Cadmium in foods and the diet

The Protection of Zinc against Acute Cadmium Exposure: A Morphological and Molecular Study on a BBB In Vitro Model

Cadmium (Cd) is a well-known occupational and environmental pollutant worldwide, and its toxicity is widely recognised. Cd is reported to increase the permeability of the blood–brain barrier (BBB) and to penetrate and accumulate in the brain. Although many lines of evidence show that Cd toxicity is induced by different mechanisms, one of the best known is the Cd-dependent production of reactive oxygen species (ROS). Zinc is a trace element known as coenzyme and cofactor for many antioxidant proteins, such as metallothioneins and superoxide dismutase enzymes. To date, very little is known about the role of Zn in preventing Cd-induced blood–brain barrier (BBB) alterations. The goal of this study was to test the Zn antioxidant capacity against Cd-dependent alterations in a rat brain endothelial cell line (RBE4), as an in vitro model for BBB. In order to mimic acute Cd poisoning, RBE4 cells were treated with CdCl₂ 30 µM for 24 h. The protective role of ZnCl₂ (50 µM) was revealed by evaluating the cell viability, reactive oxygen species (ROS) quantification, cytochrome C distribution, and the superoxide dismutase (SOD) protein activity. Additionally, the effectiveness of Zn in counteracting the Cd-induced damage was investigated by evaluating the expression levels of proteins already known to be involved in the Cd signalling pathway, such as GRP78 (an endoplasmic reticulum (ER) stress protein), caspase3 pro- and cleaved forms, and BAX. Finally, we evaluated if Zn was able to attenuate the alterations of zonula occludens-1 (ZO-1), one of the tight-junction (TJ) proteins involved in the formation of the BBB. Our data clearly demonstrate that Zn, by protecting from the SOD activity impairment induced by Cd, is able to prevent the triggering of the Cd-dependent signalling pathway that leads to ZO-1 dislocation and downregulation, and BBB damage.

Cadmium exposure activates NADPH oxidase, renin-angiotensin system and cyclooxygenase 2 pathways in arteries, inducing hypertension and vascular damage

Exposure to high concentrations of cadmium (Cd), widely used in many industries and found in air, food and contaminated water, is not uncommon. Cd damages the cardiovascular system, but the vascular mechanisms involved are not fully understood. This study investigated the mechanisms involved in cardiovascular damage after exposure to high Cd concentrations. Three-month-old male Wistar rats were treated intraperitoneally for 14 days with distilled water (Untreated group) or 1 mg/kg cadmium chloride (Cd group). We investigated the systolic blood pressure (SBP) and vascular reactivity of mesenteric resistance arteries (MRA) and the aorta by analysing contractile and relaxation responses in the absence and presence of the endothelium; we also evaluated pathways involved in vascular tone regulation. Superoxide anion production, COX-2 protein expression and in situ detection of COX-2, AT-1, and NOX-1 were evaluated. Oxidative status, creatinine level and angiotensin-converting enzyme (ACE) activity in plasma were also evaluated. Fourteen-day exposure to a high Cd concentration induced hypertension associated with vascular dysfunction in MRA and the aorta. In both vessels, there was increased participation of cyclooxygenase 2 (COX2), angiotensin II type 1 (AT1) receptor and NOX1. MRA also presented endothelial dysfunction, denoted by impaired acetylcholine-mediated relaxation. All vascular changes were accompanied by increased reactive oxygen species production and COX2, NOX1 and AT1 receptor expression in vascular tissue. Overall, high Cd concentrations induced cardiovascular damage: hypertension, endothelial dysfunction and vascular damage in conductance and resistance arteries, NADPH oxidase, renin-angiotensin system and COX2 pathway activation.

Selective detection of cadmium ions using plasmonic optical fiber gratings functionalized with bacteria

Environmental monitoring and potable water control are key applications where optical fiber sensing solutions can outperform other technologies. In this work, we report a highly sensitive plasmonic fiber-optic probe that has been developed to determine the concentration of cadmium ions (Cd²⁺) in solution. This original sensor was fabricated by immobilizing the Acinetobacter sp. around gold-coated tilted fiber Bragg gratings (TFBGs). To this aim, the immobilization conditions of bacteria on the gold-coated optical fiber surface were first experimentally determined. Then, the coated sensors were tested in vitro. The relative intensity of the sensor response experienced a change of 1.1 dB for a Cd²⁺ concentration increase from 0.1 to 1000 ppb. According to our test procedure, we estimate the experimental limit of detection to be close to 1 ppb. Cadmium ions strongly bind to the sensing surface, so the sensor exhibits a much higher sensitivity to Cd²⁺ than to other heavy metal ions such as Pb²⁺, Zn²⁺ and CrO₄^2- found in contaminated water, which ensures a good selectivity.

