A rapid method for estimating log P for organic chemicals

The logarithm of the retention time (log RT) of organic chemicals on a permanently bonded (C-18) reverse-phase high-pressure liquid chromatography system is shown to be linearly related to the logarithm of the n-octanol/water partition coefficient (log P). A rapid, inexpensive technique based on reverse-phase high-pressure liquid chromatography has been developed to estimate the n-octanol/water partition coefficient of organic chemicals. The system consists of a preparative Micro-Pak^® C-10 reverse-phase column eluted with a 15% water/85% methanol solvent flowing at 2 ml min⁻¹ at room temperature.A linear calibration of the logarithm of retention time with the logarithm of the partition coefficient (log P) is attained by using a mixture of benzene, bromobenzene, biphenyl, bibenzyl, p,p'DDE, and 2,4,5,2′,5′-pentachlorobiphenyl as reference standards of known log P. Using a calibration mixture, the log P of other organic chemicals were estimated with a mean accuracy of 22.8% of the log P values reported in the literature. The technique permits estimation of log P in a maximum of 25 min and does not require a knowledge of the structure of the chemical for the estimate.     

Occurrence and removal of priority pollutants by lamella clarification and biofiltration

This study investigates the occurrence of all priority substances (n = 41) listed in the Water Framework Directive and additional substances (n = 47) in raw sewage, as well as the removal performance of lamella clarification and biofiltration techniques. Once the efficiency of both types of techniques has been assessed for typical wastewater parameters, the differences in each technique's ability to remove pollutants becomes obvious; nevertheless, pollutant removal in quantitative terms still depends on the physico-chemical properties of the compounds used and operating conditions within the selected facility. For lamella clarification, the removal of organic chemicals was found to be primarily correlated with their sorption potential and, hence, strongly dependent upon log K_ow of the compound under study. Compounds with a strong hydrophobic character (log K_ow > 4.5) are removed to a significant extent (approx. 85%), while hydrophilic compounds (log K_ow < 3.5) are poorly removed (<20%). For biofiltration, the removal of chemicals appears to be compound-dependent, although this outcome involves several mechanisms, namely: i) physical filtration of total suspended solids, ii) volatilisation, iii) sorption, and iv) biotransformation of substances. Even if the complex processes within a biofilter system do not yield an accurate prediction of pollutant removal, two groups of chemicals can still be clearly identified: i) hydrophobic or volatile compounds, for which moderate to high removal rates are observed (from 50% to over 80%); and ii) hydrophilic, non-volatile and refractory compounds for which a low removal rate would be expected (<20%).     

Exposure of the marine deposit feeder Hydrobia ulvae to sediment spiked with LAS congeners

The lethal and sub-lethal toxicity of LAS congeners to the mollusc gastropod Hydrobia ulvae were assessed in spiked sediment bioassays. This complements the little knowledge available to date on mixture effects in the sediment compartment. The LAS homologues joint effect was concentration additive (∑TU_i = 0.8-1). As opposed to the 10-d LC10 based on the sediment associated LAS concentration (91-330 mg/kg) which was independent of the homologue chain length, the LC10 based on the dissolved LAS fraction (0.804-0.068 mg/L) decreased as the homologue chain length increased from 10 to 13 carbons. The quantitative structure-activity relationship (QSAR) derived from these data was log (1/LC10 (mol/L)) = 0.64 log K_ow + 4.40 (n = 5; r² = 0.76; s = 0.24). It showed an apparent higher toxicity compared to the typical QSAR for polar narcosis in water-only systems probably due to the simultaneous exposure of the snail to LAS through the dissolved and the sediment associated fractions. The egestion rate of the surviving snails recovered after few days' exposure (1-d NOEC: 40-107 mg/kg, 9-d NOEC: 65-190 mg/kg) which suggests that the organisms were able to acclimate to LAS during the exposure.     

Partition of pollution between dissolved and particulate phases: what about emerging substances in urban stormwater catchments?

