Chemical Forms Of Cadmium Research Articles

Differential subcellular distribution and chemical forms of cadmium and copper in Brassica napus

Metal subcellular fractions and chemical profile highly reflect their level of toxicity to plants. Cadmium and Cu, two different but potentially toxic metals, were compared in the present study for their subcellular distribution and chemical forms in two Brassica napus cultivars (Zheda 622 and ZS 758). Five-week-old seedlings were hydroponically exposed to metal stress and analyzed after 15 days of treatment. In both cultivars, Cd was less retained at cell wall, thus major part of Cd accumulated in the soluble fraction. By contrast, handsome amount of Cu was sequestrated in both cell wall and vacuole containing fraction. Across sensitive organelles, Cu preferentially accumulated in chloroplasts, while Cd was equally distributed in chloroplasts and mitochondria; the two metals intruded nucleus at lesser degree. Further, Cd and Cu differentially interacted with various cellular ligands, and the extent of interaction was higher in the tolerant cultivar ZS 758. Copper was remarkably sequestrated by phosphates, and secondarily by peptide-ligands; inversely, the role of phosphates was secondary in Cd complexation, which was mainly achieved by peptide-ligands. Additional amount of Cu was aggregated with oxalates, but oxalate-bound Cd was scarcely detected. Current results have demonstrated varied toxicological and detoxification pathways of Cd and Cu in B. napus, suggesting that the efficiency of different alleviation strategies could vary against Cd and Cu toxicity to plants.

Silicon influences cadmium translocation by altering subcellular distribution and chemical forms of cadmium in peanut roots

ABSTRACTEffects of silicon (Si) on subcellular distribution and chemical forms of Cd in two contrasting peanut cultivars, Qishan 208 (low seed Cd cultivar) and Haihua 1 (high seed Cd cultivar), were investigated by a hydroponics experiment at low Cd level (0.2 μM CdCl2). Two cultivars differ in Cd translocation, subcellular distribution and chemical forms. In comparison to Qishan 208, Haihua 1 shows higher translocation factors (TFs); this may be resulted from higher Cd in the soluble fraction, and a larger proportion of inorganic Cd (extracted by 80% ethanol) and water-soluble Cd (extracted by d-H2O) in roots. Pretreatment with Si decreased Cd in the cell wall, and enhanced Cd in the soluble fraction for both cultivars. However, effects of Si on chemical forms and TFs are cultivar dependent. Si enhances Cd translocation and the d-H2O extractable Cd in Haihua 1. Positive correlations were observed between TF and Cd in the soluble fraction (r = 0.71, P < 0.05), and between TF and d-H2O extractable Cd in root (r = 0.89, P < 0.001). Therefore, larger proportion of d-H2O extractable Cd may be responsible for high TF in Si pretreated plants of Haihua 1.

Comparison of subcellular distribution and chemical forms of cadmium among four soybean cultivars at young seedlings.

The hydroponic experiment was carried out to investigate the Cd subcellular distribution and chemical forms in roots and shoots among four soybean seedling cultivars with two Cd treatments. HX3 and GC8, two tolerant and low-grain-Cd-accumulating cultivars, had the lowest Cd concentration in roots and high Cd concentration in shoots, while BX10 and ZH24, two sensitive and high-grain-Cd-accumulating cultivars, had the highest Cd concentration in roots and the lowest Cd concentration in shoots at young seedling stage. Furthermore, the sequence of Cd subcellular distribution in roots at two Cd levels was cell wall (53.4-75.5 %) > soluble fraction (15.8-40.4 %) > organelle fraction (2.0-14.7 %), but in shoots, was soluble fraction (39.3-74.8 %) > cell wall (16.0-52.0 %) > organelle (4.8-19.5 %). BX10 and ZH24 had higher Cd concentration in all subcellular fractions in roots, but HX3 and GC8 had higher Cd concentration of soluble fraction in shoots. The sequence of Cd chemical forms in roots was FNacl (64.1-79.5 %) > FHAC (3.4-21.5 %) > Fd-H2O (3.6-13.0 %) > Fethanol (1.4-21.8) > FHCl (0.3-1.6 %) > Fother (0.2-1.4 %) at two Cd levels but, in shoots, was FNacl (19.7-51.4 %) ≥ FHAC (10.2-31.4 %) ≥ Fd-H2O (8.8-28.2 %) ≥ Fethanol (8.9-38.6 %) > FHCl (0.2-9.6 %) > Fother (2.5-11.2 %). BX10 and ZH24 had higher Cd concentrations in each extracted solutions from roots, but from shoots for GC8 and HX3. Taken together, the results uncover that root cell walls and leaf vacuoles might play important roles in Cd detoxification and limiting the symplastic movement of Cd.

