Cd In Wheat Research Articles

Breeding Low-Cadmium Wheat: Progress and Perspectives

Farmland cadmium (Cd) contamination has adverse impacts on both wheat grain yield and people’s well-being through food consumption. Safe farming using low-Cd cultivars has been proposed as a promising approach to address the farmland Cd pollution problem. To date, several dozen low-Cd wheat cultivars have been screened worldwide based on a Cd inhibition test, representing candidates for wheat Cd minimization. Unfortunately, the breeding of low-Cd wheat cultivars with desired traits or enhanced Cd exclusion has not been extensively explored. Moreover, the wheat Cd inhibition test for variety screening and conventional breeding is expensive and time-consuming. As an alternative, low-Cd wheat cultivars that were developed with molecular genetics and breeding approaches can be promising, typically by the association of marker-assisted selection (MAS) with conventional breeding practices. In this review, we provide a synthetics view of the background and knowledge basis for the breeding of low-Cd wheat cultivars.

Zinc oxide nanoparticles alter the wheat physiological response and reduce the cadmium uptake by plants

An experiment was performed to explore the interactive impacts of zinc oxide nanoparticles (ZnO NPs) and cadmium (Cd) on growth, yield, antioxidant enzymes, Cd and zinc (Zn) concentrations in wheat (Triticum aestivum). The ZnO NPs were applied both in Cd-contaminated soil and foliar spray (in separate studies) on wheat at different intervals and plants were harvested after physiological maturity. Results depicted that ZnO NPs enhanced the growth, photosynthesis, and grain yield, whereas Cd and Zn concentrations decreased and increased respectively in wheat shoots, roots and grains. The Cd concentrations in the grains were decreased by 30–77%, and 16–78% with foliar and soil application of NPs as compared to the control, respectively. The ZnO NPs reduced the electrolyte leakage while increased SOD and POD activities in leaves of wheat. It can be concluded that ZnO NPs (levels used in the study) could effectively reduce the toxicity and concentration of Cd in wheat whereas increase the Zn concentration in wheat. Thus, ZnO NPs might be helpful in decreasing Cd and increasing Zn biofortification in cereals which might be effective to reduce the hidden hunger in humans owing the deficiency of Zn in cereals.

Metal(loid)-resistant bacteria reduce wheat Cd and As uptake in metal(loid)-contaminated soil

This study characterized the effect of the metal(loid)-resistant bacteria Ralstonia eutropha Q2-8 and Exiguobacterium aurantiacum Q3-11 on Cd and As accumulation in wheat grown in Cd- and As-polluted soils (1 mg kg−1 of Cd + 40 mg kg−1 of As and 2 mg kg−1 of Cd + 60 mg kg−1 of As). The influence of strains Q2-8 and Q3-11 on water-soluble Cd and As and NH4+concentration and pH in the soil filtrate were also analyzed. Inoculation with these strains significantly reduced wheat plant Cd (12–32%) and As (9–29%) uptake and available Cd (15–28%) and As (22–38%) contents in rhizosphere soils compared to the controls. Furthermore, these strains significantly increased the relative abundances of the arsM bacterial As metabolism gene and of Fe- and Mn-oxidizing Leptothrix species in rhizosphere soils. Notably, these strains significantly reduced water-soluble Cd and As concentrations and increased pH and NH4+ concentration in the soil filtrate. These results suggest that these strains increased soil pH and the abundance of genes possibly involved in metal(loid) unavailability, resulting in reduced wheat Cd and As accumulation and highlight the possibility of using bacteria for in situ remediation and safe production of wheat or other food crops in metal(loid)-polluted soils.

A multi-surface model to predict Cd phytoavailability to wheat (Triticum aestivum L.)

The prediction of metal bioavailability in soils is critical to metal risk assessments and the amount of dissolved metal in soils is a key factor determining bioavailability. Because the recently developed geochemical multi-surface models (MSMs) offer a promising tool for the determination of metal partitioning in soils, in this study, a MSM based on generic parameters was used to assess the bioavailability of Cd in wheat (Triticum aestivum L.) growing in 12 soils with a wide range of properties. The amount of MSM-calculated dissolved Cd correlated strongly with the amount of Cd uptake by wheat (R2=0.873 for roots and R2=0.837 for shoots), and the model's performance was better than that of chemical extraction methods (0.01M CaCl2, 0.43M HNO3 and soil total Cd). The reactive fraction of soil organic matter, the soil/solution ratio, and the inclusion/exclusion of background cations influenced the calculation results. The best calculation condition was optimized. The application of the MSM was also examined in 84 wheat-soil samples from the field. The amount of Cd in wheat seeds had a stronger correlation with the amount of MSM-predicted Cd than with the amount of Cd obtained using chemical extraction methods. Our results suggested that MSM-calculated Cd is an effective indicator of the bioavailability of Cd in soils and demonstrated the utility of the method as a tool to assess the risk of Cd contamination in soils.

