Digestion Methods for Total Heavy Metals in Sediments and Soils

The objectives of this study were to analyze the total contents of Cd, Cr, Cu, Ni, Pb, and Zn in the freshwater sediments and the arable and non-arable soils of Taiwan, and to compare the different digestion methods for their determination. Two hundred and thirty-nine freshwater sediments were collected from the Fei-Tsui Reservoir Watershed (FTRW) in northern Taiwan. Forty-two surface (0–15 cm) and subsurface (15–30 cm) soil samples were likewise collected from 21 representative arable soils derived from various parent materials and with varying weathered degrees in different regions of Taiwan. In addition, one hundred and ninety-four non-arable soils were collected from the different forest regions, industrial parks, resident areas, and commercial areas. Several digestion methods including the aquaregia and different combinations of concentrated acids (HClO₄, HNO₃, H₂SO₄, or HF) were compared. All samples were digested both by the aqua regia method and the Baker and Amacher method for Cd, Cr, Cu, Ni, Pb, and Zn. The Reisenauer method was used for Cr and the Burau method for Pb further. The results indicate that the best digestion methods to analyze the total contents of heavy metals in the sediments and soils were recommended as follows: the Baker and Amacher method for Cd, Cr,Cu, Ni, and Zn; the Reisenauer method for Cr, but for simplicity the Baker and Amacher method is also recommended as the flexible method for the total analysis of Cr; the aqua regia method for Cu, Ni, and Zn; and the Burau method for Pb.     

Comparison of methods for measuring heavy metals and total phosphorus in soils contaminated by different sources

The relationships between the concentrations of zinc (Zn), lead (Pb), copper (Cu), nickel (Ni) and chromium (Cr) as measured by X-ray fluorescence analysis (XRF), aqua regia, and HNO₃ pressure digestion were studied in soil samples covering a wide range of heavy metal concentrations. The soils were contaminated by sewage sludge, exhaust depositions, river sediments of mining residues, and dump material. The question was addressed whether the source of heavy metals or other soil properties affect the relationship between these three methods. The aqua regia-digestible fraction of the five heavy metals reached on average 64% of the XRF-detectable content. The pressure accelerated HNO₃-digestible fraction of the five heavy metals was on average 71% of the XRF-detectable content; the respective phosphorus (P) fraction reached a median of 75%. This suggests that HNO₃ pressure digestion can also be used for characterizing the total P content of soils. Aqua regia extraction and HNO₃ pressure digestion gave similar values for Zn, Pb, and Cu, which dominate the heavy metal load of most contamination sources. Significantly higher Cr values were obtained by HNO₃ pressure digestion than by aqua regia extraction. Additionally, the Cr contents were affected by the source, e.g. sewage sludge had relatively high contents of aqua regia and HNO₃ pressure extractable contents in comparison to the XRF values. The element-specific relationships between the three methods were all highly significant. However, the respective multiple linear regression models were in most cases affected by soil organic carbon (C), in some cases by clay or soil pH.     

Relationships of Heavy Metals in Natural Lake Waters with Physico-chemical Characteristics of Waters and Different Chemical Fractions of Metals in Sediments

The relationships between heavy metal concentrations and physico-chemical properties of natural lake waters and also with chemical fractions of these metals in lake sediments were investigated in seven natural lakes of Kumaun region of Uttarakhand Province of India during 2003–2004 and 2004–2005. The concentrations of Cr, Mn, Fe, Ni, Cu, Zn, Cd and Pb in waters of different lakes ranged from 0.29–2.39, 10.3–38.3, 431–1407, 1.0–6.6, 5.3–12.1, 12.6–166.3, 0.7–2.7 and 3.9–27.1 μg l^?1 and in sediments 14.3–21.5, 90.1–197.5, 5,265–6,428, 17.7–45.9, 13.4–32.0, 40.0–149.2, 11.1–14.6 and 88.9–167.4 μg g^?1, respectively. The concentrations of all metals except Fe in waters were found well below the notified toxic limits. The concentrations of Cr, Mn, Ni, Cu, Zn, Cd and Pb were positively correlated with pH, electrical conductivity, biological oxygen demand, chemical oxygen demand and alkalinity of waters, but negatively correlated with dissolved oxygen. The concentrations of Cr, Ni, Zn, Cd and Pb in waters were positively correlated with water soluble + exchangeable fraction of these metals in lake sediments. The concentrations of Zn, Cd and Pb in waters were positively correlated with carbonate bound fraction of these metals in lake sediments. Except for Ni, Zn and Cd, the concentrations of rest of the heavy metals in waters were positively correlated with organically bound fraction of these metals in lake sediments. The concentrations of Cr, Mn, Ni, Cu and Zn in waters were positively correlated with reducible fraction of these metals in lake sediments. Except for Cd, the concentrations of rest of the metals in waters were positively correlated with residual fraction and total content of these heavy metals in lake sediments.     

