Combined Metal Treatment Research Articles

Immunohistochemical Investigations of the Thalamic Region in Rats Following Combined Exposure to Metals and Restraint Stress

Chronic exposure to stress has been linked to the perturbation of normal brain functioning. Further, metal overexposure due to their increasing applications can negatively impact brain health. Combined exposure to stressful events and metals is common but has not yet been studied. Thus, this study focused on the thalamic region for its role as a vital relay station in the brain to investigate apoptotic and microglia activation, oxidative stress regulation, and myelin damage following co-exposures to restraint stress and metals, manganese (Mn) and nickel (Ni). Thirty-six adult male rats were divided into six groups and, respectively, exposed to the following for 15 days: control group (normal saline), stress group (3 hours of restraint stress daily), Mn and Ni only groups (intraperitoneal injection of 25 mg/kg of metals), and stress + metal groups received Mn or Ni prior to being subjected to restraint stress. Following treatments, immunohistochemical procedures were used to evaluate relevant neurochemical markers. Results show significantly increased activation of caspase-3 in stressed, metal-only, and combined stress-plus-metal treatments, particularly with Mn treatments. Also, the results show a varying response to Iba1, the microglia activation marker. Furthermore, the study reports significant decreases in Nrf2 (nuclear factor erythroid 2-related factor 2) expression that is potentiated by combined stress and metal treatments as well as altered myelination-linked proteins, Olig2 (oligodendrocyte lineage transcription factor 2), and MBP (myelin basic protein). Overall, the result from this study indicates that the combination of stress and metal exposure could exacerbate the neurotoxic impact of metal toxicity or stressful events.

Complex soil contamination severely impacts seed-sown crop viability in Australia

Food security is a critical issue for many global communities. Heavy metal contamination in soils present a major and ongoing ecological risk associated with human activities which may impact the viability and safety of seed-sown crops. To better understand the impacts of soil contamination by heavy metals on seed-sown crop viability, we examined germination responses of eight commercially-important fruit and vegetable crop species to copper, zinc, and lead contamination at levels likely to be found in contaminated regions in Australia. We compared the germination attributes of days to first germination, germination period, and total proportion of seeds germinated under concentration limits of heavy metals detected at degraded sites and current Australian National Environment Protection Measure thresholds for domestic soils (i.e., copper 6,000 mg kg-1, zinc 4,700 mg kg-1, lead 300 mg kg-1). The combined heavy metal treatment (i.e. all three metals) significantly inhibited germination for all edible crop species with only carrots able to germinate under complex, multi-metal-contaminated conditions. Seed viability was significantly decreased in mulberry (M. alba var. tatarica, M. nigra, and M. rubra) and lettuce (L. sativa), with lowered seed germination in all metals compared to carrot (D. carota), radish (R. sativus), tomato (S. lycopersicum) and common bean (P. vulgaris). These results indicate heavy metal contamination is a notable risk to seed-sown crop species, with multi-metal contamination events likely to be severely damaging to lettuce, tomato, radish, common bean, and mulberry crops

Does combined heavy metal stress enhance iron plaque formation and heavy metal bioaccumulation in Kandelia obovata?

