Strategies to evaluate biodegradability: application to chlorinated herbicides

The biodegradability of nitrochlorinated (diuron and atrazine) and chlorophenoxy herbicides (2,4-D and MCPA) has been studied through several bioassays using different testing times and biomass/substrate ratios. A fast biodegradability test using unacclimated activated sludge yielded no biodegradation of the herbicides in 24 h. The inherent biodegradability test gave degradation percentages of around 20–30 % for the nitrochlorinated herbicides and almost complete removal of the chlorophenoxy compounds. Long-term biodegradability assays were performed using sequencing batch reactor (SBR) and sequencing batch membrane bioreactor (SB-MBR). Fixed concentrations of each herbicide below the corresponding EC₅₀ value for activated sludge were used (30 mg L^?1 for diuron and atrazine and 50 mg L^?1 for 2,4-D and MCPA). No signs of herbicide degradation appeared before 35 days in the case of diuron and atrazine and 21 days for 2,4-D, whereas MCPA was partially degraded since the early stages. Around 25–36 % degradation of the nitrochlorinated herbicides and 53–77 % of the chlorophenoxy ones was achieved after 180 and 135 days, respectively, in SBR, whereas complete disappearance of 2,4-D was reached after 80 days in SB-MBR.     

Sorption-desorption of atrazine and diuron in soils from southern Brazil

The objective of this study was to investigate the behavior of sorption and desorption of the herbicides atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) and diuron [3-(3,4-dichlorophenyl)-1,1-dimethyleurea] in soil samples from a typical lithosequence located in the municipality of Mamborê (PR), southern Brazil. Five concentrations of 14C-atrazine and 14C-diuron were used for both herbicides (0.48, 0.96, 1.92, 3.84, and 7.69 mg L(-1)). Sorption of both herbicides correlated positively with the organic carbon and clay content of the soil samples. Sorption isotherms were well described by the Freundlich model. The slope values of the isotherm (N) ranged from 0.84 to 0.90 (atrazine) and from 0.75 to 0.79 (diuron) for the lithosequence samples. Sorption of diuron was high regardless of the soil texture or the concentration added. The desorption isotherms for atrazine and diuron showed good fit to the Freundlich equation (R2 >or= 0,87). Atrazine slope values for the desorption isotherms were similar for the different concentrations and were much lower than those observed for the sorption isotherms. Significant hysteresis was observed in the herbicide desorption. When the two herbicides were compared, it was found that diuron (N = 0.06-0.22) presented more pronounced hysteresis than atrazine. The results showed that, quantitatively, a greater atrazine fraction applied to these soils remains available to be leached in the soil profile, as compared to diuron.     

Sorption of atrazine and metolachlor by earthworm surface castings and soil

Atrazine and metolachlor were more strongly retained on earthworm (Lumbricus terrestris L.) castings than on soil, suggesting that earthworm castings at the surface or at depth can reduce herbicide movement in soil. Herbicide sorption by castings was related to the food source available to the earthworms. Both atrazine and metolachlor sorption increased with increasing organic carbon (C) content in castings, and Freundlich constants (Kf values) generally decreased in the order: soybean-fed > corn-fed > not-fed-earthworm-castings. The amount of atrazine or metolachlor sorbed per unit organic carbon (Koc values) was significantly greater for corn-castings compared with other castings, or soil, suggesting that the composition of organic matter in castings is also an important factor in determining the retention of herbicides in soils. Herbicide desorption was dependent on both the initial herbicide concentration, and the type of absorbent. At small equilibrium herbicide concentrations, atrazine desorption was significantly greater from soil than from any of the three casting treatments. At large equilibrium herbicide concentrations, however, the greater organic C content in castings had no significant effect on atrazine desorption, relative to soil. For metolachlor, regardless of the equilibrium herbicide concentration, desorption from soybean- and corn-castings treatments was always less than desorption from soil and not-fed earthworm castings treatments. The results of this study indicate that, under field conditions, the extent of herbicide retention on earthworm castings will tend to be related to crop and crop residue management practices.     