This paper presents results about the occurrence, the concentrations of urban priority substances on both the dissolved and the particulate phases in stormwater. Samples were collected at the outlet of a dense urban catchment in Paris suburb (2.30 km²). 13 chemical groups were investigated including 88 individual substances. Results showed that stormwater discharges contained 45 substances among them some metals, organotins, PAHs, PCBs, alkylphenols, pesticides, phthalates, cholorophenols and one volatile organic compound, i.e. methylene chloride. With respect to the European Water Framework Directive, these substances included 47% of the priority hazardous substances (n = 8), 38% of the priority substances (n = 10). The remaining substances (n = 27) belong to a list of others specific urban substances not included in the Water Framework Directive but monitored during this work. Finally, stormwater quality was evaluated by comparing the substance concentrations to environmental quality standards (EQS) and the particulate content to Canadian sediment quality guidelines. This showed that stormwater was highly contaminated and should be treated before being discharged to receiving waters in order to avoid any adverse impact on the river quality.     

Sorption-desorption column tests to evaluate the attenuation layer using soil amended with a stabilising agent

Sorption-desorption column tests using acrylic columns (? 5 cm × h 10 cm) were employed to evaluate the sorption performance of an attenuation layer against geogenic contamination. The attenuation layer material was silica sand amended with 1, 5, or 10% of a stabilising agent. The main component of the agent was magnesium oxide. The sorption behaviour of the materials was determined by a fluoride solution (C₀ = 80 mg/L F^-), while the desorption behaviour was determined by distilled water. Breakthroughs (C/C₀ > 0.05) occurred after approximately 1, 20, and 50 PVF for stabilising agent contents of 1, 5, and 10%, respectively. The one-dimensional advection-dispersion equation modelled the breakthrough curves obtained from the tests. The predictions gave unrealistic estimates, especially for the breakthrough point where C/C₀ = 0.05. For the 1% agent content, approximately 20% of the sorbed mass, S_s, was desorbed, but the percentage of desorbed mass, S_d, was much smaller for the higher agent contents. The difference between the sorbed and desorbed masses was defined as the immobilised fraction, S_s - S_d. For the 5% agent content, S_s - S_d = 4.0 mg/g. The results suggest that when silica sand is amended with magnesium oxide as an agent, the mixture can immobilise the fluoride in the attenuation layer.     

Rotating disk electrodes to assess river biofilm thickness and elasticity

The present study examined the relevance of an electrochemical method based on a rotating disk electrode (RDE) to assess river biofilm thickness and elasticity. An in situ colonisation experiment in the River Garonne (France) in August 2009 sought to obtain natural river biofilms exhibiting differentiated architecture. A constricted pipe providing two contrasted flow conditions (about 0.1 and 0.45 m s⁻¹ in inflow and constricted sections respectively) and containing 24 RDE was immersed in the river for 21 days. Biofilm thickness and elasticity were quantified using an electrochemical assay on 7 and 21 days old RDE-grown biofilms (t₇ and t₂₁, respectively). Biofilm thickness was affected by colonisation length and flow conditions and ranged from 36 ± 15 μm (mean ± standard deviation, n = 6) in the fast flow section at t₇ to 340 ± 140 μm (n = 3) in the slow flow section at t₂₁. Comparing the electrochemical signal to stereomicroscopic estimates of biofilms thickness indicated that the method consistently allowed (i) to detect early biofilm colonisation in the river and (ii) to measure biofilm thickness of up to a few hundred μm. Biofilm elasticity, i.e. biofilm squeeze by hydrodynamic constraint, was significantly higher in the slow (1300 ± 480 μm rpm^1/2, n = 8) than in the fast flow sections (790 ± 350 μm rpm^1/2, n = 11). Diatom and bacterial density, and biofilm-covered RDE surface analyses (i) confirmed that microbial accrual resulted in biofilm formation on the RDE surface, and (ii) indicated that thickness and elasticity represent useful integrative parameters of biofilm architecture that could be measured on natural river assemblages using the proposed electrochemical method.     

