Speciation distribution of Cd, Pb, Cu, and Zn in contaminated Phaeozem in north-east China using single and sequential extraction procedures.
Contamination by heavy metals in the soil environment is of great concern because of their toxicity and threat to human health (Zhou and Song 2004). Unlike organic contaminants, most metals in the soil environment do not undergo microbial or chemical degradation, and therefore concentrations of metals persist in soils for a long time after their input (Guo et al. 2006). Heavy metals remaining in the soil environment seep into groundwater or even channel into the food chain in crops growing on contaminated soils (Lin et al. 1998). Much research has been conducted on heavy metal contamination in soils from various anthropogenic sources such as industrial waste, automobile emission, mining or processing activities, and agricultural practice (Zhou and Huang 2001). Originally, most analytical measurements dealt with the total content of particulate metals in analysed samples. Fewer attempts have been made to evaluate the speciation of metals in particulate forms (i.e. the partitioning among various forms in which they might exist) (Tessier et al. 1979; Li et al. 1995; McGrath et al. 1999; Kot and Namiesnik 2000). The use of total concentration as a criterion to assess potential effects of soil contamination is not sufficient, because fate and toxicity of heavy metals in a contaminated soil is greatly controlled by speciation in the soil (Ernst 1996; Lo and Yang 1998; Peakall and Burger 2003). Biochemical and toxicological investigations have also shown that, for living organisms, chemical forms of a specific element, or the oxidation state in which that an element is introduced into the environment, is crucial, as well as the quantities (Lock and Janssen 2001). It is widely recognised that to assess environmental impact of heavy metal contamination in soils, the determination of the metal speciation will give more information about the potential for release of contaminants and further derived processes of migration and toxicity (Navas and Lindhorfer 2003). Therefore, in ecological risk assessment, it is necessary to determine chemical partitioning among various soil-chemical phases (Qian et al. 1996; Kot and Namiesnik 2000; Navas and Lindhorfer 2003).
The occurrence of heavy metals in soils affects their solubility, which directly influences their bioavailability (Ma and Rao 1997; Zhou and Sun 2002). Metal bioavailability is often correlated with the free-metal concentration, because the free ion is often the most bioavailable form of a dissolved metal. A method widely used to assess the lability and bioavailability of heavy metals in soils is the leaching of soils by chemical extractants. According to this, single and sequential extraction procedures have been applied using various extractants. Single extraction is a short procedure that evaluates the most labile, mobile, and mobilisable forms in soils, and allows a substantial time saving (Maiz et al. 1997). Single extraction with less aggressive solutions, called 'soft' or 'mild' extractants, such as neutral salts, provides a relative empirical method for evaluating the mobility of heavy metals, while extraction by chelating agents such as DTPA and EDTA and dilute acids could provide the correlation between extractability and plant uptake (Maiz et al. 2000; Fangueiro et al. 2002). Sequential extraction provides detailed information on distribution in different association forms, which are the potential source of metal available to biota (Qian et al. 1996; Zhou 2003). Usually, the fractions considered are: (1) exchangeable, (2) bound to carbonates, (3) bound to Fe and Mn oxides, (4) bound to organic matter, (5) residues (Salomons and Forstner 1980; Maiz et al. 2000; Zhou and Sun 2002).
Phaeozem (http://www.fao.org/ag/agl/agll/key2soil.stm) is a typical soil type in north-east China, which is one of the national food provision areas because of its high organic matter contents and intensive farming. The quality and quantity of agricultural products in this area were influenced by interruptions during various agricultural and industrial processes in recent decades. However, most researchers consider this a 'clean' area (Guo and Zhou 2004). Very little information on contamination status of this area exists at present. The first survey conducted at a regional scale analysed the distribution of contamination sources of the cadmium (Cd), lead (Pb), copper (Cu), and zinc (Zn) in a wide variety of land uses and indicated a close relation between metal contents and source types. Several sites with possible multiple contamination were also identified after analysing the total contents of contaminants (Guo and Zhou 2006). Based on this previous research, the aim of this work was to further study the distribution of metal speciation in the contaminated Phaeozem in the Harbin industrial district, in order to determine plant availability and contaminant mobility and to provide information for risk assessment on Phaeozem contamination.
Materials and methods
The study area is situated in Harbin, Heilongjiang Province, China, which is located in the continental temperate monsoon zone, with a dry and cold winter and a warm and wet summer. The annual mean temperature is 5[degrees]C. The annual average precipitation ranges from 500 to 600 mm, of which 50-70% occurs during May-September, and the frostless duration is around 120 days per year. The study site (Fig. 1) was near the Chemo-Industrial Road, with different industries such as plastic, paint, pesticide, and cement factories. Other major anthropogenic effects in this area are traffic exhaust emissions and agricultural activities. The soil is loose and black in colour. High contents of organic matter and cation exchange capacity are the main points of this kind of soil.
