Total Heavy Metal Concentrations Research Articles

Removal of heavy metals from sewage sludge by chemical leaching with biodegradable chelator methyl glycine diacetic acid

The heavy metals (HMs) contained in sewage sludge are some of the largest obstacles that hamper the usage of sewage sludge in land application (e.g. fertilizer, soil improver). The conventional chelators, e.g., ethylenediaminetetraacetic acid (EDTA), were effective in the remediation of HMs polluted sewage sludge, but suffered from an evident drawback of low biodegradability. Therefore, the applicability of a new biodegradable chelator, methyl glycine diacetic acid (MGDA), to extract HMs from sewage sludge was carried out and compared with EDTA. The experimental parameters affecting the performance of MGDA were optimized. Leaching results showed that in general, MGDA exhibited higher Zn leaching efficiency and similar Cu, Ni and Cr leaching efficiencies with EDTA at same pH and dosage conditions. The maximum Zn, Cu, Ni and Cr leaching efficiencies of MGDA were 94.1% ± 4.5%, 58.2% ± 3.1%, 78.2% ± 2.3% and 54.6% ± 2.5%, respectively. The leaching efficiency plateaued within a reaction time of 4 h, but that of Cu and Ni showed a slightly decreasing trend during hours 4 to 10. In raw sewage sludge, the Zn and Cu were mainly presented in the organically bound fraction, i.e., 45.3 ± 3.2% of total Zn and 48.3 ± 1.4% of total Cu. The addition of MGDA and EDTA caused obvious distribution transformations in Zn and Cu from the organically bound fraction to soluble fraction. According to the reduced partition index calculation, the mobility of Zn, Cu, Ni, and Cr was not significantly lowered after the MGDA treatment. However, the HMs secondary pollution risk of the sludge was reduced due to the drop of the total HMs content after chelator leaching. Findings from this study suggest that MGDA could be a potential environment-friendly alternative for refractory chelators (e.g. EDTA) in the decontamination of HMs from sludge.

Performance evaluation of a novel two-stage biodegradation technique through management of toxic lignocellulosic terrestrial weeds

The present study investigates the biodegradation of two potentially toxic terrestrial weeds Parthenium hysterophorus and Lantana camara, implementing a novel two-stage biodegradation technique; Rotary drum composting followed by vermicomposting (RV). The RV approach was refined for a 7-day thermophilic degradation in an in-vessel rotary drum composter, followed by a 20-day mesophilic degradation utilizing Eisenia fetida and Eudrilus eugeniae vermi-monocultures. However, rotary drum composting (RDC) was performed for both the weeds (for 27 days), facilitating only initial thermophilic degradation to compare the efficacy of the RV technique. Lignocelluloses analysis revealed that cellulose degradation doubled during RV technique, indicating efficient biodegradation in reactors administered with E. fetida vermiculture compared to RDC (19.60 to 42.80% and 26.80 to 66.50% in P. hysterophorus and L. camara feedstocks). Further, these results also correlated with the X-Ray diffractograms of all trials showing the degradation of crystalline cellulose at 2θ: 20–50° for RV. Moreover, to ensure product safety, the analyzed total heavy metals content also unveiled the advantage of RV over RDC as validated by the accumulation of higher concentrations of zinc (45% and 33% in P. hysterophorus and L. camara feedstocks) and lead (55% and 45% in P. hysterophorus and L. camara feedstocks) in reactors with E. fetida. The material’s seed germination index increased to 80% in the final product of all trials in the RV technique, indicating the diminishing of the phytotoxic nature. Subsequently, pot studies also indicated that the RV technique was coherent in managing noxious weeds.