Seasonal stability of Cladophora-associated Salmonella in Lake Michigan watersheds

The bacterial pathogens Shigella, Salmonella, Campylobacter, and shiga toxin-producing E. coli (STEC) were recently found to be associated with Cladophora growing in southern Lake Michigan. Preliminary results indicated that the Salmonella strains associated with Cladophora were genetically identical to each other. However, because of the small sample size (n = 37 isolates) and a lack of information on spatial-temporal relationships, the nature of the association between Cladophora and Salmonella remained speculative. In this study, we investigated the population structure and genetic relatedness of a large number of Cladophora-borne Salmonella isolates from Lake Michigan (n = 133), as well as those isolated from stream and lake water (n = 31), aquatic plants (n = 8), and beach sands and sediments (n = 8) from adjacent watersheds. Salmonella isolates were collected during 2005-2007 between May and August from Lake Michigan beachsheds in Wisconsin, Illinois, and Indiana. The genetic relatedness of Salmonella isolates was examined by using the horizontal, fluorophore-enhanced rep-PCR (HFERP) DNA fingerprinting technique. While the Salmonella isolates associated with Cladophora exhibited a high degree of genetic relatedness (≥92% similarity), the isolates were not all genetically identical. Spatial and temporal relationships were evident in the populations examined, with tight clustering of the isolates both by year and location. These findings suggest that the relationship between Salmonella and Cladophora is likely casual and is related to input sources (e.g. wastewater, runoff, birds) and the predominant Salmonella genotype surviving in the environment during a given season. Our studies indicate that Cladophora is likely an important reservoir for Salmonella and other enteric bacterial pathogens in Lake Michigan beachsheds, which in turn may influence nearshore water quality.     

Sorption of emerging trace organic compounds onto wastewater sludge solids

This work examined the sorption potential to wastewater primary- and activated-sludge solids for 34 emerging trace organic chemicals at environmentally relevant concentrations. These compounds represent a diverse range of physical and chemical properties, such as hydrophobicity and charge state, and a diverse range of classes, including steroidal hormones, pharmaceutically-active compounds, personal care products, and household chemicals. Solid-water partitioning coefficients (K_d) were measured where 19 chemicals did not have previously reported values. Sludge solids were inactivated by a nonchemical lyophilization and dry-heat technique, which provided similar sorption behavior for recalcitrant compounds as compared to fresh activated-sludge. Sorption behavior was similar between primary- and activated-sludge solids from the same plant and between activated-sludge solids from two nitrified processes from different wastewater treatment systems. Positively-charged pharmaceutically-active compounds, amitriptyline, clozapine, verapamil, risperidone, and hydroxyzine, had the highest sorption potential, log K_d = 2.8-3.8 as compared to the neutral and negatively-charged chemicals. Sorption potentials correlated with a compound’s hydrophobicity, however the higher sorption potentials observed for positively-charged compounds for a given log D_ow indicate additional sorption mechanisms, such as electrostatic interactions, are important for these compounds. Previously published soil-based one-parameter models for predicting sorption from hydrophobicity (log K_ow > 2) can be used to predict sorption for emerging nonionic compounds to wastewater sludge solids.     

Implications of organic matter on arsenic mobilization into groundwater: Evidence from northwestern (Chapai-Nawabganj), central (Manikganj) and southeastern (Chandpur) Bangladesh

