Microg Cd Research Articles

Assessment of Metallothioneins in Tissues of the Clam Megapitaria squalida as Biomarkers for Environmental Cadmium Pollution From Areas Enriched in Phosphorite

The aim of this study was to evaluate the use of metallothionein (MT) concentrations in tissues of the clam Megapitaria squalida as biomarkers of environmental cadmium (Cd) pollution from phosphorite enrichments in the marine environment, which resulted from mining activities in La Paz Bay, Baja California Sur, Mexico. Cd and MT were quantified in gills, digestive gland, and kidney of clams exposed to 0.2 or 0.5 mg Cd l(-1) for 10, 20, or 30 days. In addition, clams from four strategically selected natural sites of La Paz Bay were collected for analysis. In tissues of bioassayed and untreated clams, the gradient of Cd concentrations was digestive gland>>gills>kidney, whereas that of MT was digestive gland>gills>kidney. Digestive gland of the clams exposed to 0.5 mg Cd l(-1) for 30 days showed the highest concentrations of Cd (16.3+/-3.9 microg Cd g(-1)). The highest statistically significant MT concentrations were found in digestive gland at 10 days of exposure to Cd. In the untreated clams, one of the highest Cd concentrations, but not MT levels, was found in digestive glands of the organisms collected from the area close to phosphorite mining activities. For environmental monitoring, MT levels in digestive gland can be used as a first approximation of the presence of high levels of divalent metals in the environment. However, in this study, MT levels did not correlate with high Cd levels in clams that had been collected from areas associated with phosphorite enrichment.

Mycorrhizal colonization and grain Cd concentration of field‐grown durum wheat in response to tillage, preceding crop and phosphorus fertilization

A 3-year field trial was conducted to investigate the effect of agricultural management practices including tillage, preceding crop and phosphate fertilization on root colonization by arbuscular mycorrhizal (AM) fungi and grain cadmium (Cd) concentration of durum wheat (Triticum turgidum L.). The relationship between grain Cd and soil and plant variables was explored to determine the primary factors affecting grain Cd concentration. Mycorrhizal colonization of the roots was reduced by conventional tillage or when the preceding crop was canola (Brassica napus L.), compared to minimum tillage or when the preceding crop was flax (Linum usitatissimum L.). In contrast, grain Cd was not consistently affected by any treatment. Grain Cd was generally below the maximum permissible concentration (MPC) of 100 microg Cd kg(-1) proposed by WHO. Grain Cd varied substantially from year to year, and could be predicted with 70% of variance accounted for by using the model: grain Cd concentration = - 321.9 + 44.5x ln(grain yield) + 0.26x soil DTPA-Cd + 182.5x soil electrical conductivity (EC)- 0.98x grain Zn concentration. These common agricultural management practices had no effect on grain Cd concentration in durum wheat though they impacted mycorrhizal colonization of roots. Grain yield and to a lesser extent soil conditions of EC and DTPA-Cd and grain Zn influenced grain Cd, whereas mycorrhizal colonization levels did not.

Effects of Cadmium on Protocerebral Neurosecretory Neurons and Fitness Components in Lymantria dispar L.

Changes in fitness components including larval stage duration, relative growth rate (RGR), and mass of the gypsy moth, Lymantria dispar L. (Lepidoptera: Lymantriidae), were investigated in caterpillars fed a synthetic diet with or without a cadmium supplement (10, 30, 100, 250 microg Cd/g dry food weight). Morphometric changes of large protocerebral dorsomedial A2 neurosecretor neurons, their nuclei and the electrophoresis profiles of brain proteins were analyzed in the 4 instar gypsy moths fed the examined diets. The duration of the fourth larval instars were prolonged and RGR and body mass reduced if the caterpillars were fed diets containing high concentrations of cadmium (100 and 250 microg). The size of large A2 dorsomedial neurosecretory neurons and their nuclei were significantly higher in larvae fed the diets supplemented with 10, 100 and 250 microg Cd. A large amount of neurosecretory material appeared in dorsomedial neurosecretory neurons in larvae fed diets with 100 and 250 microg Cd. Differences in larval brain protein profiles in the region of molecular mass ranges (Mr) of 98 kDa, 46 kDa and 3.4-6.1 kDa were identified in the experimental groups.