[FIGURE 1 OMITTED]
The studied area is about 10 000 [m.sup.2]. Fifteen surface (0-0.20m) and 15 subsurface (0.20-0.40 m) soil samples were collected following a tessellation pattern on August 2004 from a contaminated site in the studied area. Soil samples were air dried, ground to pass through a 2-mm plastic sieve, and milled in an agate pot to a fine powder (<170 um), then stored at room temperature in polyethylene flasks. Representative plants of Zea mays (L.) (Longdan 23), Glycine max (L.) Merr, Artemisia annua (L.), Artemisia sieversiana (Ehrh.) Willd., and Erigeron canadensis (L.) mainly growing in the contaminated site were harvested at the reproductive flowering phase. The aboveground material of the plant samples was rinsed with distilled water, dried at 105[degrees]C for I h and at 80[degrees]C for 24 h, ground, and stored in glass containers until analysis.
Soil properties and total metal contents
Soil pH was determined in a soil : water (1:2.5) suspension by using a pH meter. Organic matter and cation exchange capacity (CEC) determinations were carried out following the standard methods of chemical analysis (Zhou et al. 2003). Some main soil properties for the surface and subsurface samples are listed in Table 1. The pH values ranged from acidic to basic (6.2-6.9). The organic matter contents were in a broad range and the average at the surface was <32 mg/kg. CEC ranged from 15 to 32 cmol/kg. These values were mostly below the usual ranges of agricultural Phaeozem (Li and Zheng 1989; Shen 1998).
In order to assess the extent of metal contamination that was accumulated in the soil and plant samples and to provide an assessment of the long-term potential effects, total metal contents were determined after strong acid digestion. The acids used for soil and plant samples were HN[O.sub.3]-HCl[O.sub.4] (HN[O.sub.3]:HCl[O.sub.4] 3:1) (Guo and Zhou 2006).
Single extraction procedure
Aliquots of the dry soil samples were accurately weighed into 100-mL acid-cleaned polystyrene centrifuge tubes. Different extraction solutions were added and the tubes were shaken at ambient temperature on a variable speed reciprocal shaker at 220 strokes/min for 2 h (Maiz et al. 2000). Experimental details are listed in Table 2. After the extraction, the sample solutions were centrifuged at 5000 r.p.m, for 15 min and then filtered. The supernatant was used for analysis. All experiments were carried out at a room temperature of 25 [+ or -] 1[degrees]C.
The sequential extraction was developed from that of Tessier et al. (1979) using the same terminology. This procedure was selected because it is well documented, widely used, and has been adapted to the study of soils and dusts (Clevenger 1990; Navas and Lindhorfer 2003). The extraction was carried out progressively on an initial weight of 2.0 g of test material, which was contained in a centrifuge tube (polypropylene, 100 mL) and shaking with variable speed reciprocal shaker. The shaking speed was kept at 220 strokes/min. The extractants and operationally defined chemical fractions were as follows:
Fraction 1, exchangeable phase: the samples were extracted at room temperature for 1 h with 16 mL of 1 mol Mg[Cl.sub.2]/L (pH 7) with continuous stirring;
Fraction 2, carbonate phase: the wash residue of step 1 was extracted at room temperature with 16 mL of 1 mol NaOAc/L (adjusted to pH 5 with HOAc) for 5 h with continuous shaking;
Fraction 3, Fe-Mn oxide phase: the residue of step 2 was further extracted with 16 mL of 0.04 mol N[H.sub.2]OH.HCl/L in 25% HOAc (v/v) heated in a water bath for 6 h at 96[degrees]C with occasionally agitation;
Fraction 4, organic phase: the residue from the Fe-Mn oxide fraction was extracted with 4 mL of 0.02 tool HN[O.sub.3]/L and 6 mL of [H.sub.2][O.sub.2] 30% (adjusted to pH 2 with HN[O.sub.3]). The mixture was heated to 85[degrees]C for 2 h, with occasional agitation. A second 6 mL of [H.sub.2][O.sub.2] 30% (pH 2 with HN[O.sub.3]) was added and the mixture heated again to 85[degrees]C for another 3 h with intermittent agitation. After cooling, 6 mL of 3.2 M N[H.sub.4]OAc in 20%(v/v) HN[O.sub.3] was added and the samples diluted to 30 mL and agitated continuously for 30 min;
Fraction 5, residue: the residue of step 4 was digested with 18 mL HN[O.sub.3] (65%) and 6 mL HCl[O.sub.4] (40%) in 180 [+ or -] 5[degrees]C electro-thermal tank. When the sample was closely dried and became opalescent, it was diluted to 25 mL in a test tube with 5% HN[O.sub.3].
