Particulate Cd Research Articles

Impact of Wastewater Discharge Diversion on some Heavy Metals Content in Alexandria Coast

Impact of wastewater discharge diversion on some heavy metals content in Alexandria Coast Ramzy B. Nessim* Mohamed Hassan Ramadan** Amaal E. Abou-Taleb* * National Institute of Oceanography and Fisheries, Alexandria University ** Environmental Health Dept., High Institute of Public Health, Alexandria University Publisher: Bulletin of High Institute of Public Health, 2004, Vol. (34) No(3): 621-640 Abstract: Alexandria is the second largest city in Egypt and includes about 40% of the nation’s industry. In the past, Alexandria city was discharging its wastewater either into the Mediterranean Sea along the city beaches or into Lake Maryut. In 1993, these outlets were closed except two main outlets at Qayet-Bey and EL-Mex Bay. The diverted wastewater is treated primarily and discharged into the sea at EL-Mex Bay. In the mean time, Environment Law 4/1994 prohibited all polluting establishments to discharge untreated wastes, which may cause pollution, along the Egyptian sea shores. The present work aims at assessing the improvement in the levels of some heavy metals in Alexandria coastal water after the diversion and the execution of Environment Law 4/1994. The study concluded that Abou-Qir water, and to a less extent Qayet-Bey water, was characterized by high averages of dissolved Cu, Zn, Pb, and Cr. El-Agamy Bay water sustained the highest levels of Cd, Co, and Cr. Qayet-Bey water represented the highest Ni average. Qayet-Bey water sustained the highest levels of particulate Cu, Zn, and to a less extent Co, Ni, and Cr. El-Agamy water contained the highest levels of both dissolved and particulate Cd. Contrary to the case of dissolved form, spring and to a less extent summer achieved the highest concentration of particulate Zn, Cd, and Ni. The results displayed that dissolved forms of most studied metals were higher in concentration than particulate ones. Zn and Cr, on the other hand, were found in particulate form to be slightly higher than those in dissolved forms. The presence of heavy metals in considerable levels in all the studied sites indicates that Alexandria coast is still subjected to the polluting land-based sources. The study suggested some recommendations to improve the situation including: industries should be enforced to treat their wastewater to comply with Law 4/1994, environmental impact assessment should be done for the new activities, continuous monitoring of the water quality of the beaches, and fishing from polluted areas should be prohibited.

Seasonal cycle and mass balance of cadmium in an estuary with an agricultural catchment: The Morlaix River estuary (Brittany, France)

Cadmium (Cd) variations were investigated over an annual cycle (12 surveys between February 1998–January 1999) in the Morlaix estuary (Brittany, France) in both the water column and the benthic compartment in relation to hydrological conditions. The drainage basin of the Morlaix River estuary is predominantly agricultural in character. Dissolved Cd concentrations in the water column varied from 0.04 to 0.48 nM. Particulate Cd concentrations ranged from 1 to 64 nmol g−1. These concentrations reach levels commonly observed in estuaries affected by heavy industrial activities. Extensive agricultural activities in the drainage basin may be responsible for Cd levels above pristine conditions. Metal concentrations varied significantly over the seasonal cycle and the dissolved fraction exhibited high values in summer months. Particulate concentrations were always lowest during this season. In the benthic compartment, Cd concentrations in surface sediment varied from 0.4 to 5.0 nmol g−1 and from 0.2 to 5.0 nM in porewaters. Concentrations in sediment were slightly affected by Cd contamination and temporal changes were important over the seasonal cycle. The variations seem to be controlled by the succession of sedimentation and erosion processes, which are tightly linked to seasonal changes in river discharge. A box model was constructed based on known Cd sources and sinks in the estuary. Cd is chiefly brought into the estuary by the Morlaix River and accumulates within the estuary. The accumulation within the estuary represents from 6.3 to 7.2 kg yr−1.