Heavy Metals in Freshly Deposited Stream Sediments of Rivers Associated with Urbanisation of the Ganga Plain,India

Freshly deposited stream sediments from six urban centres of the Ganga Plain were collected and analysed for heavy metals to obtain a general scenery of sediment quality. The concentrations of heavy metals varied within a wide range for Cr (115–817), Mn (440–1 750), Fe (28 700–61 100), Co (11.7–29.0), Ni (35–538), Cu (33–1 204), Zn (90–1 974), Pb (14–856) and Cd (0.14–114.8) in mg kg^-1. Metal enrichment factors for the stream sediments were <1.5 for Mn, Fe and Co; 1.5–4.1 for Cr, Ni, Cu, Zn and Pb; and 34 for Cd. The anthropogenic source in metals concentrations contributes to 59% Cr, 49% Cu, 52% Zn, 51% Pb and 77% Cd. High positive correlation between concentrations of Cr/Ni, Cr/Cu, Cr/Zn, Ni/Zn, Ni/Cu, Cu/Zn, Cu/Cd, Cu/Pb, Fe/Co, Mn/Co, Zn/Cd, Zn/Pb and Cd/Pb indicate either their common urban origin or their common sink in the stream sediments. The binding capacity of selected metals to sediment carbon and sulphur decreases in order of Zn > Cu > Cr > Ni and Cu > Zn > Cr > Ni, respectively. Stream sediments from Lucknow, Kanpur, Delhi and Agra urban centres have been classified by the proposed Sediment Pollution Index as highly polluted to dangerous sediments. Heavy metal analysis in the <20-μm-fraction of stream sediments appears to be an adequate method for the environmental assessment of urbanisation activities on alluvial rivers. The present study reveals that urban centres act as sources of Cr, Ni, Cu, Zn, Pb and Cd and cause metallic sediment pollution in rivers of the Ganga Plain.     

Transport and distribution of heavy metals in Cauvery river

Heavy metal transport in Cauvery river chiefly takes place in the particulate form. Tributaries Hemevathi and Kabini draining highly mineralized areas contribute significantly to the heavy metal load of the Cauvery river. Particulate metal transport is influenced by the presence of major dams built across the river. Factor analysis of the elemental data identifies two major group of heavy metals, (a) Fe, Mn, Cr, V and Ti and (b) Cu, Pb and Zn in the suspended sediments of Cauvery river. Heavy metals in surface sediments show wide variations in their concentrations due to the non-uniform grain size distribution of the sediments. The elements Fe, Mn, Pb, Cu, Zn, Ni, Co and As are dominantly present in the <20 μm fraction of the river sediments. Speciation studies show that Fe-Mn oxide phase held the largest share of heavy metals in the sediments. The depth variation of heavy metals in the core sediments suggest their similar mobility during diagenesis. Geoaccumulation indices calculated suggest that Cd, Zn, Cr, Pb, Cu and Ni are enriched in sediments several times over background values.     

Determination of trace elements in Saudi Arabian soils by inductively coupled plasma mass spectrometry (ICP‐MS)

Abstract

Saudi Arabian soil samples from different locations have been collected and analyzed for traces of barium (Ba), cobalt (Co), nickel (Ni), titanium (Ti), vanadium (V), silver (Ag), gold (Au), copper (Cu), lithium (Li), and lead (Pb). Inductively coupled plasma mass spectrometry (ICP/MS) has been found to be useful for soil analysis. Two commonly used digestion methods, one employing nitric acid and the other aqua regia, are employed for sample pretreatment. Percentage recovery of added element quantities are found to be within the 97.4 to 101.2% range for Ba, Co, Ni, Ti, and V using aqua regia digestion and within the 95.0 to 05.0% range for Ag, Au, Cu, Li, and Pb when using the nitric acid digestion method. The percentage relative standard deviation (% RSD) for five replicate samples for the two digestion procedures is less than 5% for the analyzed elements.     

