Adsorption,desorption, soil mobility,aqueous persistence and octanol‐water partitioning coefficients of terbufos,terbufos sulfoxide and terbufos sulfone

Abstract

Terbufos, t. sulfoxide and t. sulfone (5 μg ml^‐1) were incubated in natural, sterilized natural and distilled water, with initial pH values of 8.8, 8.8 and 6.0, respectively, at 20°C. First‐order disappearance was observed for the three compounds. Rates in natural and sterilized water were similar indicating chemical degradation predominated. Terbufos disappeared rapidly (t½>=3 days) in all systems. T. sulfoxide and t. sulfone were more persistent in the natural (t½>=18–40 days) and distilled water (t½>=280–350 days). Adsorption data for the three compounds in four soil‐water systems showed the decreasing order of adsorption to be terbufos>>t. sulfoxide=t. sulfone. Desorption from soils fortified at 5 μg g^‐1 with water was examined for 4 successive 18‐hr cycles. T. sulfoxide and t. sulfone were totally desorbed; terbufos was too unstable to study. The mobility of the compound in soil eluted with water was in the order, t. sulfoxide=t. sulfone>> terbufos, in agreement with adsorption‐desorption results. The octanol‐water partitioning coefficients for terbufos, t. sulfoxide and t. sulfone, at 23°C, were 3:30 x 10 , 164, and 302, respectively.     

Degradation of fenamiphos in soils collected from different geographical regions: The influence of soil properties and climatic conditions

The persistence of fenamiphos (nematicide) in five soils collected from different geographical regions such as Australia, Ecuador and India under three temperature regimes (18, 25 and 37°C) simulating typical environmental conditions was studied. The effect of soil properties (soil pH, temperature and microbial biomass) on the degradation of fenamiphos was determined. The rate of degradation increased with increase in temperature. Fenamiphos degradation was higher at 37°C than at 25 and 18°C (except under alkaline pH). The degradation pathway differed in different soils. Fenamiphos sulfoxide (FSO) was identified as the major degradation product in all the soils. Fenamiphos sulfone (FSO₂), and the corresponding phenols: fenamiphos phenol (FP), fenamiphos sulfoxide phenol (FSOP) and fenamiphos sulfone phenol (FSO₂P) were also detected. The degradation of fenamiphos was faster in the alkaline soils, followed by neutral and acidic soils. Under sterile conditions, the dissipation of the pesticide was slower than in the non-sterile soils suggesting microbial role in the pesticide degradation. The generation of new knowledge on fenamiphos degradation patterns under different environmental conditions is important to achieve better pesticide risk management.     

Toxicity of fenamiphos and its metabolites to the cladoceran Daphnia carinata: the influence of microbial degradation in natural waters

The acute toxicity of an organophosphorous pesticide, fenamiphos and its metabolites, fenamiphos sulfoxide, fenamiphos sulfone, fenamiphos phenol, fenamiphos sulfoxide phenol and fenamiphos sulfone phenol, to a cladoceran, Daphnia carinata was studied in both cladoceran culture medium and natural water collected from a local river. The toxicity followed the order: fenamiphos>fenamiphos sulfone>fenamiphos sulfoxide. The hydrolysis products of fenamiphos, F. sulfoxide (FSO) and F. sulfone (FSO(2)) (F. phenol, FSO phenol and FSO(2) phenol) were not toxic to D. carinata up to 500microgl(-1) water, suggesting hydrolysis reaction leads to detoxification. Also the toxicity was reduced in natural water compared to the cladoceran culture medium due to microbial mediated degradation of toxicants in the natural water. Fenamiphos and its metabolites were stable in both cladoceran water and filter-sterilised natural water while these compounds showed degradation in unfiltered natural water implicating the microbial role in degradation of these compounds. To our knowledge this is the first study on acute toxicity of fenamiphos metabolites to cladoceran and this study suggests that the organophosphate pesticides are highly toxic to fresh water invertebrates and therefore pollution with these compounds may adversely affect the natural ecosystems.     