Cadmium transport in the Lot–Garonne River system (France) – temporal variability and a model for flux estimation

Fluvial cadmium (Cd) inputs into the Gironde estuary via the Lot–Garonne River system were evaluated using nine years of daily measurements of water discharge and total suspended sediment content (TSS) combined with monthly analyses of dissolved and particulate Cd concentrations. This study demonstrates that dissolved and particulate Cd concentrations in the Lot River have strongly decreased in the early 1990s. However, dissolved and particulate Cd concentrations in the Lot River are still higher than those in the Garonne River. In 1992–1998 mean annual Cd concentrations are more or less constant and thus, annual Cd fluxes mainly depend on hydrology. Daily total Cd fluxes range from 0.26 to 966 kg day −1 in the Lot River and from 0.31 to 1360 kg day −1 in the Garonne River, downstream their confluence. During dry years, Cd fluxes at La Réole are dominated by inputs from the upstream Garonne River, whereas during wet years they are controlled by inputs from the polluted Lot River watershed. The relation between particulate and dissolved Cd fluxes depends on TSS concentrations, which appear to be mainly controlled by the succession of floods and low waters reflecting short-term basin-scale climate variability. Cadmium concentrations, fluxes and the ratio between the particulate and dissolved Cd fluxes depends on the absolute value and instantaneous evolution (strong relative increase or decrease) of discharge. An empiric model permits deducing intervals of daily dissolved Cd fluxes from discharge, hydrological key situation and related intervals of ‘typical’ dissolved Cd concentrations. In 1992–1998 the Lot–Garonne River system shows close relations between annual dissolved and particulate Cd fluxes. These relations allow deducing annual particulate Cd fluxes using annual dissolved Cd fluxes obtained from the model. The validation a posteriori shows that our empiric model accurately reproduces the annual Cd fluxes estimated from the field data with uncertainty lower than 25% for dissolved fluxes and lower than 30% for the particulate fluxes. Consequently, the empiric model permits estimating annual dissolved and particulate Cd fluxes in the Lot–Garonne River system, from daily discharge data, without Cd analysis. Cadmium fluxes obtained from the model may be used as approximate values for gross fluvial Cd inputs into the Gironde estuary.

Cadmium in the Lot-Garonne River system: Fluxes, predictive model and mass balance

The evolution of the Cd pollution in the Lot-Garonne-Gironde fluvio-estuarine system was evaluated by a ten-years-observation (1990-2000) based on high frequency sampling and measurements. Data of water discharge and Suspended Particular Matter content (SPM), combined with monthly analyses of dissolved and particulate Cd concentrations permitted determining annual dissolved and particulate Cd fluxes. Based on the dataset for 1990-1998, an empiric predictive model of Cd fluxes and Cd mass balance is proposed for the Lot-Garonne fluvial system. The model permits predicting 90% of the annual gross dissolved and particulate Cd fluxes entering the Gironde Estuary, only using hydrological data. The empiric model reliably reproduces annual dissolved and particulate Cd fluxes estimated from field data in 1999 and for dissolved Cd fluxes in 2000 with discrepancies lower than 25% and 30% for dissolved and particulate fluxes, respectively. Cadmium mass balances and model-predicted particulate Cd fluxes in 2000, suggest that human activities, as river-bed dredging, create new point sources modifying the budget of the fluvial system. Mass balances show that the anthropogenic Cd point source in the upper Lot River watershed accounts for ∼43% of the gross Cd inputs into the Gironde Estuary via the Garonne River.

