Records and sources of metal pollutants in a dated Loch Lomond sediment core

Lead, zinc, copper, chromium, arsenic and cadmium were measured in a sediment core from southern Loch Lomond for which ²¹⁰Pb dating indicated a sedimentation rate of 22±2 mg/cm²/yr corresponding to a mean accumulation rate of 0.36 mm/yr.While copper and chromium were enriched to only a minor extent, the lead, zinc, arsenic and cadmium concentrations were markedly enhanced in upper sections. Increasing anthropogenic input associated with industrial activity centred on Glasgow seems responsible for the vertical distribution of lead, zinc and cadmium but a high 0–1 cm level of arsenic (474 μg/g), strongly correlated with enhanced iron content in the surface oxidising layer of sediment, appears attributable to post-depositional diagenetic mobilisation and upward migration in the reducing zone of the sediment column.Leaching, using CH₃CO₂H/NH₂OH·HCl, released over 90% and 80% of the common metal pollutants, lead and zinc, from surface sediment. Onset of an approximately tenfold increase in lead and zinc concentrations above “background” levels of 13±2 μg/g and 47±13 μg/g to upper section levels of 140–170 μg/g and 450–460 μg/g respectively was placed at late-18th century, in accord with the records of the commencement of significant industrial activity in the Glasgow area. Current anthropogenic fluxes (μg/cm² /yr) of lead (2.51±0.34) and zinc (8.84±1.20) to the sediment are in agreement with recent atmospheric deposition data for the adjoining Clyde Sea Area.The general concordance between anthropogenic metal fluxes to Loch Lomond sediment and atmospheric deposition fluxes endorses the potential usefulness of Loch Lomond sediment data to the resolution of pollution sources in the adjoining sea lochs and firth of the Clyde Sea Area, illustrated here through consideration of the comparative distribution of chromium in relation to its historical use.     

Lead in coastal sediments: The case of the elefsis gulf,Greece

Lead was determined in surface sediments and cores of a typical, polluted, almost enclosed Mediterranean embayment, the Gulf of Elefsis, near Athens. Total lead concentrations of 500–600 μg g⁻¹ were found in the surface sediments of the northeast section of the gulf, near major industries. However, a few kilometers from the source the concentrations decrease to ∼ 40m μg g⁻¹; the background pre-industrial levels are ∼ 10 μg g⁻¹ (in the < 61 μm fraction). Sequential extractions, consideration of the Pb/Al and Pb/Zn ratios, etc., indicate that the upper 5–15 cm of the sediment column are greatly enriched with lead of anthropogenic origin, which is mainly associated with fine particles. Redox reactions play an important role in the distribution and chemistry of lead, most of which (∼ 40%) is associated with organic matter and sulphides (extracted by EDTA); another ∼ 30% is associated with iron and manganese coatings and carbonates, with only a small but significant 3–4% of the total in a readily exchangeable form. The latter, under given conditions, may influence the lead concentrations in the overlying waters.     

The use of Pb/210Pb ratios in lake sediments for estimating atmospheric fallout of stable lead in South-Central Ontario,Canada

The ratio of Pb concentrations (μg g⁻¹) to excess ²¹⁰Pb (²¹⁰Pb_exc) activities (dpm g⁻¹) in the surface (0–1 cm) sediments of lake cores, together with a knowledge of atmospheric ²¹⁰Pb fluxes, were used to estimate the atmospheric deposition of stable Pb in south-central Ontario, Canada. Between three and five cores were collected from each of 10 lakes, while in one lake (Red Chalk - Main Basin) a total of 25 cores were obtained.The average atmospheric ²¹⁰Pb_exc flux to the main basin of Red Chalk Lake was calculated to be 1.1 dpm cm⁻² year⁻¹, a value which compares favourably with literature estimates of ²¹⁰Pb deposition for Ontario. The surface Pb/²¹⁰Pb_exc ratios for 61 cores ranged between 1.26 and 3.44 μg dpm⁻¹(average 2.15 ± 0.45 μg dpm⁻¹). Therefore, the predicted atmospheric Pb deposition was 14–38 mg m⁻² year⁻¹ (average 24 ± 5.0 mg m⁻² year⁻¹). This estimate of stable Pb fallout is similar to those measured by alternate methods and indicates that elemental ratios in lake sediments might be useful for predicting the behaviour of other contaminants in lakes.     