After each successive extraction, separation was done after centrifuging for 30min. The supernatant was filtered and placed in a tube for measuring. The residue was washed with 20 mL deionised water (DIW) followed by vigorous shaking, and then followed by centrifuging for the separation before the next extraction. All experiments were carried out at a room temperature of 25 [+ or -] 1[degrees]C.
Guaranteed reagents and DIW were used throughout the study. All pipettes, tubes, and containers were washed with a detergent, then soaked for 24 h in 2% nitric acid (HN[O.sub.3]) solution and rinsed repeatedly with DIW. Total metal concentrations of the supernatants from each step were analysed by the graphite furnace atomic absorption spectrophotometer. Blanks were used for background correction and other sources of error. At least l duplicate and 1 spike sample were run for 5 samples in the acid digestion to verify precision of the analytical methods. The spike recovery and precision were found to be within 100 [+ or -] 10%. Samples were in triplicate in both single and sequential extraction procedures (LSR test, P < 0.05).
Results of single extraction
Eight reagents classified in the 3 types are listed in Table 2 and were used to evaluate the potential mobility and bioavailability of metals in the contaminated Phaeozem. The metal extraction efficiency obtained with the single extraction procedures studied can be compared from the results presented in Table 3.
In the surface soil samples, the extractabilities of the 4 metals obtained with chelating reagents were generally higher than with dilute acid and neutral salts. The 2 chelating reagents could extract out >80%, 40%, 30%, and 20% of the total Cd, Pb, Cu, and Zn, respectively. EDTA hads a higher chelating capacity for the 4 metals in Phaeozem than DTPA. HOAc had higher extracting efficiency than HCl. The neutral salts had different extraction efficiencies for the 4 metals. The lowest extraction efficiency of Cd was obtained with the Mg[(N[O.sub.3]).sub.2], but it had a higher efficiency for Zn and Cu. Among the neutral salts, high Cd and Pb extractability was obtained with N[H.sub.4]Cl.
In the subsurface soil, the extraction procedure with HOAc had the highest efficiency for Cd and Pb. Among the neutral salts, Mg[(N[O.sub.3]).sub.2] had the most stable extraction efficiency for the 4 metals. The lowest extraction efficiency was obtained with Ca[Cl.sub.2], but differences among extractants with neutral salts or chelating reagents were not as clear as that for the surface soil samples.
Results of sequential extraction
As shown in Fig. 2, the fractions of Pb, Cu, and Zn were mainly bound to the residual phase with 40-72% recovery for the surface and 68-84% for the subsurface soil samples. Compared with the residual phase, much lower proportions of Pb, Cu, and Zn were extracted in the exchangeable and carbonate phases, which on average account, respectively, for 1.2% and 3.3% of total Pb concentration, 4.6% and 2.1% of total Cu, and 0.7% and 7.3% of total Zn in the surface soil samples. In the subsurface soil samples, insignificant amounts of Pb and Cu were retained in the carbonate and exchangeable phases and, similarly, negligible amounts of Zn were retained in these phases.
[FIGURE 2 OMITTED]
The percentage distribution of Cd was different from the rest of the metals. The residual of Cd was <10% in the surface and 30% in the subsurface samples. However, 32% and 47% of Cd from surface and subsurface samples, respectively, was associated with the exchangeable phases. In the surface samples, the lower proportion of total Cd was extracted in the organic phase (9.4%), and 22% and 33% of Cd was associated with the carbonate and oxide phase, respectively. In the subsurface samples, Cd in association with the carbonate phase was below detection limit (2 [micro]g/kg), and 4.4% was associated with oxide phase.
Assessment of bioavailability and mobility of the heavy metals
As can be seen in Table 4, the plant species on the contaminated Phaeozem had different contents of the 4 metals. Erigeron canadensis had the highest contents of the 4 metals. The 4 metals presented different relationships between extractability and plant uptake (Fig. 3). The Cd concentration in surface soil samples extracted by chelating reagents was close to the concentrations in Erigeron canadensis and Artemisia annua, and the concentrations of Cd in Glycine max and Artemisia sieversiana were close to those from the dilute acid. Concentration of Cd in Zea mays was much lower than that in the surface soil sample extracted by different reagents. Pb concentrations in the 5 plant species were close to the available Pb extracted by neutral salts. The concentration of Cu in Zea mays was similar to the Cu extracted by dilute acids, whereas concentrations in the other 4 plant species were close to that extracted by chelators in the surface soil samples. Zn concentration in the plants was higher than the potentially available Zn extracted by the 3 types of reagents.