Iron plaque (IP) has significant impact on rhizosphere environment, and affects the uptake and translocation of heavy metals in plants. However, information on IP formation and heavy metal bioaccumulation for mangrove plants under combined heavy metal stress is currently limited. Based on a 120-day pot experiment, this study explored the temporal changes of IP formation on root surface of Kandelia obovata, and heavy metal bioaccumulations under combined heavy metal stress of Cu, Pb and Zn. The results showed that IP formations on root tip, middle and basal roots were improved with combined heavy metal stress and treatment time (root tip: 0.49−0.61 mg g−1 to 2.55–4.77 mg g−1; middle root: 0.27−0.31 mg g−1 to 3.01–4.22 mg g−1; basal root: 0.16−0.23 mg g−1 to 2.24–4.10 mg g−1). IP formation was accompanied with improved depositions of Cu and Pb on root surface, regardless of root tip, middle and basal roots. IP and roots deposited large amounts of Cu (24.97–69.52 μg g-1, 9.39–154.75 μg g−1), Pb (8.35–84.53 μg g-1, 12.29–191.49 μg g-1) and Zn (85.71–139.19 μg g-1, 51.07–195.65 μg g−1), inhibiting their translocations to aboveground leaves. Based on subcellular distribution and chemical forms of heavy metals in roots, the improved depositions of phosphate-integrated Cu (6.77 %–25.13 %), oxalate-integrated Pb (34.89 %–57.88 %), as well as pectate- and protein-integrated Zn (14.22 %–35.41 %) were detected in root cell vacuoles. In conclusion, the combined heavy metal stress enhanced IP formation and heavy metals deposition (especially for Cu and Pb) on root surface, and improved their vacuolar sequestration and chelation in roots of K. obovata.

Potential of ornamental monocot plants for rhizofiltration of cadmium and zinc in hydroponic systems.

Cadmium (Cd) and zinc (Zn) accumulation and uptake ability have been investigated in three ornamental monocot plants (Heliconia psittacorum x H. spathocircinata, Echinodorus cordifolius, and Pontederia cordata) grown in hydroponic systems. All study plants in the highest heavy metal treatments were found to be excluders for Cd and Zn with translocation factor values < 1 and bioconcentration factor (BCF) values > 100. The highest Cd and Zn accumulations were found in roots of E. cordifolius (4766.6 mg Zn kg-1 and 6141.6 mg Cd kg-1), followed by H. psittacorum x H. spathocircinata (4313.5 mg Zn kg-1) and P. cordata (3673.3 mg Cd kg-1), respectively, whereas shoots had lower performances. However, P. cordata had the lowest dry biomass production compared to the other two plant species in this study. As a result of dilution effects, heavy metal accumulation for all study plants was lower in the combined heavy metal treatments than in solely Cd and Zn only treatments. At the end of experiments, the highest uptakes of Cd and Zn were found in H. psittacorum x H. spathocircinata (62.1% Zn2+ from 10 mg Zn L-1 solution) and E. cordifolius (27.3% Cd2+ from 2 mg Cd L-1 solution). Low percentage metal uptakes were found in P. cordata; therefore, E. cordifolius and H. psittacorum x H. spathocircinata are clearly better suited for removing Cd and/or Zn from contaminated waters and hydroponic systems.

Intergenerational effects of resuspended sediment and trace metal mixtures on life cycle traits of a pelagic copepod

Multiple stressors like metal toxicity, organic compounds and sediment pollution from the Seine estuary are raising concern and novel toxicological approaches are needed to better assess and monitor the risk. In the present study, the copepod Eurytemora affinis from the Seine, was exposed to two different sources of contaminants, which were resuspended polluted sediments and a mixture of trace metals (dissolved phase). The exposure continued for four generations (F0, F1, F2, F3) where F0 is a generation for acclimation to the exposure condition and F3 is a generation for decontamination followed without any exposure, to detect possible maternal carryover effects of pollutants (F0 – F2) and the role of recovery (in F3). Higher accumulation of metals resulted in higher mortalities at both exposure conditions, with particularly F1 being the most sensitive generation showing highest bioaccumulation of metals, highest mortality, and smallest population size. Copper accumulation was highest of all metals in mixture from both the resuspended sediment and the combined trace metal treatment. A significantly lower naupliar production was seen in copepods exposed to resuspended sediment compared to trace metal exposed copepods. However, the decontamination phase (F3) indicated that E. affinis pre-exposed to resuspended sediment had a higher ability to recover the total population size, increase naupliar production, and depurate accumulated Cu. The population exposed to a trace metal mixture showed lower recovery and lower ability to discharge accumulated toxic metals indicating its greater effect on our experimental model when compared to resuspended sediment.