Vertical Distributions and Bioavailabilities of Heavy Metals in Soil in An-Tea Plantations in Qimen County, China

Heavy metals mainly enter tea from the soil. In this study, stratified soil samples were collected, at a depth of 0–60 cm, using a soil drill in An-tea plantations. Speciation of As, Cd, Cr, Cu, Ni, Pb, and Zn was determined using the European Community Bureau of Reference sequential extraction method, and the heavy metal concentrations in the extracts were determined by inductively coupled plasma−mass spectrometry. Compared with other soil layers, the mean Cd, Cu, Pb, and Zn concentrations were highest in the 0–20 cm layer, the Ni concentrations were highest in the 20–40 cm layer, and the As and Cr concentrations were highest in the 40–60 cm layer. The mean contributions of the non-residual fractions, including the acid-soluble, reducible, and oxidizable fractions, to the total concentrations were higher than those of the residual fraction for Cr, Cu, and Ni at all depths in soil from a flat area, as well as for Cd and Zn at all depths in soil from a sloping area. The contributions of non-residual fractions to the total As and Pb concentrations were higher than those of the residual fraction in soil from a depth of 0–20 cm from the flat area and soil from a depth of 20–60 cm from the sloping area. The total heavy metal concentrations correlated well with the acid-soluble fraction and reducible fraction concentrations in soil from 0–40 cm.

Quantifying Total Phosphorus and Heavy Metals in Residential Septage

Septic systems are used for wastewater treatment in rural areas. Septic tanks promote stratification of wastewater into solid (sludge and scum) and liquid layers. Pollutant concentrations in the layers of residential septic tanks may be highly variable, and thus septage pumped from tanks with different layer thicknesses may also be variable. The goal of this study was to quantify the total phosphorus (TP) and heavy metal concentrations and masses of residential septage. The solid and liquid layer thicknesses were measured in 37 septic tanks. Samples were collected from each layer for pollutant concentration analysis. The median TP concentration (10.6 mg L−1) was greatest in the sludge layer, followed by the scum (5.3 mg L−1) and liquid (1.8 mg L−1) layers. Concentrations of heavy metals were highly variable for each layer type. The masses of the TP, cadmium, copper, lead, nickel, and zinc contained median (range) values of 19.4 g (0.9–1041 g), <0.01 g (<0.01–1.99 g), 1.3 g (0.1–520 g), 1.8 g (<0.01–44.2 g), 1.3 g (<0.01–4.3 g), and 13.8 g (0.3–788 g), respectively. Since septage is typically applied on land as a soil amendment for crop growth, it is important that representative composite samples are collected to prevent excess buildup of TP and metals, which may harm yields or environmental health.

Bioaccumulation of heavy metals in Acanthopagrus latus collected from Al-Razazah Lake, middle of Iraq

Concentrations of cadmium, cobalt, cupper, iron, manganese and nickel were determined in four organs (liver, gills, ovaries and muscles) of Acanthopagrus latus, which belong to family of Sparidae collected from Al- Razazah Lake. Heavy metals have been determined by means of Atomic Absorption Spectrophotometry. The fish average weight was 378 g and the average length was 215 mm. Iron showed the highest value (1029.114 μg/g dry weight), while manganese showed the lower value (60.335 μg/g dry weight). This study showed that the concentration of heavy metals distributed in the organs was as follows: liver > gills > muscles > ovaries, while the total heavy metals concentration had been distributed as follow: iron > cupper > cadmium > nickel > manganese > cobalt.

Spatiotemporal estimation of heavy metals pollution in the Mediterranean Sea from Volturno River, southern Italy: distribution, risk assessment and loads

ABSTRACT With the aim of assess the pollutant load from the Volturno River into the Mediterranean Sea, the amount of some heavy metals (As, Hg, Cd, Cr, Cu, Ni, Pb and Zn) was determined in water dissolved phase (DP), suspended particulate matter (SPM) and sediment samples. Total heavy metal concentrations were in the range 0.20–65.67 μg L−1 (mean value of 12.95 μg L−1) for DP, 1.37–601.77 μg L−1 (mean value of 105.39 μg L−1) for SPM and 14.62–157.33 mg kg−1 (mean value of 55.24 mg kg−1) for sediments. The total heavy metals input are evaluated in about 620.39 kg year−1, suggesting that the river could be an important source of heavy metals in the Tyrrhenian Sea. The ecological risk characterisation was assessed based on the National Water Quality Criteria, by comparison with criterion concentration for chronic and acute toxicity (CCC and CMC), and sediment quality guidelines. Hg and Cd showed higher values than CMC and CCC for most water samples. The Index of Geoaccumulation (I geo), Contamination Factor, Contamination degree, Pollution Load Index (PLI) and Potential Ecological Risk Index were evaluated. According to I geo and PLI, the Volturno River was uncontaminated or moderately polluted by heavy metals.