[FIGURE 3 OMITTED]
A large number of single extraction procedures were reviewed by Ginepro et al. (1996) and Pueyo et al. (2004). They stated that wide ranges of extracting efficiencies are possible depending on the different chemical properties of the selected extractants. In this study, the part of the 4 metals extractable by chelating reagents was greater than that extractable by dilute acids and by neutral salts in surface and subsurface soil samples. The maximum percentage extractable by chelating reagents was closer to the plant concentrations of Cd, Cu, and Zn in the contaminated Phaeozem. The acid-base properties of EDTA and DTPA could result in competition on the binding sites of metal ions and production of the new compound in the soil. They tend to release metals out of the non-silicate bound phase and, therefore, correlate well with plants contents and with the plant-available fraction for the 3 metals. The percentage extractable by neutral salts generally demonstrated the potentially mobile portion of the metals in Phaeozem. This part is far lower than that extracted by dilute acid and chelating reagent, but the contents of Pb in the 5 plant species were close to the portion extractable by neutral salts. Conductimetric experiments showed that the binding of Cd, Cu, and Zn has a significant electrostatic contribution, whereas for Pb there is a higher level of covalence in the binding of humic acids, which could result in the higher release and movement of Cd but lower mobility of Pb in the soil-plant system (Pinheiro et al. 1994). Results indicated N[H.sub.4]Cl had the most stable extractability among the 4 neutral salts. This could be due to the possible reaction of these elements with N[H.sub.3] and to the higher salt concentration of the N[H.sub.4]Cl solution (Pueyo et al. 2004). Based on the comparison of the available parts extracted by chelating reagents with those by neutral salts in the surface soil samples, Cd and Zn could be more easily accumulated in the plants, whereas Pb and Cu were less mobile and fixed in soils. Pb and Cu have lower solubility and are more stable in compound form than Cd and Zn in the studied area, with a high content of organic matter, which had been noted in previous work (Pinheiro et al. 1994; Zhang et al. 2001; Weng et al. 2002).
Metal concentrations in the 5 plants varied over a wide range. Owing to the variety of soil chemical conditions in metal-contaminated soil and the evolutionary potential of plants to adapt to extreme environments, a number of plant species are able to colonise naturally metal-enriched soils and to maintain a functional ecosystem. Metal concentrations of Cd, Cu, and Zn in Zea mays were low, and it can grow naturally in the contaminated site owing to its metal-resistant characteristics with the help of mycorrhizal fungi, by binding heavy metals into the roots and restricting their ability to migrate into the plant. The metal-binding capacity of mycorrhizal fungi is so striking that both the uptake of metals from the soil and their subsequent translocation to Zea mays may be effectively restricted when exposed to pollution, whereas it can enhance the plant access to nutrients such as P (Ernst 1996; Christie et al. 2004; Gaur and Adholeya 2004; Chiu et al. 2005). Metal concentrations of Cd, Cu, and Zn in Erigeron canadensis and Artemisia annua are higher and close to those in the soils. The major processes involved in the accumulation of heavy metals from soil to the plants possibly include bioactivation of metals in the rhizosphere through root-microbe interaction; and detoxification of metals by distributing to the apoplasts, e.g. binding to cell walls and chelation of metals in the cytoplasm with various ligands, such as phytochelatins, metallothioneins, metal-binding proteins, and sequestration of metals into the vacuole by tonoplast-located transporters (Wei and Zhou 2004; Yang et al. 2005; Qureshi et al. 2005). The results have shown high availability of Cd and Zn in Glycine max. This important crop in the study site could be at risk with increasing input of the 2 metals.
In sequential extraction, Cu, Pb, and Zn were strongly retained in the residual phase in all the samples. These heavy metals are contained in the crystal lattices of minerals with strong bonds and consequently they will not be released into the environment. According to Navas and Lindhorfer (2003), processes of metal mobilization-immobilisation are affected by a variety of soil properties. The free ion activity in the soil is largely determined by metal bonding to the solid phase. Solid organic matter, dissolved organic matter, clay, and ion hydroxides could have a significant impact on the metal activity. High contents of organic matter in Phaeozem would contribute to the different bonding capacities of heavy metals. For example, Pb has a much greater and more stable affinity than Cd with soil sorbents after introducing into the soil environment. In this study, a higher proportion (33%) of Pb was associated with the oxide phase, and only in the case of a change in the redox conditions towards reductive would it be released from oxides. The high percentage of Cd in the exchangeable phase (32-47%) represents the mobile and bioavailable fractions. In this phase, Cd has the more labile bonds and can be more easily released into the environment. The Cd bound to the carbonate fraction would be released if conditions become acidic. This could be the supplement for the available Cd equilibrium in soil solution. Insignificant amounts of Cu in the exchangeable phase appeared in the sequential extraction. This could be closely connected with its lower background concentration in the tested samples (Guo and Zhou 2004).