Zinc excess increases cellular demand for iron and decreases tolerance to copper in Escherichia coli

Transition metals serve as an important class of micronutrients that are indispensable for bacterial physiology but are cytotoxic when they are in excess. Bacteria have developed exquisite homeostatic systems to control the uptake, storage, and efflux of each of biological metals and maintain a thermodynamically balanced metal quota. However, whether the pathways that control the homeostasis of different biological metals cross-talk and render cross-resistance or sensitivity in the host-pathogen interface remains largely unknown. Here, we report that zinc (Zn) excess perturbs iron (Fe) and copper (Cu) homeostasis in Escherichia coli, resulting in increased Fe and decreased Cu levels in the cell. Gene expression analysis revealed that Zn excess transiently up-regulates Fe-uptake genes and down-regulates Fe-storage genes and thereby increases the cellular Fe quota. In vitro and in vivo protein-DNA binding assays revealed that the elevated intracellular Fe poisons the primary Cu detoxification transcription regulator CueR, resulting in dysregulation of its target genes copA and cueO and activation of the secondary Cu detoxification system CusSR-cusCFBA Supplementation with the Fe chelator 2,2'-dipyridyl (DIP) or with the reducing agent GSH abolished the induction of cusCFBA during Zn excess. Consistent with the importance of this metal homeostatic network in cell physiology, combined metal treatment, including simultaneously overloading cells with both Zn (0.25 mm) and Cu (0.25 mm) and sequestering Fe with DIP (50 μm), substantially inhibited E. coli growth. These results advance our understanding of bacterial metallobiology and may inform the development of metal-based antimicrobial regimens to manage infectious diseases.

Bioavailability of adsorbed and coprecipitated Cu, Ni, Pb, and Cd on iron and iron/aluminum hydroxide to Phragmites australis.

The bioavailability of heavy metals strongly depends on their speciation in the environment. Adsorption (ADS) and coprecipitation (CPT) on amorphous metal hydroxides are important processes, controlling the fates of heavy metals in an aqueous environment. This work studied the bioavailability of Cu, Cd, Ni, and Pb adsorbed on and/or coprecipitated with amorphous iron and iron/aluminum mixed hydroxides to the wetland plant Phragmites australis. After a 13-day treatment, there was an apparent uptake of the heavy metals by the plant, and the amount of metal bioaccumulation was measurably different for different association forms (ADS vs. CPT). The bioaccumulation of Cd associated with Fe0.5Al0.5(OH)3 was greater than that with Fe(OH)3; the adsorbed metals were found to be more bioavailable than the coprecipitated forms for most of the treatments while the aging treatment significantly reduced the bioaccumulation of ADS metals. In the single metal treatment, root metal concentrations in the Fe(OH)3 ADS system followed the order Ni (68mgkg-1) > Cu (32mgkg-1) > Cd (28mgkg-1) > Pb (9mgkg-1), while the CPT system followed the order of Cu (30mgkg-1) > Ni (22mgkg-1) > Pb (9mgkg-1) > Cd (7mgkg-1). The order of metal accumulation in a combined metal treatment was similar to that for single metal treatments, but observed Ni concentration declines by 22 and 71% and Cu and Cd concentrations increase by 30 and 50% (for CPT and ADS treatments, respectively), while Pb concentrations increased by 30~50% in both of them. When treated with low-molecular-weight organic acids (LMWOAs), metal desorption, indicative of metal oxide bonding strength and metal bioavailability, was consistent with metal accumulation in the plant.

