Cadmium speciation and accumulation in periphyton in a small stream with dynamic concentration variations

Accumulation of cadmium in periphyton was investigated under field conditions while Cd concentration and speciation were dynamically varying in a small stream during rain events. Speciation in water was determined in situ by diffusion gradient in thin-films (DGT) and by modeling of complexation with fulvic acids. During the rain events, dissolved Cd concentrations increased from 0.17 nM to 0.27-0.36 nM, and 70-97% were DGT-labile. Cd content in periphyton closely followed Cd concentrations in water, despite higher concentrations of Zn and Mn, and may be controlled by either free or DGT-labile Cd concentrations. Decrease of Cd content in periphyton after the rain events was slower than the decrease of Cd concentration in water. Concentrations of Zn, Mn, Cu, Pb and Fe in periphyton also followed the dynamic variations of metal concentrations in water. Repeated exposure of periphyton to elevated dissolved Cd may lead to Cd accumulation.     

The potential of willow for remediation of heavy metal polluted calcareous urban soils

Growth performance and heavy metal uptake by willow (Salix viminalis) from strongly and moderately polluted calcareous soils were investigated in field and growth chamber trials to assess the suitability of willow for phytoremediation. Field uptakes were 2-10 times higher than growth chamber uptakes. Despite high concentrations of cadmium (≥80 mg/kg) and zinc (≥3000 mg/kg) in leaves of willow grown on strongly polluted soil with up to 18 mg Cd/kg, 1400 mg Cu/kg, 500 mg Pb/kg and 3300 mg Zn/kg, it is unsuited on strongly polluted soils because of poor growth. However, willow proved promising on moderately polluted soils (2.5 mg Cd/kg and 400 mg Zn/kg), where it extracted 0.13% of total Cd and 0.29% of the total Zn per year probably representing the most mobile fraction. Cu and Pb are strongly fixed in calcareous soils.     

Canopy influence on trace metal atmospheric inputs on forest ecosystems: Speciation in throughfall

Atmospheric inputs of selected Trace Metals (TM: Cd, Cu, Ni, Pb, Sb, Zn, as well as Al, Fe and Mn) were studied on six forested sites in France. In order to evaluate canopy interaction with atmospheric inputs, TM were measured in both Open Field Bulk Deposition (BD) and Throughfall (TF). Anthropogenic contribution to BD composition is high for Zn, Cd and Sb, reflecting actual TM emissions trends. Canopy greatly influences precipitation composition, through different processes, including assimilation and leaching by canopy, complexation as well as accumulation/dissolution of dry deposition. TM and Dissolved Organic Carbon (DOC) physical fractionation between colloidal and truly dissolved phases was performed with ultrafiltration. Al, Fe, Pb and Cu are found in the colloidal fraction whereas Cd, Ni, Zn and Sb are mostly in the truly dissolved fraction. Chemical speciation predicted with WHAM-VI shows that in throughfall, Al, Fe, Pb and Cu are almost entirely complexed by DOC, whereas Ni, Cd and Zn are present in average 30% in the free metal ion form. TM present in labile forms (Cd, Ni, Zn) interact with the canopy, are cycled in the ecosystem, and their concentration is either slightly increased or even decreased in throughfall. Sb, Pb and Cu concentration are increased through canopy, as a consequence of dry deposition accumulation.     

Uptake of Cd(II) and Pb(II) by microalgae in presence of colloidal organic matter from wastewater treatment plant effluents

The present study addresses the key issue of linking the chemical speciation to the uptake of priority pollutants Cd(II) and Pb(II) in the wastewater treatment plant effluents, with emphasis on the role of the colloidal organic matter (EfOM). Binding of Cd(II) and Pb(II) by EfOM was examined by an ion exchange technique and flow field-flow fractionation coupled to inductively coupled plasma mass spectrometry in parallel to bioassays with green microalga Chlorella kesslerii in ultrafiltrate (<1 kDa) and colloidal isolates (1 kDa to 0.45 μm). The uptake of Cd by C. kesslerii was consistent with the speciation analysis and measured free metal ion concentrations, while Pb uptake was much greater than that expected from the speciation measurement. Better understanding of the differences in the effects of the EfOM on Cd(II) and Pb(II) uptake required to take into account the size dependence of metal binding by EfOM.     