Assessment of Bioavailability of Some Heavy Metals to Wheat and Faba Bean in Sahl El-Tina, Egypt

Accumulation of heavy metals viz., Mn, Zn, Cu, Ni, Pb, Co, Cd and Cr in soils and commonly grown crop plants (wheat and faba bean) was studied in the fields in Sahl El-Tina, located in the Northwestern Sinai Peninsula, Egypt. Irrigation water at different sites was slight to moderately saline with no sodium hazard. About 50% of irrigation water samples revealed salt combinations consisting of NaCl, MgCl2, MgSO4, CaSO4 and Ca(HCO3)2, thereby indicating marine salt pollution. The results also revealed that heavy metals in irrigation and drainage water were within the recommended levels. The total contents of Ni, Pb, Co and Cd in subsoil samples were higher than the levels in topsoil samples, suggesting strong evidence of indigenous supply. However, total contents of Mn, Zn, Cu and Cr in topsoil samples were higher than the levels in subsoil samples, implying anthropogenic source of contamination. The highest single-element pollution index value in soil was found for Cd, which ranged from 0.289 to 3.763, indicating low to high contamination levels. Except for Zn and Pb which showed low contamination level, other elements showed low to moderate contamination levels in soil. The combined pollution index ranged from 0.238 to 1.688, indicating low to moderate multi-element contamination levels in soil. Except for Zn and Cd, the levels of heavy metals in wheat and faba bean were greater than the permissible limits. The highest transfer coefficients of metals from soil to plant were found for Zn and Cd in wheat. On the other hand, the highest coefficients in faba bean were found for Pb, Cd, Zn and Cu. Faba bean showed the ability to accumulate heavy metals in higher amounts than wheat. It was evident that there is a multi-element pollution source for the growing crops in Sahl El-Tina that could be due to the anthropogenic activities in respect of some elements but inherently for others.

Interaction of Mg with heavy metals (Cu, Cd) in T. aestivum with special reference to oxidative and proline metabolism.

Little effort has been made to understand the influence of Mg on cellular processes of plant cell during Cu and Cd toxicities. The present work demonstrates the influence of magnesium (Mg) on copper (Cu) and cadmium (Cd) toxicity on Triticum aestivum (Wheat). We measured a range of parameters related to oxidative stress in wheat exposed to Cu or Cd toxicity in media with different concentrations of Mg. Decreasing Mg concentration significantly exacerbated Cu and Cd toxicity and optimum supply of Mg improved the growth and decreased the toxicity-induced oxidative stress (a substantial decline in the amount of hydrogen peroxide (H2O2) and malondialdehyde (MDA) in root and shoot tissues). Activity of antioxidant enzymes-superoxide dismutase (SOD), ascorbae peroxidase (APX), catalase (CAT) was restored upon optimum Mg concentration in the presence of Cu and Cd toxicity. An increase in proline concentration in roots and shoots that was triggered by Cu and Cd exposure was partly reversed. This was due to decline in pyrroline-5-carboxylate synthetase (P5CS) and pyrroline-5-carboxylate reductase (P5CR) activity and enhanced proline dehydrogenase (PDH) activity. In conclusion, decreasing supply of Mg effectively exacerbated the toxicities of Cu and Cd in wheat.

Alleviation effects of calcium and potassium on cadmium rhizotoxicity and absorption by soybean and wheat roots

AbstractThe objectives of the present study were to investigate the root responses of soybean (Glycine max L.) and wheat (Triticum aestivum L.) seedlings to cadmium (Cd) stress and to investigate the alleviation effects of Ca and K on rhizotoxicity and absorption of Cd by roots. Soybean and wheat seedlings in a hydroponic system were exposed to Cd‐spiked solutions (0, 4, 8, 12, and 16 μM) with different Ca (0.5, 1, and 10 mM) and K (0.3, 1.2, and 9.6 mM) levels for 7 d. The results showed a dramatic reduction in root elongation of soybean due to increased Cd, but increasing Ca and K levels alleviated this reduction in soybean. The amelioration of Cd toxicity by the addition of Ca may be associated with reduced Cd absorption. However, the addition of K in reducing Cd toxicity might not be dependent upon Cd absorption. Compared with soybean, wheat showed a relatively high tolerance to Cd. The alleviation of Cd rhizotoxicity in wheat was more apparent by K than by Ca. We found that the addition of K promoted root elongation but not directly prevent Cd stress, and that the addition of Ca minimized acute rhizotoxicity of Cd in wheat. Moreover, the addition of Ca reduced Cd absorption by soybean and wheat roots. However, the addition of K only reduced Cd absorption by wheat roots.

