Influence of liming on metal sequestration in lake sediments over recent decades

Sediment profiles from five limed and six reference softwater lakes included in Swedish monitoring programmes were subjected to multi-element analysis to investigate the influence of lime treatment since 1977 on the sequestration of metals in lake sediments. We hypothesised that liming causes increased sedimentation of elements for which the mobility is primarily controlled by pH, e.g. Al, Cd, Co, Ni and Zn, whereas elements that are less influenced by pH fluctuations, e.g. Hg and Pb, are not affected by lime treatment. Further, we introduce a normalisation of metal concentrations with respect to Cu concentration in order to separate the effects of lime treatment from those related to temporal trends in airborne metal deposition or short-term variations in environmental conditions. This approach is shown to emphasise the effect of liming on the sediment accumulation of metals, thus separating it from other sources of variability. We found that liming causes increased sequestration of Al, As, Cd, Co, Fe, Mn, Ni and Zn, in the case of As and Co probably at least partly caused by an increased adsorption to Al, Fe and Mn oxyhydroxides. On the other hand, no influence of lime treatment could be demonstrated for Hg, Pb, Cr, V and P, despite an increase of pH by about two units.     

Seasonal water quality variations in a river affected by acid mine drainage: the Odiel River (South West Spain)

This paper intends to analyse seasonal variations of the quality of the water of the Odiel River. This river, together with the Tinto River, drains the Iberian Pyrite Belt (IPB), a region containing an abundance of massive sulphide deposits. Because of mining activity dating back to prehistoric times, these two rivers are heavily contaminated. The Odiel and Tinto Rivers drain into a shared estuary known as the Ría of Huelva. This work studies dissolved contaminant data in water of the Odiel River collected by various organisations, between October 1980 and October 2002, close to the rivers entry into the estuary. Flow data for this location were also obtained. The most abundant metals in the water, in order of abundance, are zinc (Zn), iron (Fe), manganese (Mn) and copper (Cu). Arsenic (As), cadmium (Cd) and lead (Pb) are also present but in much lower quantities. The quality of the river water is linked to precipitation; the maximum sulphate, Fe, Zn, Mn, Cd and Pb concentrations occur during the autumn rains, which dissolve the Fe hydroxysulphates that were precipitated during the summer months. In winter, the intense rains cause an increase in the river flow, producing a dilution of the contaminants and a slight increase in the pH. During spring and summer, the sulphate and metal concentration (except Fe) recover and once again increase. The Fe concentration pattern displays a low value during summer due to increased precipitation of ferric oxyhydroxides. The arsenic concentration displays a different evolution, with maximum values in winter, and minimum in spring and summer as they are strongly adsorbed and/or coprecipitated by the ferric oxyhydroxides. Mn and sulphates are the most conservative species in the water. Relative to sulphate, Mn, Zn and Cd, copper displays greater values in winter and lower ones in summer, probably due to its coprecipitation with hydroxysulphates during the spring and summer months. Cd and Zn also appear to be affected by the same process, although to a lower degree than Cu, experiencing a slight reduction in summer with respect to Mn and sulphates.     

Concentrations of heavy metals and plant nutrients in water, sediments and aquatic macrophytes of anthropogenic lakes (former open cut brown coal mines) differing in stage of acidification.

Concentration of heavy metals (Al, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V and Zn) as well as macronutrients (N, P, K, Ca, Mg, S) were measured in water, bottom sediments and plants from anthropogenic lakes in West Poland. The collected plants were: Phragmites australis, Potamogeton natans, Iris pseudoacorus, Juncus effusus, Drepanocladus aduncus, Juncus bulbosus, Phalaris arundinacea, Carex remota and Calamagrostis epigeios. Two reference lakes were sampled for Nymphaea alba, Phragmites australis, Schoenoplectus lacustris, Typha angustifolia and Polygonum hydropiper. These plants contained elevated levels of Cd, Co, Cr, Cu and Mn, and part of the plants contained in addition elevated levels of Mn, Fe, Pb, Ni and Zn. Analyses of water indicated pollution with sulfates, Cd, Co, Ni. Zn, Pb and Cu, and bottom sediments indicated that some of the examined lakes were polluted with Cd, Co and Cr. Strong positive correlations were found between concentrations of Co in water and in plants and between Zn in sediments and plants, indicating the potential of plants for pollution monitoring for this metal. Heavy metal accumulation seemed to be directly associated with the exclusion of Ca and Mg.     