The influence of cadmium on life-history parameters and gut microflora of Archegozetes longisetosus (Acari: Oribatida) under laboratory conditions

We tested the effect of cadmium (25, 130 microg Cd g(-1)), administered via Chinese cabbage (Brassica chinensis L.) as food on life-history parameters and gut microflora of tritonymphs and adults of the oribatid mite, Archegozetes longisetosus Aoki. Both concentrations of Cd had an adverse effect on offspring mortality, and the higher concentration also reduced female fecundity, as well as the number of bacteria, fungi and actinomycetes, and it changed the community structure of bacteria; the proportion of gram-negative bacteria increased while that of gram-positive bacteria declined. Interestingly, at the lower Cd concentration microflora was more abundant and diverse than in the control group, especially in the tritonymphs, although the mean activity of gut microflora was reduced. The higher Cd concentration reduced microflora activity both in the tritonymphs and adults.

Determination of Sub-ppb Cadmium in Urine by Solid-Phase Extraction and Inductively Coupled Plasma–Mass Spectrometry

In order to determine low levels of Cd in urine samples, we tried to remove Mo interference using ICP-MS with a dynamic reaction-cell technique, but failed due to the low sensitivity and the variance with the standards. We then performed solid-phase extraction (SPE) before the ICP-MS measurement. A commercially available chelating resin, NOBIAS PA-1, was used for SPE, and could effectively remove Mo from urine samples, permitting the accurate determination of Cd by ICP-MS. This SPE-ICP-MS method gave 0.012 microg Cd L(-1) as the method limit of quantification, and the mean recovery of Cd spiked with 0.0505 and 5.05 microg L(-1) was 93.1 and 97.6%, respectively.

Linking Molecular and Population Stress Responses in Daphnia magna exposed to cadmium

DNA microarrays can be used to measure environmental stress responses. If they are to be predictive of environmental impact, we need to determine if altered gene expression translates into negative impacts on individuals and populations. A large cDNA microarray (14000 spots) was created to measure molecular stress responses to cadmium in Daphnia magna,the mostwidely used aquatic indicator species, and relate responses to population growth rate (pgr). We used the array to detect differences in the transcription of genes in juvenile D. magna (24 h old) after 24 h exposure to a control and three cadmium concentrations (6, 20, and 37 microg Cd2+ L(-1)). Stress responses at the population level were estimated following a further 8 days exposure. Pgr was approximately linear negative with increasing cadmium concentration over this range. The microarray profile of gene expression in response to acute cadmium exposure begins to provide an overview of the molecular responses of D. magna, especially in relation to growth and development. Of the responding genes, 29% were involved with metabolism including carbohydrate, fat and peptide metabolism, and energy production, 31% were involved with transcription/translation, while 40% of responding genes were associated with cellular processes like growth and moulting, ion transport, and general stress responses (which included oxidative stress). Our production and application of a large Daphnia magna microarray has shown that measured gene responses can be logically linked to the impact of a toxicant such as cadmium on somatic growth and development, and consequently pgr.

Elevated Cadmium Concentrations in Potato Tubers Due to Irrigation with River Water Contaminated by Mining in Potosí, Bolivia

Risk of cadmium (Cd) in the human food chain in Cd-contaminated areas is often limited by phytotoxicity from zinc (Zn) that is associated with the Cd contamination. A semiarid area, 60 km downstream of a tin mine in Bolivia, was surveyed where irrigation with Cd-contaminated river water (65-240 microg Cd L(-1)) has increased median soil Cd to 20 mg kg(-1) while median soil Zn was only about 260 mg kg(-1). Cadmium concentrations in potato tubers increased from background values (0.05 mg kg(-1) dry wt.) in soils irrigated with spring water to a median value of 1.2 mg kg(-1) dry wt. in the affected area. Median concentration of Cd in soil solutions was 27 microg L(-1) and exceeded the corresponding value of Zn almost twofold. Soil-extractable chloride ranged from 40 to 1600 mg Cl(-) kg(-1) and was positively correlated with soil total Cd. Increasing soil solution Cl(-) decreased the solid-liquid distribution coefficient of Cd in soil. Soil total Cd explained 64% of the variation of tuber Cd concentration while only 3% of the variation was explained by soil extractable Cl(-) (n = 49). The estimated dietary Cd intake from potato consumption by the local population is about 100 microg d(-1) which exceeds the WHO recommended total daily intake. It is concluded that the food chain risk of Cd in the irrigation water of the semiarid area is aggravated by the association with Cl(-) and, potentially, by the relatively large Cd/Zn ratio.

