Metal transfer to plants grown on a dredged sediment: use of radioactive isotope 203Hg and titanium

Improperly disposed of dredged sediments contaminated with metals may induce long-term leaching and an increase of metal concentrations in ground waters and vegetal cover plants. The objective of the study was to quantify the sediment-to-plant transfer of Cu, Pb, Hg and Zn with a particular focus on the pathway of Hg and to determine whether the establishment of vegetal cover modifies the metal availability. A pot experiment with rape (Brassica napus), cabbage (Brassica oleraccea) and red fescue (Festuca rubra) was set up using a sediment first spiked with the radioisotope 203Hg. Zinc concentrations (197-543 mg kg(-1) DM) in leaves were higher than Cu concentration (197-543 mg kg(-1) DM), Pb concentration (2.3-2.6 mg kg(-1) DM) and Hg concentration (0.9-1.7 mg kg(-1) DM). Leaves-to-sediment ratios decreased as follows: Zn > Cu > Hg > Pb. According to Ti measurements, metal contamination by dry deposition was less than 1%. Mercury concentration in plant leaves was higher than European and French thresholds. Foliar absorption of volatile Hg was a major pathway for Hg contamination with a root absorption of Hg higher in rape than in cabbage and red fescue. Growth of each species increased Cu solubility. Zinc solubility was increased only in the presence of rape. The highest increase of Cu solubility was observed for red fescue whereas this species largely decreased Zn solubility. Dissolved organic carbon (DOC) measurements suggested that Cu solubilisation could result from organic matter or release of natural plant exudates. Dissolved inorganic carbon (DIC) measures suggested that the high Zn solubility in the presence of rape could originate from a generation of acidity in rape rhizosphere and a subsequent dissolution of calcium carbonates. Consequently, emission of volatile Hg from contaminated dredged sediments and also the potential increase of metal solubility by a vegetal cover of grass when used in phytostabilisation must be taken into account by decision makers.     

Spatial variations in the fate and transport of metals in a mining-influenced stream, North Fork Clear Creek, Colorado

North Fork Clear Creek (NFCC) receives acid-mine drainage (AMD) from multiple abandoned mines in the Clear Creek Watershed. Point sources of AMD originate in the Black Hawk/Central City region of the stream. Water chemistry also is influenced by several non-point sources of AMD, and a wastewater treatment plant (WWTP). In-stream conditions immediately downstream from point-source inputs result in a visual and rapid precipitation of hydrous iron oxides (HFO). Hydrous manganese oxides (HMO) are seen to coat rocks further downstream during some seasons. Synoptic spatial sampling was used to assess the fate and transport of Cu, Fe, Mn, and Zn during different years and hydrological seasons. Visual-MINTEQ was used to compare observed and model-calculated percentage particulate Cu and Zn as influenced by sorption to both HFO and HMO and aqueous complexation with dissolved organic carbon (DOC). Over distance, Cu and Fe were transported predominantly in the particulate phase, Mn in the dissolved phase, and Zn was intermediate in its distribution, with generally about 50% being in each phase. Under higher flows, a larger fraction of the total metals was present in the dissolved phase, along with a lower total suspended sediment (TSS) concentration. This is consistent with the source of TSS being predominantly in-stream precipitation of metals, which might be kinetically limited under higher flows. Modeling results most closely represented observed percentage particulate Cu under lower flows; a strong seasonal trend was not evident for Zn. Model over-predictions of percentage particulate Cu suggest non-equilibrium with sorbent phases or that something in addition to DOC was keeping a portion of the Cu in solution; under-predictions for Zn suggest an additional sorbent. Differences between observed and modeled particulate varied significantly between sites and seasons; ranging from 1 to 54% for Cu and 1 to 34% for Zn overall.     