Sorption of fenamiphos to different soils: the influence of soil properties

Fenamiphos (0-ethyl-0(3-methyl-4-methylthiophenyl)-isopropylamido-phosphate) is a widely used nematicide and insecticide in bowling greens and agriculture, but information on its sorption including its metabolites is limited. Hence, the sorption of fenamiphos (nematicide) and its major degradation products fenamiphos sulfoxide (FSO) and fenamiphos sulfone (FSO2) were determined in thirteen contrasting soils collected from Australia and Ecuador. The sorption coefficients (Kd) exhibited a wide range of variation from 2.48 to 14.94 L/Kg for fenamiphos; from 0 to 7.42 L/Kg for FSO and from 0 to 9.49 L/Kg for FSO2. The sorption affinity of the three compounds for all soils tested was as follows: fenamiphos > fenamiphos sulfone > fenamiphos sulfoxide. The results showed that the sorption of fenamiphos and its metabolites in some soils is very low, and in one case is nonexistant for the metabolites. This is of particular concern as due to its low sorption coefficient, the compound could easily migrate and contaminate water bodies. Fenamiphos and its oxidation products have been reported to be highly toxic to aquatic invertebrates and therefore, the information generated in this study assumes great importance in the risk assessment of fenamiphos and its metabolites in the environment.     

Degradation of fenamiphos in soils collected from different geographical regions: the influence of soil properties and climatic conditions

The persistence of fenamiphos (nematicide) in five soils collected from different geographical regions such as Australia, Ecuador and India under three temperature regimes (18, 25 and 37 degrees C) simulating typical environmental conditions was studied. The effect of soil properties (soil pH, temperature and microbial biomass) on the degradation of fenamiphos was determined. The rate of degradation increased with increase in temperature. Fenamiphos degradation was higher at 37 degrees C than at 25 and 18 degrees C (except under alkaline pH). The degradation pathway differed in different soils. Fenamiphos sulfoxide (FSO) was identified as the major degradation product in all the soils. Fenamiphos sulfone (FSO2), and the corresponding phenols: fenamiphos phenol (FP), fenamiphos sulfoxide phenol (FSOP) and fenamiphos sulfone phenol (FSO2P) were also detected. The degradation of fenamiphos was faster in the alkaline soils, followed by neutral and acidic soils. Under sterile conditions, the dissipation of the pesticide was slower than in the non-sterile soils suggesting microbial role in the pesticide degradation. The generation of new knowledge on fenamiphos degradation patterns under different environmental conditions is important to achieve better pesticide risk management.     

Use of coal to retard pesticide movement in soil

Abstract

Three different coals and an activated carbon were mixed with prescribed amounts of a sandy loam soil and added to soil columns to test their ability to retard pesticide movement. The pesticides chosen were prometon, prometryn, 2,4‐D, carbofuran, dinoseb, fenamiphos, and two oxidation products of fenamiphos, fenamiphos sulfoxide, and fenamiphos sulfone. These compounds were chosen to represent different chemical classes of pesticides and because they were considered to have a high potential for transport in soils. All the coals were more effective in retaining the pesticides than the soil, however, some were more effective than others. One of the coals was the most effective in retaining the majority of the pesticides with an overall retention of 94.7% in a 4:1 soil/coal ratio compared to the soil only with a retention of 48.5%. The moisture content of the coal appears to have a positive correlation with the ability of the coal to retain the pesticides under the conditions used for this experiment.     

Leaching of fenamiphos,fenamiphos sulfoxide and fenamiphos sulfone in soil columns

Abstract

Leaching of fenamiphos and its thiooxidation products, sulfoxide and sulfone, has been studied in two different soils in laboratory conditions. Fenamiphos was much less mobile than its derivatives. A large volume of water was necessary to leach completely the three chemicals. Fenamiphos required an amount of water twice as large as that required by either sulfoxide or sulfone. Mobility and leaching efficiency of the chemicals examined were highly dependent on the properties of the two soils considered.     

The persistence of insecticidal chemicals in soils treated with granular formulations of aldicarb and their uptake by potato plants

Abstract

Potatoes were grown in Plainfield sand and muck treated, in furrow, with aldicarb (Temik 15G, 3.36 kg Al/ha). .Soils were contained in 2 m^z field plots and had not been treated previously with pesticides. Soil, seed pieces, foliage and tubers were analyzed for the insecticide and its sulfoxide and sulfone metabolites during the 12 wk following planting. The disappearance of aldicarb from the soil was accompanied by partial conversion to the sulfoxide and sulfone. After increasing rapidly during the first 2 wk, the aldicarb concentration in the seed piece declined and a similar concentration of aldicarb sulfoxide accumulated which subsequently slowly disappeared. Aldicarb sulfoxide was the major insecticidal material in the new foliage. High initial concentrations, observed at 3–4 wk, declined by about 90% after 6 wk. Aldicarb sulfoxide residues of 2–4 ppm in the first new tubers at 6 wk declined by 90% by 12 wk. Potatoes were also grown under greenhouse conditions in Plainfield sand treated with Temik 10G at rates equivalent to 1.68, 3.36 and 6.72 kg Al/ha. Maximum aldicarb sulfoxide concentrations in soil, seed piece and foliage increased with application rate. The sulfoxide was much more persistent in the soil and foliage than in the field experiment indicating the importance of environmental factors to its behaviour in both soil and potato plants.     

