Potential Groundwater Contamination Research Articles

Terrestrial sedimentary pyrites as a potential source of trace metal release to groundwater – A case study from the Emsland, Germany

Pyrite is a common minor constituent of terrestrial freshwater sediments and a sink for trace elements. Different amounts and morphological types (framboids and euhedral crystals) of sedimentary pyrites were found in the heavy mineral fraction of cores obtained from several drillholes located in the Emsland region, NW Germany. Their trace element contents were investigated to assess their potential for groundwater contamination after oxidation, e.g. induced by dewatering or autotrophic denitrification. Nickel, arsenic and cadmium were found in significant concentrations in pyrite. Geochemical modeling showed that elevated trace metal concentrations in groundwater, potentially exceeding drinking water standards, should preferentially occur in a less than 1 m thick zone situated around the depth of the redoxcline, where nitrate is reduced by pyrite. This was confirmed by depth-specific groundwater sampling in the Emsland and by previously published studies. The absolute concentration of released trace metals depends on their content in the pyrite but also strongly on the nitrate load of groundwater.

Distribution of groundwater arsenic in Xinjiang, P.R. China

Although potential contamination of groundwater As is expected to occur in Xinjiang, P.R. China, few data are available for the regional distribution of groundwater As. In this study, the spatial distribution of groundwater As was investigated in the Chepaizi (CPZ-N) and Shihezi (SHZ-N) areas of northern Xinjiang, the Balikun-Yiwu Basin (BY-E) in eastern Xinjiang, and the Tarim (TRM-S) and Yanqi (YQ-S) basins in southern Xinjiang. Arsenic concentrations greater than 10 μg/L were found in 12% of analyzed groundwaters. All groundwater samples collected in CPZ-N had As concentrations greater than 10 μg/L (25–185 μg/L), 30% in SHZ-N (<0.25–49 μg/L), 2.7% in BY-E, and 6.1% in TRM-S and YQ-S. No high As groundwater (As >10 μg/L) was found in the eastern and southern TRM-S and YQ-S. Distribution of groundwater As showed a tremendous spatial variability, which greatly varied over a short distance horizontally. Arsenic concentration generally increased with increasing sampling depth. The spatial distribution of groundwater As would be regulated by As source and hydrogeochemical processes. Higher pH and/or lower ORP values were generally observed in high As groundwater (>10 μg/L) in comparison with low As groundwater (<10 μg/L). Arsenic mobility in SHZ-N and CPZ-N may result from As desorption under relatively high pH conditions, and more tentatively from reductive dissolution of Fe(III) oxides in BY-E and TRM-S. However, detailed mechanisms of As mobilization in these regions need further investigation.

Effectiveness evaluation of objective and subjective weighting methods for aquifer vulnerability assessment in urban context

Groundwater vulnerability assessment has been an accepted practice to identify the zones with relatively increased potential for groundwater contamination. DRASTIC is the most popular secondary information-based vulnerability assessment approach. Original DRASTIC approach considers relative importance of features/sub-features based on subjective weighting/rating values. However variability of features at a smaller scale is not reflected in this subjective vulnerability assessment process. In contrast to the subjective approach, the objective weighting-based methods provide flexibility in weight assignment depending on the variation of the local system. However experts’ opinion is not directly considered in the objective weighting-based methods. Thus effectiveness of both subjective and objective weighting-based approaches needs to be evaluated. In the present study, three methods – Entropy information method (E-DRASTIC), Fuzzy pattern recognition method (F-DRASTIC) and Single parameter sensitivity analysis (SA-DRASTIC), were used to modify the weights of the original DRASTIC features to include local variability. Moreover, a grey incidence analysis was used to evaluate the relative performance of subjective (DRASTIC and SA-DRASTIC) and objective (E-DRASTIC and F-DRASTIC) weighting-based methods. The performance of the developed methodology was tested in an urban area of Kanpur City, India. Relative performance of the subjective and objective methods varies with the choice of water quality parameters. This methodology can be applied without/with suitable modification. These evaluations establish the potential applicability of the methodology for general vulnerability assessment in urban context.

