Influences on copper bioaccumulation,growth, and survival of the midge,Chironomus tentans,in metal-contaminated sediments

Sediment bioassays with larvae of the midge, Chironomus tentans, were used to evaluate influences on the bioavailability and toxicity of copper (Cu) in sediments with a wide range of concentrations of metals, acid-volatile sulfide (AVS), and other physicochemical characteristics. Sediments were collected from sixteen lakes in Michigan, USA, and from twelve sites in the Clark Fork River drainage of Montana, USA, which are contaminated with metals from mining activities and from other anthropogenic sources. Bioassays with C. tentans larvae were conducted for ten days in a static-renewal test system, with endpoints of survival, growth, and metal bioaccumulation. Bioaccumulation of copper (Cu) was strongly correlated with Cu concentrations in porewater, and was increased significantly at Cu concentrations less than those affecting growth or survival. Midge survival and growth were not significantly correlated with concentrations of Cu in sediment or porewater, and were poorly predicted by ratios of acid-extractable metals to AVS in sediments. Principal components analysis indicated that Cu concentrations in porewater and bioaccumulation of Cu by midge larvae were influenced by AVS, sediment organic carbon, and porewater pH, and that toxicity was associated with high concentrations of Cu, high concentrations of zinc (Zn) and ammonia. No toxicity was observed in several sediments which contained low concentrations of AVS and high concentrations of Cu and Zn. In sediments which contain little AVS, bioavailability of metals may be controlled by constituents other than sulfides, such as organic matter and metal hydrous oxides. These results indicate that assessments of toxicity in metal-contaminated sediments should evaluate the importance of metal-binding phases other than sulfides, and the possible contributions of ammonia or other toxicants to toxicity in sediment bioassays.The U.S. Government right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.     

The Effect of Sediment Type and pH-Adjustment on the Porewater Chemistry of Copper- and Zinc-Spiked Sediments

The spiking of metals into sediments lowers pH, raises the oxidative state, and exacerbates the partitioning of Fe, Mn, and spiked metal to the porewater. This study reports the geochemical response of three sediments of varying metal-binding capacity to Cu-/Zn-additions and the influence of pH-adjustment on the major metal-partitioning processes. The increase in redox potential and porewater metal concentrations observed in metal-spiked sediment was minimized by sediment neutralization to pH 7 irrespective of sediment type. In the presence of minimal sulfide concentrations, porewater metal concentrations suggested a greater affinity of copper for organic carbon than zinc, which was thought more dependent on iron oxyhydroxide phases. The amount of iron in the porewater of metal-spiked pH adjusted sediment was, in turn, affected by the type and concentration of spiked metal in the porewater. Increasing porewater concentrations of copper and zinc corresponded to decreasing and increasing porewater iron concentrations, respectively. Porewater copper appeared to act as a toxicant of Fe(III) reducing bacteria, while porewater zinc is thought to have had a stimulatory effect. The present study provides further insight on geochemical changes occurring to metal-spiked sediments and their implications for the interpretation of toxicity tests.     

Distribution and concentrations of naturally-occurring radionuclides in sediments in a uranium mining area of northern Saskatchewan,Canada

Uranium mining and milling operations can contribute to environmental degradation through the increased release of naturally-occurring radionuclides. However, studies of the interactions of these radionuclides with freshwater sediments have been limited. The present study examined the vertical distribution of uranium, thorium, radium-226, polonium-210 and lead-210 in undisturbed sediment cores collected in the vicinity of mining, milling and exploration activities. Uranium levels in surface sediments ranged from 1.9 to 5650 μg g⁻¹, Ra-226 from <0.1 to 480 pCi g⁻¹ and Pb-210 from 0.8 to 931 pCi g⁻¹ in the samples reported here, with the highest values occurring downstream of waste rock disposal areas. Concentrations usually decreased with depth, and there was little evidence of any strong effect of bioturbation on radionuclide profiles at the scale examined here. Mathematical models of uranium and radium-226 adsorption on and movement into the sediment were constructed, based on expected adsorption coefficients and estimated loading. The model predictions of radionuclide distribution with depth were qualitatively similar to those actually measured, but the predicted concentrations were generally lower than those observed, both in unaffected areas and in areas adjacent to uranium extraction activities.     