Natural attenuation processes in two water reservoirs receiving acid mine drainage

Characteristics of water profiles and sulphide formation processes in sediments were studied in two water reservoirs affected by acid mine drainage in order to investigate the mechanisms controlling the physical and chemical processes that, under favourable conditions, act to reduce the toxicity, mobility and concentration of metals and metalloids in the water column. Water columns and pore-waters from sediments were analysed for Fe species, trace elements (As, Cd, Co, Cu, Mn, Ni, Pb, Zn, Cr), sulphide, sulphate and bicarbonate. Inorganic reduced sulphur compounds (acid volatile sulphur, pyrite sulphur and elemental sulphur) and reactive Fe were determined in the sediments. A sequential extraction was also performed. Both reservoirs behave like holomictic and monomictic lakes, with a summer thermal stratification that disappears during winter. pH values between 4 and 7 can be observed along the water columns. Pore-water concentrations of up to 25 mg/l of Fe, 4 mg/l of Al, 1.3 mg/l of Zn, 170 µg/l of Pb, 11 µg/l of As, etc. have been found. The results suggest that toxic elements such as Cu, Zn, Co, Pb, Cr, As, etc. are mainly found in the bioavailable fraction which is the most hazardous for the environment. The calculated degree of sulphidization (DOS) and degree of pyritization (DOP) values indicates that removal of trace elements from anoxic pore-waters occurs by coprecipitation and/or adsorption on newly formed Fe sulphides (framboidal pyrite), attenuating the contamination. However oxidation of the sediments during turnover periods also occurs, which releases toxic elements back into the water column.     

Species of dissolved metals derived from oligotrophic hard water

By fractioning of dissolved organic carbon (DOC) and of associated metals Na, K, Mg, Ca, Al, Fe, Mn, Ni, Cr, Cu, Pb, Cd, and Zn according to the molecular sizes by means of gel chromatography in several stages, it could be shown that all metals, even the alkaline and alkaline earth metals, are, to a measurable degree, present in chelated form. This type of association covers 97.3% with Pb, 94.6% with Al, 91.5% with Cr, 82.2% with Fe of the total concentrations of each metal mentioned. About 69% of all metal chelates are represented by Mg-compounds. This may be caused by pre-treatment procedures, nevertheless the Mg-concentrations of the different DOC-fractions indicating to be one regulating factor for the uptake of other metals in the studied hard water. The chelated form was also obtained with Mn, Cd, Zn, and Mg, while with Cu, Ni, Na, Ca, and K there is an abundance of ionic forms.The metal distribution within the different molecular size fractions of the DOC proves the existence of specific distribution pattern for Pb and Mn: Pb is preferably chelated by macromolecular substances, whereas Mn combines mainly with minor ones. Cr seems to behave similar as Pb. Regulation' mechanisms for the different metal distribution patterns within the DOC-fractions as well as ecophysiological aspects of the results are discussed.     

