Atrazine and metolachlor residues in brookston Cl following conventional and conservation tillage culture

Atrazine and metolachlor are extensively used in Ontario, Canada for control of broadleaf weeds and annual grasses in corn. Conservation tillage may alter the physical and biological environment of soil affecting herbicide dissipation. The rate of dissipation of these two herbicides in soil from conventional, ridge and no-tillage culture was followed. Herbicide dissipation was best described by first order reaction kinetics. Half life, the time for herbicide residues to dissipate to half their initial concentration, was unaffected by tillage. Half life for atrazine and metolachlor was similar and ranged from 31 to 66 d. The rate of dissipation decreased in dry years when soil moisture content was low. In a dry year, herbicide residues during the growing season were significantly greater on ridge tops than in the other tillage treatments. However, after harvest no differences in herbicide residues were detected among tillage treatments. Residues of atrazine (6 to 9% of applied) and metolachlor (4 to 6%) were detected in soil before planting a year after application. De-ethyl atrazine, the primary degradation product of atrazine, increased in concentration during the growing season with the greatest concentrations measured at harvest and in years when atrazine dissipated fastest. De-ethyl atrazine one year after application accounted for about 12% of the remaining triazine residue. These herbicide residues would not be phytotoxic to subsequent crops but are a potential source for leaching to ground and surface waters.     

除草剂阿特拉津(Atrazine)的环境行为综述

阿特拉津（２－氯－４－乙胺基－６－异丙氨基－１，３，５，－三氮苯）是目前应用广泛的化学除草剂之一。在世界许多国家和地区的地表水和地下水中已检出了阿特拉津的残留物。阿特拉津对人类的威胁究竟有多大，已成为目前研究的热点。本文从阿特拉津的检测方法、动力学性质、生化性质及风险评估四个方面进行了综述，并提出了自己的观点。     

Triazine and metolachlor herbicide residues in farm areas of the Lower Fraser valley, British Columbia, Canada

Crop soils, ditch sediments and water flowing from several Lower Fraser River (LFR) farm areas of British Columbia, Canada, to salmon tributary streams of that river were sampled in 2004-2005 to quantify for residues of triazine [atrazine, desethylatrazine (a transformation product of atrazine), propazine, and simazine] and metolachlor (a chloroacetamide) herbicides. Average concentrations [microg kg-1 dry weight (d.w.)] of triazine (10,110) and metolachlor (8,910) herbicides detected in crop soils at the start (May 2004, 2005) of the growing season were about 17 and 6 times, respectively, higher than those found for both herbicide groups during (June-Sept, 2004, 2005) the growing season. In contrast, mean concentrations (microg L-1) of triazines (0.092) and metolachlor (0.014) in permanent ditches adjacent to farms were about 7 and 28 times, respectively, lower at the start than during the growing season. Both herbicide groups in ditch sediments were detected only during the growing season at concentrations averaging about 315 microg kg-1 d.w. The risk potential of these herbicides for non-target aquatic organisms inhabiting permanent farm ditches contiguous to tributary streams of the LFR during the growing season is evaluated and discussed.     

Release behavior of triazine residues in stabilised contaminated soils

This paper reports the release behavior of two triazines (atrazine and simazine) in stabilised soils from a pesticide-contaminated site in South Australia. The soils were contaminated with a range of pesticides, especially with triazine herbicides. With multiple extractions of each soil sample with deionised water (eight in total), 15% of atrazine and 4% of simazine residues were recovered, resulting in very high concentrations of the two herbicides in leachate. The presence of small fractions of surfactants was found to further enhance the release of the residues. Methanol content up to 10% did not substantially influence the concentration of simazine and atrazine released. The study demonstrated that while the stabilisation of contaminated soil with particulate activated carbon (5%) and cement mix (15%) was effective in locking the residues of some pesticides, it failed to immobilise triazine herbicides residues completely. Given the higher water solubility of these herbicides than other compounds more effective strategies to immobilise their residues is needed.     