First and second order stereology of hyaline cartilage: Application on mice femoral cartilage

Stereological techniques could be considered in research on cartilage to obtain quantitative data. The present study aimed to explain application of the first- and second-order stereological methods on articular cartilage of mice and the methods applied on the mice exposed to cadmium (Cd). The distal femoral articular cartilage of BALB/c mice (control and Cd-treated) was removed. Then, volume and surface area of the cartilage and number of chondrocytes were estimated using Cavalieri and optical dissector techniques on isotropic uniform random sections. Pair-correlation function [g(r)] and cross-correlation function were calculated to express the spatial arrangement of chondrocytes-chondrocytes and chondrocytes-matrix (chondrocyte clustering/dispersing), respectively. The mean±standard deviation of the cartilage volume, surface area, and thickness were 1.4±0.1mm³, 26.2±5.4mm², and 52.8±6.7μm, respectively. Besides, the mean number of chondrocytes was 680±200 (×10³). The cartilage volume, cartilage surface area, and number of chondrocytes were respectively reduced by 25%, 27%, and 27% in the Cd-treated mice in comparison to the control animals (p<0.03). Estimates of g(r) for the cells and matrix against the dipole distances, r, have been plotted. This plot showed that the chondrocytes and the matrix were neither dispersed nor clustered in the two study groups. Application of design-based stereological methods and also evaluation of spatial arrangement of the cartilage components carried potential advantages for investigating the cartilage in different joint conditions. Chondrocyte clustering/dispersing and cellularity can be evaluated in cartilage assessment in normal or abnormal situations.

Daily dietary intakes of zinc, copper, lead, and cadmium as determined by duplicate portion sampling combined with either instrumental analysis or the use of food composition tables, Shiraz, Iran

Estimation of essential and toxic element intakes is crucial to evaluate the risks of deficiency or toxicity. The purpose of this study was to investigate and also to compare the dietary intakes of zinc (Zn) and copper (Cu) by adults living in Shiraz, Iran, determined by two procedures: duplicate portion sampling of 21 hospital meals combined with either instrumental analysis (voltammetric measurement) or the use of food composition tables (FCTs). The level of exposure to lead (Pb) and cadmium (Cd) was evaluated as well. The daily Zn intakes of both methods were not significantly different and were higher than the RDA values except the value measured by the instrumental analysis which was lower than the RDA established for a male adult. Daily intake of Cu determined by instrumental analysis was significantly lower and closer to RDA for adults compared with the value estimated by FCTs. The dietary intakes of Pb and Cd were 313 and 61% of the respective provisional tolerable weekly intakes (PTWIs), respectively. The accuracy of two methods used for estimation of Zn intake was similar. In the case of Cu, the use of FCTs, in which the influence of environmental conditions and dietary habits of meal preparation is not taken into account, overestimated dietary intake. The risk of zinc deficiency was found in adult males. Moreover, the estimated intake of Pb, but not Cd, could be a cause of concern for Shiraz population. Thus, conducting regular periodic studies to assess the dietary intake of mentioned elements are recommended.

Schiff bases as cadmium(II) selective ionophores in polymeric membrane electrodes

The construction and performance characteristics of polymeric membrane electrodes based on two neutral ionophores, N,N'-[bis(pyridin-2-yl)formylidene]butane-1,4-diamine (S1) and N-(2-pyridinylmethylene)-1,2-benzenediamine (S2) for quantification of cadmium ions, are described. The influences of membrane compositions on the potentiometric response of the electrodes have been found to substantially improve the performance characteristics. The best performance was obtained with the electrode having a membrane composition (w/w) of (S1) (2.15%):PVC (32.2%):o-NPOE (64.5%):KTpClPB (1.07%). The proposed electrode exhibits Nernstian response in the concentration range of 7.9x10(-8) to 1.0x10(-1) M Cd2+ with limit of detection 5.0x10(-8) M, performs satisfactorily over wide pH range (2.0-8.0) with a fast response time (10 s). The sensor has been found to work satisfactorily in partially non-aqueous media up to 30% (v/v) content of methanol, ethanol and acetonitrile and could be used for a period of 2 months. The analytical usefulness of the proposed electrode has been evaluated by its application in the determination of cadmium in real samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants.

