Medium composition affects the degree and pattern of cadmium inhibition of naphthalene biodegradation

Metals have been reported to inhibit organic pollutant biodegradation; however, widely varying degrees and patterns of inhibition have been reported. To investigate the roles of medium composition and metal bioavailability on these different degrees and patterns of inhibition, we assessed the impact of cadmium on naphthalene biodegradation by a newly isolated strain of Comamonas testosteroni in three chemically-defined minimal salts media (MSM): Tris-buffered MSM, PIPES-buffered MSM, and Bushnell-Haas medium. Cadmium (total concentrations of 100 and 500 microM) inhibited biodegradation in each medium. Degrees of inhibition were different in each medium. Cadmium was most inhibitory in PIPES-buffered MSM and least inhibitory in Bushnell-Haas. For example, in Bushnell-Haas medium, 100 microM cadmium reduced the cell yield more than 4-fold compared to controls not containing cadmium. The same concentration of cadmium completely inhibited growth in PIPES-buffered MSM. No difference in inhibition was observed in any medium when cadmium was added 24 h before inoculation rather than when added within one minute of inoculation. Two patterns of inhibition were observed. Inhibition occurred in a dose dependent pattern in Tris- and PIPES-buffered MSM and in a non-dose dependent pattern in Bushnell-Haas. Specifically, in Bushnell-Haas, 100 microM total cadmium extended the lag phase by 23+/-8.66 h, whereas 500 microM did not extend the lag phase. Soluble, ionic cadmium (Cd2+) concentrations were measured and modeled in each medium to assess cadmium bioavailability. In media containing 500 microM total cadmium, bioavailability was highest in Tris- and PIPES-buffered MSM and lowest in Bushnell-Haas. In Bushnell-Haas, cadmium bioavailability was initially higher in the 500 microM treatments (196+/-21.2 microM) than in the 100 microM treatments (78.2+/-2.04 microM); however, after 12 h, bioavailability was higher in the 100 microM treatments (56.4+/-24.8 micro) than the 500 microM treatments (13.3+/-1.2 microM). These data suggest that the type of medium determines the degrees and patterns by which metals inhibit biodegradation and emphasize the importance of coupling metal toxicity and bioavailability data.     

硫化钠对土壤中铅镉的固定效果简

研究了硫化钠用于固定土壤中铅镉的可行性，考察了硫化钠用量及土壤pH、有机质对固定过程中土壤铅、镉赋存形态及固定效果的影响。结果表明，添加硫化钠可改变土壤中铅镉的形态分布，明显降低可交换态铅镉的含量。条件适当时，铅镉可交换态下降值分别为63%和73%。硫化钠在固定铅的过程中，固定效率对土壤pH、有机质含量的变化较为敏感，在有机质含量较低或酸性土壤中，硫化钠对铅固定效率较高；相对于铅，有机质含量和pH变化对镉的固定效率影响不是很大。     

Influences of macroalga-derived dissolved organic carbon on the aquatic toxicity of copper and cadmium

In this study, the effect of dissolved organic carbon (DOC) derived from macroalga (Sargassum) on the acute toxicity of copper (Cu) and cadmium (Cd) to a freshwater cladoceran (Daphnia magna) was investigated. Potassium-loaded macroalga was incubated with ultrapure water to extract macroalgal DOC, which was then spiked with the constituents of the Elendt M7 hard water media. The 48 h median lethal concentration of Cu increased linearly with DOC levels but that of Cd was relatively independent of DOC levels (0-44 mg l(-1)). The independence of Cd toxicity on DOC level might be due to the competitive effect of high calcium concentrations in the media with Cd for the binding sites of DOC. The decreased Cu toxicity was a result of reduced Cu uptake as evidenced in a separate accumulation test. Also, the capability of the macroalgal DOC on reducing Cu toxicity was found to be comparable to DOC tested in other studies. Therefore, the present study suggested that the biosorption treatment process using macroalgae should consider the effect of DOC release from the biomass as a step of modifying the metal toxicity as well as influencing metal biosorption capacity.     