Heavy metal conservation in Lake Cadagno sediments: Historical records of anthropogenic emissions in a meromictic alpine lake

Currently, pollution by heavy metals is one of our most serious environmental problems. Metals such as lead and cadmium enter the biosphere through biogenic and anthropogenic emissions and have been steadily accumulating in soils and sediments. We report on a remote mountain lake in the Swiss Alps where the unusual conditions present have led to the accumulation of several heavy metals in the sediments. The sulfide rich environment contains precipitates of cadmium, lead and zinc. The anoxic conditions and prevalence of sulfate reducing bacteria in the water column have prevented the remobilisation of the metals leaving them trapped in the sediments. This has resulted in the formation of surprisingly “stable” metal profiles which have been correlated to levels of human and industrial activity and provide the means of reconstructing a record of human impact and pollution over the past 50 to 100 years. We suggest that such metals in sediment profiles can also be used as chronological markers in cases where cost or sampling difficulties preclude the use of radiological ¹³⁷Cs and ²¹⁰Pb dating. Stable metal profiles are valuable sources of environmental data, they reveal pertinent information on the atmospheric transport of contaminants and are relatively simple to analyse.     

Distribution of artificial radionuclides in deep sediments of the Mediterranean Sea

Artificial radionuclides enter the Mediterranean Sea mainly through atmospheric deposition following nuclear weapons tests and the Chernobyl accident, but also through the river discharge of nuclear facility effluents. Previous studies of artificial radionuclides impact of the Mediterranean Sea have focussed on shallow, coastal sediments. However, deep sea sediments have the potential to store and accumulate pollutants, including artificial radionuclides. Deep sea marine sediment cores were collected from Mediterranean Sea abyssal plains (depth > 2000 m) and analysed for ^239,240Pu and ¹³⁷Cs to elucidate the concentrations, inventories and sources of these radionuclides in the deepest areas of the Mediterranean. The activity — depth profiles of ²¹⁰Pb, together with ¹⁴C dating, indicate that sediment mixing redistributes the artificial radionuclides within the first 2.5 cm of the sedimentary column. The excess ²¹⁰Pb inventory was used to normalize ^239,240Pu and ¹³⁷Cs inventories for variable sediment fluxes. The ^239,240Pu/²¹⁰Pb_xs ratio was uniform across the entire sea, with a mean value of 1.24 × 10^− 3, indicating homogeneous fallout of ^239,240Pu. The ¹³⁷Cs/²¹⁰Pb_xs ratio showed differences between the eastern (0.049) and western basins (0.030), clearly significant impact of deep sea sediments from the Chernobyl accident. The inventory ratios of ^239,240Pu/¹³⁷Cs were 0.041 and 0.025 in the western and eastern basins respectively, greater than the fallout ratio, 0.021, showing more efficient scavenging of ^239,240Pu in the water column and major sedimentation of ¹³⁷Cs in the eastern basin. Although areas with water depths of > 2000 m constitute around 40% of the entire Mediterranean basin, the sediments in these regions only contained 2.7% of the ^239,240Pu and 0.95% of the ¹³⁷Cs deposited across the Sea in 2000. These data show that the accumulation of artificial radionuclides in deep Mediterranean environments is much lower than predicted by other studies from the analysis of continental shelf 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.     

Total mercury distribution in sediment cores from Kuwait Bay

Five sediment cores from Kuwait Bay were taken in order to study the present distribution of total mercury (THg) in the vicinity of the Salt and Chlorine Plant (SCP) operated in the 1963–1985 period. The THg concentration profiles were also determined in four sediment cores from the northern part of Kuwait Bay. Additionally, average THg contents were measured in the surface layer (40 cm) of five sediment samples in the entrance of Kuwait Bay, in order to compare the present Hg levels in other parts of this reservoir. The cores were dated by ²¹⁰Pb method. The observed contents of mercury were in the range of 35 to 2000 µg/kg dry weight (ppb). Thus, the bottom sediments in these three areas of Kuwait Bay are still contaminated by Hg. In a few cases, the depth concentration profiles of THg were disturbed as an effect of partial mixing of the sediment layers, especially in the shallow, northern part of Kuwait Bay. This suggestion was supported by the results of additional measurements of the anthropogenic ¹³⁷Cs profiles in the same cores.     

