Removal of atrazine and its by-products from water using electrochemical advanced oxidation processes.

Atrazine (ATZ) is one of the most common pesticides detected in surface water in Quebec (Canada). The present study was mainly focused on the degradation of ATZ and its by-products using electrochemical advanced oxidation processes such as photo-electro-Fenton (PEF), electro-Fenton (EF) and anodic-oxidation with simultaneous H2O2 formation (AO - H2O2). The comparison of these processes showed that PEF process was found to be the most effective process in removing ATZ and its by-products from both synthetic solution (ATZ0 = 100 µg L-1) and real agricultural surface water enriched with ATZ (ATZ0 = 10 µg L-1). Different operating parameters, including wavelength of the light, pH, current density and the presence of natural organic matter (humic acids) were investigated for PEF process using boron-doped diamond (BDD) anode and graphite cathode. The current density and the wavelength of the light were the most important parameters in the ATZ degradation efficiency. The best operating conditions were recorded for the synthetic samples at a current density of 18.2 mA cm-2, a pH of 3.0 and treatment time of 45 min. Results showed that atrazine-desethyl-desisopropyl (DEDIA) was the most important by-product recorded. More than 99% of ATZ oxidation was recorded after 15 min of treatment and all the concentrations of major by-products were less than the limit of detection after 45 min of treatment. The PEF process was also tested for real surface water contaminated by ATZ: i) with and without addition of iron; ii) without pH adjustment (pH âˆ¼ 6.7) and with pH adjustment (pH âˆ¼ 3.1). In spite of the presence of radical scavenger and iron complexation the PEF process was more effective to remove ATZ from real surface water when the pH value was adjusted near to 3.0. The ATZ removal was 96.0% with 0.01 mM of iron (kapp = 0.13 min-1) and 100% with 0.1 mM of iron (kapp = 0.17 min-1).

Degradation of atrazine in aqueous solution with electrophotocatalytic process using TiO2-x photoanode.

The present study investigates the efficiency of a sustainable treatment technology, the electrophotocatalytic (EPC) process using innovative photoanode TiO2-x prepared by a magnetron sputter deposition process to remove the herbicide atrazine (ATZ) from water. The coexistence of anatase and rutile were identified by X-ray diffraction (XRD) and the presence of oxygen vacancies reduce the value of the observed bandgap to 3.0 eV compared to the typical 3.2 eV TiO2, this reduction is concomitant with a partial phase transition which is probably responsible for the increase in photoactivity. The experimental results with an initial concentration of ATZ (100 µg L(-1)) show that more than 99% of ATZ oxidation was obtained after 30 min of treatment and reaction kinetic constant was about 0.146 min(-1). This good efficiency indicates that EPC process is an efficient, simple and green technique for degradation of pesticides such as ATZ in water. The analysis with liquid chromatography technique permits to identify, quantify and see the evolution of ATZ by-products which are generated by dechlorination, dealkylation and alkylic-oxidation mechanisms. Finally, the possible pathways of ATZ degradation by hydroxyl radicals were proposed.

Potential Efficiency of Riparian Vegetated Buffer Strips in Intercepting Soluble Compounds in the Presence of Subsurface Preferential Flows.

Buffer strips have been widely recognized as to promote infiltration, deposition and sorption of contaminants for protecting surface water against agricultural contamination. However, such strips do not intercept all contaminants, particularly soluble ones. Although preferential flow (PF) has been suggested as one factor among several decreasing the efficiency of buffer strips, the mechanisms involved are not well understood. This project examines buffer strip efficiency at intercepting solutes when subsurface PF occurs. Two soluble sorbed tracers, FD&C Blue #1 and rhodamine WT, were applied on an agricultural sandy loam soil to evaluate the ability of a naturally vegetated buffer strip to intercept soluble contaminants. Rhodamine was applied about 15 m from the creek, while the Blue was applied 15 m to 165 m from the creek. Tracer concentration was measured over a two-year period in both the creek and the buffer strip through soil and water samples. Although the tracers traveled via different pathways, they both quickly moved toward the creek, passing beneath the buffer strip through the soil matrix. Our results demonstrate that the risk of water contamination by soluble contaminants is high in such systems, even when a well-vegetated buffer strip is used. The design of buffer strips should be modified to account for underground bypass, either by using plants that have deep, fine roots that do not favour PF or by adding a filter extending deep underground that can be regularly changed.

