Heavy metals in the lagos lagoon sediments

Concentrations of cadmium, cobalt, copper, chromium, iron, manganese, nickel, lead and zinc were determined in surface sediments of the Lagos Lagoon, Nigeria. The results revealed largely anthropogenic heavy metal enrichment and implicated urban and industrial wastes and runoff water transporting metals from land‐derived wastes, as the sources of the enrichment. Higher levels (F < 0.05) of cadmium, iron, manganese, nickel and zinc occurred in sediment samples collected near industrialized‐urban areas than in those from unindustrialized‐rural areas only in the wet season. While iron constituted about 1% of dry sediment by weight, the other metals were present in trace amounts.     

Sources of heavy metals and polycyclic aromatic hydrocarbons in urban stormwater runoff

Polycyclic aromatic hydrocarbons (PAHs) and heavy metals were measured in road debris collecting in urban areas and in the suspended sediment (SS) component of runoff from two stormwater catchments in Dunedin, New Zealand. Levels in the road debris ranged from 119-527 microg/g for lead, 50-464 microg/g for copper, 241-1 325 microg/g for zinc and 1.20-11.6 microg/g for sigma16PAH. The SS from the largely rural catchment (20% urban) had similar concentrations to the road debris, indicating that this urban material was the main source of the contaminants measured in the stormwater. Similar PAH fingerprint profiles and isomer ratios indicative of dominant pyrogenic (combustion) sources were also found in these two groups of materials. The SS from the 100% urban catchment contained 2- to 6-fold higher concentrations of metals and 10-fold greater levels of sigma16PAH. The higher levels of lead and copper were probably a result of industrial land uses in this catchment, while the additional zinc was linked to an abundance of zinc-galvanised roofing iron in the catchment's residential suburbs. The PAH profiles and isomer ratios were different for this urban catchment and suggested that a disused gasworks was contributing PAHs to the stormwater runoff.     

Cu, Pb and Zn contamination in Nuuanu watershed, Oahu, Hawaii

Trace metal contamination in urban aquatic ecosystems in Hawaii is a significant problem, especially in terms of Cu, Pb, and Zn. These trace metals are linked to automobile usage. An in-depth study was designed to determine the influence of road sediments and storm sewers on bioavailable (0.5 M HCl) trace metal concentrations in bed sediments of Nuuanu stream, Oahu. Lead was the most enriched trace metal in the watershed. Compared to baseline Pb concentrations of <3 mg/kg, road sediments averaged 186 mg/kg, with a maximum value of 3140 mg/kg. Stream bed sediments had average Pb values of 122 mg/kg, with a maximum of 323 mg/kg. Al-normalized enrichment ratios (ERs) for the <63 microm fraction indicated that the watershed was significantly polluted in the lower, urbanized reaches, with maximum ER values of 560 and 94 for Pb in road sediments and stream sediments, respectively. Median ER values for Cu, Pb, and Zn in stream sediments were 2, 36, and 5, respectively. Rainfall events prior to sediment sampling masked any influence that storm sewer outlets might have had on the localized spatial distribution of metals associated with bed sediments. However, there was a general pattern of increasing trace metal concentrations downstream as the fluvial network traversed residential areas and commercial, highly trafficked areas in the lower portions of the watershed.     

DYNAMICS OF SEDIMENT-ASSOCIATED METALS IN A HIGHLY URBANISED CATCHMENT: BRADFORD, WEST YORKSHIRE

Urban watercourses are potential hazards because of their rapid flow changes, poor water quality and contaminated sediments. This study is a preliminary field investigation into fine sediment-associated metal contamination and its transport dynamics in a highly urbanised catchment in West Yorkshire, UK. Spatial and temporal changes in the concentration of channel-bed sediment-associated metals are investigated, and the fluxes of selected suspended sediment-associated metals, during an extreme high flow event, are determined. Channel-bed sediments were more contaminated at the most heavily urbanised sites. Data suggest that contaminated bed sediments could accumulate and possibly become increasingly contaminated between high-flow events, prior to being flushed from the system. Fluxes of contaminated suspended sediments were very high at the peak of the high flow event. The spatial and temporal dynamics of contaminated fine sediment which were identified in this study could inform planners with regard to future monitoring strategies.     

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.     

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.     