Ammonium adsorption in sediments of a tropical mangrove forest (Thailand) and a temperate Wadden Sea area (Denmark)

Dimensionless ammonium adsorption coefficients (K) were determined for tropical mangrove forest sediments and temperate Wadden Sea sediments. The K values were obtained from ammonium adsorption isotherms of KCl (2 M) extractable ammonium versus dissolved ammonium in the porewater; relationships that can be described by a linear model. Linearity was evident even at low porewater concentrations for mangrove sediment, according to isotherms based on KCl extractions on untreated sediment profiles. K-values were low in mangrove forest sediments (0.04–0.10), and higher in Wadden Sea sediments (0.17–1.12). The vertical range in K-values was larger at the vegetated sites, with highest values in subsurface sediments, which suggests differences in quantity and quality of the fine organic and inorganic fractions. The low ammonium adsorption in the mangrove sediments can be explained by a higher concentration of competitive cations, especially iron, in this iron-rich environment. The low adsorption of ammonium in mangrove sediments and vegetated surface sediment of the Wadden Sea was negatively related to the organic content of the sediments, which is in contrast to findings for other marine sediments. We suggest that organic material may have a diluting effect on the exchange capacity in fine-grained sediments, and that organic coatings may block ion exchange sites on clay surfaces. Thus, there may be a organic-rich ‘wetland’ versus organic-poor ‘sediment’ effect. This revised version was published online in July 2006 with corrections to the Cover Date.     

A study on heavy metal partitioning in sediments from Poyang Lake in China

The partitioning of heavy metals in sediment from Poyang Lake, the largest freshwater lake in China, was studied. The majority of the heavy metals, copper, lead and zinc, were found to be bound to the organic matter and iron oxide phases. The distribution of the metals among the different geochemical phases in sediments was controlled by the abundance of the geochemical phases. An equilibrium adsorption model developed by Oakley et al. (1981) and Davies-Colley et al. (1984) was applied to predict the partitioning of copper among different geochemical phases in the sediments of Poyang Lake. The conditional equilibrium constants (slopes of the linear portions of the adsorption isotherms) were determined using an artificial water-sediment system at various pH's. This model was used to describe the heavy metal partitioning in sediment samples from Poyang Lake and the predicted results were consistent with those measured in the laboratory.     

Sediment toxicity and heavy metals in the Kattegat and Skaggerak

Superficial (0 to 2 cm) sediments were sampled from 62 sites in Kattegat and Skagerrak during autumn 1989 and spring 1990, tested for toxicity to Daphnia magna and Nitocra spinipes (Crustacea) and analyzed for heavy metals (Cd, Cr, Cu, Hg, N, Pb, Zn), nutrients (N and P) and organic carbon. Whole sediment toxicity to Nitocra spinipes, expressed as 96-h LC50, ranged from 1.8 to > > 32 percent sediment (wet wt), which is equivalent to 0.63 to 53 percent dry wt. Sediment total metal concentrations (mg kg^-1 dry wt) ranged from 0.01 to 0.32 for Cd, 8 to 57 for Cr, 3 to 40 for Cu, 0.03 to 0.86 for Hg, 3 to 43 for Ni, 6 to 37 for Pb and 21 to 156 for Zn. Analyzed concentrations of heavy metals were tested for correlation with whole sediment toxicity normalized to dry wt, and significant correlations (Spearman p<0.05) were found for Cd, Cr, Cu, Hg, and Ni. However, the analyzed concentrations of these metals were below the spiked sediment toxicity of these heavy metals to N. spinipes, except for Cr and Zn for which analyzed maximum concentrations approached the 96-h spiked sediment LC50s. There was no improvement in correlation between the sum of heavy metal concentrations normalized to their spiked toxic concentrations (Toxic Unit approach) and the whole sediment toxicity. Calculated heavy-metal-derived toxicity based on toxic units and whole sediment toxicity ranged from 0.1 to 24 (mean value 2.3 and SD 4.2). Theoretically, a value of 1.0 would explain whole sediment toxicity from measured metal concentrations using this approach. Thus, in spite of the fact that the total concentrations of the heavy metals were sufficient to cause toxicity based on an additive model for most of these sediments, the observed toxicity of the sediments from Kattegat and Skagerrak could not exclusively be explained by the concentrations of heavy metals, except for Cr and Zn at their maximum concentrations. Therefore, other pollutants than these heavy metals must also be considered as possible sediment toxicants.     