The distribution of heavy metal speciation in the surface soil samples was different from that in the subsurface soil samples. The total and extractable metal concentrations in surface soil samples are generally higher than in the subsurface samples and clean soils (Table 1). Total concentrations of Cd, Pb, and Zn greatly increased compared with the background values at the study site (Guo and Zhou 2006). The increasing contents of the 3 metals were mostly concentrated in the surface soil. External sources were the main contributors to the increasing Cd, Pb, and Zn. The percentage of the residual fraction of the metals apparently increased in the subsurface soil samples, whereas the percentage of exchangeable phase Cd was relatively similar in the 2 soil layers. The source of Cd could result in the high bioavailability and mobility. According to its total content in the study area, Cd is the biggest danger in the contaminated site corresponding with its source and speciation distribution. The most mobile fraction of Cd in the contaminated area could transfer to the plants or the groundwater and endanger public safety.
This work was financially supported by the Ministry of Science and Technology, People's Republic of China as a 973 project (approval No. 2004CB418503) and by the National Natural Science Foundation of China as a project for 'Distinguished Young Scholars' (approval No. 20225722), and the China-Russia Joint Centre of Natural Resources, Ecology and Environmental Sciences, Chinese Academy of Sciences. The authors would like to thank all the helpers in the Key Laboratory of Ecological Process, Chinese Academy of Sciences.
Manuscript received 12 July 2005, accepted 11 January 2006
Chiu KK, Ye ZH, Wong MH (2005) Enhanced uptake of As, Zn, and Cu by Vetiveria zizanioides and Zea mays using chelating agents. Chemosphere 60, 1365-1375. doi: 10.1016/ j.chemosphere.2005.02.035
Christie P, Li X, Chen B (2004) Arbuscular mycorrhiza can depress translocation of zinc to shoots of host plants in soils moderately polluted with zinc. Plant and Soil 261, 209-217. doi: 10.1023/B:PLSO.0000035542.79345.1b
Clevenger TE (1990) Use of sequential extraction to evaluate the heavy metals in mining waste. Water, Air, and Soil Pollution 50, 241-254. doi: 10.1007/BF00280626
Ernst WHO (1996) Bioavailability of heavy metals and decontamination of soils by plants. Applied Geochemistry 11, 163-167. doi: 10.1016/ 0883-2927(95)00040-2
Fangueiro D, Bermond A, Santos E, Carapuca H, Duarte A (2002) Heavy metal mobility assessment in sediments based on a kinetic approach of the EDTA extractions: search for optimal experimental conditions. Analytica Chimica Acta 459, 245-256. doi: 10.1016/S0003-2670(02)00134-4
Gaur A, Adholeya A (2004) Prospects of arbuscular mycorrhizal fungi in phytoremediation of heavy metal contaminated soils. Current Science 86, 528-534.
Ginepro M, Gulmini M, Ostacoli G, Zelano V (1996) Microwave desorption treatment after the oxidation step in Tessier sequential extraction scheme. Journal of Environmental Analytical Chemistry 63, 147-154.
Guo GL, Zhou QX (2000) Contaminative trends of heavy metals in Phaeozem of northeast China. Journal of the Graduate School of the Chinese Academy of Science 21,386-392.
Guo GL, Zhou QX (2006) Evaluation of heavy metals pollution in Phaeozem in northeast China. Environmental Geochemistry and Health, (In press).
Guo GL, Zhou QX, Lena M (2006) Availability and assessment of fixing additives for the in situ remediation of heavy metal contaminated soils: a review. Environmental Monitoring and Assessment, (In press).
Houba VJG, Lexmond TM, Novozamsky JJ, Van der Lee JJ (1996) State of the art and future developments in soil analysis for bioavailability assessment. The Science of the Total Environment 178, 21-28. doi: 10.1016/0048-9697(95)04793-X
Kot A, Namiesnik J (2000) The role of speciation in analytical chemistry. Trends in Analytical Chemistry 19, 69-79. doi: 10.1016/S0165-9936(99)00195-8
Li J, Zheng CJ (1989) 'The handbook of environmental background value.' (Chinese Environmental Science Press: Beijing)
Li XD, Coles BJ, Ramsey MH, Thornton I (1995) Sequential extraction of soils for multielement analysis by ICP-AES. Chemical Geology 124, 109-123. doi: 10.1016/0009-2541(95)00029-L
Lin CF, Lo SS, Lin HY, Lee Y (1998) Stabilization of cadmium contaminated soils using synthesized zeolite. Journal of Hazardous Materials 60, 217-226. doi: 10.1016/S03043894(98)00092-2
Lo IMC, Yang XY (1998) Removal and distribution of metals from contaminated soils by a sequential extraction method. Waste Management 18, 1-7. doi: 10.1016/S0956-053X(97)10005-8
Lock K, Janssen CR (2001) Cadmium toxicity for terrestrial invertebrates: taking soil parameters affecting bioavailability into account. Ecotoxicology i 0, 315-322.
Lu AX, Zhang SZ, Shan XQ, Wang SX, Wang ZW (2003) Application of microwave extraction for the evaluation of bioavailability of rare earth element in soils. Chemosphere 54, 54-63.