A high-sensitive and durable electrochemical sensor based on Geobacter-dominated biofilms for heavy metal toxicity detection

A highly sensitive electrochemical sensor for detecting low concentrations of heavy metals (Cd2+, Ni2+, Pb2+ and Cu2+) based on Geobacter-dominated biofilms was developed. The biosensor showed a high sensitivity for the determination of Cd2+ (109.7 μAμM−1cm−2) and the determination of Pb2+ (161.7 μAμM−1cm−2). The performance of three fitting models for biosensor response to heavy metal toxicity was investigated based on the relationship between total coulomb yield and heavy metal concentration. The full-area model (Equation a) provided the best fit, and the response times tended to be the fastest based on the peak current model (Equation c). Recovery methods were proposed to ensure the electrical activity of the biofilm for long-term monitoring. 16S rRNA gene sequence analysis showed that the most dominant genus in the anodic biofilm was Geobacter (44.1%–45.8%), indicating a stable community structure after continuous toxicity shock for 22 days. The confocal laser scanning microscope (CLSM) further proved the restorable and reusability of the biosensor. Thanks to the thin and electrically active Geobacter-dominated biofilms, it could be a good alternative biosensor for groundwater analysis etc. The results of this study contribute to the development of a highly sensitive and accurate biosensor with long-term usage towards on-site monitoring of heavy metals at low concentrations, improving the test performance of the biosensor for practical application.

Ecological Assessment, Spatial Analysis, and Potential Sources of Heavy Metals (HMs) in Soils with High Background Values in the Lead-Zinc Mine, Hezhang County, Southwestern China

The heavy metals (HMs) usually have high natural background levels in lead-zinc mines. Strengthening the ecological risk assessment and accurate identification sources of HMs is an important component of land resource utilization and food security. A total of 795 soil samples (with a depth of 0~20 cm) were collected in Hezhang County, an area of typical high background levels of HMs with more than 18 large lead-zinc deposits. In this study, inductively coupled plasma emission spectrometry (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), atomic fluorescence spectrometry (AFS), and the potentiometric method (POT) were used to test the total concentration of HMs and pH values. The geographic information system was used to model the concentration distribution of HMs, and the ecological risk was assessed according to the source analysis results. The results suggest that: (1) the mean concentration of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were 24.55, 2.25, 176.4, 89.6, 0.19, 64.2, 102, and 257 mg·kg−1, respectively, which exceeded the average background value of soils in Guizhou Province by 1.23, 3.41, 1.84, 2.80, 1.73, 1.64, 2.90, and 2.58 times, respectively, and the average concentrations of Cd, Cr, Cu, Ni, Pb and Zn exceed the screening values specified in soil contamination risk in agricultural land; (2) the results of enrichment factor (EF) showed that 29.73% of Cd are moderately polluted, and other HMs were slightly polluted in a small area or near the baseline value (EF ≈ 1); and (3) PMF analysis showed that there are five main sources, pyrite, lead-zinc ore, basalt, carbonate rock, and agricultural production, with the risk contribution ratios of 5.25%, 27.37%, 28.94%, 17.91%, and 20.53%, respectively.

Quantification of Total Phenols and Antioxidants in Coffee Samples of Different Origins and Evaluation of the Effect of Degree of Roasting on Their Levels.

Phenolic and antioxidant compounds have received considerable attention due to their beneficial effects on human health. The aim of this study is to determine the content of total phenols and antioxidants in fifty-two coffee samples of different origins, purchased from the Jordanian local market, and investigate the effect of the degree of roasting on the levels of these compounds. The coffee samples were extracted using the hot water extraction method, while Folin–Ciocalteu (FC) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay methods were used to analyze these compounds. The results showed that the highest content of total phenol (16.55 mg/g equivalent to GAE) was found in the medium roasted coffee, and the highest content of antioxidants (1.07 mg/g equivalent to TEAC) content was found in the green coffee. Only light and medium roasted coffee showed a significant correlation (p < 0.05, R2 > 0.95) between the average of total phenolic and antioxidant content. A negative correlation between the antioxidant content and the degree of roasting (p < 0.05, R2 > 0.95) were shown, while it did not correlate with phenolic contents. Previously, a positive correlation between antioxidant and chlorogenic acids content was observed, with no correlation between the origin of coffee samples nor heavy metal content, which was previously determined for the same coffee samples. These findings suggest that the antioxidant content for coffee extracts is largely determined by its chlorogenic acid content, rather than the coffee origin or total phenolic and heavy metals content.