Boreholes (50 m depth) and piezometers (50 m depth) were drilled and installed for collecting As-rich sediments and groundwater in the Ganges, Brahmaputra, and Meghna flood plains for geochemical analyses. Forty-one groundwater samples were collected from the three areas for the analyses of cations (Ca²⁺, Mg²⁺, K⁺, Na⁺), anions (Cl⁻, NO₃⁻, SO₄²⁻), total organic carbon (TOC), and trace elements (As, Mn, Fe, Sr, Se, Ni, Co, Cu, Mo, Sb, Pb). X-ray powder diffraction (XRD) and X-ray fluorescence (XRF) were performed to characterize the major mineral and chemical contents of aquifer sediments. In all three study areas, results of XRF analysis clearly show that fine-grained sediments contain higher amounts of trace element because of their high surface area for adsorption. Relative fluorescent intensity of humic substances in groundwater samples ranges from 30 to 102 (mean 58 ± 20, n = 20), 54-195 (mean 105 ± 48, n = 10), and 27-243 (mean 79 ± 71, n = 11) in the Ganges, Brahmaputra and Meghna flood plains, respectively. Arsenic concentration in groundwater (20-50 m of depth) ranges from 3 to 315 μg/L (mean 62.4 ± 93.1 μg/L, n = 20), 16.4-73.7 μg/L (mean 28.5 ± 22.4 μg/L, n = 10) and 4.6-215.4 μg/L (mean 30.7 ± 62.1 μg/L, n = 11) in the Ganges, Brahmaputra and Meghna flood plains, respectively. Specific ultra violet adsorption (SUVA) values (less than 3 m⁻¹ mg⁻¹ L) indicate that the groundwater in the Ganges flood plain has relatively low percentage of aromatic organic carbon compared to those in the Brahmaputra and Meghna flood plains. Arsenic content in sediments ranges from 1 to 11 mg/kg (mean 3.5 ± 2.7 mg/kg, n = 17) in the three flood plains. Total organic carbon content is 0.5-3.7 g/kg (mean 1.9 ± 1.1 g/kg) in the Ganges flood plain, 0.5-2.1 g/kg (mean: 1.1 ± 0.7 g/kg) in the Brahmaputra flood plain and 0.3-4.4 g/kg (mean 1.9 ± 1.9 g/kg) in the Meghna flood plain. Arsenic is positively correlated with TOC (R² = 0.50, 0.87, and 0.85) in sediments from the three areas. Fourier transform infrared (FT-IR) analysis of the sediments revealed that the functional groups of humic substances in three areas include amines, phenol, alkanes, and aromatic carbon. Arsenic and Fe speciation in sediments were determined using XANES and the results imply that As(V) and Fe(III) are the dominant species in most sediments. The results also imply that As (V) and Fe (III) in most of the sediment samples of the three areas are the dominant species. X-ray absorption fine structure (EXAFS) analysis shows that FeOOH is the main carrier of As in the sediments of three areas. In sediments, As is well correlated with Fe and Mn. However, there is no such correlation observed between As and Fe as well as As and Mn in groundwater, implying that mobilizations of Fe, Mn, and As are decoupled or their concentrations in groundwater have been affected by other geochemical processes following reductive dissolution of Fe or Mn-hydroxides. For example, dissolved Fe and Mn levels may be affected by precipitation of Fe- and Mn-carbonate minerals such as siderite, while liberated As remains in groundwater. The groundwaters of the Brahmaputra and Meghna flood plains contain higher humic substances in relative fluorescence intensity (or fluorescence index) and lower redox potential compared to the groundwater of Ganges flood plain. This leads to the release of arsenic and iron to groundwater of these three plains in considerable amounts, but their concentrations are distributed in spatial variations.     

Comparison of chlorine and chloramine in the release of mercury from dental amalgam

The purpose of this project was to compare the ability of chlorine (HOCl/OCl⁻) and monochloramine (NH₂Cl) to mobilize mercury from dental amalgam. Two types of amalgam were used in this investigation: laboratory-prepared amalgam and samples obtained from dental-unit wastewater. For disinfectant exposure simulations, 0.5 g of either the laboratory-generated or clinically obtained amalgam waste was added to 250 mL amber bottles. The amalgam samples were agitated by end-over-end rotation at 30 rpm in the presence of 1 mg/L chlorine, 10 mg/L chlorine, 1 mg/L monochloramine, 10 mg/L monochloramine, or deionized water for intervals of 0 h, 2 h, 4 h, 8 h, and 24 h for the clinically obtained amalgam waste samples and 4 h and 24 h for the laboratory-prepared samples. Chlorine and monochloramine concentrations were measured with a spectrophotometer. Samples were filtered through a 0.45 µm membrane filter and analyzed for mercury with USEPA standard method 245.7. When the two sample types were combined, the mean mercury level in the 1 mg/L chlorine group was 0.020 mg/L (n = 25, SD = 0.008). The 10 mg/L chlorine group had a mean mercury concentration of 0.59 mg/L (n = 25, SD = 1.06). The 1 mg/L chloramine group had a mean mercury level of 0.023 mg/L (n = 25, SD = 0.010). The 10 mg/L chloramine group had a mean mercury level of 0.024 mg/L (n = 25, SD = 0.011). Independent samples t-tests showed that there was a significant difference between the natural log mercury measurements of 10 mg/L chlorine compared to those of 1 mg/L and 10 mg/L chloramine. Changing from chlorine to chloramine disinfection at water treatment plants would not be expected to produce substantial increases in dissolved mercury levels in dental-unit wastewater.     