Common Pattern of Gene Expression in Response to Hypoxia or Cadmium in the Gills of the European Glass Eel (Anguilla anguilla)

European eel (Anguilla anguilla) populations are in decline. Glass eel recruitment has fallen 10-fold since the early 1980s. Estuaries play a fundamental role in the life history of eels because glass eels must pass through them to reach freshwater ecosystems. Unfortunately, because of their geographical position at the upstream basin slopes, estuaries accumulate metals like cadmium and are important sites of hypoxia events. In this context, we studied the effect of the oxygen level on the ventilation of the glass eel. In parallel, glass eels were submitted to different dissolved cadmium concentrations (0, 2, and 10 microg L(-1)) under two oxygen levels (normoxia PO2 = 21 kPa and Hypoxia PO2 = 6 kPa). The expression level of various genes involved in the mitochondrial respiratory chain, in the cellular response to metal and oxidative stresses, was investigated. Our results showed that hypoxia enhances (1) ventilation of the postlarval stage and (2) Cd accumulation in gills only at the lowest metal water concentration tested (2 microg Cd L(-1)). At the gene level, Cd exposure mimics the effect of hypoxia since we observed a decrease in expression of genes involved in the respiratory chain and in the defense against oxidative stress.

Comparative Effects of Direct Cadmium Contamination on Gene Expression in Gills, Liver, Skeletal Muscles and Brain of the Zebrafish (Danio rerio)

The effects of cadmium (Cd) on gene expression were examined in four organs (gills, liver, skeletal muscles and brain) of the zebrafish. Adult male fish were subjected to three different water contamination pressures over periods of 7 and 21 days: control medium (C(0): no Cd added) and two contaminated media (C(1): 1.9 +/- 0.6 microg Cd l(-1), and C(2): 9.6 +/- 2.9 microg Cd l(-1)). Fourteen genes involved in antioxidant defences, metal chelation, active efflux of organic compounds, mitochondrial metabolism, DNA repair and apoptosis were selected and their expression levels investigated by quantitative real-time PCR. Cadmium concentrations were determined in the four organs and metallothionein (MT) protein levels investigated in brain, liver and gills. Although skeletal muscle was a poor Cd-accumulating tissue, many genes were up-regulated at day 7: mt1, cyt, bax, gadd and rad51 genes. Three additional genes, c-jun, pyc and tap, were up-regulated in muscles at day 21 whereas bax, gadd and rad51 had returned to basal levels. Surprisingly, mt1 and c-jun were the only genes displaying a differential induction after 21 days in liver, although this organ accumulated the highest cadmium concentration. In brain, only mt1, mt2 and c-jun genes were up-regulated after 21 days. In gills, the highest response was observed after 7 days, featuring the differential expression of oxidative stress-response hsp70 and mitochondrial sod genes, along with genes involved in mitochondrial metabolism and metal detoxification. Then, after 21 days, the expression of almost every genes returned to basal levels while both mt1 and mt2 genes were up-regulated.

Valve movement response of the mussel Mytilus galloprovincialis to metals (Cu, Hg, Cd and Zn) and phosphate industry effluents from Moroccan Atlantic coast