Determination of commonly used polar herbicides in agricultural drainage waters in Australia by HPLC

The present study describes the application of different extraction techniques for the preconcentration of ten commonly found acidic and non-acidic polar herbicides (2,4-D, atrazine, bensulfuron-methyl, clomazone, dicamba, diuron, MCPA, metolachlor, simazine and triclopyr) in the aqueous environment. Liquid-liquid extraction (LLE) with dichloromethane, solid-phase extraction (SPE) using Oasis HLB cartridges or SBD-XC Empore disks were compared for extraction efficiency of these herbicides in different matrices, especially water samples from contaminated agricultural drainage water containing high concentrations of particulate matter. Herbicides were separated and quantified by high performance liquid chromatography (HPLC) with an ultraviolet detector. SPE using SDB-XC Empore disks was applied to determine target herbicides in the Murrumbidgee Irrigation Area (NSW, Australia) during a two-week survey from October 2005 to November 2005. The daily aqueous concentrations of herbicides from 24-h composite samples detected at two sites increased after run-off from a storm event and were in the range of: 0.1-17.8 microg l(-1), < 0.1-0.9 microg l(-1) and 0.2-17.8 microg l(-1) at site 1; < 0.1-3.5 microg l(-1), < 0.1-0.2 microg l(-1) and < 0.2-3.2 microg l(-1) at site 2 for simazine, atrazine and diuron, respectively.     

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.     

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.     

Atmospheric concentrations and dry and wet deposits of some herbicides currently used on the Canadian Prairies

High volume air sampling in the Canadian Prairies was used to characterize atmospheric concentrations for 10 herbicides (alachlor, atrazine, ethalfluralin, metolachlor, 2,4-D, dicamba, bromoxynil, MCPA, trifluralin, and triallate) along a 500-km north-south transect. Atmospheric concentration measurements at various altitudes identified that of the six herbicides present in the highest concentrations, triallate was strongly influenced by local sources, while 2,4-D, dicamba, bromoxynil, MCPA and trifluralin were dominated by regional atmospheric transport. Concentrations of the herbicides measured at various altitudes were compared with dry deposition rates measured using a dry/wet deposition sampler and used to calculate deposition velocities V(d). The primary atmospheric transport mechanism for MCPA and bromoxynil was shown to be adsorption to particles dispersed in the atmosphere, with the same mechanism also confirmed for 2,4-D and dicamba, while trifluralin was shown to be transported mainly in the gas phase. This method of calculation indicated that transportation of triallate was influenced by particle adsorption. Weekly maximum atmospheric loadings of the major herbicides present in the Prairies were estimated to range from 73 kg for trifluralin to 541 kg for 2,4-D.     

Sorption of atrazine and metolachlor by earthworm surface castings and soil

Abstract

Atrazine and metolachlor were more strongly retained on earthworm (Lumbricus terrestris L.) castings than on soil, suggesting that earthworm castings at the surface or at depth can reduce herbicide movement in soil. Herbicide sorption by castings was related to the food source available to the earthworms. Both atrazine and metolachlor sorption increased with increasing organic carbon (C) content in castings, and Freundlich constants (K_f values) generally decreased in the order: soybean‐fed > corn‐fed > not‐fed‐earthworm‐castings. The amount of atrazine or metolachlor sorbed per unit organic carbon (K_oc values) was significantly greater for corn‐castings compared with other castings, or soil, suggesting that the composition of organic matter in castings is also an important factor in determining the retention of herbicides in soils. Herbicide desorption was dependent on both the initial herbicide concentration, and the type of absorbent. At small equilibrium herbicide concentrations, atrazine desorption was significantly greater from soil than from any of the three casting treatments. At large equilibrium herbicide concentrations, however, the greater organic C content in castings had no significant effect on atrazine desorption, relative to soil. For metolachlor, regardless of the equilibrium herbicide concentration, desorption from soybean‐ and corn‐castings treatments was always less than desorption from soil and not‐fed earthworm castings treatments. The results of this study indicate that, under field conditions, the extent of herbicide retention on earthworm castings will tend to be related to crop and crop residue management practices.     

