Evaluation of pH-Dependent Metal Speciation Artifacts in Whole-Cell Bioreporter Analysis.

Whole-cell bacterial biosensors (bioreporters) are commonly applied for determination of metal toxicity and bioavailability in environmental samples. This is accomplished using a standard procedure whereby the sample is mixed with bioreporter cells suspended in a buffered medium at a fixed pH (set-point pH assay). This experimental approach can alter the sample pH. We therefore hypothesized that metal speciation artifacts compromising our ability to use bioreporters for determination of the "true" metal bioavailability in environmental samples may be introduced. Using the copper-specific bioreporter DF57-Cu15 as a model, we compared the conventional set-point pH assay to a flexible pH assay allowing for bioavailability determination at in situ sample pH. Our results demonstrate that pH-dependent metal speciation bias may occur when using the conventional set-point pH assay, and we recommend performing bioreporter measurements and calibrations at in situ sample pH. Although we only studied copper bioavailability, our results also have implications for bioreporter determination of other analytes displaying pH-dependent speciation such as other metals and some organics. We call for additional bioreporter studies of chemical speciation artifacts as this represents a problem hitherto overlooked in bioreporter literature. We thus conclude that there may be considerable scope for optimization of existing bioreporter assays for assessment of environmental pollutant bioavailability.

Interaction mechanisms between polycyclic aromatic hydrocarbons (PAHs) and organic soil washing agents.

Understanding interaction mechanisms between polycyclic aromatic hydrocarbons (PAHs) and soil-washing agents can help in choosing efficient agents which are able to desorb and solubilize PAHs. This study investigated interaction mechanisms between pyrene and four washing agents including: two dissolved organic matters (DOM) F-DOM and CRC-DOM, and two commercial bio-based surfactants BBE-1000 and Supersolv using fluorescence spectroscopy combined with multivariate curve resolution alternating regression (MCR-AR). The efficiencies of these washing agents in removing PAHs from the soil were tested in a soil washing experiment. Pyrene showed π-π interactions with F-DOM and no interaction with CRC-DOM. This could be attributed to the more aromatic structures in F-DOM compared to CRC-DOM. The two DOMs were inefficient in soil washing which might be attributed to the relatively weak effect of π-π interactions in releasing PAHs from the soil. Interaction mechanisms between pyrene and the bio-based surfactants were elucidated with MCR-AR, which resolved three spectroscopically active species from pyrene emission spectra as a function of pyrene and bio-based surfactants concentrations. These species resembled pyrene emission in a polar and nonpolar microenvironment, respectively and of an excimer. Concentration profiles retrieved by the model for the three species showed that, below the critical micelle concentration (CMC), Supersolv created more nonpolar interactions with pyrene compared to BBE-1000. In soil washing, Supersolv showed the highest efficiency in extracting PAHs from the soil. This highlighted the importance of nonpolar interactions in desorbing PAHs from soils, which could then be solubilized in micelles. This study demonstrated the potential of fluorescence spectroscopy combined with the MCR-AR model for selecting efficient soil-washing agents.

Screening of inorganic and organic contaminants in floodwater in paddy fields of Hue and Thanh Hoa in Vietnam.

In the rainy season, rice growing areas in Vietnam often become flooded by up to 1.5 m water. The floodwater brings contaminants from cultivated areas, farms and villages to the rice fields resulting in widespread contamination. In 2012 and 2013, the inorganic and organic contaminants in floodwater was investigated in Thanh Hoa and Hue. Water samples were taken at 16 locations in canals, paddy fields and rivers before and during the flood. In total, 940 organic micro-pollutants in the water samples were determined simultaneously by GC-MS method with automatic identification and quantification system (AIQS), while ICP-MS was used for determination of ten trace elements in the samples. The concentrations of 277 organic micro-pollutants and ten elements (As, Cu, Cd, Cr, Co, Pb, Zn, Fe, Mn, Al) ranged from 0.01 to 7.6 µg L-1 and 0.1 to 3170 µg L-1, respectively, in the floodwater. Contaminants originated from industrial sources (e.g. PAH) were detected at low concentrations, ranged from 0.01 to 0.18 µg L-1, while concentrations of pollutants originated from domestic sources (e.g. sterols, pharmaceuticals and personal care products and pesticides) were ranged from 0.01 to 2.12 µg L-1. Isoprocarb had the highest detection frequency of 90%, followed by isoprothiolane (88%) and fenobucarb (71%). The results indicated that contaminants in floodwater come from untreated wastewater from villages, and the agricultural activities are the major sources of increased pesticides resuspended in the floodwater in this study.