Distribution and modelling of rare earth elements in Chinese river sediments

Fifty-nine sediment samples were collected from the major rivers of China and analysed using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The background rare earth element (REE) concentrations (μg/g) of these samples were: Sc, 11.1 (1.3–23.1); Y, 13.7 (3.3–24.8); La, 30.8 (7.6–57.2); Ce, 64.4 (16.5–122.6); Pr, 7.3 (1.6–14.4); Nd, 27.8 (5.6–58.5); Sm, 5.74 (1.1–11); Eu, 0.98 (0.05–1.7); Gd, 8.9 (1.6–16.8); Tb, 0.62 (0.12–1.2); Dy, 3.0 (0.53–5.0); Ho, 0.55 (0.09–1.00); Er, 1.4 (0.26–2.4); Tm, 0.19 (0.06–0.4); Yb, 1.0 (0.22–2.9); Lu, 0.16 (0.05–0.42). The total REE concentration (ΣREE), light-REE concentration (LREE) and heavy-REE concentration (HREE) were 44.5–315.8, 38.1–264.6 and 6.36–51.2 μg/g, respectively. The ratio of LREE to HREE ranged from 3.7 to 7.7. The average ratio was approx. 5.1 and did not show much variation with location. Total and individual element concentrations were normally distributed. The variation in the average REE concentration was not greater than 25 μg/g. A high degree of correlation was found between the REEs. Factor analysis indicated that REE concentrations in sediments were mainly described by two factors and the loading of the first two factors could be described by: Y = 1 − X². Factor score plots were employed to distinguish between samples of natural and anthropogenic origin. Based on the inter-correlation determined between REEs in sediment samples, a model was developed to predict REE concentrations.     

Pb and 210Pb in a tropical river environment

The Periyar River in south India receives the major share of Pb and ²¹⁰Pb from effluents released by factories along its bank that process monazite ore and rock phosphate. Their distribution in the river system is influenced by the rains during the monsoon and by salinity during the non-monsoon period. The concentration of both Pb and ²¹⁰Pb in the sediments from the backwater zone was observed to increase during the monsoon due to sediment transport from the upstream industrial zone. The water in the backwater zone showed increased levels of Pb and ²¹⁰Pb in the non-monsoon period, due possibly to solubilization from the sediments as a result of salinity changes. The levels of Pb and ²¹⁰Pb in the river water are much lower than the international standards for safe limits in drinking water. No significant concentration of Pb and ²¹⁰Pb above a background level was observed in fish obtained from the river.     

Distribution,cycling and mean residence time of 226Ra, 210Pb and 210Po in the Tagus estuary

Results for dissolved and particulate ²²⁶Ra, ²¹⁰Pb and ²¹⁰Po in the Tagus river, estuary and coastal sea system show different distribution and chemical behaviour patterns for these radionuclides in the three aquatic environments. ²²⁶Ra from riverborne particles dissolves in the estuary and contributes to increased concentrations of dissolved ²²⁶Ra in estuarine water. In the estuary, dissolved ²¹⁰Pb and ²¹⁰Po from river discharge and atmospheric deposition are scavenged by suspended matter, which in turn becomes enriched in these nuclides in comparison with riverborne particles. As a result of these processes, the estuarine water flowing into the coastal sea contains enhanced concentrations of dissolved ²²⁶Ra, but is depleted in dissolved ²¹⁰Pb and ²¹⁰Po. Under average river flow conditions, mass balance calculations for dissolved ²¹⁰Po and ²¹⁰Pb in the estuary allowed their mean residence times to be estimated as 18 and 30 days, respectively. Due to the rapid sorption of these radionuclides on to settling particles, bottom sediments in the estuary represent a sink for ²¹⁰Pb and ²¹⁰Po from both natural sources and industrial waste releases. Results also suggest that partial re-dissolution of these radionuclides from bottom sediments and intertidal mudflats is likely to occur in the mid- and low-estuary zones. Nevertheless, box-model computations indicate that the discharge of ²¹⁰Pb and ²¹⁰Po into the coastal sea takes place mainly with the transport of sediment, whereas the discharge in the dissolved fraction can only account for one third of the activities entering the estuary in the soluble phase. Implications of these results to the cycling of radionuclides in phosphate waste releases into estuarine environments are discussed.     