Spatial distribution of cadmium over a cyclonic eddy in the southern East China Sea

Eddy systems are a unique ecosystem, usually having high biological masses and primary production in the sea. In this study, both particulate and dissolved phases of cadmium in the water column of 15 stations over a cyclonic eddy in the southern East China Sea were determined to obtain their spatial distributions. This allows us to confirm that cyclonic eddy systems play the role of a Cd pump in the sea. Results showed that particulate Cd (PCd) and dissolved Cd (DCd) concentrations in water varied greatly, ranging over two orders and one order of magnitude, respectively. Large spatial variability was found not only for PCd but also for DCd in the upper water, apparently due to the effects of the cyclonic eddy system on the Cd distributions over the study area. DCd accounts for about 99% of the total Cd. For the surface water, DCd concentration at the eddy center was about five times the average of the water surrounding the eddy center. The depth distributions of DCd exhibited a typical surface depletion and a subsequent increase with depth; however, the PCd distribution showed the opposite, i.e. a surface maximum and a subsequent decline with depth. In general, the DCd maxima were found at depths of 600–1000 m, agreeing well with the literature. It reflected the internal biogeochemical cycling of Cd in the water column, which was driven by the utilization of Cd by plankton in the euphotic zone and by the regeneration of Cd at depth. In addition, a remarkably high DCd concentration existed in near-bottom water around the cyclonic eddy center. The horizontal distributions of both PCd and DCd in the upper water shared a common feature with elevated concentrations centering around the eddy center and a decline in concentration with distance from the eddy center. This shows that the cyclonic eddy could bring up the Cd-rich deep water to the surface water around the eddy center and could then expand toward eddy's vicinity via advection–diffusion. It is thus likely that it produces ample biological masses over the eddy system. Hence, this work can demonstrate that the ascending nutrient-rich water driven by the cyclonic eddies can serve as an important source not only for many nutrients but also for Cd in the sea.

The distributions of particulate heavy metals and its indication to the transfer of sediments in the Changjiang Estuary and Hangzhou Bay, China

Particulate heavy metals (Cu, Pb, Cd) were measured following intensive sampling in June and October 1994 at 70 stations in the Changjiang Estuary and Hangzhou Bay, China. In the study area, particulate Cu and Pb have a similar level that is higher than the concentration of particulate Cd. Cu, Pb and Cd concentrations in suspended sediments are higher than those in bed load. In the middle of Hangzhou Bay, heavy metal concentrations in suspended sediments and bed load are similar. This may be the result of the frequent exchange between them, which is due to the strong dynamic condition. A negative relationship was observed between concentrations of heavy metals in bed load and bulk density. Fine-grained sediments were the main carriers of heavy metals. Sedimentary dynamics dominate the fate of heavy metals in these sites. The distributions of metals (especially Cu) in suspended sediments can indicate the transfer of sediments in this area.

Ten-year observation of the Gironde tributary fluvial system: fluxes of suspended matter, particulate organic carbon and cadmium

A program of long-term observation of suspended solids (TSS), particulate organic carbon (POC) and cadmium transported into the Gironde estuary (France) by its major tributaries has been carried out between 1990 and 1999. This decade included contrasting hydrologic cycles and appears representative of a much longer period (1959–1999). The Garonne and the Dordogne river systems are the main tributaries of the Gironde estuary and derive their waters from drainage basins with different geological, industrial and agricultural features. To better understand their respective contributions, they have been observed separately and compared. Water and TSS fluxes of the Garonne River show greater temporal variations and discharge is more related to the hydrology of the drainage basin (e.g. wet/dry years, local flood events etc.). As POC and particulate Cd concentrations in suspended matter are much less variable than turbidity, their fluxes are mainly controlled by the TSS transport. A major part of annual fluxes of TSS and associated pollutants may occur within few flood days (depending on various parameters, e.g. intensity, duration, season, etc.), and also the succession of dry and wet years has an important influence on annual fluxes. The presented data allow calculating fluvial inputs into the Gironde as the sum of fluxes transported by its major tributaries, the Garonne and the Dordogne river systems. Mean annual fluxes into the Gironde observed in 1990–1999 are about 34×109 m3 year−1 for river water, 3.24×106 t year−1 for suspended solids (TSS) and 9.88×109 mol year−1 for particulate organic carbon (POC). Generally, these fluxes are dominated by the contributions of the Garonne River. However, in dry years, the mean contribution of the Dordogne river system (including Dronne and Isle rivers) to the POC input into the estuary exceeded that of the Garonne. This reflects significant differences in vegetation and soil due to natural properties and land management of the basins. Mean Cd fluxes into the estuary are about 110×103 mol year−1 of which 19.6×103 mol year−1 are transported in the dissolved and 90.8×103 mol year−1 in the particulate phases, respectively. In 1991 (dry year), the net (dissolved) Cd flux towards the ocean exceeded the gross fluvial input of total Cd, suggesting the release of Cd from an important stock in the maximum turbidity zone (MTZ) or the fluid mud of the Gironde estuary.

