High Cd Treatment Research Articles

Evaluating the phytoremediation potential of Phragmites australis grown in pentachlorophenol and cadmium co-contaminated soils

Pot-culture experiments were conducted to evaluate the phytoremediation potential of a wetland plant species, Phragmites australis in cadmium (Cd) and pentachlorophenol (PCP) co-contaminated soil under glasshouse conditions for 70 days. The treatments included Cd (0, 5 and 50 mg kg(-1)) without or with PCP (50 and 250 mg kg(-1)). The results showed that growth of P. australis was significantly influenced by interaction of Cd and PCP, decreasing with either Cd or PCP additions. Plant biomass was inhibited and reduced by the rate of 89 and 92% in the low and high Cd treatments and by 20 and 40% in the low and high PCP treatments compared to the control. The mixture of low Cd and low PCP lessened Cd toxicity to plants, resulting in improved plant growth (by 144%). Under the joint stress of the two contaminants, the ability of Cd uptake and translocation by P. australis was weak, and the BF and TF values were inferior to 1.0. A low proportion of the metal is found aboveground in comparison to roots, indicating a restriction on transport upwards and an excluding effect on Cd uptake. Thus, P. australis cannot be useful for phytoextraction. The removal rate of PCP increased significantly (70%) in planted soil. Significant positive correlations were found between the DHA and the removal of PCP in planted soils which implied that plant root exudates promote the rhizosphere microorganisms and enzyme activity, thereby improving biodegradation of PCP. Based on results, P. australis cannot be effective for phytoremediation of soil co-contaminated with Cd and PCP. Further, high levels of pollutant hamper and eventually inhibit plant growth. Therefore, developing supplementary methods (e.g. exploring the partnership of plant-microbe) for either enhancing (phytoextraction) or reducing the bioavailability of contaminants in the rhizosphere (phytostabilization) as well as plant growth promoting could significantly improve the process of phytoremediation in co-contaminated soil.

Effects of cadmium and nitrogen on lipid composition of Chlorella vulgaris (Trebouxiophyceae, Chlorophyta)

Investigations were carried out to evaluate lipid class and fatty acid composition of Chlorella vulgaris in relation to several combinations of cadmium (2 × 10−8; 10−7 M Cd) and nitrogen (2.9 × 10−6 to 1.1 × 10−3 M N) concentrations. Triacylglycerols (TAG), acetone mobile polar lipids (AMPL) and phospholipids (PL) were the major lipid classes of C. vulgaris under all the tested conditions. TAG was the lipid class accumulated in the highest amount in N-limited C. vulgaris. The AMPL lipid class was lowest at the lowest N and highest Cd treatment. High proportions of saturated fatty acids (SAFA) and monounsaturated fatty acids (MUFA) in the total lipid extracts were recorded under N limitation in the presence of Cd. 16:1(n-11) was an exception among the MUFA as its levels decreased at low N. Total polyunsaturated FA (PUFA), ω3 PUFA levels, and PUFA:SAFA ratios increased with increasing N concentrations, but when exposed to Cd, their levels were significantly reduced. Unlike the other PUFA, 18:2(n-6) increased with increasing N limitation. Significant negative relationships between TAG, MUFA and SAFA with N were recorded. Cd had a positive correlation with TAG, while N was with AMPL, PL and PUFA. In conclusion, a combination of N limitation and Cd stress significantly altered the lipid composition of C. vulgaris, and N limitation had the most significant overall effect on lipid class and fatty acid composition of the microalga.

Biochars immobilize soil cadmium, but do not improve growth of emergent wetland species Juncus subsecundus in cadmium-contaminated soil