Simultaneous multielement determination of trace metals in lake waters by ICP emission spectrometry with preconcentration and their background levels in Japan

An analytical method combining a preconcentration followed by determination with inductively coupled plasma emission spectrometry (ICPES) was developed for monitoring background levels of trace metals in natural waters. Complexes of trace metals (Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb) and 8-hydroxyquinoline were absorbed to a C₁₈ chemically bonded silica gel disposable plastic column. They were eluted with methanol and digested with nitric acid. With this preconcentration procedure, about 500-fold preconcentration is possible. Simultaneous multielement analysis with ICPES ensures the necessary sensitivity to measure the trace metals in Lake Mashu water at concentration ranges from μg l^?1 (ppb) to ng l^?1 (ppt).Lake Mashu is a deep oligotrophic lake in Hokkaido, Japan and famous for the highest transparency in the world. The trace metal concentrations in Lake Mashu were extremely low: Fe 2.6; Al 1.2; Mn 0.76; Zn 0.63; V 0.15; Cu 0.069; Ti 0.06; Pb 0.05; Ni 0.027; Cd < 0.006; and Co < 0.004 μg l^?1. The suitability of Lake Mashu for a background level monitoring station for global environmental pollution was assessed by the comparison to reference data for other lakes in the world.     

Mobility of trace metals in pore waters of two Central European peat bogs

Vertical peat profiles can only be used as archives of past changes in pollution levels if atmogenic elements are immobile after their burial. For mobile elements, similar pore-water concentrations can be expected at different peat depths. Concentrations of Pb, Cu, Zn, Cr, Mn, Fe, Co and Cd were determined in surface bog water and bog pore water 40 cm below surface in two Sphagnum-dominated peat bogs in the Czech Republic. Velke jerabi jezero (VJJ) is an upland bog located in an industrial area, Cervene blato (CB) is a lowland bog located in a rural area. Metal concentrations were monitored seasonally over 3 years (2002--2005) at both sites. Higher concentrations of Pb, Cu, Zn, Cr and Cd and lower concentrations of Mn, Fe and Co were found at the less polluted CB compared to VJJ. No clear-cut seasonality was observed in metal concentrations in bog waters, despite seasonal differences in industrial emission rates of pollutants (more coal burning in winter than in summer). This contrasts with an earlier observation of distinct seasonality in sulfate concentration and isotope composition in these stagnating bog waters. Peat substrate 40 cm below current bog surface represented pre-industrial low-pollution environment, yet pore waters at such depths contained the same metal concentrations as surface waters. The only exception was Pb, whose concentration in water solutes increased with increasing depth. Lack of vertical stratification in pore-water contents of Cu, Zn, Cr, Mn, Fe and Co indicated vertical mobility of these metals.     

Metal burdens in surface sediments of limed and nonlimed lakes

Acidification has been shown to increase the concentrations of many metals in lake water as a result of increased mobility at lower pH, whereas liming has been found to decrease lake water metal concentrations. We hypothesise that increased sedimentation as a result of liming increases the metal burdens in the sediments of limed lakes, but especially those that have been treated directly on the lake surface. We also hypothesise that acidification results in decreased metal burdens in the sediments, whereas near neutral reference lakes and lakes where the lime has been applied on wetlands or upstream have intermediate metal burdens in the sediments. In order to test the hypothesis, we statistically compare the areal metal and P burdens in the sediments of four groups of lakes: (1) Mainly surface limed lakes, (2) Mainly upstream/wetland limed lakes, (3) Near neutral reference lakes and, (4) Acidified reference lakes. The statistical analysis reveals that the surface limed group have significantly higher areal burdens of As, Cd, Co and Zn in the sediment compared to the acidified reference group, despite large variations within the groups. The investigation indicates that surface liming increases the areal burdens in the sediments of Cd and Pb, probably of As, Ca and Mn and possibly Co and Zn, whereas acidification decreases the areal burdens in sediments of Cd, Fe, Mn and possibly Co, P and Zn. The results of the study confirm the hypothesis.     