Valve activity was measured in the Mediterranean mussel Mytilus galloprovincialis in response to sublethal concentrations of four metals (Hg, Cu, Zn and Cd) and two phosphate industry effluents from the Atlantic coast of Morocco. Valve movements were monitored using a proximity inductive sensor which could display all activity figures from full closure to wide opening of the shell valves. In a 1 h exposure experiments, all metals induced a decrease in the time of normal opening and the appearance of sequences of stress behaviour, including enhanced valve adductions and complete closure at high concentrations. Mercury (tested from 5 to 75 microg Hg l(-1)) was the most toxic to the valve activity, with a threshold effective concentration at 10 microg Hg l(-1) and full valve closure occurring at 50 microg Hg l(-1). Copper (15-150 microg Cu l(-1)) showed a toxic effect starting at threshold concentration of 20 microg Cu l(-1) and induced full valve closure at 150 microg Cu l(-1). Zinc (100-500 microg Zn l(-1)) was effective in reducing the time of normal opening (threshold concentration at 100 microg Zn I(-1)) but no complete closure was recorded in any of the tested concentrations. For cadmium (1000-5000 microg Cd l(-1)), the valve activity was insensitive for exposures under 2000 microg Cd l(-1). Results for the testing of several samplings of the phosphate industry effluents (Safi and Jorf Lasfar) showed that their toxicity varied over the time. The effluent of the Jorf Lasfar plant (2-9.4%) was, however, more toxic than that of Safi (1-25%). In the light of these results, the sensitivity of the valve activity of Mytilus galloprovincialis to pollutants and its usefulness for in situ monitoring of coastal pollution in Morocco are discussed.

Brevibacillus brevis Isolated from Cadmium- or Zinc-Contaminated Soils Improves in Vitro Spore Germination and Growth of Glomus mosseae under High Cd or Zn Concentrations

In this study we investigated the saprophyte growth of two arbuscular-mycorrhizal fungi (Glomus mosseae isolate) under increasing Cd or Zn levels and the influence of a selected bacterial strain of Brevibacillus brevis. Microorganisms here assayed were isolated from Cd or Zn polluted soils. B. brevis increased the presymbiotic growth (germination rate growth and mycelial development) of Glomus mosseae. Spore germination and mycelial development of both G. mosseae isolate were reduced as much as the amount of Cd or Zn increased in the growth medium. In medium supplemented with 20 microg Cd mL(-1), the spore germination was only 12% after 20 days of incubation, but the coinoculation with B. brevis increased this value to 40% after only 15 days. The addition of 20 microg Cd mL(-1) to the growth medium drastically inhibited hyphal development, but the presence of the bacterium increased hyphal growth of G. mosseae from 195% (without Cd) until 254% (with 20 microg Cd mL(-1)). The corresponding bacterial effect increasing micelial growth ranged from 125% (without Zn) to 232% (200 microg Zn mL(-1)) in the case of G. mosseae isolated from Zn-polluted soil. Mycelial growth under 5 microg Cd mL(-1) (without bacterium) was similarly reduced from that produced at 15 microg Cd mL(-1) in the presence of the bacteria. As well, 50 microg Zn mL(-1) (without bacterium) reduced hyphal growth as much as 200 microg Zn mL(-1) did in the presence of B. brevis. The bacterial effect on the saprophytic growth of G. mosseae in absence of metal may be due to the involvement of indole acetic acid (IAA) produced by these bacteria. The Cd bioaccumulation ability exhibited (76%) by Cd-adapted B. brevis reduced the Cd damage on G. mosseae in Cd-contaminated medium. These capabilities of B. brevis isolates partially alleviate the inhibitory effects of Cd or Zn on the axenic growth of G. mosseae.

Cadmium in Food Production Systems: A Health Risk for Sensitive Population Groups

This paper gives an overview of the cadmium (Cd) situation in agricultural systems and human exposure in Sweden. Cadmium levels in agricultural soils (the plow layer) increase by 0.03% to 0.05% per year. Feed can give substantial contributions of Cd to local agricultural systems. Effects on human kidney function are indicated by some measurements already at today's exposure levels. If food products reach the maximum permissible levels given by the European Union, 10% to 25% of the Swedish population will be exposed to Cd levels above the provisional tolerable weekly intake (PTWI 7 microg Cd kg(-1) body weight). Sensitive groups in the population are individuals with low iron status (mainly women) and kidney disorders. Recent studies indicate that Cd plays a role in osteoporosis and that further research is needed to clarify if Cd is neurotoxic in early developmental stages. Firm actions have to be taken in order to stop a further increase of Cd in agricultural soils. Suggestions for prevention and measures are given in this paper.

Cadmium disrupts behavioural and physiological responses to alarm substance in juvenile rainbow trout (Oncorhynchus mykiss).