Effect of pH, ionic strength, dissolved organic carbon, time, and particle size on metals release from mine drainage impacted streambed sediments

Acid-mine drainage (AMD) input to a stream typically results in the stream having a reduced pH, increased concentrations of metals and salts, and decreased biological productivity. Removal and/or treatment of these AMD sources is desired to return the impacted stream(s) to initial conditions, or at least to conditions suitable for restoration of the aquatic ecosystem. Some expected changes in the water chemistry of the stream following removal of AMD input include an increase in pH, a decrease in ionic strength, and an increase in dissolved organic carbon (DOC) concentrations from increased biological activity in the absence of toxic metals concentrations. These changes in water chemistry may cause the existing contaminated bed sediments to become a source of metals to the stream water. Streambed sediments, collected from North Fork Clear Creek (NFCC), Colorado, currently impacted by AMD, were assessed for the effects of pH, ionic strength, DOC concentration, time, and particle size on metals release using a factorial design. The design included two levels for each chemical parameter (ionic strength = 40 and 80% lower than ambient; pH = 6 and 8; and DOC = 1 and 3 mg/l higher than ambient), ten sampling times (from zero to 48 h), and two size fractions of sediments (63 μm ≤ x < 2 mm and <63 μm). Greater concentrations of metals were released from the smaller sized sediments compared with the larger, with the exception of Cu. A mild acid digestion (0.6 M HCl) evaluated the amount of each metal that could be removed easily from each of the sediment size fractions. Release of all metals over all time points, treatments, and from both sediment sizes was less than 1% of the extractable concentrations, with the exception of Mn, which ranged from 4 to 7% from the smaller sized sediment. Greater percentages of the 0.6 M HCl-extractable concentrations of Cu, Fe, and Zn were released from the larger sized sediment, while this was true for release of Cd and Mn from the smaller sized sediment. Thus, at least for Cd and Mn, the observed higher concentrations released from the smaller sized sediment with each treatment solution is not simply a function of these particles having higher concentrations available for release, but that these metals also are more readily released from the smaller sediment particles versus the larger. DOC concentration strongly influenced the release of Cu; ionic strength strongly influenced the release of Cd, Mn, and Zn; and interaction effects were observed with the release of Cu, Mn, and Zn from the larger size fraction and with the release of Zn from the smaller size fraction. Overall, results suggest that the expected changes in water chemistry following removal/treatment of the AMD sources would result in a release of metals from the existing sediments, with a greater effect on the release of Cu and Fe, than on the release of Cd, Mn, and Zn.     

Interactions among phosphate amendments, microbes and uranium mobility in contaminated sediments

The use of sequestering agents for the transformation of radionuclides in low concentrations in contaminated soils/sediments offers considerable potential for environmental cleanup. This study evaluated the influence of three types of phosphate (rock phosphate, biological phosphate, and calcium phytate) and two microbial amendments (Alcaligenes piechaudii and Pseudomonas putida) on U mobility. All tested phosphate amendments reduced aqueous U concentrations more than 90%, likely due to formation of insoluble phosphate precipitates. The addition of A. piechaudii and P. putida alone were found to reduce U concentrations 63% and 31%, respectively. Uranium removal in phosphate treatments was significantly reduced in the presence of the two microbes. Two sediments were evaluated in experiments on the effects of phosphate amendments on U mobility, one from a stream on the Department of Energy's Savannah River Site near Aiken, SC and the other from the Hanford Site, a Department of Energy facility in Washington state. Increased microbial activity in the treated sediment led to a reduction in phosphate effectiveness. The average U concentration in 1 M MgCl(2) extract from U contaminated sediment was 437 microg/kg, but in the same sediment without microbes (autoclaved), the extractable U concentration was only 103 microg/kg. The U concentration in the 1 M MgCl(2) extract was approximately 0 microg/kg in autoclaved amended sediment treated with autoclaved biological apatite. These results suggest that microbes may reduce phosphate amendment remedial effectiveness.     

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.     

Arsenic and heavy metals in soils associated with regional geochemical anomalies in South-West England

Regional geochemical maps have shown extensive anomalies of arsenic, copper and other heavy metals in those parts of South-West England associated with mineralised zones around the granite intrusion. Studies in the vicinity of the River Tamar and of the metamorphic aureole around Dartmoor have confirmed significantly higher concentrations of arsenic and heavy metals in soils contaminated by mining, smelting and mineralisation compared with those from nearby control areas. Arsenic and copper show the greatest degree of enhancement ranging up to 900 ppm As and 2000 ppm Cu in both alluvial and upland topsoils within the Tamar area. Preliminary analyses indicate that the trace metal content of pasture herbage-reflects in part the degree of soil contamination. Maximum concentrations of 35 ppm As and 22 ppm Cu in autumn sampled herbage were found at contaminated sites compared with mean values of less than 0.5 ppm As and 8 ppm Cu in control areas. Geochemical reconnaissance surveys based on stream sediment sampling provide a useful indication of areas wherein widescale soil contamination may occur.     