Cadmium dietary intake in the Canary Islands, Spain

Cadmium (Cd) in the human diet constitutes a potential chronic hazard to health. In the nonsmoking general population, diet is the major source of cadmium exposure; therefore, it is important to monitor the dietary intake of this heavy metal to quantify and improve the understanding of Cd accumulation in the human body. The purpose of this study was to determine the levels of Cd in a range of food and drink commonly consumed in the Canary Islands. Food samples (420) were analyzed for Cd by atomic absorption spectrometry. The most recent nutritional survey conducted for the Canarian population was used to define the food and drink groups analyzed. The measured Cd concentrations combined with the food consumption data resulted in a total Cd intake in the Canary Islands of 0.16 microg/kg of body weight/day, which is well below the respective provisional tolerable weekly intake of Cd of 1 microg/kg of body weight per day determined by the FAO/WHO. The results are also compared with values reported for other national and international communities.

Increased cadmium tolerance and accumulation by plants expressing bacterial arsenate reductase

•  Cadmium (Cd) is a major environmental pollutant that poses a serious threat to natural ecosystems. However, most initial attempts to engineer phytoremediation of Cd have not succeeded in developing sufficient Cd tolerance for vigorous plant growth. •  We found that the bacterial arsenate reductase gene (arsC) provided Cd(II) resistance to Escherichia coli. When ArsC is overexpressed in tobacco (Nicotiana tabacum) and Arabidopsis thaliana, both transgenic plant species showed significantly greater Cd tolerance than wild-type controls. •  At 50, 75, and 100 µm concentrations of Cd (II), the ArsC expressing transgenic lines grew bigger with broader leaves and longer roots than wild-type controls, which were stunted, turned yellow, flowered early, and often died. At the various Cd(II) concentrations, ArsC transgenic plants attained f. wt 2-3-fold higher than the wild-type plants and had roots significantly longer than wild-type plants. These transgenic plants also contained 30-50% higher Cd concentrations than wild-type plants. •  It is likely that the arsC gene directs Cd tolerance via the electrochemical reduction of Cd(II) to Cd(0).

Cadmium exposure in tobacco workers: possible renal effects

Cadmium is a nephrotoxic metal widely used in industry and the main source of Cd in general population is smoking. Considering that the source of Cd in cigarettes is the tobacco leaf, the exposure to Cd was evaluated in workers employed at a tobacco leaf processing factory. Blood and urinary Cd levels were measured by flameless atomic absorption spectrometry in 87 workers and 35 controls. Urinary enzymes, total protein, albumin and uric acid were also determined to investigate the possible nephrotoxic effects of Cd. Blood Cd levels were significantly higher in workers (1.63 +/- 1.95 microg/L) than in controls (0.91 +/- 1.15 microg/L) (p = 0.044). The increase observed in urinary Cd levels of workers was non significant (0.56 +/- 0.5 microg/g creatinine in workers and 0.46 +/- 0.5 microg/g creatinine in controls). Both in workers and in controls, subjects smoking >10 cigarettes/day showed significantly increased blood Cd levels compared to non-smokers (p = 0.000 and p = 0.011, respectively). In workers, urinary alkaline phosphatase (ALP), gamma glutamyl transferase (GGT), total protein, and uric acid were observed to be significantly increased (p = 0.013, p = 0.000, p = 0.000, p = 0.025, respectively), ALP, GGT and total protein being positively correlated with Cd in urine. In conclusion, the workers in the tobacco leaf processing factory were found to be exposed to Cd compared to the general population. The increase in the urinary enzymes and proteins suggests that an exposure to Cd affects kidney functions even below the toxic limits generally accepted.

Trace element inputs into soils by anthropogenic activities and implications for human health

Trace element definition and functions, and inputs into soils from the most important anthropogenic sources, related and not related to agricultural practices, of general and local or incidental concern, are discussed in the first part of this review. Trace element inputs include those from commercial fertilizers, liming materials and agrochemicals, sewage sludges and other wastes used as soil amendments, irrigation waters, and atmospheric depositions from urban, industrial, and other sources. In the second part of the review, the most important ascertained effects of soil trace elements on human health are presented. The possible relations found between some specific soil trace elements, such as Cd, Se, As and others, and cancer incidence and mortality, and diffusion of other important human diseases are reviewed. Brief conclusions and recommendations conclude this review.