Impact of recent manure applications on natural estrogen concentrations in streams near agricultural fields.

Few studies on natural estrogens have been conducted in agricultural ecosystems. High (up to 58 ng/L) estrone concentrations were measured shortly after applications of manure in a small agricultural watershed. No other estrogens (17ß-estradiol, estrone or estriol) were detected afterward (first three rainfalls after applications). Results suggest that aquatic organisms in agricultural watersheds could be exposed to estrone shortly after manure applications, probably from leaching of land-applied animal wastes, but that this exposure would be short-lived.

Impact of vegetated filter strips on sorbed herbicide concentrations and sorption equilibrium in agricultural plots.

The objective was to investigate the impact of vegetated filter strips on exported atrazine and deethylatrazine concentrations [dissolved and sorbed to eroded sediments (>1.5 µm)], the deethylatrazine to atrazine ratio in water and sediments, the ratio of sorbed to dissolved herbicides in runoff and subsurface infiltration as well as field equilibrium state under natural climate during two seasons. We hypothesize that sorption equilibrium was not achieved in 2004 because of the short delay (<24 h) between herbicide application and the first rain event. In 2005, observations suggest that possible changing sorption equilibrium conditions were reached (20 days after atrazine application), especially for eroded sediments submitted to changing environmental conditions in subsurface. If confirmed by other experiments, this will raise the question of the representativeness of laboratory-determined soil sorption coefficients to predict the fate of pesticides.

A hydrological modeling framework for defining achievable performance standards for pesticides.

This paper proposes a hydrological modeling framework to define achievable performance standards (APSs) for pesticides that could be attained after implementation of recommended management actions, agricultural practices, and available technologies (i.e., beneficial management practices [BMPs]). An integrated hydrological modeling system, Gestion Intégrée des Bassins versants à l'aide d'un Système Informatisé, was used to quantify APSs for six Canadian watersheds for eight pesticides: atrazine, carbofuran, dicamba, glyphosate, MCPB, MCPA, metolachlor, and 2,4-D. Outputs from simulation runs to predict pesticide concentration under current conditions and in response to implementation of two types of beneficial management practices (reduced pesticide application rate and 1- to 10-m-wide edge-of-field and/or riparian buffer strips, implemented singly or in combination) showed that APS values for scenarios with BMPs were less than those for current conditions. Moreover, APS values at the outlet of watersheds were usually less than ecological thresholds of good condition, when available. Upstream river reaches were at greater risk of having concentrations above a given ecological thresholds because of limited stream flows and overland loads of pesticides. Our integrated approach of "hydrological modeling-APS estimation-ecotoxicological significance" provides the most effective interpretation possible, for management and education purposes, of the potential biological impact of predicted pesticide concentrations in rivers.

Experimental design methodology applied to electrochemical oxidation of the herbicide atrazine using Ti/IrO(2) and Ti/SnO(2) circular anode electrodes.

The degradation of the herbicide atrazine in aqueous medium (initial concentration of 100 µg l(-1)) has been studied by electrooxidation process using Ti/IrO(2) and Ti/SnO(2) circular anode electrodes. The performance of the electrolytic cell resulted from its capability of reacting on the pollutants by using indirect effect of electrical current where active chlorine is electrochemically generated. A factorial experimental design was firstly used for determining the influent parameters on the herbicide atrazine degradation. The current intensity and treatment time were the main influent parameters on the degradation rate. Using a 2(4) factorial matrix, the best performance for atrazine degradation (removal of 95%) was obtained by selecting Ti/IrO(2) anode operated at a current intensity of 2.0 A during 40 min of treatment time in the presence of 1.0 g Na Cl l(-1). Then, the optimal experimental parameters for atrazine degradation have been investigated by using a Central Composite methodology. Under the optimal conditions determined by this method, electrooxidation can economically be applied to oxidise atrazine (73% of degradation for a total cost of 0.057 US$m(-3)) while using Ti/IrO(2) anode operated at a current intensity of 1.4A during 22 min of treatment time in the presence of 1.0 g NaCl l(-1).