The importance of organic matter distribution and extract soil:solution ratio on the desorption of heavy metals from soils

The lability (mobility and bioavailability) of metals varies significantly with soil properties for similar total soil metal concentrations. We studied desorption of Cu, Ni and Zn, from 15 diverse, unamended soils. These studies included evaluation of the effects of soil:solution extraction ratio and the roles of soil properties on metal desorption. Dcsorption was examined for each metal by computing distribution coefficients (Kd) for each metal in each soil where Kd = [M]soil/[M]solution, Results from soil:solution ratio studies demonstrated that Kd values for the metals tended to increase with increasing soil:solution ratio. This result also held true for distribution of soil organic matter (SOM). Because the soil:solution ratio has a significant effect on measured metal distributions, we selected a high soil:solution ratio to more closely approach natural soil conditions. Copper showed strong affinity to operationally defined dissolved organic matter (DOM). In this study, DOM was operationally defined based on the total organic carbon (TOC) content in 0.45-microm or 0.22-microm filtrates of the extracts. The Kd of Cu correlated linearly (r2 = 0.91) with the Kd of organic matter (Kd-om) where the Kd-om is equal to SOM as measured by Walkley-Black wet combustion and converted to total carbon (TC) by a factor of 0.59. These values representing solid phase TC were then divided by soluble organic carbon as measured by TOC analysis (DOM). The conversion factor of 0.59 was employed in order to construct Kd-om values based on solid phase carbon and solution phase carbon. SOM plays a significant role in the fate of Cu in soil systems. Soil-solution distribution of Ni and Zn, as well as the activity of free Cu2+, were closely related to SOM, but not to DOM. Kd values for Ni, Zn and free Cu2+ in a particular soil were divided by the SOM content in the same soil. This normalization of the Kd values for Ni, Zn, and free Cu2+ to the SOM content resulted in significant improvements in the linear relationships between non-normalized Kd values and soil pH. The semi-empirical normalized regression equations can be used to predict the solubility of Ni and Zn and the activity of free Cu2+ as a function of pH.     

Geochemical survey and metal bioaccumulation of three bivalve species (Crassostrea gigas, Cerastoderma edule and Ruditapes philippinarum) in the Nord Medoc salt marshes (Gironde estuary, France)

A 15-month experiment combining a geochemical survey of Cd, Cu, Zn and Hg with a bioaccumulation study for three filter-feeding bivalve species (oysters, Crassostrea gigas; cockles, Cerastoderma edule; and clams, Ruditapes philippinarum) was conducted in a breeding basin of the Nord Medoc salt marshes connected to the Gironde estuary, which is affected by historic polymetallic pollution. Regular manual surface measurements of temperature, salinity, pH and dissolved O(2) concentration and hourly multiprobe in situ measurements throughout several periods for 6-8 weeks were performed. The geochemical behavior of metals in water, suspended particulate matter and sediment and their ecotoxicological impact on the three bivalve species were evaluated by in situ exposure of juvenile oysters (water column) and adult cockles and clams (sediment surface). The physico-chemical parameters reflected seasonal variations and basin management. A distinct daily periodicity (except salinity) indicated intense photosynthesis and respiration. In summer, low dissolved O(2) saturations ( approximately 40-50%) occurred in the early morning at 30 cm above the sediment, whereas in depressions, the water column near the sediment surface was suboxic. Cadmium, Zn and Cu concentrations in suspended particulate matter exceeded typical estuarine values and were much higher than the homogeneously distributed concentrations in different depth ranges of the basin sediment. Particles collected in sediment traps showed intermediate metal concentrations close to sediment values. These results suggest trace metal recycling due to reductive dissolution under suboxic conditions at the sediment surface resulting in trace metal release to the water column and adsorption onto suspended particles. Dissolved Cd, Zn and Hg concentrations (e.g. 13-136 ng l(-1); 0.3-25.1 microg l(-1) and 0.5-2.0 ng l(-1), respectively) in the basin corresponded to the concentration range typically observed in the Gironde estuary, except for some maximum values attributed to metal recycling. In contrast, dissolved Cu concentrations (1.08-6.08 microg l(-1)) were mostly higher than typical estuarine values, probably due to recycled Cu complexation by dissolved organic matter. Growth, bioaccumulation rates and kinetics in the whole soft body of the bivalves were analyzed every 40 days. Although Cd bioaccumulation of oysters was lower in the basin than in the estuary during the same period (27,000 ng g(-1), dry weight and 40,000 ng g(-1), respectively) these values are largely above the new human consumption safety level (5000 ng g(-1), dw; European Community, 2002). For cockles and clams, Cd bioaccumulation was lower, reaching 1400 ng g(-1) and 950 ng g(-1), respectively. Similar results were obtained for Zn and Cu suggesting physiological differences between the species and/or differences in the exposure of the organisms due to physico-chemical conditions and metal distribution between dissolved and particulate phases. In contrast, Hg bioaccumulation was highest for cockles reaching bioconcentration factors of approximately 200,000, which even exceeded that of Cd in oysters (50,000) for the same exposition period. Nevertheless, Hg concentrations remained relatively low in the three bivalve species.     