New strategy for the evaluation of CdTe quantum dot toxicity targeted to bovine serum albumin

The biological toxicity of CdTe quantum dots (QDs) to bovine serum albumin (BSA) has been investigated mainly by fluorescence spectra, UV-vis absorption spectra and circular dichroism (CD) under simulative physiological conditions. Fluorescence data revealed that the quenching mechanism of BSA by CdTe QDs was a static quenching process and the binding constant is 6.05 × 10³ and the number of binding sites is 0.7938. The thermodynamic parameters (ΔH = − 62.33 kJ mol^− 1, ΔG = − 21.21 kJ mol^− 1, and ΔS = − 140.3 J mol^− 1 s^− 1) indicate that hydrogen bonds and van der Waals forces between the protein and the QDs are the main binding forces stabilizing the complex. In addition, UV-vis and CD results showed that the addition of CdTe QDs changed the conformation of BSA.     

Specific detection of viable Listeria monocytogenes in Spanish wastewater treatment plants by Fluorescent In Situ Hybridization and PCR

Listeria monocytogenes detection in wastewater can be difficult because of the large amount of background microbiota and the presence of viable but non-culturable forms in this environment. The aim of this study was to evaluate a Fluorescent In Situ Hybridization (FISH) assay combined with Direct Viable Count (DVC) method for detecting viable L. monocytogenes in wastewater samples, as an alternative to conventional culture methods. 16S rRNA sequence data were used to design a specific oligonucleotide probe. In order to assess the suitability of the method, the assays were performed on naturally (n = 87) and artificially (n = 14) contaminated samples and results were compared to those obtained with the isolation of cells on selective media and with a PCR method. The detection limit of FISH and PCR assays was 10⁴ cells/mL without enrichment and 10 cells/mL after enrichment. A total of 47 samples, including 3 samples from effluent sites, yielded FISH positive results for L. monocytogenes. Using DVC-FISH technique, the presence of viable L. monocytogenes cells was detected in 23 out of these 47 FISH positive wastewater samples. PCR and culture methods yielded 27 and 23 positive results, respectively. According to these results, FISH technique has the potential to be used as a sensitive method for the detection and enumeration of L. monocytogenes in environmental wastewater samples.     

Measuring the saturation limit of low-volatility organic compounds in soils: implications for estimates of dermal absorption

Estimating dermal absorption from contaminated soils typically requires extrapolations from measurements obtained on soils artificially contaminated at much larger concentrations. Such extrapolations should be constrained by the fact that maximum absorption will occur for the largest possible concentration of chemical on the soil without neat chemical being present; i.e., at the soil saturation limit (S_soil). Saturation limits of two low-volatility model compounds (4-cyanophenol and methyl paraben) were determined on the 38-63 μm sieve fraction of four soils with different fractions of organic carbon (f_oc = 0.015-0.45) and specific surface areas (σ_soil = 4-34 m² g^− 1) using two methods: equilibrium uptake into silicone rubber membranes and differential scanning calorimetry. Except for Pahokee peat, which had the largest f_oc, a model assuming contributions from both surface adsorption and organic carbon absorption provided excellent predictions of S_soil. In all soils, the surface saturation concentration of both chemicals was estimated at 2.2 mg m^− 2. The saturation concentration of 4-cyanophenol in the soil organic carbon was 1.7-fold higher than methyl paraben, which is consistent with the estimated solubility limits of these two chemicals in octanol.     

Inactivation of environmental mycobacteria by free chlorine and UV

The resistance of environmental mycobacteria (EM) against chlorine and ultraviolet (UV) was evaluated for determination of the Ct value and UV dose to inactivate EM. Chlorine disinfection experiments were done on Mycobacterium fortuitum in oxidant demand-free buffered water at the worst condition (pH 8.5, 4 °C) and normal condition (pH 7.0, 20 °C). The Ct value for 3 log inactivation of M. fortuitum was 600 times greater than that of Escherichia coli. UV experiments were performed for various species of Mycobacterium avium, M. fortuitum, Mycobacterium intracellulare, and Mycobacterium lentiflavum. A UV collimated beam device was used for irradiation of four species suspended in phosphate buffered saline with doses of 5, 10, 20, 50, and 100 mJ/cm². UV sensitivity of mycobacteria was species-specific. More than 3 log of M. avium, M. intracellulare, and M. lentiflavum could be inactivated at 20 mJ/cm², whereas M. fortuitum was so resistant that 3 log inactivation required a dose of more than 50 mJ/cm². Mycobacteria were found 2-10 times more resistant to UV than E. coli for 3 log inactivation. There was no significant difference in the inactivation of mycobacteria with either low-pressure or medium-pressure UV irradiation.     