Sorption-Desorption of Atrazine and Diuron in Soils from Southern Brazil

The objective of this study was to investigate the behavior of sorption and desorption of the herbicides atrazine (6-chloro-N ²-ethyl-N ⁴-isopropyl-1,3,5-triazine-2,4-diamine) and diuron [3-(3,4-dichlorophenyl)-1,1-dimethyleurea] in soil samples from a typical lithosequence located in the municipality of Mamborê (PR), southern Brazil. Five concentrations of ¹⁴C-atrazine and ¹⁴C-diuron were used for both herbicides (0.48, 0.96, 1.92, 3.84, and 7.69 mg L^?1). Sorption of both herbicides correlated positively with the organic carbon and clay content of the soil samples. Sorption isotherms were well described by the Freundlich model. The slope values of the isotherm (N) ranged from 0.84 to 0.90 (atrazine) and from 0.75 to 0.79 (diuron) for the lithosequence samples. Sorption of diuron was high regardless of the soil texture or the concentration added. The desorption isotherms for atrazine and diuron showed good fit to the Freundlich equation (R ² ≥ 0,87). Atrazine slope values for the desorption isotherms were similar for the different concentrations and were much lower than those observed for the sorption isotherms. Significant hysteresis was observed in the herbicide desorption. When the two herbicides were compared, it was found that diuron (N = 0.06–0.22) presented more pronounced hysteresis than atrazine. The results showed that, quantitatively, a greater atrazine fraction applied to these soils remains available to be leached in the soil profile, as compared to diuron.     

Phytotoxicity of atrazine, isoproturon, and diuron to submersed macrophytes in outdoor mesocosms

The submersed macrophytes Elodea canadensis, Myriophyllum spicatum and Potamogeton lucens were constantly exposed over a five-week period to environmentally relevant concentrations of atrazine, isoproturon, diuron, and their mixture in outdoor mesocosms. Effects were evaluated investigating photosynthetic efficiency (PE) of the three macrophytes and growth of M. spicatum and E. canadensis. Adverse effects on PE were observed on days 2 and 5 after application. M. spicatum was found to be the more sensitive macrophyte. E. canadensis and P. lucens were less sensitive to atrazine, diuron and the mixture and insensitive to isoproturon. PE of M. spicatum was similarly affected by the single herbicides and the mixture demonstrating concentration addition. Growth of E. canadensis and M. spicatum was not reduced indicating that herbicide exposure did not impair plant development. Although PE measurements turned out to be a sensitive method to monitor PSII herbicides, plant growth remains the more relevant ecological endpoint in risk assessment.     

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.     

Impact of hairy vetch cover crop on herbicide transport under field and laboratory conditions.

This study was conducted to evaluate the effect of hairy vetch cover crop residue on runoff losses of atrazine and metolachlor under both no-till corn field plots and from a laboratory runoff system. A 2-year field study was conducted in which losses of atrazine and metolachlor from vetch and non-vetch field plots were determined from the first runoff event after application (5 and 25 days after application in 1997 and 1998, respectively). A laboratory study was conducted using soil chambers, designed to simulate field soil, water, vegetation, and herbicide treatment conditions, subjected to simulated rain events of 5, 6, 20 and 21 days after application, similar to the rainfall pattern observed in the field study. Atrazine losses ranged from 1.2 to 7.2% and 0.01 to 0.08% and metolachlor losses ranged from 0.7 to 3.1% and 0.01 to 0.1% of the amount applied for the 1997 and 1998 runoff events, respectively. In the laboratory study, atrazine runoff losses ranged from 6.7 to 22.7% and 4.2 to 8.5% and metolachlor losses ranged from 3.6 to 9.8% and 1.1 to 4.7% of the amount applied for the 5-6 and 20-21 day events, respectively. The lower losses from the field study were due to smaller rainfall amounts and a series of small rains prior to the runoff event that likely washed herbicides off crop residue and into soil where adsorption could occur. Runoff losses of both herbicides were slightly higher from non-vetch than vetch field plots. Losses from the laboratory study were related to runoff volume rather than vegetation type.     