Investigation of mangrove macroalgae as biomonitors of estuarine metal contamination

This study examined the potential use of macroalgae epiphytic on mangrove aerial roots as biomonitors of estuarine contamination. The metal concentrations of macroalgae were investigated in four estuaries in the vicinity of Sydney, Australia, and compared to water and sediment metal concentrations over three seasonal surveys. Macroalgal metal concentrations (copper, zinc, cadmium, chromium, lead, nickel, manganese and iron) appeared to be more associated with sediment metal concentrations than water concentrations, suggesting they may be useful biomonitors of estuarine sediment contamination. Algae in the more contaminated estuaries generally contained higher metal concentrations. However, concentrations of iron, nickel and manganese appeared to be similar in the algae despite the varying sediment concentrations, while accumulation of copper, zinc, lead and chromium appeared to be associated with ambient environmental concentrations. The uptake of metals also varied among the different species, suggesting that algal parameters, such as morphology, may also influence metal uptake and accumulation.     

Assessment of fly ash-aided phytostabilisation of highly contaminated soils after an 8-year field trial: part 1. Influence on soil parameters and metal extractability

Sustainable management of large surface areas contaminated with trace elements is a real challenge, since currently applied remediation techniques are too expensive for these areas. Aided phytostabilisation appears to be a cost efficient technique to reduce metal mobility in contaminated soils and contaminated particle spread. In this context, this study aimed at evaluating the long-term efficiency of aided phytostabilisation on former agricultural soils highly contaminated with trace elements. The influence of afforestation and fly ash amendments to reduce metal mobility was investigated. Before being planted with a tree mix, the study site was divided into three plots: a reference plot with no amendment, the second amended with silico-aluminous fly ash and the third with sulfo-calcic fly ash. After eight years, some soil physico-chemical parameters, including cadmium (Cd), lead (Pb) and zinc (Zn) extractability were modified. In particular, pH decreased on the whole site while organic carbon content increased. The alteration of these parameters influencing trace element mobility is explained by afforestation. Over time, concentrations of CaCl₂-extractable metals increased and were correlated with the soil pH decrease. In the amended soils, extractable Cd, Pb and Zn concentrations were lower than in the reference soil. The results indicated that the two fly ashes buffered natural soil acidification due to vegetation development and limited trace element mobility and thus could limit their bioavailability. For long-term phytostabilisation, special attention should be focused on the soil pH, metal mobility and phytoavailability analysis.     

Heavy metals in the surficial sediments of Fontana Lake, North Carolina

Concern about the possible contamination by heavy metals of Fontana Lake (reservoir) and potential sources of such materials led to a study of surficial sediments. Samples of sediment were collected in the main body of the lake and near the mouths of its major tributaries and analayzed for magnesium, iron, aluminum, manganese, zinc, copper and mercury. Although the drainage area of the reservoir is primarily forested and rural without major industrial developments, the results indicated that manganese, copper and zinc were present in concentrations similar to areas receiving industrial pollution. Chemical analyses of pyritic materials in the watershed (e.g. schists or Anakeesta formation) showed relatively high concentrations of many of the same metals present in Fontana sediments. It appears, therefore, that the metals in the lake sediments represent materials derived from geological sources, although airborne contributions of certain metals cannot be ruled out.     

Quality of dredged material in the river Seine basin (France). II. Micropollutants

Dredging rivers is needed to ensure safe navigable waters, rivers and waterways. To anticipate the management of dredged materials in the case of the river Seine basin, the quality of the sediments in the river is checked every 3 years before dredging operations. The river Seine Basin is heavily submitted to pollution pressure from nearby industrial activities and urban expansion of Paris and its region. Here, the micropollutant content of the sediment sampled in 1996, 1999 and 2000 before dredging is discussed compared to regulatory standards. The results indicate that most of the sediment samples from the river Seine basin are lightly to moderately contaminated with organic and inorganic micropollutants (heavy metals, PAH, PCB), which makes the management after dredging easier. This pollution is strongly correlated with the organic matter content and to the fine fraction (<50 microm) of the sediment. These results can lead to other management options than the ones already used in the river Seine basin: (1) dumping of lightly to moderately polluted sediments in quarries; and (2) physical treatment (sieving, hydrocycloning) of contaminated sediments issued from 'hot spots'.     

