Heavy metal mobility in intertidal sediments of the Scheldt estuary: Field monitoring

The current paper aims to check whether the factors affecting metal mobility in intertidal sediments and floodplain soils of the river Scheldt, as identified under controlled greenhouse conditions in previous studies, also play a similar role under variable field conditions. Moreover, we aimed to assess the importance of these factors as a function of sampling time and depth, with respect to the natural variations in water table levels. This field monitoring revealed that the mobility of metals in intertidal sediments of the Scheldt estuary indeed are affected by factors which were identified to affect the metal fate in the upper sediment layer in previous greenhouse experiments. However, the effects were often less pronounced under field conditions. This can be attributed to the lower sampling resolution, the occurrence of interactions between factors, the disturbance of microbial communities during setup of greenhouse experiments and the more moderate environmental conditions in the field, affecting microbial and enzymatic activities. At most of the sampled wetlands, the level of the water table fluctuated only slightly during fall, winter and spring, whereas it decreased substantially during summer, especially at the sites with more sandy sediments. The highest sulphide concentrations were found at the sites where the water table level never decreased considerably. These sulphides primarily suppress the availability of Cd, Cu, Ni and Zn. Organic complexation resulted in the mobilisation of Cu, Ni and Cr. The concentrations of Cd, Ni and Zn in the pore water were affected by Fe/Mn oxide reduction, whereas Cd and Zn concentrations appeared to be also affected by the salinity.     

Trace metal concentrations in water,sediments and fish tissue from Lake Tanganyika

Trace metal (Cu, Pb, Fe, Mn, Zn, Cd) concentrations were determined in water, sediments, various fin fish species and a bivalve (Mutela spekei) from Lake Tanganyika using an atomic absorption spectrophotometer. Integrated water samples to depths of 10 m were collected using a pre-rinsed flexible plastic pipe. Sediment samples were collected using a ponar mud sampler. Fish samples were obtained using a variety of fishing techniques. No differences in trace metal concentrations were observed in both inshore and offshore waters. Levels in inshore sediments were much higher than for the offshore ones. Sediment input through run-off may have been the cause for the differences. However, the levels were much lower than those reported for Lake Malawi sediments. The concentrations in the fish tissue were within ranges reported elsewhere for Lake Tanganyika fish species. The centrapomid Lates stappersii and the clupeids Limnothrissa miodon and Stolothrissa tanganicae are the most important commercial species in the lake followed by Lates marie. Lead and cadmium are of concern to human health. The mean concentrations of the two metals in the commercial fish species were as follows: L. stappersii (5.03 microg Pb/g, 0.28 microg Cd/g); L. marie (4.96 microg Pb/g, 0.25 microg Cd/g); L. miodon (4.64 microg Pb, 0.38 microg Cd); and S. tanganicae (4.96 microg Pb/g, 0.39 microg Cd/g). Levels of lead and iron in the bivalve species were exceptionally very high, being 11.08 and 6.54 mg/g, respectively.     

Kinetics of trace metal partitioning in model anoxic marine sediments

A model anaerobic sediment consisting of humic acid, clay, ferrous sulfide, sand, and seawater was utilized to study the partitioning of Cu, Cd, Pb, and Zn between different geochemical phases. An extraction scheme was developed that was selective for each geochemical phase. Metals were dosed on one phase separately, and then mixed into the other undosed phrases. The kinetics of partitioning were rapid, regardless of which phase was initially dosed; equilibrium was reached within 2–5 days. The stoichiometry of distribution was also indepencent of the initially dosed phase. The final metal distributions showed that the metal sulfide phase was not necessarily the dominant trace metal sink in anaerobic sediments.     

Comparison of the feasibility of three extraction procedures for trace metal partitioning in sediments from south-west Spain

The feasibility of three sequential extraction schemes (a modification of the Tessier procedure, the scheme proposed by Meguellati and the protocol designed by BCR (now called the Standards, Measurements and Testing Programme, M&T) have been compared to study the distribution of As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn in sediment samples. The comparison has been performed by analyzing Certified Reference Material (CRM-601), a test material (S-12) and seven sediments from the Odiel Marshes Natural Park (located at the Atlantic coast of southern Spain). Samples were classified as sandy (with low iron oxide and organic matter contents) and clay-silty (with high iron oxide and organic matter contents) sediments. A higher metal mobility, especially under reducing conditions, was more properly assessed using the modified Tessier scheme compared to both the BCR and Meguellati procedures, these two later presenting comparative results for the reducible and residual phases. Significant Hg losses were found using the BCR procedure but the quantification of the acid phase for Cd, Cr and Ni was more reliable than that obtained with the modified Tessier and Meguellati schemes.     