Alarm substance is a chemical signal released from fish skin epithelial cells after a predator causes skin damage. When other prey fish detect alarm substance by olfaction, they perform stereotypical predator-avoidance behaviours to decrease predation risk. The objective of this study was to explore the effect of sublethal cadmium (Cd) exposure on the behavioural and physiological responses of juvenile rainbow trout (Oncorhynchus mykiss) to alarm substance. Waterborne exposure to 2 microg Cd l(-1) for 7 days eliminated normal antipredator behaviours exhibited in response to alarm substance, whereas exposures of shorter duration or lower concentration had no effect on normal behaviour. Furthermore, dietary exposure to 3 microg Cd g(-1) in the food for 7 days, which produced the same whole-body Cd accumulation as waterborne exposure to 2 microg l(-1), did not alter normal behaviour, indicating that an effect specific to waterborne exposure alone (i.e. Cd accumulation in the olfactory system) results in behavioural alteration. Whole-body phosphor screen autoradiography of fish exposed to (109)Cd demonstrated that Cd deposition in the olfactory system (rosette, nerve and bulb) during waterborne exposure was greater than in all other organs of accumulation except the gill. However, Cd could not be detected in the brain. A short-term elevation in plasma cortisol occurred in response to alarm substance under control conditions. Cd exposures of 2 microg l(-1) waterborne and 3 microg g(-1) dietary for 7 days both inhibited this plasma cortisol elevation but did not alter baseline cortisol levels. Our results suggest that exposure to waterborne Cd at environmentally realistic levels (2 microg l(-1)) can disrupt the normal behavioural and physiological responses of fish to alarm substance and can thereby alter predator-avoidance strategies, with potential impacts on aquatic fish communities.

Impacts of Cd and Zn on the development of periphytic diatom communities in artificial streams located along a river pollution gradient.

Many field and experimental studies have been conducted to reveal modifications of periphytic diatom communities under metal pollution, but most of the approaches presented drawbacks: variability of environmental factors for field studies and lack of representativity for experimental ones. An original approach that allows growth of periphytic communities under conditions more controlled than in the field and more realistic than experimental investigations was developed to try conclusions being drawn on the real impact of metallic pollution. Artificial streams were placed on the river bank at three sites along the pollution gradient (Cd/Zn) of the River Lot (SW France): reference (upstream pollution discharge), slightly polluted (around 1.5 microg Cd x L(-1) and 50 microg Zn x L(-1)), and polluted (around 6 microg Cd x L(-1) and 400 microg Zn x L(-1)) sites. Structural characteristics of diatom communities growing in these artificial streams, on glass substrates, and under homogenized current velocity and water depth were compared after four durations (1, 2, 3, and 4 weeks) to study effects of metal on first steps of community development. Marked perturbations of diatom community development were observed overall in the polluted site: after 1 week, early biofilms differed already by taxonomic composition; after 4 weeks, cell density was significantly lower than in the reference site and taxonomic composition was very different. These results, generated by a methodology intermediate between field and experimental approaches, compare well with literature findings based on more traditional approaches, strongly attesting that metallic pollution affects diatom community architecture and induce rising of abnormal cells.

Laboratory simulation of a mining accident: acute toxicity, hsc/hsp70 response, and recovery from stress in Gammarus fossarum (Crustacea, Amphipoda) exposed to a pulse of cadmium.

The rate of survival and stress protein (hsc/hsp70) response were investigated in the freshwater amphipod, Gammarus fossarum Koch, 1835, during a 20-day stress and recovery experiment. Adult females and males, were separately exposed to 9 different cadmium concentrations for 5 days to simulate a short-term pulse of xenobiotics in an aquatic environment, followed by a recovery period of 15 days. In terms of mortality, females were much more sensitive to cadmium than males; 4.28 +/- 2.45 microg Cd2+/l resulted in strong effects on the rate of survival of females but not males. In both sexes, mortality occurred predominantly within the first 5 days of the recovery period. At the cellular level, cadmium induced an hsc/hsp70 response. The lower Cd2+ concentrations we used led to an induction of stress proteins while higher Cd2+ concentrations resulted in a proportionately reduced hsc/hsp70 response, most likely due to pathological damage. Surviving individuals retained their capacity to induce stress protein production in the recovery period, even if the stress protein response system was overwhelmed by cadmium during the exposure period.

