Levels of organochlorine pesticides in soils and rye plant tissues in a field study

The organochlorine pesticides are lipophilic and persistent and tend to accumulate in soils and growing plants. The contamination of growing plants occurs by adhesion of volatile substances from the air to the plant surface and by the migration of contaminants through xylem in inner ascendant transport. Persistent organochlorine pesticides (HCB, alpha,gamma-HCH, pp'DDE, op'DDT, pp'DDT) levels were determined in soils and rye plants. The aims of the study were the monitoring of organochlorine pesticide concentrations and the comparison of these levels among soil, rye straw, and rye grains. Fifty soil samples and 50 rye plant (50 straw and 50 grains) samples were taken. The GLC-ECD chromatographic results indicated the following contamination levels distributed among soil, straw, and grains: HCB (0.7-1.2-0.7 microg.kg(-1)), alpha-HCH (0.6-3.4-1.2 microg.kg(-1)), gamma-HCH (1.8-27.3-4.4 microg.kg(-1)), Sigma-HCH (2.5-30.7-5.6 microg.kg(-1)), pp'DDE (1.0-7.8-5.5 microg.kg(-1)), op'DDT (16.1-20.4-17.0 microg.kg(-1)), pp'DDT (38.0-41.7-49.6 microg.kg(-1)), and Sigma-DDT (54.2-63.2-72.1 microg.kg(-1)). The study verified the presence of organochlorine pesticides in the Mexican agricultural environment and their migration from soil to the growing rye plants. However, DDT has been banned since 1999 for sanitary reasons, and Lindane is applied only in some cases as a seed dresser. The determined organochlorine pesticide levels in rye plants are low, at residual levels that are below Codex Alimentarius Commission maximum residue limits.     

Pesticide Leaching from Agricultural Fields with Ridges and Furrows

In the evaluation of the risk of pesticide leaching to groundwater, the soil surface is usually assumed to be level, although important crops like potato are grown on ridges. A fraction of the water from rainfall and sprinkler irrigation may flow along the soil surface from the ridges to the furrows, thus bringing about an extra load of water and pesticide on the furrow soil. A survey of the literature reveals that surface-runoff from ridges to furrows is a well-known phenomenon but that hardly any data are available on the quantities of water and pesticide involved. On the basis of a field experiment with additional sprinkler irrigation, computer simulations were carried out with the Pesticide Emission Assessment at Regional and Local scales model for separate ridge and furrow systems in a humic sandy potato field. Breakthrough curves of bromide ion (as a tracer for water flow) and carbofuran (as example pesticide) were calculated for 1-m depth in the field. Bromide ion leached comparatively fast from the furrow system, while leaching from the ridge system was slower showing a maximum concentration of about half of that for the furrow system. Carbofuran breakthrough from the furrow system began about a month after application and increased steadily to substantial concentrations. Because the transport time of carbofuran in the ridge soil was much longer, no breakthrough occurred in the growing season. The maximum concentration of carbofuran leaching from the ridge-furrow field was computed to be a factor of six times as high as that computed for the corresponding level field. The study shows that the risk of leaching of pesticides via the furrow soil can be substantially higher than that via the corresponding level field soil.     

Effects of the soil on the activity of pentachlorophenol

There is little doubt that pesticides have contributed in no small measure to modern agriculture. However, it is apparent that many pesticides pollute agricultural products, soils, and water, affecting ecosystems. Pesticides should be examined not only from the standpoint of expanding agricultural production but also the aspect of environmental pollution should be considered. The major fractions of the pesticides applied to crops are known to enter the soil eventually, where they follow various fates, such as; absorption by organisms including crop plants, adsorption by soil colloids, chemical and biological degradation and decomposition, leaching from soils with gravitational water, all according to the properties of the pesticide, the nature of the soil and climate.     