Relationships among total recoverable and reactive metals and metalloid in St. Lawrence River sediment: bioaccumulation by chironomids and implications for ecological risk assessment

The availability and bioaccumulation of metals and metalloids, and the geochemical interactions among them, are essential to developing an ecological risk assessment (ERA) framework and determining threshold concentrations for these elements. The purpose of this study was to explore the relationships among total recoverable and reactive metals and metalloid in sediment and their bioaccumulation by chironomids. In the fall of 2004 and 2005, 58 stations located in the three fluvial lakes of the St. Lawrence River and its largest harbour area in Montreal, Canada, were sampled. Nine total recoverable and reactive metals (Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) and one metalloid (As) were measured in whole sediment using two extraction methods: HCl/HNO(3) and HCl 1N, respectively. The bioaccumulation of six metals (Cd, Cr, Cu, Ni, Pb and Zn) and As by chironomids was evaluated in a subset of 22 stations. Strong collinearities were observed between some total recoverable or reactive metal concentrations in sediment; two principal clusters, including collinear metals, were obtained. The first one included metals of mainly geological origin (Al, Cr, Fe, Mn, Ni), while the second one included As, Cd, Cu, Pb and Zn, which likely derive mainly from point sources of anthropogenic contamination. Each element also showed strong collinearity between their total recoverable and reactive forms (0.65< or =r < or =0.97). We can conclude that both chemical forms are equivalent for use in statistical models needed to explain biological responses and also in screening risk assessment. However, these relationships are not always proportional. Lower availability percentages were observed for Cd, Cu and Zn in the highly mixed-contaminated area of the Montreal Harbour, even though concentrations in sediment were higher. We observed a significant correlation (0.50< or =r < or =0.56) between concentrations in chironomids and concentrations of both total recoverable and reactive Cr and Pb in sediment. Arsenic was an exception, with accumulation by chironomids being highly related to reactive sediment concentrations. Finally, we observed variable influences of explanatory factors (e.g. sediment grain size, Al, Fe, Mn, S, TOC), depending on which metal or metalloid was being predicted in chironomids. In this context, it is difficult to choose a universal predictive method to explain the bioaccumulation of specific metals, and more research is still needed into normalization procedures that consider a combination of explanatory factors.     

Accumulation of heavy metals in a lake ecosystem

The concentrations of Cu, Zn, Fe, Mn, Ni, Cd, Pb and Co have been determined in water, bottom sediments, plankton, zoobenthos and ichthyofauna of mesotropic Lake Piaseczno located in eastern Poland. In water, sediments, plankton and benthos the most abundant heavy metals were Fe, Zn and Mn, whereas in fish Zn, Cu, and Mn were most abundant. The amount of heavy metals in the biotic components was dependent upon their concentration in water and partly upon the concentration in bottom sediments. A considerably less important role in the translocation of heavy metals is probably played by trophic interactions.     

Estuarine capacity in removal of trace metals from contaminated river water, Southern Caspian Sea

In the present investigation, the flocculation of dissolved Cd, Cu, Ni, Pb, Mn and Zn with initial concentrations of 1, 2.5 and 5 mg/L in Tadjan River water during mixing with the Caspian Sea water has been studied in order to determine estuarine capacity to remove dissolved metals in the accidental contamination of the river. The flocculation process was investigated on a series of mixtures with salinities ranging from 0.1 to 11 p.p.t. The flocculation rates were indicative of the nonconservative behaviour of Cd, Cu, Ni, Pb, Mn and Zn during estuarine mixing. The order of the final flocculation rate of dissolved metals at 1, 2.5 and 5 mg/L of initial metal concentrations in the river water is as follows:Cu (99%)>Cd (95%)>Zn (88%)>Mn (85%)>Pb (83%)>Ni (73%), Cu(95.6%)>Pb(92.4%)>Cd (90%)>Zn(88.4%)>Mn (81.6%)>Ni(78.8%) and Cd (100%)>Cu(88%)>Ni (85.2%)>Pb (84%)>Zn (83.2%)>Mn (81.2%), respectively. The results also revealed that removal of dissolved metals is not influenced by pH changes and precipitation processes. The flocculation rates revealed that the overall dissolved metal pollution loads may be reduced to about 70% up to about more than 90% during estuarine mixing of Tadjan River with the Caspian Sea water.     

