Effect of soil sterilization by mercuric chloride on herbicide sorption by soil

Microbial inhibitors such as mercuric chloride are frequently used to sterilize soil or soil-water slurries in experimental studies on the fate of xenobiotics in the environment. This study examined the influence of mercuric chloride additions to soil-water slurries on the sorptive behaviour of a phenoxy herbicide (2,4-D) in soil. The results demonstrated that mercuric chloride strongly decreased the capacity of the soil to retain herbicides, and that the interference of mercuric chloride with herbicide sorption increased with increasing soil organic carbon contents. Because of the competitive sorption between mercuric chloride and the phenoxy herbicide, we conclude that mercuric chloride may not be a good soil sterilization procedure for use in xenobiotic fate studies.     

Comparison of Microbial Pyrene and Benzo[a]Pyrene Mineralization in Liquid Medium,Soil Slurry,and Soil

The microbial degradation of ¹⁴C-pyrene and ¹⁴C-benzo[a]pyrene by a bacterial mixed culture was studied within a mixture of the PAHs phenanthrene, anthracene, pyrene, fluoranthene, and benzo[a]pyrene as sole carbon source in the different culture systems: (i) liquid medium, (ii) soil slurry (surface and grinding influence), and (iii) soil. The fate of these two labeled compounds was followed in these systems with an emphasis on mineralization to carbon dioxide, extractability, and adsorption to humic materials and formation of unextractable residual. Mineralization showed the most obvious differences: soil slurries achieved the best results both concerning the extent of mineralization and the time required. The highest extent of pyrene mineralization (54% within 21 days) was observed in soil slurries; in liquid media, pyrene mineralization was slower, but reached approximately the same extent (54% in 150 days); in soils, mineralization reached only 36% of added pyrene after 160 days. Benzo[a]pyrene was mineralized in a mixture of PAHs in soil slurries to an extent of 34% within 70 days, whereas mineralization in liquid medium and soil occurred in the range of 5% (70 days). Mineralization of benzo[a]pyrene in sand slurries was lower compared to soil slurries (19% in sand slurries vs. 32% in soil slurries within 50 days).     

ADSORPTION–DESORPTION,PERSISTENCE, AND LEACHING BEHAVIOR OF DITHIOPYR IN AN ALLUVIAL SOIL OF INDIA

Investigations were undertaken to determine the adsorption–desorption, persistence and leaching of dithiopyr (S,S′-dimethyl 2-difluoromethyl-4-isobutyl-6-trifluoromethyl pyridine-3,5-dicarbothioate) in an alluvial soil under laboratory condition. The adsorption–desorption studies were carried out using batch equilibration technique. The mass balance studies showed that 83–97% of the pesticide was recovered during adsorption–desorption studies. The results revealed strong adsorption of dithiopyr in alluvial soil with K_d values ranging from 3.97–5.78 and Freundlich capacity factor (K_F) value of 2.41. The strong adsorption was evident from the hysteresis effect observed during desorption. The hysteresis coefficients ranged from 0.17–0.40.

The persistence studies were carried out at two concentrations (1.0 and 10.0 μg g^?1 level) under field capacity moisture and submerged condition by incubating the treated soil at 25±1°C. In general, dithiopyr persisted beyond 90 days with half-life varying from 11.5–12.9 days under different conditions. The rate of application and moisture regimes had no overall effect on the persistence. The leaching studies carried out in packed column under saturated flow condition revealed that dithiopyr was highly immobile in alluvial soil. Only small amounts (0.02–0.04%) were recovered from leachate whereas major portion (99.9%) remained in top layer of the soil column. The data suggest that strong adsorption of dithiopyr will cause a greater persistence problem in the soil. However, the chances of its movement to ground water will be negligible due to its immobility.     

Assessment of phenylurea herbicides sorption on various Mediterranean soils affected by irrigation with wastewater

The retention values of two herbicides, chlorotoluron and isoproturon, in five Mediterranean soils were assessed by two different approaches, a dynamic method, using a batch technique (BT) and a static method, using a soil saturated paste (SP). The SP method led in all cases to lower herbicide sorption when compared with BT, although pesticide distribution constants from both methods were linearly related for the set of used soils (R² ? 0.99) showing that both methods similarly reflected the behaviour of the different soils. Low-quality water, evaluated by employing recycled urban wastewater, did not modify herbicide sorption when compared with high quality water, in any soil and with any method.     