Subcellular distribution and chemical forms of cadmium in a dark septate endophyte (DSE), Exophiala pisciphila.

Our objective was to understand the cadmium (Cd) tolerance mechanisms by investigating the subcellular distribution, chemical forms of Cd and adsorptive groups in the mycelia of Exophiala pisciphila. We grew E. pisciphila in the liquid media with increasing Cd concentrations (0, 25, 50, 100, 200, and 400 mg L(-1)). Increased Cd in the media caused a proportional increase in the Cd uptake by E. pisciphila. Subcellular distribution indicated that 81 to 97% of Cd was associated with the cell walls. The largest amount and proportion (45-86%) of Cd was extracted with 2% acetic acid, and a concentration-dependent extraction was observed, both of which suggest that Cd-phosphate complexes were the major chemical form in E. pisciphila. A large distribution of phosphate and Cd on the mycelia surface was observed by scanning electron microscopy-energy dispersive spectrometer (SEM-EDS). The precipitates associated with the mycelia were observed to contain Cd by transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX). Fourier transform infrared (FTIR) identified that hydroxyl, amine, carboxyl, and phosphate groups were responsible for binding Cd. We conclude that Cd associated with cell walls and integrated with phosphate might be responsible for the tolerance of E. pisciphila to Cd.

Subcellular distribution and chemical forms of cadmium in Impatiens walleriana in relation to its phytoextraction potential

Impatiens (Impatiens walleriana) has been shown to be a potential cadmium (Cd) hyperaccumulator, but its mechanisms in accumulation and detoxification have not been reported. Rooted cuttings of Impatiens were planted in artificially Cd-contaminated soils for 50days with total target concentrations of 0, 10, 20, 40, 80, and 120mg/kg. The subcellular distribution and chemical forms of Cd in the different organs were analyzed after the pot experiment. Compared with the control group, various Cd treatments affected the growth exhibitions of Impatiens, but most of them were not statistically significant. The Cd accumulation of different organs increased with an increase in the soil Cd concentrations for most of the treatments, and it was in the decreasing order of root>stem>leaf. In the roots of Impatiens, Cd was mainly compartmentalized in the soluble fraction (Fs), which has a high migration capacity and will further translocate to the shoot. The Cd was mainly compartmentalized in the cell wall fraction (Fcw) in the shoots as a mechanism of tolerance. Most of the Cd in the various organs of Impatiens was mainly in the forms of pectate and protein-integrated (FNaCl), whereas a minor portion was a water soluble fraction (FW). The experimental results show that the Cd in the Fs, FW, and FNaCl in the roots of Impatiens had a high mobility and will further translocate to the shoot. They could be used to estimate the Cd accumulated in the shoots of Impatiens.

Chemical forms of cadmium in a calcareous soil treated with different levels of phosphorus-containing acidifying agents

Calcareous soils with high background cadmium (Cd) levels are widely distributed in south-west China and soil acidity is a major environmental problem. However, little effort has been made to study the changes in chemical speciation as affected by soil acidification other than by acidic rain. In the present study, we investigated the impact of mono-ammonium phosphate (MAP) and phosphoric acid on soil pH and chemical transformation of Cd in calcareous soils. Calcareous soils collected from south-west China were treated with three concentrations (0.1, 0.2 and 0.4 mol kg–1 soil) of MAP and phosphoric acid, and without the addition of acidifying agent, before being incubated at 25 ± 2°C near field capacity moisture content for 60 days. The chemical forms of Cd in the soils were determined by the Tessier sequential extraction scheme. The concentration of Cd in the form bound to iron and manganese oxides (CdFeOx+MnOy) decreased significantly with increasing levels of the two acidifying agents, but the concentration of exchangeable Cd (CdEx) exhibited a significant increase, indicating that the two acidifying agents can effectively promote the transformation of CdFeOx+MnOy to CdEx. MAP may promote the same amount of CdFeOx+MnOy to CdEx as phosphoric acid at the same rate of addition, but the soil pH clearly differed, implying that an increase in water-soluble P with addition of acidifying agent may be one major factor affecting the chemical transformation of Cd. MAP and phosphoric acid should be used carefully as sources of water-soluble phosphorus for calcareous soils with high background concentrations of Cd.

