八种水生植物对重金属富集能力的比较研究

通过野外采样和系统分析方法,研究了芜湖市四褐山工业区附近水域中Cu、Pb、Cd、Zn和Mn5种重金属的含量及其在8种水生植物体内的积累特性。结果表明,工业区水体污染严重,重金属含量严重超标,分别为标准值的9、10.1、400、3和438倍;8种水生植物的重金属积累量均较大,其中以水鳖根、茎叶的Cu、Pb、Cd、Zn含量最高,分别为水体中重金属浓度的9.12和2.59倍、33.41和5倍、0.8和0.3倍、26.9和9.1倍,明显高于其它7种水生植物;8种水生植物不同器官对Cu、Pb、Zn的富集系数均>1,富集能力较强。其中,香蒲对Pb、Cd的吸收能力表现为茎叶>根。结果表明,在Cu、Pb和Zn等重金属复合污染水域的植物治理中,浮萍、香蒲、水鳖、中华慈姑、芦苇、空心莲子草等植物有着较大的发展潜力和应用前景。     

Soil Heavy Metal Pollution Assessment Near the Largest Landfill of China

To assess the extent and potential hazards of heavy metal pollution at Shanghai Laogang Landfill, the largest landfill in China, surface soil samples were collected near the landfill and concentrations of Cu, Zn, Cd, Pb, and Cr were determined. The results revealed that the concentrations of heavy metals, except Pb, were higher in the surface soil near the landfill than in the background soil. Principal component analysis and hierarchical cluster analysis suggested that the enrichment of Cu in soil was probably related to agricultural activities and Cd and Pb to landfill leachates, whereas Zn and Cr concentrations were probably controlled by soil matrix characteristics. The pollution indices (PIs) of the metals were: Cd > Cu > Cr > Zn > Pb. Among the five measured metals, Cd showed the largest toxic response and might cause higher ecological hazards than other metals. The integrated potential eco-risk index (RI) of the five metals ranged from 26.0 to 104.9, suggesting a low-level eco-risk potential. This study indicated the accumulations of Cu, Zn, Cd, Pb, and Cr did not reach high pollution levels, and therefore posed a low eco-risk potential in surface soil near the landfill.     

Source analysis and health risk of heavy metals in the different seasons from Taizihe River,China

Twenty five water samples were collected along the Taizihe River, the concentration and health risks of Zn, Cu, Pb, Cr and Cd were detected and evaluated, and the pollution sources was analyzed through principal components analyses. The results indicated that the order of average concentration of heavy metals was follows: Pb > Cr > Cu > Zn and Cd. Among that, the concentrations of Zn, Cu and Cr were at the permissible levels, but Pb and Cd exceeded grade V standard at some sites. The concentrations of Zn and Cu in the wet season were significant higher than that in the dry season (p < 0.05), but the average concentrations of Pb, Cr and Cd were not significantly different in the two seasons (p > 0.05). The annual average risks of human health caused by Cd and Cr were 10⁻³/a and 10⁻⁴/a, respectively, which were higher than the recommended maximum acceptable risk level. The human health risk values of Zn, Pb and Cu were all concentrated at 10⁻⁸/a or 10⁻⁹/a levels, which did not exceed the recommended standard. On the whole, Cd and Cr were the main health risk pollutants of Taizihe River. Pollution sources of Pb was different from other heavy metals in wet and dry season, Cd and Cr were similar in the wet and dry season. The mainly pollution source of heavy metals was industry, especially mining, metal smelting and electroplating industry.     