Effect of Municipal Biowaste Biochar on Greenhouse Gas Emissions and Metal Bioaccumulation in a Slightly Acidic Clay Rice Paddy

A field trial was performed to investigate the effect of municipal biowaste biochar (MBB) on rice and wheat growth, metal bioaccumulation, and greenhouse gas emissions in a rice paddy in eastern China. MBB was amended in 2010 before rice transplanting at rates of 0 and 40 t ha-1 in a field experiment lasting one cropping year. MBB soil amendment significantly increased soil pH, total soil organic carbon, and total nitrogen. The growth and grain yield of rice and wheat was not affected with MBB application at 40 t ha-1. MBB amendment did not influence the soil availability of Pb, Cu, and Ni, but significantly increased the soil availability of Zn and decreased the soil availability of Cd during both rice and wheat seasons. While MBB did not change the bioaccumulation of Pb, Cu, and Ni, the rice and wheat Cd accumulation was significantly reduced, and wheat Zn accumulation slightly increased with MBB amendment. Furthermore, total N2O emission during both rice and wheat seasons was greatly decreased, though total seasonal CH4 emission was significantly increased in the rice season. On the other hand, soil CO2 emission remained unaffected across crop seasons. Thus, MBB can be used in rice paddy for low carbon and low-Cd grain production, but the long-term effects remain unknown.

The effect of rate and Cd concentration of repeated phosphate fertilizer applications on seed Cd concentration varies with crop type and environment

Limited information is available on how cadmium (Cd) applied in phosphate fertilizer interacts with soil and environmental conditions over time to affect crop Cd concentrations. Field studies from 2002 to 2009 at seven locations evaluated the cumulative effects of P fertilizer rate and Cd concentration on seed Cd concentration of durum wheat (Triticum turgidum L.) and flax (Linum usitatissiumum L.). Soil characteristics and environment affected Cd availability. Durum wheat grain Cd increased with P fertilizer rate but effect on flaxseed Cd concentration was smaller. Cadmium concentration in fertilizer had a greater effect on flaxseed than durum wheat Cd concentration. Seed Cd concentration of both crops was greatest with the highest rate P fertilizer containing the highest Cd concentration. There was not a strong cumulative effect of fertilization over the 8 years of the study, indicating attenuation of Cd availability over time. Cadmium in phosphate fertilizer increases Cd available for crop uptake, but crop Cd concentration is also affected by soil characteristics and annual environmental conditions. Type of crop produced and soil and environmental characteristics that affect phytoavailability must be taken into account when assessing the Cd risk from P fertilization.

THE REDUCTION OF WHEAT Cd UPTAKE IN CONTAMINATED SOIL VIA BIOCHAR AMENDMENT: A TWO-YEAR FIELD EXPERIMENT

A field study involving wheat production was extended in order to study the effects of biochar (BC) amendment in paddy soil that had long-term contamination of Cd. The BC was used as an amendment in Cd-contaminated soil for its special property. BC was amended at rates of 10 to 40 t ha-1 during the rice season before rice transplantation in 2009. BC amendments increased soil pH by 0.11 to 0.24 and by 0.09 to 0.24 units, respectively, while the soil CaCl2-extracted Cd was reduced by 10.1% to 40.2% and by 10.0% to 57.0% in 2010 and 2011, respectively. Consequently, the total wheat Cd uptake was decreased by 16.8% to 37.3% and by 6.5% to 28.3%. Wheat grain Cd concentration was reduced by 24.8% to 44.2% and by 14.0% to 39.2% in 2010 and 2011, respectively. The BC application in soil reduced Cd phyto-availability in two wheat seasons possibly by raising soil pH and soil organic carbon (SOC). Therefore, BC may be used for soil remediation, but not to reduce Cd uptake to an adequate level for food production on Cd contaminated soils.