Appendix

Abstract

An atrazine‐degrading bacterial isolate (M91–3) was able to utilize simazine and cyanazine as N sources for glucose‐dependent growth. The degradation of these three 5‐triazine herbicides was also investigated in binary and ternary mixtures. The organism used atrazine and simazine indiscriminately, whereas cyanazine degradation was slow and delayed until the depletion of the two other herbicides. There was no apparent effect of other commonly used herbicides on the rate of atrazine degradation by M91–3.     

Monitoring of triazine and phenylurea herbicides in the surface waters of Greece

A large-scale study was implemented to monitor triazine and phenylurea herbicides in the main surface water bodies of continental Greece from October 1998 to September 1999. Samples from 10 rivers and 7 lakes were analyzed for the presence of five triazine (atrazine, cyanazine, prometryne, simazine, terbuthylazine) and five phenylurea (chlorotoluron, diuron, linuron, metobromuron, monolinuron) herbicides. The samples were extracted with C18 cartridges and analyzed by high-performance liquid chromatography-diode array detection (HPLC-DAD). The most frequently detected herbicides were atrazine, followed by prometryne, cyanazine, and simazine. The concentrations of the compounds were generally low (< 0.78 micro g/L) and are not considered harmful for the freshwater ecosystem. Most of the positive samples were taken from the water bodies of northern Greece where agricultural activity is more intense.     

Monitoring of Triazine and Phenylurea Herbicides in the Surface Waters of Greece

A large-scale study was implemented to monitor triazine and phenylurea herbicides in the main surface water bodies of continental Greece from October 1998 to September 1999. Samples from 10 rivers and 7 lakes were analyzed for the presence of five triazine (atrazine, cyanazine, prometryne, simazine, terbuthylazine) and five phenylurea (chlorotoluron, diuron, linuron, metobromuron, monolinuron) herbicides. The samples were extracted with C18 cartridges and analyzed by high-performance liquid chromatography–diode array detection (HPLC-DAD). The most frequently detected herbicides were atrazine, followed by prometryne, cyanazine, and simazine. The concentrations of the compounds were generally low (< 0.78 μ g/L) and are not considered harmful for the freshwater ecosystem. Most of the positive samples were taken from the water bodies of northern Greece where agricultural activity is more intense.     

Triazines in the aquatic systems of the Eastern Chinese Rivers Liao-He and Yangtse

The results of a one-year monitoring program on the two Eastern Chinese River systems, i.e. the Liao-He and the Yangtse, with special emphasis on the presence of triazine herbicides are presented. Sediment, suspended solids and water samples from both rivers were analyzed. Additionally, recovery experiments on the SPE-in-field-enrichment procedure and the extraction methods were performed. The samples were measured by gas chromatography coupled with mass spectrometry, electron capture detection and a newly developed mu-plasma atomic emission detector. A typical result of a one-year monitoring was obtained in case of the Liao-He: During winter, at low water period, low triazine values were found. A similar situation was found in early spring. Highest concentrations of atrazine up to 1600 ng/l were found in late spring in the water samples. Maximum concentrations of atrazine, simazine, propazine, simetryn and prometryn were observed in this season as a result of the actual use of triazines. Finally, after the high water period in autumn the triazine concentrations decreased. Additionally, atrazine adsorbed on sediment (up to 2.8 ng/g) and suspended solids was determined (up to 8 ng/l) during late spring sampling. Therefore, the logarithm of the organic carbon based sorption coefficient of atrazine could be calculated. Low levels of atrazine were measured in the water of Yangtse (up to 18.3 ng/l). The concentrations from all sampling points and sampling stations of a particular sampling date were similar, which indicates a homogeneous distribution of this herbicide. Due to the high discharge rate of up to 79,000 m3/s in case of the Yangtse a considerable mass transport of up to 57.5 kg per day atrazine may take place, even at concentrations below the European drinking water limit of 100 ng/l.     