Relationship between heavy metals concentrations in egret species,their environment and food chain differences from two Headworks of Pakistan

Concentration of ten metals (Cd, Cr, Co, Cu, Fe, Li, Mn, Ni, Pb and Zn) were analyzed in the egg contents, prey and soil samples of little egret (Egretta garzetta) and cattle egret (Bubulcus ibis) from two Headworks to determine habitat and species-specific differences; to assess the importance of prey and habitat contamination as an exposure source for heavy metals. Concentration of Cu, Mn, Cr and Pb in egg contents, Fe, Co, Cu, Mn, Zn in prey and Fe, Co, Cu, Ni, Li in surface soils were significantly different (P < 0.05). Mean metal concentrations of Cr, Pb and Cd were relatively higher in little egret whereas Cu and Mn were higher in the egg contents of cattle egret. The mean concentrations of Cu, Mn and Zn were higher in prey samples of cattle egrets and Cr, Cd and Pb in prey samples of little egrets. In soil samples collected from little egret heronries metal concentrations were higher except Cu and Ni. Correlation Analysis and Hierarchical Agglomerative Cluster Analysis (HACA) identified relatively similar associations of metals and their source identification. Metals such as Fe, Cu, Mn, and Li were related with geochemical origin from parent rock material as well as anthropogenic input whereas Cr, Cd, Pb, Ni, Co and Zn were associated mostly with anthropogenic activities. The study suggested that eggs are useful bio-monitor of local heavy metal contamination.     

Heavy metal exposure in large game from a lead mining area: Effects on oxidative stress and fatty acid composition in liver

The Pb mining area of the valley of Alcudia and the Sierra Madrona mountains (S. Spain) has been exploited intermittently for over 2100 years, since Roman occupation and up until the late 1900s. Red deer (n = 168) and wild boar (n = 58) liver and bone (metacarpus) were analyzed for Pb, Zn, Cu, Cd, As and Se. Lipid peroxidation, total and oxidized glutathione (GSH), superoxide dismutase (SOD), GSH peroxidase (GPX) and fatty acid composition were studied in liver of red deer. The concentrations of Pb in liver and bone of red deer and wild boar were higher in the mining area than in the control area, and higher in the wild boar than red deer, but well below the level associated with clinical signs of Pb poisoning. Liver levels of Cu, Cd and Se were also higher in red deer from the mining area. Red deer from the mining area had 39% less total GSH than in the control area. The percentage of docosahexaenoic acid in liver of red deer from the mining area was 16% lower than in the control area.     

Phytoextraction of heavy metal polluted soils using Sedum plumbizincicola inoculated with metal mobilizing Phyllobacterium myrsinacearum RC6b

The aim of this study was to investigate the effects of metal mobilizing plant-growth beneficial bacterium Phyllobacterium myrsinacearum RC6b on plant growth and Cd, Zn and Pb uptake by Sedum plumbizincicola under laboratory conditions. Among a collection of metal-resistant bacteria, P. myrsinacearum RC6b was specifically chosen as a most favorable metal mobilizer based on its capability of mobilizing high concentrations of Cd, Zn and Pb in soils. P. myrsinacearum RC6b exhibited a high degree of resistance to Cd (350 mg L⁻¹), Zn (1000 mg L⁻¹) and Pb (1200 mg L⁻¹). Furthermore, P. myrsinacearum RC6b showed multiple plant growth beneficial features including the production of 1-aminocyclopropane-1-carboxylic acid deaminase, indole-3-acetic acid, siderophore and solubilization of insoluble phosphate. Inoculation of P. myrsinacearum RC6b significantly increased S. plumbizincicola growth and organ metal concentrations except Pb, which concentration was lower in root and stem of inoculated plants. The results suggest that the metal mobilizing P. myrsinacearum RC6b could be used as an effective inoculant for the improvement of phytoremediation in multi-metal polluted soils.     