Inaccuracy quality control in the monitoring of trace metal concentrations in biological fluids.

Quality assurance in trace element analysis requires continual surveillance of the accuracy and precision of results. A review of difficulties encountered in performing quality control programs of trace metal analysis in biological fluids is presented. Examples to clarify the inadequacy of available biological reference materials for quality control in biological monitoring of environmental and occupational low level exposure to metals are reported.     

Comparison of sediments and organisms in identifying sources of biologically available trace metal contamination

Sediments and an indicator organism (Macoma balthica, a deposit-feeding bivalve) were used to assess the relative importance of secondary sewage, urban runoff, a landfill containing metal-enriched ash wastes and a yacht harbor in contributing to Ag, Cu and Zn enrichment in South San Francisco Bay. Spatial gradients in sediments and organisms showed Cu and Ag enrichment originated from sewage discharge, whereas Zn enrichment originated from both sewage and urban runoff. Elevated concentrations of Cu in the sediments of the yacht harbor resulted from a high abundance of fine particles. The biological availability of Cu, Ag and Zn did not coincide with metal enrichment in sediments. The availability of Cu and Ag was greatest nearest the sewage outfall and greater in winter and spring than in summer. The availability of Zn in urban runoff appeared to be lower than the availability of Zn associated with sewage.     

Heavy metal concentrations in water and bottom sediments of a Mexican reservoir.

Metal concentrations have been measured in water and sediments of the Jose Antonio Alzate Reservoir, Mexico, using EDXRF and ICP techniques. Spatial and temporal distributions of total metal levels have been identified; no organised pattern was detected for any particular metal concentration. Temporal variations of metal concentrations show evidence of the water self-cleaning capacity of the reservoir, despite the high-level metal contamination determined.     

Significance and interspecific variability of accumulated trace metal concentrations in Antarctic benthic polychaetes

Trace metals were analysed in polychaetes collected on Polarstern cruise ANT XXI/2 (2003/04) to the Weddell Sea. Pb concentrations were largely less than 1.3 mg kg⁻¹ DW in all samples analysed. Statistical results indicate that the accumulated Cd, Cu and Zn concentrations are related to the feeding guild to which the animals are belonging. Relatively low Cd and Cu concentrations are found in macrophagous carnivores and relatively high concentrations in microphagous detritus feeders. The relationship between Zn concentrations and the feeding guilds of polychaetes is reverse. Cd concentrations range from (median values and interquantile ranges in brackets) 2.6 (1.5-3.2) mg kg⁻¹ DW in the carnivorous Trypanosyllis gigantea to 133 (37-176) mg kg⁻¹ in the microphagous detritus feeder Lanicides bilobata; Cu concentrations from 16 (11-19) mg kg⁻¹ in the carnivorous Antarctinoe spicoides to 40 (23-68) mg kg⁻¹ in the microphagous detritus feeder Phyllocomus crocea and Zn from 89 (69-97) mg kg⁻¹ in the microphagous detritus feeder Isocirrus yungi to 396 (372-404) mg kg⁻¹ in the carnivorous Aglaophamus trissophyllus. Ni is ranging from 3.7 (1.8-6.0) mg kg⁻¹ in Polyeunoa laevis to 34 (20-41) mg kg⁻¹ in A. spicoides, but no significant differences are obvious regarding the feeding guilds. Since information on metals in Antarctic polychaetes is almost completely lacking, our results suggest further studies to clarify the role of feeding in the bioaccumulation of metals in this ecologically important taxonomic group.     

Heavy metals in human primary teeth: some factors influencing the metal concentrations

Human primary teeth have been used as indicators of heavy metal exposure for several decades, but the knowledge about the influence of factors such as tooth type and the presence of caries and roots on metal concentrations is limited. Samples of tooth powder from more than 1200 Norwegian primary teeth without fillings have been analyzed for lead, zinc and cadmium content, and 554 of them for mercury. The material represents all groups of tooth types (incisors, canines and molars), carious and non-carious teeth, and teeth with and without roots. Here we investigate how tooth group and the presence of caries and roots are related to metal concentrations in the teeth. We find that carious teeth have higher metal concentrations than non-carious teeth; the difference was statistically significant for lead, mercury and zinc. Teeth with roots have higher lead and zinc concentrations than teeth without roots. We find differences in metal concentrations between the tooth groups for lead, mercury and zinc. Significant, positive correlations are found between lead and the three other metals and between mercury and zinc. We conclude that metal concentrations in primary teeth are affected by the presence of caries and roots and by tooth group.     