Metal behaviour in an estuary polluted by acid mine drainage: the role of particulate matter

The concentrations of dissolved and suspended particulate Cd, Cu and Zn have been determined in water samples obtained during two axial transects of the Rio Tinto-Huelva Ria system in south-west Spain, which is severely impacted by acid mine drainage. Although the metal concentrations in both phases were elevated, dissolved metals were dominant and, in the upper estuary, constituted >99% of total metal in the water column. Dissolved metals behaved non-conservatively on each transect, with maximum concentrations in the low salinity region. There was no evidence of metal adsorption within the turbidity maximum zone, despite the high specific surface areas of resuspending particles. Measurements of electrophoretic mobility showed that the suspended particulate matter (SPM) had a positive surface charge in the salinity range 0–4, where the waters had a pH<3. Desorption experiments were carried out in which SPM from the turbidity maximum zone was resuspended in coastal seawater. The desorption of the metals was monitored for 24 h, using anodic stripping voltammetry (ASV) to detect the variation in total dissolved Cd, Cu and Zn and the species of Cu and Zn. Total dissolved Cd concentrations doubled during the incubation period, whereas the concentration of total dissolved Cu declined and that of Zn remained rather constant. The ASV-labile fraction of dissolved Cu and Zn showed an initial sharp release followed by a slower uptake. However, desorption was shown to be a minor source of dissolved metals and made little contribution to the non-conservative behaviour in the low salinity zone. The results are used to predict the effects of acid mine drainage on estuarine ecology.

Resuspension, reactivity and recycling of trace metals in the Mersey Estuary, UK

Distributions of dissolved and non-detrital (available to 1 M HCl) particulate Cd, Co, Cu, Ni, Pb and Zn have been determined in samples collected from the Mersey Estuary, UK, during four high-resolution axial transects. With the exception of Cu, dissolved metal concentrations displayed positive deviations from conservative behaviour. Cobalt and Ni appeared to have a common source, while dissolved Pb peaks coincided with maximum turbidities in the upper estuary. Concentrations of Cd, Co, Ni and Pb in the <63-μm grain size fraction of bed sediment were greater than those in suspended particulate matter (SPM). Magnitudes of dissolved metal peaks reflected the extent of metal enrichment in fine bed sediment compared with SPM, suggesting that addition of dissolved metal was effected primarily by desorption from resuspendable bed particles. An empirical sorption model, based on the mass balance of metal resuspended from the bed, was able to reproduce the axial distributions of dissolved metals that exhibited the most pronounced peaks (namely, Co and Pb) with reasonable success. More generally, model results indicated that bed sediment need only be moderately enriched in trace metal compared with SPM to cause measurable addition of dissolved metal to the overlying water column. Addition of dissolved metals on estuarine mixing is a common observation in macrotidal environments of western Europe, and it is proposed that resuspension of metal-enriched, fine bed sediment may be a significant agency for metal remobilisation in contaminated, turbid estuaries.

Modeling of Cadmium Speciation and Dynamics in the Seine Estuary (France)

A complexation model (MOCO) was used to describe cadmium (Cd) speciation during estuarine transit in the Seine estuary. This model was developed from field data. Laboratory experiments based on the use of109Cd enabled checking of certain model simplifications and hypotheses and evaluation of parameters which could not be measured directly. MOCO was coupled with a 3D multivariable hydrosedimentary model (SAM3D) to simulate Cd dynamics in the estuary. These results were compared with measurements (dissolved and particulate Cd) obtained during cruises representative of various hydrodynamic conditions. The purpose of this article is to present the modeling approach used, and its expected applications and limits.