Investigation of trace metal binding properties of lignin by diffusive gradients in thin films

The binding behavior of lignin for Pb, Cu, Co, Mn, Cd and Ni was studied using the diffusive gradients in thin films technique (DGT). Samplers with different structures of diffusive gel were used in the well-stirred systems containing known concentrations of metals along with (a) 10, 20 and 40 μM lignin and; (b) 0.64 and 6.47 μM Suwannee river fulvic acid + 40 μM lignin at an ionic strength of 0.01 M (NaNO₃) and pH = 7. Diffusion coefficients of lignin complexes in acrylamide gels were estimated and found to be less than 5% of the equivalent coefficients for the uncomplexed metal ions. These values were used to calculate concentrations of labile metals from DGT measurements in solutions, where lignin could discriminate metals in the order of Pb⁺² > Cu⁺² > Cd⁺² > Ni⁺² > Co⁺² > Mn⁺². Stability constants (Log K) were calculated using Visual MINTEQ II and WHAM V software. The K values were compared with the stability constants from titration of Pb and Cd with 10 μM lignin aqueous samples and with those of humic substances in natural waters. The constants obtained from measurement of complexing capacities might bias the real corresponding values unless two line regression analyses on titration data are considered. The DGT study of fractionation of metal species at varying ratios indicated that the proportion of organic complexes decreased with increasing ratios and gradually more metals were exchanged with inorganic phases. Speciation of Pb and Cd is affected by the concentrations of FA, Cd is dominantly bound with FA while Pb is evenly partitioned between the ligands. The comprehensive knowledge of metal-lignin complexes sheds some light on in situ operational speciation information that can be achieved by DGT.     

Freshwater Ulva (Chlorophyta) as a bioaccumulator of selected heavy metals (Cd, Ni and Pb) and alkaline earth metals (Ca and Mg)

We analyzed the ability of freshwater taxa of the genus Ulva (Ulvaceae, Chlorophyta) to serve as bioindicators of metal in lakes and rivers. Changes in heavy metal (Ni, Cd and Pb) and alkaline earth metal (Ca and Mg) concentrations in freshwater Ulva thalli were investigated during the period from June to August 2010. The study was conducted in two ecosystems in Western Poland, the Malta lake (10 sites) and the Nielba river (six sites). Three components were collected for each sample, including water, sediment and Ulva thalli. The average concentrations of metals in the water sample and in the macroalgae decreased in the following order: Ca > Mg > Ni > Pb > Cd. The sediment revealed a slightly altered order: Ca > Mg > Pb > Ni > Cd. Ca and Mg were found at the highest concentrations in thalli due to the presence of carbonate on its surface. Among the examined heavy metals in thalli, Ni was in the highest concentration, and Cd found in the lowest concentration. There were statistically significant correlations between the levels of metals in macroalgae, water and sediment. Freshwater populations of Ulva exhibited a greater efficiency to bioaccumulate nickel as compared to species derived from marine ecosystems.     

Heavy metal contamination in surface sediments of Yangtze River intertidal zone: An assessment from different indexes

Surface sediments (0-5 cm) from 59 stations within the Yangtze River intertidal zone (YRIZ) were sampled for metal contamination analysis in April and August 2005. The concentrations ranged (in mg kg⁻¹ dry weight): Al, 40,803-97,213; Fe, 20,538-49,627; Cd, 0.12-0.75; Cr, 36.9-173; Cu, 6.87-49.7; Mn, 413-1,112; Ni, 17.6-48.0; Pb, 18.3-44.1; and Zn, 47.6-154; respectively. Among the 59 sampling stations, enrichment factors (EF) indicate enrichment of Cd (52 stations), Cr (54 stations), Cu (5 stations), Ni (26 stations), Pb (5 stations) and Zn (5 stations). Geoaccumulation indexes (I_geo) also suggest individual metal contamination in localized areas. This study indicates that Cd, Cr and Ni enrichment in the YRIZ sediment is widespread whereas Cu, Mn, Pb and Zn enrichment is localized or nonexistent. Factor and cluster analyses indicate that Cd is associated with total organic carbon whereas Cu, Cr, Ni, Pb and Zn have a close association with Mn.     

Accumulation of Al, Mn, Fe, Cu, Zn, Cd and Pb by the bryophyte Scapania undulata in three upland waters of different pH.