On the performance of a hybrid process to mineralize the herbicide tebuthiuron using a DSA® anode and UVC light: A mechanistic study

A hybrid electrochemical and photochemical (HEP) process was used to oxidize and mineralize the herbicide tebuthiuron (TBT), which is a potential contaminant of ground water, using a DSA® anode and UVC light. The electrochemical and photochemical experiments were carried out in flow reactors and the investigated variables were: i) power of the Hg lamp (5, 9, 80, and 125W), ii) solution pH (3, 7, 11, and no control), iii) NaCl concentration (0, 1, 2, and 4gL−1), and iv) electric current density (10, 20, and 30mAcm−2). The performance of the oxidation and mineralization process of TBT and its intermediates was assessed by high performance liquid chromatography coupled to mass spectrometry and total organic carbon analyses. The use of a 9WHg lamp led to complete oxidation and mineralization of TBT, and its intermediate compounds, from acidic to neutral solutions, independently of the applied electric current density, and with increasing NaCl concentration. High CO2 conversions were obtained using the HEP process, as the generated intermediates (including an organochlorine) were completely eliminated. TBT removal rates similar to those of an electrochemical experiment using a boron-doped diamond anode were attained using the HEP process, but with higher energy consumption; however, chlorinated carboxylic acids were no longer present in the final treatment stages. The HEP process could be regarded as an advanced oxidation process, being an interesting option to treat effluents contaminated with organics if a proper optimization of the UVC lamp is done.

Environmental Impact and Physicochemical Assessment of Pond Ash for its Potential Application as a Fill Material

Thermal power plants (TPPs) produce a large quantity of coal ash, whose disposal is a big environmental issue. A major portion of coal ash is dumped as pond ash in ash pond near TPPs. Properties of pond ash vary from TPP to TPP and also within the same ash pond at inflow and outflow point. To assess the feasibility of pond ash as a fill material, pond ash samples were collected from inflow and outflow points of three TPPs in Haryana. This paper presents a detailed characterization study on the physico-chemical, mineralogical and morphological properties of pond ash samples. Leaching study was also carried out to assess the potential contamination of ground water from coal ash fills. Results reveal that all inflow and outflow pond ashes have low specific gravity (2.03–2.27) as compared to soil (2.6–2.7), i.e. natural fill material, low amount of unburned carbon content (1.79–3.49 %) and the values of maximum dry density and optimum moisture content are within the permissible limits as per design standards of embankment construction. The results of leaching study indicate that concentration of lead (Pb) and chromium (Cr) are quite high from standard land disposal limit, prescribed by Ministry of Environment and Forest in all pond ash samples. So it can be effectively used as construction fill materials for low-lying areas and as embankment materials etc., with caution to protect ground water from contamination due to the high concentration of lead (Pb) and chromium (Cr).

Combining natural background levels (NBLs) assessment with indicator kriging analysis to improve groundwater quality data interpretation and management

The natural background level (NBL) concept is revisited and combined with indicator kriging method to analyze the spatial distribution of groundwater quality within a groundwater body (GWB). The aim is to provide a methodology to easily identify areas with the same probability of exceeding a given threshold (which may be a groundwater quality criteria, standards, or recommended limits for selected properties and constituents). Three case studies with different hydrogeological settings and located in two countries (Portugal and Italy) are used to derive NBL using the preselection method and validate the proposed methodology illustrating its main advantages over conventional statistical water quality analysis. Indicator kriging analysis was used to create probability maps of the three potential groundwater contaminants. The results clearly indicate the areas within a groundwater body that are potentially contaminated because the concentrations exceed the drinking water standards or even the local NBL, and cannot be justified by geogenic origin. The combined methodology developed facilitates the management of groundwater quality because it allows for the spatial interpretation of NBL values.

Spills of Hydraulic Fracturing Chemicals on Agricultural Topsoil: Biodegradation, Sorption, and Co-contaminant Interactions.