Release of cadmium, copper and lead from urban soils of Copenhagen.

We studied the bonding and release kinetics of Cd, Cu and Pb from different soils in the older metropolitan area of Copenhagen. Total Cd, Cu and Pb concentrations were elevated 5-27 times in the urban soils compared to an agricultural reference soil, with Cd and Pb in mainly mobilisable pools and Cu in strongly bound pools. The soils were subjected to accelerated leaching studies in Ca(NO3)2 or HNO3 solutions resulting in release up to 78, 18 and 15% of total Cd, Cu and Pb soil concentrations over a period of 15 weeks. The relative initial Cd and Pb release rates increased 10 fold when pH decreased 2 and 3 units, respectively, while increases in Cu release rates were only seen at pH below 4. The total leachable Cu and Pb pools were higher in urban soils compared the agricultural reference soil but not for Cd.

Copper use and accumulation in catfish culture in the Mekong Delta, Vietnam.

Aquaculture of Pangasius hypophthalmus (striped catfish) in Vietnam reached 1.1 million tonnes in 2011 and catfish fillets are exported worldwide. The intensive cultures of catfish mainly in earth ponds have made it necessary to apply CuSO4 and other chemicals to control external parasites and other pathogens. However, accumulation of Cu in aquaculture ponds may pose a hazard to growth of fish or to the aquatic environment. The aim of this study was to determine accumulation of Cu in sediment, water and fish in a catfish pond with a history of repeated treatment with CuSO4 in the Mekong Delta, Vietnam. Copper concentrations in pond sediment were in the interval 21.3-45.7 mg kg(-1) dw and did not exceed the Vietnamese values for soil to be used for agricultural production (70 mg kg(-1) dw.). During three samplings the total mean concentration of Cu in pond water (4 µg L(-1)) did not exceed the LC50-value (70 µg L(-1)) for catfish and the mean dissolved concentration of Cu (0.986 µg L(-1)) did not seem to constitute a risk for the stability of the aquatic ecosystem. No significant variation in Cu concentrations between sampling sites in the pond and depth of sediment profile were determined. The accumulation of Cu in catfish was highest in the liver compared to the skin, gills and muscle tissue. With the current practice of removing pond sludge three to four times during a production cycle little if any Cu seems to accumulate in catfish ponds despite repeated anti-parasite treatments with CuSO4. Further studies are needed to assess the eco-toxicity and impact on agricultural production when pond sediment is discharged into aquatic recipients and used as soil fertilizer.

The use of elements as a substitute for biomass in toxicokinetic studies in small organisms.