Toxicity and subcellular distribution of cadmium in wheat as affected by dissolved organic acids

We aim to investigate the effects of humic acid (HA) and citric acid (CA) on the toxicity and subcellular distribution of Cd in wheat. Results show that the toxicity and uptake of Cd decreased with increasing HA. The EC50 values of Cd increased from 3.36 μmol/L to 4.96 and 7.33 μmol/L at 50 and 250 mg/L HA, respectively, but decreased to 1.39 μmol/L in the presence of CA based on free ion activity model (FIAM). HA decreased the relative subcellular distribution of Cd in the heat-denatured proteins (decreased from 54% to 33%) but increased Cd in the heat-stable proteins in root (from 25% to 50%) at 7.61 μmol/L {Cd2+} (free Cd activity), which resulted in decreasing Cd toxicity. However, CA increased Cd toxicity due to the increased internalization of Cd although the relative subcellular distributions of Cd exhibited a decrease in the heat-denatured proteins and increase in the granule fraction compared to the control at high-level Cd. The FIAM could not predict the toxicity of Cd in the presence of organic acids. Alternatively, the internal Cd accumulation and subcellular Cd concentration were better to describe the toxicity of Cd to wheat.

Combined cadmium and elevated ozone affect concentrations of cadmium and antioxidant systems in wheat under fully open-air conditions

Pollution of the environment with both ozone (O3) and heavy metals has been steadily increasing. An understanding of their combined effects on plants, especially crops, is limited. Here we studied the effects of elevated O3 on oxidative stress and bioaccumulation of cadmium (Cd) in wheat under Cd stress using a free-air concentration enrichment (FACE) system. In this field experiment in Jiangdu (Jiangsu Province, China), wheat plants were grown in pots containing soil with various concentrations of cadmium (0, 2, and 10mgkg−1 Cd was added to the soil) under ambient conditions and under elevated O3 levels (50% higher than the ambient O3). Present results showed that elevated O3 led to higher concentrations of Cd in wheat tissues (shoots, husk and grains) with respect to contaminated soil. Combined exposure to Cd and elevated O3 levels strongly affected the antioxidant isoenzymes POD, APX and CAT and accelerated oxidative stress in wheat leaves. Our results suggest that elevated O3 levels cause a reduction in food quality and safety.

Joint stress of chlorimuron-ethyl and cadmium on wheat Triticum aestivum at biochemical levels

Biochemical responses to joint stress of chlorimuron-ethyl and cadmium (Cd) in wheat Triticum aestivum were examined. The joint action of chlorimuron-ethyl and Cd weakened the inhibition of Cd or chlorimuron-ethyl on the formation of chlorophyll. It was deduced that wheat plants had the capability to protect themselves by increasing the activity of the antioxidant enzyme peroxidase (POD) with the exposure time. The joint effect of chlorimuron-ethyl and Cd on the superoxide dismutase (SOD) activity in leaves was additive, while the joint effect on the SOD activity in roots was determined by the interaction of chlorimuron-ethyl and Cd in wheat. It was also concluded that the change of malondialdehyde (MDA) content in wheat might not be a good biomarker in the oxidative damage by chlorimuron-ethyl, while a decrease in the soluble protein content and POD activity in roots could be considered as a biomarker in the damage of wheat by chlorimuron-ethyl and Cd.

Probabilistic quality standards for heavy metals in soil derived from quality standards in crops

This paper contributes to the development of critical levels of heavy metals in soil at which functions of the soil are safeguarded. For agriculture production, one of the key aspects is food safety. In this study, a quality standard for Cd in soil is derived from the EC-food quality standard for Cd in wheat. The transfer of the Cd in the soil to the crop is modelled by a regression model. Such models offer the possibility of calculating probabilistic soil quality standards from food quality standards. Given the food quality standard and a maximum acceptable probability of exceeding this standard, the Cd concentrations in soil at which the probability of excess Cd in wheat equals this maximum is calculated by the inverse use of the regression model. It is important to account for errors in the Cd measurements in wheat used to calibrate the model. Neglecting these errors gives conservative estimates of the p% critical threshold for p smaller than 50. For representative arable soils, the 5% critical threshold varies from 0.5 mg kg −1 (non-calcareous sand soils) to 3 mg kg −1 (calcareous clay soils). Even at low probability levels, the model must be extrapolated for many arable soils, and therefore, more calibration data must be collected, especially from sand soils with relatively low pH values. Validation of the model with data from contaminated bed sediments in the floodplain of the Meuse showed that the model seriously overestimated the critical threshold, which can be explained by the higher availability of Cd in contaminated soils.

