Adsorption of sugar beet herbicides to Finnish soils

Three sugar beet herbicides, ethofumesate, phenmedipham and metamitron, are currently used on conventional sugar beet cultivation, while new varieties of herbicide resistant (HR) sugar beet, tolerant of glyphosate or glufosinate-ammonium, are under field testing in Finland. Little knowledge has so far been available on the adsorption of these herbicides to Finnish soils. The adsorption of these five herbicides was studied using the batch equilibrium method in 21 soil samples collected from different depths. Soil properties like organic carbon content, texture, pH and partly the phosphorus and oxide content of the soils were tested against the adsorption coefficients of the herbicides. In general, the herbicides studied could be arranged according to their adsorption coefficients as follows: glyphosate>phenmedipham>ethofumesate approximately glufosinate-ammonium>metamitron, metamitron meaning the highest risk of leaching. None of the measured soil parameters could alone explain the adsorption mechanism of these five herbicides. The results can be used in model assessments of risk for leaching to ground water resulting from weed control of sugar beet in Finland.     

Mixture toxicity of the antifouling compound irgarol to the marine phytoplankton species Dunaliella tertiolecta

This study examined the toxicity of irgarol, individually and in binary mixtures with three other pesticides (the fungicide chlorothalonil, and the herbicides atrazine and 2,4-D), to the marine phytoplankton species Dunaliella tertiolecta. Standard 96-h static algal bioassays were used to determine pesticide effects on population growth rate. Irgarol significantly inhibited D. tertiolecta growth rate at concentrations > or = 0.27 micro g/L. Irgarol was significantly more toxic to D. tertiolecta than the other pesticides tested (irgarol 96 h EC50 = 0.7 micro g/L; chlorothalonil 96 h EC50 = 64 micro g/L; atrazine 96 h EC50 = 69 micro g/L; 2,4-D 96 h EC50 = 45,000 micro g/L). Irgarol in mixture with chlorothalonil exhibited synergistic toxicity to D. tertiolecta, with the mixture being approximately 1.5 times more toxic than the individual compounds. Irgarol and atrazine, both triazine herbicides, were additive in mixture. The toxicity threshold of 2,4-D was much greater than typical environmental levels and would not be expected to influence irgarol toxicity. Based on these interactions, overlap of certain pesticide applications in the coastal zone may increase the toxicological risk to resident phytoplankton populations.     

Glyphosate adsorption in soils compared to herbicides replaced with the introduction of glyphosate resistant crops

Use of glyphosate resistant crops was helpful in addressing observed increases in environmental contamination by herbicides. Glyphosate is a broad-spectrum herbicide, and its behaviour-as well as that of other herbicides-in soils is an important consideration for the overall environmental evaluation of genetically resistant crop introduction. However, few data have been published comparing glyphosate behaviour in soil to that of the herbicides that would be replaced by introduction of glyphosate resistant crops. This work compares glyphosate adsorption in soil with that of other herbicides frequently used in rape (trifluralin and metazachlor), sugarbeet (metamitron) and corn (sulcotrione). Herbicide adsorption was characterised in surface soils and in the complete soils profiles through kinetics and isotherms using batch equilibration methods. Pedological and molecular structure factors controlling the adsorption of all five herbicides were investigated. Glyphosate was the most strongly adsorbed herbicide, thus having the weakest potential for mobility in soils. Glyphosate adsorption was dependent on its ionisable structure in relation to soil pH, and on soil copper, amorphous iron and phosphate content. Trifluralin adsorption was almost equivalent to glyphosate adsorption, whereas metazachlor, metamitron and sulcotrione adsorption were lower. Trifluralin, metazachlor and metamitron adsorption increased with soil organic carbon content. Sulcotrione was the least adsorbed herbicide in alkaline soils, but its adsorption increased when pH decreased. Ranking the adsorption properties among the five herbicides, glyphosate and trifluralin have the lowest availability and mobility in soils, but the former has the broadest spectrum for weed control.     