Measurements were made of the contents of Al, Mn, Fe, Cu, Zn, Cd and Pb in Scapania undulata in three streams (D2, D5, D11) in the English Lake District. The stream waters had average pH values of 5.35 (D2), 5.81 (D5) and 7.26 (D11), the main differences in other major chemical components being in Mg, Al, Ca and alkalinity. There was generally more metal accumulation in the older parts of the plants, but this was not significant in all cases. Extents of accumulation varied with stream pH and dissolved metal concentration. For Al, accumulation was greatest in streams D2 and D5. Mn accumulated most in D5 and Fe was without preference. Cu, Zn and Cd accumulated mostly in the plants in stream D11 and Pb accumulated more in D5 and D11. In terms of enrichment factors (amount of metal in the plants divided by stream water concentration) the sequence was Zn < Cd < Cu < Mn < Pb < Al < Fe. Laboratory experiments supported the findings of the field data, providing evidence that uptake increases with pH at constant total metal concentration. The results are interpreted qualitatively in terms of the chemical speciation of the metals in the stream water and competition between metal ions and protons at the plant-water interface. It is suggested that Al, Cu, Zn, Cd and Pb behave according to chemical complexation, whereas redox processes and/or colloidal interactions may be significant for Mn and Fe.     

Vaporization of heavy metals during thermal treatment of model solid waste in a fluidized bed incinerator

This paper investigated the volatilization behavior of heavy metals during thermal treatment of model solid waste in a fluidized bed reactor. Four metal chlorides (Cd, Pb, Cu and Zn) were chosen as metal sources. The influence of redox conditions, water and mineral matrice on heavy metal volatilization was investigated. In general, Cd shows significant vaporization especially when HCl was injected, while Cu and Pb vaporize moderately and Zn vaporization is negligible. Increasing oxygen concentration can lower heavy metal vaporization. Heavy metal interactions with the mineral matter can result in the formation of stable metallic species thus playing a negative effect on their behavior. However, HCl can promote the heavy metal release by preventing the formation of stable metallic species. The chemical sorption (either physical or chemical) inside the pores, coupled with the internal diffusion of gaseous metal species, may also control the vaporization process. With SO₂ injected, Cd and Pb show a higher volatility as a result of SO₂ reducing characteristics. From the analysis, the subsequent order of heavy metal volatility can be found: Cd > Cu ? Pb ? Zn.     

Effects of rapeseed residue on lead and cadmium availability and uptake by rice plants in heavy metal contaminated paddy soil

Rapeseed (Brassica napus L.) has been cultivated for biodiesel production worldwide. Winter rapeseed is commonly grown in the southern part of Korea under a rice-rapeseed double cropping system. In this study, a greenhouse pot experiment was conducted to assess the effects of rapeseed residue applied as a green manure alone or in combinations with mineral N fertilizer on Cd and Pb speciation in the contaminated paddy soil and their availability to rice plant (Oryza sativa L.). The changes in soil chemical and biological properties in response to the addition of rapeseed residue were also evaluated. Specifically, the following four treatments were evaluated: 100% mineral N fertilizer (N100) as a control, 70% mineral N fertilizer + rapeseed residue (N70 + R), 30% mineral N fertilizer + rapeseed residue (N30 + R) and rapeseed residue alone (R). The electrical conductivity and exchangeable cations of the rice paddy soil subjected to the R treatment or in combinations with mineral N fertilizer treatment, N70 + R and N30 + R, were higher than those in soils subjected to the N100 treatment. However, the soil pH value with the R treatment (pH 6.3) was lower than that with N100 treatment (pH 6.9). Use of rapeseed residue as a green manure led to an increase in soil organic matter (SOM) and enhanced the microbial populations in the soil. Sequential extraction also revealed that the addition of rapeseed residue decreased the easily accessible fraction of Cd by 5-14% and Pb by 30-39% through the transformation into less accessible fractions, thereby reducing metal availability to the rice plant. Overall, the incorporation of rapeseed residue into the metal contaminated rice paddy soils may sustain SOM, improve the soil chemical and biological properties, and decrease the heavy metal phytoavailability.     