Hydraulic fracturing frequently occurs on agricultural land. Yet the extent of sorption, transformation, and interactions among the numerous organic frac fluid and oil and gas wastewater constituents upon environmental release is hardly known. Thus, this study aims to advance our current understanding of processes that control the environmental fate and toxicity of commonly used hydraulic fracturing chemicals. Poly(ethylene glycol) surfactants were completely biodegraded in agricultural topsoil within 42-71 days, but their transformation was impeded in the presence of the biocide glutaraldehyde and was completely inhibited by salt at concentrations typical for oil and gas wastewater. At the same time, aqueous glutaraldehyde concentrations decreased due to sorption to soil and were completely biodegraded within 33-57 days. While no aqueous removal of polyacrylamide friction reducer was observed over a period of 6 months, it cross-linked with glutaraldehyde, further lowering the biocide's aqueous concentration. These findings highlight the necessity to consider co-contaminant effects when we evaluate the risk of frac fluid additives and oil and gas wastewater constituents in agricultural soils in order to fully understand their human health impacts, likelihood for crop uptake, and potential for groundwater contamination.

Recycled Construction and Demolition Wastes as filling material for geosynthetic reinforced structures. Interface properties

Construction and Demolition Wastes (C&DW) are increasingly being reused in civil engineering applications, mainly in concrete production and base layers of roadway infrastructures. However, frequently the fine grain portion of these recycled aggregates is not considered suitable for those applications being landfilled instead of recycled. Moreover, the value-added utilisation of recycled C&DW in the construction of geosynthetic reinforced structures (steep slopes and retaining walls) is almost an unexplored field. This research assesses the feasibility of using fine-grain recycled C&DW as filling material of geosynthetic reinforced structures (GRS), appraising the physical, mechanical and environmental characterization of the construction and demolition material (C&DM), as well as, the direct shear and pullout behaviour of the interfaces between this material and three distinct geosynthetics (two geogrids and one geocomposite reinforcement or high strength geotextile). Direct shear tests results have shown that fine-grain recycled C&DW, properly compacted, exhibit similar shear strength to natural soils used commonly in the construction of GRS. The potential contamination of groundwater by these recycled C&DW was evaluated through laboratory leaching tests and, excepting the values of sulphate and total dissolved solids (TDS), this recycled C&DW complies with the provisions of European Council Decision 2003/33/EC for inert materials. High values of coefficients of interaction for C&DW/geosynthetic interfaces, a parameter of utmost importance in the design and performance of GRS, were achieved. The results herein presented support the viability of using these recycled C&DW as filling material for GRS construction.

Distribution and origin of dissolved methane, ethane and propane in shallow groundwater of Lower Saxony, Germany

More than 90% of Germany's domestic natural gas production and reserves are located in Lower Saxony, North Germany. Recently, research has been intensified with respect to unconventional shale gas, revealing a large additional resource potential in northern Germany. However, many concerns arise within the general public and government/political institutions over potential groundwater contamination from additional gas wells through hydraulic fracturing operations.In order to determine the naturally occurring background methane concentrations, ∼1000 groundwater wells, covering ∼48 000 km2, have been sampled and subsequently analyzed for dissolved methane, ethane and propane and the isotopic composition of methane (δ13C).Dissolved methane concentrations cover a range of ∼7 orders of magnitude between the limit of quantification at ∼20 nl/l and 60 ml/l. The majority of groundwater wells exhibit low concentrations (<1 μl/l), a small number of samples (65) reveal concentration in the range >10 ml/l. In 27% of all samples ethane and in 8% ethane and propane was detected. The median concentration of both components is generally very low (ethane 50 nl/l, propane 23 nl/l).Concentrations reveal a bimodal distribution of the dissolved gas, which might mirror a regional trend due to different hydrogeological settings. The isotopic composition of methane is normally distributed (mean ∼ −70‰ vs PDB), but shows a large variation between −110‰ and +20‰. Samples with δ13C values lower than −55‰ vs PDB (66%) are indicative for methanogenic biogenic processes. 5% of the samples are unusually enriched in 13C (≥25‰ vs PDB) and can best be explained by microbial methane oxidation.According to a standard diagnostic diagram based on methane δ13C values and the ratio of methane over the sum over ethane plus propane (“Bernard”-diagram) less than 4% of the samples plot into the diagnostic field of typical thermogenic natural gases. However, in most cases only ethane has been detected and the remaining less than 15 samples demonstrate an uncommon ratio of ethane to propane compared to typical thermogenic hydrocarbons. These data do not suggest a migration of deeper sourced gases, but a thermogenic source cannot be excluded entirely for some samples. However, ethane and propane can also be generated by microbial processes and might therefore represent ubiquitous background groundwater abundances of these gases. Nevertheless, our data suggest that due to the exceedingly low concentration of ethane and propane, respective concentration changes might prove to be a more sensitive parameter than methane to detect possible migration of deeper sourced (thermally generated) hydrocarbons into a groundwater aquifer.

