Uptake and accumulation of potentially toxic metals (Zn, Cu and Pb) in soils and plants of Durgapur industrial belt

Uptake and accumulation of metals in crops may cause possible health risks through food chain. A field survey was conducted to investigate the accumulation of potentially toxic metals contamination in soil and plants irrigated with complexed industrial effluents. Concentration of Zn, Cu and Pb was 205-255,101-130,118-177 microg g(-1) in rhizosphere soils and 116-223, 57-102 and 63-95 microg g(-1) d. wt. in root and 95-186, 44-75 and 27-58 microg g(-1) d. wt. in shoot, respectively. The trend in Cu and Pb was in the order: soil > root > shoot > seed while in Zn it was soil > root > seed > shoot. Roots accumulated a larger fraction of soil Cu (70%) > Zn (67%) > Pb (54%). Bioaccumulation coefficient of soil to root ranged from 51-98 for Zn, 54-85 for Cu and 43-63 for Pb.Analysis of variance showed marginal change in bioaccumulation coefficient, noticed between plants (p > 0.05) while it varied significantly (p < 0.01) between tissues and metals. It increased from root to seed/fruit (root > shoot > seed/fruit) while decreased between metals from Zn to Pb (Zn > Cu > Pb). Out of the three, two Cu and Pb accumulated to phyotoxic levels while Zn was within threshold limit of phytotoxicity.     

Accumulation and translocation of heavy metals in soil and plants from fly ash contaminated area

The present investigation deals with the accumulation of heavy metals in fields contaminated with fly ash from a thermal power plant and subsequent uptake in different parts of naturally grown plants. Results revealed that in the contaminated site, the mean level of all the metals (Cd, Zn, Cr, Pb, Cu, Ni, Mn and Fe) in soil and different parts (root and shoots) of plant species were found to be significantly (p<0.01) higher than the uncontaminated site. The enrichment factor (EF) of these metals in contaminated soil was found to be in the sequence of Cd (2.33) > Fe (1.88) > Ni (1.58) > Pb (1.42) > Zn (1.31) > Mn (1.27) > Cr (1.11) > Cu (1.10). Whereas, enrichment factor of metals in root and shoot parts, were found to be in the order of Cd (7.56) > Fe (4.75) > Zn (2.79) > Ni (2.22) > Cu (1.69) > Mn (1.53) > Pb (1.31) > Cr (1.02) and Cd (6.06) approximately equal Fe (6.06) > Zn (2.65) > Ni (2.57) > Mn (2.19) > Cu (1.58) > Pb (1.37) > Cr (1.01) respectively. In contaminated site, translocation factor (TF) of metals from root to shoot was found to be in the order of Mn (1.38) > Fe (1.27) > Pb (1.03) > Ni (0.94) > Zn (0.85) > Cd (0.82) > Cr (0.73) and that of the metals Cd with Cr, Cu, Mn, Fe; Cr with Pb, Mn, Fe and Pb with Fe were found to be significantly correlated. The present findings provide us a clue for the selection of plant species, which show natural resistance against toxic metals and are efficient metal accumulators.     

Risk assessment for safety of soils and vegetables around a lead/zinc mine

Concentrations of heavy metals (Pb, Zn, Cd, Cu) were determined in soils and vegetables (chrysanthemum, spinach and four cultivars of Chinese cabbage from the area adjacent to a Pb/Zn mine in Shaoxing, Zhejiang province, China, and compared with the Chinese National Standards for Soil Environmental Quality. The accumulation of heavy metals in cabbage cv. Siyuegreen was investigated at different distances from the center of the mine. The vegetable plantation soils were polluted with Pb, Cd, Cu and Zn, especially by Pb and Cd. The levels of Pb and Cd were 20 and 30 times higher than the permitted standards, indicating that this Pb/Zn mining area is unsuitable for agricultural use. Chinese cabbage, chrysanthemum and spinach had different enrichment coefficients. The enrichment coefficient of Cd from soil to roots of chrysanthemum was >80% and from roots to leaves of cabbage cv. Shanghaigreen was >120%. These vegetables were polluted by heavy metals and could not be regarded as safe for human consumption. Environmental accumulation of heavy metals in the vegetable plantation soils was proportional to heavy metal accumulation in vegetables and both were inversely proportional to the distance from the lead/zinc mine.     