Patterns of metal bioaccumulation in two filter-feeding macroinvertebrates: Exposure distribution, inter-species differences and variability across developmental stages

This study focused on the metal bioaccumulation of two aquatic insects (Ephoron virgo and Hydropsyche spp.) in order to evaluate the spatial distribution of metals, the interspecific differences between both filter-feeders and the bioaccumulation dynamics during E. virgo development stages. Hg, Cd, Ni, Cr, As, Pb, Cu, Ti, Zn and Mn were quantified in insects and in suspended particulate matter (SPM) sampled downstream and upstream of a chemical plant, where more than 300,000 t of polluted sediments are deposited. Hg concentrations were one order of magnitude higher downstream of the sediment dump, which showed that the Hg pollution originated in the chemical plant. Cd, Ni, Cr, Pb, Ti, Zn and Mn in invertebrates revealed that metal pollution was present upstream in other parts of the river. Interspecific differences were observed for all metals but Mn; significantly higher concentrations were observed in E. virgo over Hydropsyche exocellata, except for Cd, which showed 10-fold higher values. Hg and Cd increased until E. virgo nymphs reached 11 mm and decreased afterwards in late instars when nymphs were about to emerge. Cr, Pb, Ti and Mn decreased along early instars followed by a steady state in late instars. Similar values were obtained for Cu, As and Zn along all instars. Sexual differences between males and females of E. virgo were observed for Cd, Cu and Mn. Hg and Cd persistence was strong across developmental stages since high concentrations were found in eggs and emerging adults. Because the behavior of different metals varied for the two species and during the developmental stages of E. virgo, care should be taken in the interpretation of insect metal concentrations when analyzing the food chain transfer of metals in river ecosystems.     

Influence of sediment redox conditions on release/solubility of metals and nutrients in a Louisiana Mississippi River deltaic plain freshwater lake

The influence of sediment redox conditions on solubility of selected metals and nutrients in sediment from a coastal Louisiana freshwater lake (Lake Cataouatche) receiving diverted Mississippi River water was quantified. Sediment redox was cycled step wise in 50 mV increments between oxidized (-200 to +500 mV) and reduced (+500 to -200 mV) conditions. Changes in sediment oxidation/reduction status and pH influenced solubility of both metals and nutrients. When redox potential (Eh) was increased from -200 to +500 mV, sediment pH decreased from 7.1 to 5.7. When the sediment Eh decreased from +500 to -200 mV, pH increased from 5.7 to 7.1. The increase in sediment acidity upon oxidation resulted in the release of the Pb, Ca, Mg, Al, and Zn into solution. The solution concentration of these elements was inversely proportional to Eh (P相似文献   

Metal speciation in sulphidic sediments: a new method based on oxidation kinetics modelling in the presence of EDTA