Ma LQ, Rao GN (1997) Chemical fractionation of cadmium, copper, nickel, and zinc in contaminated soils. Journal of Environmental Quality 26, 259-264.
Maiz I, Arambarri I, Garcia R, Miilan E (2000) Evaluation of heavy metal availability in polluted soils by two sequential extraction procedures using factor analysis. Environmental Pollution 110, 3-9. doi: 10.1016/S0269-7491(99)00287-0
Maiz I, Esnaola MV, Millan E (1997) Evaluation of heavy metal availability in contaminated soils by a short sequential extraction procedure. The Science of the Total Environment 206, 107-115. doi: 10.1016/S0008-9697(97)00223-4
McGrath SP, Knight B, Killham K, Preston S, Paton GI (1999) Assessment of the toxicity of metals in soils amended with sewage sludge using a chemical speciation technique and a lux-based biosensor. Environmental Toxicology and Chemistry 18, 659-663. doi: 10.1897/1551-5028(1999)018<0659:AOTTOM>2.3.CO;2
Navas A, Lindhorfer H (2003) Geochemical speciation of heavy metals in semiarid soils of the central Ebro Valley (Spain). Environment International 29, 61-8. doi: 10.1016/S0160-4120(02)00146-0
Peakall D, Burger J (2003) Methodologies for assessing exposure to metals: speciation, bioavailability of metals, and ecological host factors. Ecotoxicology and Environmental Safety 56, 110-121. doi: 10.1016/S0147-6513(03)00055-1
Pinheiro JP, Mota AM, Goncalves MLS (1994) Complexation study of humic acids with cadmium (II) and lead (II). Analytica Chimica Acta 284, 525-528. doi: 10.1016/0003-2670(94)85059-3
Prokop Z, Cupr P, Zlevorova-Z V, Komarek J, Dusek L, Holoubek I (2003) Mobility, bioavailability, and toxic effects of cadmium in soil samples. Environmental Research 91, 119-126. doi: 10.1016/S0013-9351(02)00012-9
Pueyo M, Lopex-S JF, Rauret G (2000) Assessment of Ca[Cl.sub.2], NaN[O.sub.3] and N[H.sub.4]N[O.sub.3] extraction procedures for the study of Cd, Cu, Pb and Zn extractability in contaminated soils. Analytica Chimica Acta 504, 217-226. doi: 10.1016/j.aca.2003.10.007
Qian J, Wang z, Shan XQ, Tu Q, Wen B, Chen B (1996) Evaluation of plant availability of soil trace metals by chemical fraction and multiple regression analysis. Environmental Pollution 91,309-315. doi: 10.1016/0269-7491(95)00066-6
Qureshi MI, Israr M, Abdin MZ, Iqbal M (2005) Responses of Artemisia annua L. to lead and salt-induced oxidative stress. Environmental and Experimental Botany 53, 185-193. doi: 10.1016/j.envexpbot.2004.03.014
Salomons W, Forstner U (1980) Trace metal analysis on polluted sediments. Parts 2. Evaluation of environmental impact. Environmental Technology Letters 1,506-517.
Shao XH, Xing GX, Hun WH (1994) Research and application of sequential extraction in identifying metal speciation in soils. Progress in Soil Science 22, 40-46.
Shen SM (1998) 'Soil fertility in China.' (Agriculture Press: Beijing) Tessier A, Campbell PGC, Bissun M (1979) Sequential extraction procedure for the speciation of particulate trace metals. Analytical Chemistly 51,844-851. doi: 10.1021/ac50043a017
Ure AM, Quevauviller P, Muntau H, Griepink B (1993) Speciation of heavy metals in soils and sediments. An account of the improvement and harmonization of extraction techniques undertaken under the auspices of the BCR of the Commission of the European Communities. Journal of Environmental Analytical Chemistry 51, 135-151.
Wei SH, Zhou QX (2004) Identification of weed species with hyperaccumulative characteristics of heavy metals. Progress in Natural Science 14, 404-503.
Weng I, Temminghoff EJ, Lofts S, Van Riemsdijk WH (2002) Complexation with dissolved organic matter and solubility control of heavy metals in a sandy soil. Environmental Science and Technology 36, 4804-4810. doi: 10.1021/es0200084
Xia SY, Liu Q (1994) The extraction of different speciation of lead and sampling depth in soil. Environmental Pollution and Control 16, 27-29.
