Species In Groundwater Research Articles

Prevalence of Campylobacter species in ground water in Sokoto, Sokoto state, Nigeria

Aim: The present study was conducted to determine the presence and prevalence of Campylobacter species in ground water in Sokoto, Sokoto State. Materials and Methods: The prevalence of Campylobacter species was determined by collecting a total of 74 water samples from wells in Sokoto over a period of four months from May to August 2011 and analyzed using cultural isolation techniques and biochemical characterization. Results: Totally 39 (52.70%) water samples were Campylobacter positive. The species identified were Campylobacter jejuni 23 (58.97%), Campylobacter coli 11 (28.21%) and Campylobacter hyointestinalis 5 (12.82%). Conclusion: Based on this study, the isolation of Campylobacter species from ground water (wells) in this study is of serious public health importance as untreated water has been implicated as the cause of sporadic infections and outbreaks of Campylobacteriosis worldwide.

Three-component spectroelectrochemical sensor module for the detection of pertechnetate (TcO4-)

This review looks at the advancements in the development of a sensor for technetium (Tc) that is applicable to characterizing and monitoring the vadose zone and associated subsurface water. Subsurface contamination by Tc is of particular concern for two reasons: the extremely long lifetime of its most common isotope 99Tc (half-life = 2 x 105 years) and the fast migration in soils of pertechnetate (TcO4–) which is considered to be the dominant 99Tc species in ground water. TcO4– does not have a characteristic spectral signature which prevents its rapid, sensitive, and economic in-situ detection. To address this problem, a novel spectroelectrochemical sensor has been designed that combines three modes of selectivity (electrochemistry, spectroscopy, and selective partitioning) into a single sensor to substantially improve specificity which is critical in the specific detection of an analyte in the presence of potential interfering species. The sensor consists of a basic spectroelectrochemical configuration: a waveguide with an optically transparent electrode (OTE) that is coated with a thin chemically-selective film that preconcnetrates the analyte. The key to adapting this generic sensor to detect TcO4– and Tc complexes lies in the development of chemically-selective films that preconcentrate the analyte and, when necessary, chemically convert it intomore » a complex with electrochemical and spectroscopic properties appropriate for sensing. This review focuses on the general concept of the sensor and the rationale for the selection of the specific components of choice, the development and characterization of the sensor for the different detection modules, the synthesis and characterization of complexes relevant in the detection of technetium, and the progress in the utilization of the sensor module for the effective detection of these complexes.« less

Thermodynamics of AFm-(I2, SO4) solid solution and of its end-members in aqueous media

► Solid solution formation between AFm-SO 4 and AFm-I 2 . ► AFm-SO 4 as a good candidate for retarding 129 I. ► Gibbs energy of AFm-(I 2 , SO 4 ) solid solution obtained from solubility experiments. ► Sub-regular solid solution model with end-members defined using Vanselow convention. Cementitious materials are foreseen as being used for the immobilization of radionuclides in deep-storage facilities for nuclear waste. The 129 I contained in the waste is of major concern due to its long half-life and its anionic speciation in groundwater (I − ), which hinders the retention by most minerals due to their negatively charged structural surfaces at near-neutral pH. AFm-SO 4 is one of the phases present in cementitious materials. Experimental data suggest that the formation of solid solution between AFm-SO 4 and AFm-I 2 has the potential to retard 129 I mobility. In order to improve the present geochemical models, thermodynamic properties of AFm-I 2 and of its solid solution with AFm-SO 4 were evaluated based on precipitation and dissolution experiments in aqueous solutions between 4 °C and 60 °C. The solubility product of AFm-I 2 was determined at 23 °C ± 2 °C to be log K s 0 = - 13.57 ± 0.28 (2 σ ) for the dissolution reaction Ca 2 Al ( OH ) 6 I · 2 H 2 O ↔ 2 Ca 2 + + Al ( OH ) 4 - + 2 OH - + I - + 2 H 2 O . The Gibbs energy of formation of AFm-I 2 at standard state (1 bar, 25 °C) was assessed to be −3325.0 ± 2.4 (2 σ ) kJ mol −1 . The experimental data for AFm-(I 2 , SO 4 ) phases were consistent with the formation of a continuous solid solution without miscibility gaps. A good fit to these data was obtained using a sub-regular solid solution model with negative Margules interaction parameters W SO4 = −1.0 kJ mol −1 and W I = −8.0 kJ mol −1 , and end-members (Ca 2 Al(OH) 6 I and Ca 4 Al 2 (OH) 12 SO 4 ) defined according to the Vanselow convention for ion exchange. The results show the potential of AFm-SO 4 to act as a sink for 129 I, notably in carbonate-free systems. Small amounts of calcite can hamper the formation of AFm-(I 2 , SO 4 ) solid solution. The study provides relevant thermodynamic data for geochemical modeling of 129 I in the cementitious near-field of a nuclear waste repository.