青山水库表层沉积物重金属污染特征及生态风险评价

在位于浙江省临安市的青山水库采集了具有代表性的8个样点的表层沉积物样品,分析比较了样品中As、Cr、Cu、Ni、Mn、Pb、Zn等7种重金属总量的差异,采用BCR连续提取法对重金属不同形态(酸提取态、可还原态、可氧化态、残渣态)进行分析.采用地积累指数法(I_geo)和Hakanson潜在生态风险指数法,对青山水库不同采样点表层沉积物中重金属的污染程度和潜在毒性与生态风险进行评价.结果表明: 青山水库表层沉积物重金属污染程度存在明显的空间差异,流经城区和工业园区的青山水库支流入库河口附近的表层沉积物重金属含量明显高于其他采样点.青山水库表层沉积物7种重金属中,Mn主要以酸提取态存在;Cu和Pb主要以可还原态形式存在;As主要以残渣态形式存在.流经城区的支流入库河口附近表层沉积物还原态和酸提取态重金属比例较高,对水生生物有一定的毒性风险.8个样点的表层沉积物7种重金属中,以As污染程度最高,潜在生态风险最大,其次是Cu、Ni、Mn、Pb和Zn,均处于轻度污染状态,而Cr处于清洁水平,潜在生态风险较低.不同采样点比较发现,分别流经城区的锦溪和工业园区的横溪入库河口附近表层沉积物重金属污染程度和潜在生态风险明显高于其他采样点.     

Internal wave-induced redox shifts affect biogeochemistry and microbial activity in sediments: a simulation experiment

Internal waves (seiches) are well-studied physical processes in stratified lakes, but their effects on sediment porewater chemistry and microbiology are still largely unexplored. Due to pycnocline oscillations, sediments are exposed to recurrent changes between epilimnetic and hypolimnetic water. This results in strong differences of environmental conditions, which should be reflected in the responses of redox-sensitive biogeochemical processes at both, the sediment–water interface and deeper sediment layers. We tested in a series of mesocosm experiments the influence of seiche-induced redox changes on porewater chemistry and bacterial activity in the sediments under well controlled conditions. Thereby, we excluded effects of changes in current and temperature regimes. For a period of 10 days, intact sediment cores from oligotrophic Lake Stechlin were incubated under constant (either oxic or anoxic) or alternating redox conditions. Solute concentrations were measured as porewater profiles in the sediment, while microbial activity was determined in the upper 0.5 cm of sediment. Oxic and alternating redox conditions resulted in similar ammonium, phosphate, and methane porewater concentrations, while concentrations of each analyte were considerably higher in anoxic cores. Microbial activity was clearly lower in the anoxic cores than in the oxic and the alternating cores. In conclusion, cores with intermittent anoxic phases of up to 24 hours do not differ in biogeochemistry and microbial activities from static oxic sediments. However, due to various physical processes seiches cause oxygen to penetrate deeper into sediment layers, which affects sediment redox gradients and increase microbial activity in seiche-influenced sediments.     