Trends of heavy metal components in the Arctic aerosols and their relationship to the emissions in the Northern Hemisphere

Twenty-one years of observations (1980-2000) of weekly mean concentrations of major anthropogenic and natural metals in the aerosol of the lower Arctic troposphere at Alert have been analyzed by time series analysis for seasonal and long-term trends and by positive matrix factorization for major aerosol components with which metals are associated. Metals at Alert exhibit distinct seasonal variations depending on the source and origin of the metals. Anthropogenic metals such as Pb, Zn and Cu and the sea-salt components Na and Mg exhibit maxima in winter and minima in summer. Similar variations were observed for non-soil fractions of V and Mn. Weak seasonal variations were found for soil-related metals such as Al, Ba, Ca and Fe. If any trend is evident in anthropogenic metals, it is a slight decrease from 1980 to mid-1990s but generally the variation is not monotonic. It is found through the winter observations of Pb, Zn, Ni and Cu concentrations that the decline trends have been leveled off and started to increase again around 1995. No long-term trends were detected in Na, Mg and Ca concentrations but a slight decrease is observed for soil components Al, Fe and Ti after 1995. Analysis showed that these trends are mostly associated with the anthropogenic emission variations surrounding the Arctic regions.     

Meteorological simulations of boundary-layer structure during the 1996 Paso del Norte Ozone Study

In the Kristineberg mining area in northern Sweden, massive, pyrite-rich Zn Cu ores are intercalated in ca. 1.9 Ga volcano-sedimentary rocks. Investigations of a tailings impoundment remediated by means of both till coverage and raising the groundwater table have been undertaken. The aim of the study was to characterise the tailings with respect to mineralogy, the chemical composition of both the tailings and the pore water, and to try to identify the significant reactions that may have occurred before and after remediation. It was found that the oxidation front had reached down to depths of between approximately 0.1 and 1.15 m before remediation. The oxidation of sulfides has produced high concentrations of some metals in the pore water; up to 26, 16, 4.1, 2.7 and 82 mg/l have been measured for Al, Mn, Fe and Zn, respectively. Concentrations of metals such as Cd, Co, Cu, Ni and Pb are lower, with average concentrations of 18.4, 83.8, 45, 79.6 and 451 microg/l, respectively. Higher concentrations of major elements such as Ca, Fe, Mn, Mg and S have been measured at depth in pore water than at shallower levels. This is probably caused by flush out of elements after remediation and vertical transport from the upper parts before remediation. The pH is relatively high, approximately 5.5 at most depths in the tailings, except in and around the former oxidation zone where it is lower, and where the highest dissolved concentrations of elements such as As, Cd, Co, Cu, Pb and Zn occur. This is probably due to the release of metals secondarily retained below the oxidation front prior to the remediation. Since the groundwater table is raised, the groundwater reaches the retained metals, which leads to desorption of metals and dissolution of secondary minerals.     

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.     

Dissolved and particulate metal chemistry of the Central and Eastern Basins of Lake Erie

Dissolved and particulate forms of Al, Cd, Co, Cu, Fe, Mn, Ni, Pb and Zn were determined in the Central and Eastern Basins of Lake Erie during May, August and September 1978.No temporal or spatial differences in the average concentrations of dissolved Cu, Ni, Al and Fe were observed between May and September. In contrast, Mn and Zn showed significant seasonal variations with Mn having distinct concentration maxima in both basins during September. This behaviour is attributed to net release of Mn and Zn from the bottom sediments.Phytoplankton activity is shown to be important in causing large increases (1.8–5.4 times the concentrations in May) in particulate elemental concentrations during the bloom periods. The removal of Cu, Ni, Pb and Zn from the water column is mediated by the decay of plankton populations.     

