Photocatalytic oxidation of monuron in the suspension of WO3 under the irradiation of UV-visible light

A comprehensive study of the degradation of monuron, one of the phenylurea herbicides, was conducted by UV-Vis/WO₃ process. It was found that hydroxyl radicals played a major role in the decay of monuron while other radicals (e.g. superoxide) and hole might also contribute to the decomposition of monuron. The oxidation path likely plays a major role in the generation of hydroxyl radicals. The effects of initial pH level, initial concentration of monuron, and inorganic oxidants on the performance of UV-Vis/WO₃ process were also investigated and optimized. Comparison between monuron decay pathways by UV-Vis/WO₃ and UV/TiO₂ was conducted. The decay mechanisms, including N-terminus demethylation, dechlorination and direct hydroxylation on benzene ring, were observed to be involved in the oxidation of monuron in these two processes. Sixteen intermediates were identified during the photodegradation of monuron and degradation pathways were proposed accordingly.     

Use of whole-body and subcellular Cu residues of Lumbriculus variegatus to predict waterborne Cu toxicity to both L. variegatus and Chironomus riparius in fresh water

We tested the use of whole-body and subcellular Cu residues (biologically-active (BAM) and inactive compartments (BIM)), of the oligochaete Lumbriculus variegatus to predict Cu toxicity in fresh water. The critical whole-body residue associated with 50% mortality (CBR₅₀) was constant (38.2-55.6 μg g⁻¹ fresh wt.) across water hardness (38-117 mg L⁻¹ as CaCO₃) and exposure times during the chronic exposure. The critical subcellular residue (CSR₅₀) in metal-rich granules (part of BIM) associated with 50% mortality was approximately 5 μg g⁻¹ fresh wt., indicating that Cu bioavailability is correlated with toxicity:subcellular residue is a better predictor of Cu toxicity than whole-body residue. There was a strong correlation between the whole-body residue of L. variegatus (biomonitor) and survival of Chironomus riparius (relatively sensitive species) in a hard water Cu co-exposure. The CBR₅₀ in L. variegatus for predicting mortality of C. riparius was 29.1-45.7 μg g⁻¹ fresh wt., which was consistent within the experimental period; therefore use of Cu residue in an accumulator species to predict bioavailability of Cu to a sensitive species is a promising approach.     

Eichhornia crassipes capability to remove naphthalene from wastewater in the absence of bacteria

The aim of the current study was to investigate the potential of an aquatic plant, the water hyacinth (Eichhornia crassipes) devoid rhizospheric bacteria, to reduce naphthalene (a polyaromatic hydrocarbon) present in wastewater and wetlands.The capability of sterile water hyacinth plants to remove naphthalene from water and wastewater was studied in batch systems. Water hyacinths enhance the removal of pollutants through their consumption as nutrients and also through microbial activity of their rhizospheric bacteria.Experimental kinetics of naphthalene removal by water hyacinth coupled with natural rhizospheric bacteria was 100% after 9 d. Plants, decoupled of rhizospheric bacteria, reduced naphthalene concentration up to 45% during 7 d. Additionally, naphthalene uptake by water hyacinth revealed a biphasic behavior: a rapid first phase completed after 2.5 h, and a second, considerably slower rate, phase (2.5-225 h). In conclusion, water hyacinth devoid rhizospheric bacteria reduced significantly naphthalene concentration in water, revealing a considerable plant contribution in the biodegradation process of this pollutant.     

Detection of early effects of a single herbicide (diuron) and a mix of herbicides and pharmaceuticals (diuron, isoproturon, ibuprofen) on immunological parameters of Pacific oyster (Crassostrea gigas) spat