Metaux lourds dans les sediments de l'estuaire de la loireHeavy metals in the sediments of the loire estuary

Estuaries, being interfaces between fluviatile and marine environments, are the scene of considerable physico-chemical and biological gradients which can have an effect on the distribution of metallic elements between the solid and dissolved phases. The purpose of the present study was to determine the relative influence of each parameter in this distribution.The study included two series of samples (ICOLO 26 and ICOLO 32) taken by means of the Schipeck grab at 19 selected points of the estuary as indicated in Fig. 1.Within the framework of this study we first investigated and were able to determine the origin and evolution of the metallic elements in the Loire estuary.Pollution levelTable 1 and Fig. 2 summarize the results: firstly, the metallic element contents are relatively low, indicating that pollution is not very strong. Secondly, the contents measured in the different samples vary considerably due to the great heterogeneity of sample composition and particle-size distribution.Upstream-downstream evolutionFigure 2 shows that the longitudinal profiles for metals are very similar to those obtained for the different characteristics of the sediments. Such an observation has already been made by various authors. Owing to the existence of these relationships, we believe, as do Boust et al. (1981), that it is preferable to interpret the results relative to metals obtained on a given site in terms of the various characteristics of the sediment. In Fig. 3, the metallic element contents (ICOLO 26 samples) is thus plotted against organic carbon. As shown in the figure, there is a very good relationship between the two parameters. Figures 2 and 3 indicate that the contents are uniform throughout the estuary with no evidence of further significant sedimentation this uniformity being due to tidal action. Owing to this uniformity, the impact of significant discharges is highly localized except for the wastewater from the city of Nantes as a whole, whose impact which is felt along the entire estuary.The relationship between copper and volatile matter for the ICOLO 32 samples, as represented in Fig. 4, shows that the points fall into two groups, which are the same whatever the explanatory parameter involved. Though the results are more uniform for the ICOLO 26 than for the ICOLO 32 samples, Fig. 6 clearly shows that the “marine” points stand out in both series of samples. This is indicative of a reduction in contents in the downstream direction, especially noticeable beyond point B (Zn, Cr, Ni) or even M (Cd, Cu, Pb).The seasonal evolution is clearly shown on the “metal-characteristic of sediment” graphs by the comparison of the slopes of the lines linking the same point sampled during the two sampling campaigns. The example of copper is shown in Fig. 7.On the whole, analysis of the results derived from the study of one characteristics of the sediment, indicates that only limited enrichment or depletion occurs at a point over a period of time. This probably reflects a good constancy over time of the metallic flux in the estuary. There is little doubt that changes in the composition of the sediment, will cause changes in the trapping of the metallic flux. In this case, variations in contents do not reflect alterations in the metallic flux over the sediment, but the varying capacity of the sediment under investigation to trap the same polluting flux according to is own composition.This study was also productive in the investigation of the various phenomena responsible for the reduction in metal contents during estuarial transit, which phenomenon can be expected to occur in a large number of estuaries.The impact depends on the chemical properties of the element under investigation.Solubilization of metallic elements due to to increased salinity occurs but plays only a secondary role in the upstream-downstream reductions. This is presumably because of the low percentages of metal absorbed in relation to the total amount of metals associated with the sediments.The reduction in metal contents related to the degradation of organic matter also occurs but it is of little significance compared with the overall phenomenon. The disappearance of metals associated with organic matter could well be related to salinity.The considerable reduction of contents in the lower estuary markedly occurs downstream of the salinity front and precisely where the first sediments characteristic of the marine environment are encountered. Consequently, the most obvious parameter responsible for the reduction in the metallic element contents is the mixing of relatively laden fluviatile sediment with “clean” marine sediments.     

Modelling Escherichia coli concentrations in the tidal Scheldt river and estuary

Recent observations in the tidal Scheldt River and Estuary revealed a poor microbiological water quality and substantial variability of this quality which can hardly be assigned to a single factor. To assess the importance of tides, river discharge, point sources, upstream concentrations, mortality and settling a new model (SLIM-EC) was built. This model was first validated by comparison with the available field measurements of Escherichia coli (E. coli, a common fecal bacterial indicator) concentrations. The model simulations agreed well with the observations, and in particular were able to reproduce the observed long-term median concentrations and variability. Next, the model was used to perform sensitivity runs in which one process/forcing was removed at a time. These simulations revealed that the tide, upstream concentrations and the mortality process are the primary factors controlling the long-term median E. coli concentrations and the observed variability. The tide is crucial to explain the increased concentrations upstream of important inputs, as well as a generally increased variability. Remarkably, the wastewater treatment plants discharging in the study domain do not seem to have a significant impact. This is due to a dilution effect, and to the fact that the concentrations coming from upstream (where large cities are located) are high. Overall, the settling process as it is presently described in the model does not significantly affect the simulated E. coli concentrations.     