A comparison of native and transplanted Fontinalis antipyretica Hedw. as biomonitors of water polluted with heavy metals

Native and transplanted mosses of the species Fontinalis antipyretica were studied to assess their capacity as biomonitors of heavy metals. Assays were carried out with transplanted mosses (sampled from an unpolluted control stream) exposed for 60 days to five streams polluted with heavy metals. At the same time, native mosses were collected from the exposure sites. Concentrations of N, P, K, Ca, Mg, S, Fe, Al, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, V, and Zn were determined in the mosses (native and transplants), stream waters, and sediments of both exposure and control sites. The results showed that the transplanted mosses accumulated significantly more Al, Cr, Cu, Pb, V, and Zn than the native mosses. The concentrations of Co and Mn in all streams were significantly higher in the native mosses.     

Effect of imposed anaerobic conditions on metals release from acid-mine drainage contaminated streambed sediments

Remediation of streams influenced by mine-drainage may require removal and burial of metal-containing bed sediments. Burial of aerobic sediments into an anaerobic environment may release metals, such as through reductive dissolution of metal oxyhydroxides. Mining-impacted aerobic streambed sediments collected from North Fork Clear Creek, Colorado were held under anaerobic conditions for four months. Eh, pH, and concentrations of Cd, Cu, Fe, Mn, and Zn (filtered at 1.5 μm, 0.45 μm, and 0.2 μm), sulfate, and dissolved organic carbon (DOC) were monitored in stream water/sediment slurries. Two sediment size fractions were examined (2 mm-63 μm and <63 μm). Sequential extractions evaluated the mineral phase with which metals were associated in the aerobic sediment. Released Cu was re-sequestered within 5 weeks, while Fe and Mn still were present at 16 weeks. Mn concentration was lower than in the initial stream water at and beyond 14 weeks for the smaller sized sediment. Cd was not released from either sediment size fraction. Zn was released at early times, but concentrations never exceeded those present in the initial stream water and all was re-sequestered over time. The greatest concentrations of Cu, Fe, Mn, and Zn were associated with the Fe/Mn reducible fraction. Sulfate and Fe were strongly correlated (r = 0.90), seeming to indicate anaerobic dissolution of iron oxy-hydroxy-sulfate minerals. DOC and sulfate were strongly correlated (r = 0.81), with iron having a moderately strong correlation with DOC (r = 0.71). Overall concentrations of DOC, sulfate, Cu, Fe, and Zn and pH were significantly higher (p < 0.05) in the water overlying the small sized sediment samples, while the concentrations of Mn released from the larger sized sediment samples were greater.     

Concentrations and leachability of chemical elements in estuarine sulfur-rich sediments, W. Finland

Concentrations, distributions and mobility of chemical elements were investigated in reduced sulfur-rich estuarine sediments located in western Finland. The main objective was to determine the possible extent of metal leaching when dredged masses of these sulfur-rich sediments are dumped on the land and thus exposed to air. When dredged, the reduced sulfur in the sediments oxidises resulting in a lowering of pH, which in turn is expected to leach metals. The study area is an artificial lake claimed from the Botnian sea in 1962. In this lake, several mass-kills of fish have occurred, believed partly to be due to dredging. Two sediment samples (0-50 and 50-100 cm) were taken from 39 sampling points in the lake. These samples were leached in aqua regia (2:2:2 HNO3/HCl/H2O1) and analysed for Fe, Al, Mg, Ca, K, P, Na, Mn, Zn, Ba, V, Sr, Cr, Ni, Cu, Co, As, Pb, B, Mo and Cd with ICP-AES. Sulfur and organic carbon were analysed with Leco. In a controlled laboratory experiment, the sediments were allowed to oxidise for 1 year while moisturised with deionised water every month. The pH and conductivity were determined in the beginning of the experiment (reduced state) and in the end (oxidised state). In the supernatants in the oxidised states the amount of leached metals (Na, Al, Mn, Zn, Sr, Co, Ni, Cu, Cd, Cr, Pb, U, Li, Rb and As) were determined with ICP-MS. The sediments were found to contain low levels of toxic metals but, as expected, high concentrations of sulfur. In the experiment, pH was lowered (down to 3.0) and the conductivity increased in all samples due to oxidation and release of metal ions. The extent of leaching varied between 0.03% for As and 12.3% for Na. Critical pH values, at which high amounts of metals begin to leach, were obtained graphically. These values varied between 4.8 (Ni) and 3.3 (Cr). Not all elements were controlled by pH, e.g. Mn correlated well with its aqua regia leachable concentration. In a planned dredging operation in the area some 23,300 t (10,500 m3) (dry wt.) of sediments will be dredged. The amounts of metals likely to be leached, according to the results from this study, are as follows (kg): Al (1710), Mn (1230), Zn (59), Sr (39), Co (13), Ni (12), Cu (2) and less than 1 kg of Cd-Cr-As-Pb.     