The effect of multiple soil applications of disulfoton on enhanced microbial degradation in soil and subsequent uptake of insecticidal chemicals by potato plants

Abstract

Potatoes were grown during 1992 in 2 m² plots of loam which had received 1, 2 or 3 annual treatments of Di‐Syston 15G, equivalent to 3.36 kg AI/ha, in furrow at planting. The presence of enhanced degradative activity to the sulfoxide and sulfone metabolites of disulfoton in the soil treated in the previous two years was confirmed by laboratory tests prior to the 1992 treatments. Soil, seed potato and foliage from the three treatments were analyzed for disulfoton and its sulfoxide and sulfone metabolites for 12 wk following planting/treatment. Disulfoton was the major insecticidal component of the soil, a minor component of the seed piece and was not detected (<0.02 ppm) in potato foliage. Disulfoton concentrations in each of the three substrates sampled were similar for the three treatments. Disulfoton sulfoxide and sulfone were the major insecticidal components of the seed piece and foliage. Their maximum concentrations in 1st year soil, seed pieces and foliage were ca. 2x, 2x and 6x, respectively, those measured in the 2nd and 3rd year treatments. The results demonstrate that enhanced microbial degradation of relatively minor insecticidal compounds in the soil can profoundly affect insecticide levels in the plant when these compounds are the major insecticidal components accumulated. The broader implications for crop protection using soil‐applied systemic insecticides are discussed.     

The persistence of insecticidal chemicals in soils treated with granular formulations of disulfoton and their uptake by potato plants

Abstract

Potatoes were grown from cut seed in Plainfield sand treated in‐furrow with disulfoton (Di‐Syston 15G, 3.36 kg Al/ha) in 1983 and from whole seed in similarly treated loam in 1991. Soils were contained in 2 m² field plots. Soil, seed potato and foliage were analyzed for the insecticide and its sulfoxide and sulfone metabolites during the 8–12 wk following planting. Disulfoton disappeared at different rates from the two soils (k_sand=0.024 day^‐1, k_loam=0.056 day^‐1) with partial conversion to the sulfoxide and sulfone in both. Larger quantities of the three insecticidal components were absorbed by the seed potato in the cut‐seed/sand combination. The relative amounts of these components in the seed potato also differed between treatments with disulfoton being the largest component of the cut‐seed/sand and smallest in the whole‐seed/loam. Disulfoton sulfoxide and sulfone were the major insecticidal components of the foliage and concentrations in the initial foliage (each ca. 10 ppm) were similar for both treatments. Sulfoxide concentrations in the foliage decreased more rapidly than the sulfone and the decrease in concentration of each of the components was similar for the two treatments.     

Adsorption, desorption, soil mobility and aqueous persistence of fensulfothion and its sulfide and sulfone metabolites

Soil/water interactions with the insecticide fensulfothion and its sulfide and sulfone metabolites and described. Adsorption to, and desorption from four soils were studied. There was a general inverse relationship between water solubilities of the three chemicals and their adsorption K values. Order of adsorption was f. sulfide greater than f. sulfone greater than fensulfothion. Adsorption K values correlated significantly with soil organic content. Desorption of fensulfothion and the sulfone were similar whereas the less soluble sulfide desorbed to a lesser extent. To facilitate comparison of desorption tendencies of the three compounds of desorption index was developed. Mobilities through the soils were directly related to the water solubilities of the three chemicals. Mobilities in decreasing order were - fensulfothion greater than f. sulfone greater than f. sulfide. Persistence of fensulfothion was similar in both sterile and non-sterile natural water - about 50% remaining at the end of the 16 wk experiment. Under reducing conditions fensulfothion disappeared from water in 8-12 wk with almost complete conversion to the sulfide.     