Combined toxicity of cadmium and copper in Avicennia marina seedlings and the regulation of exogenous jasmonic acid

Seedlings of Avicennia marina were exposed to single and combined metal treatments of cadmium (Cd) and copper (Cu) in a factorial design, and the combined toxicity of Cu and Cd was tested. The effects of the exogenous jasmonic acid (JA) on chlorophyll concentration, lipid peroxidation, Cd and Cu uptake, antioxidative capacity, endogenous JA concentration, and type-2 metallothionein gene (AmMT2) expression in seedlings of A. marina exposed to combined metal treatments were also investigated. A binary mixture of low-dose Cd (9µmolL−1) and high-dose Cu (900µmolL−1) showed toxicity to the seedlings, indicated by the significant augmentation in leaf malondialdehyde (MDA) and reduction in leaf chlorophylls. The toxicity of the combined metals was significantly alleviated by the addition of exogenous JA at 1µmolL−1, and the chlorophyll and MDA contents were found to be restored to levels comparable to those of the control. Compare to treatment with Cd and Cu only, 1 and 10µmolL−1 JA significantly enhanced the ascorbate peroxidase activity, and 10µmolL−1 JA significantly decreased the uptake of Cd in A. marina leaves. The relative expression of leaf AmMT2 gene was also significantly enhanced by 1 and 10µmolL−1 JA, which helped reduce Cd toxicity in A. marina seedlings.

Effect of tapeworm parasitisation on cadmium toxicity in the bioindicator copepod, Cyclops strenuus

The ubiquitous nature of crustaceans has meant that they have been considered as useful bioindicators of water quality. Although crustaceans e.g. Cyclops strenuus serve as intermediate hosts to many metazoan parasites, the effect of infection on toxicity of heavy metal pollution has not been established. The interaction between the procercoid stage of the tapeworm, Bothriocephalus acheilognathi, and its copepod host when exposed to cadmium toxicity was investigated. Exposure to 100μg Cd/l caused a significant (P<0.001) decrease in copepod survival of crustaceans exposed to combined parasite infection and metal treatment, compared with all other groups which had been exposed to these stressors individually. This effect was not dependent on infection intensity. Although cadmium could not be detected by EDXMA, optical emission spectroscopy revealed Cd accumulation in both treated uninfected and infected copepods. Overall, the data suggest that parasitic infection is an important consideration in determining the suitability of a bioindicator of water pollution.

Liver Function and Structure in Rats Treated Simultaneously with Cadmium and Mercury

The effect of cadmium chloride (150 mg/l) and mercury (II) chloride (80 mg/l) either alone or in combination in drinking water for 4 weeks on function and structure of the liver of male rats was studied. Results indicated that the ratio of liver weight to body weight and the activities of serum alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase noted in rats co-exposed to cadmium and mercury were intermediate between those noted in the individually metal treated rats. The histopathological study showed that the individual metal and the combined metal treatments caused severe liver damage. The degree of these changes noted in rats co-exposed to cadmium and mercury was not higher than those signalized in individual treatment. The biochemical and the histological changes observed in rats co-exposed to cadmium and mercury show that there is not an additive effect between these two metals.

Single and combined toxicity of copper and cadmium toH. vulgaregrowth and heavy metal bioaccumulation

The single and combined effects of copper (Cu) and cadmium (Cd) (0.1-10 mg L -1 ) in spring barley (Hordeum vulgare L.) plants grown in hydroponics are investigated. The aim of the study was to investigate the interactive effect of the binary mixture of Cu and Cd to the growth of H. vulgare and accumulation of these metals by the plants. Single and combined metal treatment led to major effects in the growth of roots and shoots and dry weight of barley. Exposure to metals altered the content of photosynthetic pigments and caused lipid peroxidation. It was observed that combined effects of heavy metals to plants are endpoint and concentration depending. The binary mixture Cu+Cd exhibited additive or less than additive interaction for dry weight, root length and shoot height. Analysis of tissue metal concentrations showed that Cu and Cd were mainly accumulated in the roots and the combination of Cu+Cd had less than additive response of metal bioaccumulation in the leaves and roots.