Trace metals in Shatt al-Arab River,Iraq

The distribution of 10 trace metals Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn have been determined along the northern section of the Shatt al-Arab River, Iraq. Analyses were carried out, employing a flameless AAS instrument. The mean concentrations of the dissolved species were as follows (expressed in μg l^?1): 0.25 Cd, 0.9 Cu, 716 Fe, 1.3 Mn, 0.3 Pb, 0.2 V and 1.8 Zn. Mean concentrations of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn in the particulate matter were 55.2, 6.0, 188, 77, 31 472, 1731, 3807, 93, 207 and 77 μg g^?1 respectively. In the exchangeable fraction of the sediment were 0.15, 5.5, 11.1, 11.9, 1625, 482, 42, 30.5, 25.7 and 6 μg g^?1, whereas in the residual were 0.025, 11.5, 96.1, 22, 5176, 258, 613, 3.9, 162 and 56.8 μg g^?1 respectively. Thus, the exchangeable trace metals represent the following mean percentage of the total; 75% Cd, 33% Co, 10% Cr, 34% Cu, 24% Fe, 63% Mn, 7% Ni, 74% Pb, 14% V and 23% Zn. The concentration of Ni and V were relatively high, this was attributed to the petroleum-rich deposits of the region. The concentrations observed for other metals were lower or equal to those reported for control sites except for Pb which was slightly higher. The data obtained were subjected to simple linear regression analysis and expressed in the form of correlation coefficients. It was found that the inter-elemental relationships are rather complex.     

Behavior of Mn, Fe, Cu, Zn, Cd and Pb discharged from a wastewater treatment plant into an estuarine environment

To obtain information on the fate of trace metals discharged to an estuarine environment, analyses have been made on water and sediment samples from Back River, MD., and on effluent from the large wastewater treatment plant that discharges there. Within 2–3 km of the outfall, the concentration (in μg 1⁻¹) of all metals decreases as follows: Mn, > 120-90; Fe, > 570-300; Cu, 53-7; Zn, 280-9; Cd, 3.5-0.5 and Pb, 31-<4. Except possibly for Mn and Fe, these decreases are much greater than can be ascribed to simple dilution, so physical, chemical or biological processes must be removing metals to the sediments. Correspondingly, sediment concentrations of Cu, Zn, Cd and Pb are approximately one order of magnitude higher than normally found in uncontaminated areas. After the initial decrease, concentrations of Mn and Cd in the water begin to rise again, suggesting remobilization from the sediments. Comparison of the estimated annual discharge of 8 trace metals to the Chesapeake Bay from wastewater treatment plants and from rivers suggests that the wastewater input may be within one order of magnitude of the fluvial input for Cr, Cu, Zn, Cd and Pb. Of the metals studied, Cd presents the greatest potential for serious pollution because its input from wastewater probably exceeds fluvial input, it appears to be readily remobilized from sediments, and it is known to be toxic to many organisms.