Analytical and sampling constraints in ²¹⁰Pb dating

²¹⁰Pb dating provides a valuable, widely used means of establishing recent chronologies for sediments and other accumulating natural deposits. The Constant Rate of Supply (CRS) model is the most versatile and widely used method for establishing ²¹⁰Pb chronologies but, when using this model, care must be taken to account for limitations imposed by sampling and analytical factors. In particular, incompatibility of finite values for empirical data, which are constrained by detection limit and core length, with terms in the age calculation, which represent integrations to infinity, can generate erroneously old ages for deeper sections of cores. The bias in calculated ages increases with poorer limit of detection and the magnitude of the disparity increases with age. The origin and magnitude of this effect are considered below, firstly for an idealised, theoretical ²¹⁰Pb profile and secondly for a freshwater lake sediment core. A brief consideration is presented of the implications of this potential artefact for sampling and analysis.     

Sources of anthropogenic lead in sediments from an artificial lake in Brasília-central Brazil

Pb concentration and Pb isotopic composition are known to represent powerful tools to investigate the history of Pb pollution in water and sediments. In this paper, we present and discuss the results of a detailed study of sediments deposited in the Paranoá Lake, a 44-year-old artificial reservoir in Brasília, central Brazil. Pb concentration and isotopic composition of the sediments were obtained by ID-TIMS, on three different sample fractions: leachate, residue, and bulk sample. The leachate phase has proven to be most efficient to distinguish between anthropogenic and natural Pb inputs. In the Paranoá lake, important sources of contamination were recognized, producing higher Pb concentrations (max. 37.68 ppm) and significant variations in Pb isotopic composition, relative to the regional geogenic background. Contamination of the sediments due to anthropogenic activity produced less radiogenic Pb isotopic compositions (206Pb/207Pb=1.15-1.17), compared with the regional natural composition (206Pb/207Pb=1.19-1.25). 210Pb analyses along one bore hole which sampled the entire sediment section indicated a sedimentation rate of 8.2+/-1.8 mm/year. The combined use of the 210Pb ages and Pb isotopic compositions of these samples revealed three distinct periods in the lake history: (1) the period of the time formation of the lake in 1959 until ca. 1970 was characterized by the deposition of sediments displaying more radiogenic Pb isotopic signature, (2) the time interval from the start of the process of eutrophication at 1970, until 1995, was characterized by the deposition of sediments having less radiogenic average compositions, and (3) from 1995 until the present represents a period of recovery of water quality, after two sewage treatment stations started to operate.     

A comparison of phosphorus retention in lakes determined from mass balance and sediment core calculations

Phosphorus retention (TP_acc) was determined in 7 lakes in Ontario, Canada from mass balances and from the direct measurement of phosphorus accumulation in the sediments. Phosphorus retentions determined using the mass balance technique ranged between 20 ± 4.0 and 95 ± 23 mg/m²/yr and were slightly lower than those calculated by multiplying sediment total phosphorus (TP) concentrations by sediment accumulation rates (49 ± 14 to 148 ± 37 mg/m²/yr). The lower TP_acc values measured using the mass balance approach may result from the underestimation of external TP inputs. Alternatively, it is suggested that in the more acidic lakes, a decrease in TP concentrations in the lakewaters and/or a decrease in TP export from the catchment may have resulted in a decrease in TP_acc through time. Thus, relatively higher TP_acc values would be calculated using the sediment approach (since TP_acc values calculated from the sediment data are averaged over a greater number of years than those calculated from the mass balance data).Provided several cores are collected from the lake, the direct measurement of sediment TP and sediment accumulation rates for estimating TP_acc may be a suitable alternative to mass balances, especially in situations where it is not possible to measure all inputs of TP to the lake.     