The solid phase partitioning of metals (Zn, Cu and Pb) was determined in four anoxic, metal polluted sediments by investigating at pH 8 the 1 day oxidation kinetics of the metal sulphide phases present in the sediments in a background solution containing excess EDTA. A mathematical model consisting of a combination of two pseudo-first order reactions was used to fit the metal release data as a function of oxidation time. The model permitted to fractionate the trace metals in a 'quickly-oxidizable' and a 'slowly-oxidizable' fraction, which could be assigned to two different trace metal pools, respectively (1) FeS minerals (e.g. amorphous FeS, mackinawite) and (2) discrete trace metal sulphide phases. The sum of the fractions associated with these sulphide pools was taken as an approximation for the sulphide-associated fraction of the trace metals and coincided (for the case of Zn and Pb) with the sulphide-associated fraction derived from the analysis of acid volatile sulphide (AVS) and simultaneously extracted metals (SEM). Oxidation kinetics modelling allowed also determining the sulphide-associated fraction of a broad range of trace metals (as demonstrated for Cu) more accurately than the AVS/SEM method, which suffers from non-efficient extraction of a number of trace metal sulphides. A correction was made for the determination of the sulphide-associated fraction by subtracting the trace metal fraction dissolved after 1 day under anoxic conditions in the background EDTA solution. The combination of (1) one day oxidation kinetics modelling and (2) correction for the 1 day anoxic EDTA-soluble fraction is a suitable method to determine accurately the true sulphide speciation of trace metals in anoxic sediments.     

Effects of experimental CO2 leakage on solubility and transport of seven trace metals in seawater and sediment

The impact of CO₂ leakage on solubility and distribution of trace metals in seawater and sediment has been studied in lab scale chambers. Seven metals (Al, Cr, Ni, Pb, Cd, Cu, and Zn) were investigated in membrane-filtered seawater samples, and DGT samplers were deployed in water and sediment during the experiment. During the first phase (16 days), “dissolved” (< 0.2 µm) concentrations of all elements increased substantially in the water. The increase in dissolved fractions of Al, Cr, Ni, Cu, Zn, Cd and Pb in the CO₂ seepage chamber was respectively 5.1, 3.8, 4.5, 3.2, 1.4, 2.3 and 1.3 times higher than the dissolved concentrations of these metals in the control. During the second phase of the experiment (10 days) with the same sediment but replenished seawater, the dissolved fractions of Al, Cr, Cd, and Zn were partly removed from the water column in the CO₂ chamber. DNi and DCu still increased but at reduced rates, while DPb increased faster than that was observed during the first phase. DGT-labile fractions (Me_DGT) of all metals increased substantially during the first phase of CO₂ seepage. DGT-labile fractions of Al, Cr, Ni, Cu, Zn, Cd and Pb were respectively 7.9, 2.0, 3.6, 1.7, 2.1, 1.9 and 2.3 times higher in the CO₂ chamber than that of in the control chamber. Al_DGT, Cr_DGT, Ni_DGT, and Pb_DGT continued to increase during the second phase of the experiment. There was no change in Cd_DGT during the second phase, while Cu_DGT and Zn_DGT decreased by 30% and 25%, respectively in the CO₂ chamber. In the sediment pore water, DGT labile fractions of all the seven elements increased substantially in the CO₂ chamber. Our results show that CO₂ leakage affected the solubility, particle reactivity and transformation rates of the studied metals in sediment and at the sediment-water interface. The metal species released due to CO₂ acidification may have sufficiently long residence time in the seawater to affect bioavailability and toxicity of the metals to biota.     

Distribution of some trace metals in Lochnagar, a Scottish mountain lake ecosystem and its catchment

Anthropogenic trace metals enter the entire ecosystem of Lochnagar solely through atmospheric deposition. Trace metals, including Hg, have been monitored in atmospheric deposition and lake water, and measured in catchment vegetation, aquatic plants and zooplankton, revealing contamination levels in the ecosystem. Furthermore, 17 sediment cores were taken from different areas of the lake. Hg, Pb, Cd, Zn and Cu were analysed in all the cores, which show that the sediments have been heavily contaminated by these trace metals since the 1860s. The distribution of trace metals in the lake sediments was found to be heterogeneous, with concentrations in the surface sediments varying significantly: 110-250 ng/g, 100-360 microg/g, 39-180 microg/g, 0.3-1.9 microg/g and 8-25 microg/g for Hg, Pb, Zn, Cd and Cu, respectively. Trends in the concentration profiles for different trace metals in the same core are different, as are the trends of the profiles for the same metal in different cores. Hence, a single sediment core cannot represent the pollution history of the whole lake. As the soils and sediments contain a high proportion of plant debris and the debris has a high affinity for Hg, resulting in Hg enrichment. Hg was measured in plant debris (> 63 microm) separated from catchment soils and lake sediments. Plant debris may play an important role in storing and transferring Hg in this ecosystem.     