Relationship between Cadmium Fractions Obtained by Sequential Extraction of Soil and the Soil Properties in Contaminated and Uncontaminated Paddy Soils

The method for the sequential extraction of cadmium from soil was adapted to investigate the relationship between different chemical forms of cadmium in soils and the soil properties of Cd-contaminated and uncontaminated paddy soils. Air-dried soil samples from each field site were sequentially fractionated into five forms: exchangeable Cd, inorganically bound Cd, organically bound Cd, oxide-occluded fraction, and residual Cd. The average and range of soil properties such as pH, total C, total N, CEC, exchangeable Ca, Mg, K, base saturation, available phosphate, particle size distribution, free iron oxide, oxalate extractable Al, and Fe were somewhat similar between uncontaminated and contaminated soils. The average total Cd in uncontaminated and contaminated soils was 0.26 and 0.65 mg kg−1, respectively. The proportions of soil Cd fractions did not differ between the uncontaminated and contaminated soils, although the Cd concentration of several fractions in contaminated soils was statistically higher than those in uncontaminated soils except for residual fraction. The proportion of exchangeable Cd was correlated with the CEC and phosphate absorption coefficient in contaminated soil but not in uncontaminated soil. Thus, soil properties appear to affect the proportions of soil Cd fractions in contaminated soil and should be considered when evaluating soil Cd mobility.

Subcellular distribution and chemical forms of cadmium in the edible seaweed, Porphyra yezoensis

The subcellular distribution and chemical forms of Cd were investigated in the edible seaweed, Porphyra yezoensis. The seaweed was exposed to different Cd concentrations (0.01, 0.05, 0.1, 0.5, 1.0 and 5.0mgl−1) for up to 96h. In both the controls (no Cd added) and treatment groups, 41.2–79.2% of Cd was localised in the cell wall, and the proportion of Cd in the cell wall increased with increasing concentrations of Cd and exposure time. In the control groups, 74.8% of Cd was extracted by 1M NaCl, followed by 2% acetic acid, HAC (18.9%). In the treatment groups, most Cd was extracted by 2% HAC. The proportion of Cd extracted by 2% HAC increased with exposure to increasing concentrations of Cd and over time. Cell wall deposition and forming of precipitates with phosphate may be a key strategy to reduce Cd toxicity in P. yezoensis.

Subcellular Distribution and Chemical Forms of Cadmium in Two Hot Pepper Cultivars Differing in Cadmium Accumulation

A greenhouse experiment was conducted to compare the subcellular distribution and chemical forms of cadmium (Cd) in roots, stems, leaves, and fruits between a low-Cd cultivar (Yeshengchaotianjiao, YCT) and a high-Cd cultivar (Jinfuzaohuangjiao, JFZ) of hot pepper (Capsicum annuum L.). The Cd concentrations in the root's subcellular fractions, and in all chemical forms in roots, were 1.85-4.88- and 1.84-4.90-fold higher, respectively, in YCT than in JFZ. Compared with JFZ, YCT had significantly lower Cd concentrations in the subcellular fractions (1.10-2.42-fold) of stems and leaves and in almost all chemical forms (1.17-2.97-fold) in the stems and leaves. Also, in fruits, the concentrations of Cd in the cell wall and soluble fractions were 1.18-2.24-fold significantly lower in YCT than in JFZ, and there were lower Cd concentrations (1.36-2.08-fold) in the chemical forms in YCT than in JFZ.

Effects of zinc on physiologic characterization and cadmium accumulation and chemical forms in different varieties of pepper

The effects of zinc (Zn) at different spray concentrations (0, 500, and 1 000 μmol·L−1) on the plant growth, the activities of antioxidant enzymes chemical forms of cadmium (Cd), and the accumulation of Cd were studied and compared between two varieties, Shijichaotianjiao (SJCTJ) and Yanjiao425 (YJ425) of pepper (Capsicum annuum L.) in Cd-contaminated soil (Cd 10 ·mg kg−1). The activities of catalase (CAT) and peroxidase (POD) were generally enhanced by Zn. However, superoxide dismutase (SOD) decreased. Addition of Zn decreased the ethanol-extractable Cd, NaCl-extractable Cd, and acetic acid-extractable Cd in the fruit by 34.6%–55.3%, 2.0%–17.7% and 0.4%–32.9%, and reduced the accumulation of Cd in fruit and plant total Cd by 12.8%–68.6% and 9.0%–29.3% in both varieties, respectively.