An assessment of potential pesticide transmission,considering the combined impact of soil texture and pesticide properties: A meta-analysis

Pesticides are widely employed as a cost-effective means of reducing the impacts of undesirable plants and animals. The aim of this paper is to develop a risk ranking of transmission of key pesticides through soil to waterways, taking into account physico-chemical properties of the pesticides (soil half-life and water solubility), soil permeability, and the relationship between adsorption of pesticides and soil texture. This may be used as a screening tool for land managers, as it allows assessment of the potential transmission risks associated with the use of specified pesticides across a spectrum of soil textures. The twenty-eight pesticides examined were differentiated into three groups: herbicides, fungicides and insecticides. The highest risk of pesticide transmission through soils to waterways is associated with soils containing <20% clay or >45% sand. In a small number of cases, the resulting transmission risk is not influenced by soil texture alone. For example, for Phenmedipham, the transmission risk is higher for clay soils than for silt loam. The data generated in this paper may also be used in the identification of critical area sources, which have a high likelihood of pesticide transmission to waterways. Furthermore, they have the potential to be applied to GIS mapping, where the potential transmission risk values of the pesticides can be layered directly onto various soil textures.     

Environmental distribution of acetochlor, atrazine, chlorpyrifos, and propisochlor under field conditions

The environmental behavior, movement, distribution, persistence, and runoff by rainfall of the pesticides acetochlor, atrazine, chlorpyrifos, and propisochlor were studied under field conditions during a five-month period at normal weather conditions. The pesticide concentrations in soil depths of 0-5 and 5-20 cm, and in sediment and runoff water samples (collected from an artificial reservoir built in the lower part of the experimental plot) were measured every second week and following every runoff event. The contamination of a stream running across the lowest part of the plot was also monitored. The weather conditions were also recorded at the experimental site. The pesticide residues were quantified by a capillary gas chromatograph equipped with a nitrogen phosphorus selective detector (GC-NPD). There was a consistent decrease in pesticide residues in the 0-5 cm soil layer with time after spaying. At 140 days after treatment only atrazine and chlorpyrifos were present; acetochlor and propisochlor were not detected in this soil layer. Atrazine and chlorpyrifos in the soil at a depth of 5-20 cm were detectable during the whole experimental interval, whereas acetochlor and propisochlor concentrations were below the limit of detection. Pesticide losses by the surface runoff process and the contamination of the stream were closely related to the time of rainfall elapsed after treatment and amount of rain at the experimental plots. Losses were primarily dependent on surface rainfall volume and intensity. The maximum detected residues of atrazine and acetochlor in stream water were 1 order of magnitude higher than the maximum residue limit specified by the European Union (EU) for environmental and drinking water (0.1 microg/L for individual compounds and 0.5 microg/L for total pesticides). Chlorpyrifos and propisochlor were not detected in this matrix.     

Removal of carbaryl, linuron, and permethrin by Lupinus angustifolius under hydroponic conditions

The metabolism of organic pollutants by plants normally requires contaminant direct uptake by cells. Factors affecting this uptake and the later distribution of chemicals within the plant include the physicochemical properties of the compounds (concentration, structure, solubility, log k(ow), diffusion rate) and the biochemical characteristics of the plant. This paper reports the tolerance, uptake, and effects of the pesticides carbaryl, linuron, and permethrin on Lupinus angustifolius germination and growth as well as contaminant intraplant distribution and possible degradation. Lupine plants were grown in hydroponic culture containing either 1 or 5 mg of the individual pesticides, or combinations of these (1, 5, or 10 mg of each), in 100 mL nutrient and water solutions. Analysis of the remaining solutions 8 days post-germination showed the water solutions to have higher remaining pesticide concentrations than nutrient solutions. Furthermore, in the presence of pesticides, germination was more frequent in the water solutions. After 16 days of growth, the plants were harvested, and their tissues were microwaved digested and analyzed by reversed-phase liquid chromatography. Although only minor quantities of each pesticide were detected in plant tissues, their amount in the roots was higher than in the stems. No accumulation was noted in the cotyledons, and only 2% of linuron was detected in the leaves. Mass recovery at the end of the experiment showed that 57, 53, and 55% of carbaryl, linuron, and permethrin, respectively, were degraded and/or bound in an irreversible manner to plant material. The results suggest that L. angustifolius could be useful for the cleaning/remediation of pesticide-contaminated water.     