Using porewater profiles to assess nutrient availability in seagrass-vegetated carbonate sediments

We measured porewater profiles of inorganic (NH₄ ⁺, NO₃ ^–(+NO₂ ^–), PO₄ ^3– (hereafter referred to as DIP)) and organic (DON, DOP) nutrients in seagrass-vegetated sediments at two sites in a shallow bay in Bermuda within close proximity (200 m) but subject to different nutrient loading. At both sites, total dissolved and inorganic nutrient concentrations were usually 1–2 orders of magnitude higher in the sediments than in the water column, with the exception of NO₃ ^–. Organic N and P were significant components of the total dissolved nutrient pools both in the sediment porewater and in the overlying water column (up to 75% for DON and 40% for DOP), and may be important in meeting plant nutrient demands. We used two approaches to examine how well porewater nutrient concentrations reflected the relative availabilities of N and P for seagrasses: (1) a simple stoichiometric nutrient regeneration model based on the N:P ratio of decomposing organic matter and porewater NH₄ ⁺ concentrations to predict porewater DIP, and (2) fitting of the porewater profiles to estimate rates of net nutrient production (or consumption), which reflects the balance between nutrient sources and sinks in the rhizosphere. The stoichiometric model indicated that sediment porewaters were depleted in P relative to N in the low-nutrient outer bay site, and enriched in P relative to N in the higher-nutrient inner bay site. These results are consistent with the mechanism of carbonate sediments in oligotrophic tropical environments being a strong sink for dissolved inorganic P and our previous work suggesting that nutrient enrichment causes P to become disproportionately more available than N. Net nutrient production rates of porewater P at both sites and N at the inner bay site were low (typically < 2%) relative to the nutrient demands of the seagrasses. The implications of the profile interpretation are two-fold: (1) the low rates of net nutrient production indicate diffusive losses from the root zone were insignificant and that nutrient turnover rates were high, except in the P-limited outer bay where N accumulated in sediment porewaters; and (2) because standing stock nutrient concentrations often represent a small fraction of the total nutrients cycled in the sediments, they are in many cases a poor indicator of nutrient availability. Based on our estimates of losses from the root zone, decomposition, and plant uptake we have constructed a rough budget for the cycling of P and N at our two sites.     

Adsorption of Cu and Zn onto Mn/Fe Oxides and Organic Materials in the Extractable Fractions of River Surficial Sediments

The roles of the extractable components (Mn oxides, Fe oxides, and organic materials) of surficial sediments in controlling metals adsorption were investigated. Cu and Zn adsorptions were conducted before and after the surficial sediments extracted with hydroxylamine hydrochloride, an oxalate solution, and H ₂ O ₂ , respectively. The extraction removed target components with extraction efficiencies from 63 to 98%. Nonlinear regression analyses of Cu and Zn adsorptions based on the assumption of additive Langmuir adsorption isotherm were employed to estimate the relative contributions of sediment components to Cu and Zn adsorptions. The results indicate that the greatest contribution to total Cu and Zn adsorption to the surficial sediments on a molar basis was from Mn oxides in the extractable fractions. Both Cu and Zn adsorption capacities of Mn oxides exceeded those of Fe oxides by approximately one order of magnitude, fewer roles were attributed to the adsorption of organic material (OM), and the estimated contribution of the residual fraction to total Cu and Zn adsorption was insignificant. These information implied that the roles of metal oxides (Fe and Mn oxides) in the extractable form of the surficial sediments, especially Mn oxides, was the most important component in controlling heavy metal transportation in aquatic environments.     

Bioavailability and Concentration of Heavy Metals in the Sediments and Leaves of Grey Mangrove, <Emphasis Type="BoldItalic">Avicennia marina</Emphasis> (Forsk.) Vierh,in Sirik Azini Creek,Iran

The concentration and bioavailability of Ni, Cu, Cd, Zn, and Pb in the sediments and leaves of grey mangrove, Avicennia marina, were studied throughout Sirik Azini creek (Iran) with a view to determine heavy metals bioavailability, and two methods were used. Results show that Zn and Ni had the highest concentrations in the sediments, while Cd and Cu were found to have the lowest concentrations in the sediments. Compared to the mean concentrations of heavy metals in sedimentary rock (shales), Zn and Cu showed lower concentration, possibly indicating that the origin of these heavy metals is natural. A geo-accumulation index (I _geo) was used to determine the degree of contamination in the sediments. I _geo values for Zn, Cu, Pb, and Ni showed that there is no pollution from these metals in the study area. As heavy metal concentrations in leaves were higher than the bioavailable fraction of metals in sediments, it follows that bioconcentration factors (leaf/bioavailable sediment) for some metals were higher than 1.     