Effect of cadmium on ATPase activities in rats fed on iron-deficient and sufficient diets

Male Sprague-Dawley rats were fed on different levels of cadmium mixed with purified diets containing iron or no iron for 8 weeks. The body weight gain, tissue weights, hemoglobin, hematocrit, liver and brain ATPase were measured at 2, 4 and 8 weeks after feeding. The hemoglobin and hematocrit values were the same in all rats fed on cadmium. The rats fed on iron-deficient diets mixed with cadmium showed a significant decrease in body weight gain. However, the rats receiving only the 100 ppm of cadmium in iron-sufficient diet showed a significant decrease in body weight gain. There were no significant changes in the weights of thymus, spleen, kidney, heart, brain and testes. However, the liver weights were decreased in the highest treatment of cadmium but the liver weight/body ratios were uneffected. Na+-K+ activated ATPase activity in brains of rats fed on cadmium were significantly decreased at 2, 4 and 8 weeks of treatment. The decrease was more pronounced in rats fed on iron-deficient diets. Oligomycin-sensitive (Mitochondrial) Mg2+ ATPase activity was also significantly decreased in liver and brain tissues of rats fed on cadmium. Oligomycin-insensitive Mg2+ ATPase activity, however, was not altered in any tissues tested. It appears that cadmium may be interfering with energy (ATP) production and utilization processes in rat brain and liver tissues.     

Multi-generation cadmium acclimation and tolerance in Daphnia magna Straus

The cladoceran Daphnia magna was acclimated for seven generations to cadmium concentrations ranging from 0 (control) to 250 microg/l Cd (corresponding to a free ion activity of 4.60 nM Cd2+). Acute and chronic cadmium tolerance as well as cadmium accumulation were monitored as a function of acclimation time. After two to three generations of acclimation to concentrations ranging from 0.23 to 1.11 nM Cd2+ increases in acute tolerance were maximal (factor 7.2) and significant. Acclimation for seven generations to the same acclimation concentrations did result in an increased chronic cadmium tolerance (21 days EC50 values increased). Organisms acclimated to 1.93 nM Cd2+ were equally or more sensitive than non-acclimated daphnids in acute and chronic toxicity tests. Cadmium contents in D. magna increased significantly as a function of the acclimation concentration. Maximum body burdens of 236+/-30 microg Cd/g dry weight were measured in organisms exposed to 4.60 nM Cd2+, but detoxification mechanisms were only successful up to 82+/-20 microg Cd/g dry weight as this concentration did not cause major decreases in survival and reproduction in chronic toxicity tests. As the potential positive effect of acclimation on cadmium tolerance disappeared with successive acclimation generations and increasing acclimation concentrations, it is concluded that multi-generation acclimation studies are important for the evaluation of the long-term effects of environmental toxicants.     

Modelling the absorption and desorption of cadmium on paper pulp using kinetic approaches

The presence of toxic metals on paper pulp and the migration of these metals to food from the food package is receiving significant attention. The final exposure levels for consumers depend on two main processes. First the potential of metals to bind paper pulp during manufacture. Second, the metal potential to migrate from paper to food during storage and use. Binding and unbinding processes are modelled for cadmium kinetics through kinetic approaches. The cadmium concentration in paper pulp is estimated from the cadmium concentration in the water-pulp liquor during manufacture, the temperature, and contact time. Two food simulants have been employed for desorption studies, water and acetic solution (3%, w/w). As expected, under acidic conditions desorption is total and rapid (close to 100% desorption reached in a few minutes). However, the desorption of cadmium into the neutral food simulant depends on the initial cadmium concentration in the paper pulp, temperature and contact time. Surface response curves for each combination are presented. Temperature did not affect cadmium binding, but played a significant role for the desorption processes into the neutral food simulant. The proposed equations offer a good fitting of the experimental values, with p < 0.001 and residuals within a factor of 3 for over 99% of the measured data. These models allow estimations of the expected exposure levels in consumers, on the basis of manufacture and use conditions. Linking the expected exposure with toxicity thresholds, such as the admissible daily intake (ADI), would allow a scientific assessment of the maximum acceptable cadmium levels in water-pulp liquors during manufacture and in the final paper pulp on the basic of the use patterns of each food packaging material.     