Effect of redox potential on heavy metal binding forms in polluted canal sediments in Delft (The Netherlands)

Heavy metal binding forms for Cu, Zn and Pb were determined at four representative sediment sites in the canals of Delft (The Netherlands), using selective chemical extraction methods. Small differences (on average <5%) were found between duplicate extraction experiments. The dominant Cu binding form was always related to sulphide and organics in the sediment. Zn was mainly bound to iron+manganese (hydr)oxides, whereas Pb was rather evenly distributed over the different labile and non-labile binding fractions. A gradual (over about 1 month) increase in redox potentials of the anaerobic sediments led to a 7-37% sediment release of the above heavy metals; this could mainly be ascribed to oxidation of the heavy metal-sulphide bindings. Part of the released heavy metals was re-adsorbed by the labile binding phases ("exchangeable" and "carbonate bound"). Contrary to expectations, we found a decrease rather than an increase in the Fe+Mn (hydr)oxide binding forms. This can probably be ascribed to non-equilibrium reactions in the time span of the experiments, as well as side reactions such as complexation with humic acids and hindered precipitation reactions due to organic matter coatings.     

Influence of a salt marsh plant (Halimione portulacoides) on the concentrations and potential mobility of metals in sediments

Influence of Halimione portulacoides, commonly found in temperate salt marshes, on sediment metal contents, speciation and potential mobility in case of sediment re-suspension was evaluated. Both colonized and non-colonized sediments were studied for total Cd, Cu, Pb and Zn contents and metal fraction exchangeable to water collected in situ. Sediment elutriates, prepared with water collected from each site, were used to simulate a sediment re-suspension phenomenon. As the characteristics and degree of contamination of sediments may influence system behaviour, salt marshes of two Portuguese estuaries, Cavado (NW coast) and Sado (SW coast), were studied. Cu, Pb and Zn contents higher than ERL (quality guideline, effect range-low) were observed, indicating potential risks for living organisms. Strong Cu-complexing organic ligands, also determined in both water and elutriates, were higher in rhizosediment elutriates, at concentrations similar, or even higher, to those of Cu. Such ligands condition metals speciation in the water column and probably also metal bioavailability. From rhizosediment significant amounts of Cu and Zn were transferred to the aqueous phase, concentrations 2-8 times higher than concentrations present in water. In contrast, elutriates of non-colonized sediment removed metals from water, Cu and Zn levels in elutriates being 2-6 times lower than initial ones. Cd and Pb levels in water and elutriates were not measurable in most cases. Results clearly indicate that metals potential solubility in the rhizosphere of plants was markedly higher than that in the surrounding sediment. The obtained results indicated that H. portulacoides presence (and probably other salt marsh plants) may cause a marked increase in metals concentrations in dissolved phase (pore water or even water column if rhizosediment is re-suspended). As salt marsh plants may be abundant in temperate and subtropical estuaries and costal lagoons, this phenomenon should not be disregard in future studies towards the sustainable management of such environments.     

Cadmium and zinc uptake by volunteer willow species and elder rooting in polluted dredged sediment disposal sites

Salix species and Sambucus nigra L. (elder) naturally invade dredged sediment landfills and are commonly encountered on substrates contaminated with heavy metals. Foliar concentrations of Cd and Zn in four Salix species and elder were explored in the field. Metal contents in dredged sediment derived soils were elevated compared to baseline concentration levels reported for Flanders. To evaluate foliar concentrations, reference data were compiled from observations in nurseries, young plantations and unpolluted sites with volunteer willow vegetation. Willows grown on polluted dredged sediment landfills showed elevated foliar Cd and Zn concentrations (>6.6 mg Cd/kg DW and >700 mg Zn/kg DW). This was not the case for elder. For willow, a significant relation was found between soil total Zn or Cd and foliar Zn or Cd, regardless of age, species, or clone. Willows proved to be useful bioindicators. Results indicated a possible threat in long-term habitat development of willow brushwood from transfer of Cd and Zn to the food web.     