Characterization of physicochemical parameters and bioavailable heavy metals and their interactions with microbial community in arsenic-contaminated soils and sediments.

Mobility and toxicity of heavy metal contamination in the environment are highly dependent on its bioavailability. Most of previous studies focused on total heavy metal contents and their influence on microbial community in soils and sediments. Little were concerned about bioavailable fractions. In the current study, soil and sediment samples were collected near an abandoned realgar mine in Shimen County, China. Bioavailable heavy metals including Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, Sb, and Pb in the samples were extracted using three-step sequential extraction method. Interactions among physicochemical parameters, total and bioavailable heavy metals, and microbial community in the collected samples were investigated. The study area has been severely contaminated by As with a concentration up to 2158mg·kg-1 detected. The result of principal component analysis showed that the abundance of operational taxonomic units (OTUs) in the soils were obviously different from those in the sediments. In the soil samples, pH made a dominant contribution on the OTU abundance of microbial community. Correlation analyses revealed that the alpha diversity indices and microbial taxon were most correlated with bioavailable fractions of heavy metals in all the samples. That means bioavailable heavy metals rather than total heavy metals or physicochemical parameters played a more important role on richness and diversity of microbial community. Little connections were observed between microbial community and As no matter total concentration or bioavailable fraction. However, bioavailable Fe and Mn were recognized as the major driving force shaping the taxonomic structure of microbial community due to their relatively high concentrations and high affinity to other heavy metal contamination in soils and sediments.

Assessment of aflatoxin and heavy metals levels in maize and poultry feeds from Delta State, Nigeria

The aim of this study was to determine the concentration of total aflatoxin and heavy metals (lead cadmium, chromium and copper) in poultry feed and ingredients from two regions (north and central) in Delta State, Nigeria. A total of 120 samples collected (comprising of maize, soybean meal, layers mash and broiler finisher) directly from poultry farms, feed mills and poultry feed dealers were analysed for moisture content, total aflatoxin and heavy metals (lead, cadmium, chromium and copper) concentrations. Moisture content was analysed using standard Association of Official Agricultural Chemists method, while total aflatoxin and heavy metals concentrations were determined by enzyme-linked immunosorbent assay and atomic absorption spectrometry, respectively. Total aflatoxins concentrations ranged from 12.0 to 20 µg/kg and 21 to 31 µg/kg in samples from north and central region, respectively. Apart from maize, aflatoxin content in other samples from the north was marginally lower (18–20 µg/kg) than permitted levels. On the other hand, aflatoxin levels in samples from the central were all above tolerable limits. Copper content in samples was less than permissible limit, while 44.4, 29.1 and 21% of samples had concentrations of lead, cadmium and chromium, respectively, above permissible limit. The presence of aflatoxin and lead in poultry feeds above permissible limits of 20 µg/kg and 5 mg/kg, respectively, may pose a risk for animal productivity and human health.

Floodplain soils contamination assessment using the sequential extraction method of heavy metals from past mining activities

Floodplains are among the most precious and threatened ecosystems in the world. The study deals with floodplain soil contamination caused by 8 heavy metals (HMs) (Cd, Co, Cr, Cu, Mo, Ni, Pb, Zn) originating and transported from old mine works along the Štiavnica River in Slovakia. We determined the total HMs content and the HM fractions using BCR sequential extraction method. We selected 12 alluvial sites (AS), two contaminated sites (CS), and one reference site (RS). The sampling points were located within the riparian zones (RZ), arable lands (AL), and grasslands (GL). We confirmed soil contamination by HMs and the related ecological risk by different factors. The contamination by HMs at many AS localities was similar or even higher than at CS localities. The highest contamination factor was calculated for Cu (39.8), followed by Pb (27.4), Zn (18.2), and Cd (7.2). The HMs partitioning in the different fractions at the CS and AS localities revealed that Cd, Zn, and Pb were mainly associated with the exchangeable and reducible fractions, while Cu was mainly associated with the oxidisable fraction. The soil properties were selectively correlated with the HM fractions. Based on the ANOVA results, the effect of different ecosystem types on HM fractions was revealed.