Comparisons in subcellular and biochemical behaviors of cadmium between low-Cd and high-Cd accumulation cultivars of pakchoi (Brassica chinensis L.)

Subcellular distributions and chemical forms of cadmium (Cd) in the leaves, stems and roots were investigated in low-Cd accumulation cultivars and high-Cd accumulation cultivars of pakchoi (Brassica chinensis L.). Root cell wall played a key role in limiting soil Cd from entering the protoplast, especially in the low-Cd cultivars. The high-Cd cultivars had significantly higher leaf and stem Cd concentrations than the low-Cd cultivars in cell wall fraction, chloroplast/trophoplast fraction, organelle fraction and soluble fraction. In low-Cd cultivars, which were more sensitive and thus had greater physiological needs of Cd detoxification than high-Cd cultivars, leaf vacuole sequestrated higher proportions of Cd. Cd in the form of pectate/protein complexes (extracted by 1 mol·L−1 NaCl) played a decisive role in Cd translocation from root to shoot, which might be one of the mechanisms that led to the differences in shoot Cd accumulation between the two types of cultivars. Furthermore, the formation of Cdphosphate complexes (extracted by 2% HAc) was also involved in Cd detoxification within the roots of pakchoi under high Cd stress, suggesting that the mechanisms of Cd detoxification might be different between low- and high-Cd cultivars.

Effects of iron deficiency on subcellular distribution and chemical forms of cadmium in peanut roots in relation to its translocation

Effects of iron deficiency on subcellular distribution and chemical forms of Cd in four peanut (Arachis hypogaea L.) cultivars were investigated by a hydroponics experiment, at low Cd level (0.2μM CdCl2). The results show that, compared with high Cd accumulating cultivars, the low Cd accumulating cultivars show higher biomass production, more chlorophyll, and less Cd accumulation in shoots. Higher proportion of Cd in the soluble fraction was also observed in low Cd accumulating cultivars that may contribute to low Cd accumulation in their shoots. Fe deficiency increases Cd uptake and accumulation in plants, but decreases Cd translocation from roots to shoots. It was also observed that Fe deficiency increase the proportion of Cd in the soluble fraction and the proportion of NaCl extractable Cd, which were negatively correlated with shoot Cd concentration. The percentage of NaCl extractable Cd was negatively and exponentially related to the percentage of Cd in shoots and translocation factors of Cd to shoots. It seems that a high proportion of Cd in the soluble fraction (mainly in vacuoles) and a high proportion of NaCl extractable Cd (pectate and protein-bound Cd) are responsible for the decreased Cd translocation by Fe deficiency.

Chemical forms of cadmium in a calcareous soil treated with different levels of phosphorus and cadmium and planted to spinach

The objective of the investigation was to evaluate the effect of applied phosphorus (P) and cadmium (Cd) on Cd chemical forms determined by sequential extraction and the relationship between these forms and plant responses, i.e., dry weights, concentration, and total uptake of Cd and P in a greenhouse experiment. Treatments consisted of five levels of Cd (5, 10, 20, 40 and 80 mg kg−1 soil as cadmium sulfate) and four levels of P (0, 15, 30 and 60 mg kg−1 soil as monocalcium phosphate), which were added to the soil and left to equilibrate for 1 month under greenhouse conditions. Spinach seeds (Spinacea oleracea L., cv Viroflay) were sown and then grown for 8 weeks. The chemical composition in the aerial part of the pant and soil was determined. Application of Cd decreased plant dry matter and increased Cd concentration in the plant, whereas at each level of applied Cd, P increased plant dry matter and decreased plant Cd concentration. All chemical forms of Cd in soil, as determined by a fractionation method, were increased following Cd application, the highest being the carbonatic form. Phosphorous application decreased exchangeable and carbonatic forms of Cd, whereas it increased other forms.