Biodegradation in laboratory activated sludge plants and aquatic toxicity of herbicides

The biodegradation and the aquatic toxicity of four herbicides (isoproturon, terbuthylazine, mecoprop, metamitron) were investigated. Laboratory activated sludge plants were used for biodegradation experiments. The biodegradation of mecoprop reached nearly 100%, the other herbicides were not eliminated by biodegradation. The acute Daphnia magna 24-h assay, the algal 72-h inhibition test, and the recently developed lemna growth inhibition 7-d test were applied to evaluate the biological effects of herbicides as original substances. EC 50 and EC 10 values were determined. Algal and lemna test show that isoproturon and terbuthylazine are both much more toxic than mecoprop and metamitron. Daphnids are generally less sensitive against herbicides than plants. Biodegradation and toxicity test were coupled for mecoprop to assess biological long-term effects of possible biodegradation products of this herbicide. The effluents of the laboratory activated sludge units were used in toxicity tests (Daphnia magna 21-d reproduction test, lemna growth inhibition 7-d test). No inhibiting effect on the tested organisms was observed.     

Mixture Toxicity of the Antifouling Compound Irgarol to the Marine Phytoplankton Species Dunaliella tertiolecta

This study examined the toxicity of irgarol, individually and in binary mixtures with three other pesticides (the fungicide chlorothalonil, and the herbicides atrazine and 2,4-D), to the marine phytoplankton species Dunaliella tertiolecta. Standard 96-h static algal bioassays were used to determine pesticide effects on population growth rate. Irgarol significantly inhibited D. tertiolecta growth rate at concentrations ≥ 0.27 μ g/L. Irgarol was significantly more toxic to D. tertiolecta than the other pesticides tested (irgarol 96 h EC₅₀ = 0.7 μ g/L; chlorothalonil 96 h EC₅₀ = 64 μ g/L; atrazine 96 h EC₅₀ = 69 μ g/L; 2,4-D 96 h EC₅₀ = 45,000 μ g/L). Irgarol in mixture with chlorothalonil exhibited synergistic toxicity to D. tertiolecta, with the mixture being approximately 1.5 times more toxic than the individual compounds. Irgarol and atrazine, both triazine herbicides, were additive in mixture. The toxicity threshold of 2,4-D was much greater than typical environmental levels and would not be expected to influence irgarol toxicity. Based on these interactions, overlap of certain pesticide applications in the coastal zone may increase the toxicological risk to resident phytoplankton populations.     

Pesticides impact on Clavibacter michiganensis ssp. sepedonicus biofilm formation

The effect of various pesticides on the biofilm formation by the phytopathogenic bacterium Clavibacter michiganensis ssp. sepedonicus (Cms), the potato ring rot causative agent, was explored for the first time. Systemic herbicides: 2,4-D, diuron, glyphosate, clopyralid, fluorodifen, as well as the commercial preparations “Lazurite,” “Ridomil Gold,” and the mitochondria inhibiting pesticides analog, sodium monoiodoacetate, were studied. These pesticides' effect on the Cms biofilm formation was shown to be distinct and dependent on the agent under question. Cms biofilm formation was reduced when exposed to sodium monoiodoacetate, as well as “Lazurite” preparation, that could be due to the bactericidal effect of these agents. 2,4-D and “Ridomil Gold” preparation stimulated the biofilm formation. Systemic herbicides diuron, glyphosate, clopyralid, fluorodifen did not exert appreciable influence on the process of bacterial biofilm formation.     