Multiple Heavy Metal Tolerance of Soil Bacterial Communities and Its Measurement by a Thymidine Incorporation Technique

A thymidine incorporation technique was used to determine the tolerance of a soil bacterial community to Cu, Cd, Zn, Ni, and Pb. An agricultural soil was artificially contaminated in our laboratory with individual metals at three different concentrations, and the results were compared with the results obtained by using the plate count technique. Thymidine incorporation was found to be a simple and rapid method for measuring tolerance. Data obtained by this technique were very reproducible. A linear relationship was found between changes in community tolerance levels obtained by the thymidine incorporation and plate count techniques (r = 0.732, P < 0.001). An increase in tolerance to the metal added to soil was observed for the bacterial community obtained from each polluted soil compared with the community obtained from unpolluted soil. The only exception was when Pb was added; no indication of Pb tolerance was found. An increase in the tolerance to metals other than the metal originally added to soil was also observed, indicating that there was multiple heavy metal tolerance at the community level. Thus, Cu pollution, in addition to increasing tolerance to Cu, also induced tolerance to Zn, Cd, and Ni. Zn and Cd pollution increased community tolerance to all five metals. Ni amendment increased tolerance to Ni the most but also increased community tolerance to Zn and, to lesser degrees, increased community tolerance to Pb and Cd. In soils polluted with Pb increased tolerance to other metals was found in the following order: Ni > Cd > Zn > Cu. We found significant positive relationships between changes in Cd, Zn, and Pb tolerance and, to a lesser degree, between changes in Pb and Ni tolerance when all metals and amendment levels were compared. The magnitude of the increase in heavy metal tolerance was found to be linearly related to the logarithm of the metal concentration added to the soil. Threshold tolerance concentrations were estimated from these linear relationships, and changes in tolerance could be detected at levels of soil contamination similar to those reported previously to result in changes in the phospholipid fatty acid pattern (Å. Frostegård, A. Tunlid, and E. Bååth, Appl. Environ. Microbiol. 59: 3605-3617, 1993).     

Heavy metal contamination in vegetables grown around peri-urban and urban-industrial clusters in Ghaziabad,India

Heavy metal contamination of agricultural soils resulting from rapid industrialization and urbanization is of great concern because of potential health risk due to dietary intake of contaminated vegetables. The present study aims to evaluate the status of heavy metals contamination of agricultural soils and food crops around an urban-industrial region in India. Transfer factor values of Cu, Cr, Pb, Cd, Zn, and Ni from soil to vegetable was estimated. The mean heavy metal concentrations (mg/kg) in agricultural soils (Cu: 17.8, Cr: 27.3, Pb: 29.8, Cd: 0.43, Zn: 87, Mn: 306.6, Fe: 16984, and Ni: 53.8) were within allowable concentrations for Indian agricultural soil. The concentrations of Pb, Cd, Zn, and Ni in crops/vegetables exceeded the World Health Organization/Food and Agriculture Organization safe limits. Relative orders of transfer of metals from soil to edible parts of the crops/vegetables were Cd > Pb > Ni > Zn > Cu > Cr. The enrichment factors of heavy metals in soil indicated minor to moderately severe enrichment for Pb, Cd, and Ni; minor to moderate enrichment for Zn; no enrichment to minor enrichment for Mn; and no enrichment to moderate enrichment for Cu at different sites. Ecological risk index of soil showed considerable contamination in one of the wastewater irrigated sites.     

Leaching Behavior of Heavy Metals and Transformation of Their Speciation in Polluted Soil Receiving Simulated Acid Rain

Heavy metals that leach from contaminated soils under acid rain are of increasing concern. In this study, simulated acid rain (SAR) was pumped through columns of artificially contaminated purple soil. Column leaching tests and sequential extraction were conducted for the heavy metals Cu, Pb, Cd, and Zn to determine the extent of their leaching as well as to examine the transformation of their speciation in the artificially contaminated soil columns. Results showed that the maximum leachate concentrations of Cu, Pb, Cd, and Zn were less than those specified in the Chinese Quality Standards for Groundwater (Grade IV), thereby suggesting that the heavy metals that leached from the polluted purple soil receiving acid rain may not pose as risks to water quality. Most of the Pb and Cd leachate concentrations were below their detection limits. By contrast, higher Cu and Zn leachate concentrations were found because they were released by the soil in larger amounts as compared with those of Pb and Cd. The differences in the Cu and Zn leachate concentrations between the controls (SAR at pH 5.6) and the treatments (SAR at pH 3.0 and 4.5) were significant. Similar trends were observed in the total leached amounts of Cu and Zn. The proportions of Cu, Pb, Cd, and Zn in the EXC and OX fractions were generally increased after the leaching experiment at three pH levels, whereas those of the RES, OM, and CAR fractions were slightly decreased. Acid rain favors the leaching of heavy metals from the contaminated purple soil and makes the heavy metal fractions become more labile. Moreover, a pH decrease from 5.6 to 3.0 significantly enhanced such effects.     