Evaluation of regional heavy metal deposition by multivariate analysis of element contents in pine tree barks

The airborne immission of heavy metals in the conservation area “Dübener Heide” nearby Bitterfeld was evaluated by biomonitoring studies with bark samples of 60-years-old scots pine (Pinus sylvestris L.). Nitric acid digestion and hydrochloric acid extraction of bark was followed by ICP-AES and ICP-MS analysis of the elements Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn. Fe and especially Cr were only partly soluble in hydrochloric acid. These elements deposited mostly as insoluble oxides, and their contents in the bark correlate significantly with Ca and S as elements of alkaline and acid deposition. Factor and cluster analysis of all element contents are used for the characterization and evaluation of heavy metal deposition types, which is shown to be a useful tool in forest monitoring control.     

Total soil heavy‐metal concentrations and mobile fractions after 10 years of biowaste‐compost fertilization

The accumulation of heavy metals (HMs) in soils is the most often cited potential risk of compost application. As the ecological effects of metals are related to mobile fractions rather than to total concentrations in the soil, we measured the total (aqua regia–extractable) HM concentrations, the readily available water‐soluble and the potentially bioavailable LiCl‐extractable fraction of soil HMs in a field experiment after 10 y with total applications of 95, 175, and 255 t ha^–1 biowaste compost (fresh matter). Total soil concentrations of Cd, Cr, Cu, Ni, and Pb in the compost treatments were not significantly higher than in the unfertilized control. Total Zn concentrations increased in the treatment with the highest application rate, as expected from the calculation of the Zn load in the composts. In the mobile fractions, as measured in soil saturation extract and LiCl extract, Cd and Pb were not detectable. Concentrations of Cr, Ni, and Zn were in the range published for unpolluted soils in other studies and did not show any differences according to treatment. Easily exchangeable Cu (in LiCl extract) was increased with compost fertilization, most probably due to complexation with low‐molecular organic complexants. Except for Cd and Zn, the results of the mobile HM fractions in the soil were in good agreement with plant HM concentrations. In conclusion, fertilization with high‐quality biowaste compost at such rates and after 10 y of application gives no cause for concern with regard to both total HM concentrations and available HM fractions.     

Evaluation of Different Extraction Methods for the Assessment of Heavy Metal Bioavailability in Various Soils

The main objective of this study was to compare the effectiveness of different methods (heavy metals in pore water (PW), diffusive gradients in thin films (DGT), diethylene triamine pentaacetic acid (DTPA) extraction, and total heavy metals (THM) in soil) for the assessment of heavy metal bioavailability from soils having various properties and heavy metal contents. The effect of soil heavy metal pollution on shoot yield and sulfatase enzyme activity was also studied. Wheat (Triticum aestivum) was grown in different soils from Spain (n?=?10) and New Zealand (n?=?20) in a constant environment room for 25 days. The bioavailabilities of Cd, Cr, Cu, Ni, Pb, and Zn were assessed by comparing the metal contents extracted by the different methods with those found in the roots. The most widely applicable method was DGT, as satisfactory Cu, Ni, Pb, and Zn root concentrations were obtained, and it was able to distinguish between low and high Cr values. The analysis of the metal concentrations in PW was effective for the determination of Cr, Ni, and Zn content in root. Copper and Pb root concentrations were satisfactorily assessed by DTPA extraction, but the method was less successful with determining the Ni and Cr contents and suitable just to distinguish between high and low concentrations of Zn. The THM in soil method satisfactorily predicted Cu and Pb root concentrations but could only be used to distinguish between low and high Cr and Zn values. The Cd root concentration was not successfully predicted for any of the used methods. Neither shoot yield nor sulfatase enzyme activity was affected by the metal concentrations.     