Adsorption and degradation of phenoxyalkanoic acid herbicides in soils: A review.

The primary aim of the present review on phenoxyalkanoic acid herbicides-2-(2,4-dichlorophenoxy) acetic acid (2,4-D), 2-(4-chloro-2-methylphenoxy) acetic acid (MCPA), (2R)-2-(2,4-dichlorophenoxy) propanoic acid (dichlorprop-P), (2R)-2-(4-chloro-2-methylphenoxy) propanoic acid (mecoprop-P), 4-(2,4-dichlorophenoxy) butanoic acid (2,4-DB), and 4-(4-chloro-2-methylphenoxy) butanoic acid (MCPB)-was to compare the extent of their adsorption in soils and degradation rates to assess their potential for groundwater contamination. The authors found that adsorption decreased in the sequence of 2,4-DB > 2,4-D > MCPA > dichlorprop-P > mecoprop-P. Herbicides are predominantly adsorbed as anions-on organic matter and through a water-bridging mechanism with adsorbed Fe cations-and their neutral forms are adsorbed mainly on organic matter. Adsorption of anions of 2,4-D, MCPA, dichlorprop-P, and mecoprop-P is inversely correlated with their lipophilicity values, and modeling of adsorption of the compounds based on this relationship is possible. The predominant dissipation mechanism of herbicides in soils is bacterial degradation. The contribution of other mechanisms, such as degradation by fungi, photodegradation, or volatilization from soils, is much smaller. The rate of bacterial degradation decreased in the following order: 2,4-D > MCPA > mecoprop-P > dichlorprop-P. It was found that 2,4-D and MCPA have the lowest potential for leaching into groundwater and that mecoprop-P and dichlorprop-P have slightly higher potential. Because of limited data on adsorption and degradation of 2,4-DB and MCPB, estimation of their leaching potential was not possible.

Chromate adsorption from chromite ore processing residue eluates by three Indian soils

Environmental context Chromate (CrO42–)-containing waste is illegally dumped in some places in the state of Uttar Pradesh, north India, although CrO42– is known to be toxic and carcinogenic. Because CrO42– is leached from the landfills, this study investigated the adsorption of CrO42– by soils. The results indicated that CrO42– is highly leachable and adsorption is inhibited, which leads to contamination of the groundwater and drinking water in this area. Abstract Chromite ore processing residue (COPR) is a harmful waste of the chromate (CrO42–) extraction roasting process. Nevertheless, deposition of COPR in uncontrolled surface landfills is still common practice in some countries. Leaching of carcinogenic CrO42– and contamination of groundwater is a key environmental risk arising from COPR sites. The objective of this study was to evaluate the adsorption behaviour of CrO42– from COPR eluates by soils. Prior to the adsorption experiments, batch studies at varying solid-to-liquid ratios were performed to evaluate the solubility of CrO42– from COPR. Chromate adsorption experiments were carried out in a batch system with eluates obtained from two different Indian COPRs to assess potential groundwater contamination by CrO42–. Three soils that originate from the surroundings of COPR dumping sites were chosen in order to provide realistic adsorption conditions. The data were evaluated with the Freundlich and Langmuir equation. Chromate adsorption was inhibited because of the high pH of both of the soils (pH 6.7 to 7.2) and the eluates (pH 12.3) as well as the high carbonate concentration of the eluates. The extent and behaviour of CrO42– adsorption from both eluates was similar. The main difference between the eluates was the solubility of CrO42– from COPR and thus the initial CrO42– concentration. The results presented in this study provide an improved understanding of the mobility of CrO42– in the affected area, which is important because the local population uses the groundwater not only for the needs of livestock but also as drinking water.