Inhibition of 8-hydroxyguanine repair in testes after administration of cadmium chloride to GSH-depleted rats

The main goal of this study is to investigate the mechanism of cadmium (Cd)-induced carcinogenesis by reactive oxygen species. Rats were divided into four groups and were treated with (i) saline (control), (ii) cadmium chloride (CdCl2), (iii) l-buthionine-[S, R]-sulfoximine (BSO, an inhibitor of GSH biosynthesis), and (iv) CdCl2 and BSO, respectively. They were euthanized at 0, 24, 48, and 72 hr after these treatments, and the lungs and testes were analyzed. After treatment with both CdCl2 and BSO, the testicular 8-OH-Gua level increased (48 hr), its repair activity decreased (48 and 72 hr), the GSH content was markedly suppressed (48 and 72 hr), the superoxide dismutase activities slightly (48 and 72 hr) decreased, and the lipid peroxidation level increased (24 and 72 hr) in the testes as compared to the control levels. These results suggest that under GSH-depleted conditions, CdCl2 inhibits 8-OH-Gua repair activity in the rat testis and 8-OH-Gua accumulates in the DNA, which may pertain to testicular carcinogenesis.

Cadmium-induced lipid peroxidation and the antioxidant system in rat erythrocytes: the role of antioxidants

Cadmium (Cd)-induced oxidative damage in erythrocytes causes loss of membrane function by enhancing lipid peroxidation (LPO) and altering the erythrocyte antioxidant system. Vitamin E and/or selenium (Se) was administered to rats, prior to Cd intoxication, in order to prepare the animals to withstand oxidative assault. The treatment with Cd increased LPO in erythrocytes while animals pretreated with vitamin E and/or Se prior to Cd treatment showed decreased LPO as compared with animals given Cd alone. The erythrocyte SOD and CAT activities decreased significantly with Cd treatment. The pretreatment with vitamin E and/or Se prior to Cd administration partially reversed such changes. The erythrocytes showed a marked depletion in glutathione (GSH) content with Cd treatment. The antioxidant treatments before Cd administration helped to maintain the erythrocyte GSH content. The erythrocyte glutathione reductase (GSH-R) activity increased markedly when treatments with vitamin E and Se were applied. The GSH-R activity was not observed to decrease in animals treated with antioxidant prior to Cd intoxication, which may mean that the replenishment of erythrocyte GSH content is via GSH-R. The glutathione-S-transferase (GST) activity increased significantly with Cd intoxication; however, treatment with antioxidants prior to Cd treatment decreased erythrocyte GST activity. The results show that Cd-induced LPO decreased the antioxidant capability of the erythrocytes, causing erythrocyte membrane damage.

Oral cadmium exposure of adults in Germany. 1: Cadmium content of foodstuffs and beverages

The cadmium contents of 94 and 105 foodstuffs bought in six-fold repetition in 1988 and in nine-fold repetition in 1991, respectively were analysed within the framework of a market-basket study. These foodstuffs were typical of German eating habits. Additionally, 170 samples of drinking water were investigated. The cadmium concentrations of the foodstuffs were comparable with results of recent studies carried out in Europe and North America. Fruit, milk and dairy products, sugar and sugar-rich foodstuffs as well as beverages showed mean cadmium contents < or = 5 ng/g fresh matter or ng/ml, respectively. The cadmium content of meat, sausage, fish and tinned fish was also low. Pork and beef, the most important kinds of meat, contained 5.4 and 2.5 ng/g on average. The majority of the vegetables investigated, including potatoes, had cadmium concentrations < 25 ng/g. However, individuals samples of lettuce showed very high cadmium levels. The cadmium content of bread, cakes and pastries as well as farinaceous products were within the range of 20-40 ng/g. The most important bread, cakes and pastries (wheat and rye bread, toasted bread, rolls) contained 25-35 ng/g. A median cadmium concentration of 0.2 micrograms/l was found in the drinking water. As expected, liver and kidneys showed the highest cadmium levels of 73 and 204 ng/g, respectively on average.