Yang XE, Feng Y, He ZL (2005) Molecular mechanisms of heavy metal hyperaccumulation and phytoremediation. Journal of Trace Elements in Medicine and Biology 18, 339-353. doi: 10.1016/j.jtemb.2005.02.007
Zhang H, Zhao FJ, Sun B, Davison W, McGratb SP (2001) A new method to measure effective soil solution concentration predicts copper availability to plant. Environmental Science and Technology 35, 2602-2607. doi: 10.1021/es000268q
Zhou QX (2003) Interaction between heavy metals and nitrogen fertilizers applied in soil-vegetable systems. Bulletin of Environmental Contamination and Toxicology 71, 338-344. doi: 10.1007/s00128-003-0169-z
Zhou QX, Song YF (2004) 'Principles and method of treating contaminated soils.' (Science Press: Beijing)
Zhou QX, Huang GH (2001) 'Environmental biogeochemistry and global environmental changes.' (Science Press: Beijing)
Zhou QX, Rainbow PS, Smith BD (2003) Comparative study of the tolerance and accumulation of the trace metals zinc, copper and cadmium in three populations of the polychaete Nereis diversicolor. Journal of the Marine Biological Association of the United Kingdom 83, 65-72.
Zhou QX, Sun TH (2002) Effects of chromium (VI) on extractability and plant uptake of fluorine in agricultural soils of Zhejiang Province, China. Water, Air, and Soil Pollution 133, 145-160. doi: 10.1023/A:1012948131082
G. L. Guo (A,B), Q. X. Zhou (A,C,E), P. V. Koval (D), and G. A. Belogolova (D)
(A) Key Laboratory of Terrestrial Ecological Process, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, P.R. China.
(B) Graduate School of the Chinese Academy of Sciences, Beijing 100039, P.R. China.
(C) College of Environmental Sciences and Engineering, Nankai University, Tianjin 300071, P.R. China.
(D) Vinogradov Institute of Geochemistry, PO Box 4019, Irtutsk-33, 664033, Russia.
(E) Corresponding author. Email: Zhouqixing2003@yahoo.com
Table 1. Properties of the studied Phaeozem samples Soil pH Organic matter (g/kg) Surface Range 6.2-6.9 24.3136 Mean 6.47 31.6 Subsurface Range 6.3-6.7 13.2-31.8 Mean 6.35 15.8 Clean soil Range 6.35-6.67 18.6-58.4 Mean 6.51 37.8 Soil CEC Cd (cmol/kg) Surface Range 15.8-31.4 0.68-2.29 Mean 20.1 1.93 Subsurface Range 15.1-23.6 0.13-0.59 Mean 17.2 0.45 Clean soil Range 15.0-41.9 0.06-0.19 Mean 35.5 0.099 Soil Total metal concentration (mg/kg) Zn Pb Cu Surface Range 103.2-214.3 48.6-07.9 18.3-25.4 Mean 145.23 57.5 19.8 Subsurface Range 41.3-68.2 14.9-23.5 11.4-18.3 Mean 53.60 17.2 13.4 Clean soil Range 44.42-61.29 3.44-29.62 10.34-20.26 Mean 52.0 11.43 16.91 Table 2. Summary of the experimental procedures for the single-step extractions Extractant Abbreviation Magnesium chloride Mg[Cl.sub.2] Magnesium nitrate Mg[(N[O.sub.3]).sub.2] Calcium chloride Ca[Cl.sub.2] Ammonium chloride N[H.sub.4]Cl Hydrochloric acid HCl Acetic acid HOAc Ethylenediaminetetraacetic acid EDTA Diethylenetriaminepentaacetic acid DTPA Extractant Condition Magnesium chloride 1 mol/L, pH 7 Magnesium nitrate 1 mol/L, pH 7 Calcium chloride 0.1 mol/L Ammonium chloride 1 mol/L, pH 7 Hydrochloric acid 0.1 mol/L Acetic acid 0.43 mol/L Ethylenediaminetetraacetic acid 0.05 mol/L, pH 7 Diethylenetriaminepentaacetic acid 0.01 mol/L, pH 7 Extractant Reference Magnesium chloride Navas and Lindhorfer (2003) Magnesium nitrate Shao et al. (1994) Calcium chloride Houba et al. (1996) Ammonium chloride Xia and Liu (1994) Hydrochloric acid Lu et al. (2003) Acetic acid Ure et al. (1993) Ethylenediaminetetraacetic