Geochemical cycling of heavy metals in a marine coastal area: benthic flux determination from pore water profiles and in situ measurements using benthic chambers

Concentrations of the heavy metals Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn were measured in sea water, suspended matter, sediments and pore water samples collected in a coastal area of the middle Tyrrhenian Sea. Concentration factors between pore water (extracted from the first centimeter of the sediments) and the overlying sea water (taken 30 cm above the sea bed) were less than 1 for Cr, Cu and Pb, 1–10 for Cd and Ni, 10–100 for Fe and Co, 100–1000 for Mn, and 1–100 for Zn.The benthic fluxes of heavy metals at the sediment-water interface were measured directly using in situ benthic chambers and calculated using Fick's first law during two experimental periods, one in 1986 and the other in 1988. The fluxes of Cu, Ni, Pb and Zn varied significantly over time; this appeared to be related to their relatively low ( 10) concentration factors. From the benthic chamber experiments, metals with positive fluxes were in the order: Mn > Fe > Co > Cd, while those with negative fluxes were: Zn > Pb > Ni Cu. Fluxes calculated using Fick's Law were: positive – Mn > Fe > Zn (or Zn > Fe) > Ni > Co > Cd, negative fluxes Pb > Cu > Cr.Measured (benthic chamber) and calculated (Fick's first law) fluxes for Co, Cd, Mn, Pb and Fe were comparable within an order of magnitude, although less agreement was found for Cu, Ni and Zn. Removal of Ni and Zn at the sediment-water interface has been proposed to explain the fact that the measured and calculated fluxes have opposite directions for these metals.     

Effects of Municipal Sewage Sludge Doses on the Chlorophyll Contents and Heavy Metal Concentration of Sugar Beet (Beta vulgaris var. saccharifera)

The present study was conducted to assess the suitability of sewage sludge amendment (SSA) in soil for Beta vulgaris var. saccharifera (sugar beet) by evaluating the heavy metal accumulation and physiological responses of plants grown at a 10%, 25%, and 50% sewage sludge amendment rate. The sewage sludge amendment was modified by the physicochemical properties of soil, thus increasing the availability of heavy metals in the soil and consequently increasing accumulation in plant parts. Cd, Pb, Ni, and Cu concentrations in roots were significantly higher in plants grown at 25% as compared to 50% SSA; however, Cr and Zn concentration was higher at 50% than 25% SSA. The concentrations of heavy metal showed a trend of Zn > Ni > Cu > Cr > Pb > Cd in roots and Zn > Cu > Ni > Cr > Pb > Cd in leaves. The only instance in which the chlorophyll content did not increase after the sewage sludge treatments was 50%. There were approximately 1.12-fold differences between the control and 50% sewage sludge application for chlorophyll content. The sewage sludge amendment led to a significant increase in Pb, Cr, Cd, Cu, Zn, and Ni concentrations of the soil. The heavy metal accumulation in the soil after the treatments did not exceed the limits for the land application of sewage sludge recommended by the US Environmental Protection Agency (US EPA). The increased concentration of heavy metals in the soil due to the sewage sludge amendment led to increases in heavy metal uptake and the leaf and root concentrations of Ni, Zn, Cd, Cu, Cr, Pb, and Zn in plants as compared to those grown on unamended soil. More accumulation occurred in roots and leaves than in shoots for most of the heavy metals. The concentrations of Cd, Cr, and Pb were more than the permissible limits of national standards in the edible portion of sugar beet grown on different sewage sludge amendment ratios. The study concludes that the sewage sludge amendment in the soil for growing sugar beet may not be a good option due to risk of contamination of Cr, Pb, and Cd.     