Triazine and Metolachlor Herbicide Residues in Farm Areas of the Lower Fraser Valley,British Columbia,Canada

Crop soils, ditch sediments and water flowing from several Lower Fraser River (LFR) farm areas of British Columbia, Canada, to salmon tributary streams of that river were sampled in 2004–2005 to quantify for residues of triazine [atrazine, desethylatrazine (a transformation product of atrazine), propazine, and simazine] and metolachlor (a chloroacetamide) herbicides. Average concentrations [μg kg^?1 dry weight (d.w.)] of triazine (10,110) and metolachlor (8,910) herbicides detected in crop soils at the start (May 2004, 2005) of the growing season were about 17 and 6 times, respectively, higher than those found for both herbicide groups during (June–Sept, 2004, 2005) the growing season. In contrast, mean concentrations (μg L^?1) of triazines (0.092) and metolachlor (0.014) in permanent ditches adjacent to farms were about 7 and 28 times, respectively, lower at the start than during the growing season. Both herbicide groups in ditch sediments were detected only during the growing season at concentrations averaging about 315 μg kg^?1 d.w. The risk potential of these herbicides for non-target aquatic organisms inhabiting permanent farm ditches contiguous to tributary streams of the LFR during the growing season is evaluated and discussed.     

Bioconcentration, biomagnification and metabolism of 14C-terbutryn and 14C-benzo[a]pyrene in Gammarus fossarum and Asellus aquaticus

The contribution of bioconcentration and biomagnification of 14C-terbutryn and 14C-benzo[a]pyrene via food and water to the bioaccumulation in Gammarus fossarum and Asellus aquaticus was investigated in single species-tests. In this investigation the uptake of 14C-terbutryn and 14C-benzo[a]pyrene via food and water by G. fossarum (L.) and A. aquaticus (L.) was examined. Bioconcentration factors (BCFs) and biomagnification factors (BMFs) were determined. Calculated BCFs were clearly higher than BMFs, indicating that water is the primary route of uptake. The uptake of terbutryn and benzo[a]pyren via water in G. fossarum and A. aquaticus is faster than uptake via food. The elimination and metabolism of the two chemicals by G. fossarum and A. aquaticus were studied. Terbutryn was eliminated almost completely in both species. In general, the elimination of terbutryn from G. fossarum and A. aquaticus was fast with half-life of 5 h. The elimination of terbutryn by G. fossarum after biomagnification is slower than after bioconcentration. No difference was found in elimination of terbutryn by A. aquaticus after biomagnification and after bioconcentration. Metabolites of terbutryn in G. fossarum and A. aquaticus were analyzed by HPLC. After the bioconcentration experiment a higher percentage of metabolites was found in G. fossarum than in A. aquaticus. This was confirmed for the experiment with uptake via food. The spectrum of metabolites was similar in both species, with hydroxyterbutryn being the major metabolism product in water. 14C-B[a]P could nearly completely be eliminated by G. fossarum (rest of activity 2%) after uptake via water. 14C-B[a]P could not be eliminated by G. fossarum and A. aquaticus after uptake via food. The metabolite could not be identified.     

Effects of bensulfuron-methyl and cinosulfuron on growth of four freshwater species of phytoplankton

The acute toxicity of sulfonylurea herbicides bensulfuron-methyl and cinosulfuron was tested on the five species of freshwater phytoplankton: Scenedesmus acutus, Scenedesmus subspicatus, Chlorella vulgaris and Chlorella saccharophila. Herbicide concentrations eliciting a 50% growth reduction over 96 h (EC50) ranged from 8 to 104 mg/l for cinosulfuron and from 0.015 to 6.2 mg/l for bensulfuron-methyl. The pesticides bensulfuron-methyl, atrazine and benthiocarb were more toxic than cinosulfuron, chlorsulfuron, molinate, fenitrothion and pyridaphenthion in a toxicity study with the same algal species. The transformation of effective concentrations of bensulfuron-methyl and cinosulfuron and other pesticides, obtained from toxicity measurements, into percent of the saturation level in water is used as a first evaluation of potential hazard to aquatic systems. The herbicides cinosulfuron, methyl-bensulfuron, atrazine and chlorsulfuron were more dangerous than the herbicides benthiocarb and molinate and than the insecticides fenitrothion and pyridaphenthion, in a study of hazard evaluation. The two species of Chlorella were more tolerant to both herbicides than the two species of Scenedesmus. A potential environmental hazard of sulfonylurea herbicides to aquatic systems has to be expected even at low environmental concentrations.     