Long-term effect of temperature on bioaccumulation of dietary metals and metallothionein induction in Sparus aurata

Previous studies have demonstrated that the commercial feed of aquacultured fish contains trace amounts of toxic and essential metals which can accumulate in tissues and finally be ingested by consumers. Recently rising temperatures, associated to the global warming phenomenon, have been reported as a factor to be taken into consideration in ecotoxicology, since temperature-dependent alterations in bioavailability, toxicokinetics and biotransformation rates can be expected. Sparus aurata were kept at 22 °C, 27 °C and 30 °C for 3 months in order to determine the temperature effect on metallothionein induction and metal bioaccumulation from a non-experimentally contaminated commercial feed. A significant temperature-dependent accumulation of cadmium (Cd), copper (Cu), mercury (Hg), zinc (Zn), lead (Pb) and iron (Fe) was found in liver, together with that of manganese (Mn), Fe and Zn in muscle. Hg presented the highest bioaccumulation factor, and essential metal homeostasis was disturbed in both tissues at warm temperatures. An enhancement of hepatic metallothionein induction was found in fish exposed to the highest temperature.     

Trophic transfer of Cd from natural periphyton to the grazing mayfly Centroptilum triangulifer in a life cycle test

In streams, periphyton biofilms are important sinks for trace metals such as cadmium and are primary food sources of many invertebrate consumers. To study Cd trophic transfer, we produced differentially contaminated diets by exposing natural periphyton to environmentally relevant dissolved Cd ranging from 0 to 10 μg L⁻¹ for 6-7 days using a radiotracer approach. On average, periphyton grown during three different seasons bioconcentrated Cd similarly - approximately 1315 (±442) -fold above dissolved concentrations. However, mayfly larvae (Centroptilum triangulifer) raised on these differentially contaminated diets (first instar through adulthood) had significantly higher trophic transfer factors from periphyton grown in Aug and Nov 2008 (4.30 ± 1.55) than from periphyton grown in Jan 2009 (0.85 ± 0.21). This Cd bioaccumulation difference is only partially explained by apparent food quality and subsequent growth differences. Taken together, these results suggest that primary producers at the base of food webs drive metal bioaccumulation by invertebrate grazers.     

Challenges with tracing the fate and speciation of mine-derived metals in turbid river systems: implications for bioavailability

The fast-flowing and highly turbid Lagaip River (0.5–10 g/L suspended solids) in the central highlands of Papua New Guinea receives mine-derived metal inputs in both dissolved and particulate forms. Nearest the mine, metal concentrations in suspended solids were 360, 9, 90, 740 and 1,300 mg/kg for As, Cd, Cu, Pb and Zn, while dissolved concentrations were 2.7, 0.6, 3.1, 0.1 and 25 μg/L, respectively. This creates a significant metal exposure source for organisms nearer the mine. However, because the Lagaip River is diluted by a large number of tributaries, the extent to which mine-derived metals may affect biota in the lower catchments is uncertain. To improve our understanding of the forms of potentially bioavailable metals entering the lower river system, we studied the partitioning and speciation of metals within the Lagaip River system. Dissolved and particulate metal concentrations decreased rapidly downstream of the mine due to dilution from tributaries. As a portion of the particulate metal concentrations, the more labile dilute acid-extractable forms typically comprised 10–30 % for As and Pb, 50–75 % for Cu and Zn, and 50–100 % for Cd. Only dissolved Cd, Cu and Zn remained elevated relative to the non-mine-impacted tributaries (<0.03, 0.5 and 0.3 μg/L), but the concentrations did not appreciably change with increasing dilution downriver. This indicated that release of Cd, Cu and Zn was likely occurring from the more labile metal phases of the mine-derived particulates. Chelex-labile metal analyses and speciation modelling indicated that dissolved copper and lead were largely non-labile and likely complexed by naturally occurring organic ligands, while dissolved cadmium and zinc were predominantly present in labile forms. The study confirmed that mine-derived particulates may represent a significant source of dissolved metals in the lower river system; however, comparison with water quality guidelines indicates the low concentrations would not adversely affect aquatic life.     

