.g.,Fe-O/Si-O)played a vital role in the binding of Pb and Cd to surface sediments.Additionally,mineral components rather than organic groups were mainly bound to thesemetals in the bottom sediments.Collectively,our findings provide key insights into the potential health effects and binding characteristics of potentially toxic metals in sediments,as well as their dynamic behavior under varying sediment depths at a microscale.

EFFECT OF TOXIC METAL ON THE STRUCTURAL DRY WEIGHT OF A PLANT： A MODEL

A two compartment mathematical model for the individual plant growth under the stress of toxic metal is studied. In the model it is assumed that the uptake of toxic metal by the plant is through root compartment. The toxic metal present in the soil interfere with the uptake and distribution of essential nutrients in plant causing decrease in the nutri- ent uptake eventually damaging the root structure. In the model it is further assumed that the resistance to nutrient transport from root to shoot compartment increases and nutrient use efficiency decreases due to the presence of toxic metal. In order to visualize the effect of toxic metal on plant growth, we have studied two models, that is, model for plant growth with no toxic effect and model for plant growth with toxic effect. From the analysis of the models the criteria for plant growth with and without toxic effects are derived. The numerical simulation is done using Matlab to support the analytical results.

Assessment of Heavy Metal Exposure in Soils of Ihwrekreka Communities, Delta State, Nigeria

Crude oil pollution in the Niger Delta, perpetrated by both local communities and industrial actors, has brought about soil pollution with its consequent ecological, human health and food challenges. The purpose of this research was to examine the concentration and distribution of heavy metals in soil from communities contaminated by crude oil in Niger Delta, and to evaluate the potential health risks to residents from exposure to these contaminants. To achieve this, soil samples were collected from the Ihwrekreka community and analyzed for heavy metal content using inductively coupled plasma mass spectrometry (ICP-MS). The analytical results in mg/kg revealed a significant metals pollution level derived from the oil spill in the soil ranging from 4.85 - 17,078 (Cu), 1.01 - 16.1 (Cd), 0.22 - 36.8 (Cr), 8.28 - 40.9 (Ni), 7.51 - 6474 (Pb), and 8.84 - 12,851 (Zn) respectively. Most of the metals were above the permissible limits of World Health Organization, with Cu, Zn, and Pb as the most contaminating metals. Lead was found to be the main contributor to the hazard index (HI) values for both children and adults in the study area, with its concentration exceeding the permitted limits set by the WHO and the EC. The hazard index (HI) values of Pb, Cu, Zn, Cd, Ni, and Cr were significantly higher than 1. These findings suggest that the release of heavy metals from an oil-contaminated site may pose a risk to human health and the environment.

Effects of Glomus mosseae on the toxicity of heavy metals to Vicia faba

A glasshouse pot experiment was conducted to investigate effects of the arbuscular mycorrhizal fungus Glomus mosseae on the growth of Vicia faba and toxicity induced by heavy metals （HMs） （Cu, Zn, Pb and Cd） in a field soil contaminated by a mixture of these metals. There was also uninoculation treatment （NM） simultaneously. Mycorrhizal （GM） plants have significantly increased growth and tolerance to toxicity induced by heavy metals compared with NM plants. P uptake was significantly increased in GM plants. Mycorrhizal symbiosis reduced the transportation of HMs fi＇om root to shoot by immobilizing HMs in the mycorrhizal, shown by increasing the ratios of HMs from root to shoot. Oxidative stress, which can induce DNA damage, is an important mechanism of heavy metal toxicity. GM treatment decreased oxidative stress by intricating antioxidative systems such as peroxidases and non-enzymic systems including soluble protein. The DNA damage induced by heavy metals was detected using comet assay, which showed DNA damage in the plants was decreased by the GM treatment.