A coupled geomechanics and fluid flow model for induced seismicity prediction in oil and gas operations and geothermal applications

The combined horizontal drilling and hydraulic fracturing has revitalized economically viable production from tight oil and gas shale reservoirs. This joint technology application enabled extensive unconventional resource exploration and development activities first in the United States followed by around the globe for unlocking the vast hydrocarbon resources. While the contributions from these accomplishments also created an enhancement in the local economies and technological advancements, these activities also have raised significant concern on potential surface and groundwater contamination and air pollution issues and more recently induced seismicity for geohazard risk. In this research study, we provide a summary of induced seismic activities related to oil, gas and geothermal operations in the U.S. The role of the stress alteration and behavior of physicochemical interactions taking place between the fracturing fluids used and the shale matrix under stress have been presented using a coupled geomechanics, fluid flow and physicochemical model. Examples of fluid injection in shale reservoir hydraulic fracturing and waste disposal operations have been provided toward better understanding of the predictive methodologies for induced seismicity and preventive effort for sustainable and safe unconventional operations. The impact of the presence of a fault at various distances away from the injection site nearby the disposal and injection operations on occurrence of the induced seismicity was studied. It was shown that microseismic monitoring along with the coupled geomechanics, fluid flow models and statistical analysis of the microseismic data can provide a good lead for prediction of potential fault reactivation and induced seismicity generation in association with oil and gas production, EOR and EGS fluid injection and waste disposal operations.

A study on control of contaminant transport through the soil using equal double sheet piles

Abstract Control of groundwater moving using sheet pile is very important for minimizing the potential of groundwater contamination. Present study aims to control the contaminant transport through soil by using equal double sheet piles. Physical sand box model was implemented symmetrically in order to examine the effect of depths of double sheet piles, distance between them and distance of contaminant upstream the sheet piles. The regional contaminated porous field is studied numerically using simulation software MODEFLOW and M3DMS. Average absolute difference time between experimental and numerical results that contamination moved from upstream to point under the second sheet pile and arrives the surface of soil at downstream, equals 9.31% and 6.11% respectively. Design charts are presented for quantifying the effects of equal double sheet piles on the hydraulic control of the groundwater flow field. From the charts, the double sheet piles depth can be selected according to the needed condition.

Mobility and degradation of disulfoton in coffee culture soil

Abstract Mobility and degradation of the insecticide disulfoton (DST) in the soil were studied in this work, through leaching columns spiked with the analytical standard solution and the commercial product Baysiston ® . In both experiments, the DST presented low mobility, keeping the upper layer of the soil, while its degradation products, mainly the disulfoton sulfone (DSA) and oxygen analogue of disulfoton sulfone (OADSA) percolated into deeper soil layers. Such behavior confirms its potential for contamination of soil and groundwater. It has also been proposed a new DST degradation route wherein oxygen analogue of disulfoton (AODST) can be oxidized to the final degradation product (AODSA) by direct and/or indirect conversion.

Adsorption and attenuation behavior of 3-nitro-1,2,4-triazol-5-one (NTO) in eleven soils.

