Water-soluble Herbicide Research Articles

Changes in juvenile coho salmon electro‐olfactogram during and after short‐term exposure to current‐use pesticides

For anadromous salmonids, olfaction is a critical sense, enabling return migration. In recent years, several pesticides have been identified that interfere with salmonid olfaction at concentrations in the microg/L range; thus, they may pose a risk to species longevity. In the present study, we investigated the acute effects of five agricultural pesticides on juvenile coho salmon (Oncorhynchus kisutch) olfaction using the electro-olfactogram (EOG), a measure of odorant-evoked field potentials. Electro-olfactogram responses to the odorant L-serine were measured during and following a 30-min exposure of the left olfactory rosette to chlorothalonil, endosulfan, glyphosate acid, iodocarb (IPBC), trifluralin, and 2,4-dichlorophenoxyacetic acid. With the relatively insoluble pesticides endosulfan and trifluralin, decreases in EOG amplitude were only apparent at relatively high concentrations (100 and 300 microg/L, respectively) following 20 min of exposure and were absent for chlorothalonil (1 mg/L). With the water-soluble herbicide glyphosate, significant EOG reductions occurred within 10 min of exposure to 1 mg/L and more rapidly with higher concentrations. Recovery of EOG post-glyphosate exposure was concentration-dependent, and complete recovery was not observed with some concentrations at 60 min postexposure. Dichlorophenoxyacetic acid only affected EOG at high concentration (100 mg/L), where it eliminated EOG within 2 min of exposure. With IPBC, EOG was decreased at 25 min of exposure to 1 microg/L; higher concentrations caused decreases to occur more rapidly. Excluding IPBC and glyphosate, all EOG reductions occurred at concentrations greater than the current Canadian water-quality guidelines and reported 96-h lethality values. Our results show that olfactory neurons can be impaired rapidly by some current-use pesticides, even at exposures in the low-microg/L range.

Vegetated biofilters: The relative importance of infiltration and adsorption in reducing loads of water-soluble herbicides in agricultural runoff

Abstract Runoff from cropland containing agricultural pesticides is the main contributor to poor water quality on the Liverpool Plains, Australia. The potential for vegetated biofilters to reduce the loads of two moderately soluble herbicides (atrazine and metolachlor) in runoff water was studied in grassed filter strips (1.25 m × 4 m) on cracking vertisol soil. Run-on with known concentrations of herbicide and sediment was introduced to field plots as surface flow. Cumulative depths of 80, 160, 320 and 800 mm were applied to dry, cracked soil, and 20, 40, and 80 mm to plots that had previously been watered in an attempt to induce crack closure. Volumes of runoff and pollutant concentrations were measured to allow load reduction to be partitioned between infiltration and reduced concentration. Biofilters reduced total loads by 40–85% for atrazine, 44–85% for metolachlor and 57–93% for sediment, demonstrating their benefits even where run-on depths are high. The reduction in atrazine and metolachlor concentrations was substantial (∼25–49% and ∼30–61%, respectively) for run-on depths of 80 mm or less, despite the moderate solubility of atrazine (∼33 mg L−1) and high solubility of metolachlor (520 mg L−1). Loads of sediment were reduced at even greater total run-on depths (up to 320 mm). Where run-on depths were in the range 160–800 mm, infiltration was the only mechanism that significantly reduced herbicide loads. The possible errors associated with small plot studies are discussed. The clarification of role of adsorption and infiltration in filtering processes provides a foundation for improving simulation models in order to produce realistic appraisal of biofilter effectiveness.