The influence of humic acids on the phytoextraction of cadmium from soil

Cadmium poses a major environmental and human health threat because of its constant release through anthropogenic activities. A need, therefore, exists for cost-effective remediation procedures. Phytoremediation, the use of plants to extract contaminants from soils and groundwater, has revealed great potential. However, it is limited by the fact that plants need time, nutrient supply and, moreover, have a limited metal uptake capacity. Synthetic chelators have shown positive effects in enhancing heavy metal extraction through phytoremediation, but they have also revealed a vast number of negative side-effects. The objective of this research was to investigate the use of humic acids as an alternative to synthetic chelators. Humic acids were applied to a cadmium-contaminated soil at various dosages, and the uptake of cadmium into Nicotiana tabacum SR-1 was determined in relation to the amounts of total and bioavailable cadmium in the soil. It was found that the theoretical bioavailability of cadmium, as determined by diethylenetriaminepentaacetic acid (DTPA) extraction, did not change, but its plant uptake was enhanced significantly, in some cases up to 65%. Humic acids added at a rate of 2 g kg(-1) soil increased the cadmium concentration in the shoots from 30.9 to 39.9 mg kg(-1). A possible reason for this enhancement is the decrease in pH, resulting in higher cadmium availability. Another possibility taken into account is that plants may take up cadmium complexes with humic acid fragments, which result from microbiological degradation or, self-dissociation.     

Effects of pH on the toxicity of cadmium, copper, lead and zinc to Folsomia candida Willem, 1902 (Collembola) in a standard laboratory test system

EC₅₀s for cadmium, copper, lead and zinc were determined for juvenile production of Folsomia candida at pH6.0, 5.0 and 4.5 in a standard laboratory test system. In contrast to most previous studies where metal toxicity was increased at low pHs, in our experiments there was no clear relationship between soil acidity and EC_{50-reproduction} in this species. The EC_{50-reproduction} values (μg g⁻¹) for cadmium and zinc were similar at all three pHs (pH6.0: Cd 590, Zn 900; pH5.0: Cd 780, Zn 600; pH4.5: Cd 480, Zn 590). In contaminated field sites adjacent to primary zinc smelters, zinc is invariably present in soils at concentrations of at least 50 times that of cadmium Thus deleterious effects of mixtures of these metals on populations of Collembola in such sites can be attributed to zinc rather than cadmium.     

Effet du cadmium sur la toxicite du mercure vis-a-vis de la moule Mytilus edulis (L.)

Mussels have been simultaneously or successively exposed to cadmium and mercury. The presence of cadmium before or during the exposure to mercury led to a decrease of mercury toxicity. When compared with a single metal exposure the association of the two metals had no significant effect on the mercury accumulation, but induced a decrease of the cadmium accumulation by the organisms.     

The impact of inorganic tin on the planktonic cyanobacterium Synechocystis aquatilis: the effect of pH and humic acid

The influence of inorganic tin compounds on the unicellular cyanobacterium Synechocystis aquatilis was studied, and its dependence on changing pH of the surrounding medium and the presence of humic acid. Both Sn(II) and Sn(IV), used as chlorides (at the concentrations 1-10 mg litre(-1)), inhibit the growth and chlorophyll a content of the cyanobacterium cultures, but only under alkaline conditions. Generally, the observed tin toxicity increased with increase of metal concentration, time of exposure and pH value of the medium (in the range 7-9.8). Sn(II) seems to be more toxic than Sn(IV). At the lowest studied metal concentration (1 mg litre(-1)), Sn(II) caused a 36 and 40% decrease in growth and chl a content, respectively, after 96 h exposure at pH 9.8, while Sn(IV) caused even a slight increase of both physiological parameters (hormetic effect). Similar increases in growth and chl a content were also observed at a high Sn (II) and Sn(IV) concentration (10 mg litre(-1)), but only in cultures exposed to metal at pH 7. At high pH (9.8), 10 mg litre(-1) of Sn(II) and Sn(IV) significantly suppressed both the growth of the cyanobacterium (by 54.2 and 26.1%, respectively) and the chl a content in cultures (by 58.2 and 24%, respectively). Humic acid reduced the toxicity of tin towards the cyanobacterium. The observed effects of pH and complexing ligand on the inorganic tin toxicity are discussed in the context of changing, chemical metal speciation and bioavailability.     