Purpose An addition of biochar mixed into the substrate of constructed wetlands may alleviate toxicity of metals such as cadmium (Cd) to emergent wetland plants, leading to a better performance in terms of pollutant removal from wastewater. The objective of this study was to investigate the impact of biochars on soil Cd immobilization and phytoavailability, growth of plants, and Cd concentration, accumulation, and translocation in plant tissues in Cd-contaminated soils under waterlogged conditions. Materials and methods A glasshouse experiment was conducted to investigate the effect of biochars derived from different organic sources (pyrolysis of oil mallee plants or wheat chaff at 550 °C) with varied application amounts (0, 0.5, and 5 % w/w) on mitigating Cd (0, 10, and 50 mg kg −1 ) toxicity to Juncus subsecundus under waterlogged soil condition. Soil pH and CaCl2/EDTA-extractable soil Cd were determined before and after plant growth. Plant shoot number and height were monitored during the experiment. The total root length and dry weight of aboveground and belowground tissues were recorded. The concentration of Cd in plant tissues was determined. Results and discussion After 3 weeks of soil incubation, pH increased and CaCl2-extractable Cd decreased significantly with biochar additions. After 9 weeks of plant growth, biochar additions significantly increased soil pH and electrical conductivity and reduced CaCl2-extractable Cd. EDTAextractable soil Cd significantly decreased with biochar additions (except for oil mallee biochar at the low application rate) in the high-Cd treatment, but not in the low-Cd treatment. Growth and biomass significantly decreased with Cd additions, and biochar additions did not significantly improve plant growth regardless of biochar type or application rate. The concentration, accumulation, and translocation of Cd in plants were significantly influenced by the interaction of Cd and biochar treatments. The addition of biochars reduced Cd accumulation, but less so Cd translocation in plants, at least in the low-Cd-contaminated soils. Conclusions Biochars immobilized soil Cd, but did not improve growth of the emergent wetland plant species at the early growth stage, probably due to the interaction between biochars and waterlogged environment. Further study is needed to elucidate the underlying mechanisms.

Effects of low, moderate and relatively high chronic exposure to cadmium on long bones susceptibility to fractures in male rats

The study investigated the risk of the femur and tibia fractures on a male rat model of low, moderate and relatively high human exposure to cadmium (1, 5 and 50 mg Cd/l in drinking water for 12 months). Bone mineral density (BMD) and biomechanical properties at the proximal and distal femur, and femoral and tibial diaphysis as well as the bone content of mineral and organic components, were evaluated. The exposure to 1 mg Cd/l caused only very subtle changes in biomechanical properties at the femoral neck and distal femur. In the rats treated with 5 mg Cd/l, a decrease in the distal femur BMD (by 5.5%) and enhanced vulnerability to fracture at the femoral neck, distal femur, and tibia diaphysis were observed. At the highest Cd treatment, the BMD decreased (by 6.5–11%) and the biomechanical properties weakened at all regions of the femur and tibia. Moreover, a decrease in the femur and tibia content of mineral components (by 11.5% and 10%, respectively) and the tibia content of organic components (by 7%) was noted. The results seem to indicate that low chronic exposure to Cd can have no influence on the bone resistance to fracture, whereas moderate (and particularly relatively high) exposure seriously increases the risk of fracture of long bones in males. The observations, together with our findings on an analogous female rat model, provide evidence that males are less vulnerable to Cd-induced demineralization and weakening of biomechanical properties of the femur and tibia than females.

Variation in Cadmium Accumulation among 30 Cultivars and Cadmium Subcellular Distribution in 2 Selected Cultivars of Water Spinach (Ipomoea aquatica Forsk.)

To reduce the influx of cadmium (Cd), a toxic heavy metal, into the human food chain through vegetable intake, a pot experiment for the selection of a pollution-safe cultivar (PSC) of water spinach (Ipomoea aquatica Forsk.) was carried out. The experiment with 30 tested cultivars revealed that the maximum differences in Cd concentration between the cultivars containing the highest and the lowest Cd were 3.0-3.9-fold under low-Cd treatment (soil Cd = 0.593 mg kg(-1)), 2.7-3.5-fold under middle-Cd treatment (soil Cd = 1.091 mg kg(-1)), and 2.6-2.7-fold under high-Cd treatment (soil Cd = 1.824 mg kg(-1)), large enough to define the Cd-PSCs. Concentrations of Cd in edible parts of six cultivars, cv. Daxingbaigu, Huifengqing, Qiangkunbaigu, Qiangkunqinggu, Shenniuliuye, and Xingtianqinggu, were lower than 0.2 mg kg(-1), the maximum level (ML) of Cd allowed by the Codex Alimentarius Commission (CAC) standard, even under middle-Cd treatment. Accordingly, these cultivars were treated as typical Cd-PSCs. Four cultivars, cv. Jieyangbaigeng, Xianggangdaye, Sannongbaigeng, and Taiwan 308, contained Cd in edible parts exceeding the ML even under low-Cd treatment, and they were defined as typical non-Cd-PSCs. The correlations of the Cd concentrations among the tested cultivars between the three treatments were significant at the p < 0.05 level. A conspicuous difference in Cd subcellular distribution in hydroponic plant tissues between cv. Qiangkunqinggu (a typical Cd-PSC) and cv. Taiwan 308 (a typical non-Cd-PSC) were observed. Cd absorbed by cv. Qiangkunqinggu seemed to be well-compartmentalized in root and in cell wall fragment, which may be one of the mechanisms leading to its low Cd accumulating property. The results indicated that water spinach, a leafy vegetable, could be easily polluted by soils contaminated with Cd, as 80% of the tested cultivars had exceeded the ML of Cd according to the CAC standard even under the middle-Cd treatment. Much of the evidence obtained from the present study proved that the high Cd-accumulating ability of water spinach is a stable biological property at cultivar level and, thus, is genotype dependent. Therefore, application of the PSC strategy to produce water spinach that is safer to consume is feasible and necessary.