Mobility of Pb in salt marshes recorded by total content and stable isotopic signature

Total lead and its stable isotopes were analysed in sediment cores, leaves, stem and roots of Sacorconia fruticosa and Spartina maritima sampled from Tagus (contaminated site) and Guadiana (low anthropogenic pressure) salt marshes. Lead concentration in vegetated sediments from the Tagus marsh largely exceeded the levels in non-vegetated sediments. Depth profiles of (206)Pb/(207)Pb and (206)Pb/(208)Pb showed a decrease towards the surface ((206)Pb/(207)Pb=1.160-1.167) as a result of a higher proportion of pollutant Pb components. In contrast, sediments from Guadiana marsh exhibited low Pb concentrations and an uniform isotopic signature ((206)Pb/(207)Pb=1.172+/-0.003) with depth. This suggests a homogeneous mixing of mine-derived particles and pre-industrial sediments with minor inputs of anthropogenic Pb. Lead concentrations in roots of plants from the two marshes were higher than in leaves and stems, indicating limited transfer of Pb to aerial parts. A similar Pb isotopic signature was found in roots and in vegetated sediments, indicating that Pb uptake by plants reflects the input in sediments as determined by a significant anthropogenic contribution of Pb at Tagus and by mineralogical Pb phases at Guadiana. The accumulation in roots from Tagus marsh (max. 2870 microg g(-1) in S. fruticosa and max. 1755 microg g(-1) in S. maritima) clearly points to the dominant role of belowground biomass in the cycling of anthropogenic Pb. The fraction of anthropogenic Pb in belowground biomass was estimated based on the signature of anthropogenic Pb components in sediments ((206)Pb/(207)Pb=1.154). Since no differences exist between Pb signature in roots and upper sediments, the background and anthropogenic levels of Pb in roots were estimated. Interestingly, both background and anthropogenic Pb in roots exhibited a maximum at the same depth, although the proportion of anthropogenic Pb was relatively constant with depth (83+/-4% for S. fruticosa and 74+/-8% for S. maritima).     

Temporal trends of pollution Pb and other metals in east-central Baffin Island inferred from lake sediment geochemistry

Concentrations and stable isotope ratios of lead (Pb) from lake sediments were used to quantify temporal patterns of anthropogenic Pb pollution in the Clyde River region of Baffin Island, Arctic Canada. Surface sediments from eight lakes on eastern Baffin Island and one from northern-most Greenland, spanning a gradient of 20° latitude, showed great variability with respect to Pb concentration and stable isotopic Pb ratios, with little apparent latitudinal trend. To constrain the temporal evolution of regional Pb pollution, a well-dated core from one of the sites, Lake CF8 on east-central Baffin Island, was analyzed geochemically at high stratigraphic resolution. A pronounced decrease in the ²⁰⁶Pb/²⁰⁷Pb ratio occurs in sediments deposited between 1923 and the mid-1970s, likely reflecting alkyl-Pb additives derived from the combustion of fossil fuels at a global scale. A two-component mixing model indicates that 17-26% of the Pb in the labile fraction of sediments deposited in Lake CF8 between 2001 and 2005 is from anthropogenic input. A Pb-Pb co-isotopic plot (²⁰⁶Pb/²⁰⁷Pb vs.²⁰⁸Pb/²⁰⁶Pb ratios) of the Lake CF8 time series data indicates multiple possible sources of industrial Pb pollution. Despite widespread reductions in industrial Pb emissions since the 1970s, there is no evidence for attendant reductions of pollution Pb at Lake CF8. Enhanced scavenging from increased primary production as well as changing precipitation rates as climate warms may represent important factors that modulate Pb deposition to Lake CF8, and Arctic lakes elsewhere.     