acid Fangueiro et al. (2002) Diethylenetriaminepentaacetic acid Prokop et al. (2003) Table 3. Metal contents (mean concentration [+ or -] s.d., mg/kg) from the single extraction on surface and subsurface contaminated Phaeozem by different reagents Within columns, values followed by the same letter are not significantly different at P = 0.05 (LSR test) Surface soil (mg/kg) Extractant Cd Pb Mg[Cl.sub.2] 0.87 [+ or -] 0.04d 0.79 [+ or -] 0.106f Mg[(N[O.sub.3]) .sub.2] 0.25 [+ or -] 0.032g 0.82 [+ or -] 0.24f Ca[Cl.sub.] 0.45 [+ or -] 0.003f 1.09 [+ or -] 0.123e N[H.sub.4]Cl 0.86 [+ or -] 0.096d 1.3 [+ or -] 0.121e HCl 0.64 [+ or -] 0.061e 2.1 [+ or -] 0.112d HOAc 1.05 [+ or -] 0.045c 9.72 [+ or -] 0.22c EDTA 1.68 [+ or -] 0.016a 26.65 [+ or -] 0.2a DTPA 1.53 [+ or -] 0.041b 23.06 [+ or -] 0.325b Surface soil (mg/kg) Extractant Cu Zn Mg[Cl.sub.2] 0.64 [+ or -] 0.021f 0.83 [+ or -] 0.233f Mg[(N[O.sub.3]) .sub.2] 0.79 [+ or -] 0.086e 2.41 [+ or -] 0.006e Ca[Cl.sub.] 0.25 [+ or -] 0.055g 0.30 [+ or -] 0.006f N[H.sub.4]Cl 0.34 [+ or -] 0.027g 2.07 [+ or -] 0.398e HCl 1.12 [+ or -] 0.012d 7.80 [+ or -] 0.246d HOAc 1.52 [+ or -] 0.02c 13.43 [+ or -] 1.048c EDTA 8.46 [+ or -] 0.153a 34.43 [+ or -] 0.099a DTPA 6.37 [+ or -] 0.097b 29.44 [+ or -] 0.3376 Subsurface soil (mg/kg) Extractant Cd Pb Mg[Cl.sub.2] 0.25 [+ or -] 0.043bc 0.69 [+ or -] 0.06c Mg[(N[O.sub.3]) .sub.2] 0.10 [+ or -] 0.011d 0.93 [+ or -] 0.01c Ca[Cl.sub.] 0.10 [+ or -] 0.006d 0.26 [+ or -] 0.025c N[H.sub.4]Cl 0.12 [+ or -] 0.007cd 0.23 [+ or -] 0.046c HCl 0.23 [+ or -] 0.003bcd 0.88 [+ or -] 0.084c HOAc 0.59 [+ or -] 0.003a 4.54 [+ or -] 0.006a EDTA 0.37 [+ or -] 0.149b 3.44 [+ or -] 1.04ab DTPA 0.30 [+ or -] 0.148b 2.81 [+ or -] 0.993b Subsurface soil (mg/kg) Extractant Cu Zn Mg[Cl.sub.2] 0.38 [+ or -] 0.006e 0.77 [+ or -] 0.195de Mg[(N[O.sub.3]) .sub.2] 0.56 [+ or -] 0.133d 1.22 [+ or -] 0.163cd Ca[Cl.sub.] 0.13 [+ or -] 0.01f 0.02 [+ or -] 0.006f N[H.sub.4]Cl 0.17 [+ or -] 0.065f 0.41 [+ or -] 0.08ef HCl 1.10 [+ or -] 0.006c 1.42 [+ or -] 0.031c HOAc 1.70 [+ or -] 0b 1.51 [+ or -] 0.006c EDTA 3.67 [+ or -] 0.145a 4.50 [+ or -] 0.338a DTPA 3.66 [+ or -] 0.051a 3.21 [+ or -] 0.58lb Table 4. Metal concentrations (mean [+ or -] s.d., mg/kg) in the representative plants growing in the contaminated Phaeozem Within columns, values followed by the same letter are not significantly different at P= 0.05 (LSR test) Plants Cd Pb Erigeron canadensis 2.33 [+ or -] 0.48a 3.31 [+ or -] 0.66a Artemisia annua 1.62 [+ or -] 0.45b 1.56 [+ or -] 0.43b Artemisia sieversiana 0.93 [+ or -] 0.12c 1.25 [+ or -] 0.20b Glycine max 0.62 [+ or -] 0.13cd 0.75 [+ or -] 0.21b Zea mays 0.14 [+ or -] 0.04d 0.83 [+ or -] 0.41b Plants Cu Zn Erigeron canadensis 6.89 [+ or -] 0.85a 52.83 [+ or -] 10.53a Artemisia annua 5.28 [+ or -] 1.09ab 56.42 [+ or -] 10.12a Artemisia sieversiana 3.24 [+ or -] 0.86cd 31.78 [+ or -] 7.11a Glycine max 3.77 [+ or -] 0.86bc 51.57 [+ or -] 5.28a Zea mays 1.82 [+ or -] 0.43d 22.73 [+ or -] 5.46b
|Printer friendly Cite/link Email Feedback|
|Author:||Guo, G.L.; Zhou, Q.X.; Koval, P.V.; Belogolova, G.A.|
|Publication:||Australian Journal of Soil Research|
|Date:||Mar 15, 2006|
|Previous Article:||Influence of long-term irrigation on the distribution and availability of soil phosphorus under permanent pasture.|
|Next Article:||The geochemistry of soils on a catena on sedimentary rock at Nam Phong, north-east Thailand.|