Heavy metal stabilization in contaminated road-derived sediments

There is increasing interest in the stabilization of heavy metals in road-derived sediments (RDS), to enable environmentally responsible reuse applications and circumvent the need for costly landfill disposal. To reduce the mobility of heavy metals (i.e. Cu, Pb and Zn) the effectiveness of amendments using phosphate, compost and fly ash addition were investigated using batch leaching experiments. In general, phosphate amendments of RDS were found to be ineffective at stabilizing heavy metals, despite being used successfully in soils. Phosphate amendment resulted in enhanced concentrations of dissolved organic carbon (DOC), which increased the solubilisation of heavy metals via complexation. Amendment with humified organic matter (compost) successfully stabilized Cu and Pb in high DOC leaching RDS with an optimum loading of 15-20% (w/w). Compost, however, was ineffective at stabilizing Zn. Increasing the pH by amending RDS/compost blends with 2.5-15% (w/w) coal fly ash resulted in the stabilization of Zn, Cu and Pb. However, above a pH of ∼ 7.5 and 8 enhanced leaching of organic matter resulted in an increase in leached Cu and Pb, respectively. Accordingly, the optimum level of fly ash amendment for the RDS/compost blends was estimated to be ca. 10%. Boosted regression trees analysis (BRT) of the data revealed that DOC accounted for 56% and 65% of the Cu and Pb leaching, respectively, whereas pH only accounted for ca. 18% of Cu and Pb leaching. RDS sample characteristics (i.e. metal concentrations, size fractionation and organic matter content) were more important at reconciling the leaching concentrations of copper Cu (27%) than Pb (16%). The most important parameter explaining Zn leaching was pH. Overall, the choice of a suitable stabilization agent/s depends on the composition of RDS with respect to the amount of organic matter present, and the sorption chemistry of the heavy metal of interest.     

Assessment of river Po sediment quality by micropollutant analysis

Trace metals, PCB congeners and DDT homologues were determined in composite sediment samples collected from 10 representative sites along the river Po in two separate seasons. The aim was to identify the most anthropogenically impacted areas for future monitoring programmes and to aid development of Italian sediment quality criteria. The surface samples were collected during low flow conditions. Trace metal concentrations were assayed by electrothermal (Cd, Co, Cr, Cu, Ni, Pb), flame (Fe, Mn, Zn) or hydride generation (As) atomic absorption spectrometry after microwave assisted acid digestion. Hg was determined on solid samples by automated analyser. Organic microcontaminants were determined by gas-chromatography with 63Ni electron capture detector after Soxhlet extraction. Concentrations of trace metals, total PCB and DDT homologues showed two distinct peaks at the sites immediately downstream of Turin and Milan, respectively, and in each case decreased progressively further downstream. Principal component analysis identified three major factors (from a multi-dimensional space of 35 variables) which explained 85-90% of the total observed variance. The first and second factors corresponded to anthropogenic inputs and geological factors on sediment quality; the third included seasonal processes of minor importance. Sediment quality assessment identified Cd, Cu, Hg, Pb, Zn and organic microcontaminants as posing the most serious threats to river sediment quality. A reference site within the Po basin provided useful background values. Moderate pollution by organochlorine compounds was ascribed both to local sources and to atmospheric deposition.     