Field dissipation of oxyfluorfen in onion and its dynamics in soil under Indian tropical conditions

Oxyfluorfen, a diphenyl-ether herbicide is being used to control annual and perennial broad-leaved weeds and sedges in a variety of field crops including onion. The present study was aimed to investigate the dynamics and field persistence of oxyfluorfen in onion plant, bulb and soil under Indian tropical conditions. Application of four rates of oxyfluorfen viz., 200, 250, 300 and 400 g AI ha^?1 as pre-emergence gave good weed control in field experiment with onion. The oxyfluorfen residue dissipated faster in plant than in soil respectively, with a mean half-life of 6.1 and 11.2 days. Dissipation followed first-order kinetics. In laboratory column leaching experiments, 17 percent of the applied oxyfluorfen was recovered from the soil and indicates its solubility in water and mobility in sandy clay loam soil was low. A sorption study revealed that the adsorption of oxyfluorfen to the soil was highly influenced by the soil organic carbon with the K_oc value of 5450. The study concludes that the dissipation of oxyfluorfen in soil and onion was dependent on the physico-chemical properties of the soil and environmental conditions.     

Mobility of adsorbed arsenic in two calcareous soils as influenced by water extract of compost

The mobility of arsenic (As) in soil affects both the bio-toxicity of As and the groundwater quality, which in turn indirectly affects the quality of edible part of crops and human health, if the crops were irrigated with As contaminated groundwater. A vertical soil column simulates the depth of a soil profile in a real soil environment. Thus soil column experiment is much more pertinent to soil environment than a batch experiment to simulate solute movement as well as leaching through soil profile. A laboratory soil column experiment was conducted to determine the extent of As leaching from soil percolated with influent that contained organic substances. The water extract of compost (WEC) was used as the source of organic substances. The results of As breakthrough curves (BTCs) showed that less pore volumes of influents were required to reach the relative concentration ratio of 1 (C/C0=1) for the two calcareous soils treated with influent that contained WEC. The concentrations of As in the column effluents of soils percolated with 0.01M KCl in WEC were significantly higher than those percolated with 0.01M KCl with the same volumes of effluents collected. This clearly indicates that dissolved as well as deprotonated organic substances which are negatively charged have higher potential for competing the adsorption sites with As on soils, leading to increasing mobility of As in soil and associated environments. Further, it is observed that the characteristics of soil components related to As adsorption affected the adsorption as well as desorption processes and subsequent mobility of As in soil environment as influenced by organic substances.     

The environmental dynamics of the carbamate insecticide aldicarb in soil and water

Aldicarb is a soil-applied systemic pesticide the USEPA is now considering banning in the USA. Aldicarb is fairly rapidly oxidized to the sulfoxide, with a half-life of approximately 7 days in some soils, and much more slowly to the sulfone (pH-dependent with half-lives varying from a few minutes at a pH of > 12 to approximately 560 days at a pH of 6.0). Persistence, carry-over and translocation vary with soil and environmental conditions. Drainage aquifers and drinking water wells are known to be susceptible to contamination, levels of approximately 550 ppb have been recorded. Foods are also known to take up the pesticide; levels of 600 ppb have been found in potatoes.     

Persistence of fensulfothion in a sandy‐loam soil and uptake by rutabagas,carrots and radishes using microplots

Abstract

Field microplots were treated with 141 and 282 ppm fensulfothion and 37.1 and 74.2 ppm fensulfothion sulfone. These concentrations are equivalent to field treatment rates of 8.48 and 16.96 kg Al/ha, fensulfothion, and 2.23 and 4.47 kg Al/ha, fensulfothion sulfone, respectively, for banded application (10 cm wide, rows 80 cm apart). The half‐lives in a sandy loam soil were 30–39 and 14–23 days, respectively. Fensulfothion sulfone and sulfide were the main derivatives found in fensulfothion treated soil.

The maximum levels of these derivatives were 21.22 and 22.95 ppm, respectively for the 8.48 kg/ha treatment and 33.90 and 42.45 ppm, respectively, for the higher treatment, which occurred between 30–60 days.

Carrots appeared to take up more fensulfothion from soil than rutabagas or radishes. The residue levels at harvest decreased in the order carrot peel > pulp > rutabagas root > peel > pulp. Residue levels of fensulfothion and sulfone in radishes were similar to those found in rutabagas. The ratio sulfoxide/sulfone in rutabagas ranged from 0.4–1.5 and in carrots from 1.7–7.6. This phenomenon is thought to be due to oxidative enzyme systems present in rutabagas. Dimethyl phosphorothioic acid, but not dimethyl phosphoric acid was detected (max. 1.33 ppm) in some rutabagas samples but not in carrots.     