Cadmium-induced lipid peroxidation and the status of the antioxidant system in rat tissues

Cadmium may induce oxidative damage in different tissues by enhancing peroxidation of membrane lipids and altering the antioxidant system of the cells. The peroxidative damage to the cell membrane may cause injury to cellular components due to the interaction of metal ions with the cell organelles. The treatment with Cd (0.4 mg/kg body wt, ip) significantly increased lipid peroxidation (LPO) in heart within 3 h of the Cd injection, while the increase in kidney and liver followed 6 to 12 h after Cd intoxication. The antioxidant enzymes and other antioxidants provide protection to the cells against oxidative damage. The superoxide dismutase (SOD) activity increased in heart, kidney and liver within 24 h of Cd intoxication. The CAT activity increased significantly in heart 9 h after Cd injection; however, no significant change in CAT activity was observed in kidney and liver tissues. The GSH content and the activity of GR decreased in heart, kidney and liver 72 h after Cd administration, which has been suggested to be the cause for increased LPO in the tissues. The hexose monophosphate (HMP) shunt enzymes generate NADPH required for the activity of GR which may affect the GSH content in the tissues. The generalised decrease in glucose 6-phosphate dehydrogenase (G6PDH) and 6 phospho gluconate dehydrogenase (6PGDH) at 9 h followed by an increase in these enzymes in tissues 72 h after Cd intoxication suggest that the production of NADPH by the HMP shunt is required to reduce the oxidative damage. The results show that Cd induced LPO in the tissues and the condition was partially counteracted by the antioxidant system.

Role of rice and cereal products in dietary cadmium and lead intake among different socio-economic groups in south India

A study was conducted to evaluate the concentration of cadmium and lead in rice and cereal products commonly consumed in South India. Samples from retail outlets were purchased and analysed for cadmium and lead using graphite tube atomic absorption spectrophotometry. The results indicated varying concentrations of these metals in different rice and cereal products. The daily dietary intake of cadmium and lead varied among different socio-economic groups, based on occupation, and choice of consumption. The findings suggest that rice is the major source of cadmium and lead among the rural population and economically-deprived class. The source of intake of toxic metals appears to be more diverse in the case of the urban middle class and the economically privileged class of South India.

Lipid components of mustard seeds (Brassica juncea L.) as influenced by cadmium levels

In a pot experiment the soil application of different levels of Cd2+ (0, 10, 20, 30, 40 and 60 micrograms g-1 soil) affected the lipid components of mustard seeds (Brassica juncea L. Cv. RH-30) markedly. Total lipids declined with the Cd2+ levels regularly while phospho and glycolipids increased only at higher levels. Fatty acids profile of total, neutral and polar lipid fractions were affected considerably. Erucic acid in total and neutral lipids was observed to increase while it decreased in polar lipids with Cd2+ as compared to control. On the other hand palmitic, oleic and linoleic acids had reverse trend. Cadmium concentration increased consistently with increasing levels of Cd2+. Plant dry weight was also decreased significantly with Cd2+ levels.

Expression of mouse metallothionein-I gene confers cadmium resistance in transgenic tobacco plants

Transgenic tobacco plants containing a mouse metallothionein-I (MT-I) gene fused to the cauliflower mosaic virus 35S (CaMV 35S) promoter and nopaline synthase (nos) polyadenylation site were obtained by transforming tobacco leaf discs with an Agrobacterium tumefaciens strain carrying the chimaeric gene. Transformants were directly selected and rooted on medium containing cadmium and kanamycin. A total of 49 individual transgenic tobacco plants were regenerated. Among them 20% showed a very high expression level and their growth was unaffected by up to 200 microM cadmium, whereas the growth of control plants was severely affected leaf chlorosis occurred on medium containing only 10 microM cadmium. The concentration of microM cadmium. The concentration of MT-I in leaves of control and transgenic tobacco was determined with Cd/haemoglobin saturation assay, a polarographic method and western blotting. In addition, seeds from self-fertilized transgenic plants were germinated on medium containing toxic levels of cadmium and scored for tolerance/susceptibility to this heavy metal. The ratio of tolerant to susceptible plants was 3:1 indicating that the metallothionein gene is inherited as a single locus.

Accumulation of cadmium by channel catfish (Ictalurus punctatus): influx from environmental solutions

1. The accumulation of cadmium (Cd) from external environmental solutions was measured in channel catfish (Ictalurus punctatus) with the aid of 109Cd and by direct analysis of tissues. 2. Acute uptake (with 109Cd) was concentration dependent and was increased by changing the external pH from 7.3 to 5.0 and decreased by raising the Ca concentration from 0.1 mM to 3.0 mM. 3. The presence of external Zn did not change the uptake of the Cd. 4. In chronic 7-day experiments, fasted catfish were found to accumulate the toxic metal in their liver and kidneys from external media with Cd concentrations as low as 10(-9) M (about 0.1 microgram/l). 5. Concentrations were greater in the kidneys than the liver. 6. Detectable amounts of Cd (less than 0.03 microgram/g net wt) were not found in muscle in this time at external concentrations of Cd less than 10(-5) M (less than 1.0 mg/l).