Determining pollutant concentrations in the tissues of experimental test organisms is necessary for understanding uptake and excretion mechanisms of toxicants. Using small organisms can make the determination of organism biomass inaccurate. We here propose the use of selected tissue element contents as a proxy for tissue biomass. Forty different elements were determined in tissues of the two worm species Enchytraeus crypticus and Caenorhabditis elegans derived from cultures exposed to combinations of varying temperatures and sublethal concentrations of Cu and Cd. Three criteria were used to select good biomass indicators: The element concentration must (1) be present in concentrations above the limit of quantification of the analytical method, (2) must be stable and (3) must not be affected by the treatment. If the organisms are believed to have significant amounts of soil in their gut, the element must also be present at higher concentrations in the tissue compared to the soil. The three elements K, Mg and P all lived up to the first three criteria for both worm species, showing correlation coefficients between element content and tissue biomass of 0.97, 0.96 and 0.97 (n = 25) and 0.997, 0.998 and 0.992 (n = 10) for K, Mg and P in the E. crypticus and C. elegans, respectively. Only P would be an appropriate biomass indicator for organisms with a soil gut uptake assuming the tissue concentrations in soil eating organisms are similar to those measured in the present study. Using Mg as a biomass indicator on a verification dataset of Cu and Cd uptake in E. crypticus, compared to giving Cu and Cd content per individual organism, decreased the coefficient of variation from 31 ± 21 to 21 ± 17 % and from 34 ± 22 to 9.3 ± 6.4 % for tissue Cu and Cd, respectively. We therefore conclude that the use of an element as a biomass indicator can reduce tissue concentration variability.

Pollution and potential mobility of Cd, Ni and Pb in the sediments of a wastewater-receiving river in Hanoi, Vietnam.

Large quantities of untreated industrial and domestic wastewater are discharged from the city of Hanoi into urban rivers. Sediment samples from three sites in the To Lich River in Hanoi were assessed with respect to the concentrations and potential mobility of cadmium (Cd), nickel (Ni) and lead (Pb). Due to very high Cd concentrations up to 700 mg kg(-1) at one site, the sediment was considered highly unsuitable for any types of land use if dredged and disposed of on land. Chemical sequential extractions of wet and anoxic sediment samples showed that Cd and Pb were largely associated with the redox-sensitive fractions and could thus be mobilised following measures such as resuspension or dredging. To assess the potential mobilisation of heavy metals from the anoxic sediment due to oxidation, the samples were exposed to different oxidants (i.e. atmospheric air and hydrogen peroxide) and afterwards submitted to a leaching test. These experiments showed that although oxidation may increase the equilibrium pore water concentrations of heavy metals in the sediments, other sediment mineral fractions seem to effectively immobilise heavy metals potentially released from the oxidisable fraction.

Low temperatures enhance the toxicity of copper and cadmium to Enchytraeus crypticus through different mechanisms.

Knowledge about how toxicity changes with temperature is important for determining the extent of safety factors required when extrapolating from standard laboratory conditions to variable field scenarios. In the present study, the authors evaluated the toxicity of Cu and Cd to the potworm Enchytraeus crypticus at 6 temperatures in the range of 11 °C to 25 °C. For both metals, reproductive toxicity decreased approximately 2.5-fold with increasing temperature. This is contrary to what most other studies have found. Measurements of the bioavailable fraction of the metals in the soils and the internal metal concentrations in the worms over time showed that the major cause of change in toxicity with temperature for Cu was the worms' ability to regulate internal concentration at high temperatures. Uptake of Cd increased with time at all temperatures and with higher rates at high temperatures. Hence, the lower toxicity of Cd at high temperatures is proposed to be due to the E. crypticus being more efficient at immobilizing Cd and/or repairing damages at high compared to low temperatures. The present study concludes that no consistent relationship between metal toxicity and temperature across species can be made. The metabolic dependence of the species in terms of regulating metal uptake, excretion, immobilization, damage, and repair processes, will be crucial factors in determining species susceptibility to metals at varying temperatures.

Dietary exposure to essential and potentially toxic elements for the population of Hanoi, Vietnam.