Potential toxic risk of heavy metals from sediment of the Pearl River in South China

Based on the monitoring of five heavy metal elements in the surface sediments of the Pearl River in South China, potential toxicity of the heavy metals was assessed using consensus-based sediment quality guidelines （SQGs） method and geo-accumulation （Igeo） index method. The monitoring results showed the heavy metal concentrations were significantly and positively correlated with each other, demonstrating a common trend in variation of concentration in the surface sediments. The assessment using the consensus-based SQGs method showed the potential toxicity of Cu was the highest, and Cd was the lowest. The evaluation based on mean probable effect concentration （PEC） quotient showed the region was seriously polluted with high toxicity heavy metals. Correlation analysis revealed a significant and positive correlation between the mean PEC quotient and the average of Igeo with a correlation coefficient of 0.926 （n = 23, P 〈 0.01）. In conclusion, the consensus-based SQGs and mean PEC quotient are applicable to assess potential toxicity risks of heavy metals in freshwater sediments in the Pearl River.

Toxic Effects of Three Heavy Metallic Ions on Rana zhenhaiensis Tadpoles

Heavy metal pollution is widespread in some areas of China and results in contamination of land, water, and air with which all living organisms interact. In this study, we used three heavy metallic ions （Cu^2＋, Pb^2＋ and Zn^2＋） to assess their toxicity effects on mortality, blood biomarker and growth traits （body length and body mass） of Rana zhenhaiensis tadpoles. The results showed that the toxicity levels of the three metallic ions were different when conducted with different experiment designs. For acute toxicity tests, Cu^2＋ was the most toxic with the highest tadpole mortality. The mortalities of tadpoles showed significant differences among the treatments at the same exposure time endpoints （24, 48, 72 and 96h）. Results from repeated measures ANOVA indicated that metallic ion concentration, exposure time and their interactions significantly affected the mortalities of R. zhenhaiensis tadpoles. Also, the toxicity effects of all binary combinations of the three metallic ion treatments showed synergism. The half lethal concentrations （LCs0） decreased with increasing exposure time during the experimental period, and the safe concentration （SC）values of Cu^2＋, Pb^2＋ and Zn^2＋ were different from each other. Combined and compared LC50 values with previous data reported, it is suggestes that the toxicity levels of metal pollution to anuran tadpoles should be species-and age-related. For blood biomarker tests, Zn^2＋ was the most toxic with the highest total frequencies of abnormal erythrocytic nucleus. All three metallic ions caused higher abnormal erythrocytic nucleus compared with control groups. In a chronic toxicity test, Pb^2＋ was the most toxic with lowest growth traits. Survival rate （except for 18 days）, total body length and body mass showed significant differences among the treatments. These findings indicated that tadpoles of R. zhenhaiensis should be as a bioindicator of heavy metals pollution.

Insights into the Roles of Melatonin in Alleviating Heavy Metal Toxicity in Crop Plants

Alleviating heavy metal pollution in farmland soil,and heavy metal toxicity in plants is the focus of global agricultural environmental research.Melatonin is a kind of indoleamine compound that wide exists in organisms;it is currently known as an endogenous free radical scavenger with the strongest antioxidant effect.As a new plant growth regulator and signaling molecule,melatonin plays an important role in plant resistance to biotic or abiotic stress.Recent studies indicate that melatonin can effectively alleviate heavy metal toxicity in crop plants,which provides a new strategy to minimize heavy metal pollution in crop plants.This study summarizes the research progress on the role of melatonin in alleviating heavy metal toxicity in crop plants and the related physiological and ecological mechanisms such as reducing the concentration of heavy metals in the rhizosphere,fixing and regionally isolating of heavy metals,maintaining the mineral element balance,enhancing the antioxidant defense system and interacting with hormonal signaling.Furthermore,future prospects for the mechanism of melatonin in regulating heavy metal toxicity,the pathway regulating synthesis and catabolism,and the interaction mechanism of melatonin signaling and other phytohormones are presented in this paper,with the goal of providing a theoretical basis for controlling heavy metal ion accumulation in crop plants grown in contaminated soil.