Accumulation of heavy metals in soil and paddy crop (Oryza sativa), irrigated with water of Ramgarh Lake,Gorakhpur, UP,India

Heavy metals, a highly polluting group of constituents known to exert adverse effects, tend to accumulate in living organisms. The objective of this study was to determine the accumulation and translocation of heavy metals in soil and in paddy crop irrigated with lake water compared to soil and paddy crop irrigated with bore-well water. The quantities of heavy metals (Cd, Cr, Cu, Pb, Zn, As, Mn, and Hg) were determined in different parts of rice plants (Oryza sativa). Results revealed that the mean levels of soil Cd, Cr, Pb, Zn, As, Mn, and Hg in experimental soil and in different parts of rice plant (root, straw, and grain) were higher than the control except for Cu. The content of eight toxic metals was significantly higher in root than in aerial parts of the rice (straw and grains). Rice roots were enriched in Cd, As, Hg, and Pb from the soil, while Cr, Cu, Zn, and Mn were hardly taken by the roots. Bioaccumulation factor for Hg was significantly higher than other heavy metals. Metal transfer factors from soil to rice plants were significant for Cd, Cr, Cu, Pb, Zn, As, Mn, and Hg. The concentrations of metals in lake water were found to be within the permissible limit of Indian standard prescribed by Central Pollution Control Board (2000), except for Hg and As, which were higher than the limit of Indian standard. However, the concentrations of heavy metals in soil and rice grains were still below the maximal levels, as stipulated by Indian Prevention of Food Adulteration Act (PFA, 1954) and World Health Organization (WHO, 1993) guidelines.     

螯合剂对小麦幼苗吸收金属以及土壤金属形态的效应

本文通过盆栽试验研究三种螯合剂(EDTA、[S,S]-EDDS、DTPA)对小麦幼苗吸收土壤中重金属及其它微量元素的效应,并且通过改进的BCR连续提取法分析了种植后土壤样品中金属元素的形态。结果表明:EDTA、DTPA的添加导致小麦幼苗地上部分生物量以及叶片叶绿素a含量显著下降。螯合剂的存在明显增加了Pb和Mn在幼苗根部和茎叶的富集,并增加其由根部向茎叶的传输,但对Fe和Ni的作用比较小。小麦幼苗收获时,除Zn之外,其它元素酸溶/可交换态金属含量与对照组相比均有非常显著的增加,而各元素的可还原态由于EDTA等螯合剂的添加而有明显下降。添加螯合剂的情况下,富集量与酸溶/可交换态含量之间的相关系数大大提高,且各处理组茎叶富集量与酸溶/可交换态之间呈显著(P0.05)或极显著相关(P0.01)。因此,三种螯合剂的添加主要影响的是生物可利用形态以及潜在的生物可利用形态,并且可能导致可还原态以及可氧化态向酸溶/可交换态转变,增加金属的生物可利用性,从而也增加潜在生态风险。     

Effects of cadmium on nutrient uptake and translocation by Indian Mustard

Plants that hyperaccumulate metals are ideal subjects for studying the mechanisms of metal and mineral nutrient uptake in the plant kingdom. Indian Mustard (Brassica juncea) has been shown to accumulate moderate levels of Cd, Pb, Cr, Ni, Zn, and Cu. In this experiment, 10 levels of Cd concentration treatments were imposed by adding 10-190 mg Cd kg(-1) to the soils as cadmium nitrate [Cd(NO3)2]. The effect of Cd on phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and the micronutrients iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in B. juncea was studied. Plant growth was affected negatively by Cd, root biomass decreased significantly at 170 mg Cd kg(-1) dry weight soils treatment. Cadmium accumulation both in shoots and roots increased with increasing soil Cd treatments. The highest concentration of Cd was up to 300 mg kg(-1) d.w. in the roots and 160 mg kg(-1) d.w. in the shoots. The nutrients mainly affected by Cd were P, K, Ca, Fe, and Zn in the roots, and P, K, Ca, and Cu in the shoots. K and P concentrations in roots increased significantly when Cd was added at 170 mg kg(-1), and this was almost the same level at which root growth was inhibited. Zn concentrations in roots decreased significantly when added Cd concentration was increased from 50 to 110 mg kg(-1), then remained constant with Cd treatments from 110 to 190 mg kg(-1). However, Zn concentrations in the shoots seemed less affected by Cd. It is possible that Zn uptake was affected by the Cd but not the translocation of Zn within the plant. Ca and Mg accumulation in roots and shoots showed similar trends. This result indicates that Ca and Mg uptake is a non-specific process.     