The significance of atmospheric deposition of heavy metals in four Danish lakes

The atmospheric deposition rate of heavy metals was determined throughout a seventeen month period at four lakes and a control station across Mid-Jutland, Denmark, and its significance was assessed in relation to the concentrations of Zn, Cu, Pb, and Cd in water, sediment and aquatic macrophytes (Phragmites australis (Cav.) Trin, Littorella uniflora (L.) Ashers., Isoetes lacustris L. and Juncus bulbosus L.) from Lake Hampen, Lake Meldgaard, Lake Sortesø, and Lake Gødstrup. Mean annual deposition rates of 1.81–2.77 mg Cu m^?2, 4.09–8.73 mg Pb m^?2, and 0.21–0.37 mg Cd m^?2 were determined. For Zn a mean deposition rate of 15 mg Zn m^?2 year^?1 was used (Hovmand, 1979). The atmospheric deposition per m² of Zn and Cu amounts to 0.2–37%, 0.05–4.3% and 3.4–107% of the contents present in the water column of the lakes, the upper 10 cm of the littoral sediment and in dense vegetation of aquatic macrophytes, respectively. Equivalent figures for Pb and Cd are 1.8–649%, 0.8–30.6%, and 16.8–951%. In the profundal sediments of the oligotrophic Lake Hampen, post-war atmospheric deposition has increased the heavy metal concentration and content up to 180 times. The Pb concentrations in sediments from different depths were significantly correlated with the post-war consumption of gasoline in Denmark. It is concluded that atmospheric deposition of heavy metals results in a significant contamination of lakes, especially oligotrophic lakes for which aerial fallout is the major source. It is further concluded that lake sediments uncontaminated with heavy metals are probably no longer found in Denmark.     

Natural rates of sediment containment of PAH, PCB and metal inventories in Sydney Harbour, Nova Scotia

Analyses of metal and organic contaminants were carried out on 41 sediment cores, dated using ²¹⁰Pb and ¹³⁷Cs, from the heavily industrialized region of Sydney Harbour, N.S. to evaluate the history of contamination and to predict the rates of natural containment of the harbour by sediment burial. Geochronologies for metals (eg. Pb, As) and polycyclic aromatic hydrocarbons (PAHs) are correlated with the development of the steel and coke industries in the Sydney region while polychlorinated biphenyl (PCB) geochronologies reflect the disposal of electrical equipment used in the steel mill/coking operations. Pb was derived mainly from atmospheric emissions and its concentration has declined exponentially with time in harbour sediments since the closure of the steel mill/coke ovens in the 1980s with a time constant of about 15 years. This represents the time scale for the circulation of this particle-associated contaminant in transient catchment basins prior to permanent deposition in the sediments. PAH and PCB sediment concentrations have also declined exponentially with time since the 1980s, but with a smaller time constant of 10 years owing to the fact that they enter the harbour directly with steel mill and coke oven effluent rather than through atmospheric pathways. Since the time dependence for the burial of metal and organic inventories can be modeled by first order processes, future contaminant levels can be predicted for surface sediments in Sydney Harbour. Mean sediment concentrations of metal and organic contaminants in the upper 5 cm throughout most of the harbour are predicted to decline to levels below the effects range-medium (above which organisms are very likely to be negatively affected by the presence of a contaminant) by 2030.     

Pollution status of the Indus River,Pakistan, through heavy metal and macronutrient contents of fish,sediment and water

Concentrations of Ag, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn and Hg, together with Na, K, Ca and Mg in 19 species of fish captured from the Indus River, Pakistan, are estimated by the atomic absorption method. Corresponding data for sediment and water from 11 sites along the down-stream route of the river are also reported. Mercury and arsenic concentrations were high (3.920 and 3.072 μg/g, respectively) in the muscle of fish from Guddu barrage as compared with those from other sites. Hetroptirus fossilus showed maximum concentrations of Ag, Cu and Pb in its muscle as compared with other fish. Labeo calbasu from Guddu barrage showed highest As concentration at 3.072 μg/g. Mystus vitatus from Chashma barrage contained maximum cadmium concentration at 0.990 μg/g. Several other fish exhibited elevated levels of metals along the downstream route of the river, a trend exhibited also by the elevated metal contents of sediment and water at Guddu and Lloyd barrages. The study indicated a gross pollution of the sediment and water at various locations of the river, e.g. As (7.452 μg/g) in sediment from Lloyd barrage, Hg (5.710 μg/g) in sediment from Jinnah barrage, Pb (2.709 μg/g) in sediment from Guddu barrage and Mn (0.038 μg/g) in water from Lloyd barrage. The macronutrients showed an inverse relationship with trace metals. Hetroptirus fossilus could be used as indicator species for Ag, Cu and Pb.     