Application of an artificial sea salt solution to determine acute toxicity of herbicides to Proisotoma minuta (Collembola)

The acute toxicity test is described in this experiment where the Collembola species Proisotoma minuta was exposed to herbicides in an artificial sea salt solution for seven days. The salt solution did not prohibit the insects' reproduction system. The seven day LD50 values for trifluralin, pendimethalin, metolachlor, prometryn, paraquat, atrazine, fluometuron, and diuron were 3.48, 10.4, 12.4, 13.0, 23.1, 33.4, 250, and 711 mg L(-1), respectively. A good correlation between toxicity of the compounds and their lipophilicity and vapor pressure was recorded in this study.     

Assessment of metolachlor and diuron leaching in a tropical soil using undisturbed soil columns under laboratory conditions

In the present study, diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-metoxi-1-methylethyl)acetamide] leaching was studied in undisturbed soil columns collected in a cotton crop area in Mato Grosso State, Brazil. The pesticides were applied to the soil surface in dosages similar to those used in a cotton plantation. To assess the leaching process, soil columns were submitted to simulated rain under laboratory conditions at 25 ± 3°C, in the absence of wind and direct solar radiation. During the rain simulations, leachate solutions were collected and herbicide concentrations were determined. At the end of the experiment, the soil columns were cut into 10 cm sections to determine the remaining herbicide concentrations through the soil profile. Metolachlor was detected in all soil sections, and approximately 4% of the applied mass was leached. Diuron was detected only in the upper two soil sections and was not detected in the leachate. A linear correlation (r > 0.94) between the metolachlor soil concentrations and the organic contents of the soil sections was observed. Mass balance suggests that around 56% of diuron and 40% of metolachlor were degraded during the experiments. Measurements of the water table depth in the area where the samples were collected showed that it varied from 2 to 6 m and is therefore vulnerable to contamination by the studied herbicides, particularly metolachlor, which demonstrated a higher leaching potential.     

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.     

Sorption of atrazine and metolachlor by burrow linings developed in soils with different crop residues at the surface

Atrazine and metolachlor sorption by earthworm (Lumbricus terrestris L.) burrows was measured by introducing herbicides into the burrows and collecting the effluent between 0 to 3, 3 to 6, and 6 to 9 min of simulated burrow flow. On average, sorption by burrow linings reduced the herbicide concentration to 78% (atrazine) and 74% (metolachlor) of the applied herbicide solution concentration. For both herbicides, the amount sorbed was dependent on the food source available to the earthworm, as well as the duration of burrow flow. On average, soybean-fed- and corn-fed-earthworm-burrows significantly retained more herbicides relative to the Control Treatment (unfed-earthworms). More herbicides were transported through the burrows with time because the lateral flow movement from the burrow wall into the soil matrix decreased. It is also likely that herbicides retained on burrow linings during the first 3 min of flow saturated the adsorption sites on the burrow wall, which decreased the subsequent retention potential of herbicides in flow between 3 to 9 min. Based on these results, we conclude that herbicide transport through earthworm burrows in the field will be related to crop and crop residue management practices.     