Predicting sediment metal concentrations in lakes without point sources 1

Surficial sediments (0 to 2 cm) from 189 sites in 52 Quebec and Ontario lakes were analyzed for Al, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn by atomic adsorption spectrometry after extraction in dilute aqua regia. Empirical models using sediment texture (water content), site morphometry (depth) and geology (categorical variables) as predictors explain 82 to 87% of the between-site and between lake variation in sediment concentrations of Cu, Cr, Ni, Pb, and Zn, and 52 to 68% of the variation of Al, Co, Fe, and Mn. Over a broad geologic range, geologic variables are only significant in models predicting Co, Cr, and Ni. These three elements are low in concentration in lakes with catchments on the Grenville shield, while Cr and Ni are enriched in catchments containing ophiolite geology. These models explain both between-site and between-lake variation in sediment metal concentrations, and due to the lack of geologic influence on most metals, may be valid for other regions. The models appear promising as a means to identify point source contamination without assumptions about the relevant sediment fractions or inter-element relationships.     

Increasing the Knowledge of Heavy Metal Contents and Sources in Agricultural Soils of the European Mediterranean Region

This paper contributes to increase the knowledge of the contents and sources of heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) to agricultural soils in Castellón province (Spain), a representative area of the European Mediterranean region. The surface horizons of 77 agricultural soils under vegetable crops were sampled and heavy metals were analysed by atomic absorption spectroscopy (AAS) after microwave extraction using the USEPA 3051A method. Mean heavy metal contents were similar to those obtained in other areas of this region. However, heavy metal contents (e.g. Cr, Pb) in some soils were above the maximum limit set in the 86/278/CEE Directive. Multivariate analysis (correlation analysis and principal component analysis – PCA) was performed so as to identify the sources of heavy metals to soils. Co, Fe and Ni were highly correlated amongst them (r?>?0.800; p?<?0.01), whereas Cr and Mn were less correlated with Co, Fe and Ni (r?>?0.500; p?<?0.01). Other relationships among heavy metals (i.e. Cu, Pb and Zn) were also identified, although correlation coefficients were not so high as those among Co, Fe and Ni (r?<?0.500; p?<?0.01). Contents of Co, Fe, Mn and Ni were interpreted to be mainly associated with parent rocks corresponding to the first principal component (PC1). On the other hand, Cd, Cu, Pb and Zn were interpreted to be mainly related to anthropogenic activities and comprised the second (Pb and Zn) and the third (Cd and Cu) principal components (PC2 and PC3, respectively), designated as anthropogenic components. Remarkably, Cr appears to be related in the study area to both the lithogenic and the anthropogenic components. Lithogenic elements were highly correlated with soil properties. Positive relationships with CEC (r?>?0.200; p?<?0.05) and clay (r?>?0.400; p?<?0.01), and negative relationships with carbonates (r?>??0.400; p?<?0.01) and sand (r?>??0.300; p?<?0.01) were observed. Anthropogenic elements were less correlated with soils properties, since these elements are generally more mobile because they form more soluble chemical species associated to anthropogenic sources. Particularly, no correlation was found between Cd and Zn and soil properties. These findings extend results achieved in other parts of the region, highlighting the need to set soil quality standards in order to declare soils affected by anthropogenic pollution, particularly in the case of anthropogenic metals such as Cd, Cu and Pb, and also Cr and Zn in some areas. Further knowledge from other areas in this region would improve the basis for proposing such standards at regional level, which is a priority objective in Europe according to the European Thematic Strategy for Soil Protection.     

Influence of pH on the release and chemical fractionation of heavy metals in sediment from a suburban drainage stream in an arid mine-based oasis

Purpose

The objectives of this study were to explore the influences of pH on the release of Cu, Zn, Cd, Pb, Ni, and Cr in sediments derived from the upstream, middle, and downstream reaches of Dongdagou stream in Gansu Province, Northwest China, and to examine the fractionation changes of heavy metals in the sediments after reaching their release equilibrium under different pH conditions.

Materials and methods

Sediment samples were obtained using a stainless steel grab sampler to collect the uppermost 10 cm of sediment from the channel bed. The pH-dependent release experiment was conducted in the solid-to-liquid ratio of 1:20 at different pH values (2, 4, 6, 8, 10, and 12) at room temperature. The total Cu, Zn, Cd, Pb, Ni, and Cr concentrations in the sediments were digested using an acid digestion mixture (HNO₃ + HF + HClO₄) in an open system. Metal fractionation of selected sediments was obtained using the Tessier sequential extraction procedure. Heavy metal concentrations in the samples were determined using atomic absorption spectrophotometry.