Effect of Manure on Glyphosate and Trifluralin Mineralization in Soil

Manure additions to soil may alter soil chemical, physical, and biological characteristics, and thereby change pesticide fate processes in soil. This is the first study to examine the impact of liquid hog manure amendments on glyphosate and trifluralin mineralization in soil. Experiments were conducted in soil microcosms in the laboratory for a total of 332 (glyphosate) and 430 (trifluralin) days. The rate and amount of mineralization of both glyphosate and trifluralin were significantly influenced by the additions of fresh manure to soil in the laboratory and by the history of manure applications in the field. However, the maximum difference in herbicide mineralization between soils that were free of manure application and those amended with manure in the field or in the laboratory was only 6.1% and 7.3% of that initially applied, for trifluralin and glyphosate, respectively. Therefore, we conclude that liquid hog manure application to soil will have no significant effect on the mineralization of glyphosate and trifluralin under field conditions.     

The effects of particle size, organic matter content, crop residues and dissolved organic matter on the sorption kinetics of atrazine and isoproturon by clay soil

Reliable predictions of the fate and behaviour of pesticides in soils is dependent on the use of accurate ‘equilibrium’ sorption constants and/or rate coefficients. However, the sensitivity of these parameters to changes in the physicochemical characteristics of soil solids and interstitial solutions remains poorly understood. Here, we investigate the effects of soil organic matter content, particle size distribution, dissolved organic matter and the presence of crop residues (wheat straw and ash) on the sorption of the herbicides atrazine and isoproturon by a clay soil. Sorption K_d's derived from batch ‘equilibrium’ studies for both atrazine and isoproturon by <2 mm clay soil were approximately 3.5 L/kg. The similarity of K_oc's for isoproturon sorption by the <2 mm clay soil and <2 mm clay soil oxidised with hydrogen peroxide suggested that the sorption of this herbicide was strongly influenced by soil organic matter. By contrast, K_oc's for atrazine sorption by oxidised soil were three times greater than those for <2 mm soil, indicating that the soil mineral components might have affected sorption of this herbicide. No significant differences between the sorption of either herbicide by <2 mm clay soil and (i) <250 μm clay soil, (ii) clay soil mixed with wheat straw or ash at ratios similar to those observed under field conditions, (iii) <2 mm clay soil in the presence of dissolved organic matter as opposed to organic free water, were observed.     

Enhanced Co-Metabolism of TCDD in the Presence of High Concentrations of Phenoxy Herbicides

Chemical residue studies were conducted from 1977-1987 on sites where spills of Agent Orange had occurred in the Herbicide Storage Sites at the Naval Construction Battalion Center, Gulfport, Mississippi, and on Johnston Island, Central Pacific Ocean. The soil persistence time of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was significantly decreased when in the presence of massive amounts of phenoxy herbicides (> 62,000 microg of herbicide/g of soil). Although microbial populations doubled in the most highly contaminated sites, fungal species diversity decreased. The dominant fungal species that appeared to be associated with the metabolism of the residues were of the genera Penicillium, Mucor, and Fusarium. TCDD level decreased from a mean high of 180 ng/g (ppb) to less than 1 ng/g of soil over a ten-year period.     

Dissipation and runoff transport of metazachlor herbicide in rapeseed cultivated and uncultivated plots in field conditions

The environmental fate of metazachlor herbicide was investigated under field conditions in rapeseed cultivated and uncultivated plots, over a period of 225 days. The cultivation was carried out in silty clay soil plots with two surface slopes, 1 and 5 %. The herbicide was detectable in soil up to 170 days after application (DAA), while the dissipation rate was best described by first-order kinetics and its half-life ranged between 10.92 and 12.68 days. The herbicide was detected in the soil layer of 10–20 cm from 5 to 48 DAA, and its vertical movement can be described by the continuous stirred tank reactor (CSTR) in series model. Relatively low amounts of metazachlor (less than 0.31 % of the initial applied active ingredient) were transferred by runoff water. More than 80 % of the total losses were transferred at the first runoff event (12 DAA), with herbicide concentrations in runoff water ranging between 70.14 and 79.67 μg L⁻¹. Minor amounts of the herbicide (less than 0.07 % of the initial applied active ingredient) were transferred by the sediment, with a maximum concentration of 0.57 μg g⁻¹ (12 DAA), in plots with 5 % inclination. Finally, in rapeseed plants, metazachlor was detected only in the first sampling (28 DAA) at concentrations slightly higher than the limit of quantification; when in seeds, no residues of the herbicide were detected.