Trace metals and their source in the catchment of the high altitude Lake Respomuso, Central Pyrenees

Lake Respomuso is a dammed lake of glacial origin at 2200 m altitude in the Central Pyrenees. This study investigated the source of a number of trace elements (As, Cd, Co, Cu, Mn, Ni, Pb and Zn) in its catchment and their possible link to the local geology. Altogether 24 sediment and 29 water samples were collected from all major streams feeding the lake. The sediments were analysed for trace elements, major mineral components, minerals and organic matter whilst water samples were analysed for dissolved metal concentrations.The trace element levels in the catchment sediment and water were relatively high compared to other similar altitude sites, with concentrations in the headwaters being generally higher than in the lower basin because of the source being concentrated in these areas. The principal component analysis revealed that the source of sediment-bound trace elements in the Lake Respomuso catchment is geogenic, and originated possibly in the sulphide minerals from slate formations.Except at one site, none of the water samples exceeded the WHO drinking water guideline for arsenic. Arsenic in water was significantly correlated with its concentration in the sediments, possibly due to the oxidation of arsenic bearing minerals. The dissolved concentrations of all other trace elements were generally lower than the WHO drinking water guide values and they were not related to their sediment concentrations.The As, Cd, Ni contents in sediment from several catchment streams exceeded their sediment quality thresholds. This geogenic source may pose risk to the stability of fragile local biodiversity and to the wider environment in the valley bellow particularly if the metals are mobilised, possibly due to environmental change.     

A statistical assessment of the form of trace metals in oxidized estuarine sediments employing chemical extractants

The thin layer of oxidized sediment at the sediment—water interface plays an important role in the chemical and biological interactions of trace metals in estuaries. Chemical extractants can be useful in defining trace metal interactions in sediments. Extractions may aid in determining the abundance of the operationally-defined forms of substrates which are the most active in binding metals in sediments; in operationally-defining an “extractable” phase of trace metals in sediments; and in providing information necessary for determining the bioavailability of sediment-bound metals. Comparison of 10 techniques for metal and substrate extractions among the sediments of 19 estuaries from south and west England indicate substrate characterization is best accomplished by Fe and Mn extractions with acid ammonium oxalate or 1N HCl, and humic substances extraction with 0.1N NaOH or 1N ammonia. Partial fractionation of trace metals is best accomplished with 1N HCl. Statistical relationships indicate the extractable phase of Fe is more important than total Fe in binding Ag, Cd, Cu, Pb and Zn in oxidized sediments, and the operationally-defined humic substance fraction of organic materials is highly important in binding Ag and Cu. Statistical analysis within specific subsets of data indicate trace metals are partitioned among several substrates in most sediments, the substrates compete with one another for the metals, and the outcome of the competition is strongly influenced by the concentrations of the different substrates in the sediment.     

Anthropogenic contamination and risk assessment of heavy metals in stream sediments influenced by acid mine drainage from a northeast coalfield,India

The total concentrations and chemical partitioning of heavy metals in streambed sediments, collected around the Jaintia Hills coal deposit of northeast India, were studied using pollution indices and multivariate techniques to evaluate the risk and contamination levels from heavy metals and their possible origins. Results show that sediments close to mining sites have low pH (<4), high organic carbon, and contain significant amounts of Fe-oxyhydroxide phases (mainly, goethite and schwertmannite), which implies direct impact of coal mine drainage. The average concentrations of Fe, Cu, Co, Cd, Cr, and Zn exceeded the World average, and in some cases, Cd, Cu, Ni, and Cr concentrations exceeded the threshold effects level, which suggests they will be toxic to aquatic biota. Contamination factors (CF) show that the sediments are low to highly contaminated with Cd, Cu, Mn, Pb, Fe, and Zn and low to moderately contaminated with Co, Cr and Ni. The pollution load index (PLI), degree of contamination index (C _deg) and Nemerow integrated pollution index (NIPI) show that the sediments are moderately to highly contaminated, with the extent of pollution greatest nearest to the collieries. The potential ecological risk index (RI) shows low to considerable ecological risk from heavy metals in the sediments, with Cd having the high potential of risk, which also agrees with the risk assessment code (RAC). Multivariate statistical analysis suggests that the concentrations of the heavy metals in stream sediments are strongly influenced by Fe-oxyhydroxide phases and organic carbon derived from anthropogenic sources, mainly coal mining activities. Although a significant proportion of the Cd, Mn, and Ni in the sediments are partitioned into exchangeable and organic fractions, a sizable amount of metals are also found in the Fe–Mn fraction, suggesting that Fe-oxyhydroxides play a dominant role in controlling metal mobility in these stream sediments.     