宝山堇菜多金属吸收特征和耐性策略

宝山堇菜Viola baoshanensis Shu,Liu et Lan是一种Cd超富集植物,但它对不同重金属的吸收和转运能力有待进一步研究。从湖南桂阳宝山多金属矿区中筛选4个宝山堇菜优势分布的小生境,分析这些生境中宝山堇菜及其根区土壤的重金属质量分数。化学分析结果显示,宝山堇菜优势分布土壤中Cd、Pb、Zn、Cu、Mn和Fe的平均质量分数（mg/kg）分别为471、15 044、8 273、1 776、4 702和69 054。宝山堇菜地上部Cd、Pb、Zn、Cu、Mn和Fe的平均质量分数（mg/kg）分别为387、1 077、1 037、99、379和1 812,其中Cd、Pb超过超富集植物标准,Zn、Cu的平均质量分数大约是Zn、Cu超富集植物标准的10%,Mn的平均质量分数低于Mn超富集植物标准的5%,Fe的平均质量分数高于1 000 mg/kg。上述结果表明,宝山堇菜可以超富集Cd和Pb,富集Zn、Cu和Fe以及低积累Mn。此外,宝山堇菜对不同重金属差别化吸收模式可能也代表了超富集植物适应重金属复合污染土壤的一种策略。     

Effects of Cadmium on Nutrient Uptake and Translocation by Indian Mustard

Plants that hyperaccumulate metals are ideal subjects for studying the mechanisms of metal and mineral nutrient uptake in the plant kingdom. Indian Mustard (Brassica juncea) has been shown to accumulate moderate levels of Cd, Pb, Cr, Ni, Zn, and Cu. In this experiment, 10 levels of Cd concentration treatments were imposed by adding 10–190 mg Cd kg^–1 to the soils as cadmium nitrate [Cd(NO₃)₂]. The effect of Cd on phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and the micronutrients iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in B. juncea was studied. Plant growth was affected negatively by Cd, root biomass decreased significantly at 170 mg Cd kg^–1 dry weight soils treatment. Cadmium accumulation both in shoots and roots increased with increasing soil Cd treatments. The highest concentration of Cd was up to 300 mg kg^–1 d.w. in the roots and 160 mg kg^–1 d.w. in the shoots. The nutrients mainly affected by Cd were P, K, Ca, Fe, and Zn in the roots, and P, K, Ca, and Cu in the shoots. K and P concentrations in roots increased significantly when Cd was added at 170 mg kg^–1, and this was almost the same level at which root growth was inhibited. Zn concentrations in roots decreased significantly when added Cd concentration was increased from 50 to 110 mg kg^–1, then remained constant with Cd treatments from 110 to 190 mg kg^–1. However, Zn concentrations in the shoots seemed less affected by Cd. It is possible that Zn uptake was affected by the Cd but not the translocation of Zn within the plant. Ca and Mg accumulation in roots and shoots showed similar trends. This result indicates that Ca and Mg uptake is a non-specific process.     