     

Comparison of microbial pyrene and benzo[a]pyrene mineralization in liquid medium, soil slurry, and soil

The microbial degradation of 14C-pyrene and 14C-benzo[a]pyrene by a bacterial mixed culture was studied within a mixture of the PAHs phenanthrene, anthracene, pyrene, fluoranthene, and benzo[a]pyrene as sole carbon source in the different culture systems: (i) liquid medium, (ii) soil slurry (surface and grinding influence), and (iii) soil. The fate of these two labeled compounds was followed in these systems with an emphasis on mineralization to carbon dioxide, extractability, and adsorption to humic materials and formation of unextractable residual. Mineralization showed the most obvious differences: soil slurries achieved the best results both concerning the extent of mineralization and the time required. The highest extent of pyrene mineralization (54% within 21 days) was observed in soil slurries; in liquid media, pyrene mineralization was slower, but reached approximately the same extent (54% in 150 days); in soils, mineralization reached only 36% of added pyrene after 160 days. Benzo[a]pyrene was mineralized in a mixture of PAHs in soil slurries to an extent of 34% within 70 days, whereas mineralization in liquid medium and soil occurred in the range of 5% (70 days). Mineralization of benzo[a]pyrene in sand slurries was lower compared to soil slurries (19% in sand slurries vs. 32% in soil slurries within 50 days).     

Environmental fate and bioavailability of agent orange and its associated dioxin during the vietnam war

BACKGROUND: In 1996, the Committee on the Assessment of Wartime Exposure to Herbicides in Vietnam of the National Academy of Sciences' Institute of Medicine (IOM) issued a report on an exposure model for use in epidemiological studies of Vietnam veterans. This exposure model would consider troop locations based on military records; aerial spray mission data; estimated ground spraying activity; estimated exposure opportunity factors; military indications for herbicide use; and considerations of the composition and environmental fate of herbicides, including changes in the TCDD content of the herbicides over time, the persistence of TCDD and herbicides in the environment, and the degree of likely penetration of the herbicides into the ground. When the final report of the IOM Committee was released in October 2003, several components of the exposure model envisioned by the Committee were not addressed. These components included the environmental fate of the herbicides, including changes in the TCDD content over time, the persistence of TCDD and herbicides in the environment, and the degree of likely penetration of herbicides into the ground. This paper is intended to help investigators understand better the fate and transport of herbicides and TCDD from spray missions, particularly in performing epidemiological studies. METHODS: This paper reviews the published scientific literature related to the environmental fate of Agent Orange and the contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and discusses how this affected the potential exposure to TCDD of ground troops in Vietnam. Specifically, the mechanisms of dissipation and degradation as they relate to environmental distribution and bioavailability are addressed. RESULTS: The evaluation of the spray systems used to disseminate herbicides in Vietnam showed that they were capable of highly precise applications both in terms of concentrations sprayed and area treated. Research on tropical forest canopies with leaf area indices (a measure of foliage density) from 2 to 5 indicated that the amount of herbicide and associated TCDD reaching the forest floor would have been between 1 and 6% of the total aerial spray. Studies of the properties of plant surface waxes of the cuticle layer suggested that Agent Orange, including the TCDD, would have dried (i.e., be absorbed into the wax layer of the plant cuticle) upon spraying within minutes and could not be physically dislodged. Studies of Agent Orange and the associated TCDD on both leaf and soil surface have demonstrated that photolysis by sunlight would have rapidly decreased the concentration of TCDD, and this process continued in shade. Studies of 'dislodgeable foliar residues' (DFR, the fraction of a substance that is available for cutaneous uptake from the plant leaves) showed that only 8% of the DFR was present 1 hr after application. This dropped to 1% of the total 24 hrs after application. Studies with human volunteers confirmed that after 2 hrs of saturated contact with bare skin, only 0.15-0.46% of 2,4,5-T, one of the phenoxy acetic acid compounds that was an active ingredient of Agent Orange, entered the body and was eliminated in the urine. CONCLUSIONS: The prospect of exposure to TCDD from Agent Orange in ground troops in Vietnam seems unlikely in light of the environmental dissipation of TCDD, little bioavailability, and the properties of the herbicides and circumstances of application that occurred. Photochemical degradation of TCDD and limited bioavailability of any residual TCDD present in soil or on vegetation suggest that dioxin concentrations in ground troops who served in Vietnam would have been small and indistinguishable from background levels even if they had been in recently treated areas. Laboratory and field data reported in the literature provide compelling evidence on the fate and dislodgeability of herbicide and TCDD in the environment. This evidence of the environmental fate and poor bioavailability of TCDD from Agent Orange is consistent with the observation of little or no exposure in the veterans who served in Vietnam. Appreciable accumulation of TCDD in veterans would have required repeated long-term direct skin contact of the type experienced by United States (US) Air Force RANCH HAND and US Army Chemical Corps personnel who handled or otherwise had direct contact with liquid herbicide, not from incidental exposure under field conditions where Agent Orange had been sprayed.     