Response of metallothionein gene-1 to laboratory exposure to heavy metals and thermal stress in the freshwater prawn Macrobrachium rosenbergii

Metallothioneins, metal-inducible proteins, are being characterized from different organisms and shown as potential biomarkers of exposure to pollution by certain heavy metals. Here we report the identification of a new metallothionein cDNA (433 bp) from the shrimp Macrobrachium rosenbergii, putatively encoding a 61 residue polypeptide. Tissue specific analysis indicated that Mar-MT-I ( M. rosenbergii Metallothionein Gene-1) is expressed with the highest levels in the hepatopancreas and lowest in the thoracic ganglia, and none in the gills or muscles. In addition, our data showed that Mar-MT-I is differentially regulated in the hepatopancreas by certain heavy metals and thermal stress: Cd and Cu produce somewhat similar expression profile patterns, Zn has a reductional effect and thermal stress alone entirely stops its expression. These results show that Mar-MT-I mRNA levels can potentially be used as biomarkers for Cd, Cu or Zn pollution individually. However, in the case of combined metal treatment, different combinations of these metals have quite different effect on Mar-MT-I expression. Therefore, factors of such differential behaviors should be kept as a priority for further biomonitring studies.

The influence of dentin and/or metal surface treatment on the retention of cemented crowns in teeth with an increased taper

Objectives To evaluate the effect of dentin and/or metal surface treatments on retention of cast crowns cemented to preparations with compromised retention. Methods Cast crowns ( n = 105) were fabricated on extracted molars prepared to 40° convergence and standard height. 60 teeth were randomly divided into: (A) cemented with zinc phosphate cement; (B–D) cemented with resin cement (Compolute, 3M) with either no surface treatment (B), dentin etched and bonded (EBS multi, 3M) (C), or dentin etched and bonded, and metal tribochemically treated (Co-Jet, 3M) (D); 45 teeth were randomly divided and crowns cemented with another resin cement (Rely-X Arc, 3M) with either no surface treatment (E), dentin etched and bonded (Single Bond, 3M) (F), or dentin etched and bonded and metal tribochemically treated (G). Teeth were stored in 100% humidity for 3 months and thermocycled 5000 cycles. Crowns were dislodged from the preparations and retention (MPa) was calculated. Results Group D showed significantly higher retention (3.52 ± 1.3 MPa) compared to Group C (2.26 ± 0.9 MPa), Group B (0.85 ± 0.4 MPa), and Group A (1.22 ± 0.4 MPa). Group G exhibited significantly higher retention (5.4 ± 1.4 MPa) compared to F (2.6 ± 1.2 MPa) and E (2.0 ± 0.6 MPa). Higher retention corresponded with more cohesive cement type of failure. Significance Cast crowns with compromised retention cemented by resin cement should undergo combined tribochemical metal treatment and dentin bonding. The crucial link is the interaction of different brands of resin cements with the metal tribochemically treated.

Comparative toxicity of cadmium, zinc, and mixtures of cadmium and zinc to daphnids

Investigations were conducted to determine acute (48-h) effects of cadmium and zinc presented individually and in combination on Ceriodaphnia dubia, Daphnia magna, Daphnia ambigua, and Daphnia pulex. Toxicity tests were conducted with single metals to determine lethal effects concentrations (lethal concentrations predicted for a given percent [x] of a population, LCx value). These were used to derive metal combinations that spanned a range of effects and included mixtures of LC15, LC50, and LC85 values calculated for each metal and species. In single-metal tests, 48-h LC50 values ranged from 0.09 to 0.9 micromol/L and 4 to 12.54 micromol/L for cadmium and zinc, respectively. For each metal, D. magna was most tolerant and showed a different pattern of response from all others as determined by slope of concentration-response curves. In the combined metal treatments, all daphnids showed a similar pattern of response when LC15 concentrations were combined. This trend continued with few exceptions when LC15 concentrations of cadmium were combined with LC50 or LC85 values for zinc. However, when this treatment was reversed (LC15, zinc + LC50 or LC85, cadmium), responses of all species except D. magna indicated less-than-additive effects. For C. dubia, a near complete reduction in toxicity was observed when the LC15 for zinc was combined with LC85 for cadmium. Multimetal tests with D. magna did not differ from additive. Collectively, these studies suggest that D. magna may not be representative of other cladocerans.