Lysimeter experiment to investigate the potential influence of diffusion-limited sorption on pesticide availability for leaching

Pesticide leaching from soil has been shown to decrease with increasing time from application to irrigation. It is hypothesized that the availability of compounds for leaching decreases due to diffusion and sorption inside soil aggregates. Previous work showed that pesticide sorption inside soil aggregates increases significantly during the first days after application. The study presented here tested if diffusion into aggregates could explain the leaching of four aged pesticides from manually irrigated soil cores. Azoxystrobin, chlorotoluron, cyanazine, and bentazone were applied to 30 undisturbed cores (25 cm long, 23.7 cm diameter) from a clay loam soil. The soil cores were irrigated 1, 3, 7, 14, and 28 days after application. Leachate was collected and analyzed. The amount of pesticide found in leachate decreased rapidly with time from application. Pesticide losses in leachate declined 2.5-27 times faster than total residues in soil. The decline was 4-5 times faster for the more strongly sorbed pesticides (azoxystrobin, chlorotoluron, and cyanazine) than for bentazone. In previous work, we derived a model to describe sorption and diffusion of the pesticides in small aggregates from the same soil. The diffusion model was used here to describe sorption inside the large aggregates in the soil cores and extended to describe pesticide leaching by interaggregate flow. The model showed a significant decline in leaching with time from application, which supports the theory that diffusion-limited sorption in aggregates influences the availability for pesticide leaching, although it does not exclude alternative explanations for this decline. The model well described the decline in leaching for three out of four pesticides. The interaggregate transport model could, however, not account for the amount of preferential flow in the cores and underestimated the leaching of bentazone.     

Pesticides‐non target plants interactions: An overview

Pesticides are widely used for crop protection in agriculture, plantation and forestry. Pesticides, when sprayed or dusted in the fields, only a small amount fall directly on the target organisms due to the small size and mobility of the pests. Most of them come to the soil or to the plants by direct precipitation or spray drift. Plants growing in the contaminated soil take up these chemicals along with water and mineral nutrients and translocate them to the aerial parts. Pesticides fallen on the leaf surface may find their way inside through leaf cuticle, stomata, hydrathodes, lenticels or tissues in the bark. Several factors influence pesticide uptake by plants. Pesticides are highly toxic chemicals and may not be absolutely specific in their actions. Impact of pesticide on plant depends upon its absorption, translocation and metabolism within the plant. Pesticides are usually detoxified in plants through series of degradation reactions and conjugation processes forming bound or insoluble residues. Failing to do so, plants show phytotoxic effects. Pesticides may affect different physiological processes in plants vital to their normal growth. They may also alter genetic materials in plants inducing gene mutation, chromosomal aberrations and chromosome break influencing their physiology and growth. Interaction of pesticides and their degradation products with non‐target plants is discussed here on different areas of research that are of particular interest in the context of this discussion.     

Computed leaching of pesticides from soil under field conditions

With a computer model, pesticide behavior in soil after spring application to a sandy loam field with a potato crop, was simulated. Special attention was paid to the risk of leaching through the upper meter of soil in catchment areas. Unsaturated water flow resulting from rainfall was modeled in some detail. Uptake of water and solute by the developing root system of the annual crop was included in the model. The computations were carried out for hypothetical pesticides with first-order decomposition rate constants in soil of 0.03, 0.01, 0.003, and 0.001 day^–1 at 20°C. Adsorption decreased with increasing soil depth and the adsorption coefficient for the top layer ranged from 0.0 to 10.0. For 20 combinations of decomposition rates and adsorption strengths, the extent of leaching from a top layer 1 m thick was computed. With a decomposition rate constant at 20°C of 0.03 day^–1 or higher, leaching was extremely low; with 0.01 days^–1 leaching was 1.7% of the dosage or lower. For compounds with a high persistence and mobility, leaching from the soil ranged up to about 10% of the dosage or more. Besides decomposition, uptake by plants was an important factor in reducing leaching, particularly for the weakly adsorbed and comparatively persistent compounds.     