2,4-Dichlorophenoxy Acetic Acid Mineralization in Amended Soil

The application of municipal biosolid or liquid hog manure to agricultural soils under laboratory conditions at 20°C influenced the fate of the herbicide 2,4-D [2,4-(dichlorophenoxy)acetic acid] in soil. When 2,4-D was added to soil at agronomic rates immediately after the addition of manure or biosolids to a coarse-textured soil, the percentage of 2,4-D mineralized at 100 days was about 47% for both treatments, compared to only 31% for control soils without amendments. The enhanced 2,4-D mineralization as a result of amendment addition was due to an increased heterotrophic microbial activity, with the greatest increases in soil respiration occurring for soils amended with biosolids. When additions of 2,4-D were delayed for one, two, or four weeks after the amendments were applied, the additions of amendments generally reduced 2,4-D mineralization in soil, particularly for manure, indicating that the effect of amendments on enhancing soil microbial activities diminished over time. In contrast, the mineralization of 2,4-D in control soils was less dependent on when 2,4-D was applied in relation to pre-incubations of soil for zero, one, two, or four weeks. The effect of manure on decreasing 2,4-D mineralization in specific soils was as large as the effect of soil texture on differences in 2,4-D mineralization across soils. Because manure was not found to impact 2,4-D sorption by soil, it is possible that 2,4-D mineralization decreased because 2,4-D transformation products were strongly sorbed onto organic carbon constituents in manure-amended soils and were therefore less accessible to microorganisms. Alternatively, microorganisms were less likely to metabolize the herbicide because they preferentially consumed the type of organic carbon in manure that is a weak sorbent for 2,4-D.     

Aminocyclopyrachlor sorption-desorption and leaching from three Brazilian soils

This study aimed to evaluate the sorption-desorption and leaching of aminocyclopyrachlor from three Brazilian soils. The sorption-desorption of ¹⁴C-aminocyclopyrachlor was evaluated using the batch method and leaching was assessed in glass columns. The Freundlich model showed an adequate fit for the sorption-desorption of aminocyclopyrachlor. The Freundlich sorption coefficient [K_{f (sorption)}] ranged from 0.37 to 1.34 µmol ^(1–1/n) L^1/n kg^?1 and showed a significant positive correlation with the clay content of the soil, while the K_{f (desorption)} ranged from 3.62 to 5.36 µmol ^(1–1/n) L^1/n kg^?1. The K_{f (desorption)} values were higher than their respective K_{f (sorption)}, indicating that aminocyclopyrachlor sorption is reversible, and the fate of this herbicide in the environment can be affected by leaching. Aminocyclopyrachlor was detected at all depths (0?30 cm) in all the studied soils, where leaching was influenced by soil texture. The total herbicide leaching from the sandy clay and clay soils was <0.06%, whereas, ～3% leached from the loamy sand soil. The results suggest that aminocyclopyrachlor has a high potential of leaching, based on its low sorption and high desorption capacities. Therefore, this herbicide can easily contaminate underground water resources.     