Tolerance and bioaccumulation of cadmium by Phragmites australis grown in the presence of elevated concentrations of cadmium, copper, and zinc

The effects of cadmium and of combined treatments of cadmium, copper and zinc on growth, tolerance indices, mineral composition (N, P, K, Fe, Zn and Mn) and metal uptake of reed ( Phragmites australis [(Cav.) Trin. ex Steudel]) were investigated in hydroponic experiments, with Cd concentrations ranging from 4.4 to 17.6 μM, either alone or combined with different treatments of Cu and Zn. Neither root nor shoot growth were affected by the treatments with 4.4 and 8.8 μM Cd alone. However, root and shoot length were significantly reduced by 17.6 μM Cd. Combined metal treatments significantly decreased shoot length, root number and plant fresh weight further than Cd alone, but not plant dry weight. Cd alone had no effect on tissue concentrations of N, P or K, while Mn concentration decreased in both shoot and root, and Zn concentration increased. As a result of the Cd, Cu and Zn (combined treatment) toxicity, the concentrations of N and K decreased in shoot and root tissues, respectively, and Mn concentration decreased in both shoot and root. Fe concentration increased in roots, leading to a significant relationship between root tissue Fe and Cd concentrations with increasing individual concentration of Cd (log 10 basis, P < 0.01) and in all the combined treatments of Cd, Cu and Zn ( P < 0.001). Metal bioconcentration (tissue concentration/solution concentration) was higher in roots than in shoots, ranging from 287.5 to 1193 for Cd, 849 to 1554 for Cu and 166 to 915 for Zn. The tolerance level of reed to Cd suggests that reed could be useful in wastewater treatments for the removal of Cd. However, the simultaneous presence of elevated concentrations of Cd, Cu and Zn in the effluents may limit the efficiency.

Metal insensitivity in ericoid mycorrhizal endophytes from Woollsia pungens (Epacridaceae)

The influence of Cd2+, Cu2+ and Zn2+ on biomass production by 13 ericoid mycorrhizal endophytes (all putative Leotiales ascomycetes) from Woollsia pungens (Epacridaceae), along with three isolates of Hymenoscyphus spp., was investigated in axenic liquid culture. Inter- and intraspecific variation was observed in effective concentration values that inhibited growth by 50% (EC50) for each metal; however, values varied by only a single order of magnitude for a particular metal (16.67–261.00 mmol m–3 for Zn2+, 2.50–12.33 mmol m–3 for Cd2+ and 3.00–43.88 mmol m-3for Cu2+). Values of EC50 for the endophytes from W. pungens were thus broadly similar to those from H. ericae. Combined metal treatments had either additive or ameliorative effects on the toxicity of individual metals to the various isolates. The data suggest that resistance to toxic metals is broadly similar in ericoid mycorrhizal endophytes from Northern Hemisphere Ericaceae and Australian Epacridaceae.

Prolonged, simulated acid rain and heavy metal deposition: separated and combined effects on forest soil microbial community structure

The separate and combined effects of moderate levels of acid load and Cu-Ni deposition on humus (F/H layer) microbial community structure were examined six growing seasons after the start of an artificial irrigation experiment. A 22-factorial design with acid load (pH 3.1) and Cu-Ni addition was used. The acid application resulted in acidification as defined by humus chemistry, including a decrease in the concentration of base cations and an increase in the concentration of H+, Al and Fe, leading to a decrease in humus pH from 4.10 to 3.95. The metal additions resulted in a 2–3-fold increase in humus total Cu and Ni concentrations. The treatments did not affect the total microbial biomass, measured by substrate-induced respiration, or the basal respiration rate. However, the microbial community structure determined by phospholipid fatty acid (PLFA) analysis showed that the acid load affected the bacterial part of the community. The relative amount of branched PLFAs common to Gram-positive bacteria increased with decreasing humus pH, and the bacterial community was also adapted to more acidic conditions. The metal addition alone did not cause clear changes in the microbial community structure or bacterial tolerance to Cu or Ni. The combined acid and metal treatment induced similar changes in the microbial community structure as the acid treatment alone.