Runoff and leaching of atrazine and alachlor on a sandy soil as affected by application in sprinkler irrigation

Abstract

Rainfall simulation was used with small packed boxes of soil to compare runoff of herbicides applied by conventional spray and injection into sprinkler‐irrigation (chemigation), under severe rainfall conditions. It was hypothesized that the larger water volumes used in chemigation would leach some of the chemicals out of the soil surface rainfall interaction zone, and thus reduce the amounts of herbicides available for runoff. A 47‐mm rain falling in a 2‐hour event 24 hours after application of alachlor (2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl)‐acetamide) and atrazine (6‐chloro‐N‐ethyl‐N‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine) was simulated. The design of the boxes allowed a measurement of pesticide concentrations in splash water throughout the rainfall event. Initial atrazine concentrations exceeding its’ solubility were observed. When the herbicides were applied in 64000 L/ha of water (simulating chemigation in 6.4 mm irrigation water) to the surface of a Tifton loamy sand, subsequent herbicide losses in runoff water were decreased by 90% for atrazine and 91% for alachlor, as compared to losses from applications in typical carrier water volumes of 187 L/ha. However, this difference was not due to an herbicide leaching effect but to a 96% decrease in the amount of runoff from the chemigated plots. Only 0.3 mm of runoff occurred from the chemigated boxes while 7.4 mm runoff occurred from the conventionally‐treated boxes, even though antecedent moisture was higher in the former. Two possible explanations for this unexpected result are (a) increased aggregate stability in the more moist condition, leading to less surface sealing during subsequent rainfall, or (b) a hydrophobic effect in the drier boxes. In the majority of these pans herbicide loss was much less in runoff than in leachate water. Thus, in this soil, application of these herbicides by chemigation would decrease their potential for pollution only in situations where runoff is a greater potential threat than leaching.     

Calibration and field application of a solvent-based cellulose membrane passive sampling device for the monitoring of polar herbicides

A passive sampler device selective for hydrophilic analytes was constructed from cellulose membrane (40microm thickness) pre-stained with ruthenium red for 96-168h to impede degradation of the cellulose. The sampling device consisted of pre-stained cellulose membrane tubing containing a binary mixture of the solvents 1-dodecanol and 2,2,4-trimethylpentane as the sequestering medium. A laboratory flow-through system was used to investigate the rates of uptake of herbicides into the solvent mixture of the device and their release. The target herbicides were diuron, atrazine, metolachlor and molinate. Uptake of the herbicides into the solvent mixture of the cellulose membrane device was linear for up to 22 days, and daily sampling rates were determined. Release half-lives from the solvent mixture of the sampling device varied from 14 days for diuron, 15 days for atrazine, 84 days for metolachlor and 28 days for molinate. A field study was undertaken to determine if herbicide concentrations in agricultural drainage water derived from the passive sampler devices deployed for periods from 7 to 22 days, using the laboratory-derived sampling rates, would compare closely with time-weighted average herbicide concentrations determined from extractions of daily composite water samples. The concentrations of diuron, atrazine, metolachlor and molinate determined using the cellulose membrane devices were within twofold of the cumulated mean of the daily drainage water extractions.     