Cadmium tolerance of carbon assimilation enzymes and chloroplast in Zn/Cd hyperaccumulator Picris divaricata

To better understand the photosynthesis under stress, the effect of cadmium on carbon assimilation and chloroplast ultrastructure of a newly found Zn/Cd hyperaccumulator Picris divaricata in China was investigated in solution culture. The shoot and root Cd concentrations increased with increase in Cd supply, reaching maxima of 1109 and 5604 mg kg −1 dry weight at 75 μM Cd, respectively. As Cd supply to P. divaricata increased, the shoot and root dry weight, leaf water content (except 75 μM Cd), concentrations of chlorophyll a and b, chlorophyll a/b ratio and the concentration of carotenoids were not depressed at high Cd. However, the stomatal conductance, transpiration rate, net photosynthetic rate and intercellular CO 2 concentration were significantly affected when the Cd concentration reached 10, 10, 25 and 75 μM, respectively. Meanwhile, carbonic anhydrase (CA; EC 4.2.1.1) activity and Rubisco (EC 4.1.1.39) content reached maxima in the presence of 50 and 5 μM Cd, respectively. In addition, CA activity correlated positively with shoot Cd in plants treated with Cd at a range of 0–50 μM. Moreover, the activities of NADP +-glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13), Rubisco and fructose-1, 6-bisphosphatase (EC 3.1.3.11) were not significantly suppressed by increased Cd supply. Although the mesophyll cell size was reduced, chloroplast ultrastructure remained intact at the highest Cd treatment. Our finding revealed that P. divaricata chloroplast and the enzymes of carbon assimilation tolerate high levels of Cd, demonstrating its potential in possible application in phytoremediation.

Cadmium accumulation in Atriplex halimus subsp. schweinfurthii and its influence on growth, proline, root hydraulic conductivity and nutrient uptake

Atriplex halimus subsp. schweinfurthii is a newly found cadmium (Cd)-hyperaccumulator, but there have been no detailed studies on its physiological responses when Cd is hyperaccumulated. A. halimus was grown in hydroponic conditions to investigate the effect of cadmium chloride (CdCl 2) on growth, water status, leaf chlorophyll concentration, proline and Cd accumulation. Treatments were prepared by adding 0, 50, 100, 200 and 400 μM CdCl 2 to the nutrient medium. Plant growth was significantly affected at high-Cd treatments. Increased CdCl 2 decreased chlorophyll concentration, transpiration and root hydraulic conductivity ( L 0). Hence water flux had only a little effect on the uptake of Cd in A. halimus seedlings. In contrast, proline content increased with increasing CdCl 2 concentration. Plants accumulated substantial amount of Cd in different plant parts (shoot and root). Most of the Cd taken up was retained in roots (606.51 μg g −1DW after 15 d at 400 μM CdCl 2). The addition of Cd in the culture medium affected calcium (Ca) and potassium (K) nutrition in both shoot and root. A. halimus provides a new plant resource for exploring the mechanism of Cd hyperaccumulation and has potential for use in the phytostabilization of Cd-contaminated salt soils.

Cadmium phytoextraction capacity in eight C3 herbage grass species

AbstractGrasses are excellent candidates for phytoremediation because of their high biomass production, high adaptability and low management cost. This study assesses interspecific variation of cadmium (Cd) phytoextraction capabilities in eight C3 grass species. Populations of 30‐day‐old C3 grass species – namely, Agrostis alba, Anthoxanthum odoratum, Dactylis glomerata, Festuca arundinacea, Festuca pratensis, Lolium multiflorum, Lolium perenne and Poa pratensis– were grown hydroponically for 15 days with different concentrations of Cd (0, 5, 10 and 50 µM). For each species, shoot biomass, the proportion of growth inhibition (GI, %), shoot Cd concentration and accumulation, shoot nutrient uptake, and the proportion of uptake inhibition (UI, %) of nutrient minerals were evaluated. Effects of Cd application included stunted growth. The GI increased from 5% to 70% with an increase in Cd concentrations. For all Cd treatments, L. multiflorum showed the highest shoot dry biomass. Shoot Cd concentrations negatively affected mineral nutrient uptake. The highest Cd treatment caused UI of various elements of 37–95%. Under 50‐µM Cd treatment, Cd accumulation varied by 20 times among species, and L. multiflorum showed the highest Cd accumulation (116.46 µg plant−1). Our results indicate that L. multiflorum exhibited high degrees of both Cd tolerance and Cd phytoextraction capacity among grass species.