In the context of massive summer mortality events of the Pacific oyster Crassostrea gigas, the aim of this study was to investigate the early effects on genes, enzymes and haemocyte parameters implicated in immune defence mechanisms in C. gigas oysters exposed to a potentially hostile environment, i.e. to an herbicide alone or within a mixture. Following 2 h of exposure to the herbicide diuron at 1 μg L⁻¹, the repression of different genes implicated in immune defence mechanisms in the haemocytes and the inhibition of enzyme activities, such as laccase-type phenoloxidase (PO) in the plasma, were observed. The inhibition of superoxide dismutase (SOD) activity in the plasma was also observed after 6 and 24 h of exposure. In the mixture with the herbicides diuron and isoproturon, and the pharmaceutical ibuprofen, catecholase-type PO activity in the plasma and the percentage of phagocytosis in the haemocytes were reduced after 6 h of exposure. Our results showed that early effects on molecular, biochemical and cellular parameters can be detected in the presence of diuron alone or within a mixture, giving an insight of its potential effect in situations that can be found in natural environments, i.e. relatively high concentrations for short periods of time.     

PCE dissolution and simultaneous dechlorination by nanoscale zero-valent iron particles in a DNAPL source zone

While the capability of nanoscale zero-valent iron (NZVI) to dechlorinate organic compounds in aqueous solutions has been demonstrated, the ability of NZVI to remove dense non-aqueous phase liquid (DNAPL) from source zones under flow-through conditions similar to a field scale application has not yet been thoroughly investigated. To gain insight on simultaneous DNAPL dissolution and NZVI-mediated dechlorination reactions after direct placement of NZVI into a DNAPL source zone, a combined experimental and modeling study was performed. First, a DNAPL tetrachloroethene (PCE) source zone with emplaced NZVI was built inside a small custom-made flow cell and the effluent PCE and dechlorination byproducts were monitored over time. Second, a model for rate-limited DNAPL dissolution and NZVI-mediated dechlorination of PCE to its three main reaction byproducts with a possibility for partitioning of these byproducts back into the DNAPL was formulated. The coupled processes occurring in the flow cell were simulated and analyzed using a detailed three-dimensional numerical model. It was found that subsurface emplacement of NZVI did not markedly accelerate DNAPL dissolution or the DNAPL mass-depletion rate, when NZVI at a particle concentration of 10g/L was directly emplaced in the DNAPL source zone. To react with NZVI the DNAPL PCE must first dissolve into the groundwater and the rate of dissolution controls the longevity of the DNAPL source. The modeling study further indicated that faster reacting particles would decrease aqueous contaminant concentrations but there is a limit to how much the mass removal rate can be increased by increasing the dechlorination reaction rate. To ensure reduction of aqueous contaminant concentrations, remediation of DNAPL contaminants with NZVI should include emplacement in a capture zone down-gradient of the DNAPL source.     

Developmental exposure to diuron causes splenotoxicity in male Sprague-Dawley rat pups

This study investigated whether perinatal exposure to diuron [3-(3,4-dichlorophenyl)-1-1-dimethylurea] might exert adverse effects on rat lymphoid organs. Pregnant Sprague-Dawley (SD) rats were exposed to diuron at 500, 750 or 1250 ppm in the diet from gestational days (GD) 12-21 and during lactation. At postnatal day (PND) 42, male pups were euthanized and thymus, spleen, mesenteric lymph node and femur were collected for histopathological analysis. Food consumption and body weight gain were significantly reduced in dams exposed to 1250 ppm during gestation period. Also, Diuron at 750 and 1250 ppm produced: (1) increased relative spleen weight associated histologically with severe congestion in red pulp, (2) enhanced extramedullary hematopoiesis and hemosiderosis as well as (3) depletion of lymphoid follicles in white pulp. Flow cytometric analysis revealed a significant reduction in B lymphocytes (CD45RA+) in male pups but T lymphocytes (CD4+, CD8+ and CD4+/CD8+) were not markedly affected. Thus, data suggest that Diuron-induced maternal toxicity in dams exposed to high dose and perinatal exposure to this herbicide produced spleen toxicity as evidenced by a reduction in B lymphocyte number in male SD pups.     