Dissipation of alachlor in cotton plant, soil and water and its bioaccumulation in fish

Dissipation of alachlor in soil and plant in field condition (cotton cropping system), and in soil, water and fish in simulated model ecosystem was investigated. The acetanilide herbicide, alachlor (50% w/w EC) was applied as pre-emergence at 2.5 and 5.0 kg a.i.ha(-1) three days after sowing the cotton seeds in the field. Soil and plant samples were collected at intervals and analyzed for alachlor residues. To study the fate of alachlor in water and fish, a simulated model ecosystem was constructed and fish was introduced one day after herbicide application. The dissipation of alachlor in water and soil and bioaccumulation in fish was observed in model ecosystem. At harvest, cotton lint and seed samples were found to contain alachlor well below the detectable level. However, trace amounts of residues were found in cotton oil. After harvest of cotton, coriander (Coriandrum sativum) and edible amaranth (Amaranthus mangostanus L.) were raised for herbicide bioassay. The green leafy vegetable samples did not show any toxic symptoms of alachlor residues.     

Dissipation of 2,4-D in soils of the Humid Pampa region, Argentina: a microcosm study

Phenoxy herbicides like 2,4-dichlorophenoxyacetic acid (2,4-D) are widely used in agricultural practices. Although its half life in soil is 7-14d, the herbicide itself and its first metabolite 2,4-dichlorophenol (2,4-DCP) could remain in the soil for longer periods, as a consequence of its intensive use. Microcosms assays were conducted to study the influence of indigenous microflora and plants (alfalfa) on the dissipation of 2,4-D from soils of the Humid Pampa region, Argentina, with previous history of phenoxy herbicides application. Results showed that 2,4-D was rapidly degraded, and the permanence of 2,4-DCP in soil depended on the presence of plants and soil microorganisms. Regarding soil microbial community, the presence of 2,4-D degrading bacteria was detected even in basal conditions in this soil, possibly due to the adaptation of the microflora to the herbicide. There was an increment of two orders of magnitude in herbicide degraders after 15d from 2,4-D addition, both in planted and unplanted microcosms. Total heterotrophic bacteria numbers were about 1x10(8) CFUg(-1) dry soil and no significant differences were found between different treatments. Overall, the information provided by this work indicates that the soil under study has an important intrinsic degradation capacity, given by a microbial community adapted to the presence of phenoxy herbicides.     

Determination of sulfosulfuron residues in soil under wheat crop by a novel and cost-effective method and evaluation of its carryover effect

A novel and cost-effective method of sulfosulfuron extraction has been developed using distilled water as an extraction solvent. Using this method, the environmental fate of sulfosulfuron was investigated in soil under wheat crop. Studies were conducted under natural field conditions in randomized block design and herbicide (75% water dispersible granules (WG)) was applied after 24 days of sowing. The rates of applications were 25 and 50 g of active ingredient (a.i.) per hectare. Soil samples were collected at predetermined intervals and analyzed by high performance liquid chromatography (HPLC). The minimum detection limit was found to be 0.001 μ g g^{? 1}. The dissipation of sulfosulfuron followed first-order rate kinetics and dissipated with a half-life of 5.4–6.3 days. After harvest, field soil was used for conducting a pot experiment with bottle gourd (Lagenaria siceraria) as test plants to study the carry over effect of sulfosulfuron. No phytotoxicity was observed to bottle gourd in pot experiment with harvest soil.     

Factors Influencing 2,4-D Sorption and Mineralization in Soil

Abstract

This study quantified 2,4-D [(2,4-dichlorophenoxy)acetic acid] sorption and mineralization rates in five soils as influenced by soil characteristics and nutrient contents. Results indicated that 2,4-D was weakly sorbed by soil, with Freundlich distribution coefficients ranging from 0.81 to 2.89 µg^1?1/n  g^?1 mL^{1/ n} . First-order mineralization rate constants varied from 0.03 to 0.26, corresponding to calculated mineralization half-lives of 3 and 22 days, respectively. Herbicide sorption generally increased with increasing soil organic carbon content, but the extent of 2,4-D sorption per unit organic carbon varied among the soils due to differences in soil pH, clay content and/or organic matter quality. Herbicide mineralization rates were greater in soils that sorbed more 2,4-D per unit organic carbon, and that had greater soil nitrogen contents. We conclude that the effect of sorption on herbicide degradation cannot be generalized without a better understanding of the effects of soil characteristics and nutrient content on herbicide behavior in soil.     