强还原过程对设施菜地土壤重金属形态转化的影响

设施菜地由于污水灌溉、粪肥施用等导致重金属污染.本文通过土柱淹水同时添加玉米秸秆培养和后期通水淋洗,研究强还原法对设施土壤重金属(Cd、Cu、Pb和Zn)形态转化的影响.结果表明: 强还原处理使土壤pH显著降低,玉米秸秆处理变化更显著;土壤氧化还原电位(Eh)迅速下降至-280 mV左右.玉米秸秆处理可以促进土壤中Cd、Cu、Pb和Zn活化,第9天土壤中有机物及硫化物结合态和残渣态Cd、Cu、Pb和Zn含量比重下降;至15 d培养结束,土壤中4种重金属含量较对照分别减少18.1%、19.0%、16.1%和15.7%.玉米秸秆处理可以增加土壤中Cd和Zn的溶出量,但是Cu的溶出量减少;胶体结合态Cd和Pb含量较对照增加、Cu较对照显著减少、Zn没有显著变化.强还原可以引起设施土壤重金属活化,提高蔬菜积累重金属的风险,而且其随土壤水分的运移可能导致水体的污染.     

Distribution and contamination pattern of heavy metals from surface sediments in the southern part of Caspian Sea,Iran

This study concentrates on the speciation and distribution patterns of some heavy metals (Pb, Ni, Cd, Zn, and Cu) in surface sediments in the southern part of the Caspian Sea, the biggest lake in the world, to obtain an overall classification for the origins of metals in the area using a sequential extraction technique. At all sampling stations, Pb, Ni, Zn, and Cu were mostly (>50%) accumulated in the resistant fraction, which indicated that there were no significant anthropogenic inputs of Pb, Ni, Zn, and Cu into the surface sediments of the south Caspian Sea. Guilan province on the west coast of Caspian Sea accumulated higher percentages of non-resistant fractions of Pb and Zn, while Mazandaran and Golestan provinces in the middle and western parts of the Caspian Sea, in the Iranian zone, accumulated higher percentages of non-resistant fractions of Ni and Cu. The present study revealed that the coastal area of the south Caspian Sea is still not seriously contaminated. Cadmium in Guilan and Golestan provinces were dominated by non-resistant fractions (55–69%), which indicated more anthropogenic inputs of Cd on the south coast of the Caspian Sea in comparison with other metals.     

Heavy metal contamination and health risk assessment in soil-rice system near Xinqiao mine in Tongling city,Anhui province,China

In this study, paddy soil and rice grain samples were collected from the vicinity around the Xinqiao mine in Tongling, China to test for the presence of heavy metals (Cd, Ni, Cr, Cu, Zn, and Pb) in soil-rice system. Results indicated that the soil samples were primarily contaminated with Cd and Cu and followed with Zn and Pb. In rice grains, Cd, Cu, and Cr concentrations exceeded recommended guidelines. However, the regional distribution of heavy metals in rice grains and soil was inconsistent. The bioaccumulation factor of heavy metals in rice grains decreased in the order of Cd > Zn > Cu > Ni > Cr > Pb. The BAF was significantly positively correlated with TCLP-extractable metals and significantly negatively correlated with soil pH. However, the relationship between soil organic matter and the BAF in rice grains was complex. Health risk assessment through rice intake showed that hazard quotients of Cu and Cd were greater than 1 and could pose a considerable non-cancer health risk to adults and children; meanwhile, Cr, Ni, and Cd could pose an unacceptable cancer risk. The results indicated that the government must take measures to reduce heavy metal contents in paddy soil and rice.     