Mixture design of high performance recycled liquid crystal glasses concrete (HPGC)

This study investigated the best mixture design of high performance recycled liquid crystal glasses concrete (HPGC) using waste liquid crystal glass sand to replace part of the fine aggregate. The design of experiment (DOE) method was adopted to design the specimen variables. Fresh properties were examined, including slump, flowing slump and unit weight and hardened properties were examined, including compressive strength, elastic modulus, impact-echo, ultrasonic pulse velocity and surface resistance. Range analysis and analysis of variance (ANOVA) were conducted to determine the relationships between these properties and W/B, replacement ratios and n values. The results demonstrated that the ultrasonic pulse velocity and surface resistance of HPGC was higher than those of the control group. For the three n values, higher than ultrasonic pulse velocity was found at a replacement ratio of 30%. The replacement ratios, W/B, and relationships between n values were analyzed. F statistics indicated significant impact on the replacement ratio of 4.97 and W/B of 3.87, indicating that the main properties of the HPGC are determined by the replacement ratio and W/B. The range analysis results showed that the interaction between various factors with W/B = 0.28:1 and n = 1.4 has the most significant impact on compressive strength.     

Sorption of antibiotics to biofilm

Using a continuous-flow rotating annular bioreactor, sorption of three selected antibiotics (sulfamethoxazole (SMX), ciprofloxacin (CIP), and erythromycin (ERY)) to bacterial biofilm was investigated. CIP had the greatest biofilm partition coefficient (K_oc = 92,000 ± 10,000 L/kg) followed by ERY (K_oc = 6000 ± 1000 L/kg) and then SMX (K_oc = 4000 ± 1000 L/kg). Antibiotic sorption to biofilm did not correlate with experimentally-determined K_ow values (CIP: −0.4; ERY: 0.98; SMX: <-0.59 at pH 7), suggesting that hydrophobic interactions do not drive the sorption of these relatively hydrophilic compounds to the biofilm. It appears that speciation (i.e. charge) and molecular size of the antibiotics are important in explaining their sorption to typically negatively charged biofilm. SMX is neutral to negatively charged at circumneutral pH while CIP and ERY are both positively charged. The decreased extent of sorption of ERY relative to CIP is likely due to the larger molecular size of ERY that results in a decreased rate of mass transfer (i.e. diffusion) to and through the biofilm. In conclusion, the results of this research suggest that hydrophobic interactions (predicted by K_ow) do not control sorption of relatively hydrophilic antibiotics to biofilm and that antibiotic speciation and molecular size are important factors affecting the interactions between antibiotics and biofilm.     

A multi-beach study of Staphylococcus aureus, MRSA, and enterococci in seawater and beach sand

Incidences of Staphylococcus aureus and methicillin resistant S. aureus (MRSA) have risen worldwide prompting a need to better understand routes of human exposure and whether standard bacterial water quality monitoring practices adequately account for this potential threat. Beach water and sand samples were analyzed during summer months for S. aureus, enterococci, and MRSA at three southern California beaches (Avalon, Doheny, Malibu Surfrider). S. aureus frequently was detected in samples of seawater (59%, n = 328) and beach sand (53%, n = 358). MRSA sometimes was detected in seawater (1.6%, n = 366) and sand (2.7%, n = 366) at relatively low concentrations. Site specific differences were observed, with Avalon Beach presenting the highest concentrations of S. aureus and Malibu Surfrider the lowest in both seawater and sand. S. aureus concentrations in seawater and sand were correlated to each other and to a variety of other parameters. Multiple linear regression on the combined beach data indicated that significant explanatory variables for S. aureus in seawater were S. aureus in sand, water temperature, enterococci in seawater, and the number of swimmers. In sand, S. aureus concentrations were related to S. aureus in seawater, water temperature, enterococci in seawater, and inversely to surf height classification. Only the correlation to water temperature held for individually analyzed beaches and for S. aureus concentrations in both seawater and sand. To provide context for these results, the prevalence of S. aureus in sand was compared to published fomite studies, and results suggested that beach prevalence was similar to that in homes.     