Impacts of wet thermal treatment on heavy metals speciation in contaminated waste activated sludge using a modified sequential extraction scheme

The mobility and the bioavailability of heavy metals in waste activated sludge were determined according to their total content and chemical speciation. A modified three-step sequential extraction procedure was used to determine the total content and metal speciation distribution pattern of various heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) pretreated at a temperature of 100 °C to 200 °C. It was found that the organics solubilization was enhanced at higher temperature, increased by 1.75, 183 and 3.03 folds over the soluble chemical oxygen demand (SCOD) at 100 °C. The total contents of Cd, Pb and Zn exceeded the threshold value established in GB/T standard 23486 (2009), as a function of pH, due to the pollution from the local nonferrous metals industry. For most cases, the impacts of thermal pretreatment on the species distribution were limited and obscure. Cr was the only element showing a potential risk of metal mobilization, such that its residual fraction shifted towards oxidizable fraction at higher treatment temperature. The speciation distribution pattern of Ni, Cr, Cu, and Zn showed potential risks of contamination due to their bioavailability, mobility, or toxicity.

Development and Validation of Procedures for Determination of Elemental Toxicants in Herbal Substances and Herbal Medicinal Products

When the approach to quality control of herbal substances (HSs) and herbal medicinal products (HMPs) changed from determination of the total content of heavy metals by calorimetry to selective determination by spectrometric techniques, many manufacturers of such products failed to meet the new requirements in their registration dossiers. Test procedures submitted by manufacturers often need to be clarified, and validation protocols often lack data.The aim of the study was to provide recommendations to HS and HMP manufacturers on the choice of test methods, materials, reagents, methods of organic matrix mineralisation, and main validation parameters, as well as recommendations on validation of the procedure for elemental toxicants determination, and preparation of the “Heavy metals and arsenic” part of the regulatory submission.Materials and methods: the study included analysis and systematisation of scientific literature, requirements of the Russian and foreign pharmacopoeias, guidelines, manuals on instrumental methods of analysis, and first-hand experience in elemental analysis of various types of HSs and HMPs.Results: the authors formulated recommendations on the choice of sample mineralisation conditions for quantification of elemental impurities in biological products, and substantiated requirements for the reagents, materials, and equipment. The paper compares different methods of elemental analysis. It was demonstrated that the main mistakes made by manufacturers stem from disregard to the organic matrix effect on the measurement results and lack of agreement between the impurity concentration being determined and the range of the calibration curve used. The paper gives acceptance criteria for validation parameters of test procedures for heavy metals and arsenic determination in HSs and HMPs.Conclusions: it is not correct to use reference standards containing heavy metals as inorganic salts not bound to organic compounds, for HS and HMP analysis. The criteria given in the European Pharmacopoeia and the United State Pharmacopoeia can be used for a number of validation parameters, when they are not included in the Russian Pharmacopoeia.

Health risk assessment of heavy metals and poly-aromatic hydrocarbons in particulate matter adsorbed by indoor air purifiers

Particulate matter (PM) adsorbed by air purifiers, normally used in residential buildings, was collected and analysed by this study. The concentrations of eight heavy metals and 16 poly-aromatic hydrocarbons (PAHs) in PM were determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES) and gas chromatography-mass spectroscopy (GC-MS). The health risk of heavy metals and PAHs was assessed using the health assessment model recommended by the US Environment Protection Agency (EPA). The results showed that the total concentrations of heavy metals during the heating period and non-heating period were 771.27 mg/kg and 441.10 mg/kg, respectively. The carcinogenicity and non-carcinogenicity of chemicals found are higher during the heating period than the non-heating period. The exposure of children was higher than that of adults. Eight heavy metals would pose non-carcinogenic risks for children, but four of these would pose carcinogenic risks for adults and children. The total concentrations of 16 PAHs during the heating period and non-heating period were 106.69 μg/kg and 68.72 μg/kg, respectively. Total toxicity equivalents (TEQs) were 16.37 μg/kg and 9.20 μg/kg, respectively. Among them, 4-rings PAHs accounted for the highest proportion, followed by 5-rings PAHs and 6-rings PAHs. The proportion of 2-rings and 3-rings PAHs were the lowest. 16 PAHs could pose a high carcinogenic risk to adults and children during the heating period, and there was a potential carcinogenic risk during the non-heating period.