Biotransformation of metamitron by human p450 expressed in transgenic tobacco cell cultures

In the present investigation, the oxidative metabolism of 14C-labeled metamitron was examined in plant cell cultures of tobacco overexpressing human P450 enzymes CYP1A1 or CYP1A2; special interest was in the aromatic hydroxylation of the herbicide. The oxidative metabolites deaminometamitron (DAM) and 4-hydroxydeaminometamitron (4-HDAM) were found in the untransformed control culture as well as in the transgenic culture. The transgenic cultures, however, exhibited higher turnover rates after 48 h of incubation with 20 microg 14C-metamitron per assay (untransformed: 40%, CYP1A1: 80%, CYP1A2: 100%). Primary metabolite 4-HDAM was partially found in glucosylated form in the transgenic cultures. As minor oxidative metabolites, 6-hydroxyphenyl-3-methoxymethyl-1,2,4-triazine-5(4H)-one and 3-hydroxymethyl-6-phenyl-1,2,4-triazine-5(4H)-one were identified in the transgenic cultures by GC-MS, LC-MS. Additionally, it could be demonstrated that both foreign enzymes (CYP1A1, CYP1A2) also catalyzed the deamination of metamitron. In a large-scale study (up to 400 microg per assay) with the transgenic culture expressing CYP1A2, the high efficiency of this P450 system toward metamitron was demonstrated: turnover of the xenobiotic was almost complete with 400 microg. Since large portions of unglucosylated 4-H-DAM were found, the activity of foreign CYP1A2 apparently exceeded that of endogenous O-glucosyltransferases of the tobacco cell culture. We concluded that in comparison to the nontransformed cell culture, the extent of metabolism was considerably higher in the transgenic cultures. The transgenic cell cultures expressing human CYP1A1 or CYP1A2 are thus suitable tools for the production of large quantities of primary oxidized metabolites of metamitron.     

Biotransformation of Metamitron by Human P450 Expressed in Transgenic Tobacco Cell Cultures

In the present investigation, the oxidative metabolism of ¹⁴C-labeled metamitron was examined in plant cell cultures of tobacco overexpressing human P450 enzymes CYP1A1 or CYP1A2; special interest was in the aromatic hydroxylation of the herbicide. The oxidative metabolites deaminometamitron (DAM) and 4-hydroxydeaminometamitron (4-HDAM) were found in the untransformed control culture as well as in the transgenic culture. The transgenic cultures, however, exhibited higher turnover rates after 48 h of incubation with 20 μg ¹⁴C-metamitron per assay (untransformed: 40%, CYP1A1: 80%, CYP1A2: 100%). Primary metabolite 4-HDAM was partially found in glucosylated form in the transgenic cultures. As minor oxidative metabolites, 6-hydroxyphenyl-3-methoxymethyl-1,2,4-triazine-5(4H)-one and 3-hydroxymethyl-6-phenyl-1,2,4-triazine-5(4H)-one were identified in the transgenic cultures by GC-MS, LC-MS. Additionally, it could be demonstrated that both foreign enzymes (CYP1A1, CYP1A2) also catalyzed the deamination of metamitron. In a large-scale study (up to 400 μ g per assay) with the transgenic culture expressing CYP1A2, the high efficiency of this P450 system toward metamitron was demonstrated: turnover of the xenobiotic was almost complete with 400 μ g. Since large portions of unglucosylated 4-H-DAM were found, the activity of foreign CYP1A2 apparently exceeded that of endogenous O-glucosyltransferases of the tobacco cell culture. We concluded that in comparison to the nontransformed cell culture, the extent of metabolism was considerably higher in the transgenic cultures. The transgenic cell cultures expressing human CYP1A1 or CYP1A2 are thus suitable tools for the production of large quantities of primary oxidized metabolites of metamitron.     

Comparing aquatic risk assessment methods for the photosynthesis-inhibiting herbicides metribuzin and metamitron