Assessment of vanadium distribution in shallow groundwaters

Shallow groundwater samples (filtered at 0.2μm) collected from a catchment in Western France (Petit Hermitage catchment) were analyzed for their major- and trace-element concentrations (Fe, Mn, V, Th and U) as well as their dissolved organic carbon (DOC) concentrations, with the aim to investigate the controlling factors of vanadium (V) distribution. Two spatially distinct water types were previously recognized in this catchment based on variations of the rare earth element (REE) concentrations. These include: (i) DOC-poor groundwater flowing below the hillslope domains; this type has low V contents; and (ii) DOC-rich groundwater originating from wetlands, close to the river network; the latter water type displays much higher V concentrations. The temporal variation of the V concentration was also assessed in the wetland waters; the results show a marked increase in the V content at the winter–spring transition, along with variations in the redox potential, and DOC, Fe and Mn contents.In order to allow the study of organo-colloidal control on V partitioning in water samples, ultrafiltration experiments were performed at different pore size cut-offs (30kDa, 10kDa and 5kDa). Two shallow, circumneutral waters were sampled: one was both DOC- and Fe-rich and the other was DOC-rich and Fe-poor. In terms of major- and trace-cations and DOC concentrations, the data were processed using an ascendant hierarchical classification method. This revealed the presence of two main groups: (i) a “truly” dissolved group (Na, K, Rb, Ca, Mg, Ba, Sr, Si, Mn, Co, Ni, Cr, Zn and Ni), and (ii) a colloidal group carrying DOC, Fe, Al, Pb, Cu, REE, U, Th and V. Vanadium has an unpredictable behavior; it can be either in the organic pool or in the inorganic pool, depending on the sample.Moreover, V speciation calculations—using Model VI and SCAMP—were performed on both samples. Speciation modeling showed approximately the same partitioning feature of these elements as compared to ultrafiltration data, namely: a slight change of the V speciation in groundwaters along the studied topographic sequence.This implies that vanadium in hillslope groundwater wells occurs as a mixing of organic and inorganic complexes, whereas V in wetland groundwater wells comprises mainly organic species. Using the dataset described above, factors such as aquifer–rock composition or anthropogenic input were demonstrated to probably play a minor role in determining the V distribution in shallow groundwaters. Although an anthropogenic impact can be ruled out at this local scale, we cannot preclude a perturbation in the global V cycle. Most likely, the two dominant factors involved are the organic matter content and the redox state either promoting competition with Fe-, Mn-oxides as V carriers in groundwater or not. In this context, it appears challenging to determine whether organic matter or redox-sensitive phases are the major V carriers involved, and a further study should be dedicated to clarify this partition, notably to address the processes affecting large-scale V transport.

Speciation of selenium in groundwater: Seasonal variations and redox transformations