Comparative abiotic or biotic degradation of carboxin by two Entisols with different surface properties or Pseudomonas aeruginosa strain: A toxicity study using the crustacean Thamnocephalus platyurus

The microcrustacean Thamnocephalus platyurus was used to detect the toxicity reduction of carboxin in abiotic degradation compared to biotic degradation. The abiotic degradation was obtained using two sterilized Entisols with different surface properties while the biotic degradation by Pseudomonas aeruginosa was obtained using the fungicide as the only C source. The results showed that the highest toxicity reduction rates for the abiotic degradation were achieved in 20 days with 49.2% for the coarser soil, 60.7% for the soil with a finer texture, whereas for the biotic degradation, 60.6%. Analysis (¹H NMR) showed that the soils transformed carboxin to produce sulfoxide and enol in different concentrations depending on the soil properties, while P. aeruginosa metabolized the fungicide to produce inorganic compounds such as ammonium and nitrite, minor degradation pathways were oxidized to sulfoxide and hydrolytic ring-opening to 2-[(2-hydroxyethyl)thio]acetoacetanilide enol. These results indicated that the degradation of carboxin occurred via abiotic catalytic processes as well as via biotic transformation leading to less toxic derivatives and such phenomena are caused by exchange/surface features of soils, rather than by the mere content of clay or organic matter fractions.     

Persistence of fensulfothion in a sandy-loam soil and uptake by rutabagas, carrots and radishes using microplots

Field microplots were treated with 141 and 282 ppm fensulfothion and 37.1 and 74.2 ppm fensulfothion sulfone. These concentrations are equivalent to field treatment rates of 8.48 and 16.96 kg AI/ha, fensulfothion, and 2.23 and 4.47 kg AI/ha, fensulfothion sulfone, respectively, for banded application (10 cm wide, rows 80 cm apart). The half-lives in a sandy loam soil were 30-39 and 14-23 days, respectively. Fensulfothion sulfone and sulfide were the main derivatives found in fensulfothion treated soil. The maximum levels of these derivatives were 21.22 and 22.95 ppm, respectively for the 8.48 kg/ha treatment and 33.90 and 42.45 ppm, respectively, for the higher treatment, which occurred between 30-60 days. Carrots appeared to take up more fensulfothion from soil than rutabagas or radishes. The residue levels at harvest decreased in the order carrot peel greater than pulp greater than rutabagas root greater than peel greater than pulp. Residue levels of fensulfothion and sulfone in radishes were similar to those found in rutabagas. The ratio sulfoxide/sulfone in rutabagas ranged from 0.4-1.5 and in carrots from 1.7-7.6. This phenomenon is thought to be due to oxidative enzyme systems present in rutabagas. Dimethyl phosphorothioic acid, but not dimethyl phosphoric acid was detected (max. 1.33 ppm) in some rutabagas samples but not in carrots.     

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.     

Ag~+改性复合钛铌酸钾盐对二甲基硫醚和乙硫醇吸附与光催化氧化研究

采用高温固相法合成具有不同Nb/Ti摩尔比的复合钛铌酸钾盐,通过Ag+离子交换对其进行改性。在静态下评价了Ag+改性复合钛铌酸钾盐对二甲基硫醚(DMS)和乙硫醇(EM)的吸附与紫外光催化氧化作用,使用红外光谱技术对催化剂表面滞留物种进行表征。结果表明,Ag+改性复合钛铌酸钾盐对DMS的吸附作用力比EM弱。随着Nb/Ti摩尔比增加,Ag+改性复合钛铌酸钾盐对EM的吸附作用力增强。在紫外光辐射下,Ag+改性的复合钛铌酸钾盐将DMS氧化为亚砜、砜和硫酸盐,而EM则被氧化为磺酸和单齿硫酸盐。     

The destruction of ground water threatening pesticides using high intensity UV light

Abstract

A high‐intensity short‐wavelength UV light system was studied for its ability to degrade the pesticides carbofuran, fenamiphos sulfoxide (nemacur sulfoxide), and propazine in aqueous solutions. Half‐lives, rate constants, and breakdown products were determined for all chemicals. The presence of hydrogen peroxide, an oxidant and potential source of hydroxyl radicals, had no effect on the rate of breakdown of any of the chemicals investigated. Short‐wavelength UV light appears to be solely responsible for the observed pesticide breakdown. The breakdown of all three pesticides followed first order kinetics. Carbofuran, nemacur sulfoxide, and propazine had half lives of 3.9, 1.1, and 3.9 minutes, respectively. Breakdown product analysis was performed using capillary gas chromatography/mass spectrometry.