Grab and passive sampling applied to pesticide analysis in the São Lourenço river headwater in Campo Verde – MT,Brazil

In this study, the quality of surface water in the headwaters of São Lourenço River in Mato Grosso, Brazil, was evaluated in relation to contamination by pesticides. For this purpose, samples were collected between December 2015 and June 2016 by grab sampling and by passive sampling using an integrative polar organic compound sampler installed in the field during four 14-day cycles between March and June 2016. The analyses were performed by gas chromatography (CG/MS) and by liquid chromatography (UPLC-MS/MS). The results showed the detection of two pesticides (atrazine and pyraclostrobin) of the five analyzed by passive sampling and eight active principles among the 20 analyzed (malathion, diuron, carbofuran, carbendazim, trifluralin, imidacloprid, metolachlor, and acetamiprid) by grab sampling. The detection of 10 pesticides, even almost a decade after the beginning of a recovery process of the ciliary forest, confirms the headwaters' vulnerability to these contaminants and passive sampling proved to be an important tool in capturing small concentrations of pesticides constituting an interesting complement to grab sampling.     

Sorption kinetics of atrazine and diuron in soils from southern Brazil

Sorption kinetics of atrazine and diuron was evaluated in soil samples from a typical landscape in Paraná. Samples were collected (0-20 cm) in a no-tillage area from Mamborê, PR, which has been cultivated under a crop rotation for the last six years. Six sampling points of the slope were selected to represent a wide range of soil chemical and physical properties found in this area. Radiolabeled tracers (14C-atrazine and 14C-diuron) were used and the radioactivity was detected by liquid scintillation counting (LSC). Sorption was accomplished for increasing equilibration periods (0.5, 1.5, 3, 6, 12, 24, and 48 h). Kinetics data fitted adequately well to Elovich equation, providing evidences that soil reaction occurs in two distinct stages: a fast, initial one followed by a slower one. During the fast phase, 34-42 and 71-79% of total atrazine and diuron applied were sorbed to soil samples. No important differences were found among combinations of soil and herbicide sorption during the slow phase. The unrealistic conditions under batch experiments should be overestimating sorption in the fast phase and underestimating diffusion in the slow phase. Sorption of both herbicides was positively correlated to organic carbon and clay contents of soils, but atrazine was much less sorbed than diuron, showing its higher potential to contaminate groundwater, specially in sandy, low organic carbon soils.     

Application of an Artificial Sea Salt Solution to Determine Acute Toxicity of Herbicides to Proisotoma minuta (Collembola)

The acute toxicity test is described in this experiment where the Collembola species Proisotoma minuta was exposed to herbicides in an artificial sea salt solution for seven days. The salt solution did not prohibit the insects' reproduction system. The seven day LD₅₀ values for trifluralin, pendimethalin, metolachlor, prometryn, paraquat, atrazine, fluometuron, and diuron were 3.48, 10.4, 12.4, 13.0, 23.1, 33.4, 250, and 711 mg L^?1, respectively. A good correlation between toxicity of the compounds and their lipophilicity and vapor pressure was recorded in this study.     

Sorption Kinetics of Atrazine and Diuron in Soils from Southern Brazil

Abstract

Sorption kinetics of atrazine and diuron was evaluated in soil samples from a typical landscape in Paraná. Samples were collected (0–20 cm) in a no-tillage area from Mamborê, PR, which has been cultivated under a crop rotation for the last six years. Six sampling points of the slope were selected to represent a wide range of soil chemical and physical properties found in this area. Radiolabeled tracers (¹⁴C-atrazine and ¹⁴C-diuron) were used and the radioactivity was detected by liquid scintillation counting (LSC). Sorption was accomplished for increasing equilibration periods (0.5, 1.5, 3, 6, 12, 24, and 48 h). Kinetics data fitted adequately well to Elovich equation, providing evidences that soil reaction occurs in two distinct stages: a fast, initial one followed by a slower one. During the fast phase, 34–42 and 71–79% of total atrazine and diuron applied were sorbed to soil samples. No important differences were found among combinations of soil and herbicide sorption during the slow phase. The unrealistic conditions under batch experiments should be overestimating sorption in the fast phase and underestimating diffusion in the slow phase. Sorption of both herbicides was positively correlated to organic carbon and clay contents of soils, but atrazine was much less sorbed than diuron, showing its higher potential to contaminate groundwater, specially in sandy, low organic carbon soils.