Speciation of selenium in groundwater is essential from the viewpoint of toxicity to organisms and biogeochemical cycling. Selenium speciation in groundwater is controlled by aquifer redox conditions, microbial transformations, dissolved oxygen (DO) and other redox couples. A suburban area of Chennai city in India, where improper waste disposal measures have been practiced is selected for this study. Se(IV), Se(VI) and other hydrochemical parameters were monitored in shallow ground water during pre- and post-monsoon seasons for a period of three years. The objective of the study was to investigate the effect of groundwater recharge on selenium speciation. The concentration of Se(IV), and Se(VI) ranged between 0.15–0.43 μg L −1 and 0.16–4.73 μg L −1, respectively. During post-monsoon period the concentration of Se(IV), and Se(VI) ranged between 0.15–1.25 μg L −1 and 0.58–10.37 μg L −1, respectively. Se(VI) was the dominant species of selenium during the pre- and post-monsoon periods. During the post-monsoon periods, leaching of selenium from soil was more effective due to the increased oxidizing nature of the groundwater as indicated by the DO and redox potential (Eh) measurements. This finding has important implications on the behavior of selenium in groundwater, and also on the health of people consuming groundwater from seleniferous areas.

Strong chemical evidence for high Fe(II)-colloids and low As-bearing colloids (200nm–10kDa) contents in groundwater and flooded paddy fields in Bangladesh: A size fractionation approach

Arsenic speciation in groundwater and interstitial waters from soil irrigated with As-rich groundwater in Bangladesh was investigated through a size fractionation approach performed in the field and under conditions that allowed the preservation of natural anoxic conditions. Based on a simple chemical characterization, the presence of Fe(II) in the colloidal fraction (<200 nm–>10 kDa) in anoxic groundwaters and soil waters of flooded paddy fields was assessed. Arsenic was found to be present mainly as a ”solute” oxyanion as indicated by the small amount of As associated with the 200 nm–10 kDa colloidal fraction (most of the time, less than 10 ± 5% of total As). When As-colloids were observed, they were linked to high Fe concentration and the As-colloid percentage was relatively well correlated with the total Fe concentration in solution. This study underlined that under natural anoxic conditions, there was no impact of PO43-, SiO44- and Mn on the As-bearing colloids, which is not in agreement with results obtained under laboratory controlled conditions. Therefore, it is suspected that the impact of other naturally occurring ligands, such as organic matter, could modify Fe(II) speciation, and, in turn, As speciation. To assess the complexation of Fe(II) by organic matter, the WinHumicV model was used to calculate Fe(II) speciation. Using the standard parameters to describe organic matter reactivity, results showed that organically-bound Fe(II) ranges from 5% to 100% and 30% to 100%, for groundwater and soil water, respectively, depending on the pH and the Fe(II) and DOC contents. Evidence for independent speciation of Fe and As under natural anoxic conditions is of great importance for predictive modelling of the mobility, the availability and then the bioavailability of As in As-affected areas.

Arsenic distribution, concentration and speciation in groundwater of the Osijek area, eastern Croatia

Abstract Groundwater is the main source of drinking water for the population of nearly 200,000 people in eastern Croatia. The largest town in the region is Osijek whose citizens are supplied with drinking water obtained from groundwater from the “Vinogradi” well field. This study investigated and determined As occurrence in groundwater of the Osijek area. Groundwater samples were taken from 18 water wells and 12 piezometers with a depth ranging between 21 and 200 m. Over the 10-a period to 2007, a mean As concentration of 240 μg L −1 was found. There was no statistically significant secular change in concentration over that period, however small but significant seasonal variations were noted, with the highest seasonal As concentrations over the period May 2006–February 2007 being observed in summer. The predominant As species observed was As(III), constituting 85% and 93% of total As in piezometers and water wells, respectively. Higher concentrations of As tended to be found in deeper wells with the mean As concentration in shallow groundwater ( 50 m) being 27 μg L −1 , and 205 μg L −1 , respectively. Geochemically, the groundwaters show similarities to those in other parts of the Pannonian Basin. Arsenic(tot) is weakly correlated with pH and Fe, negatively correlated with Mn and has no significant correlation with any of EC, COD-Mn or alkalinity.