Three different risk assessment procedures are described that aim to protect freshwater habitats from risks of the photosynthesis-inhibiting herbicides metribuzin and metamitron. These procedures are (1) the first-tier approach, based on standard toxicity tests and the application of an assessment factor, (2) the Species Sensitivity Distribution (SSD) approach, based on laboratory tests with a wider array of species and the application of a statistical model to calculate the HCx (the Hazardous Concentration for x% of the species), and (3) the model ecosystem approach, based on the evaluation of treatment-related effects in field enclosures. A comparison of the risk assessment procedures reveals that the first-tier approach is the most conservative for metamitron and metribuzin, and that HC5 values (and even HC10 values) based on acute EC50 values of algae and aquatic vascular plants may be used to derive maximum permissible concentrations for single applications. For both compounds these HC5 values were very similar to the ecological threshold concentrations in the enclosure studies. In contrast to model ecosystem experiments, however, HCx values based on lab toxicity tests do not provide information on the recovery potential of sensitive endpoints and on indirect effects, which may be important for regulatory decision-making. In the enclosure study, indirect effects of metribuzin on invertebrate populations were observed at an exposure concentration that was approximately 20 times lower than the corresponding HC5 value based on lab toxicity data for aquatic invertebrates.     

Effects of ionic strength on the production of short chain volatile hydrocarbons by Dunaliella salina (Teodoresco)

The effect of ionic strength on the production of short chain volatile hydrocarbons was studied in cultures of Dunaliella salina. Axenic cultures of D. salina were grown at three different ionic strengths 0.5, 2 and 3 M of NaCl in Johnson (J/1) culture medium [Journal of Bacteriology 95 (1968) 1461] under the following laboratory growth conditions: a 12:12 h photoperiod, 300 micromolm(-2)s(-1) of photosynthetic active radiation (PAR) provided by a fluorescent lamp of 40 W combined with a 100 W incandescent lamp at 20 +/- 1 degrees C at pH 7.5. C1 to C5 hydrocarbons were detected using a head space technique and GC-FID. Cell numbers and growth rate was greatest at 2 M NaCl 4.3 x 10(6) cellml(-1) after a 15 days period of culture. Maximum hydrocarbon production was measured in the concentration of 0.5 NaCl with lower production rates in the more concentrated solutions. The principal hydrocarbon was pentane at 0.5 M but was ethane in 2 and 3 M solutions. Production rates for individual compounds ranged between 0.13 and 22 x 10(-15) microgCcell(-1)h(-1). It is suggested that the ability to produce and release volatile organic compounds of D. salina is related to osmotic conditions established by the ionic strength of growth solution.     

A qualitative sampling method for monitoring water quality in temporary channels or point sources and its application to pesticide contamination

A water-sampling device to monitor the quality of water periodically and temporarily flowing out of concrete tubes, sewers or channels is described. It inexpensively and easily enables a qualitative characterization of contamination via these point-source entry routes. The water sampler can be reverse engineered with different sizes and materials, once installed needs no maintenance, passively samples the first surge, and the emptying procedure is short. In an agricultural catchment area in Germany we monitored an emergency overflow of a sewage sewer, an outlet of a rainwater sewer and two small drainage channels as input sources to a small stream. Seven inflow events were analysed for 20 pesticide agents (insecticides, fungicides and herbicides). All three entry routes were remarkably contaminated. We found parathion-ethyl concentrations of 0.3 microg l(-1), diuron up to 17.3 microg l(-1), ethofumesate up to 51.1 microg l(-1), metamitron up to 92 microg l(-1) and prosulfocarb up to 130 microg l(-1).     

Multivariate analysis of photo-Fenton degradation of the herbicides tebuthiuron, diuron and 2,4-D

The degradation of herbicides in aqueous solution by photo-Fenton process using ferrioxalate complex (FeOx) as source of Fe2+ was evaluated under blacklight irradiation. The commercial products of the herbicides tebuthiuron, diuron and 2,4-D were used. The multivariate analysis, more precisely, the response surface methodology was applied to evaluate the role of FeOx and hydrogen peroxide concentrations as variables in the degradation process, and in particular, to define the concentration ranges that result in the most efficient degradation of the herbicides. The degradation process was evaluated by the determination of the remaining total organic carbon content (TOC), by monitoring the decrease of the concentrations of the original compounds using HPLC and by the chloride ion release in the case of diuron and 2,4-D. Under optimized conditions, 20 min were sufficient to mineralize 93% of TOC from 2,4-D and 90% of diuron, including oxalate. Complete dechlorination of these compounds was achieved after 10 min reaction. It was found that the most recalcitrant herbicide is tebuthiuron, while diuron shows the highest degradability. However, under optimized conditions the initial concentration of tebuthiuron was reduced to less than 15%, while diuron and 2,4-D were reduced to around 2% after only 1 min reaction. Furthermore, it was observed that the ferrioxalate complex plays a more important role than H2O2 in the photodegradation of these herbicides in the ranges of concentrations investigated.     