The effects of in situ drying on sediment–phosphate interactions in sediments from an old wetland

We examined the effects of drying on sediment–P interactions for sediments from a shallow wetland ca. 6000 years old. Sediments from this wetland would have been subjected to numerous drying and wetting episodes during the life of the wetland. The factors affecting potential orthophosphate release were compared in surface sediments that had previously been desiccated for 3 months, surface sediments that had remained inundated and wet sediment 25–30 cm below the surface. All sediments released small amounts of orthophosphate once subjected to anaerobic conditions. Sulfate alone stimulated phosphate release from the surface sediment, irrespective of the previous hydrological status, whereas orthophosphate release from deep sediments was co-limited by carbon and sulfate. Decreases in soluble Fe (II) were measured concurrently with sulfate-stimulated P release, which is consistent with formation of iron sulfides. Similar numbers of culturable sulfate-reducing bacteria were obtained from the wet and dry sediments, their tolerance to desiccation explaining why release could occur after extensive drying of the sediment. Phosphate adsorption isotherms of the sediments showed that sediments from all sites had a relatively low affinity for ortho-phosphate. The adsorption data showed reasonable fit to the Freundlich adsorption isotherm. No difference in the maximum amount of ortho-phosphate uptake was observed if the sediment isotherm experiments were done under an inert atmosphere or, following exposure to air, suggesting that even anoxic sediments were not highly reduced. However, significant variations in the value of the Freundlich constants were observed. The results presented in this study are consistent with the hypothesis that repeated wetting/drying cycles select for bacteria that are tolerant to periods of desiccation and/or oxidation. Furthermore, repeated wetting and drying cycles may result in changes to sediment mineralogy.     

铜锈环棱螺对沉积物中重金属的生物积累及其与重金属赋存形态的关系

以铜锈环棱螺（Bellamya aeruginosa）为测试生物,采用28 d沉积物生物积累试验研究铜锈环棱螺对污染河流沉积物中重金属的生物积累,并探讨其与重金属赋存形态的关系.结果表明：铜锈环棱螺肝胰脏对Cd、Pb、Cu、Cr、Zn和Mn均具有较强的积累作用.不同重金属的积累量存在较大差别,Zn的积累量最多,占重金属总积累量的84.32%±4.36%,其次为Cu,占7.67%±2.84%;Pb、Cr和Mn的比例相对较少,分别为3.62%±1.84%、2.22%±1.03%和1.33%±0.15%;Cd所占比例最少,为0.83%±0.53%.肝胰脏中重金属元素之间的相关性均不显著.肝胰脏金属污染指数与沉积物污染综合指数具有显著的正相关关系,铜锈环棱螺可以作为沉积物重金属污染的监测生物.不同沉积物Cd、Cr、Zn和Mn的生物-沉积物积累因子（BSAF）具有较大的差异,Cu和Pb的BSAF比较稳定.Cd的生物积累与沉积物中Cd的可交换的与酸可溶态及可氧化态显著相关;Pb的生物积累与Pb的可还原态显著相关;Cu的生物积累与Cu的可氧化态显著相关;Mn的生物积累与Mn的可交换的与酸可溶态和可还原态显著相关;Cr和Mn的生物积累与其不同形态和总量均不相关.BSAF不宜作为衡量铜锈环棱螺对沉积物中重金属生物积累能力的指标.     