Results and discussion

The mean concentrations of heavy metals in sediments decreased in the following order: Zn (1676.67 mg kg^?1) > Pb (528.65 mg kg^?1) > Cu (391.34 mg kg^?1) > Cr (53.48 mg kg^?1) > Ni (34.27 mg kg^?1) > Cd (11.53 mg kg^?1). Overall, the solubility of Cu, Zn, Cd, Pb, and Ni decreased with increasing pH, and they were strongly released at pH 2. Moreover, the solubility of Cr increased with increasing pH, and its release was highest at pH 12. After reaching the release equilibrium of heavy metals under different pH conditions, the percentages of organic Cu, Zn, Cd, and Fe-Mn oxyhydroxide Pb decreased, compared to their initial fractions. The residual fractions of Ni and Cr were dominant, regardless of pH.

Conclusions

The average concentrations of Cu, Zn, Cd, and Pb in sediments were highly elevated compared with the soil background values in Gansu Province, China. The results of this pH-dependent release experiment showed that the release behaviors of Cu, Zn, Pb, and Cr followed an asymmetric V-shaped pattern, whereas Cd and Ni followed an irregular L-shaped pattern. The changes in the release of heavy metals in sediments were related to their redistribution between chemical fractionations.

     

Comparison of two methods of sample preparation for determination by atomic absorption spectro‐photometry of heavy metals in soils and sediments

Abstract

Two commonly used methods of dissolution of heavy metals in soils and sediments for atomic absorption spectrophotomety (AAS) determination were compared. Dry ashing and subsequent dissolution with 3 N HCl in a block digestor was shown to give a better estimate of the aqua regia‐soluble fraction than wet ash digestion with a mixture of HNO₃ and HClO₄ acids using reference materials. But both methods extracted significantly less than the certified total contents of most metals.

In soils and sediments from SW Spain, the amounts extracted by the block heater method were generally greater than those obtained by wet ash digestion. In agricultural soils, highly significant differences were found between the amounts of Fe, Cu, and Zn extracted by both methods, but the significance decreases if both methods are used on soils or sediments from mining areas where metal contents are likely to be from recent deposits.     

Vergleich zwischen Total- und königswasserextrahierbaren Elementgehalten in natürlichen Böden und Sedimenten

Comparison between total- and aqua regia extractable contents of elements in natural soils and sediments Total- and aqua regia extractable contents of 19 elements from 28 soil samples with widely varying composition of the ISE ring analytical program (INTERNATIONAL SOIL-ANALYTICAL EXCHANGE) of the year 1995 to 1997 have been taken to find out the comparability between the two fractions. The relations between the two fractions and pH, organic matter and clay content were considered by means of single and multiple regressions. The correlations between the total and aqua regia extractable contents of As, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Ni, P, Pb and Zn are very close, whereas Al, Ba, K, Na and Sr are not or only weakly correlating. The multiple regressions show that the content of some aqua regia extractable elements and the proportion (in %) of the total contents is correlated with pH, organic matter and/or content of clay. In the same way the proportion of aqua regia extractable elements is closely related (except Fe and Hg) to the soil pH. Hereby the proportion of the aqua regia extractable content increases with increasing pH in the range 3,5—7,7. The determined equations are tested for As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb and Zn by using the values of certified reference material. The estimated aqua regia extractable contents are being compared with values of reference material. The average proportion of the calculated to the measured aqua regia contents of an element in percent are 99 for Zn, 98 for Co, Cu and Mn, 94 for Cd, 90 for Ni, 88 for Cr, 105 for Hg, 113 for As and 114 for Pb.     