Mercury accumulation and attenuation at a rapidly forming delta with a point source of mining waste

The Walker Creek intertidal delta of Tomales Bay, California is impacted by a former mercury mine within the watershed. Eleven short sediment cores (10 cm length) collected from the delta found monomethylmercury (MMHg) concentrations ranging from 0.3 to 11.4 ng/g (dry wt.), with lower concentrations occurring at the vegetated marsh and upstream channel locations. Algal mats common to the delta's sediment surface had MMHg concentrations ranging from 7.5 to 31.5 ng/g, and the top 1 cm of sediment directly under the mats had two times greater MMHg concentrations compared to adjacent locations without algal covering. Spatial trends in resident biota reflect enhanced MMHg uptake at the delta compared to other bay locations. Eighteen sediment cores, 1 to 2 m deep, collected from the 1.2 km² delta provide an estimate of a total mercury (Hg) inventory of 2500 ± 500 kg. Sediment Hg concentrations ranged from pre-mining background conditions of approximately 0.1 μg/g to a post-mining maximum of 5 μg/g. Sediment accumulation rates were determined from three sediment cores using measured differences of ¹³⁷Cs activity. We estimate a pre-mining Hg accumulation of less than 20 kg/yr, and a period of maximum Hg accumulation in the 1970s and 1980s with loading rates greater than 50 kg/yr, corresponding to the failure of a tailings dam at the mine site. At the time of sampling (2003) over 40 kg/yr of Hg was still accumulating at the delta, indicating limited recovery. We attribute observed spatial evolution of elevated Hg levels to ongoing inputs and sediment re-working, and estimate the inventory of the anthropogenic fraction of total Hg to be at least 1500 ± 300 kg. We suggest ongoing sediment inputs and methylation at the deltaic surface support enhanced mercury levels for resident biota and transfer to higher trophic levels throughout the Bay.     

Heavy metal pollution profiles of dated sediment cores from hebe haven, Hong Kong

Eight sediment cores from Hebe Haven were collected and studied for metals including Cd, Cr, Cu, Fe, Ni, Pb, Zn and Ca. ²¹⁰Pb and ¹³⁷Cs activities were determined to date the time of deposition of the sediment. Hebe Haven is a yacht area and is close to the urbanized coast with several dyeing factories. Except Cd, the greatest enrichment was found at locations closest to the Ho Chung Stream which carried domestic and industrial wastewater to Hebe Haven. Concentrations as high as 0.930, 120, 131, 42.3 and 50.9 mg/kg were found for Cd, Cr, Zn, Cu and Pb, respectively. The corresponding enrichment factors are 13(Cd), 7.0(Cr), 2.9(Zn), 5.2(Cu) and 2.4(Pb). The extent of pollution diminishes from the riverine source. Cr is a typical example because its enrichment was mostly attributed to the nearby dyeing operation. The distribution of Cd appears more complicated. A maximum concentration of 3.60 mg/kg was found at a location far from Ho Chung Stream and with no nearby municipal or industrial activity. No significant Fe and Ni enrichment was found in the area. Ca in all cores decreases towards the sediment-water interface. It is probable that the abundance of shellfish has decreased as a result of excessive exploitation as seafood and pollution. ²¹⁰Pb activity and heavy metal concentrations of surficial layers have been “diluted” by excessive deposition of Fe-deficient particles. This likely indicates the rapid deposition of coarser and sandy particles during the construction of a nearby large housing estate. Some ²¹⁰Pb activity profiles have periodic low values in deeper layers, which should correspond to events of rapid deposition of erosion during heavy typhoons and rainstorms. Overall, the sedimentation rates calculated were in the range of 0.351–0.561 cm/yr. In one site (Core S4) close to the riverine source and with the best available dating data, the recent anthropogenic fluxes of heavy metals in μg cm⁻² yr⁻¹ are estimated as: 0.081(Cd), 22(Cr), 20(Zn), 6.4(Cu) and 7.4(Pb).