不同锰处理对镉胁迫下2种油菜重金属累积和根系形态的影响

采用水培试验,研究Cd胁迫(10μmol·L~(-1))条件下,不同浓度Mn(0,0.1,1,10,100μmol·L~(-1))处理对2种镉累积能力不同的油菜生物量、Cd和Mn含量以及根系形态参数的影响。结果表明,与正常营养处理Mn1相比,缺Mn和Mn过量处理显著降低2种油菜的地上部和镉低积累油菜"华骏"的根部生物量,而对普通油菜"寒绿"的根部生物量没有显著影响。与Mn1处理相比,缺Mn处理下2种油菜的Cd累积总量和"华骏"地上部Cd含量显著降低;Mn过量处理下2种油菜根部和地上部Cd含量均呈升高趋势,2种油菜的Cd累积总量无显著变化或显著降低。随Mn处理浓度升高,2种油菜地上部和根部Mn含量显著升高,缺Mn处理下2种油菜根部的Mn含量低于Mn缺乏的临界值。与Mn1处理相比,缺Mn处理下"华骏"的根长、表面积、体积、平均直径和根尖数显著降低;Mn过量处理下"寒绿"的根长以及"华骏"的根系表面积、体积显著降低;缺Mn处理下2种油菜细根表面积所占的比例增加,粗根表面积比例降低;Mn过量时,"寒绿"的粗根表面积比例增加,细根比例降低,而"华骏"则相反。总的来看,缺Mn处理影响油菜根系和地上部生长,减少地上部Cd含量和植株Cd累积总量;Mn过量处理下油菜生长也受到抑制,但是油菜地上部和根部Cd含量有所升高;2种油菜的根系形态学参数在不同Mn处理下变化规律不同,表现出不同的响应策略。     

粉煤灰钝化污泥人工土壤上高麦草生长发育及营养状况研究

通过温室盆栽试验研究不同比例粉煤灰钝化污泥人工土壤上高麦草的生长发育及营养状况，试验结果表明：土壤中加入粉煤灰钝化污泥显著增加了高麦草的干物重．脱水污泥加入其鲜重的10％粉煤灰钝化后再按1∶1和1∶5体积比与土壤混合配成的人工土处理和加入其鲜重的35％粉煤灰钝化后再按1∶1体积比与土壤混合配成的人工土处理高麦草的产量都显著高于自然土壤施用化肥的处理，高麦草的发芽率也不受影响．随着粉煤灰加入量的增加，高麦草地上部Ca，Mg和B的浓度（w／％或w／mg．kg－1）增加而K，Fe，Mn和Zn的浓度下降，高麦草根中Fe，Mn，Cu和Zn的浓度显著高于其地上部中的浓度．所有粉煤灰钝化后污泥人工土壤高麦草都没有出现N和P的缺乏和重金属毒害，说明合适比例的粉煤灰钝化污泥人工土壤是高麦草的良好生长介质．     

根表铁膜对水稻铅吸收转运的影响

通过温室土壤盆栽试验研究不同生育期水稻根表铁膜形成对水稻吸收和转运Pb的影响。结果表明,两种水稻根表铁膜形成量(以DCB-Fe含量计)及铁膜中吸附的Pb量均随着生育期的延长而减少。水稻根表铁膜Fe含量与铁膜吸附的Pb量呈显著的正相关关系(r=0.798,p0.01)。水稻根系和茎叶吸收积累Pb随着不同品种和不同生育期而变化。品种NK57籽粒Pb含量显著高于品种YD6,前者为后者的1.9倍。从富集系数和分配比率来看,Pb主要富集在水稻的铁膜和根系中,而积累在茎叶和籽粒中的比率较少。Pb从水稻根表铁膜、根系和茎叶向籽粒中的转运系数在两个水稻品种间差异均不显著。水稻分蘖期和孕穗期根表铁膜量与根系Pb含量均呈显著的正相关关系(p0.05),但是成熟期水稻根表铁膜量与根系、茎叶和籽粒中Pb含量相关性均不显著,说明根表铁膜形成对水稻分蘖期和孕穗期吸收积累Pb有一定影响,但对水稻成熟期根系、茎叶和籽粒吸收积累Pb影响不大。     

Introducing a new metal accumulator plant and the evaluation of its ability in removing heavy metals