Prolonged, simulated acid rain and heavy metal deposition: separated and combined effects on forest soil microbial community structure

The separate and combined effects of moderate levels of acid load and Cu-Ni deposition on humus (F/H layer) microbial community structure were examined six growing seasons after the start of an artificial irrigation experiment. A 2 2-factorial design with acid load (pH 3.1) and Cu-Ni addition was used. The acid application resulted in acidification as defined by humus chemistry, including a decrease in the concentration of base cations and an increase in the concentration of H +, Al and Fe, leading to a decrease in humus pH from 4.10 to 3.95. The metal additions resulted in a 2–3-fold increase in humus total Cu and Ni concentrations. The treatments did not affect the total microbial biomass, measured by substrate-induced respiration, or the basal respiration rate. However, the microbial community structure determined by phospholipid fatty acid (PLFA) analysis showed that the acid load affected the bacterial part of the community. The relative amount of branched PLFAs common to Gram-positive bacteria increased with decreasing humus pH, and the bacterial community was also adapted to more acidic conditions. The metal addition alone did not cause clear changes in the microbial community structure or bacterial tolerance to Cu or Ni. The combined acid and metal treatment induced similar changes in the microbial community structure as the acid treatment alone.

DNA single-strand breakage in rat lung, liver and kidney after single and combined treatments of nickel and cadmium

Single-strand breaks were observed in rat lung and kidney after acute treatment of animals with CdCl 2 (4 mg/kg body weight) injected intraperitoneally and NiCl 2 (44.4 mg/kg body weight) injected subcutaneously. In the rat liver, no single-strand breakage was evident with those doses in single and combined metal treatments. The most susceptible tissue in rats to cadmium or nickel chloride treatment was the lung tissue. The single-strand breaks were higher in cadmium treatment than in nickel treatment in the rat lung. Also the response to cadmium treatment was obtained earlier than nickel. Rat kidney was also responsive to cadmium treatment. However, the response, although statistically significant, was much lower than the one obtained in rat lung. The combined treatment, which was done by administrating cadmium prior to nickel administration, reduced the number of single-strand breaks significantly and reversed them to control values in rat lung and kidney. This study confirms that cadmium and nickel create single-strand breaks when administered alone in the rat lung. This effect, which was seen in the single metal treatments, was reduced in the combined treatments.

Comparison of the effects of Cu, Pb, and As on plant residue decomposition, microbial biomass, and soil respiration

Comparisons were made among the effects of Cu, Pb, and As on the plant residue decomposition, microbial biomass, and soil respiration using soils artificially enriched with Cu, Pb, and As. A total of eight metal treatments, consisting of a control, single metal treatments (10 mmol Cu kg−1, 20 mmol Cu kg−1, 10 mmol Pb kg−1, and 10 mmol As kg−1), and combined metal treatments (5 mmol Cu kg−1+2.5 mmol Pb kg−1+1 mmol As kg−1, 10 mmol Cu kg−1+5 mmol Pb kg−1 + 2 mmol As kg−1, and 20 mmol Cu kg−1 + 10 mmol Pb kg−1 +4 mmol As kg−1) were prepared. The inhibition of orchard grass decomposition was estimated by the difference in the contents of organic C and total N of soils treated with individual metals with and without orchard grass amendment following incubation under field conditions for 3 years. In the metal concentration range studied, Cu inhi~ited severely the orchard grass decomposition, Pb slightly inhibited it, while As had no notable effect on it. The amounts of microbial biomass C and N and the soil respiration were measured for the soils with and without orchard grass amendment at the end of the field incubation. When compared on a molarity basis, the toxicity was in the order of Cu≫Pb> As with respect to both the microbial biomass and the soil respiration, regardless of the orchard grass amendment. Furthermore, the addition of heavy metals tended to increase the respiration per unit of biomass C in the soils without orchard grass amendment. Nevertheless, the biomass specific respiration showed a highly negative exponential correlation with the amount of biomass C.