Sediment and Water Nutrient Characteristics in Patches of Submerged Macrophytes in Running Waters

(1) The relative importance of sediments and water as nutrient sources for submerged macrophytes in running waters is poorly understood. Here we present water and sediment nutrient characteristics within macrophyte patches in Bavarian rivers. (2) No significant differences between early (June/July) and late summer (August/September) sediment nutrient characteristics could be detected within macrophyte patches. Therefore, a single sediment sample per macrophyte patch was considered to be sufficient for characterising nutrient concentrations during the main growing season in running waters. (3) Sediment TP (total phosphorus) is not a useful parameter for predicting trophic status in running waters. Sediment porewater SRP (soluble reactive phosphorus) concentration is not correlated to water body SRP or TP concentration; nor is it correlated with sediment TP content. Potamogeton coloratus, a oligotrophic species, is associated with low overlying and porewater SRP concentrations but high sediment TP content. Eutrophic species, such as Potamogeton pectinatus, are associated with low sediment TP. (4) It is hypothesized that Chara hispida primarily takes up sediment ammonia for nitrogen nutrition. (5) Nutrient characteristics of the water body and the sediment of eight macrophyte species in Bavarian rivers are described.     

HCl-Extractable Metal Profiles Correlate with Bacterial Population Shifts in Metal-Impacted Anoxic Coastal Sediment from the Wet/Dry Tropics

Metal impacted, anoxic sediments from five sites at a coastal location in the wet/dry tropics of Australia were sampled during both wet and dry seasons. Metal concentrations in total sediment and porewater, and in potentially bioavailable and bioaccessible fractions, were measured. Pyrosequencing was used to sequence bacterial DNA extracted from the sediment, and the sequence data was used to generate community profiles at each sample site. Changes in bacterial populations between sites reflected changes in the concentrations of 7 metals/metalloids (Al, V, Mo, Ga, Zn, Cd, As), and best correlated with the HCl-extractable fraction of metals. Bacterial community structure was also related to physicochemical factors, such as redox potential and organic carbon. Despite a strong sulphide gradient across the transect, acid-volatile sulphide was not significantly correlated to bacterial community structure. We conclude that the bioaccessible fraction of metals to bacteria is partly comprised of particulates, and porewater alone is not a sufficient model for potential metal impact.

[Supplementary materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the two supplementary tables.]     

Heavy metals in the water and sediments of Oued Es-Souk,Algeria, a river receiving acid effluents from an abandoned mine

The Sidi Kamber Mine, abandoned since 1976, is still a source of acidic drainage entering the Oued Es-Souk River. An investigation of the rate of pollution of the Oued Es-Souk and the variation of its water quality showed that the mining waters are very acidic, with high concentrations of sulphate ions and dissolved heavy metals. Only lead reaches a significant level in the suspended matter. During mixing of the acid stream waters with uncontaminated river water, an amorphous orange precipitate forms and contributes to the removal of sulphate and certain heavy metals by adsorption and co-precipitation. Downstream, zinc and lead are concentrated in the sediments, while cadmium is mainly transported in the dissolved phase.     

Aquatic vegetation and trophic condition of Cape Cod (Massachusetts,U.S.A.) kettle ponds

The species composition and relative abundance of aquatic macrophytes was evaluated in five Cape Cod, Massachusetts, freshwater kettle ponds, representing a range of trophic conditions from oligotrophic to eutrophic. At each pond, aquatic vegetation and environmental variables (slope, water depth, sediment bulk density, sediment grain size, sediment organic content and porewater inorganic nutrients) were measured along five transects extending perpendicular to the shoreline from the upland border into the pond. Based on a variety of multivariate methods, including Detrended Correspondence Analysis (DCA), an indirect gradient analysis technique, and Canonical Correspondence Analysis (CCA), a direct gradient approach, it was determined that the eutrophic Herring Pond was dominated by floating aquatic vegetation (Brasenia schreberi, Nymphoides cordata, Nymphaea odorata), and the algal stonewort, Nitella. Partial CCA suggested that high porewater PO₄-P concentrations and fine-grained sediments strongly influenced the vegetation of this eutrophic pond. In contrast, vegetation of the oligotrophic Duck Pond was sparse, contained no floating aquatics, and was dominated by emergent plants. Low porewater nutrients, low sediment organic content, high water clarity and low pH (4.8) best defined the environmental characteristics of this oligotrophic pond. Gull Pond, with inorganic nitrogen-enriched sediments, also exhibited a flora quite different from the oligotrophic Duck Pond. The species composition and relative abundance of aquatic macrophytes provide good indicators of the trophic status of freshwater ponds and should be incorporated into long-term monitoring programs aimed at detecting responses to anthropogenically-derived nutrient loading.     