Dietary intakes of some essential and non-essential trace elements, nitrate, nitrite and N-nitrosamines, by Dutch adults: estimated via a 24-hour duplicate portion study

Duplicate portions of 24-hour diets of 110 adults have been analyzed for aluminium, cadmium, copper, lead, manganese, mercury, zinc, nitrate, nitrite and volatile N-nitrosamines. The mean daily intake of copper (1.2 mg) is only about 50% of recommended values; mean daily intakes for manganese (3.3 mg) and zinc (8.4 mg) are adequate and marginal respectively with respect to recommended amounts. For the non-essential elements Al, Cd, Hg and Pb, mean daily intakes of 3.1 mg, 0.01 mg, 0.002 mg and 0.034 mg were found, respectively. For Cd this amounts to 17% of the acceptable daily amount, for Al, Hg and Pb 5%, 5% and 8%, respectively. Since 1976-1978 the dietary intake of lead has been reduced by a factor three; for the other six elements daily dietary intakes are almost the same as in 1976-1978. Average nitrate intake was 52 mg NO3-/day, about 25% of the ADI. Only 16 diets contained a measurable amount of nitrite. The highest daily intake (0.7 mg NO2-) is less than 10% of the ADI. Volatile N-nitrosamines were detectable in two duplicate diets (NDMA and NPIP). It is estimated that the daily dietary intake of volatile N-nitrosamines is around 0.1 microgram or less.

Lead and cadmium in urban allotment and garden soils and vegetables in the United Kingdom

In order to assess the intake of lead and cadmium by consumers of home grown vegetables in urban areas, replicated experimental plots of uniform size, comprising summer and winter crops, were established in 94 gardens and allotments in nine towns and cities in England.The geometric mean lead and cadmium concentrations for the soils (n = 94) were 217 μg g(-1) (ranging from 27 to 1,676 μg g(-1)) and 0.53 μg g(-1) (<0.2-5.9 μg g(-1)), respectively. Compared with agricultural soils, the garden and allotment soils contained elevated levels of lead but not cadmium.Lead concentrations in the vegetables ranged from <0.25 μg g(-1) to 16.7 μg g(-1) dry weight and cadmium concentrations ranged from <0.025 μg g(-1) to 10.4 μg g(-1) dry weight. Lead concentrations were higher than reported "background" levels, although <1% exceeded the statutory limit for saleable food in the UK (1 μg g(-1) fresh weight). Cadmium concentrations were generally similar to "background" levels.

A comparison of the effects of dietary cadmium on heart and kidney antioxidant enzymes: evidence for the greater vulnerability of the heart to cadmium toxicity

This study demonstrates the greater susceptibility of the heart as compared to the kidney to cadmium in the presence of high dietary selenium. Male weanling rats were fed an adequate-copper low-selenium feed supplemented with 0, 10 or 50 ppm copper with or without 50 ppm dietary cadmium for 7 weeks. All rats received 0.5 ppm selenium in their drinking water. Cadmium treatment resulted in histopathological lesions in the heart, but not in the kidney. Although cadmium treatment resulted in more extensive effects on glutathione peroxidase and superoxide dismutase in the heart as compared to the kidney, no increase in peroxidation was noted in either organ, suggesting that cadmium cardiotoxicity can be dissociated from tissue peroxidation. Mean cadmium concentrations in the heart ranged from 0.55 to 1.22 micrograms cadmium g-1 tissue, wet weight, and in the kidney from 11.53 to 21.04 micrograms cadmium g-1 tissue, wet weight. In both tissues examined, cadmium levels were influenced by dietary copper and heart cadmium concentrations did not correlate with either the biochemical or histological lesions observed. Thus, tissue cadmium levels alone may not be adequate for predicting cadmium toxicity.