Impact of cadmium and nickel on ion homeostasis in the yeast Schizosaccharomyces pombe

Abstract

Toxicity of heavy metals to living organisms is a worldwide research topic. Although, much has been discovered about cadmium and nickel impact on biological systems, a lot still remains unclear. We used inductively coupled plasma – optical emission spectroscopy to address the question of the effect of two different heavy metals nickel, and cadmium on intracellular ion balance. Increase or decrease of the content of several essential cations including Ca²⁺, Na⁺, K⁺, Mg²⁺, Cu²⁺, Fe³⁺ in the yeast Schizosaccharomyces pombe was determined. Our results revealed that the cell exposure to high nickel and cadmium concentrations led to significant elevation of Ca²⁺, Na⁺, Mg²⁺, Cu²⁺, Fe³⁺ levels in the yeast cell, while the content of K⁺ decreased. Correlation analyses showing in the presence of nickel and cadmium strong positive correlation among each tested element (Ca²⁺, Na⁺, Cu²⁺, Mg²⁺ and Fe³⁺) except for K⁺, demonstrate the significant impact of heavy metal treatment to ion homeostasis of the cell. Our data indicate that acute nickel and cadmium contamination leads to substantial ionome misbalance in yeast.     

Metabolic rate and uptake and loss of cadmium from food by the fish Noemacheilus barbatulus L. (stone loach)

Fish, Noemacheilus barbatulus (stone loach), of different body weights were used to study rates of uptake and loss of cadmium during and after dietary exposure. Fish were kept singly in a continuous-flow system, and fed tubificid worms. The worms had a range of cadmium levels, but all levels were below that needed to cause acute lethal toxicity in the fish. Body weight affected both the maintenance ration and the amount of food consumed ad libitum, but the exponent for body weight (0.78+/-0.04), relating body weight to food consumption, was unaffected by either temperature or the size of feeding ration. The cadmium content of the worms did not affect the size of the maintenance ration. Metal burden in fish changed rapidly both during and after exposure. After exposure, the cadmium burden of starved fish usually declined more rapidly than in fed fish. A 58-fold increase in cadmium content in the food produced a 28% increase of body burden in the fish, and there was no evidence for biomagnification. Maintenance ration and ration ad libitum and rates of uptake and loss of cadmium increased with temperature within the range 8-18 degrees C, but exposure to cadmium at 16 degrees C yielded a higher asymptotic body burden than either 8 degrees C or 18 degrees C. Rate constants for loss of cadmium after exposure appear to be lower than for loss during exposure. Rates of uptake and loss of cadmium vary with metabolic rate. A maximum in the rate of oxygen consumption was measured at 16 degrees C, above which the rate dropped, presumably due to stress. The exponent for body weight was unaffected by activity or temperature. Body weight of fish appeared to affect both the rates of uptake and loss of cadmium, and feeding rations and respiration to the same extent: body weight exponents were not dissimilar.     

Effect of anions and cations on cadmium sorption kinetics from aqueous solutions by chitin: experimental studies and modeling

The effect of ions, including Na(+), Mg(2+), Ca(2+), Cl(-), SO(4)(2-) and CO(3)(2-), at various initial concentrations, on the kinetics of cadmium sorption by chitin was studied at 25 degrees C and free initial pH solution in batch conditions. The presence of these ions in solution was found to inhibit the uptake of cadmium by chitin to different degrees: sodium and chloride ions have no significant effect. For Mg(2+), Ca(2+), SO(4)(2-) and CO(3)(2-) ions, the effects ranged from a large inhibition of cadmium by Ca(2+) and CO(3)(2-) to a weak inhibition by Mg(2+) and SO(4)(2-). These results indicate that the uptake sites of these ions are the same. No ion was found to enhance cadmium uptake. The results also showed that the kinetics of sorption are best described by a pseudo second-order expression than a first or second-order model.     