Uncertainty and sensitivity analysis of spatial predictions of heavy metals in wheat.

Heavy metals seriously threaten the health of human beings when they enter the food chain. Therefore, policymakers require precise predictions of heavy metal concentrations in agricultural crops. In this paper we quantify the uncertainty of regression predictions of Cd and Pb in wheat (Triticum aestivum L.) and the contributions to the uncertainties in these predictions associated with inputs to the regression model. For each node of the 500- x 500-m grid covering the arable soils in The Netherlands, a latin hypercube sample size of 1000 is constructed from the uncertainty distributions of the explanatory variables (pH, soil organic matter [SOM], and heavy metal concentration in soil), the regression coefficients, and the random term of the regression model. This sample is used as input for the regression model to obtain 1000 values from the uncertainty distributions of the log(Cd) and log(Pb) concentration in wheat. There were no nodes where the recent EU quality standards for Cd and Pb (0.2 mg kg(-1) fresh wt.) in wheat were almost certain to be exceeded. For most nodes with clay soils, the quality standard for Cd in wheat almost certainly will not be exceeded; for Pb this is much less certain. The uncertainty in the Cd concentration in soil contributes most to the uncertainty in the predicted Cd concentrations in wheat (36% on the average), followed by the random term of the regression model (23%). For Pb the contribution of the random term is by far the largest (52%).

Predicting cadmium concentrations in wheat and barley grain using soil properties.

The entry of Cd into the food chain is of concern as it can cause chronic health problems. To investigate the relationship between soil properties and the concentration of Cd in wheat (Triticum aestivum L.) and harley (Hordeum vulgare L.) grain, we analyzed 162 wheat and 215 barley grain samples collected from paired soil and crop surveys in Britain, and wheat and barley samples from two long-term sewage sludge experiments. Cadmium concentrations were much lower in barley grain than in wheat grain under comparable soil conditions. Multiple regression analysis showed that soil total Cd and pH were the significant factors influencing grain Cd concentrations. Significant cultivar differences in Cd uptake were observed for both wheat and barley. Wheat grain Cd concentrations could be predicted reasonably well from soil total Cd and pH using the following model: log(grain Cd) = a + b log(soil Cd) - c(soil pH), with 53% of the variance being accounted for. The coefficients obtained from the data sets of the paired soil and crop surveys and from long-term sewage sludge experiments were similar, suggesting similar controlling factors of Cd bioavailability in sludge-amended or unamended soils. For barley, the model was less satisfactory for predicting grain Cd concentration (22% of variance accounted for). The model can be used to predict the likelihood of wheat grain Cd exceeding the new European Union (EU) foodstuff regulations on the maximum permissible concentration of Cd under different soil conditions, particularly in relation to the existing Directive and the proposed new Directive on land applications of sewage sludge.

RESPONSES OF LEGUME AND NON-LEGUME CROP SPECIES TO HEAVY METALS IN SOILS WITH MULTIPLE METAL CONTAMINATION

ABSTRACT Field and glasshouse investigations were conducted on the responses of two legumes (field pea and fodder vetch) and three non-leguminous crops (maize, wheat and rapeseed) to the heavy metals Cd, Cr, Zn, Pb, Cu and Mn in soil with multiple metal contamination. In general, the results indicate that the two legumes and wheat were more susceptible to soil metals than were rapeseed and maize. The dry matter yields of field pea, wheat, fodder vetch, rapeseed and maize decreased by up to 169, 123, 113, 93 and 68%, respectively, in metal-contaminated soil. Among the crops, maize had the highest concentrations of Mn, Zn and Cd, rapeseed had the highest concentrations of Cr, the concentration of Cu was highest in fodder vetch, and wheat was the highest accumulator of Pb. The bioconcentration factors (BCF) of the metals decreased as the soil metal loading rates increased except for Cr in fodder vetch and Cd in wheat, whose BCF increased as the metal loading rate increased. Significant linear correlations were found between plant and soil metal concentrations. Patterns of metal distribution in plant parts varied with different crops and metals, with more Cd and Cu accumulating in the grain of wheat than of maize, suggesting that growing wheat would represent a higher risk of food contamination than growing maize in Cd- or Cu-contaminated soil. The results suggest that on sites with multiple metal contamination, growing maize and rapeseed would be safer than growing wheat or legumes. However, maize could perhaps be used for phytoremediation of lightly contaminated soils, providing that the crop residues were safely disposed of.