A review of the effects of humidity, humectants, and surfactant composition on the absorption and efficacy of highly water-soluble herbicides

It is well known that environmental conditions have an important influence on herbicide efficacy. In particular, the effect of humidity on herbicide uptake has been attributed to changes in cuticle hydration and droplet drying. As early as the 1950s, it was hypothesized that humectants such as glycerol would enhance herbicide uptake by not letting droplets dry, thus maintaining the herbicide in solution, and hence making it available for uptake. Shortly thereafter, evidence was found to support this hypothesis and humectants were used successfully in warm, dry areas to increase herbicide efficacy. However, by the mid-1980s, there was little use of humectants as research on humectants gave way to investigations on the effect of ethylene oxide (EO) content on surfactant performance to improve herbicide uptake and efficacy. While ethoxylated surfactants effectively increase the uptake of both lipophilic and hydrophilic herbicides, the suggestion that long EO chains have humectant properties is misleading, since the studies that led to this suggestion were performed at high humidity, which would prevent rapid droplet drying. Furthermore, current evidence suggests that highly water-soluble, ionic herbicides may be more sensitive to low humidity and rapid drop drying than lipophilic herbicides. Therefore, an overview is presented on the interaction of water-soluble herbicides with surfactants, the cuticle, and humidity, with particular emphasis on the impact of low humidity and humectants on herbicide uptake. It was found that when one focuses on research performed at low humidity the importance of humectants emerges, which is not in keeping with what is now commonly accepted.

Soil characteristics and water potential effects on plant-available clomazone in rice

Clomazone has been successfully used for weed control in rice, but crop injury is a potential problem on light-textured soils. Experiments were conducted to determine the effect of soil characteristics and water potential on plant-available clomazone and rice injury. A centrifugal double-tube technique was used to determine plant-available concentration in soil solution (ACSS), total amount available in soil solution (TASS), and Kdvalues for clomazone on four soils at four water potentials. A rice bioassay was conducted parallel to the plant-available study to correlate biological availability to ACSS, TASS, and Kd. TASS was significantly different in all soils. The order of increasing TASS for the soils studied was Morey < Edna < Nada < Crowley, which correlated well with soil characteristics. The order of increasing TASS after equilibrium was − 90 < − 75 < − 33 < 0 kPa. TASS values at 0 kPa were greater than two times the TASS values at − 90 kPa. It appears that severe rice injury from clomazone on these soils could occur if TASS > 110 ng g−1and Kd< 1.1 ml g−1. We propose that the double-tube technique provides a more accurate estimate of available herbicide because the solution–soil ratios are < 0.33:1 and would be more representative of a plant root–herbicide relationship. This technique or some variation possibly could be further developed such that clomazone rates could be more clearly defined particularly on lighter-textured soils. TASS may be a better predictor of plant-available herbicide than ACSS when evaluating moderately to highly water-soluble herbicides in a nonsaturated soil environment.

Herbicide Losses in Runoff of Containerized Plant Production Nurseries

Herbicide use in containerized plant production nurseries is a vital tool for weed management and the production of plants desired by the consumer. Clemson University researchers have conducted studies aimed at determining the amount of herbicide runoff during normal nursery operation, if herbicides accumulate in containment ponds at nurseries, and how herbicide runoff could be reduced. A 2-year study at commercial nurseries found that herbicide concentrations were higher in containment ponds soon after herbicide application, when compared with months with less herbicide application; and herbicides did not accumulate over the 2-year period. Herbicide runoff was greatest immediately after application and up to 15% of the herbicide applied was lost in the first irrigation event after application when using more water soluble herbicides. Bed material and herbicide formulation were also important in determining the amount of herbicide lost. Total losses were highest from plastic- and fabric-covered beds when using granular formulations and highest from gravel beds when spray formulations were used. The combination of using cyclic irrigation and grass waterways resulted in a reduction of about 25% of isoxaben loss when compared with clay and gravel waterways with continuous irrigation. The effects of reduced herbicide treatments compared to standard spray schedules were evaluated on herbicide transport, weed development, and plant growth and health. Results indicated that plant marketability was not affected, and total herbicide runoff was significantly reduced. Based on these studies, several recommendations can be made to commercial container plant production nurseries, which should reduce herbicide runoff and thereby reduce the environmental concerns associated with nurseries.