Cadmium adsorption by sediment in a turbulence tank

The mechanism of sediment motion that affects cadmium (Cd) adsorption on sediment particles was studied in a turbulence tank in the presence (and absence) of bed mud. The experimental results were verified by a mathematical model for heavy metal transport–transformation developed for the turbulence tank. The mathematical model includes the equations of water flow, sediment motion, heavy metal transport–transformation, heavy-metal reaction kinematics and equations for prescribing the initial conditions and boundary conditions for the experiment. The model conforms the transport–transformation of heavy-metal pollutants in surface waters to following the law of convective–diffusive of common tracers and the characteristics of fate and transport of sediment motion. Variations of dissolved Cd concentrations and suspended particulate Cd concentrations with time and in the water column were measured and computed. The experimental measurements correspond with the computed results. Both the experimental measurements and computed results show that it takes about 6 h to reach equilibrium condition for cadmium adsorption by sediment particles. This is different from the result obtained from experiments conducted in continuously stirred tank reactors (or batch reactors) in which adsorption equilibrium can be achieved in about 20 min. Determination of the model parameters for sediment adsorption–desorption of metals in the tank is discussed. The experimental and computed results obtained in this study are useful to solve practical engineering problems in surface waters.

Effects of Ice Melting on Cu, Cd and Pb Profiles in Ross Sea Waters (Antarctica)

In the framework of the Italian Research Programme in Antarctica, evolution of dissolved and particulate Cu, Cd and Pb profiles in the coastal waters of Gerlache Inlet (Terra Nova Bay, Western Ross Sea) was studied during the Austral Summer 1997/98. In order to relate the distributions of trace metals with the physical and biological processes, a series of temperature and salinity measures were made, and water samples were collected to determine nutrients and chlorophyll. Samples of pack ice and marine microlayer (50–150 μm) were also collected and analysed. Concerning the surface layer, it was found that metal concentrations are mainly affected by the dynamic of the pack ice melting and phytoplankton activity. The first process influences both the input of metals from meltwaters and the covering of the seawater surface, allowing atmospheric dust input only when all ice has been melt or removed. Direct release of particulate Cu from ice was clearly shown by surface maxima and by the high concentrations of suspended particulate matter and particulate metals found in the ice core section interfaced with the seawater. Differently, the high amount of Cd in the particulate included in the pack ice seems not to affect the concentration in surface particulate; on the contrary, the corresponding increase of dissolved Cd indicates that it isreleased in dissolved form when the pack ice melts. Surface distribution is further complicated by the effect of phytoplankton activity, which removes Cu and Cd from water, incorporating them into organic particulate. Finally, in absence of pack ice, there is evidence of inputs of Pb and Cu due to atmospheric dust brought into the column water through marine microlayer. In intermediate and deep waters, the vertical distribution of Pb and Cd was characterised by substantially constant profiles, while Cu shown, during the end of the summer and in absence of a well-defined water column stratification, a “scavenging-type” distribution which overlaps its “nutrient-type” behaviour.

Dynamics of Particulate Trace Metals in the Tidal Reaches of the Ouse and Trent, UK