The persistence and degradation of chlorothalonil and chlorpyrifos in a cranberry bog

The effect of a spray-tank adjuvant on the persistence, distribution, and degradation of two pesticides, chlorothalonil and chlorpyrifos, was studied in a commercial cranberry bog. Pesticides were applied according to label instructions to cranberry plants in paired plot studies. Dislodgeable foliar and whole fruit residues of both pesticides and several degradation products were assessed over a growing season. Residues were also assessed in soil samples collected at fruit harvest. Adjuvant increased both fruit and foliar residues but did not significantly alter the dissipation rate or metabolism of either pesticide. The dissipation of dislodgeable foliar chlorothalonil and chlorpyrifos residues followed first-order kinetics, with estimated half-lives of 12.7 and 3.5 d, respectively. All residue levels on harvested fruit were well below the current U.S. EPA tolerances for fresh cranberries. Chlorothalonil (58%) was the major residue in fruit at harvest (76 d post-chlorothalonil application), with 4-hydroxy-2,5,6-trichloroisophthalonitrile and 1,3-dicarbamoyl-2,4,5,6-tetrachlorobenzene accounting for 26% and 6% of the total residues, respectively. Degradation products accounted for 88% of the total chlorothalonil residues in soil at fruit harvest. The products 1,3-dicarbamoyl-2,4,5,6-tetrachlorobenzene, 1-carbamoyl-3-cyano-4-hydroxy-2,5,6-trichlorobenzene, 2,5,6-trichloro-4-methylthioisophthalonitrile, and 2,4,5-trichloroisophthalonitrile have not been previously identified in cranberry bog environments. Chlorpyrifos was detected in fruit at harvest (62 d post-chlorpyrifos application), but no metabolites were found. Chlorpyrifos-oxon and 3,5,6-trichloro-2-pyridinol, however, were detected in earlier fruit samples and in foliage and soil samples.     

Reduction of pesticide residues on produce by rinsing

In 1997 this laboratory initiated a research program with the objective of examining the effect that rinsing of produce with tap water would have on pesticide residues. Samples were obtained from local markets and/or grown at our experimental farm. Because approximately 35% of produce from retail sources contains pesticide residues, growing and treating produce at an experimental farm had the advantage that all such samples contain pesticide residues. Pesticides were applied under normal field conditions to a variety of food crops and the vegetation was allowed to undergo natural weathering prior to harvest. The resulting samples contained field-incurred or "field-fortified" residues. This experimental design was employed to mimic as closely as possible real world samples. Crops were treated, harvested, and divided into equal subsamples. One subsample was processed unwashed, whereas the other was rinsed under tap water. The extraction and analysis method used was a multi-residue method developed in our laboratory. Twelve pesticides were included in this study: the fungicides captan, chlorothalonil, iprodione, and vinclozolin; and the insecticides endosulfan, permethrin, methoxychlor, malathion, diazinon, chlorpyrifos, bifenthrin, and DDE (a soil metabolite of DDT). Statistical analysis of the data using the Wilcoxon signed-rank test showed that rinsing removed residues for nine of the twelve pesticides studied. Residues of vinclozolin, bifenthrin, and chlorpyrifos were not reduced. The rinsability of a pesticide is not correlated with its water solubility.     