A field study was conducted in a dried waste pool of a lead (Pb) mine in Arak (Iran) to find the accumulator plant(s) and to evaluate the amount of metal bioaccumulation in the root and shoot portion of the naturally growing vegetation. Concentrations of heavy metals were determined both in the soil and the plants that were grown in the dried waste pool. The concentrations of total Cu, Zn, Pb, and Ni in the waste pool were found to be higher than the natural soil and the toxic levels. The results showed that six dominant vegetations, namely, Centaurea virgata, Eleagnum angustifolia, Euphorbia macroclada, Gundelia tournefortii, Reseda lutea, and Scariola orientalis accumulated heavy metals. Based on the results, it was concluded that E. macroclada belonging to Euphorbiaceae is the best Pb accumulator and also a good accumulator for Zn, Cu, and Ni. The bioaccumulation ability of E. macroclada was evaluated in experimental pots. The study showed that the amount of heavy metals in polluted soils decreased several times during two years of phytoremediation. The accumulation of metal in the root, leaves, and shoot portions of E. macroclada varied significantly, but all the concentrations were within the toxic limits. Based on the obtained data, E. macroclada is an effective accumulator plant for soil detoxification and phytoremediation in critical conditions.     

Forage and rangeland plants from uranium mine soils: long-term hazard to herbivores and livestock?

Metalliferous uranium mine overburden soils integrated into arable land or stabilized by perennial rangeland plants evoke concern about the quality of crops and the exposure of grazing and thereby soil-ingesting (wildlife) herbivores to heavy metals (HM) and radionuclides. In a 2-year trial, thirteen annual and perennial forage and rangeland plants were thus potted on, or taken from, cultivated field soil of a metalliferous hot spot near Ronneburg (Germany). The content of soil and shoot tissues in 20 minerals was determined by ICP-MS to estimate HM (and uranium) toxicities to grazing animals and the plants themselves, and to calculate the long-term persistence of the metal toxicants (soil clean-up times) from the annual uptake rates of the plants. On Ronneburg soil elevated in As, Cd, Cu, Mn, Pb, U, and Zn, the shoot mineral content of all test plants remained preferentially in the range of “normal plant concentrations” but reached up to the fourfold to sixfold in Mn, Ni, and Zn, the 1.45- to 21.5-fold of the forage legislative limit in Cd, and the 10- to 180-fold of common herb concentrations in U. Shoot and the calculated root concentrations in Cd, Cu, Ni, and Zn accounted for phytotoxic effects at least to grasses and cereals. Based on WHO PTWI values for the tolerable weekly human Cd and Pb intake, the expanded Cd and Pb limits for forage, and reported rates of hay, roots, and adhering-soil ingestion, the tolerable daily intake rates of 0.65/11.6 mg in Cd/Pb by a 65 kg herbivore would be surpassed by the 11- to 27/0.7- to 4.7-fold across the year, with drastic consequences for winter-grazing and thereby high rates of roots and soil-ingesting animals. The daily intake of 5.3–31.5 mg of the alpha radiation emitter, U, may be less disastrous to short-lived herbivores. The annual phytoextraction rates of critical HM by the tested excluder crops indicate that hundreds to thousands of years are necessary to halve the HM and (long-lived) radionuclide load of Ronneburg soil, provided the herbage is harvested at all. It is concluded that the content in Cd/As, Cd, and Cu exclude herbage/Ronneburg soil from the commercial use as forage or pasture land soil for incalculable time spans. Caution is required, too, with the consumption of game.     

Effect of acid rain on the fractionation of heavy metals and major elements in contaminated soils