SUSCEPTIBILITY OF INDIANA WATERSHEDS TO HERBICIDE CONTAMINATION1

ABSTRACT: An index of watershed susceptibility to surface water contamination by herbicides could be used to improve source water assessments for public drinking water supplies, prioritize watershed restoration projects, and direct funding and educational efforts to areas where the greatest environmental benefit can be realized. The goal of this study is to use streamflow and herbicide concentration data to develop and evaluate a method for estimating comparative watershed susceptibility to herbicide loss. United States Geological Survey (USGS) concentration data for five relatively water soluble herbicides (alachlor, atrazine, cyanazine, metolachlor, and simazine) were analyzed for 16 Indiana watersheds. Correlation was assessed between observed herbicide losses and: (1) a herbicide runoff index using GIS‐based land use, soil type, SCS runoff curve number, tillage practice, herbicide use estimates, and combinations of these factors; and (2) predicted herbicide losses from a non‐point source pollution model (NAPRA‐Web, an Internet‐based interface for GLEAMS). The highest adjusted R2value was found between herbicide concentration and the runoff curve number alone, ranging from 0.25 to 0.56. Predictions from the simulation model showed a poorer correlation with observed herbicide loss. This indicates potential for using the runoff curve number as a simple herbicide contamination susceptibility index.

Organoclays for controlled release of the herbicide fenuron.

Organoclays were assayed as matrices in which to associate herbicides, with the aim of decreasing product losses that could give rise to water contamination from agricultural activities. Fenuron was selected as model of a very mobile and highly water-soluble herbicide. Two different organoclays of high (A-HDT) and low (H-C18) reversible fenuron sorption were selected. Herbicide-organoclay complexes were prepared from the two organoclays and with two different fenuron contents (20 and 40 g AI kg-1) and two different mixing times, so as to form a series of weak and strong complexes. The release of fenuron from those complexes into water and water/soil suspensions gave values of T50 (time to release 50% of the fenuron content) ranging from 0.3 min to 2400 h. The total fenuron released in these closed systems ranged from 48 to 80% of the fenuron in the complex. The organoclay type (high or low sorptivity) had the greatest influence on fenuron release, followed by the strong or weak complex, suggesting that herbicide-organoclay interactions are the main factors controlling release. Soil column leaching experiments showed fenuron-organoclay complexes to be effective in reducing the peak herbicide concentration in the leachate to a half (6 microns) or a quarter (3 microns) of that obtained from the free technical compound (12 microns). Herbicide lost through leaching was reduced from 78% for the free technical fenuron to 50-30%, depending on the organoclay used as carrier and the strength of the complex. Bioassay with ryegrass showed that the weak fenuron/H-C18 complex (40 g AI kg-1) gave the same herbicidal activity as technical fenuron. The potential suitability of low-sorptive organoclays for conferring slow-release properties on the fenuron complex has been demonstrated.

Relationship between the swelling process and the releases of water soluble agrochemicals from radiation crosslinked acrylamide/itaconic acid copolymers

An attempt was made in this study to relate the releases of water soluble herbicide (sodium 2,2 dichloropropionate (Dowpon)) and model fertilizers (ammonium nitrate, potassium nitrate and ammonium sulfate) from the cylindrical devices of radiation crosslinked poly(acrylamide/itaconic acid) (AAm/IA) copolymers with the swelling that may effect the release behaviour. AAm/IA copolymers containing agrochemicals are prepared by two different composition of itaconic acid and two different γ-rays doses. The agrochemicals were trapped in the gels by including it in the feed mixture of radiation polymerization. The equilibrium swelling, diffusional exponent, and diffusion and intrinsic diffusion coefficients of the process were obtained. The agrochemical dissolution was determined by conductimetric method. The maximum concentrations of releasing agrochemicals and initial releasing rates were calculated by using of second order kinetics equation. The agrochemical releases appeared to be controlled by swelling. As a result, if AAm/IA hydrogels containing agrochemicals were swelled in water, release of agrochemicals was decreased with the raising of γ-rays doses and itaconic acid quantities in the hydrogel.