Dynamics of Microbial Activity Related to N Cycling in Cd-Contaminated Soil During Growth of Soybean

The potential influences of cadmium (Cd) on the biochemical processes of the soil nitrogen (N) cycle, along with the dynamics of ammonification, nitrification, and denitrification processes in the rhizosphere and non-rhizosphere (bulk soil), respectively, were investigated in a Cd-stressed system during an entire soybean growing season. In terms of Cd pollution at the seedling stage, the ammonifying bacteria proved to be the most sensitive microorganisms, whereas the effects of Cd on denitrification were not obvious. Following the growth of soybeans, the influences of Cd on ammonification in the bulk soil were: toxic impacts at the seedling stage, stimulatory effects during the early flowering stage, and adaptation to the pollutant during the podding and ripening stages. Although nitrification and denitrification in the bulk soil decreased throughout the entire growth cycle, positive adaptation to Cd stress was observed during the ripening stage. Moreover, during the ripening stage, denitrification in the bulk soil under high Cd treatment (20 mg kg −1) was even higher than that in the control, indicating a probable change in the ecology of the denitrifying microbes in the Cd-stressed system. Changes in the activity of microbes in the rhizosphere following plant growth were similar to those in the non-rhizosphere in Cd treatments; however, the tendency of change in the rhizosphere seemed to be more moderate. This suggested that there was some mitigation of Cd stress in the rhizosphere.

Using an integrated approach to link biomarker responses and physiological stress to growth impairment of cadmium-exposed larval topsmelt

In this study, we used an integrated approach to determine whether key biochemical, cellular, and physiological responses were related to growth impairment of cadmium (Cd)-exposed larval topsmelt ( Atherinops affinis). Food intake ( Artemia franciscana nauplii), oxygen consumption rates, apoptotic DNA fragmentation (TUNEL assay), and metallothionein (MT)-like protein levels, were separately measured in relation to growth of larval topsmelt aqueously exposed to sublethal doses of Cd for 14 days. Cadmium accumulation and concentrations of abundant metals were also evaluated in a subset of fish. Fish in the highest Cd treatments (50 and 100 ppb Cd) were smaller in final mean weight and length, and consumed fewer A. franciscana nauplii than control fish. Food intake was positively correlated with final weight of larval topsmelt in Cd and control treatments; food intake increased as final weight of the fish increased. Oxygen consumption rates were positively correlated with Cd concentration and mean oxygen consumption rates were inversely correlated with final mean weight of topsmelt; the smallest fish were found in the highest Cd treatment and were respiring at higher rates than control fish. Apoptotic DNA fragmentation was concentration-dependent and was associated with diminished growth. Apoptotic DNA fragmentation was elevated in the gill of fish exposed to 50 ppb Cd, and in the gut, gill, and liver of fish exposed to 100 ppb Cd. Metallothionein (MT)-like protein levels in fish from 100 ppb Cd treatments were significantly higher than those in other treatments. Oxygen consumption rates may have increased as a compensatory response to Cd exposure. However, it is likely that the energy produced was allocated to an increased metabolic demand due to apoptosis, MT synthesis, and changes in ion regulation. This diversion of energy expenditures could contribute to growth impairment of Cd-exposed fish.

Effect of zinc fertilization on cadmium toxicity in durum and bread wheat grown in zinc-deficient soil