Arbuscular Mycorrhizal Colonization Alters Subcellular Distribution and Chemical Forms of Cadmium in Medicago sativa L. and Resists Cadmium Toxicity

Some plants can tolerate and even detoxify soils contaminated with heavy metals. This detoxification ability may depend on what chemical forms of metals are taken up by plants and how the plants distribute the toxins in their tissues. This, in turn, may have an important impact on phytoremediation. We investigated the impact of arbuscular mycorrhizal (AM) fungus, Glomus intraradices, on the subcellular distribution and chemical forms of cadmium (Cd) in alfalfa (Medicago sativa L.) that were grown in Cd-added soils. The fungus significantly colonized alfalfa roots by day 25 after planting. Colonization of alfalfa by G. intraradices in soils contaminated with Cd ranged from 17% to 69% after 25–60 days and then decreased to 43%. The biomass of plant shoots with AM fungi showed significant 1.7-fold increases compared to no AM fungi addition under the treatment of 20 mg·kg−1 Cd. Concentrations of Cd in the shoots of alfalfa under 0.5, 5, and 20 mg·kg−1 Cd without AM fungal inoculation are 1.87, 2.92, and 2.38 times higher, respectively, than those of fungi-inoculated plants. Fungal inoculation increased Cd (37.2–80.5%) in the cell walls of roots and shoots and decreased in membranes after 80 days of incubation compared to untreated plants. The proportion of the inactive forms of Cd in roots was higher in fungi-treated plants than in controls. Furthermore, although fungi-treated plants had less overall Cd in subcellular fragments in shoots, they had more inactive Cd in shoots than did control plants. These results provide a basis for further research on plant-microbe symbioses in soils contaminated with heavy metals, which may potentially help us develop management regimes for phytoremediation.

Arsenic and cadmium in the marine macroalgae (Porphyra yezoensis and Laminaria Japonica) — forms and concentrations

Total arsenic, inorganic arsenic (iAs), total cadmium concentrations and chemical forms of cadmium were analysed in Porphyra yezoensis collected monthly from January to April in 2011 and in Laminaria Japonica collected monthly from March to July in 2010. Results showed that total As concentrations in P. yezoensis were much lower than those in L. Japonica. The iAs concentrations in both macroalgae were all below the maximum limit according to the legislation in China, while total Cd concentrations in all samples of P. yezoensis exceeded the maximum limit. The percentage of iAs to total As decreased in both macroalgae with the time. The results provide important information showing that both macroalgae are able to metabolise inorganic arsenic to organic forms. Thus both macroalgae have evolved arsenic resistance which is linked to the capability of metabolising toxic inorganic arsenic. In addition, the results suggest that the transformation rate of arsenate to organic arsenic in both algae increases with the growth and metabolic rate that increase with elevated environmental temperature. Temperatures rise from January to April in Jiangsu province and from March to July in Liaoning Province. Most Cd was associated with pectates and protein (extractable by 1 M NaCl) in both algae, and only a small percentage of the Cd was inorganic (extractable by 80% ethanol). The Cd chemical forms have no obvious relationship with the time in both algae.

Effects of phosphorus supplied in soil on subcellular distribution and chemical forms of cadmium in two Chinese flowering cabbage (Brassica parachinensis L.) cultivars differing in cadmium accumulation

Differences in the subcellular distribution and chemical speciation of Cd between two Chinese flowering cabbage (Brassica parachinensis L.) cultivars, Lubao70 (LB70, low-Cd cultivar) and ChixinNO.4 (CX4, high-Cd cultivar) were investigated under various soil Cd and P treatments. Subcellular fractionation of Cd-containing tissues showed that a higher proportion of Cd was bound to the cell wall fraction of LB70 than that of CX4, indicating that Cd compartment functioned better in LB70. Compared to CX4, LB70 had lower proportions of Cd in inorganic form and water-soluble form, but higher proportions of Cd in proteins/pectates integrated form, implying that the low Cd accumulation in LB70 is associated with the low in vivo mobility of Cd. In both cultivars, shoot and root Cd concentration and translocation of Cd from the roots to the shoots obviously decreased with increasing soil P level. It was found that phosphorus (P) played important roles in Cd uptake and translocation via the processes involved in bonding Cd to the cell wall fraction and forming Cd-phosphate complexes. It is suggested that use of low-Cd cultivars in conjunction with P supply is a much useful way to reduce the pollution risk of Cd in the food chain.