Pullout Resistance of Bearing Reinforcement Embedded in Sand

Mechanically stabilized earth (MSE) structure has been widely accepted as a retaining structure. Its construction cost is mainly controlled by backfill materials, which are generally coarse-grained soils, and reinforcement type (steel volume). The present paper introduces a new cost-effective reinforcement, designated as “Bearing Reinforcement”. It is composed of a longitudinal member and transverse (bearing) members. The longitudinal member is made of a deformed bar, which exhibits a high pullout friction resistance. The transverse members are a set of equal angles, which provide high pullout bearing resistance. The maximum pullout bearing resistance of a single isolated transverse member, σ_bmax, can be determined by using the plasticity solution based on the modified punching shear failure mechanism. Influential factors governing the mobilization of pullout bearing resistance are spacing, S, leg length, B, and numbers, n of transverse members. The larger the S/B, the lower the transverse member interference. The S/B ratios of <3.75 and >25 are referred to as full and free interference, respectively. The relationship between normalized average pullout bearing stress, σ_bn/nσ_n and pullout displacement, d, where σ_bn/n is average pullout bearing stress of the bearing reinforcement with n transverse members and σ_n is applied normal stress, is practically identical for the same level of transverse member interference. This relationship can be modelled by hyperbolic function. From this finding, a suggested procedure for estimating pullout characteristics (maximum pullout resistance and pullout force versus displacement relationship) of the bearing reinforcement for any level of transverse member interference (any S, B, and n) based on a one point test on the bearing reinforcement with a single isolated transverse member is proposed. Good agreement has been obtained between the predicted and the measured pullout characteristics. This suggested method is useful for the internal stability analysis of MSE wall in terms of engineering and economic viewpoints.     

Health risk assessment of inorganic arsenic intake of Cambodia residents through groundwater drinking pathway

In order to compare the magnitudes and health impacts of arsenic and other toxic trace elements in well water, groundwater and hair samples were collected from three areas with different arsenic exposure scenarios in the Mekong River basin of Cambodia. Ampil commune in Kampong Cham province was selected as an uncontaminated area, Khsarch Andaet commune in Kratie province was selected as a moderately contaminated area, and Kampong Kong commune in Kandal Province was selected as an extremely contaminated area. Results of ICP-MS analyses of the groundwater samples revealed that As, Mn, Fe and Ba concentrations were significantly different among the three study areas (Kruskal-Wallis test, p < 0.0001). Out of 46 observed wells in the Kandal province study area, 100% detected As > 50 μg L⁻¹ and Fe > 300 μg L⁻¹; 52.17% had Mn > 400 μg L⁻¹ and 73.91% found Ba > 700 μg L⁻¹. In the Kratie province study area (n = 12), 25% of wells showed elevated arsenic levels above 10 μg L⁻¹ and 25% had Mn > 400 μg L⁻¹, whereas samples from Kampong Cham province study area (n = 18) were relatively clean, with As < 10 μg L⁻¹. A health risk assessment model derived from the USEPA was applied to calculate individual risks resulting from drinking groundwater. Computational results indicated that residents from Kandal Province study area (n = 297) confronted significantly higher non-carcinogenic and carcinogenic risks than those in Kratie (n = 89) and Kampong Cham (n = 184) province study areas (Kruskal-Wallis test, p < 0.0001). 98.65% of respondents from the Kandal province study area were at risk for the potential non-cancer effect and an average cancer risk index was found to be 5 in 1000 exposure. The calculations also indicated that, in the Kratie province study area, 13.48% of respondents were affected by non-cancer health risks and 33.71% were threatened by cancer, whereas none of respondents in the Kampong Cham province study area appeared to have non-carcinogenic effect. Positively significant correlations of the arsenic content in scalp hair (As_h) with both arsenic levels in groundwater (As_w) (r_s (304) = 0.757, p < 0.0001) and individual average daily doses (ADD) of arsenic (r_s (304) = 0.763, p < 0.0001) undoubtedly indicated that arsenic accumulation in the bodies of Cambodia residents in the Mekong River basin was mainly through a groundwater drinking pathway. To the best of our knowledge, this is the first comprehensive report comparing individual health risk assessments of arsenic exposure through a groundwater drinking pathway to enriched arsenic levels from groundwater in the Mekong River basin, Cambodia. This study indicates that elevated arsenic concentrations in groundwater may lead to thousands of cases of arsenicosis in the near future if mitigating actions are not taken.