Agricultural pesticide residues of farm runoff in the Okanagan Valley, British Columbia, Canada

The objectives of this study were to determine environmental occurrence and concentrations of selected currently-used-pesticides and some transformation products in agricultural farms in the Okanagan Valley (OKV), and to conduct a simple risk assessment of environmental pesticides levels detected in OKV on non-target aquatic organisms. The OKV is the tree fruit country of the Province of British Columbia where considerable amount of pesticides are applied annually. Water, sediment and soil samples were collected at eleven sites in early June and late September following rainfall events and/or extended periods of irrigation from drainage ditches and/or from small streams. Undisturbed reference sites were also sampled. Study results showed that forty of the eighty chemicals analyzed, including organochlorine, nitrogen-containing and organophosphate pesticides commonly used for OKV crops, were detected in runoff and small stream water samples. Among which, endosulfan-sulfate was the most frequently detected chemical. Also, azinophos-methyl (0.699-25.5 ng/L), diazinon (0.088-214 ng/L) exceeded, and α-, β- endosulfan, endosulfan sulphate approached the guidelines for the protection of aquatic life.     

Climate change impacts on the leaching of a heavy metal contamination in a small lowland catchment

The Keersop catchment (43km(2)) in the south of The Netherlands has been contaminated by the emissions of four zinc ore smelters. The objective of this study was to assess the effects of future projected climate change on the hydrology and the leaching of heavy metals (i.e. Cd and Zn) in the catchment. The numerical, quasi-2D, unsaturated zone Soil Water Atmosphere Plant model was used with 100-year simulated daily time series of precipitation and potential evapotranspiration. The time series are representative of stationary climates for the periods 1961-1990 ("baseline") and 2071-2100 ("future"). The time series of future climate were obtained by downscaling the results of eight regional climate model (RCM) experiments, driven by the SRES A2 emissions scenario, using change factors for a series of climate statistics and applying them to stochastic weather generator models. The time series are characterized by increased precipitation in winter, less precipitation in summer, and higher air temperatures (between 2°C and 5°C) throughout the year. Future climate scenarios project higher evapotranspiration rates, more irrigation, less drainage, lower discharge rates and lower groundwater levels, due to increased evapotranspiration and a slowing down of the groundwater system. As a result, lower concentrations of Cd and Zn in surface water are projected. The reduced leaching of heavy metals, due to drying of the catchment, showed a positive impact on a limited aspect of surface water quality.     

Metal stress and decreased tree growth in response to biosolids application in greenhouse seedlings and in situ Douglas-fir stands

To assess physiological impacts of biosolids on trees, metal contaminants and phytochelatins were measured in Douglas-fir stands amended with biosolids in 1982. A subsequent greenhouse study compared these same soils to soils amended with fresh wastewater treatment plant biosolids. Biosolids-amended field soils had significantly higher organic matter, lower pH, and elevated metals even after 25 years. In the field study, no beneficial growth effects were detected in biosolids-amended stands and in the greenhouse study both fresh and historic biosolids amendments resulted in lower seedling growth rates. Phytochelatins - bioindicators of intracellular metal stress - were elevated in foliage of biosolids-amended stands, and significantly higher in roots of seedlings grown with fresh biosolids. These results demonstrate that biosolids amendments have short- and long-term negative effects that may counteract the expected tree growth benefits.     

Persistence of repeated triadimefon application and its impact on soil microbial functional diversity

The effects of repeated applications of the fungicide triadimefon in agricultural soil on the microbial functional diversity of the soil and on the persistence of the fungicide in the soil were investigated under laboratory conditions. The degradation half-lives of triadimefon at the recommended dosage, simulated by a first-order kinetic model, were 23.90, 22.95, and 21.52 days for the first, second, and third applications, respectively. Throughout this study, no significant inhibition of the Shannon-Wiener index (H') was observed. However, the Simpson index (1/D) and the McIntosh index (U) were obviously reduced (p ≤ 0.05) during the initial 3 days after the first triadimefon application and thereafter, gradually recovered to or exceeded the level of the control soil. A similar trend in variation but with a faster recovery in the 1/D and U was observed after the second and third triadimefon applications, respectively. Taken together, the above results indicate that the repeated application of triadimefon enhanced the degradation rate of the fungicide and the recovery rate of the soil microbial functional diversity. It is concluded that repeated triadimefon applications in soil have a transient or temporary inhibitory effect on soil microbial communities.