云南滇池沉积物中重金属的形态分布特征

Fractionation of heavy metals in sediments can help in understanding potential hazards of heavy metals. The present study analyzed total concentrations and fractions of selected heavy metals （Cd, Cr, Cu, Pb, and Zn） in surface sediments from Dianchi Lake, Yunnan Province, China, as well as factors that may affect distributions of the various heavy metal fractions. Total concentrations of the heavy metals decreased in the order Zn 〉 Cu 〉 Pb 〉 Cr 〉 Cd. These heavy metals, except Cr, were much higher than their background levels, indicating that Dianchi Lake was polluted by Cd, Zn, Pb, and Cu. Cadmium occurred mainly as the non-residual fraction （sum of the HOAc-soluble, reducible, and oxidizable fractions） （97.6%）, and Zn （55.7%） was also predominantly found in the non-residual fraction. In contrast, most of the Cr （88.5%）, Pb （81.8%）, and Cu （59.2%） occurred in the residual fraction. Correlation analysis showed that total heavy metal concentrations, organic matter and reducible Fe were the main factors affecting the distributions of the various heavy metal fractions. In the Walhai section of Dianchi Lake （comprising 97% of the lake area）, the concentrations of Cd, Zn, Pb, and Cu in the non-residual fraction were significantly lower （P ≤ 0.01 or 0.05） than those of the Caohal section （3% of the lake area）. This indicated that potential heavy metal hazards in the Caohai section were greater than the Waihai section.     

Extractability and plant uptake of heavy metals in alum shale soils

Abstract

Fifty soil samples (0–20 cm) with corresponding numbers of grain, potatoes, cabbage, and cauliflower crops were collected from soils developed on alum shale materials in Southeastern Norway to investigate the availability of [cadmium (Cd), copper (Cu), zinc (Zn), lead (Pb), nickel (Ni), and manganese (Mn)] in the soil and the uptake of the metals by these crops. Both total (aqua regia soluble) and extractable [ammonium nitrate (NH₄NO₃) and DTPA] concentrations of metals in the soils were studied. The total concentration of all the heavy metals in the soils were higher compared to other soils found in this region. Forty‐four percent of the soil samples had higher Cd concentration than the limit for application of sewage sludge, whereas the corresponding values for Ni, Cu, and Zn were 60%, 38%, and 16%, respectively. About 70% the soil samples had a too high concentration of one or more of the heavy metals in relation to the limit for application of sewage sludge. Cadmium was the most soluble of the heavy metals, implying that it is more bioavailable than the other non‐essential metals, Pb and Ni. The total (aqua regia soluble) concentrations of Cd, Cu, Zn, and Ni and the concentrations of DTPA‐extractable Cd and Ni were significantly higher in the loam soils than in the sandy loam soils. The amount of NH₄NCyextractable metals did not differ between the texture classes. The concentrations of DTPA‐extractable metals were positively and significantly correlated with the total concentrations of the same metals. Ammonium nitrate‐extractable metals, on the other hand, were not related to their total concentrations, but they were negatively and significantly correlated to soil pH. The average concentration of Cd (0.1 mg kg^‐1 d.w.) in the plants was relatively high compared to the concentration previously found in plants grown on the other soils. The concentrations of the other heavy metals Cu, Zn, Mn, Ni, and Pb in the plants were considered to be within the normal range, except for some samples with relatively high concentrations of Ni and Mn (0–11.1 and 3.5 to 167 mg kg‘¹ d.w., respectively). The concentrations of Cd, Cu, Zn, Ni, and Mn in grain were positively correlated to the concentrations of these respective metals in the soil extracted by NH₄NO₃. The plant concentrations were negatively correlated to pH. The DTPA‐extractable levels were not correlated with plant concentration and hence DTPA would not be a good extractant for determining plant availability in these soils.     

Heavy metal contents in river sediments

Extensive sample material from river sediments of Carinthia (Austria) was investigated with regard to the contents of heavy metals that are relevant to the environment, Zn, Cd, Pb, Cu, Cr and Ni. The fraction <20 μm was separated from the total sample to minimize the effect of grain size. The disintegration was done with aqua regia. The results were related to the geochemical data of the geological background. Therefore the amount of anthropogenic pollution due to industry and overcrowded areas was determined. Especially the influence of industrial emissions from Pb-Zn smeltings is shown by extremely high values of Zn (18400 ppm), Cd (126 ppm) and Pb (7540 ppm). The contents of Cu, Cr and Ni in the metamorphic rocks from the Central Alps represent the geogenic influences, but the high values from 200 to 300 ppm Cr refer to actions of industries producing highly refrectory materials and chemical industries. The results of the elements zinc and nickel are documented in maps.     