Influence of microbial and synthetic surfactant on the biodegradation of atrazine

The present study reports the effect of surfactants (rhamnolipids and triton X-100) on biodegradation of atrazine herbicide by strain A6, belonging to the genus Acinetobacter. The strain A6 was able to degrade nearly 80 % of the 250-ppm atrazine after 6 days of growth. The bacterium degraded atrazine by de-alkylation process. Bacterial cell surface hydrophobicity as well as atrazine solubility increased in the presence of surfactant. However, addition of surfactant to the mineral salt media reduced the rate and extent of atrazine degradation by decreasing the bioavailability of herbicide. On the contrary, addition of surfactant to atrazine-contaminated soil increased the rate and extent of biodegradation by increasing the bioavailability of herbicide. As compared to triton X-100, rhamnolipids were more efficient in enhancing microbial degradation of atrazine as a significant amount of atrazine was removed from the soil by rhamnolipids. Surfactants added for the purpose of hastening microbial degradation may have an unintended inhibitory effect on herbicide degradation depending upon contiguous condition, thus highlighting the fact that surfactant must be judiciously used in bioremediation of herbicides.     

Laboratory assessment of atrazine and fluometuron degradation in soils from a constructed wetland

Constructed wetlands offer promise for removal of nonpoint source contaminants such as herbicides from agricultural runoff. Laboratory studies assessed the potential of soils to degrade and sorb atrazine and fluometuron within a recently constructed wetland. The surface 3 cm of soil was sampled from two cells of a Mississippi Delta constructed wetland; one shallow area disturbed only hydrologically, and the second excavated to provide greater water-holding capacity. The excavated area was more acidic on average (pH 4.85 versus 5.21), but otherwise the physical properties and general microbial enzyme activities in the two areas were similar. Soils were treated with 84 and 68 microg kg(-1) soil (14)C-ring labeled atrazine and fluometuron, respectively, and incubated under either saturated (88% moisture, w:w) or flooded (1cm standing water) conditions. Soils were sampled over 32 days and extracted for herbicide and metabolite analysis. Under saturated conditions, fluometuron metabolized to desmethylfluometuron (DMF) with a half-life equal 25-27 days. However, under flooded conditions, the half-life of fluometuron was more than 175 days. Atrazine dissipated rapidly in saturated and flooded soil with a half-life of approximately 23 days, but only 10% of atrazine was mineralized to CO(2). The overall atrazine and fluometuron dissipation rates were similar between the two cells, but each area had a different pattern of metabolite accumulation. The major route of atrazine dissipation was incorporation of atrazine residues into methanol-nonextractable (soil-bound) components, with minimal extractable metabolite accumulation. A mixed-mode extractant (potassium phosphate:acetonitrile) recovered greater amounts of (14)C-residues from atrazine-treated soils, suggesting that hydrolysis of atrazine to hydroxylated metabolites was a major component of the bound residues. These studies indicate the potential for herbicide dissipation in wetland soils and a differential effect of flooding on the fate of these herbicides.     

Enzyme-immunoassay techniques for the detection of atrazine in water samples: Evaluation of a commercial tube based assay

Environmental immunoassays can help lower the operating costs and improve the effectiveness of residue laboratories. The present study assesses the ability of a commercially available enzyme immunoassay (EIA) to detect triazine herbicides in water. The tube based EIA could detect atrazine in lake and river water with detection limits of 62 pg/mL and 180 pg/mL respectively. The assay's ability to quantify atrazine in a set of 124 water samples taken from many parts of Canada was compared with a reference method that used gas chromatographic separation combined with a nitrogen phosphorous detector (GC-NPD) (R=0.919). A 71 % reduction in analytical load was achieved at a threshold concentration of 1 ng/mL. There were 2.4 % false negative and 0.8 % false positive results associated with that load reduction. The variability of the assay control parameters was generally within two standard deviations of the mean response for 65 assays. The EIA for atrazine is recommended for use as a screening technique and as an inexpensive way to monitor triazine levels in waters that are known to be contaminated with those herbicides.     

