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.     

Heavy Metal Monitoring Around the Nesting Environment of Green Sea Turtles in Turkey

The concentrations of Cd, Pb, Fe, Cr, Ni, Se, Sb, As and Cu were investigated in the nesting environment of green turtles in Mediterranean Sea near Kazanl?, Mersin-Turkey. Tissues of plants growing on the beach and the adjacent environment, beach sand, sea ground sediment, sea grass as well as the egg shells from the nests were analyzed and the results showed no significant high levels of heavy metals detected. The higher levels of metals (Cr, Cu, Pb, Cd and As) were found in the samples from ground sea sediments. Ni and Sb were found at higher levels in river waters and Fe was at the highest in field soil. The high levels of Pb, Fe and Cd were also detected in sea grass, and the Cr, Cu and Ni in sea lily when comparison made with other plants. The levels of essential elements such as Fe and Cu were detected as the highest in most of the specimens. The herbivorous green turtles might be affected from the heavy metal concentrations in the future, since they feed on mainly sea grass. The accumulation of heavy metals via rivers into the sea might cause some pollution problems.     

Soil properties and metal accumulation by earthworms in the Siena urban area (Italy)

This paper reports the results of a study focused on the metal (Cd, Co, Cr, Cu, Ni, Pb, Sb, U and Zn) distribution in soils and uptake and accumulation by earthworms Nicodrilus caliginosus (Savigny) from urban, peri-urban, green-urban and non-urban zones of Siena municipality (central Italy). The main goal was to define the influence of soil properties and metal soil contents on the uptake of these contaminants by earthworms. Data indicated that Cd, Cu, Pb, Sb and Zn soil contents increased in the following order: non-urban < green-urban < peri-urban < urban soils, suggesting that vehicular traffic affects the distribution of these metals. Pb and Sb were the main soil contaminants and their highest enrichments were found in urban sites where stop-and-go traffic occurs. Concentrations of these traffic-related metals in earthworms showed a distribution pattern similar to that in soil, suggesting that soil contamination influenced the uptake of Cd, Cu, Pb, Sb and Zn by N. caliginosus. There were significant positive correlations between Cd, Pb and Sb earthworm concentrations and their soil contents. The lack of correlation for Cu and Zn could be due to the physiological regulation of these elements by earthworms. Statistical analysis pointed out that the uptake and accumulation of Cd, Cu, Pb, Sb and Zn by earthworms were affected by some soil physicochemical properties such as the organic carbon and carbonate contents that are able to rule the bioavailability of metals in soils.     

长江三角洲近岸水域表层沉积物重金属分布特征及其影响因子

采用ICP-MS测定了不同季节长江三角洲沉积物中重金属(Ni,Cu,Cr,Zn,Cd和Pb)含量并探讨了其影响因子。结果表明:(1)长江三角洲沉积物中Pb和Zn占重金属总量比例最高,Hg和Cd占重金属总量比例较小;沉积物重金属含量均以秋季和冬季最高,夏季次之,春季最低。(2)长江三角洲沉积物中Cr,Cu和Ni元素均以残渣态为主,Zn和Cd主要以弱酸提取态为主,Pb较均匀地分布于不同形态中。(3)长江三角洲沉积物中pH值和电导率基本表现为春季夏季秋季冬季,其中秋季和冬季pH值差异不显著(p0.05),二者显著低于春季和夏季(p0.05);沉积物中全碳、全氮、全磷和全钾含量均以秋季和冬季最高,夏季次之,春季最低,其中不同季节全氮和全钾含量差异均显著(p0.05)。(4)Pearson相关性分析可知,长江三角洲沉积物中Cr,Pb,Cd的弱酸浸提与重金属总量之间表现出显著的正相关关系(p0.05),而6种重金属元素的可还原态与重金属残渣态之间没有显著的相关性(p0.05);Cr,Cu,Pb的弱酸浸提与可还原态没有显著的相关性(p0.05),Ni,Zn和Cd的弱酸浸提与可还原态具有显著的相关性(p0.05)。(5)长江三角洲沉积物中6种重金属元素的不同形态均与养分等指标存在显著的正相关性,而pH值和电导率与不同形态重金属呈负相关,全碳含量是控制长江三角洲沉积物重金属元素分布的主要因素。     