Cadmium concentrations in some New Zealand wheat grain

The variation in wheat (Triticum aestivum L.) grain cadmium (Cd) concentrations between different cultivars was investigated along with a preliminary ranking of soil properties in terms of their importance in controlling wheat grain Cd concentrations. Results indicate that there is considerable variation in Cd concentrations in New Zealand wheat grain samples. The mean Cd concentration for wheat in this study is 54 μg kg1 fresh weight (FW). Ten percent of the grain samples examined in this study are non‐compliant with the maximum permissible concentration (MPC) for Cd in wheat grain. However almost 50% of non‐compliant samples were found at a single site, and at a number of sites no samples exceeded MPC. There was a 4‐fold range in the abilities of different wheat cultivars to accumulate Cd in grain. There was also seasonal variation in Cd uptake for wheat cultivars grown at the same site. Extractable soil Cd using a weak salt reagent yielded the highest correlation with grain Cd concentrations in spring wheat across all soils, whereas no significant relationships were found for winter wheat. There were no significant simple correlations between major soil properties and wheat grain Cd concentrations for either winter or spring wheat. For winter wheat, a multiple regression model with terms for total zinc (Zn) and CaCl2‐extractable Cd yielded the highest correlation with winter wheat Cd concentrations (r2 = 0.59 P < 0.05). Low Cd accumulating wheat cultivars can be selected for use at sites where the Cd concentration in grain exceeds the MPC. Future work is required to determine which soil properties are important in controlling wheat grain Cd concentrations.

Biosolids and Biosolids-ash as Sources of Heavy Metals in a Plant-Soil System

Generally, the potential for biosolids (digested or composted)to contribute heavy metals to the soil-plant system has beencompared with commercial fertilizers and other organic wastesbut not with biosolids-ash. An column study was conducted in agreenhouse to determine the availability, extractability andleachability of metals in a degraded, non-calcareous soilamended with different biosolids (200 Mg ha-1). Thebiosolids investigated were dewatered, anaerobically digestedbiosolids, composted biosolids and biosolids-ash. The columns(26 cm) were planted with wheat (Triticum aestivum L. cvMexa). The addition of digested biosolids decreased the drymatter yield of wheat. Treatments including organic biosolidsincreased Cu and Zn concentrations in wheat roots, straw andgrain, whereas the addition of biosolids-ash did not affect theconcentrations of these metals in wheat. Concentrations of Ni,Co, Pb, Cr and Cd in wheat were below reliable detection limits(0.06, 0.05, 0.1, 0.06 and 0.02 mg kg-1, respectively).After harvesting, total and AB-DTPA extractable Cu, Zn and Pbincreased in the upper layer of the soil amended with thedifferent biosolids studied, whereas levels of AB-DTPAextractable Ni and Co were affected only when the soil wasamended with digested or composted biosolids. Total chromiumincreased only in treatments including organic biosolids. TheAB-DTPA extractable Cu, Zn and Pb in the lower layer of thesoil in treatments including biosolids evidenced downwardmovement of these metals. However, absence of these metals incolumn leachates indicates that this movement was gradual.

Does organic farming reduce the content of Cd and certain other trace metals in plant foods? A pilot study

The effect of organic cultivation systems on the level of Cd in wheat was studied in two consecutive harvests. Additionally, the concentrations of Cd, Pb, Cr and Zn were analysed in single harvests of rye, carrots and potatoes from different farming systems. Wheat and rye were obtained from controlled field trials using several conventional and ecological systems at two separate locations in Sweden. Potatoes and carrots were collected at private farms with conventional or ecological production. These farms were juxtapositioned and had similar soil properties. The levels of Cd in the wheat did not correlate with the cultivation system or the Cd content in the soil. Conventionally grown wheat from one field trial showed a significantly higher Cd level compared with ecologically grown wheat, while in the other field trial significantly lower Cd levels were detected in the conventionally grown wheat. No statistically significant differences in the concentrations of Cd, Pb, Cr or Zn in rye, carrots and potatoes were detected between the cultivation systems. The results indicate that organic farming, at least in the short term, does not necessarily result in reduced levels of Cd and other potentially harmful metals in foods of vegetable origin. Factors other than cultivation system may be of greater importance for the final concentration of Cd and other metals in plant foods. © 2000 Society of Chemical Industry