Risk Element (As,Cd, Cu,Pb, and Zn) Contamination of Soils and Edible Vegetables in the Vicinity of Guixi Smelter,South China

Risk element (As, Cd, Cu, Pb, and Zn) contamination in soils and in two edible vegetables (Solanum melongena L. and Capsicum annum L.) was investigated in the vicinity of Guixi Smelter, South China. Soil As concentrations averaged 23.9 mg/kg. Sites near the smelter tailings recorded the highest levels of As and heavy metals in soils. The concentration order of heavy metals in soils was Cd < Pb < Zn < Cu. Cu and Cd in soils were abundant in the exchangeable and bound to carbonate fraction, while Pb and Zn were in the residual fraction, limiting their potential toxicity as pollutants. The proportions of the metals in the mobile fraction followed the order Pb < Zn < Cu < Cd. In Solanum melongena L. and Capsicum annum L., Zn concentration was the highest, followed by Cu, Cd, and Pb, different from that in soils and in the mobile fraction. Concentrations of heavy metals in the labile fractions in soils and in vegetables presented significant correlation (p < 0.05). Both of the two vegetables are not the Cu and Zn accumulators. As for Cd and As, Capsicum annum L. poses a higher risk to animal and human health than Solanum melongena L., with soil-plant transfer coefficients more than three. Root-stem is the main barrier for most of the heavy metals and As in the two vegetables, resulting in higher metal concentrations in roots relative to other plant tissues. The low stem-fruit transfer coefficients for Zn in Solanum melongena L. and for Pb in Capsicum annum L. suggested that very few of them could reach the fruits.     

Concentrations of heavy metals in vegetables between 2004 and 2018, and its impacts on human health in China

Abstract

Heavy metals in vegetables are of great concern worldwide due to their potential bioaccumulation in human. This review-based study researched the concentrations of heavy metals in vegetables from all provinces of China between 2004 and 2018, and assessed the health risk for the residents. The results displayed the highest Pb, Cd, Cu, and Zn concentrations in vegetables were 0.192?mg/kg (west area), 0.071?mg/kg (central area), 3.961?mg/kg (central area), and 10.545?mg/kg (central area), which were lower than the maximum allowable concentration. In the national scale, the weighted average level of heavy metals in vegetables was found to be in the order of Zn?>?Cu?>?Pb?>?Cd. The hazard index (HI) of each province showed that beside Anhui and Hunan province, residents in other provinces of China faced a low high risk of Pb, Cd, Cu, and Zn. However, people consuming vegetables faced a high risk of Pb, Cd, Cu, and Zn in Anhui and Hunan provinces. This research may provide insight into heavy metal accumulation in vegetables and forecast to residents to cope with these problems for improved human health.     

Metal concentrations in Sargassum algae from coastal waters of Nha Trang Bay (South China Sea)

The concentrations of metals, viz., Fe, Mn, Cu, Zn, Cd, Pb, and Ni, were investigated in brown algae of the genus Sargassum collected in the coastal waters of Nha Trang Bay (South China Sea). Metal concentrations in algae growing in the zone of influence of the city of Nha Trang were higher than those in macrophytes collected to the south and north of the city. Similar levels of Cu and Fe concentrations were observed in macrophytes from the urbanized coastal areas of Nha Trang Bay and in algae from the Peter the Great Bay (Sea of Japan). This is suggestive of comparable metal inputs from the anthropogenic sources of the cities of Nha Trang and Vladivostok (Peter the Great Bay). However, the concentrations of Pb, Ni, and Cd in algae from the coastal waters of Nha Trang Bay were lower than in macrophytes from the inshore zone of Vladivostok. The high level of pollution of sea water with Zn compounds near Nha Trang was local. The metal levels in macrophytes from background areas reflect the geochemical features of the environment. Sargassum algae from Nha Trang Bay had lower concentrations of Zn, Cd, and Ni and higher concentrations of Mn than algae from Peter the Great Bay. The background concentrations of Cu, Pb, and Fe in macrophytes from both bays were virtually the same.     

应用生物效应数据库法建立淡水水体沉积物重金属质量基准

重金属是水体沉积物中的重要污染物,可能对底栖生物和水生态环境产生严重的危害.生物效应数据库法是国际上广泛接受的沉积物质量基准计算方法.本文介绍了利用该方法计算沉积物质量基准的详细过程,并应用该方法初步建立了Cu、Zn、Cd、Pb、Ni 5种重金属的淡水沉积物质量基准,对建立基准值进行了可比性、可靠性和可预测性分析.结果表明: Cd、Ni、Pb、Zn、Cu的临界效应浓度(TEL)分别为3.0、31.4、47.3、74.9和45.5 mg·kg^-1(以干质量计),可能效应浓度值(PEL)为19、76.9、204.1、403.6和181.1 mg·kg^-1(以干质量计).除Zn外,其他4种重金属的TEL、PEL值与其定义的生物效应基本一致,符合针对保护底栖生物制定的沉积物质量基准的要求,具有较高的可靠性,可以作为淡水水体沉积物重金属质量基准建议值.     