Samples of suspended particulate matter (SPM) have been collected in the tidal reaches of the Ouse and Trent over seven surveys covering the annual cycle of riverine conditions. Settling experiments were carried out on water samples to differentiate permanently suspended particulate material (PSPM) from temporarily suspended particulate material (TSPM). The results indicated that PSPM, additional to the riverine component, was created within the turbidity maximum zone (TMZ) during tidal resuspension. The PSPM varied between 10% and 50% of the total SPM and could be transported quasi-conservatively down-estuary. The concentrations of particulate Cd, Fe, and Zn (available to 1M HCl) were determined in PSPM and TSPM, as well as samples of the bulk SPM. The trace metal concentrations in PSPM were seasonally variable and generally higher than in TSPM, which had relatively constant concentrations. The trace metal concentrations in PSPM and TSPM were used to develop a two-component, particle mixing model, which was applied to the interpretation of the bulk SPM concentrations of Cd and Zn. It is postulated that as the PSPM encounters the salinity gradient labile Cd and Zn desorb from the particles. On the basis of these results an additional mechanism for generating estuarine maxima in dissolved trace metals has been proposed.

The distribution and preferential biological uptake of cadmium at 6°W in the Southern Ocean

The spatial and temporal distribution of cadmium (Cd) and phosphate in the Southern Ocean are related to biology and hydrography. During a period of 18 days between transects 5/6 and 11, a phytoplankton spring bloom developed in the Polar Frontal region. Upper water Cd concentrations were not depleted and ranged from 0.2 to 0.8 nM at about 10 m depth. These relatively high Cd concentrations are attributed to upwelling of Upper Circumpolar Deep Water (0.5–1.2 nM in the core) in combination with low biological productivity (0.2 to 0.3 mg m−3 chlorophyll-a, 0.3 g C m−2 d−1). Total particulate Cd concentrations at 40 m depth were between 0.02 and 0.14 nM with the maximum in concentration in the Polar Frontal region. Most of the particulate Cd at this depth (85–94%) was detected in the first phase of a sequential chemical leaching treatment which includes adsorbed Cd as well as Cd incorporated in algae. The Polar Frontal region was characterized by minima in Cd concentration and Cd/phosphate ratio of seawater at both transects; values were the lowest at transect 11 after development of the spring bloom which was dominated by diatoms. This decreasing Cd/phosphate ratio in seawater during spring bloom development was attributed to preferential Cd gross uptake which more than compensated the process of preferential Cd recycling. Within the Upper Circumpolar Deep Water, Cd showed a maximum in concentration similar to that of the major nutrients. Both the Cd concentration and the Cd/phosphate ratio of the deeper water increased in southern direction, from 0.4 to 0.7 nM and from 0.2 to 0.3 nM/μM, respectively. Antarctic Intermediate Water has a Cd concentration of 0.21 nM with a Cd/phosphate ratio of 0.10 nM/μM. In Antarctic Bottom Water, Cd concentrations ranged from 0.60 to 0.82 nM.

A numerical transport model for predicting the distributions of Cd, Cu, Ni, Pb and Zn in the southern North Sea: the sensitivity of model results to the uncertainties in the magnitudes of metal inputs

A new transport model for metals (named NOSTRADAMUS) has been developed to predict concentrations and distributions of Cd, Cu, Ni, Pb and Zn in the southern North Sea. NOSTRADAMUS is comprised of components for water, inorganic and organic suspended particulate matter transport; a primary production module contributes to the latter component. Metal exchange between dissolved (water) and total suspended particulate matter (inorganic + organic) phases is driven by distribution coefficients. Transport is based on an existent 2-D vertically integrated model, incorporating a 35 × 35 km grid. NOSTRADAMUS is largely driven by data obtained during the Natural Environment Research Council North Sea Project (NERC NSP). The sensitivity of model predictions to uncertainties in the magnitudes of metal inputs has been tested. Results are reported for a winter period (January 1989) when plankton production was low. Simulated ranges in concentrations in regions influenced by the largest inflows, i.e. the NE English coast and the Southern Bight, are similar to the ranges in the errors of the concentrations estimated at the northern and southern open sea boundaries of the model. Inclusion of uncertainties with respect to atmospheric (up to ± 54%) and riverine (± 30%) inputs makes little difference to the calculated concentrations of both dissolved and particulate fractions within the southern North Sea. When all the errors associated with the inputs are included there is good agreement between computed and observed concentrations, and that for dissolved and particulate Cd, Cu and Zn, and dissolved Ni and Pb, many of the observations fall within, or are close to, the range of values generated by the model. For particulate Pb, model simulations predict concentrations of the right order, but do not reproduce the large scatter in actual concentrations, with simulated concentrations showing a bias towards lower values compared to those observed. A factor which could have contributed to observed concentrations, and which is not included in the model, is considered to be a substantial benthic input of dissolved lead during this winter period, coupled to a rapid and extensive scavenging of the dissolved lead to particles. Significant reductions in riverine and aeolian inputs of total Cd and Cu of 70% and 50%, respectively, consistent with aims of North Sea Conferences, are predicted to lead to minor decreases (~ 10%) in water column concentrations of dissolved and particulate Cd and Cu, except near river sources, where maximum reductions of ~ 30–40% may occur.