Acid rain is a serious environmental problem worldwide. In the present study, we investigated the effect of acid rain (1:1 equivalent basis H₂SO₄:HNO₃) at pH values of 2.0, 4.0 and 7.0 on the fractionation of heavy metals (Cd, Cu, Fe, Mn, Ni, Pb and Zn) and major elements (K, Na, Ca, and Mg) in contaminated calcareous soils over a 2084 h period. Heavy metals and major elements in soil samples were fractionated before and after 2084 h kinetic release using a sequential extraction procedure. Before kinetic studies the predominant fractions of K, Na, Ca, Mg, Cd and Ni were mainly associated with carbonate fraction (CARB), whereas Fe, Mn and Zn were associated with the Fe–Mn oxide fraction (Fe–Mn oxide). The highest percentage of Pb and Cu were found in the exchangeable (EXC) and organic matter (OM) fractions, respectively. After kinetic study using different simulated acid rain solutions, the major fractions of heavy metals (expect of Cu) and Na was the same as before release. Upon the application of different acid rain solutions, K and Mg were found dominantly in Fe–Mn oxide fraction, whereas Ca was in the EXC fraction. The results provide valuable information regarding metal mobility and indicated that speciation of metals (Cu and Zn) and major elements in contaminated calcareous soils can be affected by acid rain.     

Scalp hair metal analysis in the assessment of the occupational exposure of arc welders

Eleven metals (Ca, Mg, Fe, Zn, Cu, Mn, Cd, Co, Cr, Ni and Pb) were estimated in hair samples of metal arc welders and a control group with the same socioeconomic background. Nitric acid–perchloric acid wet digestion procedure was adopted for the estimation of endogenous metal contents by ICP-AE technique. The study exhibited the following increasing order of the metal concentrations: Cd??1, dry weight, respectively. On average, the levels of Mn, Ni, Pb and Fe were found to be 1.5–2.4 times higher in the hair of welders compared with controls. Besides age and exposure which were strongly correlated, Cu–Mg, Mn–Mg, Ca–Co and Cd–Zn also showed significantly positive correlations. The identification of metal sources, done by cluster and principal component analyses, revealed four factors: age and exposure; Cu, Mg, Mn and Fe; Ca and Co; Cd, Zn, Ni and Pb. High levels of Fe were found to have a depleting impact on Co levels. The arc welders were feared to accumulate heavy metals in their bodies due to long-term endogenous exposure.     

Heavy metal accumulation and changes in metabolic parameters in Cajanas cajan grown in mine spoil

The extent of accumulation of some heavy metals in root and aerial plant parts, total chlorophyll, protein and yield of C. cajan exposed to mine spoil were investigated. Chlorophyll and protein level on the control site increased from the basal level to 1.49 fold and 1.92 fold respectively on 150 d and attained a plateau within 210 d. The maximum decline in leaf protein and yield in selected mine spoil has been observed 37% (18.46 mg g(-1) fresh wt) and 76% at 150 d and maintained a slight decline when duration was extended up to 210 d as compared to control. Whereas in case of photo pigment content (Chlorophyll a and b) the maximum reduction was almost 42% (0.786 mg g(-1) fresh wt) during 210 d from its basal level. Plant tissues have accumulated maximum level of selected cations in control and mine spoil in the order (Fe > Mn > Zn > Cu > Pb > Ni > Cr > Cd). Metal accumulation in different plant parts was observed in the decreasing order roots > shoots > leaves > seeds. Invariably high accumulation of such cations in roots overshoots indicated accumulation, retention or restricted translocation from root to shoot. The metal share of seed varied from 1.3-39.5 fold as compared to their respective controls but their amount was quite below the toxic range. Thus the present work explores the metal accumulation in the plant tissues.     

山西省稷山和永济两地矮牡丹体内无机元素含量的比较

采用原子吸收分光光度法和比色法测定了山西省稷山和永济两地区矮牡丹体内和生境土壤中的10种元素(K、Mg、Mn、Fe、Ni、Zn、Cu、Cd、Cr、Pb),分析比较了各种元素在不同地区矮牡丹体内和生境土壤中的分布规律及不同地区矮牡丹对无机元素的吸收富集能力.结果表明,两地区矮牡丹体内和生境土壤中无机元素含量无显著性差异;土壤及植株不同器官间元素含量也无显著性差异;两地区矮牡丹对不同元素的富集系数有显著差异,差异主要表现在对Cd(永济0.457,稷山0.213)和Ni(永济0.093,稷山0.167)的富集上,植株不同器官之间的富集系数无显著差异.表4参9     