Adsorption of Highly Soluble Herbicides from Water Using Activated Carbon and Hypercrosslinked Polymers

Adsorption of water-soluble herbicides, namely benazolin, bentazone, imazapyr and triclopyr, has been investigated using commercial Chemviron F-400 activated carbon and Purolite MN-200 hypercrosslinked polymer. Batch adsorption isotherms at pH 3 and 10 show that adsorption of water-soluble herbicides is significantly greater on F-400 than MN-200. Rapid small-scale mini-column adsorption studies of each herbicide on F-400 and MN-200 have also been performed. For Chemviron F-400, the breakthrough of each herbicide at the EU limit of 0.1 μg l-1 is as follows: imazapyr (80,000 BV), bentazone (105,000 BV), benazolin (140,000 BV) and triclopyr (160,000 BV). These experiments operated at an emptybed- contact-time (EBCT) of 2.3 secondswith feed water containing 20 μg l-1 of each herbicide in the absence of natural organic matter. MN-200 is less effective in removing these herbicides from contaminated water under similar conditions. The presence of fulvic acid in the feed water significantly diminishes the uptake of each herbicide for F-400 and MN-200. Low temperature regeneration of Chemviron F-400 activated carbon and Purolite MN-200 hypercrosslinked polymer was achieved using ethanol solution at 50°C and pH 12. Virtually complete regeneration is achieved with MN-200 in 10 BV. Approximately 200 BV of eluent is required with F-400 and the regenerant efficiencies are about 100%for benazolin and triclopyr and about 40-50% for bentazone and imazapyr after two cycles.

Micro-organic compounds in the Humber rivers

The concentrations of a range of micro-organic compounds in the Humber rivers have been measured at weekly intervals over a period of 1 year. The compounds include the triazine herbicides (simazine, atrazine, propazine, desmetryn and prometryn), selected organophosphorus insecticides (fenitrothion, malathion and parathion), phenylurea (chlorotoluron, diuron, isoproturon and linuron) and phenoxyacid herbicides (2,4-D, MCPA, MCPB and mecoprop), phenol derivatives (phenol, 2-ethylphenol, 2-chlorophenol, 4-nitrophenol, 2-methylphenol, 4-ethylphenol and 2,4-dichlorophenol), organochlorine insecticides (HEOD, DDT, TDE, DDE, HCB, α-BHC and lindane), PCB's and some synthetic pyrethroid insecticides ( cis/trans-permethrin, fenvalerate and cypermethrin). The results indicate the high frequency of occurrence of many compounds in the southern Humber rivers Aire, Calder, Trent and Don compared with the more occasional concentrations found in the upland rivers with catchments dominated by low intensity agriculture. The more water soluble herbicides, atrazine, simazine, isoproturon and diuron are detected frequently in the southern rivers with the highest concentrations and abundance in the rivers Aire, Calder and Trent. The most abundant phenolic compound is 2,4-dichlorophenol usually occurring at concentrations <1 μg/1. The organochlorine insecticides and PCB's are generally at concentrations < 0.01 μg/l. cis/trans-permethrin are the only synthetic pyrethroids detected and these are found in the rivers Aire and Calder at about equal concentrations of between 0.01 and 0.11 μg/1. The results of the occurrence of simazine and atrazine in the rivers Trent, Don and Aire illustrate peaks in concentration in the spring and then later in the year during the early autumn coinciding with the first major storm after the summer. In the rivers Trent and Don, the annual exports (March 1994–1995) of atrazine are lower than for simazine whereas in the R. Calder the yield of atrazine is higher than for simazine suggesting differences in use in these catchments. The maximum triazine concentration observed, i.e. 8 μg/l of atrazine in the R. Calder, could have inhibiting effects on the phytoplankton and algal growth, although because of the transient nature of the peaks, recovery is expected to be rapid. The only other compounds measured at concentrations likely to produce detrimental ecotoxicological effects are cis/trans permethrin in the rivers Aire and Calder.