Bioaccumulation and rhizofiltration potential of Pistia stratiotes L. for mitigating water pollution in the Egyptian wetlands

The bioaccumulation and rhizofiltration potential of P. stratiotes for heavy metals were investigated to mitigate water pollution in the Egyptian wetlands. Plant and water samples were collected monthly through nine quadrats equally distributed along three sites at Al-Sero drain in Giza Province. The annual mean of the shoot biomass was 10 times that of the root. The concentrations of shoot heavy metals fell in the order: Fe < Mn < Cr < Pb < Cu < Zn < Ni < Co < Cd, while that of the roots were: Fe < Mn < Cr < Pb < Zn < Ni < Co < Cu < Cd. The bio-concentration factor (BCF) of most investigated heavy metals, except Cr and Pb, was greater than 1000, while the translocation factor (TF) of most investigated metals, except Pb and Cu, did not exceed one. The rhizofiltration potential (RP) of heavy metals was higher than 1000 for Fe, and 100 for Cr, Pb and Cu. Significant positive correlations between Fe and Cu in water with those in plant roots and leaves, respectively were recorded, which, in addition to the high BCF and RP, indicate the potential use of P. stratiotes in mitigating these toxic metals.     

Characterization of Heavy Metal Fractions in Agricultural Soils by Sequential Extraction Procedure: The Relationship Between Soil Properties and Heavy Metal Fractions

The present research was conducted to determine heavy metals in agricultural soils from Çanakkale, Turkey, using a sequential extraction procedure (acid soluble, reducible, oxidizable, and residual) as proposed by the Community Bureau of Reference (BCR) of the European Commission. Soil samples were taken from 12 different cultivated sites and analyzed for Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn concentrations. The results revealed an order of Mn > Cd > Pb > Co > Ni > Cu > Zn > Cr for the heavy metals based on the sum of the first three fractions (acid soluble + reducible + oxidizable). The relationships between soil properties and each metal fraction were identified through Pearsons's correlation analysis. Hierarchical cluster analysis was performed to determine the behaviors and similarities of metals in each fraction. While Mn, Pb, and Zn exhibited subjective behaviors in the acid-soluble fraction, Cd, Co, Cu, Cr, and Ni exhibited similar behaviors with each other.     

沈阳市住宅区小区与街道灰尘重金属污染评价

城市住宅区是人类活动的重要场所,与居民的日常生活紧密相关。为了解沈阳市住宅区小区与街道灰尘中重金属污染的空间分布,采集了不同住宅区小区与街道的灰尘样品,分析了灰尘中重金属的含量,并使用富集因子和地累积指数评估了其污染程度。结果表明,沈阳市灰尘中重金属Cr、Cd、Cu、Pb和Zn的平均含量均超过辽宁省表层土壤元素背景值。单因素方差分析表明,街道灰尘中重金属Cu、Fe、Mn和Zn的空间分布具有显著性差异,而小区灰尘中重金属Cd、Cr、Fe、Mn和Pb在空间上具有显著性差异。重金属Cd、Zn和Pb的平均污染水平较高,其中小区内Cd和Zn的污染程度高于街道。沈阳市不同方位住宅区灰尘中重金属的污染水平介于轻度污染至中度污染之间。     