NTO (3-nitro-1,2,4-triazol-5-one) is one of the new explosive compounds used in insensitive munitions (IM) developed to replace traditional explosives, TNT and RDX. Data on NTO fate and transport is needed to determine its environmental behavior and potential for groundwater contamination. We conducted a series of kinetic and equilibrium batch experiments to characterize the fate of NTO in soils and the effect of soil geochemical properties on NTO-soil interactions. A set of experiments was also conducted using sterilized soils to evaluate the contribution of biodegradation to NTO attenuation. Measured pH values for NTO solutions decreased from 5.98 ± 0.13 to 3.50 ± 0.06 with increase in NTO concentration from 0.78 to 100 mg L(-1). Conversely, the pH of soil suspensions was not significantly affected by NTO in this concentration range. NTO experienced minimal adsorption, with measured adsorption coefficients being less than 1 cm(3) g(-1) for all studied soils. There was a highly significant inverse relationship between the measured NTO adsorption coefficients and soil pH (P = 0.00011), indicating the role of NTO and soil charge in adsorption processes. In kinetic experiments, 1st order transformation rate constant estimates ranged between 0.0004 h(-1) and 0.0142 h(-1) (equivalent to half-lives of 72 and 2 d, respectively), and correlated positively with organic carbon in the soil. Total attenuation of NTO was higher in untreated versus sterilized samples, suggesting that NTO was being biodegraded. The information presented herein can be used to help evaluate NTO potential for natural attenuation in soils.

Assessing the Groundwater Contamination Potential from a Well in a Hydraulic Fracturing Operation

Assessing the Groundwater Contamination Potential from a Well in a Hydraulic Fracturing Operation

Contaminant transport in the sub-surface soil of an uncontrolled landfill site in China: site investigation and two-dimensional numerical analysis.

A field investigation of contaminant transport beneath and around an uncontrolled landfill site in Huainan in China is presented in this paper. The research aimed at studying the migration of some chemicals present in the landfill leachate into the surrounding clayey soils after 17 years of landfill operation. The concentrations of chloride and sodium ions in the pore water of soil samples collected at depths up to 15 m were obtained through an extensive site investigation. The contents of organic matter in the soil samples were also determined. A two-dimensional numerical study of the reactive transport of sodium and chloride ion in the soil strata beneath and outside the landfill is also presented. The numerical modelling approach adopted is based on finite element/finite difference techniques. The domain size of approximately 300 × 30 m has been analysed and major chemical transport parameters/mechanisms are established via a series of calibration exercises. Numerical simulations were then performed to predict the long-term behaviour of the landfill in relation to the chemicals studied. The lateral migration distance of the chloride ions was more than 40 m which indicates that the advection and mechanical dispersion are the dominant mechanism controlling the contaminant transport at this site. The results obtained from the analysis of chloride and sodium migration also indicated a non-uniform advective flow regime of ions with depth, which were localised in the first few metres of the soil beneath the disposal site. The results of long-term simulations of contaminant transport indicated that the concentrations of ions can be 10 to 30 times larger than that related to the allowable limit of concentration values. The results of this study may be of application and interest in the assessment of potential groundwater and soil contamination at this site with a late Pleistocene clayey soil. The obtained transport properties of the soils and the contaminant transport mechanisms can also be used for the design of engineered barriers for the control of the long-term pollution of the site.

Leaching of Glyphosate and Aminomethylphosphonic Acid through Silty Clay Soil Columns under Outdoor Conditions.

Glyphosate [-(phosphono-methyl)-glycine] is the main herbicide used in the Chianti vineyards. Considering the pollution risk of the water table and that the vineyard tile drain may deliver this pollutant into nearby streams, the objective of the present study was to estimate the leaching losses of glyphosate under natural rainfall conditions in a silty clay soil in the Chianti area. The leaching of glyphosate and its metabolite (aminomethylphosphonic acid [AMPA]) through soils was studied in 1-m-deep soil columns under outdoor conditions over a 3-yr period. Glyphosate was detected in the leachates for up to 26 d after treatments at concentrations ranging between 0.5 and 13.5 μg L. The final peak (0.28 μg L) appeared in the leachates approximately 319 d after the first annual treatment. Aminomethylphosphonic acid first appeared (21.3 μg L) in the soil leachate 6.8 d after the first annual treatment. Aminomethylphosphonic acid detection frequency and measured concentration in the leachates were more than that observed for the glyphosate. Aminomethylphosphonic acid was detected in 20% of the soil leachates at concentrations ranging from 1 to 24.9 μg L. No extractable glyphosate was detected in the soil profile. However, the AMPA content in the lowest layer ranged from 13.4 to 21.1 mg kg, and on the surface layer, it ranged from 86.7 to 94 mg kg. Overall, these results indicate that both glyphosate and AMPA leaching through a 1-m soil column may be potential groundwater contaminants.