Dissipation of the herbicide clopyralid in an allophanic soil: laboratory and field studies

Soil dissipation of the herbicide clopyralid (3,6-dichloropicolinic acid) was measured in laboratory incubations and in field plots under different management regimes. In laboratory studies, soil was spiked with commercial grade liquid formulation of clopyralid (Versatill, 300 g a.i. L(-1) soluble concentrate) @ 0.8 microg a.i. g(-1) dry soil and the soil water content was maintained at 60% of water holding capacity of the soil. Treatments included incubation at 10 degrees C, 20 degrees C, 30 degrees C, day/night cycles (25/15 degrees C) and sterilized soil (20 degrees C). Furthermore, a field study was conducted at the Waikato Research Orchard near Hamilton, New Zealand starting in November 2000 to measure dissipation rates of clopyralid under differing agricultural situations. The management regimes were: permanent pasture, permanent pasture shielded from direct sunlight, bare ground, and bare ground shielded from direct sunlight. Clopyralid was sprayed in dilute solution @ 600 g a.i. ha(-1) on to field plots. Herbicide residue concentrations in soil samples taken at regular intervals after application were determined by gas chromatograph with electron capture detector. The laboratory experiments showed that dissipation rate of clopyralid was markedly faster in non-sterilized soil (20 degrees C), with a half-life (t1/2) of 7.3 d, than in sterilized soil (20 degrees C) with t1/2 of 57.8 d, demonstrating the importance of micro-organisms in the breakdown process. Higher temperatures led to more rapid dissipation of clopyralid (t1/2, 4.1 d at 30 degrees C vs 46.2 d at 10 degrees C). Dissipation was also faster in the day/night (25/15 degrees C) treatment (t1/2, 5.4 d), which could be partly due to activation of soil microbes by temperature fluctuations. In the field experiment, decomposition of clopyralid was much slower in the shaded plots under pasture (t1/2, 71.5 d) and bare ground (t1/2, 23.9 d) than in the unshaded pasture (t1/2, 5.0 d) and bare ground plots (t1/2, 12.9 d). These studies suggest that environmental factors such as temperature, soil water content, shading, and different management practices would have considerable influence on rate of clopyralid dissipation.     

Population dynamics of Digitaria spp submitted to selection pressure by herbicides in sugarcane crop

The objective of this research was to study population dynamics of the weed crabgrass, genus Digitaria, submitted to selection pressure by herbicides currently applied in sugarcane crops in Brazil. In the first experiment two crabgrass species (Digitaria nuda and Digitaria ciliaris) and eight herbicide treatments applied in preemergence were used, and control percentage was evaluated at 7, 14, and 21 days after herbicide application (DAA). In the second experiment the level of tolerance through dose-response curve was determined for the species D. nuda and D. ciliaris, to the herbicides imazapyr, tebuthiuron, ametryne, and metribuzin. All the herbicides studied were efficient in controlling D. ciliaris, however, for D. nuda the best results were obtained only with ametryne, metribuzin, and isoxaflutole. The relation (T/S) between the rate required to reduce plant dry biomass (GR50) at 21 DAA of D. nuda and D. ciliaris was 16 for imazapyr and 6.3 for tebuthiuron, showing differential susceptibility of species; however for ametryne the rate T/S of 1.1 showed that D. nuda was not tolerant to this herbicide. For metribuzin, at 1.92 kg a.i. ha(-1), reduction of dry biomass was 80 and 90% to D. nuda and D. ciliaris, respectively. Even being controlled by metribuzin, D. nuda presented a higher level of tolerance to this herbicide, what was confirmed by the relationship T/S 14.4. As general conclusion of the research, it can be stated that the species D. nuda is more tolerant to ALS inhibiting herbicides and substituted urea, when compared with D. ciliaris; probably, D. nuda was selected by repetitive use of these herbicides.     