Regional monitoring of lead and cadmium contamination in a tropical grazing land site, Thailand.

An investigation was carried out to monitor Pb and Cd contamination in grazing land located near a highway. Environmental media at different distances from highway (soil, grass, water, cow's forage, fertilizer, manure and milk samples) were collected from three sampling locations. Soil and grass were characterized by high metal mobility (soil with Pb: 5.25 +/- 0.71-14.59 +/- 1.17 mg kg(-1), dry mass and Cd: 0.038-0.33 +/- 0.04 mg kg(-1), dry mass and grass with Pb: 0.76 +/- 0.05-6.62 +/- 0.18 mg kg(-1), dry mass and Cd: 0.17+/- 0.01-0.73 +/- 0.09 mg kg(-1), dry mass). One-way analysis of variane (ANOVA) was applied to find out the correlation between metal (total and bioavailable) concentrations in the soil and the distance from roadside. In most cases, the finding showed that plants growing nearer to the highway are usually exposed to more heavy metal accumulations than those away from the highway. In addition, a correlation was established between plant available metal concentrations and plant metal uptake concentrations. Analysis of fertilizer and manure showed considerable amount of metals (fertilizer with Pb: 1.53 +/- 0.06 mg kg(-1) and Cd: 0.038 mg kg(-1) and manure with Pb: 2.55-3.34 mg kg(-1) and Cd: 0.14-0.31 mg kg(-1)). Long-.term simultaneous application of fertilizer and manure on the commercial farm showed higher metal accumulation in the soil and plants than those of co-operative farm. Considerable concentrations of metals (Pb: 1.60-2.94 mg kg(-1) and Cd: 0.025-0.19 mg kg(-1)) were observed in fodder. The finding clearly demonstrated that there are seasonal variation in total daily metal intake by individual cow (Pb: 109.37 mg day(-1) (dry), 273.47 mg day(-1) (rainy) and Cd: 2.02 mg day(-1) (dry), 19.62 mg day(-1) (rainy)). The provisional tolerable weekly intake of heavy metals in cows is 390 microg Pb and 28 microg Cd per kg body weight in the rainy season and 156 microg Pb and 2 microg Cd per kg body weight in the dry season. The levels of metals (Pb: 0.014 mg L(-1) and Cd: not detectable) and bio-transfer factor (10(-5)-10(-4)) in raw milk were found to be well below the Codex Alimentarius Commissions Draft (1997). Our analysis revealed that improvements on farm management give significant reduction in elevated levels of Pb and Cd in soil and plants, and however leads to minimize the amount of Pb and Cd in consumed milk.

Assessing changes in Cd phytoavailability to tomato in amended calcareous soils.

A plot study was conducted to assess changes in Cd phytoavailability to a tomato cultivar in an agricultural soil in Southeastern Spain amended in two different ways (A and B), under controlled conditions. The experimental soil corresponded to a fine-loamy carbonatic thermic Calcidic Haploxeroll (Soil Survey Staff, Keys to Soil Taxonomy, eighth ed., USDA, Washington, 1998). (A) Soil was amended with a single application of sewage sludge from a municipal source that had a total Cd concentration of 0.5 mg kg(-1) at a rate that represented a final average concentration in the mixture of soil and sludge of less than 50 microg Cd kg(-1). (B) The amendment consisted of the addition of a mineral fertiliser with the same amount of NPK as in the sewage sludge application. The final levels of Cd were supposed to be negligible. A plot series without amendments was also performed (C). DTPA plus triethanolamine, and ammonium acetate extractable fractions in soils were analysed for all the plots. The time-dependent Cd accumulation in different parts of the tomato plants was studied by means of a Cd salt treatment. For each block (A-C) four levels of Cd (0, 3, 30, and 100 mg kg(-1)) were added as CdCl2. There was a significant increase in plant Cd after the initial cropping. Tomato stems, leaves and fruits were analysed separately for Cd determination. Differential Cd distribution and accumulation in tomato parts was detected.