Investigating speciation and toxicity of heavy metals in anoxic marine sediments—a case study from a mariculture bay in Southern China

Purpose

The pollution of marine sediments by heavy metals is still a major concern, especially in zones affected by industry or mariculture. Toxicity of sediment heavy metal contents may be assessed using sequential extraction (SE) procedures, minding inherent constraints of such approaches. In this study, we investigated heavy metal speciation and toxicity in anoxic marine sediments in Zhelin Bay, a mariculture bay in Southern China, using an SE and acid volatile sulfur-simultaneously extracted metals (AVS-SEM) approach.

Materials and methods

Speciation of Cd, Cu, Ni, Pb, and Zn were studied by a modified SE of five fractions, adapted to separate organic and sulfidic metal fractions in anoxic sediments: F1 weak acid soluble (readily available), F2 reducible fraction, F3 organic matter-bound fraction, F4 sulfide-bound fraction, and F5 residually bound fraction. Toxicity predictions based on the sum of non-residual (NR) metal fractions from sequential extraction were compared to predictions based on AVS-SEM.

Results and discussion

Results showed that Cd, Ni, and Pb predominantly occurred in the weak acid soluble fraction (F1), residual fraction (F5), and sulfide-bound fraction (F4), respectively; Cu and Zn were mainly obtained in F4 and F5. Based on the distribution of indicator elements for metal fractions, the SEM from AVS extraction included different yields of non-residual and residual fractions besides the sulfidic fraction. Estimates for potential heavy metal toxicity based on NR metals of the SE procedure were thus based on a better-defined speciation compared to the simplistic approach of the AVS-SEM method.

Conclusions

Based on the contents of NR metals and normalizing them by organic matter content, toxic effects are not expected for any of the sampling sites, irrespective of the presence or absence of mariculture. Using Pearson correlation analysis to identify predominant fractions influencing toxicity, we conclude that toxicity of heavy metals in anoxic sediments can be well predicted by their non-residual heavy metal contents.

     

泉州走马埭典型土壤重金属的赋存形态分析

采用改进的Tessier连续萃取方法研究了泉州走马埭国家农田示范保护区典型土壤中重金属(Cr、Ni、Cu、Zn、Cd、Pb)的化学形态分布,通过土壤重金属的赋存形态分析比较了6种重金属的生物可利用性。研究结果表明,土壤中不同重金属元素化学形态分布具有不同的特点:Cr和Ni主要以残渣态存在,其余形态所占的比例很小;Cu以残渣态含量最高,碳酸盐结合态含量最低;Zn以残渣态为主,可交换态含量最低;Cd以可交换态和碳酸盐结合态为主,水溶态含量最低;Pb以残渣态和铁锰氧化物结合态为主,水溶态含量最低。土壤中除Cd外,Zn、Cu、Cr、Pb、Ni在正常自然条件下相对比较稳定。     

宝鸡市某工业园区灰尘重金属含量、形态及生态风险分析

利用X射线荧光光谱法(XRF)和原子荧光分光光度法(AFS)分析了宝鸡市某工业园区灰尘中重金属的含量。结果表明,宝鸡市某工业园区灰尘中As,Co,Cr,Cu,Hg,Mn,Ni,Pb和Zn的平均含量分别为23.3,16.4,1 591.8,178.2,0.243,346.5,40.2,1 586.2和1 918.8mg/kg,其中,Cr,Cu,Hg,Pb和Zn累积比较明显;铅锌冶炼厂周边灰尘中As,Cu,Hg,Pb和Zn的含量高于电厂。采用修正BCR法(欧洲共同体标准物质局)和原子吸收分光光度法(AAS)研究了灰尘中重金属的形态特征。结果表明,灰尘中Cu主要以残渣态和可氧化态的形式存在,Pb主要以可还原态的形式存在,Zn主要以乙酸可提取态的形式存在,Mn和Co主要以乙酸可提取态和残渣态存在,Ni和Cr主要以残渣态存在。灰尘中Pb,Zn,Co,Mn和Cu有55%~85%可以发生移动,易被生物利用,危害较大。潜在生态风险评价表明,灰尘中重金属的污染及潜在生态风险达到严重水平,铅锌冶炼厂周边灰尘中重金属的污染和潜在生态风险高于电厂。