Effects of lead and cadmium exposure from electronic waste on child physical growth

Many studies indicate that lead (Pb) and cadmium (Cd) exposure may alter bone development through both direct and indirect mechanisms, increasing the risk of osteoporosis later in life. The aim of this study was to investigate the association between Pb and Cd exposure, physical growth, and bone and calcium metabolism in children of an electronic waste (e-waste) processing area. We recruited 246 children (3–8 years) in a kindergarten located in Guiyu, China. Blood lead levels (BLLs) and blood cadmium levels (BCLs) of recruited children were measured as biomarkers for exposure. Serum calcium, osteocalcin, bone alkaline phosphatase, and urinary deoxypyridinoline were used as biomarkers for bone and calcium metabolism. Physical indexes such as height, weight, and head and chest circumference were also measured. The mean values of BLLs and BCLs obtained were 7.30 μg/dL and 0.69 μg/L, respectively. The average of BCLs increased with age. In multiple linear regression analysis, BLLs were negatively correlated with both height and weight, and positively correlated with bone resorption biomarkers. Neither bone nor calcium metabolic biomarkers showed significant correlation with cadmium. Childhood lead exposure affected both physical development and increased bone resorption of children in Guiyu. Primitive e-waste recycling may threaten the health of children with elevated BLL which may eventually cause adult osteoporosis.     

Assessment of a sewage sludge treatment on cadmium, copper and zinc bioavailability in barley, ryegrass and earthworms

The toxicity and bioavailability of metals were assessed to verify the efficiency of a new chemical leaching process (METIX-AC) to minimize the risk of metals found in municipal sewage sludge. For this purpose, sludge samples were spiked with cadmium, copper and/or zinc before being treated using METIX-AC. The sludge decontamination resulted in a removal of spiked metals (79-89%), in a decrease of the more labile fractions, and in a corresponding increase of the residual fraction. The toxicity observed after exposure of two plant species, barley (Hordeum vulgare) and ryegrass (Lolium perenne), and a terrestrial invertebrate, Eisenia andrei, to sludge-soil mixtures, disappeared after treatment, although the adverse effects were minor before treatment. The sludge treatment also significantly decreased the bioaccumulation of cadmium, copper, and zinc in the exposed species. For cadmium, maximum tissue concentrations of 0.45+/-0.08 mg/kg in barley, 0.79+/-0.27 mg/kg in ryegrass, and 21.82+/-1.85 mg/kg in earthworm exposed to sludge before treatment decreased after treatment to values similar to those observed with negative controls.     

Biomarkers assessment in juvenile Cyprinus carpio exposed to waterborne cadmium

The impact of long-term exposure to waterborne cadmium (Cd) on Cyprinus carpio was evaluated through changes of selected parameters considered as biomarkers of toxicity. Fish were exposed to 1.6 mg l(-1) Cd for 14 days and then transferred to Cd-free water for 19 days. The measured parameters were gill ATPases, brain acetylcholinesterase (AchE), liver glutamate oxaloacetate (GOT) and glutamate pyruvate (GPT) transaminases, muscle water content, and protein content of liver, gills and brain. Condition factor and liver somatic index were also calculated. Branchial ATPase activities were impaired in a dissimilar way: the (Na(+),K(+))-ATPases were inhibited by approximately 30%, while the Mg(2+)-ATPase was significantly activated by 70%. Brain AchE showed no changes after Cd exposure. Both liver GOT and GPT activities were increased by the metal by 63 and 98%. Water content of the skeletal muscle showed no significant alterations. After the 19-day recovery phase, changes in the Mg(2+)-ATPase and GPT were reversed to values similar to controls, but the Cd exposure resulted in an irreversible alteration in GOT activity. Results indicate that the sublethal Cd concentrations are stressful to carp, particularly with reference to branchial enzymes which may disrupt the osmotic and ionic balance of the animals.     

Etude de l'accumulation du cadmium par une bacterie marine en fonction des conditions de cultures

The influence of different cultural conditions (temperature, salinity, pH, organic matter and cadmium concentration, presence of sulfhydryl groups) on the accumulation of cadmium by a Cd resistent marine bacterium was investigated. The results showed that each of these parameters modify to a certain extent both biomass production and cadmium accumulation. This work emphasizes the need for a higher standardization of toxicity tests to ensure a better reliability of results.     