The concentration of some trace elements in human milk from Italy

The concentration of some trace elements has been measured in samples of breast milk collected from several subjects over a period of about 1–3 months starting 15 days post-partum.A decrease of Zn concentration during the lactation period was observed in all subjects. The marked relation existing between dietary intake and milk content of trace elements is confirmed by the finding that Cs concentration in diet, fresh waters and human milk samples from Latium were one to two orders of magnitude higher than those measured in a small town in the south of Italy. In most subjects Cs, Zn, Rb, Fe concentrations during the same day, and in the same feed, are fairly constant. Larger variations are observed for concentrations of Co, Sc, and Sb.     

Heavy metal pollution in the Chao Phraya River estuary, Thailand

A study on heavy metal pollution in the Chao Phraya River estuary indicated that the accumulation of Cd, Cu, Cr and Pb in water in the river mouth vicinity was significant, which may have a long term impact on the aquatic environment through precipitation of heavy metals to the bottom sediments and bio-accumulation and bio-magnification of heavy metals in various food chains. Although the seasonal and spatial variations of heavy metals in the sediments and fish did not conform to a definite pattern, the heavy metal contents of samples were higher than those previously reported in the area and in some cases were higher than the mean world concentrations. Thus, Thai people may ingest Hg and Pb in fish in the Chao Phraya River estuary at quantities more than those reported for other countries.     

Assessment of metal mobility in dredged harbour sediments from Barcelona, Spain

In order to assess heavy metal mobility in dredged harbour sediments, six superficial sediment samples covering a range of pollution levels and environments were collected in Barcelona Harbour. Samples were characterised in terms of major compounds (Al, Ca, Fe, Mn, Si, Ti, Mg, K and Na); total C, N and S contents; organic matter; and water content. Pseudo-total trace metal contents were assessed after aqua regia digestion (ISO 11466:1995). The modified BCR three-step sequential extraction procedure (BCR-SEP) was applied, and both major compounds (Al, Ca, Fe and Mn) and trace metals (Cd, Cr, Cu, Ni, Pb and Zn) were determined in the different extracts. Both the pseudo-total digestion method and the BCR-SEP were validated using two sediment certified materials from lakes (BCR CRM 701 and BCR CRM 601). The highest metal concentrations were observed in one of the sampling points which receives an urban discharge. The observed mobility order (percentage of metal extracted in the first step) of the six trace metals studied was Cd>Zn>Pb>Cu>Ni>Cr. The good agreement observed with the results obtained as the sum of the four steps (extractable+residue) and the pseudo-total content shows that laboratory working conditions were under control.     

Preliminary studies on the leaching of some trace metals from kitchen faucets

Preliminary studies were carried out on the leaching of copper, zinc, chromium, cadmium and lead from eight kitchen faucets by samples of raw, filtered and distributed Ottawa water, a sample of well water and deionized water containing 2 mg l⁻¹ aqueous fulvic acid. Leaching was effected by allowing the test solutions to stand in the inverted faucets for two successive 24-h periods. Concentrations of the metals found in the leachates were copper: first leaching, 0.12–28.0 mg l⁻¹, second leaching, 0.08-3.54 mg l⁻¹; zinc: first leaching, 0.13-10.25 mg l⁻¹, second leaching, 0.06-2.85 mg l⁻¹; chromium: first leaching, < 1.0 × 10⁻³ − 0.395 mg l⁻¹, second leaching, < 1.0 × 10⁻³−0.032 mg l⁻¹; cadmium: first leaching, < 0.05 × 10⁻³−0.01 mg l⁻¹, second leaching, < 0.05 × 10⁻³−4 × 10⁻³ mg l⁻¹; and lead: first leaching, < 0.2−110.0 mg l⁻¹, second leaching, < 0.2−82.0 mg l⁻¹. The faucets containing lead-soldered copper joints released high concentrations of lead, particularly in the case of leaching with the aqueous fulvic acid solution. Under the conditions of the present investigations it is indicated that in some cases the concentrations of metals leached could lead to intakes in excess of the maximum permissible limits for these metals. However, further investigations will be required to determine the possible contribution of these faucets to metal intake under normal usage.     