明尼苏达州中北部沙漠地区灌水种植土豆的土壤中都尔(或: 异丙甲草胺)和嗪草酮的迁移与降解

Field studies were conducted to determine the dissipation and movement of metribuzin and metolachlor applied at conventional rates to a Verndale sandy loam (Udic Argiboroll) in north-central Minnesota under irrigated potato production in two years. The rapid dissipation of both metribuzin and metolachlor was found during the initial 10 to 15 days in both years, and more than 70% of the applied herbicide dissipated during this period. From 10 to 15 days after application up to the end of growing season in both years, the levels of both herbicides decreased slowly with time. Metolachlor dissipated at a slower rate than metribuzin in surface soil and could carry over to the next cropping season. Metribuzin and metolachlor were detected in only 6 and 1 of 154 soil samples in the first year and in 3 and 4 of 225 soil samples in the second year, taken from 15 to 75 cm, respectively. Fifty to 67% of water samples from suction samplers at 135-cm depth contained detectable levels (>0.4 μg L^-1) of herbicides in both years. Under laboratory conditions degradation of both herbicides was much slower than their dissipation in field. Therefore, it appeared that leaching might be an important dissipation pathway for metribuzin and metolachlor under irrigated potato production.     

Influence of compost of sewage sludge and low-quality water on pesticide uptake by tomato plants grown in an iron mine soil

Purpose

In mine soils, especially from arid or semiarid areas, the use of low-quality water for irrigation is a usual practice. Therefore to fill this gap, different experiments have been carried out to evaluate the effect of compost, pesticide and wastewater on the growth of tomato plants in a mine soil located at an iron extraction area.

Materials and methods

Soils proceeded from Alquife mine wastes whose most outstanding characteristics are alkaline conditions, low organic matter and electrical conductivity and high As concentration. The compost of sewage sludge (CSL) used to amend this soil had a slightly acid pH (6.8), EC 3.0?±?0.07 dS m^-1 (1/10 ratio, m/V) and 10 % organic carbon (OC) content. Irrigation was performed with distilled water (DW) or wastewater (WW) and two pesticides, the insecticide thiacloprid and the fungicide fenarimol, were applied to the soil. Tomato was grown directly from seeds on each pot. Four treatments with addition of pesticides were considered. For comparison purposes, two additional treatments without pesticides were also included.

Results and discussion

Addition of compost of sewage sludge led to a significant and sustained increase of soil OC content and dehydrogenase activity, while irrigation with wastewater had a slight or negligible effect on both properties. The plant species responded negatively to wastewater irrigation when this practice was undertaken with the application of both pesticides. No detectable amounts of thiacloprid, a relatively unstable and polar insecticide, were found in soil. The concentration of fenarimol in soil was higher after amendment with compost, but was not modified by irrigation with wastewater. In tomato shoots, the amounts of both pesticides were inversely correlated with final soil organic carbon, indicating that this soil property is relevant for their plant uptake. Besides, fenarimol concentrations in the soil and the tomato shoots were inversely related (r?=??0.836).

Conclusions

Tomato was not able to grow healthy in Alquife mine soil without compost addition. The irrigation with wastewater only reduced plant growth when used in combination with pesticides. Uptake of both pesticides by tomato plants was negligible according to the low bioaccumulation factor values, but was almost doubled for wastewater irrigation. Caution should be taken with the use of treated wastewater, because it may reduce plant growth in tomato that is a species sensitive to salinity.

     

Emission of Pesticides into the Air

During and after the application of a pesticide in agriculture, a substantial fraction of the dosage may enter the atmosphere and be transported over varying distances downwind of the target. The rate and extent of the emission during application, predominantly as spray particle drift, depends primarily on the application method (equipment and technique), the formulation and environmental conditions, whereas the emission after application depends primarily on the properties of the pesticide, soils, crops and environmental conditions. The fraction of the dosage that misses the target area may be high in some cases and more experimental data on this loss term are needed for various application types and weather conditions. Such data are necessary to test spray drift models, and for further model development and verification as well. Following application, the emission of soil fumigants and soil incorporated pesticides into the air can be measured and computed with reasonable accuracy, but further model development is needed to improve the reliability of the model predictions. For soil surface applied pesticides reliable measurement methods are available, but there is not yet a reliable model. Further model development is required which must be verified by field experiments. Few data are available on pesticide volatilization from plants and more field experiments are also needed to study the fate processes on the plants. Once this information is available, a model needs to be developed to predict the volatilization of pesticides from plants, which, again, should be verified with field measurements. For regional emission estimates, a link between data on the temporal and spatial pesticide use and a geographical information system for crops and soils with their characteristics is needed.