Phototransformation of Clodinafop-Propargyl

Abstract

Photodegradation of the herbicide clodinafop-propargyl was investigated on glass surface under sunlight and UV light. Four photoproducts were identified by NMR, IR, and MS. Major photolysis products were 2-[(5-chloro-3-fluoro-2-pyridyloxy) phenoxy] propanoic acid and prop-2-ynyl-2-[(5-chloro-3-hydroxy-2-pyridyloxy) phenoxy] propanoate, while minor were ethyl 2-[(5-chloro-3-fluoro-2-pyridyloxy) phenoxy] propanoate and 1-hydroxypropanyl-2-[(5-chloro-3-fluoro-2-pyridyloxy) phenoxy] propanoate. Rate of photodegradation followed first-order kinetics with significant correlation coefficient. The major photoproducts were observed in maximum quantity on the 7th and 10th day and further degraded within 15–20 days.     

Effect of soil and sediment composition on acetochlor sorption and desorption

Background, aim, and scope  Herbicide fate and its transport in soils and sediments greatly depend upon sorption–desorption processes. Quantitative determination of herbicide sorption–desorption is therefore essential for both the understanding of transport and the sorption equilibrium in the soil/sediment–water system; and it is also an important parameter for predicting herbicide fate using mathematical simulation models. The total soil/sediment organic carbon content and its qualitative characteristics are the most important factors affecting sorption–desorption of herbicides in soil or sediment. Since the acetochlor is one of the most frequently used herbicides in Slovakia to control annual grasses and certain annual broad-leaved weeds in maize and potatoes, and posses various negative health effects on human beings, our aim in this study was to investigate acetochlor sorption and desorption in various soil/sediment samples from Slovakia. The main soil/sediment characteristics governing acetochlor sorption–desorption were also identified. Materials and methods  The sorption–desorption of acetochlor, using the batch equilibration method, was studied on eight surface soils, one subsurface soil and five sediments collected from the Laborec River and three water reservoirs. Soils and sediments were characterized by commonly used methods for their total organic carbon content, distribution of humus components, pH, grain-size distribution, and smectite content, and for calcium carbonate content. The effect of soil/sediment characteristics on acetochlor sorption–desorption was examined by simple correlation analysis. Results  Sorption of acetochlor was expressed as the distribution coefficient (K _d). K _d values slightly decreased as the initial acetochlor concentration increased. These values indicated that acetochlor was moderately sorbed by soils and sediments. Highly significant correlations between the K _d values and the organic carbon content were observed at both initial concentrations. However, sorption of acetochlor was most closely correlated to the humic acid carbon, and less to the fulvic acid carbon. The total organic carbon content was found to also significantly influence acetochlor desorption. Discussion  Since the strong linear relationship between the K _d values of acetochlor and the organic carbon content was already released, the corresponding K _oc values were calculated. Considerable variation in the K _oc values suggested that other soil/sediment parameters besides the total soil organic carbon content could be involved in acetochlor sorption. This was revealed by a significant correlation between the K _oc values and the ratio of humic acid carbon to fulvic acid carbon (C_HA/C_FA). Conclusions  When comparing acetochlor sorption in a range of soils and sediments, different K _d values which are strongly correlated to the total organic carbon content were found. Concerning the humus fractions, the humic acid carbon content was strongly correlated to the K _d values, and it is therefore a better predictor of the acetochlor sorption than the total organic carbon content. Variation in the K _oc values was attributed to the differences in distribution of humus components between soils and sediments. Desorption of acetochlor was significantly influenced by total organic carbon content, with a greater organic carbon content reducing desorption. Recommendations and perspectives  This study examined the sorption–desorption processes of acetochlor in soils and sediments. The obtained sorption data are important for qualitative assessment of acetochlor mobility in natural solids, but further studies must be carried out to understand its environmental fate and transport more thoroughly. Although, the total organic carbon content, the humus fractions of the organic matter and the C_HA/C_FA ratio were sufficient predictors of the acetochlor sorption–desorption. Further investigations of the structural and chemical characteristics of humic substances derived from different origins are necessary to more preciously explain differences in acetochlor sorption in the soils and sediments observed in this study.