龙游硫铁矿区农田土壤重金属污染的空间 变异及在水稻中的积累

为了解浙江龙游硫铁矿区农田重金属污染状况,采集矿区265件农田土壤样品,分析8种重金属Cu、As、Hg、Zn、Cd、Ni、Pb、Cr元素全量,利用地统计学软件GS+9.0对研究区土壤各元素指标进行半变异函数拟合,并利用普通克里格法进行插值并绘制空间分布图。采集30件水稻籽粒样品,分析重金属在研究区中水稻籽粒的累积特征,并进行了健康风险评价。结果表明:矿区土壤中8种重金属元素的变异系数从0.72到1.76,离散程度较高。8种重金属的土壤空间半变异函数Cu、As、Hg元素符合指数模型,Zn、Cd、Ni、Pb符合球状模型,Cr符合高斯模型。元素Cu、Pb、Zn、Cr、Ni的块金值与基台值的比值C0/C0+C都小于0.25,说明空间变化主要受地质背景等因素影响;元素Cd、Hg和As的块金值与基台值的比值C0/C0+C在0.25~0.75之间,说明除了地质背景因素,人为活动等随机因素也有影响。矿区水稻籽粒中重金属Ni和Cd的变异系数最高,分别为0.95和0.87,说明Ni和Cd元素可能存在异常积累。矿区水稻籽粒对重金属的富集能力由大到小依次为Cd、Zn、Cu、Ni、As、Hg、Cr、Pb。健康风险评价结果表明矿区农田水稻籽粒中元素As、Cd的风险商大于1,存在潜在健康风险;而其他6种重金属Cu、Hg、Zn、Ni、Pb和Cr基本属于安全范围。     

重庆市蔬菜地土壤重金属特征研究

研究结果表明重庆市蔬菜地0~20cm和20~40cm土层土壤重金属Cr、Ni、Cu、Zn、As、Pb含量无显著差异,Cd、Hg含量差异显著。不同土壤类型平均重金属含量和变异系数差异均较小。城郊区、工矿区和一般农区重金属Ni、Cu、Zn、As、Pb含量及阳离子代换量无显著差异。不同土壤类型和不同区域重金属间均具较强相关性,重金属Cu、Ni、Cr间具有较强伴生关系。重庆市蔬菜地土壤重金属Cd污染较重。     

Assessment of Heavy Metals in Spinach (Spinacia oleracea L.) Grown in Sewage Sludge–Amended Soil

The assessment of heavy metals in spinach (Spinacia oleracea) grown in sewage sludge–amended soil was investigated. The results revealed that sewage sludge significantly (P < 0.01) increased the nutrients and heavy metals such as cadmium (Cd), chromium (Cr), copper (Cu), manganese (Mn), and zinc (Zn) in the soil. The contents of metals were found to be below the maximum levels permitted for soils in India. The most agronomic performance and biochemical components of S. oleracea were found at 50% concentrations of sewage sludge in both seasons. The contents of Cd, Cr, Cu, Mn, and Zn in S. oleracea were increased from 5% to 100% concentrations of sewage sludge in both seasons. The order of contamination factor (Cf) of different heavy metals was Mn > Cd > Cr > Zn > Cu for soil and Cr > Cd > Mn > Zn > Cu for S. oleracea plants after application of sewage sludge. Therefore, use of sewage sludge increased concentrations of heavy metals in soil and S. oleracea.     

Translocation and accumulation of heavy metals in Ocimum basilicum L. plants grown in a mining-contaminated soil

Purpose

The evaluation of the ecotoxicity effects of some heavy metals on the plant growth and metal accumulation in Ocimum basilicum L. cultivated on unpolluted and polluted soils represented the objective of the present study.