Relationships between airborne microbial community diversity, heating supply patterns and particulate matter properties

Airborne microbes play critical roles in atmospheric ecology and human health, while the connections of microbial community with anthropic activity, such as heating supply patterns and chemical compositions of particulate matter (PM), remain unclear. The present study demonstrated that district heating supply regions exhibited higher microbial richness than non-district heating supply regions, and microbial richness in PM1 (aerodynamic diameter ≤ 1 µm) was significantly lower than that in PM10 (aerodynamic diameter ≤ 10 µm). Gram-positive bacteria were dominant, and Bacilli accounts for 85% of the noted bacteria. The total concentrations of heavy metals, polycyclic aromatic hydrocarbons (PAHs) and water-soluble ions increased with PM sizes. Heavy metals and PAHs in non-district heating supply regions showed significantly higher concentrations than that in district heating supply regions. Most of tested chemical compositions negatively contributed to microbial community diversity, except for Zn, Cr, Pyrene (Pyr), and Benzo[a]pyrene (Bap). The above results were also affected by heating supply patterns (district heating supply and non-district heating supply). There was a positive correlation between microbial community richness and •OH concentration, and microbial community richness decreased as PM specific surface area increased. This work reveals connections between the properties of PMs and the microbial community diversity with heating supply patterns, and gives novel insights to atmospheric health and carbon neutrality.

Heavy Metal Concentration in Neotropical Aquatic Snakes (Helicops pastazae) and Its Potential as a Bioindicator of Water Pollution.

The purpose of this study was to test the potential role of the aquatic snake Helicops pastazae as an indicator of water pollution caused by heavy metals. In particular, we tested whether the total heavy metal concentration is related to (1) the position (upstream vs downstream) of the sampling point and its distance from the point where wastewater is discharged; (2) the taxonomic group studied: piscivorous snakes vs characid fish that occupy the same habitats; and (3) the organ or tissue examined: snake liver versus muscle. We used atomic absorption spectrophotometry with electrothermal atomization to quantify cadmium (Cd), chromium (Cr) and lead (Pb) and found significant differences between some of the sampling points, with particularly high metal concentrations detected upstream at point 1. However, we found no clear spatial pattern nor any significant differences in the concentration of any of the metals in fish and snake muscle, suggesting that both species accumulate similar amounts of the sampled elements. With regard to interactions, snake liver had the highest concentrations of Cd, while muscle had the highest concentrations of Pb and Cr, which may indicate tissue affinity differences for certain metals. Altogether, our results indicate that H. pastazae accumulates contaminants differentially, depending on the tissue and location, which highlights their potential as bioindicators of water contamination. Further research is necessary to understand their role as bioindicators based on extensive sampling and environmental contaminant data.

Variation and factors on heavy metal speciation during co-composting of rural sewage sludge and typical rural organic solid waste

In this study, a co-composting of rural organic solid waste (rural sewage sludge, kitchen waste and corn stalks) was conducted to analyze the variation of heavy metals (As, Cu, Cr, Ni, Pb, Hg, and Zn) and their major influencing factors. During composting, significant changes were observed in the total contents of heavy metals (p < 0.01): the total concentrations of As, Cu, Hg, Pb and Zn increased by 7.5%, 54.1%, 26.3%, 15.8%, and 34.2%, whereas that of Cr and Ni decreased by 71.3% and 33.4%, respectively. Heavy metals were mainly bound to the oxidizable and residual fractions. Spearman and Redundancy analysis (RDA) indicated that substances were significantly correlated with the changes in speciation of heavy metals, among all the factors, while pH and temperature were the dominating environmental influencing parameters. Several metal-resistant bacterial genera (Pseudomonas, Paenibacillus, Bacillus, Acinetobacter, Desulfovibrio, and Ochrobactrum, etc) were observed, with significant explanatory capacity for the changes in heavy metals. Composting showed a poor effect on heavy metal passivation, except for that of As. After composting, the heavy metal contents were consistent with the application standards. The evaluation of potential ecological risk showed a high cumulative ecological risk (336.9) of heavy metals. This study provides technical support and practical information for the disposal and safe recycling for rural organic solid waste.