A study on the influence of inorganic salts on the behaviour of compacted bentonites

Clay liners are frequently installed at waste disposal sites as a means of preventing pollutant migration and minimizing or eliminating the potential for ground water contamination. Because of their low hydraulic conductivity and high contaminant adsorption capacity, bentonite is used as a liner material to prevent subsurface contamination. However, presence of various chemicals in waste could affect the hydraulic and contamination adsorption capacity of bentonite and in turn reduce its usefulness as barrier material. In addition to the salt solution, a change in the mineralogical composition such as montmorillonite content, cation exchange capacity, specific surface area, exchangeable sodium percentage of the bentonite also significantly influences its swelling and hydraulic behaviour. This study was carried out to study the effect of salt solution and mineralogical composition on the behaviour of compacted bentonite. Two bentonites with varying mineralogical composition, which was reflected in their different liquid limit and free swelling value, were evaluated for their free swelling, Atterberg limits, swelling potential, swelling pressure, and hydraulic conductivity in the presence of various concentrations of NaCl and CaCl2 solution. To study the effect of initial compaction conditions on swelling and hydraulic behaviour in presence of salt solution, studies were also carried out on samples compacted at optimum moisture content (OMC)–maximum dry density (MDD) and 5% dry of OMC–MDD. The result shows that the liquid limit, swelling volume, swelling pressure of the compacted bentonites decreased, whereas, plastic limit and hydraulic conductivity increased with increase in the salt concentration. The results also show that the effect of the salt on the properties of the bentonites depends on the salt type, salt concentration and initial compaction condition of the bentonite. The effects due to salt concentration were found to be more pronounced for the bentonite of higher quality which is marked by a higher swelling capacity, liquid limit, cation exchange capacity, exchangeable sodium percentage and specific surface area.

Toxicological evaluation of ametryn effects in Wistar rats

São Paulo state, Brazil, is one of the main areas of sugar cane planting in the world. Extensive use of ametryn, a triazine herbicide, in sugar cane agriculture and the properties of this herbicide suggest it could be present in the environment as a potential contaminant of soil, surface water, groundwater, and river sediment. In order to clarify the mechanism through which ametryn could be toxic, an in vivo study with Wistar rats was conducted using hematological, biochemical, molecular, morphological and genotoxic approaches. For this purpose, two sub-lethal ametryn concentrations (15mg and 30mg/kg/day) were administered to 42 rats divided into three groups (n=12) by gavage during 56 days, whereupon blood, liver and bone marrow were collected. The results showed ametryn genotoxic activity by in vivo micronuclei testing. This event probably occurred as consequence of oxidative stress induction demonstrated by GSTM1 transcript levels increase (indicating complexation between ametryn and/or metabolites with GSH) and by SOD activity decrease. Also, Mn-SOD transcripts were increased, probably avoiding mtDNA damage caused by EROS. These mechanisms displayed hepatic stellate cell (HSCs) activation because two major biomarkers were regulated, connexin and cadherin. N-cad transcripts were increased on both exposed groups while E-cad decreased in the T1 group, indicating epithelial-to-mesenchymal transition. In addition, Cx43 transcripts were decreased suggesting an increase in collagen content. Volumetric proportion of sinusoids was significantly decreased in T1 group and no significant alteration in hepatocyte volume was observed, indicating an increase in the space of Disse, due to fibrosis. Hepatocyte nuclei showed significant decrease in diameter and volume. Few hematological alterations were found. We emphasize the importance of other approaches, such as cell death and proliferation assays, so that ametryn toxicity can better be understood.