The effect of increasing application of zinc (Zn) and cadmium (Cd) on shoot dry weight and shoot concentrations of Zn and Cd was studied in bread and durum wheat cultivars. Plants were grown in severely Zn-deficient calcareous soil treated with increasing Zn (0 and 10 mg kg −1 soil) and Cd (0, 10 and 25 mg kg −1 soil) and harvested after 35 and 65 days of growth under greenhouse conditions. Growing plants without Zn fertilization caused severe depression in shoot growth, especially in durum wheat and at high Cd treatment. Cadmium treatments resulted in rapid development of necrotic patches on the base and sheath parts of the oldest leaves of both wheat cultivars, but symptoms were more severe in durum wheat and under Zn deficiency. Decreases in shoot dry weight from increasing Cd application were more severe in Zn-deficient plants. Severity of Cd toxicity symptoms in durum and bread wheat at different Zn treatments did not show any relation to the Cd concentrations in shoot. Increasing Cd application to Zn-deficient plants tended to decrease Zn concentrations in Zn-deficient plants, whereas in plants with adequate Zn, concentrations of Zn were either not affected or increased by Cd. The results show that durum wheat was more sensitive to both Zn deficiency and Cd toxicity as compared to bread wheat. Cadmium toxicity in the shoot was alleviated by Zn treatment, but this was not accompanied by a corresponding decrease in shoot concentrations of Cd. Our results are compatible with the hypothesis that Zn protects plants from Cd toxicity by improving plant defense against Cd-induced oxidative stress and by competing with Cd for binding to critical cell constituents such as enzymes and membrane protein and lipids.

Influence of Arbuscular Mycorrhizae on Heavy Metal (Pb and Cd) Uptake, Growth, and Chemical Composition ofVitis viniferaL. (cv. Razaki)

The influence of arbuscular mycorrhizae (AM) on plant growth, mineral uptake as well as on soluble solids and acid content of the Razaki grapevine variety grafted onto 110R, in experiments with different amounts of Pb and Cd heavy metals, was studied. Mycorrhizal and non-mycorrhizal plants were grown outdoors in pots containing soil, supplemented with 0, 50, 100, and 300 mg of Pb/kg or 0, 5, 10, and 50 mg of Cd/kg soil. After 3.5 years mycorrhizal colonization was varied from 26.3% to 58.7% in Pb treatments and from 44.7% to 53.3% in Cd treatments. In the same time spore population was varied from 126 to 266 spores per 100 g soil and from 186.7 to 264.0 spores in Pb and Cd treatments, respectively. Treatments receiving 300 mg Pb/kg and 50 mg Cd/kg in the soil showed a reduction in pruning weight compared with the control (0 mg Pb or Cd/kg). Mycorrhizal colonization significantly increased pruning weight in the control and the low Pb and Cd treatments (0, 50, and 100 mg/kg and 0, 5, and 10 mg/kg respectively). In elevated soil Pb supplements, the fruits had decreased total soluble solids and increased total acidity. With the changes to Cd level, berry soluble solids and acids were not affected. No significant differences of leaf N, K, Ca, Mg, and B nutrient concentrations were found between the heavy metal Pb and Cd treatments nor between mycorrhizal and non-mycorrhizal plants. The M/NM (mycorrhizal/non-mycorrhizal) ratio for N, K, Ca, and Mg concentrations varied from 1.0 to 1.2 and for B from 1.07 to 1,5. Leaf Mn, Zn, Fe, Cu, Pb, and Cd concentrations were lower in mycorrhizal plants compared to non-mycorrhizal plants and the M/NM ratios were less than 1.0. Berry Pb concentrations in the mycorrhizal plants were low (up to 20 mg/kg) in control and increased in Pb treatments (up to 463 mg/kg and 1315 mg/kg in M and NM plants, respectively). Appreciable Cd was detected only in the high Cd treatments, in which berry concentrations were 0.8 mg/kg and 2.5 mg/kg in the M and NM plants, respectively (50 mg of Cd/ kg).

The effects of chronic cadmium stress on energy acquisition and allocation in a freshwater benthic invertebrate predator

The effects of chronic exposure to cadmium (0 (control), 5 (low), 10 (medium), or 50 (high) μg Cd 1 −1) were examined in terms of changes in energy acquisition and allocation (somatic growth, reproductive growth, faeces plus mucus, active respiration, resting respiration, activity time) in the predatory leech Nephelopsis obscura. Leeches in the high Cd treatment had significantly lower biomass production, survivorship and ingestion rate than leeches in the other treatments or control. Assimilation efficiency, reproductive investment, resting respiration and active respiration were unaffected by Cd but leeches in the high Cd treatment were significantly less active and produced more mucus. Decreased ingestion and increased mucus production in the high Cd treatment contributed to a lower growth rate. Although Cd had no significant effects on resting or active respiration, there were significant effects on total respiration as leeches exposed to high Cd exhibited a significant decrease in time spent active and thus in total respiration. Significant mortality in the high Cd treatment indicates that leeches are unable to compensate. As reproductive investment did not change with Cd exposure, the only physiological tradeoffs occurred between growth of somatic tissue and survival mechanisms.