Kinetic characterizing of soil trace metal availability using Soil/EDTA/Chelex mixture

The kinetic aspects are not usually tackled when mimicking the soil trace metal mobilization. In this work, a simple procedure is developed for measuring the kinetics of Pb, Cu and Cd transfer from the soil solid phase towards a resin sink. A ternary system of Soil/EDTA/Chelex was employed for mimicking the metal transfer from two agricultural soil samples into the Chelex. Two different kinetic regimes (P₁ and P₂) were observed. The kinetic profile of Pb was distinctly different from those of Cd and Cu. Basing on kinetic principles, two kinetic models were proposed for estimating the apparent rate constants of leaching and removal processes in, respectively, two binary mixtures of soil/EDTA and EDTA extracts/Chelex. Contrary to Pb, solid phase pools of Cd and Cu exchanged with the solution on short time scales. The kinetic rate of desorption occurred in following order: Pb < Cu ? Cd. Comparing the kinetics of binary systems, the desorption process was hypothesized to control the metal transfer. The parameters related to the desorption process were extended to the kinetic regimes of Soil/EDTA/Chelex and revealed that the soil to Chelex transfer of Pb is under kinetics control whereas the bulk concentration (affected by the size of particulate reservoir) is likely to control the Cd transfer. Cu presents an intermediate case.     

The exposition of a calcareous Mediterranean soil to toxic concentrations of Cr, Cd and Pb produces changes in the microbiota mainly related to differential metal bioavailability

The involvement of the bacterial community of an agricultural Mediterranean calcareous soil in relation to several heavy metals has been studied in microcosms under controlled laboratory conditions. Soil samples were artificially polluted with Cr(VI), Cd(II) and Pb(II) at concentrations ranging from 0.1 to 5000 mg kg⁻¹ and incubated along 28 d. The lowest concentrations with significant effects in soil respirometry were 10 mg kg⁻¹ Cr and 1000 mg kg⁻¹ Cd and Pb. However, only treatments showing more than 40% inhibition of respirometric activity led to significant changes in bacterial composition, as indicated by PCR-DGGE analyses. Presumable Cr- and Cd-resistant bacteria were detected in polluted microcosms, but development of the microbiota was severely impaired at the highest amendments of both metals. Results also showed that bioavailability is an important factor determining the impact of the heavy metals assayed, and even an inverted potential toxicity ranking could be achieved if their soluble fraction is considered instead of the total concentration. Moreover, multiresistant bacteria were isolated from Cr-polluted soil microcosms, some of them showing the capacity to reduce Cr(VI) concentrations between 26% and 84% of the initial value. Potentially useful strains for bioremediation were related to Arthrobacter crystallopoietes, Stenotrophomonas maltophilia and several species of Bacillus.     

Estimation of daily intake of potentially toxic elements from urban street dust and the role of oral bioaccessibility testing

The pseudo-total and oral bioaccessible concentration of six potentially toxic elements (PTEs) in urban street dust was investigated. Typical pseudo-total concentrations across the sampling sites ranged from 4.4 to 8.6 mg kg⁻¹ for As, 0.2-3.6 mg kg⁻¹ for Cd, 25-217 mg kg⁻¹ for Cu, 14-46 mg kg⁻¹ for Ni, 70-4261 mg kg⁻¹ for Pb, and, 111-652 mg kg⁻¹ for Zn. This data compared favourably with other urban street dust samples collected and analysed in a variety of cities globally; the exception was the high level of Pb determined in a specific sample in this study. The oral bioaccessibility of PTEs in street dust is also assessed using in vitro gastrointestinal extraction (Unified Bioaccessibility Method, UBM). Based on a worst case scenario the oral bioaccessibility data estimated that Cd and Zn had the highest % bioaccessible fractions (median >45%) while the other PTEs i.e. As, Cu, Ni and Pb had lower % bioaccessible fractions (median <35%). The pseudo-total and bioaccessible concentrations of PTEs in the samples has been compared to estimated tolerable daily intake values based on unintentional soil/dust consumption. Cadmium, Cu and Ni are well within the oral tolerable daily intake rates. With respect to As and Pb, only the latter exceeds the TDI_oral if we model ingestion rate based on atmospheric ‘dustiness’ rather than the US EPA (2008) unintentional soil/dust consumption rate of 100 mg d⁻¹. We consider it unlikely that even a child with pica tendencies would ingest as much as 100 mg soil/dust during a daily visit to the city centre, and in particular to the sites with elevated Pb concentrations observed in this study.