Regional lead isotope study of a polluted river catchment: River Wear, Northern England, UK

High precision, lead isotope analyses of archived stream sediments from the River Wear catchment, northeast England (1986-88), provide evidence for three main sources of anthropogenic lead pollution; lead mining, industrial lead emissions and leaded petrol. In the upper catchment, pollution is totally controlled and dominated by large lead discharges from historic mining centres in the North Pennine Orefield (²⁰⁸Pb/²⁰⁶Pb, ²⁰⁷Pb/²⁰⁶Pb ratios range from 2.0744-2.0954 and 0.8413-0.8554 respectively). In the lower catchment, co-extensive with the Durham Coalfield and areas of high population density, pollution levels are lower and regionally more uniform. Isotope ratios are systematically higher than in the upper catchment (²⁰⁸Pb/²⁰⁶Pb, ²⁰⁷Pb/²⁰⁶Pb ratios range from 2.0856-2.1397 and 0.8554-0.8896 respectively) and far exceed values determined for the geogenic regional background. Here, the pollution is characterised by the atmospheric deposition of industrial lead and petrol lead. Lead derived from the combustion of coal, although present, is masked by the other two sources. Recent sediments from the main channel of the River Wear are isotopically indistinguishable from older, low order stream sediments of the North Pennine Orefield, indicating that contamination of the river by lead mining waste (up to several 1000 mg/kg Pb at some locations) continues to pose an environmental problem; a pattern that can be traced all the way to the tidal reach. Using within-catchment isotope variation and sediment lead concentrations, estimates can be made of the discharges from discrete mines or groups of mines to the overall level of lead pollution in the River Wear. As well as providing information pertinent to source apportionment and on-going catchment remediation measures, the database is a valuable resource for epidemiologists concerned with the health risks posed by environmental lead.     

Bioaccumulation of heavy metals by the aquatic plants Potamogeton pectinatus L. and Potamogeton malaianus Miq. and their potential use for contamination indicators and in wastewater treatment

The concentrations of heavy metals in the leaves of two aquatic plants Potamogeton pectinatus L. and Potamogeton malaianus Miq., and the corresponding water and sediment samples from the Donghe River in Jishou City of Hunan Province, China were studied to investigate metal contamination from the intensive industrial activities in the surrounding area. Results showed that the concentrations of heavy metals in the sediments, especially Cd, Mn and Pb, were much higher than the eco-toxic threshold values developed by the U. S. Environmental Protection Agency. Between the two plant species, P. pectinatus showed the higher capacity in metal accumulation. The highest concentrations of Cd, Pb, Cu, Zn and Mn were found in the leaves of P. pectinatus, reaching 596, 318, 62.4, 6590 and 16,000 mg kg(-1) (DW), respectively. Significantly positive relationships were observed among the concentrations of Zn, Cu and Mn in the leaves of both aquatic plants and those in water, indicating the potential use of the two plants for pollution monitoring of these metals. In addition, a laboratory experiment was conducted to investigate the ability of P. pectinatus and P. malaianus to remove heavy metals from contaminated river water. The average removal efficiencies by P. pectinatus and P. malaianus for Cd, Pb, Mn, Zn and Cu from the spiked Donghe River water were 92%, 79%, 86%, 67% and 70%, respectively. The results indicated that P. pectinatus and P. malaianus had high capabilities to remove heavy metals directly from the contaminated water. The potential use of these plants in wastewater treatment is worth further exploration.     

Geochemical studies in several rivers and estuaries used for oyster rearing

Base-line studies have been carried out on the trace metal content of bottom sediments and waters of five estuaries and their catchment drainage, representing both contaminated and relatively uncontaminated environments. Relationships have been established between the composition of water and sediments in tributary drainage and those in the estuary. In particular, regional contamination of the hinterland with one or more of the elements As, Cd, Cu, Pb, Zn and Sn from mining and smelting activity was reflected by enhancement in estuarine muds in relation to the proportion of the catchment affected and the degree of contamination. Preliminary observations on young oysters showed that in general metal accumulation reflected the geochemical status of the estuary. These investigations have confirmed the potential use of geochemical reconnaissance maps based on stream sediment analysis as a means of focussing attention on rivers and estuaries affected by regional metal pollution.