Cadmium and mercury toxicity in a human fetal hepatic cell line (WRL-68 cells)

The toxic effects of cadmium (Cd) and mercury (Hg), as chloride salts, were studied using an hepatic human fetal cell line (WRL-68 cells). From viability curves and the proliferative capacity of the cell in the presence of the metal, three different cell treatments were chosen, (1) 0.5 μM of the metal chloride for 24 h (acute low dose treatment), (2) 0.5 μM of the metal chloride for 7 days (chronic treatment), and (3) 5 μM of the metal chloride for 24 h (acute high dose treatment). WRL-68 cells grown in the presence of Cd exhibited the same proliferative curve as control cells, whereas in the case of Hg, the cells increased their proliferative capacity. Both metals produced ultrastructural alterations in different degrees, mainly observed as mitochondrial and RER structural changes, depending of the treatment and concentration of the metal used. Cytotoxicity was assessed by measuring the release of lactate dehydrogenase from the cells. Acutely high dose-treated cells showed the highest value for this parameter, and Cd-treated cells presented higher lactate dehydrogenase release than the Hg-treated ones. Cell damage was also measured by alanine aminotransferase (ALAT) and aspartate aminotransferase (ASAT) activities. Acute high dose Cd treatment caused the highest value of enzymatic release. Lipid peroxidation was significantly different with respect to control cells in chronic and acute high dose treatments with both metals. Metallothionein (MT) induction in response to Hg treatment was not detected. However, a dramatic induction of this protein occurred in Cd-treated cells. WRL-68 cells differentially respond to Cd and Hg making this hepatic fetal human cell line a useful tool in investigating the mechanism of toxicity of these heavy metals.

The accumulation of lead, zinc, cadmium and fluoride in the wood mouse (Apodemus sylvaticus L.)

The concentrations of Pb, Zn, Cd, and fluoride were determined in liver, kidney and femur tissues 30 days after wood mice were provided with water containing soluble salts of these elements in their drinking water. There were eight treatment groups: Pb, Zn, Cd, and fluoride only; Zn and Cd (ZnCd); fluoride and Pb (FPb); fluoride, Pb, Zn, and Cd (FPbZnCd); and a control. Lead concentrations were highest in bone but were also significantly higher in the kidney but not liver when compared to the control. The highest kidney Pb levels were in the FPbZnCd treatment but they were not significantly higher than the Pb only group. Zinc concentrations were highest in kidney and not femur as is usually the case in field caught animals. Cadmium was also highest in the kidney in the high Cd treatments, however, the ZnCd treatment group had significantly lower kidney Cd levels than the Cd only group demonstrating the antagonistic effect of high Zn on Cd accumulation. This effect was reversed when high fluoride and Pb were also present (in the FPbZnCd group) and the kidney Cd reached its highest level. Fluoride showed the typically high levels in bone with only the combined treatment (FPbZnCd) showing a significant increase in kidney fluoride. These results are discussed in terms of the accumulation in wild small mammals caught in polluted sites particularly grasslands established on fluorspar wastes.

A Field Study of a Soil‐Soybean Plant‐Rhizobium System Amended with Cadmium

AbstractSoybean plants [Glycine max (L.) Merr.) were cropped over a period of 3 years, under field conditions, in a soil amended with Cd (as CdCl2·2½ H2O) at rates corresponding to 0, 3.3, 12.5, and 22.8 kg Cd/ha in order to evaluate the effect of Cd on seed yield, Cd accumulation in seeds, and the distribution of indigenous Rhizobium japonicum strains. Cadmium migration from the cultivated layers to the subsoil during 3 years was not significant. Soybean seed yields were affected significantly only when DTPA‐TEA‐extractable Cd was &gt; 1.57 µg Cd/g in the cultivated layers of the soil, suggesting that only in cases of extreme Cd contamination would significant yield reduction occur. Cadmium content of seeds increased from year to year with values &gt; 1 µg Cd/g being found only when Cd had been added. Grain yield decreased only in the high Cd treatments. Therefore, grain yield would be a poor indicator of Cd contamination in a soil cropped with soybeans. The results also suggested DTPA‐TEA‐extractable soil Cd does not accurately measure the readily available pool of Cd for soybean plants. Rather Cd content of seeds appears to be a better indicator of the extent of Cd contamination. Rhizobium japonicum strain distribution was not affected by the presence of Cd in the soil. Serogroups 24, 31, 76, and 94 dominated the area surveyed.