From geochemical background determination to pollution assessment of heavy metals in sediments and soils

Establishing geochemical background concentrations to distinguish the natural background from anthropogenic concentrations of heavy metals in sediments and soils is necessary to develop guidelines for environmental legislation. Due to the fact that the background concentrations strongly depend on geological characteristics such as mineral composition, grain size distribution and organic matter content, several normalization methods have been developed. Empirical (geochemical), theoretical (statistical) and integrated methods (combining both empirical and theoretical methods) are the main approaches described in literature for determination of geochemical background concentrations. In this review paper, the different approaches as well as the main normalization methods for heavy metal concentrations in sediments and soils will be discussed. Both geochemical background concentrations and added risk level (maximum permissible addition) should be taken into account for setting up legal threshold limits. Moreover, different approaches to evaluate the pollution status of heavy metals in sediments and soils, from Sediment/Soil Quality Guidelines to quantitative indices (Geo-accumulation Index-I_geo, Enrichment Factor-EF, Pollution Load Index-PLI and Risk assessment Code-RAC) will be presented. Although guidelines to establish whether a sediment or soil is polluted or not are generally only related to total metal concentrations, the available/reactive pool i.e., availability/reactivity of metals should be taken into account for sediment/soil pollution assessment.     

Bioavailability of heavy metals bound to estuarine sediments as a function of pH and salinity values

Abstract

The role of two key-variables such as pH and salinity in chemical speciation and bioavailability of heavy metals originated by mining activities bound to sediments was evaluated under estuarine conditions. Two sediment samples collected in two estuaries in southern Spain (Ría of Huelva and Guadalquivir estuary) together with dilution of toxic mud from the Aznalcóllar mining spill (April, 1998) were used to determine their chemical speciation and bioavailability at different pH (6.5, 7.5, 8.5) and salinity (10, 20, 35) values using the estuarine clam Ruditapes philippinarum. The chemical speciation was established by means of measurements of the mobilization of heavy metals from sediments to waters and determining in it pH, salinity, alkalinity and heavy metal concentration. The geochemical model MINTEQA2 was used to establish the thermodynamic species in the assays. To assess the bioavailability of the heavy metals the concentration of metallothioneins in the clam tissues and the mortality of this organism was measured at different pH and salinity values. The influence of both salinity and pH was detected in the chemical behavior of metals and in their associated biological responses established by metallothioneins and the percentage of mortality. At low values of both variables (pH=6.5 and S=10), the biological effects were highest, and it was related to the free ion Zn²⁺.     

Breeding birds from reedbeds to alpine meadows

The main processes that determine the behaviour ofheavy metals in the Scheldt estuary are tidalhydrodynamics, sediment transport, and sorption ofheavy metals on suspended matter. The water qualitymodel WASP is applied to simulate the spatialdistribution of five heavy metals in the estuary,under average hydrodynamic and suspended sedimenttransport regimes. First, the hydrodynamical part ofthe model is constructed and the results are verifiedby comparison with measured water levels and flowvelocities. Secondly, a salt transport model is set upin order to evaluate the hydrodynamical dispersivemixing characteristics. Thirdly, a suspended sedimenttransport model is constructed and finally a transportmodel for heavy metals. The simulated distributions of the sorbedamounts of heavy metals, suspended sediment andsalinity in the estuary agree well with observations.The calculated profiles of dissolved and sorbedconcentrations of heavy metals in the water columnindicate an accumulation of heavy metals in the zoneof the turbidity maximum, while closer to the sea theconcentrations diminish due to mixing of the pollutedfluvial sediments with unpolluted marine sediments andbecause of sediment deposition in the estuary. It canbe concluded that only a small part of the heavymetals reaches the sea. This revised version was published online in July 2006 with corrections to the Cover Date.