Assessment of heavy metal pollution in sediments of the Sonora River basin impacted by mining activities

The objective of this research is to assess of heavy metal pollution and its fractionation in sediments of the Sonora and Bacanuchi rivers located in arid and semi-arid climates. Sediment quality guidelines (U.S. EPA; SQGs), enrichment factor (EF) and geoaccumulation index (Igeo) were used to evaluate the extent of heavy metal pollution. Total heavy metals concentrations for both rivers were as follows (mg/kg): Cd (< BDL), Cu (2 - 103), Cr (5 - 27), Fe (9156 - 34343), Mn (114 - 573), Ni (22 - 38), Pb (12 - 59), and Zn (27 - 111). According to sediment quality guidelines Cr, Ni, Pb, and Zn were classified as moderately polluted, while Cu and Fe were strongly polluted. Metals predominated in geochemical fractions in the following order: Residual> Fe/Mn oxides> interchangeable> organic matter. A significant proportion of heavy metals (Cu, Mn, Ni, Pb, Zn) was associated to the nonresidual fraction, proving that those metals have greater mobility and may be bioavailable to living beings. EF values indicated that Cu, Cr, Mn, Ni, Pb, and Zn come from enriched sources due to anthropogenic activities. In both rivers, Igeo values indicated non contaminated or moderately contaminated levels in the sediments. The present study confirms an anthropogenic source of heavy metals, which could be a danger for biota in the surrounding areas, due to its mobility and bioavailability. Therefore, it is recommended to monitor water and sediment quality periodically.

Effects of urban wastewater application on growth, biomass, nutrition, and heavy-metal accumulation of Populus nigra L. “62/154,” P. alba L. “20/45,” P. euramericana (Dode) Guinier “92/40,” and Salix excelsa S.G. Gmel grown in heavy-metal contaminated soil

Iran is located in a dry climate zone, and climate change has substantially reduced its precipitation and water resources. Reusing wastewaters from urban communities can meet some requirements for irrigation and fertilization of tree plantations in arid environments, leading to sustainable wastewater recycling, enhanced biomass production, and reduced land degradation. The objective of this study was to test the growth, biomass, nutrition, and heavy-metal accumulation of poplars [Populus nigra L. “62/154,” P. alba L. “20/45,” P. euramericana (Dode) Guinier “92/40”], and willow (Salix excelsa S.G. Gmel) in a pot experiment at four and eight months after planting when grown in soils irrigated with tap water (SITW) and wastewater (SIWW). After four months, SIWW treatment had no significant effect on growth, biomass, nor absorption of macronutrients. After eight months, SIWW treatment of poplars and willow significantly (p = 0.000) increased: (1) height, (2) leaf area, (3) root, stem, leaf, and total biomass, and (5) phytoextraction and phytoaccumulation of macro-/micro-nutrients and heavy metals in tree tissues, over trees receiving the SITW treatment. There were significant differences in growth, biomass, and accumulation of micronutrients and heavy metals in poplar versus willow tissues, with the highest biomass production and tissue-specific content of heavy metals in P. nigra trees, and the greatest total concentrations of heavy metals in P. alba and S. excelsa trees. In contrast, uptake of Fe, Cu, Ni, Cr and Pb were similar between poplar and willow, and phytoaccumulation of these elements was primarily in the roots. Leaf concentrations were highest for Zn and Mn. While P. nigra outperformed all other species overall, tolerance index (TI; defined as the tolerance to the heavy metals as calculated by the ratio of the biomass of SIWW trees relative to SITW trees) values exceeding 100% for all one-year-old poplar and willow trees demonstrated that they can be considered for planting in soil affected by urban wastewaters with similar contaminant profiles as in the current study.