Root hair infection and nodule to lateral root relationship in lucerne seedlings as influenced by dalapon and amitrole

The effect of two water soluble herbicides, dalapon and amitrole, on the early stages of nodulation was studied. Though curling, deformation and shepherd's crook formation of root hairs were not affected, the number of nodules generally decreased in the presence of the herbicides, accompanied by an increase in the number of lateral roots in some treatments. The results provide experimental evidence in favour of the speculations of some earlier workers on lateral root and nodule relationship in herbicide treated plants.

Effect of Simulated Rainfall on Herbicide Performance

Studies were conducted to determine the effect of simulated rainfall on the phytotoxicity of several herbicides. Oil soluble herbicides 4,6-dinitro-o-sec-butylphenol (DNBP), pentachlorophenol (PCP), a 1:1 mixture of the butyl esters of 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid (2,4-D: 2,4,5-T), and a 2:2:1 mixture of the isooctyl esters of 2,4–13:2,4,5-T: 4-amino-3,5,6-trichloropicolinic acid (picloram) (hereinafter referred to as M-3140), usually were less affected by artificial rainfall than were water soluble 1,1'-dimethyl-4,4'-bipyridinium salt (paraquat), dimethylarsinic acid (cacodylic acid), and cis-2,3,5,5,5-pentachloro-4-ketopentenoic acid (hereinafter referred to as AP-20), on guava (Psidium guajava L.) and mango (Mangifera indica L.). Washing reduced the activity of some oil and water-soluble herbicides on sorghum (Sorghum bicolor (L.) Moench, var. Combine Kafir-60) and dioscorea (Dioscorea composita Hemsl). As herbicide rates were increased, washing reduced the phytotoxicity of paraquat and 2,4-D:2,4,5-T less on mango and guava. Artificial rainfall applied as a mist spray at different intervals had no effect on the phytotoxicity of paraquat; it reduced the activity of cacodylic acid and increased the effectiveness of AP-20 on mango.

LABORATORY STUDIES ON GLYCERIN AS A SUPPLEMENT IN WATER–SOLUBLE HERBICIDAL SPRAYS

WATER-SOLUBLE herbicides such as arsenicals and ammonium sulfamate, applied as sprays, have shown considerable promise for eradication of noxious vegetation. However, results with sprays have been highly variable and, due to the high concentrations of herbicide required, relatively expensive. In order to increase the effectiveness of herbicidal sprays, the following laboratory studies were undertaken during the winter season of 1943-44, to determine the factors that promote transfer of sprayed herbicides from the leaves to the base of the stem. PROCEDURE.-The tests were conducted on potgrown plants about 6 inches tall which could be easily manipulated so as to expose them to different conditions and treatments. The results given in this report were obtained with Coleus blumei Benth. and Cuphea platycentra Lem., two common house plants. The two species appeared to react similarly, so that the principles determined in this investigation may be applicable to a number of species. Two methods of application were used in the study. In the one, referred to as tip-injection, the solution of poison was placed in a small vial which was so suspended that the tip of the plant could be dipped into the liquid. This method, although not a practical field technique, indicated experimentally the action of the poison in penetrating and being conducted downward through the stem when the foliage was in continuous contact with the herbicide solution. In the second technique, referred to as leaf application, the solution was applied with a camel's hair brush to the upper leaves. This method was analogous to spraying of sprouts in the field. The solutions dried on the surface of the leaf within a short time, usually 10 to 15 minutes. For the leaf application technique, a commercial sodium lauryl sulfate mixture was added to the herbicide solutions at a rate of 0.12 per cent to serve as a wetting agent.