Characterization of copper complexation with natural dissolved organic matter (DOM)--link to acidic moieties of DOM and competition by Ca and Mg

We investigated Cu complexation by three dissolved organic matters (DOMs) collected by reverse osmosis (RO). Alkalimetric titration, pH-stat Cu and Ca titrations, pH edges of Cu–DOM complexation, and Ca/Mg–Cu exchange experiments were investigated at I=10⁻² M for DOM samples of 10 mg C/L. The proton and Cu binding characteristics indicated similarity for all three DOMs. All Cu titrations employed ion selective electrode measurement and indicated the presence of relatively small amounts of strong Cu-binding sites. Four distinct classes of Cu binding sites are required for FITEQL 4.0 to provide good fits to the entire curves. The estimated total Cu binding site density is 4.55 mmol/g C, much less than the total acidity but very close to the phenolic site content. Cu–DOM complexation increases approximately 10-fold per pH unit, even at relatively high pH (>8). We suggest that sites characterized as phenolic based on alkalimetric titration, not carboxyl sites, account for the majority of Cu complexation under natural water conditions, and Cu–DOM complexation is principally through the replacement of H⁺ by Cu²⁺ at the phenolic binding sites. The Cu–H exchange ratio is 1:1 for the first three sites and about 1:2 for the 4th site. This 4-site model describes well the pH dependency of Cu–DOM complexation and provides good estimates of free Cu concentrations throughout wide total copper (Cu_T) and pH ranges. Comparison between Ca–DOM and Cu–DOM complexation demonstrated that (i) Ca–DOM complexation increases much less than an order of magnitude per pH unit and decreases at higher Ca concentration, different from that of Cu–DOM complexation; and (ii) Cu–DOM complexation is highly non-linear, in contrast to the much reduced extent of non-linearity of Ca–DOM complexation. Ca/Mg–Cu exchange experiments showed small competition effect, less than expected by a simple competition model, and the competition tended to reduce with increasing Ca or Mg concentrations. The extent of the competition by Mg and Ca are essentially comparable. Put all together, it suggests that Ca and Mg are preferably bound by carboxyl sites, especially at relatively high concentrations, resulting in a weakened apparent competition effect.     

Contaminants in sediments: remobilisation and demobilisation

In this study, the contaminated anoxic sediment of the Mulde reservoir (Saxony, Germany) was investigated. Several sediment cores were analysed for heavy metals and organic chemicals such as chlorobenzenes and DDTs. The comparison between anoxic and oxidised sediment cores showed the potential danger for heavy metal (Zn and Cd) remobilisation from sediment due to bioturbation or resuspension by flooding. Chemical sequential extraction was used to describe partitioning of heavy metals among different mineralogical components in the sediments. Results showed remobilisation of Zn and Cd from the sediments. The stable fraction (organic/sulfidic-bound) of Zn and Cd decreased from 10 to 3%, and from 35 to 5%, respectively. Simultaneously, the carbonate fraction increased from 3 to 12% for Cd and from 10 to 22% for Zn. Furthermore, the simulation of the diffusion of organic pollutants showed remobilisation of 1,4-dichlorobenzene. The results confirmed the necessity of sediment remediation in the reservoir. Capping seems to be a promising approach for a low-cost remediation.     

Intra- and inter-annual variation of Cd, Zn, Mn and Cu in foliage of poplars on contaminated soil

The uptake of trace metals in the leaves of fast-growing woody species is a crucial factor in ecological risk assessment and in the evaluation of phytoextraction potentials. In this study, we present a long-term data series of foliar Cd, Zn, Mn and Cu concentrations in poplar (Populus trichocarpa x P. deltoides). Leaves were collected every three weeks from 2001 until 2007 on three sites, (i) a new plantation on an alluvial soil polluted by river sediments, (ii) a new plantation on an unpolluted soil and (iii) a 10-year old plantation on a polluted dredged sediment soil. In addition, tree rings were measured on the alluvial soil in order to better assess growth over the past seven years. Foliar concentrations of Cd, Zn and Mn decreased considerably with time in the new plantation on polluted soil. Concentrations of Zn and Mn decreased in the new plantation on unpolluted soil as well. The older plantation on polluted soil did not show changes in foliar concentrations for Cd, Zn or Mn. Foliar Cu concentrations slightly increased for all sites. Within one growing season, foliar concentrations of Cd, Zn, Cu and Mn increased towards the end of the season. The tree ring data of the poplars on the alluvial soil indicated a strong decrease in growth due to declining tree condition from 2005 onwards, the same year that foliar Cd and Zn concentrations markedly decreased. Lower transpiration rates probably induced a lower uptake of dissolved trace metals. It is concluded that stand health and growth rate have a strong impact on the variation of foliar trace metal concentrations over time.     