L'utilisation de souches de micro-organismes de collection pour l'etude de la biodegradabilite des pesticides

Use of Microbial strains from collection in the study of pesticide biodegradability. 5 different herbicides and 1 metabolite of herbicide were subjected to biodegradation by different microbial strains and simultaneously by soil suspensions.To take account of possible co-metabolisme a supplementary source of carbon was added in the culture media. Results were discussed.     

Conditions d'acceptation ou de rejet des valeurs obtenues apres denombrement de virus ou bacteries sur milieux de culture solides

Enumeration of viruses or bacteria on solid culture media does not ever give statistically acceptable results. When counting is impossible, we must do it again. For accepting or not the counting, the authors established some probability Tables (95% and 99%) according to microbial densities.     

Individual and mixture toxicity of three pesticides; atrazine,chlorpyrifos, and chlorothalonil to the marine phytoplankton species Dunaliella tertiolecta

This study analyzed the toxicity of three pesticides (the herbicide atrazine, the insecticide chlorpyrifos and the fungicide chlorothalonil) individually, and in two mixtures (atrazine and chlorpyrifos; atrazine and chlorothalonil) to the marine phytoplankton species Dunaliella tertiolecta (Chlorophyta). A standard 96 h static algal bioassay was used to determine pesticide effects on the population growth rate of D. tertiolecta. Mixture toxicity was assessed using the additive index approach. Atrazine and chlorothalonil concentrations > or = 25 microg/L and 33.3 microg/L, respectively, caused significant decreases in D. tertiolecta population growth rate. At much higher concentrations (> or = 400 microg/L) chlorpyrifos also elicited a significant effect on D. tertiolecta population growth rate, but toxicity would not be expected at typical environmental concentrations. The population growth rate EC50 values determined for D. tertiolecta were 64 microg/L for chlorothalonil, 69 microg/L for atrazine, and 769 microg/L for chlorpyrifos. Atrazine and chlorpyrifos in mixture displayed additive toxicity, whereas atrazine and chlorothalonil in mixture had a synergistic effect. The toxicity of atrazine and chlorothalonil combined was approximately 2 times greater than that of the individual chemicals. Therefore, decreases in phytoplankton populations resulting from pesticide exposure could occur at lower than expected concentrations in aquatic systems where atrazine and chlorothalonil are present in mixture. Detrimental effects on phytoplankton population growth rate could impact nutrient cycling rates and food availability to higher trophic levels. Characterizing the toxicity of chemical mixtures likely to be encountered in the environment may benefit the pesticide registration and regulation process.     

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

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 64,000 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.     

Effect on herbicide adsorption of organic forestry waste products used for soil remediation

Organic soil amendments can be useful for improving degraded soil, but this increase in organic matter (OM) may influence adsorption of herbicides subsequently applied to the treated soil, even though the particle size of amendments and their nature differ from typical soil OM. In this study, a batch equilibrium method was used to measure adsorption of five herbicides following application to two organic media, wood pulp and sawdust, comparing these with two cropping soils. Herbicide adsorption, quantified by distribution coefficients (k_d), was much higher in the two organic media than in the cropping soils. The increases in adsorption were strongly correlated to the percentage of organic carbon. When the k_d was normalized to adsorption coefficients corrected for OM content (k_oc), variation in results between the media was greatly reduced, indicating that OM is an important factor influencing adsorption in these media. The results of this study suggest that herbicides will be less effective when applied to soils in which sawdust and wood pulp have been added. Using organic amendments to remediate soil will increase adsorption of pesticides, reducing their bio-availability and efficacy, but also reducing their tendency to leach into root zones of deep-rooted crops and into groundwater.