EDTA and citric acid mediated phytoextraction of Zn, Cu, Pb and Cd through marigold (Tagetes erecta)

Phytoextraction is an emerging cost-effective solution for remediation of contaminated soils which involves the removal of toxins, especially heavy metals and metalloids, by the roots of the plants with subsequent transport to aerial plant organs. The aim of the present investigation is to study the effects of EDTA and citric acid on accumulation potential of marigold (Tagetes erecta) to Zn, Cu, Pb, and Cd and also to evaluate the impacts of these chelators (EDTA and citric acid) in combination with all the four heavy metals on the growth of marigold. The plants were grown in pots and treated with Zn (7.3 mg l(-1)), Cu (7.5 mg I(-1)), Pb (3.7 mg l(-1)) and Cd (0.2 mg l(-1)) alone and in combination with different doses of EDTA i.e., 10, 20 and 30 mg l(-1). All the three doses of EDTA i.e., 10, 20 and 30 mg l(-1) significantly increased the accumulation of Zn, Cu, Pb and Cd by roots, stems and leaves as compared to control treatments. The 30 mg l(-1) concentration of citric acid showed reduced accumulation of these metals by root, stem and leaves as compared to lower doses i.e., 10 and 20 mg l(-1). Among the four heavy metals, Zn accumulated in the great amount (526.34 mg kg(-1) DW) followed by Cu (443.14 mg kg(-1) DW), Pb (393.16 mg kg(-1) DW) and Cd (333.62 mg kg(-1) DW) in leaves with 30 mg l(-1) EDTA treatment. The highest concentration of EDTA and citric acid (30 mg l(-1)) caused significant reduction in growth of marigold in terms of plant height, fresh weight of plant, total chlorophyll, carbohydrate content and protein content. Thus EDTA and citric acid efficiently increased the phytoextractability of marigold which can be used to remediate the soil contaminated with these metals.     

重金属在土壤-水稻体系中的分布、变化及迁移规律分析

以佛山市南海区小塘镇和高明区杨梅镇的标准农田为研究对象,分析重金属在土壤和水稻植株不同部位的分布及其随时间变化、迁移规律。结果表明:重金属被水稻吸收以后,多数仍滞留在土壤里,只有少量向地上部分迁移。重金属在水稻植株不同部位的质量分数分布由大到小的次序为:根→茎→籽→叶。水稻地上部分中4种重金属元素分布由大到小的次序是:Zn→Cu→Pb→Cd。水稻分蘖期重金属在根、茎和叶的积累量达到最大,随着时间的延续,在根部积累的重金属就越来越少,茎和叶积累的重金属在拔节期降至最小,随后又慢慢上升。4种重金属在水稻植株中的迁移能力由大到小依次为:Cd→Zn→Cu→Pb,但也有个别情况是Cu的迁移能力大于Zn。     

Fraction distribution and migration of heavy metals in mangrove-sediment system under sulphur and phosphorus amendment

In this study, mangrove seedlings (Kandelia obovata (S. L.)) were cultivated in rhizo-boxes, which contain sediments collected from natural mangrove forest and modified with different rates of sulphate and phosphate. The fraction distributions of Zn, Cd, Cu, Ni and Pb in rhizosphere and non-rhizosphere sediments were studied by using a sequential extraction method. Metal concentrations in plant tissues and iron plaque on root surface were also determined to reveal migration variation of heavy metals in the plant-sediment system. The results showed that the activities of K. obovata roots enhance the reducible metals while reducing acid-extractable and oxidisable metals; sulphur amendment benefits the combination of metal ions with S^2– and therefore reduces the bioavailability of metal pollutants; addition of sulphur also improves the content of iron plaque on the root surface, which plays an important role in metal accumulation by K. obovata root tissue; the addition of sulphur markedly reduces the concentration of Cd in roots, but significantly enhanced the concentrations of Cu, Zn, Ni and Pb in roots. The results indicate that sulphur and phosphorus content in mangrove sediment, and the growth of mangrove plant can significantly influence the migration of heavy metals in the mangrove wetland ecosystem.