Materials and methods

The basil aromatic herb was evaluated in a laboratory experiment using soil contaminated with Cd, Co, Cr, Cu, Ni, Pb, and Zn, similar to the one from a mining area. The soils and different organs of the basil plants were analyzed, the total contents of the added elements being determined using inductively coupled plasma optical emission spectrometry. The ability of basil plants to accumulate metals from soil and to translocate them in their organs was evaluated by transfer coefficient, translocation factor, enrichment factor, and geo-accumulation index determinations.

Results and discussion

The basil plants grown in the metal-polluted soil showed stimulation effects comparing with the plants from the control soil. At the end of the exposure period, the plants had a visible increase of biomass and presented inflorescences and the leaves’ green pigment was intensified. The metals gathered differently in plant organs: Cd, Co, Cr, and Pb were accumulated in roots, while Cu, Ni, and Zn in flowers. Cr and Pb exceeded the toxic levels in roots. Also, the heavy metal intake depends on the plant development stages; thus, Cd, Cr, and Pb were accumulated more in mature plant leaves. The Cd and Pb contents were higher than the World Health Organization and European Commission permissible limits.

Conclusions

The experimental results revealed that the basil plants exposed to a mixture of heavy metals have the potential to reduce the metal mobility from soil to plants. Translocation process from roots to flowers and to leaves was observed for Cu, Ni, and Zn, emphasizing a competition between metals. The calculated bioaccumulation factors were insignificant, but Cd and Pb concentrations exceeded the legal limits in the mature plants, being restricted for human or animal consumption.

     

Heavy metal pollution of the world largest antimony mine-affected agricultural soils in Hunan province (China)

Purpose  

The present work concerns the distribution of ten heavy metals (Sb, As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, and Zn) in the surrounding agricultural soils of the world largest antimony (Sb) mine in China. The objective is to explore the degree and spatial distribution of heavy metal pollution of the Sb mine-affected agricultural soils. The presented data were compared with metal concentrations in soils from mining and smelting sites in China and other countries.     

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.     

广州市流花湖沉积物重金属污染特征及潜在生态风险评估

近年来重金属污染日益加重,对人类及水生态系统健康产生较大危害。本研究选择广州市典型城市湖泊——流花湖,利用地累积指数(Igeo)、潜在生态风险指数(RI)对沉积物中12种重金属的污染水平、垂向分布特征及其潜在生态风险进行评价,并通过多元统计分析对金属元素的来源进行解析。结果表明:①湖泊沉积物重金属含量(Mn、V除外)均显著高于区域土壤背景值,自下而上呈现先增加后减少的趋势;②地累积指数评价结果显示Cd、Zn、Sb、Cu、Pb和As这6种重金属污染较严重,其中Cd偏重度污染的状态(Igeo=3.89);③不同重金属元素污染水平有较大差异,Cd、Cu、Zn、Sb、Pb、As、Ni、Cr、Tl、Co的单个重金属污染指数(Cif)均为中等污染水平以上,而生态风险系数(Eif)表现为Cd(Eif=818.6)极严重等级,Sb(Eif=82.64)重度风险等级,其他10种重金属Eif均为轻度风险等级;④该湖RI指数变化幅度剧烈(105.85相似文献   

The transfer of heavy metals to barley plants from soils amended with sewage sludge with different heavy metal burdens

Purpose

Our main aim objective was to evaluate the transfer of Cd, Cr, Cu, Ni, Pb and Zn to barley (Hordeum vulgare) grown in various soils previously amended with two sewage sludges containing different concentrations of heavy metals. This allowed us to examine the transfer of heavv metals to barley roots and shoots and the occurrence of restriction mechanisms as function of soil type and for different heavy metal concentration scenarios.

Material and methods

A greenhouse experiment was performed to evaluate the transfer of heavy metals to barley grown in 36 agricultural soils from different parts of Spain previously amended with a single dose (equivalent to 50 t dry weight ha^?1) of two sewage sludges with contrasting levels of heavy metals (common and spiked sludge: CS and SS).