Impact of grass and grass with poplar buffer strips on atrazine and metolachlor losses in surface runoff and subsurface infiltration from agricultural plots.

In many areas of intensive corn production, atrazine and metolachlor are among the most commonly found herbicides in surface and ground water. This 2-yr study compared the impact of grass and grass+tree buffer strips on the exported masses of atrazine, metolachlor, and a degradation product of atrazine, desethylatrazine (DEA). The experimental system consisted of four replicate plots in a three-way completely randomized design (no buffer zone, grass buffer zone, and grass+tree buffer strips). The field plots were 5 m wide and 30 m long and grown in corn. The grass and grass+tree buffer strips were 5 m and had the same grass vegetation except for eight young hybrid poplars. Over the 2-yr study, surface runoff and subsurface infiltration water (under the buffer strip) were collected after the initial three rainfall events after herbicide application. Dissolved atrazine, metolachlor, and DEA were analyzed by gas chromatography/mass spectrometry. The presence of buffer strips decreased the exported masses of atrazine and metolachlor in surface runoff. A three-way ANOVA with treatment (type of buffer strip), water (surface runoff or subsurface infiltration), and time between herbicide application and rainfall event as factors showed a significant reduction (40-60% in 2004 and 75-95% in 2005) in the total (surface runoff+infiltrated water) exported masses of atrazine and metolachlor in the presence of buffer strips. Rainfall events after herbicide application were different between the 2 yr and greatly affected the flow distribution (e.g., subsurface infiltration) and the leached herbicide concentrations. No significant difference in the capacity to reduce herbicide exports was observed between grass and grass+tree buffer strip treatments; the poorly developed young poplar biomass at the time of the study may partly explain this observation.

Pesticides in fluvial wetlands catchments under intensive agricultural activities.

A survey on pesticides (73 compounds) in the Bay St. François wetland and its catchment (part of the wetlands of Lake St. Pierre area [St. Lawrence River, Québec]) was achieved in 2006. The metabolites as well as the active ingredients of pesticides (11 compounds) were detected in the wetland and its catchment. This wetland ecosystem was active in the degradation of agricultural pesticides (e.g., atrazine). The measured pesticides were individually below the criteria for aquatic species in natural water, except chlorpyrifos. Overall, the pesticides lost from agricultural field towards the streams were <1% of the quantity applied. The environmental fates of the pesticides were found to vary according to the size of the watershed. Over large catchments, half-life times were important in terms of global loss from the agricultural lands to wetlands whereas over small catchments, soil organic carbon/water distribution coefficient (Koc) was an important term for pesticides losses to water system since half-life times were not limiting factors.

Conditions for effective removal of pyrene from an artificially contaminated soil using Pseudomonas aeruginosa 57SJ rhamnolipids.

The efficacy of a new rhamnolipid biosurfactants mixture to enhance the removal of pyrene from a soil artificially contaminated was investigated. The molar solubilization ratio (MSR) and the partition coefficient between the micelles and water (log K(m)) were found to be 7.5 x 10(-3) and 5.7, respectively. From soil column studies, the pyrene removal increased linearly with the concentration of the injected biosurfactants solution above the effective critical micellar concentration (0.4 g L(-1)). Flushing with a 5.0 g L(-1) biosurfactants solution increased the pyrene concentration in the effluent by 178 times. At high biosurfactants' concentrations (2.5 and 5.0 g L(-1)), the cumulative pyrene recovery reached 70%. This pyrene remobilization takes place independently of the soil organic carbon solubilization. This study provides a combination of batch and column experiments in order to find the conditions for effective soil remediation using a new rhamnolipids mixture.