Modelling of pollutant behaviour in estuaries: Application to cadmium in the Loire estuary

A one-dimensional multivariate mathematical model was used to study the behaviour of cadmium in a macrotidal estuary. Dissolved and particulate Cd were computed using a complexation model to solve the thermodynamic equations governing balances between free ion Cd2+ and various ligands (chloride, sulfate and hydroxide ions). Suspended matter is also considered as a ligand, characterised by an adsorption constant linking free ion Cd2+ activity to concentrations of sorbed cadmium on suspended matter. The model's sensitivity study, which was applied to the Loire estuary, shows that results can be highly dependent on: (1) the adsorption constant; (2) the initial conditions determining cadmium concentrations in particulate matter at the start of each simulation; (3) the longitudinal distribution of salinity and suspended matter. The above data is often badly evaluated, introducing many uncertainties as to the results and their interpretation. The number of degrees of freedom becomes too high to permit a proper validation. However, this type of approach does allow for a rapid evaluation of the variables controlling the evolution of a given pollutant in an estuary. The results obtained show that the application and validation of a model simulating pollutant behaviour require: (1) validation of the distribution of master variables (salinity and suspended matter (S.M.) in the case of Cd); (2) relatively precise evaluation of: either the initial conditions if the simulation time scale is short, or of boundary conditions and various inputs into the estuary if the model is capable of simulating the system's evolution over a long period of time (several months).

Distribution and temporal variation of cadmium in the St. Lawrence river basin

Samples of raw water were collected at regular intevals at two transects in the St. Lawremce River and four of its tributaries from March to November 1991 and from April to June 1992. Water samples were analyzed for both the dissolved and the particulate phase for cadmium (Cd), organic carbon, iron and manganese. Mean dissolved Cd concentration was 10±5 ng/L and no spatial variability was observed. Higher concentrations were found during high flow periods, suggesting an uptake of cadmium by phytoplankton during summer. In addition, dissolved cadmium did not appear to be associated with either DOC, dissolved Fe or dissolved Mn. The mean particulate Cd concentration was 1.3±1.1 μg/g, with almost all stations presenting the same concentration except the Yamaska River, which had a concentration of 0.5±0.2 μg/g. Particulate Cd showed a negative correlation with suspended particulate matter and a positive correlation with particulate organic carbon and particulare manganese. Fifty-nine percent of the cadmium was found to be in the particulate phase. Partition coefficients for cadmium (Kd), organic carbon (Kc), iron (KdFe) and manganese (KdMn) were calculated for each sample. Log Kd varied from 3.9 to 5.9, with an average of 5.0±0.4. Log Kd decreased with increasing particulate, matter as did Log Kc and Log KdMn. No significant correlation was found between Log Kd and Log Kc, suggesting that the distribution of cadmium between the dissolved and the particulate phase is not influenced by the distribution of organic carbon. In contrast, positive correlations were observed between Log Kd, Log KdFe and Log KdMn. Cadmium distribution appears to be influenced by Fe and Mn distribution.