Disposal of heavy metal‐contaminated sediment from Ulsan Bay,South Korea: treatment processes and legal framework

The effectiveness of two different management schemes to dispose of heavy metal‐contaminated sediments from Ulsan Bay, South Korea, soil washing and solidification/stabilization, were evaluated through a series of analyses. NaOH proved to be an effective washing reagent for As, extracting 75% of the As in sediment samples. EDTA was found to significantly enhance the extraction of Cu, Pb and Zn. However, complete removal of any metals was not achieved even after application of 100 mM concentrations of washing reagents. Therefore, a solidification/stabilization technique was applied to dredged sediment samples using ordinary Portland cement (1–40%) and fly ash (～20%). Solidified sediments did not release meaningful amount of the metals via leaching tests. Our results suggest that solidification/stabilization is a better option for effective disposal of heavy metal‐contaminated sediments than soil washing. A legal framework for the treatment of hazardous wastes and contaminated soils in Korea is discussed.     

Heavy metals in the tissues of common dolphins (Delphinus delphis) stranded on the Portuguese coast.

The concentrations of Hg, Sn, Cr, Zn, Ni, Co, Cd, Mn, Fe and Cu were determined in the liver, kidney and muscle of 24 common dolphins stranded on the Portuguese coast between 1995 and 1998. Nitric acid was used to extract the metals from the tissues for analysis by inductively-coupled plasma/atomic emission spectroscopy (ICP/AES). Those metals with relatively higher concentrations included Fe, Zn and Hg, particularly in liver. Other metals including Cr, Ni and Cd tended to show much lower levels, or were even undetected (e.g. Co). Different metals seemed to show different temporal trends, although due to substantial variations of the mean concentrations for each year obtained, such temporal pattern has to be studied further. Total Hg concentration in the kidney, muscle and particularly liver, were higher in females than in males. Total Hg concentrations in all the organs increased with body length of dolphins, whilst those of Zn and Cu in muscle decreased with dolphin length. A strong correlation was found between essential metals Zn and Cu in muscle, possibly resulting from sequestration of these metals by metallothionein. In addition, significant co-associations existed between the same metal (e.g. Hg, Sn and Zn) in different organs.     

Spatial and seasonal variation in heavy metals in the sediments and biota of two adjacent estuaries, the Orwell and the Stour, in eastern England

A study was made of the concentrations of the elements As, Cd, Cu, Hg, Mn, Ni, Pb and Zn in the sediments and biota of two adjacent estuaries, the Orwell and Stour, in eastern England. The Orwell Estuary, with its urbanized head, was more contaminated with heavy metals than the Stour Estuary. Generally, in both estuaries, concentrations of metals were highest towards the head and the mouth. Saltmarsh sediments accumulated higher concentrations of most metals than mudflat sediments. Metal concentrations in the biota showed marked interspecific differences; Mytilus edulis had higher concentrations of Cd, Littorina littorea higher concentrations of Cu and Mn and Arenicola marina higher concentrations of Hg. Invertebrates from the Orwell had higher metal concentrations than those from the Stour. Algae had generally lower levels of metals than invertebrates. Metal concentrations were greatest and more variable in the top 10 cm of sediment. Metals were at greatest concentrations in winter and lowest in summer in sediments, algae and invertebrates. Mercury concentration increased with size in the three invertebrate species studied, but Cd and Zn generally were at higher concentrations in younger animals. Comparisons of sediments with average shale values indicated anthropogenic enrichment with several metals but it was considered that only Pb, at some sites, and possibly Hg posed potential threats to the ecology of the estuaries.