Knowledge of the dietary intake of essential and toxic elements in fast-developing Southeast Asian countries such as Vietnam is limited. Iron and Zn deficiency in Asia is a well-known problem and is partly due to rice constituting a major part of the diet. Dietary habits are changing and there is a need to build more knowledge so authorities can give dietary recommendations. The aim of this study was to determine the total dietary intake of essential and potentially toxic elements and to assess the nutritional quality and food safety risks of the average Hanoi diet. Twenty-two foods or food groups were identified and 14 samples of each food group were collected from markets and/or supermarkets in the period 2007-2009. Water spinach, water dropwort, watercress, water mimosa and pond fish are typically produced in wastewater-fed systems. Therefore, these samples were collected both at markets and from wastewater-fed production systems. The results showed little or no risk of toxic elements from the Hanoi diet in general. Further, element contributions from wastewater-fed products were low and does not seem to constitute a problem with respect to potentially toxic elements. A comparison of the average Hanoi dietary intake of essential elements to required intakes shows that the Hanoi diet is sufficient in most elements. However, the diet may be insufficient in Ca, Cr, Fe, K and possibly Zn for which dietary diversification of biofortification might provide solutions.

Composition, Flavor, Chemical Foodsafety, and Consumer Preferences of Bottled Water.

The worldwide consumption of bottled water has experienced an annual increase of 5.5% since 2004 and different authors have speculated that this is due to beliefs of superior flavor and health qualities of bottled water over tap water. The content of certain minerals varies by 2 to 6 orders of magnitude between bottled water brands. The major cations Ca, Mg, Na, and K can be found in concentrations up to 730, 450, 1900, and 270 mg/L but are usually below 100 mg/L; higher concentrations have only been found in some European and North American bottled water samples. The dominating anions are HCO3 - , Cl- , and SO4 2- . Sensory evaluation and description of water strongly depend on personal preferences and sensitivities. The major cations can be detected by taste in concentrations down to 2 digits in the mg/L range; however, the intensity depends on which anions are present. Most cations add different degrees of salty, sour, sweet, and bitter tastes to water depending on their concentrations. Al, Ca, Cu, Fe, Mg, and Zn may introduce metallic, astringent, and irritative sensations and for Fe and Cu also retro-nasal odors may influence the metallic sensation. Drinking water with total dissolved solids in the range of 100 to 400 mg/L results in good sensory quality. Known off-flavor problems originate from by-products of ozonation and leaching of organics from bottling material which may also be enhanced by ozonation, and microbial by-products from the source water such as geosmin and 2-methylisoborneol, lubricants, or cleaning agents used in the bottling industry.

Contents and mass balances of cadmium and arsenic in a wastewater-fed fish pond of Hoang Mai, Hanoi, Vietnam.

Wastewater-fed aquatic production has been practiced since the 1960s in peri-urban Hanoi. Wastewater is used as a cheap and reliable source of both water and nutrients but there is a risk that it may lead to accumulation of potentially toxic elements (PTEs) in the production systems and produce and thereby constitute a food safety risk. This study investigates the cadmium (Cd) and arsenic (As) concentrations in water, sediment, plant and fish of a wastewater fed-fish pond in Hoang Mai district, Hanoi, Vietnam. Cd concentrations in the water were lower than the Vietnamese quality guidelines (0.8-1.8 µg Cd/L) for protection of aquatic life but As concentrations in inlet and outlet water of 44.3 and 21.3 µg/L, respectively both were higher that the guidelines (20 µg As/L) and may cause toxicity to fish in the pond and the surrounding vegetable farms using the outlet water for irrigation. The concentrations of Cd and As in fish and Cd in water spinach did not constitute a food safety risk. However, As concentrations in water spinach may be of concern. A mass balance estimate for the fish pond showed that about 12% of the incoming As accumulate in suspended particular matters, 40% settle down to the sediment, less than 0.1% accumulate in the fish and water spinach and 48% overflow with the pond effluent. The concentrations of Cd were too low to make a mass balance for the fish pond.

The pH-dependent adsorption of tributyltin to charcoals and soot.