Controls on groundwater nitrogen contributions from on-site wastewater systems in coastal North Carolina

The goal of this study was to evaluate the influence of soil type and separation distance to water table on dissolved inorganic nitrogen concentrations in groundwater adjacent to on-site wastewater systems. Groundwater nitrogen species (NO3--N and NH4+-N) and groundwater levels adjacent to 16 on-site systems in three different soil groups (group I- sand, group II- coarse loams and group III -sandy clay loams) were monitored for 15 months (January 2007-March 2008) in coastal North Carolina. On-site systems in soil group I had the highest concentrations of dissolved inorganic nitrogen (median of 18.9 mg/L) in groundwater, and most frequently (mean 61%) exceeded 10 mg/L, followed by systems in soil group II (11.0 mg/L, 50%) and soil group III (2.6 mg/L, 9%), respectively. Groundwater NH4+-N concentrations near on-site systems in soil groups I and II that maintained a 60+cm separation to the seasonal high water table were 4 mg/L lower in relation to systems that had <60 cm separation, but median NO3--N concentrations were 6.5 mg/L higher. On-site systems in group I and II soils are prone to groundwater nitrogen loading with separation distance often controlling the nitrogen speciation in groundwater near on-site systems.

Experimental Design Optimization of Arsenic Speciation in Groundwater

The optimization of a Differential-Pulse Stripping Voltammetry (DPSV) procedure for arsenic speciation determination, using sodium diethyldithiocarbamate (DDTC-Na) as complexing agent, is described. An experimental design methodology was used to select the optimal experimental conditions. A robust regression method was used for the calibrations under these conditions that eliminate anomalous points. Electroinactive As(V) was reduced to As(III) with sodium thiosulfate prior to determination. The detection limit obtained was 1.95 × 10−9 mol dm−3. This procedure was successfully applied to the determination of arsenic speciation in groundwater.

Occurrence of arsenic in core sediments and groundwater in the Chapai-Nawabganj District, northwestern Bangladesh

Groundwater and core sediments of two boreholes (to a depth of 50 m) from the Chapai-Nawabganj area in northwestern Bangladesh were collected for arsenic concentration and geochemical analysis. Groundwater arsenic concentrations in the uppermost aquifer (10–40 m of depth) range from 2.8 μg L −1 to 462.3 μg L −1. Groundwater geochemical conditions change from oxidized to successively more reduced, higher As concentration with depth. Higher sediment arsenic levels (55 mg kg −1) were found within the upper 40 m of the drilled core samples. X-ray absorption near-edge structure spectroscopy was employed to elucidate the arsenic speciation of sediments collected from two boreholes. Environmental scanning electron microscopy and transmission X-ray microscopy were used to investigate the characteristics of FeOOH in sediments which adsorb arsenic. In addition, a pH–Eh diagram was drawn using the Geochemist's Workbench (GWB) software to elucidate the arsenic speciation in groundwater. The dominant groundwater type is Ca–HCO 3 with high concentrations of As, Fe and Mn but low levels of NO 3 − and SO 4 2−. Sequential extraction analysis reveals that Mn and Fe hydroxides and organic matter are the major leachable solids carrying As. High levels of arsenic concentration in aquifers are associated with fine-grained sediments. Fluorescent intensities of humic substances indicate that both groundwater and sediments in this arsenic hotspot area contain less organic matter compared to other parts of Bengal basin. Statistical analysis clearly shows that As is closely associated with Fe and Mn in sediments while As is better correlated with Mn in groundwater. These correlations along with results of sequential leaching experiments suggest that reductive dissolution of MnOOH and FeOOH mediated by anaerobic bacteria represents an important mechanism for releasing arsenic into the groundwater.

Chromium speciation in groundwater of a tannery polluted area of Chennai City, India

Chromium speciation in groundwater of a tannery polluted area was investigated for the distribution of chromium species and the influence of redox couples such as Fe(III)/Fe(II) and Mn(IV)/Mn(II). Speciation analysis was carried out by ammonium pyrolidinedithiocarbamate (APDC)-methylisobutylketone (MIBK) procedure. The groundwater samples were analyzed for Cr(III), Cr(VI), and Cr(III)-organic complexes. The APDC could not extract the Cr(III)-organic complexes, but HNO3 digestion of the groundwater samples released the Cr(III)-organic complexes. The groundwater of the area is relatively oxidizing with redox potential (Eh) and dissolved oxygen (DO) ranged between 65 and 299 mV and 0.25 and 4.65 mg L(-1), respectively. The Fe(II) reduction of Cr(VI) was observed in some wells, but several wells that had Fe(II)/Cr(VI) concentrations more than the stoichiometric ratio (3:1) of the reduction reaction also had appreciable concentration of Cr(VI). This could partly be due to the oxidation of Fe(II) to Fe(III) by DO. It appears that the occurrence of Mn more than the Fe(II) concentration was also responsible for the presence of Cr(VI). Other reasons could be the Fe(II) complexation by organic ligands and the loss of reducing capacity of Fe(II) due to aquifer materials, but could not be established in this study.