Particulate metals contamination in the Kishon River estuary, Israel

Suspended particulate matter (SPM) collected along the axis of the Kishon River, its estuary and Haifa Bay were analysed for trace metal concentrations together with measurements of water density, pH and dissolved oxygen. The concentrations of particulate Cd, Zn and Cu generally increased from the upper Kishon system (upstream from Tzipori-Kishon Junction) downstream and decreased from the Kishon Harbour seaward, while particulate Al concentrations decreased downstream and towards the open sea. Enrichment of Cd, Zn and Cu was found at Haifa Bay compared to the upper Kishon system. The axial profile of Mn concentrations indicated reduction of Mn at the anoxic and low pH zone of the lower river system and precipitation of Mnoxides at the estuary in response to the increase in pH and dissolved oxygen concentrations. Although Fe concentrations showed similar behavior to that of Al, the higher Fe Al ratios at the estuary are probably due to precipitation of Fe-oxides onto pre-existing particles. This spatial non-conservative behavior of metals is presumably due to the: 1. mixing between polluted river-borne particles and material of drainage basin and coastal origin; 2. changes of the distribution coefficient of metals between the particulate and solution phases (K d) with variations of salinity, pH and SPM concentrations; and 3. physical settling and currents. Short-term, tidal cycle measurements undertaken at the lower Kishon system (Julius Simon Bridge) indicated a high contribution of resuspended sediments to the SPM amounts due to the high tidal energy. It is hypothesized that the latter is the main mechanism by which SPM, which settles in the estuary, is transported landward creating a turbidity maximum zone between the Julius Simon and Histadrut bridges, i.e. about 3 km upstream from the estuary. It is proposed that the upper estuary zone acts as a purging system through which a low flux of SPM, enriched by organic and trace metal content, is transported seaward and from which a high flux of SPM is returned landward due to tidal stress.

Cd, Cr, Cu, Ni and Pb in the water column and sediments of the Ob-Irtysh Rivers, Russia

Concentrations of Cd, Cr, Cu, Ni and Pb were determined in filtered water, suspended particulate matter, and bottom sediments from a ∼2000 km section of the Ob and Irtysh Rivers. Dissolved Cd, Cr, Cu and Ni concentrations are similar to, or higher than, results from other Russian Arctic and large world river-estuaries. Concentrations of Cd, Cr, Cu, Ni and Pb in suspended particulate matter are generally comparable to results from other Russian Arctic and large world rivers and estuaries. Comparison of trace metal ratios in crustal material and suspended particulate matter and bottom sediment suggests that the source of Cr, Cu and Ni is continental weathering. Particulate Cd and Pb are elevated relative to their crustal abundance, suggesting a source of these metals to the Ob-Irtysh in addition to continental weathering.

Metal Partitioning and Toxicity in Sewage Sludge

Partition coefficients (KD) for Cd, Cu, Pb and Zn in a sludge/water solution were determined for sludge/water solutions as an operationally defined three-phase system (particulate, colloidal and electrochemically available) over a range of pH values, ionic strength, contact time and sludge/water ratios and were compared with KD values for sludge/water solutions as a two-phase system (aqueous phase and particulate phase). Partitioning results were interpreted in terms of metal mobility from sludge to colloids and in terms of potential bioavailability from colloids to electrochemically available. It was found that the partition coefficient for a two-phase system, KD2 and the partition coefficient between the colloidal metal and the particulate metal in a three-phase system, KD3p/c have similar values, which means that, for sewage sludge, the two-phase partition coefficient reflects the partitioning between particulate metal and colloidal metal, not dissolved metal. In the absence of a particulate phase, Zn and Cd partition between the colloidal phase and the electrochemically available phase, while Cu and Pb remain in the colloidal phase. Ionic strength had no clear effect on KD, while increased pH resulted in lower metal concentrations in the colloidal and electrochemically available phases. The toxicity of Pb-spiked sludge (KDtox) is well described by its partitioning in a two-phase system, KD2ads, while the toxicity of Zn is underestimated.