Biomonitoring of trace metal contamination in the Potengi estuary, Natal (Brazil), using the oyster Crassostrea rhizophorae, a local food source.

The oyster Crassostrea rhizophorae was collected in September 1997 from 10 stations along the Potengi estuary, Natal, Brazil, a mangrove-lined estuary receiving anthropogenic inputs of trace metals. C. rhizophorae is a net accumulator of trace metals and can be used as a biomonitor, the accumulated soft tissue concentrations representing integrated records of bioavailable metal fractions over the life of the oyster. Significant differences in oyster accumulated concentrations (and hence bioavailabilities) of Fe, Zn, Cu, Cr, Pb, Cd, Ni and Ag (but not Mn) were found between stations, and attributed to anthropogenic inputs including discharges of sewage and industrial effluent. The oysters are also a local food source, and concentrations of zinc, copper and lead in some of the oysters are above typical public health recommended limits.     

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.     

Effect of salinity and inorganic nitrogen concentrations on nitrification and denitrification rates in intertidal sediments and rocky biofilms of the Douro River estuary, Portugal

The regulatory effects of salinity and inorganic nitrogen compounds on nitrification and denitrification were studied in intertidal sandy sediments and rocky biofilms in the Douro River estuary, Portugal, over a 12-month period. Nitrification and denitrification rates were measured in slurries of field samples and enrichment experiments using the difluoromethane and the acetylene inhibition techniques, respectively. Salinity did not regulate denitrification in either environment, suggesting that halotolerant bacteria dominated the denitrifier communities. However, nitrification rates were stimulated when salinity increased from 0 to 15 practical salinity units. NO3- addition experiments revealed that NO3- availability stimulates denitrification rates in sandy sediments, but not in rocky biofilms; however, in rocky biofilms a positive and linear relationship was observed between denitrification rates and water column NO3- concentrations (r=0.92) during the monthly surveys. The N2O:N2 ratios increased rapidly when NO3- increased from 63 to 363 microM; however, results from monthly surveys showed that environmental parameters other than NO3- availability may be important in controlling the variation in N2O production via denitrification. Ammonium additions to sandy sediments stimulated nitrification rates by 35% for the 20 microM NH4+ addition, but NH4+ appeared to inhibit nitrification at high concentration addition (200 microM NH4+). In contrast, rocky biofilm nitrification was stimulated by 65% when 200 microM NH4+ was added.     

Partitioning of trace metals before and after biological removal of metals from sediments

Metal removal by biological solubilization in three strongly contaminated sediments was carried out in a two-liter stirred bioreactor. Biological treatment yielded metal removal efficiencies in the range of 11-30%, 43-57%, 60-79%, 61-90%, 18-21%, 0-10% for Pb, Cu, Zn, Cd, Ni and Cr, respectively. The treated sediments were then rinsed with a NaCl solution (0.5 M), resulting in an increase by nearly 47% in Pb removal for the three sediments, while for other metals (Cu, Zn, Cd, Ni, Cr), the NaCl rinse did not seem to allow any significant increase in metal solubilization. A standard procedure of sequential selective extraction (SSE) was applied to the sediments before and after each treatment. With regard to Pb, Zn and Cd, the carbonate bound fractions (2/3 sediments) represented 18-42% of metals prior to treatment, while the iron and manganese oxides bound fraction constituted 39-60% of metals for the three sediments. Between 90 and 100% of Pb, Zn and Cd removed by the process came from the fractions bound to carbonates and from those bound to Fe and Mn oxides. The organic matter and sulfide bound fractions contained 65-72% of total Cu present before treatment and the process removed, on average, 63% Cu present in this fraction. In contrast, Ni and Cr were found mainly in the residual fractions (50-80%). Finally, this biological treatment did not solubilize Cr appreciably, while removal of Ni mostly originated from the carbonate and Fe/Mn oxides fractions (70-80%).     

Physico-chemical characterization of atmospheric trace metal emissions from a primary zinc-lead smelter

Emissions from the stacks of a major primary zinc--lead smelter were characterised using X-ray powder diffraction spectrometry (XRD). The following chemical phases were identified: PbSO4, PbO X PbSO4, PbO, PbS, PbO, ZnO, alpha-ZnS, CdO. A complementary environmental investigation revealed that, within the works boundary, the airborne metals might be associated mainly with the fugitive blowage of coarse particles containing primary ore minerals. However, such fugitive emissions were found to be of low significance in the local environment outside the works perimeter, where fine particle emissions from the stacks of the smelter were the predominant source of airborne cadmium, lead and zinc.