Detection and identification of Dehalococcoides species responsible for in situ dechlorination of trichloroethene to ethene enhanced by hydrogen‐releasing compounds

Previous studies have shown that Dehalococcoides species are responsible for the anaerobic bioremediation of chloroethene pollution. It has been thought that co-operation of several species is required for complete dechlorination to ethene. In the present study, we used quantitative PCR of 16 S rRNA and RDase (reductive dehalogenase) genes to examine species changes and the population of Dehalococcoides species in ground water in which the dechlorination of TCE (trichloroethene) to ethene was enhanced by delivery of hydrogen-releasing compounds. The results have shown that at least two different Dehalococcoides species co-operate in the dechlorination of TCE to ethene. Initially, the number of strains equipped with TCE RDase increased approx. 10(5)-fold. This was followed by a decrease to the original level, according to the exhaustion of TCE. Subsequently, another strain appeared, which had a VC (vinyl chloride) RDase gene similar to bvcA of Dehalococcoides sp. BAV1 and is probably responsible for the dechlorination of VC to ethene. Analysis of several genes has suggested that the former strain is like Dehalococcoides sp. FMC-TCE, and the latter strain is similar to the Dehalococcoides sp. strain that exists in the Dehalococcoides-containing mixed culture KB1. These results support the notion that monitoring Dehalococcoides species by the presence of RDase genes as genetic markers provides detailed information on the progress of bioremediation of chloroethenes, which will be useful to improve the efficiency of bioremediation.

Mercury speciation analyses in HgCl 2-contaminated soils and groundwater—Implications for risk assessment and remediation strategies

Since the 19th century, mercury(II)chloride (HgCl 2) has been used on wood impregnation sites to prevent wooden poles from decay, leaving behind a legacy of highly contaminated soil/aquifer systems. Little is known about species transformation and mobility of HgCl 2 in contaminated soils and groundwater. At such a site the behaviour of HgCl 2 in soils and groundwater was investigated to assist in risk assessment and remediation. The soil is low in organic carbon and contains up to 11,000 mg Hg/kg. Mercury (Hg) concentrations in groundwater decrease from 230 to 0.5 μg/l within a distance of 1.3 km. Hg species transformations in soil and aqueous samples were analysed by means of solid-phase Hg pyrolysis and CV-AAS. In aqueous samples, Hg species were distinguished between ionic/reactive Hg and complex-bound Hg. Potential mobility of Hg in soils was studied through batch experiments. Most Hg in the soil is matrix-bound HgCl 2, whereas in the aquifer secondary formation to Hg 0 could be observed. Aqueous Hg speciation in groundwater and soil solutions shows that an average of 84% of soluble Hg exists as easily reducible, inorganic Hg species (mostly HgCl 2). The proportion of complex-bound Hg increases with distance due to the transformation of inorganic HgCl 2. The frequent occurrence of Hg 0 in the aquifer suggests the formation and degassing of Hg 0, which is, in addition to dilution, an important process, lowering Hg concentrations in the groundwater. High percentage of mobile Hg (3–26%) and low seepage fluxes will result in continuous Hg release over centuries requiring long-term groundwater remediation. Results of soluble Hg speciation suggest that filtering materials should be adapted to ionic Hg species, e.g. specific resins or amalgamating metal alloys.