     

Loss of pesticides from a litchi orchard to an adjacent stream in northern Thailand

In the hill country of northern Thailand use of agrochemicals is increasing steadily and contaminating streams and groundwater. We have measured pesticide leached from a litchi orchard to an adjacent stream and identified the flow components contributing to the pesticide transport after installing two discharge measurement stations with automatic water samplers in the stream. For 2 years, between June and September, we applied methomyl, and in 1 year additionally chlorothalonil, to the 2‐ha orchard and monitored water fluxes and pesticide concentrations in the stream water. Pesticide loads ranged from 1.6 to 3% of mass applied for chlorothalonil, a strongly sorbing fungicide, and 6.4–11.4% for the more weakly sorbing insecticide methomyl. Directly after application, pesticide transport was dominated by a fast flow component, reaching the flume before the discharge peak. Later, pesticides were transported mainly by preferential interflow, which peaked about 30 hours after a rain event. The groundwater pathway was not found to contribute to pesticide loss. Antecedent rain conditions proved to be important for the pesticide transport behaviour. While at the beginning of the rainy season large falls of rain did not lead to pesticide contamination, at the end of the season pesticide transport was induced by as little as 0.1 mm of rain. The occurrence of preferential interflow means that the hilly regions in northern Thailand are highly susceptible to contamination by pesticides used by farmers.     

Analysis of pesticides in honey by solid-phase extraction and gas chromatography-mass spectrometry

An analytical method for the simultaneous determination of 51 pesticides in commercial honeys was developed. Honey (10 g) was dissolved in water/methanol (70:30; 10 mL) and transferred to a C(18) column (1 g) preconditioned with acetonitrile and water. Pesticides were subsequently eluted with a hexane/ethyl acetate mixture (50:50) and determined by gas chromatography with electron impact mass spectrometric detection in the selected ion monitoring mode (GC-MS-SIM). Spiked blank samples were used as standards to counteract the matrix effect observed in the chromatographic determination. Pesticides were confirmed by their retention times, their qualifier and target ions, and their qualifier/target abundance ratios. Recovery studies were performed at 0.1, 0.05, and 0.025 microg/g fortification levels for each pesticide, and the recoveries obtained were >86% with relative standard deviations of <10%. Good resolution of the pesticide mixture was achieved in approximately 41 min. The detection limits of the method ranged from 0.1 to 6.1 microg/kg for the different pesticides studied. The developed method is linear over the range assayed, 25-200 microg/L, with determination coefficients of >0.996. The proposed method was applied to the analysis of pesticides in honey samples, and low levels of a few pesticides (dichlofluanid, ethalfluralin, and triallate) were detected in some samples.     

宁南旱区沟垄覆盖改善土壤水热状况提高马铃薯产量

垄覆塑料地膜沟内覆盖集雨种植模式可影响土壤水热状况,促进作物生长,提高作物的产量和水分利用效率。为探讨旱作条件下沟垄二元覆盖的土壤水热效应对马铃薯产量的影响效果,于2015年在宁南旱区设置垄覆地膜沟内覆盖不同材料(普通塑料地膜、玉米秸秆、生物降解膜、麻纤维地膜及液态地膜),以垄覆地膜沟不覆盖为对照,研究沟垄二元覆盖模式对土壤水分、耕层土壤温度、马铃薯生长、产量及水分利用效率的影响。结果表明:垄覆地膜沟覆地膜处理在马铃薯前期、中期土壤蓄水量较对照显著增加(P0.05),垄覆地膜沟覆秸秆处理在马铃薯生育后期土壤蓄水量最高(P0.05)。垄覆地膜沟覆地膜处理增温效果明显,马铃薯全生育期0~25 cm土壤温度较对照显著增加(P0.05),而垄覆地膜沟覆秸秆处理较对照显著降低(P0.05)。在马铃薯整个生育期,垄覆地膜沟覆秸秆处理植株株高和茎粗均明显高于对照处理(P0.05),在马铃薯生育后期垄覆地膜沟覆秸秆处理的地上部生物量显著高于对照处理(P0.05)。沟垄二元覆盖模式下马铃薯增产效果以垄覆地膜沟覆秸秆处理最为显著,较对照增产56.1%(P0.05),且水分利用效率最高(81.1kg/(hm2·mm))。总之,垄覆地膜沟覆秸秆处理对改善土壤水热状况,提高马铃薯水分利用效率和产量的效果显著,建议在宁南旱区进行推广应用。     