Widespread use of tributyltin (TBT) poses a serious environmental problem. Adsorption by black carbon (BC) may strongly affect its behavior. The adsorption of TBT to well characterized soot and two charcoals with specific surface area in the range of 62-111m(2)g(-1) have been investigated with main focus on pH effects. The charcoals but not soot possess acidic functional groups. TBT adsorption reaches maximum at pH 6-7 for charcoals, and at pH>6 for soot. Soot has between 1.5 and 15 times higher adsorption density (0.09-1.77µmolm(-2)) than charcoals, but charcoals show up to 17 times higher sorption affinities than soot. TBT adsorption is successfully described by a new pH-dependent dual Langmuir model considering electrostatic and hydrophobic adsorption, and pH effects on TBT speciation and BC surface charge. It is inferred that strong sorption of the TBTOH species to BC may affect TBT toxicity.

Nickel sorption to goethite and montmorillonite in presence of citrate.

Mobility and bioavailability of nickel (Ni) in soil strongly depends on the interaction between Ni(II), ligands, and sorbents like organic matter and minerals. Sorption of Ni(II) and Ni(II)-citrate complexes to goethite and montmorillonite was examined in batch experiments with and without citrate as ligand in the pH range pH 4-7.5. Without citrate, montmorillonite shows higher Ni sorption than goethite. Citrate strongly decreases Ni sorption to montmorillonite; in presence of 100 microM citrate goethite becomes a stronger Ni sorbent than montmorillonite. Ni and citrate sorption was modeled successfully using the diffuse double layer model with the following reactions: Goethite: 3 [triple bond]FeOH + Citrate(3-) + 3H+ <=> [triple bond] Fe3Citrate + 3H2O, [triple bond]FeOH + Ni2+ <=> [triple bond] FeONi + H+ and 2 [triple bond] FeOH + Citrate(3)- + Ni2+ <=> [triple bond] FeONiCitrate(2-) + H+. Montmorillonite: 2X- + Ni2+ <=> X2Ni and [triple bond] AIOH + Ni2+ <=> AIONi+ + H+. Sorption of Ni to a mixture of goethite and montmorillonite could be calculated by use of reactions and constants for the monomineral systems. Without citrate, the sorbed amount of Ni per mass unit in the mixture can be found as a simple average of sorption to the two single sorbents, while in presence of citrate Ni sorption to montmorillonite is strongly influenced by citrate sorption to goethite.

Element concentrations in water spinach (Ipomoea aquatica Forssk.), fish and sediment from a wetland production system that receives wastewater from Phnom Penh, Cambodia.

The Cheung Ek Lake, which is located south of Phnom Penh, Cambodia, receives most of the industrial and domestic wastewater that is produced in the city. The lake is used for fishing and production of water spinach (Ipomoea aquatica Forssk). Concentrations of 35 elements were determined in water spinach and sediment that were collected along transects of two wastewater inlets in the lake, at the lake outlet, and in a non-wastewater exposed pond. Elevated concentrations of the potentially toxic elements (PTEs) Cd, Cu, Ni, Pb, Sb, and Zn were found in the water spinach and sediment samples collected near the wastewater inlets. The highest determined PTE concentrations in water spinach were, in mg kg(- 1) fresh weight (f.w.), As 0.19, Cd 0.022, Cu 2.95, Fe 251, Pb 0.206 and Zn 9.08. For an adult person in Phnom Penh, the maximum intake of PTEs from consumption of water spinach harvested near the wastewater inlets amounts to 5.7% As, 1.4% Cd, 0.4% Cu, 20.5% Fe, 3.8% Pb and 0.6% Zn of the maximum tolerable intake set by the Codex Alimentarious Commission. Arsenic, Cd and Pb concentrations in the liver, skin, and muscle of three fish species caught in the lake were below or near the detection limits, except for a high accumulation of the three elements in the skin of the blackskin catfish. In conclusion, the consumption of water spinach and fish from Cheung Ek Lake constitutes a low food safety risk with respect to PTEs.

Content, distribution and fate of 33 elements in sediments of rivers receiving wastewater in Hanoi, Vietnam.