Inorganic selenium speciation in groundwaters by solid phase extraction on Dowex 1X2

A Dowex 1X2 resin separation technique followed by analysis with atomic absorption spectroscopy was evaluated for the study of inorganic selenium speciation in groundwaters. After Se(IV) and Se(VI) were retained on the resin column, Se(IV) and Se(VI) were eluted out by 0.1 and 1 M nitric acid solutions. The method detection limit was 5.6 ng/L for both Se(IV) and Se(VI). Analysis of synthetic solutions consistently yielded more than 90% recovery of these two selenium forms with negligible cross-contamination. The results of spiked well waters show that this method can be applied at ultra-trace level of Se in groundwater and the interference of chloride ion can be neglected. Water samples collected from the monitoring wells in the Science-based Industrial Park, Hsin-Chu, Taiwan, were analyzed. Average dissolved selenium concentrations were 32.1 ± 17.6 ng/L. The proportion of Se(VI) to the total dissolved selenium ranged from 47.6 to 61.2% and an average of 53.8% in water samples analyzed.

The occurrence and speciation of arsenic, antimony, and selenium in ground water of Poznań city (Poland)

This paper presents results of determination of total arsenic, antimony, and selenium contents as well as their species in ground water from the region of Poznań. Determinations were carried by means of atomic absorption spectrometry hyphenated with generation of hydrides and in situ preconcentration in a graphite tube (HG-GFAAS). In order to obtain the best efficiency of an analyte concentration process on the walls of the tube, palladium was used as a modifying agent. The concentration of total arsenic was up to 2.04 ng ml−1, that of antimony up to 0.71 ng ml−1, and that of selenium up to 0.44 ng ml−1. The lowest concentrations of the investigated elements in ground water and the predominance of As(III), Sb(III), and Se(IV) speciation forms over As(V), Sb(V), and Se(VI) forms were found in the region, where the thickest aquitards (glacial tills of the Vistulian Glaciation) overlay an aquifer. Moreover, the geological and hydrogeological conditions of the study area are presented.

Determination of inorganic arsenic species by flow injection hydride generation atomic absorption spectrometry with variable sodium tetrahydroborate concentrations

This work describes a study on the determination of inorganic arsenic species in ground water and synthetic experimental matrices, using a flow injection system with on-line hydride generation device coupled to an atomic absorption spectrometer with flame-heated quartz atomizer (FI HG AAS). Specific trivalent arsenic determination is based on the slow kinetics of As(V) on the hydride generation reaction using sufficiently low concentrations of sodium tetrahydroborate (NaBH 4) as reductant in highly acidic conditions (pH<0). Under these conditions, the efficiency of hydride generation from As(V) is much lower than that from As(III). The pentavalent form is determined by the difference between total inorganic arsenic and As(III). As(V) interferences were studied using As(III) solutions ranging from 0% to 50% of total inorganic As. The optimized NaBH 4 concentration was 0.035% (w/v). The detection limit was 1.4 μg l −1 As(III). As(V) interferences were 6% in the case of water samples with 6 μg l −1 As(III) in the presence of 54 μg l −1 As(V) (i.e. 10% As(III)). Interferences of methylated arsenic species (MMA and DMA) were evaluated. Speciation method was satisfactorily applied to 20 field arsenical water samples from Santa Fe, Argentina, with values ranging from 30 to 308 μg l −1 total As. We found from 0% to 36% As(III) in the 20 field samples. The developed methodology constitutes an economic, simple and reliable way to evaluate inorganic arsenic distribution in underground waters or similar systems with negligible or no content of organoarsenicals.

Heavy metal content and speciation in groundwater of the Guadiamar river basin

This work presents the conclusions of a speciation study concerning Zn, Cd, Pb and Cu in groundwater from ten wells in the alluvial aquifers of the Guadiamar river, affected by Aznalcollar mine tailing spill (April 1998). The sampling campaign took place in January 2000, almost two years after the mining accident. Four metal fractions were determined: labile metal forms, H + exchangeable metal forms, strongly inert forms (associated with organic and inorganic matter in solution), and forms associated with suspended matter. Total metal concentration in groundwater followed the trend Cd<Pb<Cu<Zn. The speciation study showed that Zn and Cd were present to a great extent in available forms (labile and H + exchangeable), while Pb and Cu were found mostly in the less available forms (strongly inert). These results can illustrate the potential value of the speciation tool for the follow-up of spill-induced pollution in the area.

Is there evidence of arsenic movement at cattle tick dip sites?