Microbial toxicity and impacts on soil enzyme activities of pesticides used in potato cultivation

In the conventional cultivation of potatoes, weed control and the control of potato late blight caused by Phytophthora infestans are carried out by the application of herbicides and fungicides. We investigated the impacts of the herbicides metribuzin and linuron and the fungicide fluazinam on soil microbiota in microcosms, in mesocosms and in the field. The toxicity of each pesticide in solution was assessed using the luminescent bacteria test and in soil by a solid phase modification. In microcosm tests, the microbial activity and biomass were estimated by measuring several soil enzyme activities together with soil ATP content. In the mesocosm tests, the separate addition of each pesticide and the simultaneous use of all the pesticides were investigated. We monitored the impacts on ten different soil enzyme activities and measured soil toxicity with the luminescent bacteria test separately in the 5 cm top layer and in the layer from 5 to about 20 cm below the surface. During one season, the impact of the use of pesticides was monitored in the field in plots receiving pesticides for the third consecutive year and in control plots cultivated without the use of pesticides for the 3 preceding years. The pesticide concentrations were monitored in each experiment. The luminescent bacteria toxicity test revealed a strong inhibition by fluazinam. In microcosms the herbicides increased several enzyme activities but metribuzin inhibited luminescence in the bacterial test. Fluazinam was highly toxic in microcosms. In the mesocosm with combined use of pesticides, decreased activities of some enzymes were observed first in the surface soil and at harvesting also deeper in the soil. In the mesocosm experiment with separate use of pesticides, less impacts were observed. In the field experiment the pesticides decreased seven enzyme activities, when calculated per soil fresh weight but activities of four enzyme decreases if calculated per soil organic matter. Controlling weeds by herbicides decreased weed growth and the decreases in enzyme activities were interpreted to be due to the lack of the stimulating impact of weed roots. A strong inhibition in the soil toxicity test and continuing bioavailability of fluazinam were detected throughout the experiments even after winter in the field.     

Sorption-desorption of "aged" sulfonylaminocarbonyltriazolinone herbicides in soil

Sorption-desorption interactions of pesticides with soil determine the availability of pesticides in soil for transport, plant uptake, and microbial degradation. These interactions are affected by the physical and chemical properties of the pesticide and soil, and for some pesticides, their residence time in the soil. The objective of this study was to characterize sorption-desorption of two sulfonylaminocarbonyltriazolinone herbicides incubated in soils at different soil moisture potentials. The chemicals were incubated in clay loam and loamy sand soils for up to 12 wks at -33 kPa and at water contents equivalent to 50 and 75% of that at -33 kPa. Chemicals were extracted sequentially with 0.01 N CaCl(2) and aqueous acetonitrile, and sorption coefficients were calculated. Sufficient sulfonylaminocarbonyltriazolinone herbicides remained (>40% of that applied) during incubation to allow calculation of sorption coefficients. Aging significantly increased sorption as indicated by increased sorption coefficients. For instance, for sulfonylaminocarbonyltriazolinone remaining after a 12-wk incubation at -33 kPa, K(d) increased by a factor of 4.5 in the clay loam soils and by 6.6 in the loamy sand as compared to freshly treated soils. There was no effect of moisture potential on sorption K(d) values. These data show the importance of characterization of sorption-desorption in aged herbicide residues in soil, particularly in the case of prediction of herbicide transport in soil. In this case, potential transport of sulfonylaminocarbonyltriazolinone herbicides would be over-predicted if freshly treated soil K(d) values were used to predict transport.