Heavy metal tolerant transgenic Brassica napus L. and Nicotiana tabacum L. plants

A chimeric gene containing a cloned human metallothionein-II (MT-II) processed gene was introduced into Brassica napus and Nicotiana tabacum cells on a disarmed Ti-plasmid of Agrobacterium tumefaciens. Transformants expressed MT protein as a Mendelian trait and in a constitutive manner. Seeds from self-fertilized transgenic plants were germinated on media containing toxic levels of cadmium and scored for tolerance/ susceptibility to this heavy metal. The growth of root and shoot of transformed seedlings was unaffected by up to 100 μM CdCl2, whereas control seedlings showed severe inhibition of root and shoot growth and chlorosis of leaves. The results of these experiments indicate that agriculturally important plants such as B. napus can be genetically engineered for heavy metal tolerance/sequestration and eventually for partitioning of heavy metals in non-consumed plant tissues.

Cadmium-induced alterations in ocular trace elements. Influence of dietary selenium and copper

The present report demonstrates, for the first time, that feeding rats 50 ppm cadmium for just 7 wk results in detectable levels of cadmium in the eye of rats. Furthermore, these ocular cadmium concentrations affect significant alterations in the levels of the essential trace elements selenium, calcium, iron, and copper in the eye. Rats were fed a low-selenium (less than 0.02 ppm selenium), high-copper basal diet (50 ppm copper) supplemented with 0, 0.1, and 0.5 ppm selenium. The animals were either untreated or treated with 50 ppm cadmium admixed with their feed. Cadmium treatment resulted in significant reductions (up to 50%) in ocular selenium. Furthermore, rats fed the basal diet and given 100 ppm cadmium via their feed for 6 wk exhibited a 69% reduction in the activity of the selenoenzyme, glutathione peroxidase, in the eye. Cadmium treatment also resulted in reductions of up to 50% in ocular calcium, irrespective of dietary selenium supplementation. Iron levels were increased by 30% in rats fed the low-selenium diet and decreased by as much as 40% in rats fed the selenium-supplemented diets, compared to animals fed identical levels of selenium without cadmium. Ocular copper levels were significantly increased only in rats fed the low-selenium diet and treated with cadmium. Ocular zinc levels were not significantly affected by dietary cadmium or selenium.

New aspects on the distribution and metabolism of essential trace elements after dietary exposure to toxic metals

Under present environmental conditions, an increase in pollution owing to metals such as cadmium (Cd), lead (Pb), and methylmercury (MeHg) must be expected. The resulting effects would be seen particularly in the food chain. The daily intake of toxic metals in various parts of the world is different and depends on both the dietary habits and the concentration in foodstuffs. Oral ingestion of these toxic metals perturbs the metabolism of essential elements, especially zinc (Zn), copper (Cu), iron (Fe), and selenium (Se). The elemental composition of body tissues and fluids is an indicator of the nutritional and pathological status of humans. This review will describe the dietary intake and gut absorption of essential and toxic elements. Furthermore, it will discuss threshold values, toxic effects in relation to body burden of toxic metals, the biological indices of exposure, and the interaction between toxic and essential elements. The overall ratio of Cu, Zn, Fe, and Se concentration to Cd in the human kidney is the lowest in comparison to Hg and Pb. Increased kidney copper and urinary losses may be common denominators in the manifestation of renal toxicity induced by heavy metals. Factors affecting availability and loss of copper should be identified and measured. The critical kidney concentration for Cd, Pb, and MeHg should be revised in relation to essential elements.

Environmental exposure to cadmium and factors affecting trace-element metabolism and metal toxicity

In the general population, food constitutes the major environmental source of cadmium (Cd) in nonsmokers. It is established that leafy vegetables, roots, and grains (wheat or rice) can accumulate relatively high amounts of Cd from the soil. Beef liver and kidney and shellfish are also major dietary sources of Cd. The daily intake of Cd in various parts of the world is different and depends on both the dietary habits and concentration of Cd in foodstuffs. Because of the long biological half-life of Cd in humans and absence of any specific indicators of its toxicity, the environmental exposure of Cd should be monitored in various countries. Although environmental Cd poisoning is rare, there are isolated reports on excessive exposure to Cd in Japan and Shipham, a zinc-mining town in England. The body retention and toxicity of Cd depends on various factors, such as daily intake, the form of Cd in food, its interactions with essential elements, and nutritional status of the population. Since kidney is considered a critical organ in Cd toxicity, the indicators of renal dysfunction have been widely used for evaluation of Cd poisoning in occupationally exposed people. It is unclear whether similar indicators can be used for monitoring environmental Cd exposure.