Root-induced changes to cadmium speciation in the rhizosphere of two rice ( Oryza sativa L.) genotypes

Our aim was to investigate rhizosphere effects on the chemical behavior of Cd. This was done in a glasshouse experiment, where two rice cultivars (Zhenong54 and Sixizhan) were grown in soil spiked with cadmium (Cd) at two levels, 3.9±0.5 and 8.3±0.5 mg kg −1 soil, placed in a rhizobox until ripening stage. Chemical forms of cadmium near the root surface were then assessed using a sequential extraction procedure (SEP). There were significant differences in Cd species, especially exchangeable Cd (EXC-Cd) between the two rice cultivars as affected by rice roots. The lowest EXC-Cd with Zhenong54 appeared in the near-rhizosphere area with little difference between tillering stage and ripening stage while Sixizhan had its lowest EXC-Cd concentration in the root compartment. Both cultivars had slight changes in the Fe/Mn oxide-bound fraction of Cd (FMO-Cd) at the grain ripening stage while the control treatments without plants had a significant increase in FMO-Cd at the same time, indicating a transformation from a less bioavailable form (FMO-Cd) to more bioavailable forms (EXC-Cd). Soil microbial biomass in the vicinity of the root surface had opposite trends to some extent with EXC-Cd, partly because of the root-induced changes to bioavailable Cd. Unlike Zhenong54, Sixizhan had a higher Cd concentration in the root, but only a small proportion of Cd translocated from the root to grain.

Possible chemical forms of cadmium and varietal differences in cadmium concentrations in the phloem sap of rice plants (Oryza sativa L.)

In rice (Oryza sativa L.), cadmium (Cd), a toxic heavy metal, is found in phloem sap and eventually accumulates in the grains. To further characterize phloem-transported Cd, the chemical forms of Cd and other metals and varietal differences in phloem sap Cd concentrations were investigated in young rice plants. The size-exclusion chromatography elution times for Cd-bound compounds indicated that phloem Cd in cv. Nipponbare exists mainly as an approximately 13 kDa complex. Protease digestion of rice phloem sap reduced the bound Cd content from 92 to 19%. The remaining Cd may bind to low-molecule SH compounds. An experiment examining in vitro addition of Cd2+ to phloem sap from non-Cd-treated plants revealed that rice phloem sap constitutively contains Cd chelators. The major Cd peak is distinguishable from those of Fe, Zn, Cu, Mn, Ni and Co, which probably bind to nicotianamine, 2′-deoxymugineic acid, citrate and histidine. The Cd concentrations of the phloem saps in three varieties (Milyang 23, LAC 23 and Koshihikari) grown under the same soil conditions were correlated with their grain Cd concentrations, which had been reported previously, whereas the concentrations of the xylem saps were not. In conclusion, rice phloem sap Cd differs from other metals as it may bind to a novel approximately 13 kDa protein and SH compounds, and the concentration of Cd in rice phloem sap may be a key determinant of its grain content.

Subcellular distribution and chemical forms of cadmium in Phytolacca americana L.

Phytolacca americana L. (pokeweed) is a promising species for Cd phytoextraction with large biomass and fast growth rate. To further understand the mechanisms involved in Cd tolerance and detoxification, the present study investigated subcellular distribution and chemical forms of Cd in pokeweed. Subcellular fractionation of Cd-containing tissues indicated that both in root and leaves, the majority of the element was located in soluble fraction and cell walls. Meanwhile, Cd taken up by pokeweed existed in different chemical forms. Results showed that the greatest amount of Cd was found in the extraction of 80% ethanol in roots, followed by 1M NaCl, d-H2O and 2% HAc, while in leaves and stems, most of the Cd was extracted by 1M NaCl, and the subdominant amount of Cd was extracted by 80% ethanol. It could be suggested that Cd compartmentation with organo-ligands in vacuole or integrated with pectates and proteins in cell wall might be responsible for the adaptation of pokeweed to Cd stress.

Bioaccumulation and chemical forms of cadmium, copper and lead in aquatic plants

The cadmium(Cd), copper(Cu) and lead(Pb) accumulation, as well as their relative content of different chemical forms in Sagittaria sagittifolia L. and Potamogeton crispus L. were determined. The results showed that both the plants had the ability to accumulate large amounts of Cd, Cu and Pb, and they absorbed metals in dose-dependent manners. The roots of S. sagittifolia appeared more sensitive to Cd and Pb than the leaves of P. crispus. The potential of Cu uptake by these two plant tissues was similar. Under the same concentration, the uptake of Cu for both the plants was higher than Pb and Cd, while that of Pb was lowest. The Cd, Cu and Pb existed with various forms in the plants. Cd and Pb were mainly in the NaCl extractable form in S. sagittifolia and P. crispus. The HAc and ethanol extractable Cu were the main forms in the root, whereas the ethanol extractable form was the dominant chemical form in the caulis and bulb of the S. sagittifolia L.