Soils at cattle tick dip sites in Australia have been contaminated by a range of chemicals, including arsenic (As). To determine if significant off-site migration of As from dip sites has occurred, 28 dip sites were surveyed to assess both surface and subsurface As transport. Although previous studies using sequential extraction techniques indicated a risk of As leaching at these sites, no evidence of such movement was found in the field from this study.The As concentration in shallow groundwater (2 m) at clay textured sites was below detection level of 1 μg/L.�At sandy textured sites, groundwater immediately adjacent to the dip bath contained significant levels of soluble arsenic, but declined sharply with distance (c. 20 m) from the bath.The distribution of As at the soil surface was consistent with disposal methods used (pumping out used fluid from the dip). No sites showed significant transport and redeposition of As.Arsenic speciation in groundwater revealed As (V) as the dominant species in all sites. As (III) was found in detectable quantities at one site only.Most dip sites in New South Wales are located on heavier textured soils rich in iron oxides that adsorb As. These sites pose a negligible risk of contaminating groundwater. However, a few dip sites also occur on coastal sand relics. These sites have potential to contaminate groundwater within small distances (c. 20 m) from the dip bath. Lack of significant surface movement of residues was attributed to good vegetation cover at the sites surveyed.

Distribution of Zn, Cd, Pb and Cu Metals in Groundwater of the Guadiamar River Basin

Traditionally, the Guadiamar River Basin (Seville, SouthwestSpain) has received pollution from two different sources. Inits upper course, from a pyrite exploitation and, in itslower reaches, from untreated urban and industrial wastes aswell as wastes from intensive agricultural activity. In 1998,the accidental release in the river of about 6 million m3 of acid water and sludge from mine tailings contributedto worsen the pollution of an already contaminated area. Themain polluting agents of the spill were heavy metals. Itaffected a large number of wells either directly or as a consequence of infiltration from polluted soils. Assessment of the pollution by total metal determination does not revealthe true environmental impact of the spill and speciation studies showing the distribution of the main pollutants are required. There is a direct association between the physicochemical speciation of an element and its bioavailability, toxicity and mobility. This article describesa distribution study of the metals Zn, Cd, Pb and Cu by speciation analysis of groundwater in six wells of the GuadiamarRiver Basin; the samples were taken several weeks after the spill. The speciation analysis resulted in the definition ofthree species categories: a) labile metal (H+ exchangeable),b) metal strongly associated to dissolved organic matter and c) metal associated with suspended material. Analysis was carried out by anodic stripping voltammetry (ASV). Metal speciation ingroundwater of the Guadiamar River Basin allows a differentiationbetween: on the one hand, metals from the mining spill, andon the other hand a less recent pollution from accumulatedinfiltration of either mining or agricultural origin, the last one due to an abuse of phytosanitary products.

Overview of actinides (Np, Pu, Am) and Tc release from waste glasses: influence of solution composition

Studies on the release of actinides from nuclear waste glasses are numerous and essentially focus on the retention of actinides in the surface layer, their mobility, solubility and speciation in the medium of interest. Even if the chemical properties of the actinides, such as solubility and speciation in groundwaters, have been studied by many researchers, everything is not yet understood. Indeed, the radionuclide behaviour during glass alteration depends on many parameters like the nature of the solution in contact with the glass (pH, E h, complexing agents, colloids). Several radionuclides are redox sensitive and their mobility is linked to the local redox conditions, expected to be reducing in deep repository environments. Their chemical species and solubilities will be greatly influenced by the redox conditions. Laboratory tests on glass corrosion in pure water under oxic or anoxic conditions show Tc and Np to be released to a greater extent than Pu or Am. Most of the Np and Tc are found in a dissolved form whereas Pu and Am are present as colloidal material with a mobility varying according to the nature of the solutions. The presence of carbonates increases more significantly the mobility of the actinides compared to phosphate and sulfate ions. Most of the released radionuclides will also adsorb on environmental materials or form colloids like Pu and Am, often associated with colloids attributed to the spallation from the alteration layer of the active glass. Parameters affecting the actinide speciation and release (redox conditions, complexation effects, colloid formation) are overviewed through a survey of literature data on active leaching tests.