Oxidative stress in duckweed (Lemna minor L.) caused by short-term cadmium exposure

The mechanisms of plant defence against cadmium toxicity have been studied by short-term exposure of Lemna minor L. (common duckweed) to concentrations of CdCl2 ranging from 0 to 500microM. High accumulation of cadmium was observed (12,320+/-2155microgg(-1) at 500microM CdCl2), which caused a gradual decrease of plant growth, increased lipid peroxidation, and weakened the entire antioxidative defence. Total glutathione concentration decreased significantly; however, the concentration of oxidized glutathione remained stable. The responses of four antioxidant enzymes showed that catalase was the most inhibited after CdCl2 exposure, ascorbate peroxidase and guaiacol peroxidase moderately, and glutathione reductase least. The total antioxidative potential revealed an induced antioxidative network at 0.1microM CdCl2 (137+/-13.2% of the control) and its reduction to only 47.4+/-4.0% of the control at higher cadmium concentrations. The possible application of the examined biomarkers in ecotoxicological research is discussed.     

Effect of cadmium on germination, amylases and rate of respiration of germinating pea seeds

Growth of embryonic axis of germinating pea seeds (Pisum sativum cv. Bonneville) was significantly inhibited by as low as 0.25 mM cadmium and the elongation of the radicle was affected more severely than that of the plumule. Total amylolytic activity, as well as activities of alpha- and beta-amylases, diminished progressively with increasing concentrations of the metal in the media. The deleterious effect on alpha-amylase persisted throughout, whereas beta-amylase activity recovered with time. The rate of respiration of seeds, measured by oxygen uptake, was markedly impeded by cadmium and the phase of rapid and linear development of respiratory activity (after 3 days of imbibition) was almost completely, suppressed in the presence of higher concentrations (1 mM) of the metal. The observed impact of cadmium on starch mobilization and on respiratory activity are discussed in relation to its adverse effects on seed germination.     

Short-term effects of compost amendment on the fractionation of cadmium in soil and cadmium accumulation in rice plants

Purpose

We used a sequential extraction to investigate the effects of compost amendment on Cd fractionation in soil during different incubation periods in order to assess Cd stabilization in soil over time.

Methods

Pot experiments using rice plants growing on Cd-spiked soils were carried out to evaluate the influence of compost amendment on plant growth and Cd accumulation by rice. Two agricultural soils (Pinchen and Lukang) of Taiwan were used for the experiments. The relationship between the redistribution of Cd fractions and the reduction of plant Cd concentration due to compost amendment was then investigated.

Results and discussion

Compost amendment in Pinchen soil (lower pH) could transform exchangeable Cd into the Fe- and Mn-oxide-bound forms. With increasing incubation time, exchangeable Cd tended to transform into carbonate- and Fe- and Mn-oxide-bound fractions. In Lukang soil (higher pH), carbonate- and Fe- and Mn-oxide-bonded Cd were the main fractions. Exchangeable Cd was low. Compost amendment transformed the carbonate-bound form into the Fe and Mn oxide form. Pot experiments of rice plants showed that compost amendment enhanced plant growth more in Pinchen soil than in Lukang soil. Compost amendment could significantly reduce Cd accumulation in rice roots in both Pinchen and Lukang soils and restrict internal transport of Cd from the roots to the shoots. Because exchangeable Cd can be transformed into the stronger bonded fractions quickly in Pinchen soil, a reduction of Cd accumulation in rice due to compost amendment of Pinchen soil was significant by 45?days of growth. However, carbonate-bonded fractions in Lukang soil may provide a source of available Cd to rice plants, and exchangeable and carbonate-bonded fractions are transformed into the other fractions slowly. Thus, reduction of Cd accumulation by rice due to compost amendment in Lukang soil was significant by 75?days of growth.

Conclusions

The results of the study suggest that the effectiveness of compost amendment used for stabilization of Cd and to decrease the phytoavailability of Cd for rice plants is different in acidic and alkaline soils. In acidic soil, Cd fractionation redistributes quickly after compost amendment and shows a significant reduction of Cd accumulation by the plant within a few weeks. In alkaline soil, due to the strongly bound fractions of Cd being in greater quantity than the weakly bound ones, a longer period (a few months) to redistribute Cd fractions is needed.