不同土壤生境下斑茅对重金属的富集特征

为了筛选Cu、Zn、Pb、Cd多重金属离子的富集植物,对不同土壤生境(铜铁矿、钨矿、铅锌矿和无矿场污染)的优势种斑茅(Saccharum arundinaceum(Retz.)Jeswiet)对Cu、Zn、Pb、Cd离子富集情况进行了调查。结果表明,斑茅对Cu、Zn、Pb、Cd离子有富集优势并以Cu富集显著,斑茅根系土壤与斑茅地上部Cu含量存在相关性(P<0.05),斑茅对Pb和Cd的富集与转运存在极显相关性(P<0.01);在强酸、多金属污染弃耕农田土壤中,斑茅不仅符合Cu超富集植物的特征,而且其对Zn、Pb和Cd3种重金属的富集系数和转运系数均>1。在Cd、Cu、Pb和Zn均低于国家土壤环境质量二级标准(GB15618-1995)的弃耕农田中,斑茅对Cu、Zn和Cd的富集系数均>1。研究表明,斑茅可以作为Cu、Zn、Pb、Cd多金属污染土壤的富集植物进行人工修复。     

Accumulation and translocation of heavy metals in the canola (Brassica napus L.)—soil system in Yangtze River Delta, China

Aims and methods

Concentrations of heavy metals such as Cd, As, Hg, Pb, Cr, Cu, Zn and Ni in different tissues (seeds, roots and shoots) of the mature canola (Brassica napus L.) plants and in the associated rhizosphere soils from Yangtze River Delta (YRD) region of China, were determined to evaluate the heavy metals’ pollution in the soils and the canola seeds, and to discuss their accumulation and translocation characteristics in canola plants. At the same time, the phytoextraction potential of the canola plant for the above heavy metals was theoretically calculated and discussed on the basis of above measured data.

Results

The results showed that the concentration ranges of Cd, As, Hg, Pb, Cr, Cu, Zn and Ni in the rhizosphere soils were 0.115–0.481, 3.40–20.5, 0.069–0.682, 9.92–27.4, 46.8–86.6, 17.7–253.3, 65.2–511.7 and 16.0–37.8?mg?kg^?1, respectively. The concentrations of Cu, Zn and Hg at some sampling sites exceeded the 2nd grade threshods of Chinese national environmental quality standard for soils. The potential ecological risk of heavy metals in the canola rhizosphere soils decreased in the order of Zhejiang > Shanghai > Jiangsu provinces. The concentration ranges of above heavy metals in the canola seeds were 0.032–0.067, 0.002–0.005, 0.001–0.005, 0.053–0.165, 0.191–0.855, 3.01–13.20, 34.82–96.95 and 0.343–2.86?mg?kg^?1, respectively, with Cu and Zn at some sampling sites exceeding the permissible concentrations in foods of China. Heavy metals’ concentrations in canola seeds didn’t increase with their increasing concentrations in the rhizosphere soils. The bioconcentration factors (BCFs) of most heavy metals in the canola seeds decreased with their increasing concentrations in the associated rhizosphere soils. The average BCFs of heavy metals decreased in the order of Zn (0.488)>Cd (0.241)>Cu (0.145)>Ni (0.038)>Hg (0.021)>Pb (0.005)=Cr (0.005)>As (0.000) in the canola seeds, Cd (1.550)>Cu (0.595)>Zn (0.422)>Hg (0.138)>Ni (0.085)>Pb (0.080)>As (0.035)>Cr (0.031) in the roots, and Cd (0.846)>Zn (0.242)>Cu (0.205)>Hg (0.159)>Ni (0.031)>Pb (0.025)>As (0.012)>Cr (0.007) in the shoots, respectively. The accumulation capacity for most of the above heavy metals in the mature canola tissues was root > shoot > seed, with the exceptions of seed > root > shoot for Zn and shoot > root > seed for Hg. Except Hg from root to shoot and Zn from root to seed, translocation factors (TFs) of above heavy metals were lower than 1.0.

Conclusions

The concentrations, BCFs and TFs of above heavy metals in the canola tissues indicated that the investigated canola plants did not meet the criteria of hyperaccumulators for the above heavy metals. The phytoextracton potential of the studied canola plants for the above heavy metals from the polluted soils was very limited. It would take 920, 3,170 and 3,762?years (assuming two crops per year) to reduce the initial soil Zn, Cu and Hg concentrations, respectively, from the most polluted soil concentrations to the 2nd grade thresholds of Chinese national environmental quality standard for soils.