Results and discussion

In soils amended with CS, heavy metals were transferred to roots in the order (mean values of the bio-concentration ratio in roots, BCF_Roots, in brackets): Cu (2.4)?~?Ni (2.3)?>?Cd (2.1)?>?Zn (1.8)?>?Cr (0.7)?~?Pb (0.6); similar values were found for the soils amended with SS. The mean values of the soil-to-shoot ratio were: Cd (0.44)?~?Zn (0.39)?~?Cu (0.39)?>?Cr (0.20)?>?Ni (0.09)?>?Pb (0.01) for CS-amended soils; Zn (0.24)?>?Cu (0.15)?~?Cd (0.14)?>?Ni (0.05)?~?Cr (0.03)?>?Pb (0.006) for SS-amended soils. Heavy metals were transferred from roots to shoots in the following order (mean values of the ratio concentration of heavy metals in shoots to roots in brackets): Cr (0.33)?>?Zn (0.24)?~?Cd (0.22)?>?Cu (0.19)?>?Ni (0.04)?>?Pb (0.02) for CS-amended soils; Zn (0.14)?>?Cd (0.09)?~?Cu (0.08)?>?Cr (0.05)?>?Ni (0.02)?~?Pb (0.010) for SS-amended soils.

Conclusions

Soils weakly restricted the mobility of heavy metals to roots, plant physiology restricted the transfer of heavy metals from roots to shoots, observing further restriction at high heavy metal loadings, and the transfer of Cd, Cu and Zn from soils to shoots was greater than for Cr, Ni and Pb. Stepwise multiple linear regressions revealed that soils with high sand content allowed greater soil-plant transfer of Cr, Cu, Pb and Zn. For Cd and Ni, soils with low pH and soil organic C, respectively, posed the highest risk.     

Effects of combinations of heavy metal pollutants on Cuscuta reflexa

The effects of combinations of Hg, As, Pb, Cu, Cd, and Cr on the variables of Cuscuta reflexa Roxb. in natural condition were studied. All of the combinations of heavy metals tested decreased Hill reaction activity, chlorophyll and protein contents and increased tissue permeability over control values. The effects were best visible with the treatments of (As + Cd + Pb + Hg + Cu + Cr) and (As + Cd + Pb + Hg + Cu), followed by (As + Cd + Pb + Hg), (As + Cd + Pb), and (As + Cd). The degree of inhibition or increase by combinations of heavy metals is much higher due to synergism as the observed effects exceed the summed amount. The general order of sensitivity was As > Cd > Pb > Hg > Cu > Cr (absolute metal concentration).     

Effects of Paper Mill Effluent Irrigation on Agronomical Characteristics of Vigna radiata (L.) in Two Different Seasons

Seven rates of paper mill effluent (viz., 0%, 5%, 10%, 25%, 50%, 75%, and 100%) were used for irrigation of V. radiata (mung bean) along with a control (bore well water). The effluent had significant (P < 0.001) effects on electrical conductivity (EC), pH, chlorides (Cl^?), organic carbon (OC), bicarbonates (HCO₃ ^?), carbonates (CO₃ ^2?), sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), iron (Fe²⁺), total Kjeldahl nitrogen (TKN), nitrate (NO₃ ^2?), phosphate (PO₄ ^3?), sulfate (SO₄ ^2?), zinc (Zn), copper (Cu), cadmium (Cd), chromium (Cr), and lead (Pb) and insignificant (P > 0.05) effects on moisture content, water-holding capacity (WHC), and bulk density (BD) in both the cultivated seasons: rainy (Kharif) and summer (Zaid) season. The agronomical performance of V. radiata was increased from 5% to 50% in the rainy season and 5% to 25% in the summer season as compared to the control. The enrichment factor (Ef) of various heavy metals were ordered for soil as Pb > Cd, Cr > Zn > Cu in rainy season and Pb > Cd > Zn > Cr > Cu in summer season and for V. radiata plants as Cu > Zn > Cr > Pb > Cd in rainy season and Cu > Zn > Cr > Pb > Cd in summer season after irrigation with paper mill effluent.     

Trace metals in sediments and aquatic plants from the Xiangjiang River, China

Purpose

The metal concentrations and Pb isotopic composition in sediments and plants from the Xiangjiang River, China, were investigated to understand the contamination and potential toxicity of metals in sediments; to determine the accumulation and distribution of metals in plant tissues; and to trace the possible pollution source of Pb in sediments and plants.