The fate of isoproturon in a freshwater microcosm with Lemna minor as a model organism

Degradation, bioaccumulation and volatile loss of the 14C-labeled phenylurea herbicide isoproturon (IPU) was examined in a freshwater microcosm with the free floating macrophyte species Lemna minor during a 21-day exposure time. Isoproturon volatilisation was very low with 0.13+/-0.01% of the initially applied herbicide. Only a minor amount of the herbicide was completely metabolised, presumably by rhizosphere microorganisms and released as 14CO2. In total, about 9% isoproturon was removed from the aquatic medium during 21 days. The major portion of the pesticide was removed by bioaccumulation of Lemna minor (5.0+/-0.8%) and the bioconcentration factor (BCF) based on freshweight was 15.8+/-0.2. However, this study indicated a high persistence of IPU in freshwater ecosystems and a potential hazard due to bioaccumulation in non-target species. The novel experimental system of this study, developed for easy use and multiple sampling abilities, enabled quantitatively studying the fate of isoproturon and showed high reproducibility with a mean average (14)C-recovery rate of 97.1+/-0.7%.     

Variation in the response of the invasive species Potamopyrgus antipodarum (Smith) to natural (cyanobacterial toxin) and anthropogenic (herbicide atrazine) stressors

In the context of increasing freshwater pollution, the impact on life-traits (survival, growth and fecundity) and locomotion of Potamopyrgus antipodarum of a 5-week field-concentration exposure to the cyanobacterial toxin microcystin-LR and the triazine herbicide, atrazine was studied. Whatever the age of exposed snails (juveniles, subadults, adults), microcystin-LR induced a decrease in survival, growth and fecundity but had no effect on locomotion. Atrazine induced a decrease in locomotory activity but had no significant effect on the life-traits. These results are discussed in terms of consequences to field populations.     

Reduced adsorption of ametryn in clay, humic acid, and soil by interaction with ferric ion under Fenton treatment conditions

Previous work in our laboratory indicated a weak interaction between ferric ion and several triazine/triazinone herbicides during a Fenton treatment process, and the intensity of the interaction was calculated. To further support the existence of this weak interaction, the adsorption of ametryn, a triazine herbicide, was investigated in kaolinite clay, humic acid, and soil under pseudo-Fenton conditions. At a low addition rate of ferric ion, the adsorption of ametryn in clay, humic acid, and soil was enhanced due to the decreased pH resulting from the hydrolysis of ferric ion. But the pH effect was totally neutralized and the adsorption of ametryn was significantly reduced by further addition of ferric ion, demonstrating the existence of the weak interaction between ametryn and ferric acid. Further study showed that the adsorption-reduction effect of ferric ion existed not only with ametryn but also with several other triazine/triazinone herbicides. This weak interaction may accelerate the desorption process during the remediation of triazine/triazinone herbicide-contaminated soil using a Fenton/Fenton-like treatment, but it may also impede the degradation of these herbicides.     

Effect of some herbicides on activities of microorganisms and enzymes in soil

Abstract

Laboratory tests were conducted with eight herbicides, atrazine, butylate, ethalfluralin, imazethapyr, linuron, metolachlor, metribuzin and trifluralin, applied to a loamy sand at rate of 10 μg/g to determine if these materials caused any serious effects on microbial and enzymatic activities related to soil fertility. Some herbicides showed an effect on bacteria and fungi for the first week of incubation, but, subsequently, the populations returned to levels similar to those obtained in the controls. After several herbicide treatments there appeared to cause a slight depression of nitrification. Sulfur oxidation was better than that obtained with untreated soil in all treatments. Oxygen consumption was increased significantly after 96 hr incubation with atrazine. The soil dehydrogenase and amylase activities were inhibited by ethalfluralin treatment respectively for 1 wk and 1 day, and p‐nitrophenol liberation was inhibited for 2 hrs by all herbicide treatments. Results indicated that the herbicidal treatments at the level tested were not drastic enough to be considered deleterious to soil microbial and enzymatic activities which are important to soil fertility.