Untreated industrial and domestic wastewater from Hanoi city is discharged into rivers that supply water for various agricultural and aqua-cultural food production systems. The aim of this study was to assess the content, distribution and fate of 33 elements in the sediment and pore water of the main wastewater receiving rivers. The sediment was polluted with potentially toxic elements (PTEs) with maximum concentrations of 73 As, 427 Cd, 281 Cr, 240 Cu, 218 Ni, 363 Pb, 12.5 Sb and 1240 Zn mg kg(-1) d.w. Observed distribution coefficients (log(10) K(d,obs)) were calculated as the ratio between sediment (mg kg(-1) d.w.) and pore water (mg L(-1)) concentrations. Maxima log(10) K(d,obs) were >4.26 Cd, >6.60 Cu, 4.78 Ni, 7.01 Pb and 6.62 Zn. The high values show a strong PTE retention and indicate the importance of both sorption and precipitation as retention mechanisms. Sulphide precipitation was a likely mechanism due to highly reduced conditions.

Element contents and food safety of water spinach (Ipomoea aquatica Forssk.) cultivated with wastewater in Hanoi, Vietnam.

Extensive aquatic or semi-aquatic production of water spinach (Ipomoea aquatica Forssk.) for human consumption takes place in Southeast Asia. The aim of this study was to assess the concentrations of 38 elements in soil and water spinach cultivated under different degrees of wastewater exposure in Hanoi, Vietnam. The results showed no effect of wastewater use on the overall element concentrations in soil and water spinach. Mean soil concentrations for selected potentially toxic elements at the studied field sites had the following ranges 9.11-18.7 As, 0.333-0.667 Cd, 10.8-14.5 Co, 68-122 Cr, 34.0-62.1 Cu, 29.9-52.8 Ni, 32.5-67.4 Pb, 0.578-0.765 Tl and 99-189 Zn mg kg(-1) dry weight (d.w.). In all samples Cd, Pb and Zn soil concentrations were below the Vietnamese Guideline Values (TCVN 7209-2002) for agricultural soils whereas As and Cu exceeded the guideline values. Maximum site element concentrations in water spinach were 0.139 As, 0.032 Cd, 0.135 Cr, 2.01 Cu, 39.1 Fe, 57.3 Mn, 0.16 Ni, 0.189 Pb and 6.01 Zn mg kg(-1) fresh weight (f.w.). The site and soil content of organic carbon were found to have high influence on the water spinach element concentrations whereas soil pH and the total soil element concentrations were of less importance. The estimated average daily intake of As, Cd, Cu, Fe, Pb and Zn for adult Vietnamese consumers amounts to <11% of the maximum tolerable intake proposed by FAO/WHO for each element. It is assessed that the occurrence of the investigated elements in water spinach will pose low health risk for the consumers.

Food safety aspects of toxic element accumulation in fish from wastewater-fed ponds in Hanoi, Vietnam.

OBJECTIVE: To evaluate the food safety of fish from production systems in Hanoi feed with domestic and industrial wastewater with respect to the potentially toxic elements such as arsenic (As), cadmium (Cd) and lead (Pb). METHODS: Common carp (Cyprinus carpio), silver carp (Hypophthalmichthys molitrix) and tilapia (Oreochromis niloticus) were sampled from wastewater-fed ponds, and total concentrations of As, Cd and Pb were determined in skin, liver and muscle. RESULTS: Arsenic, Cd and Pd concentrations were generally low and for many samples below the detection limit. The highest concentrations of Cd and Pb were found in the liver of tilapia, and the highest As concentration in the skin of tilapia. Maximum concentrations in muscle tissue were 0.120, 0.079 and 0.082 mg/kg fresh weight (f.w.) for As, Cd and Pb, respectively. Consumption of fish with maximum muscle tissue concentration will result in a human intake corresponding to 6.2%, 8.7% and 2.5% of the tolerable intake of these elements set by Codex Alimentarious Commission. CONCLUSION: The consumption of common carp, silver carp and tilapia produced in wastewater-fed ponds of Hanoi seems not to constitute a food safety problem with respect to As, Cd and Pb.