Materials and methods

Sediments and plants were collected from 43 sampling sites in the study region. After sediments were air-dried and passed through a 63-??m sieve, they were acid-digested and DTPA-extracted for determination of total and bioavailable metals. The plants were separated into roots, leaves, and stems; dried; cut into pieces; and digested with HNO₃?CH₂O₂. Metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) and Pb isotopic composition were analyzed by inductively coupled plasma-mass spectrometry.

Results and discussion

Maximum As, Cd, Cr, Cu, Ni, Pb, and Zn concentrations in sediments were 47.18, 55.81, 129.5, 161.6, 160.4, 430.7, and 1,098.8?mg?kg^?1, respectively. The bioavailable fractions of As, Cd, Cu, Pb, and Zn had significant linear relationship with their corresponding total contents in sediments while no significant relationship was observed between bioavailable and total contents of Cr and Ni. In general, plant tissues showed higher As, Cd, Cu, Pb, and Zn concentrations and lower Cr and Ni concentrations compared with sediments. The ²⁰⁶Pb/²⁰⁷Pb ratios decreased in the order of total > bioavailable > stems ?? leaves > roots. A strong linear correlation was observed between the ²⁰⁸Pb/²⁰⁶Pb and ²⁰⁶Pb/²⁰⁷Pb ratios of the plant tissues, sediments, and the possible pollution sources of Pb in the Xiangjiang River.

Conclusions

As, Cd, Cu, Pb, and Zn demonstrated higher contamination levels in sediments and plants compared with Cr and Ni. Cd had highest potential ecological risk. The Pb from anthropogenic sources with low ²⁰⁶Pb/²⁰⁷Pb ratios was preferentially associated with the bioavailable fractions in sediments and accumulated in roots. The Pb in plant tissues is mainly derived from the Pb in sediment and is taken up through the sediment-to-root pathway.     

Effect of cultivation time on soil heavy metal accumulation and bioavailability in Phyllostachys praecox stands

Phyllostachys praecox is a bamboo species cultivated for edible shoots under intensive management. However, the potential pollution risk of heavy metals in bamboo soils is not clear under the intensive management for a long term. The objective of this study was to evaluate the effect of cultivation time on soil heavy metal accumulation and bioavailability in bamboo stands subjected to intensive management. Soil samples were collected from a chronosequence of bamboo stands which had been cultivated for 0, 1, 2, 4, 8, and 10 years in Lin''an, Zhejiang Province of China. Eight heavy metals (Cu, Zn, Pb, Ni, Cr, Cd, As, and Hg) present in the soil were selected, and their potential pollution risk was evaluated by chemical speciation analysis. Possible heavy metal sources were explored using multivariate and cluster analysis. Our results showed that Zn, Cu, Hg, and Cd contents in the soil increased with the cultivation time, while Ni, Cr, Pb, and As levels were similar among all stands. Furthermore, the bioavailabilities of all analyzed heavy metals increased with the cultivation time. Multivariate and cluster analysis showed that sources of Ni, Cr, Pb, and As were likely lithogenic in origin, whereas input of Zn, Cu, Hg, and Cd was mainly due to cultivation practices. Current bamboo management strategies raised the potential risks of heavy metal pollution in bamboo shoots in the long term. Soil acidification in P. praecox stands induced by intensive cultivation should be controlled since it stimulated and improved the bioavailability of heavy metals. Appropriate management strategies should thus be adopted to ensure safe and sustainable production of bamboo shoots.     

Effects of combinations of heavy metals on hill activity of Azolla pinnata

The effects of combinations of Hg, As, Ph, Cu, Cd, and Cr on Hill activity of Azolla pinnata R.Br. were studied. All of the combinations of heavy metals decreased Hill activity of chloroplasts over control values. The effects were most pronounced with the treatments of (Hg + As + Pb + Cu + Cd + Cr), followed by (Hg + As + Pb + Cu + Cd). The degree of inhibition of Hill activity in the species by combinations of heavy metals is less due to antagonistic effects (when 2 or 3 metals in combinations), and is much higher due to synergism (when 4 or more metals in combinations) than that by individual heavy metals tested. The harmful effects of the individual metals were, in general, found by the treatments in the order: Cd > Hg > Cu > As > Pb > Cr.     

规模化猪场区域农田土壤重金属积累及影响评价分析

为了解长期灌溉猪场废水对农田土壤重金属的影响,采集了河北省京安猪场区域农田清洁区和灌溉8年猪场废水污灌区的耕层(0～20 cm)共52个土壤样品,并测定了样品的pH、养分和Zn、Cu、Cr、Ni、Pb和As全量和有效态含量,根据背景资料、相关分析和主成分分析确定重金属污染来源,应用富集因子分析重金属积累程度,并应用污染指数进行重金属影响评价分析。结果表明,灌溉猪场废水对土壤主要带来Zn和Cu的富集,对Ni、Cr和As几乎没有富集效应,Pb和As的富集主要由施用化肥引起。尽管灌溉8年猪场废水后土壤的Zn、Cu、Cr、Ni、Pb和As含量在安全范围内,但土壤重金属有效态含量不仅与重金属全量正相关,还与土壤pH负相关,而灌溉猪场废水会降低土壤pH,从而增加土壤重金属有效态含量。因此,长期灌溉猪场废水不但要注意土壤Zn和Cu积累,还需采取措施降低土壤Zn、Cu等重金属有效态含量以防重金属带来环境风险。     

Behavior of heavy metals from sewage sludge in a Chernozem of the dry belt in Saxony‐Anhalt/Germany

In a small‐plot trial different doses of sewage sludge (equivalent 82‐330 tons of dry matter per hectare) were incorporated in 0—25 cm depth (1982—1985). The aim of the investigations was to study the fate of the heavy metals Zn, Cd, Cu, Ni, Pb, and Cr, to determine their concentration in different soil fractions using a sequential extraction method and to ascertain their uptake by Zea mays L. plants. Eleven years after the last application the metals supplied with the sludge had moved as far as 50 cm in depth. The concentrations of Zn, Cd, Cu, Ni, and Cr in the saturation extract of the sampled soil layers were closely correlated with the concentrations of dissolved organic carbon (DOC). This result suggests that the heavy metal displacement was partly connected with the DOC movement in the soil. Considerable amounts of Zn and Cd coming from sewage sludge were found in the mobile fractions of the soil. Cu, Ni, and Pb were located especially in organic particles, and Cr was obviously bound by Fe‐oxides. Nine years after the last application the binding species of heavy metals were still different compared with those in the untreated soil. The whole withdrawal of heavy metals by plants yielded <1 % of the applied amounts. In the case of Zn the uptake from the sludge amended soil decreased during the experimental period. No similar tendency was observed for the other elements. In any case their annual variations of uptake exceeded the effect of sludge application.     

Standards for the contents of heavy metals and metalloids in soils

In line with the present-day ecological and toxicological data obtained by Dutch ecologists, heavy metals/metalloids form the following succession according to their hazard degree in soils: Se > Tl > Sb > Cd > V > Hg > Ni > Cu > Cr > As > Ba. This sequence substantially differs from the succession of heavy elements presented in the general toxicological GOST (State Norms and Standards) 17.4.1.02-8, which considers As, Cd, Hg, Se, Pb, and Zn to be strongly hazardous elements, whereas Co, Ni, Mo, Sb, and Cr to be moderately hazardous. As compared to the general toxicological approach, the hazard of lead, zinc, and cobalt is lower in soils, and that of vanadium, antimony, and barium is higher. The new sequence also differs from that of the metal hazard in soils according to the Russian standard on the maximal permissible concentration of mobile metal forms (MPC_mob): Cu > Ni > Co > Cr > Zn. Neither an MPC_mob nor an APC_mob has been adopted for strongly hazardous thallium, selenium, and vanadium in Russia. The content of heavy metals in contaminated soils is very unevenly studied: 11 of them, i.e., Cu, Zn, Pb, Ni, Cd, Cr, As, Mn, Co, Hg, and Se, are better known, while the rest, much worse, although there are dangerous elements (Ba, V, Tl) among them.