Atrazine degradation and residues distribution in two acid soils from temperate humid zone

Mineralization of atrazine and formation of extractable and non-extractable "bound" residues were followed under laboratory conditions in two contrasting soils (organic C, texture, and atrazine application history) from northern Spain. The soils, a Humic Cambisol (MP) and a Gleyic Cambisol (G) were incubated with labeled atrazine (ring-13C atrazine) at field application dose and measurements were made at different time intervals during 3 mo. Fate and behavior of atrazine along the incubation showed different patterns between the two soils, the time taken for degradation of 50% (DT50) being 9 and 44 d for MP and G soils, respectively. In MP soil, with 40 yr of atrazine application and lower organic C and clay content, more than 89% of U-13C-atrazine added was mineralized after 12 wk, with most mineralization occurring within the first 2 wk. G soil, with 10 yr of atrazine application, exhibited a more progressive U-13C-atrazine mineralization, reaching 54% of initially added atrazine at 12 wk. Hydroxyatrazine and deisopropylatrazine were the metabolites founded in the extractable fraction, demonstrating that both chemical and biological processes are involved in atrazine degradation. Soil G showed during all the incubation times an extractable residues fraction greater than that in MP soil, indicating a high potential risk of soil and water contamination. Rapid microbial degradation through s-triazine ring cleavage was proposed to be the main decomposition pathway of atrazine for the two soils studied. Bound residues pool also differed notably between soils accounting for 9 and 41% of initially added atrazine, the higher values shown by soil with higher organic matter and clay content (G soil).     

Salt-induced land and water degradation in the Aral Sea basin: A challenge to sustainable agriculture in Central Asia

Expansion of irrigated agriculture in the Aral Sea Basin in the second half of the twentieth century led to the conversion of vast tracks of virgin land into productive agricultural systems resulting in significant increases in employment opportunities and income generation. The positive effects of the development of irrigated agriculture were replete with serious environmental implications. Excessive use of irrigation water coupled with inadequate drainage systems has caused large‐scale land degradation and water quality deterioration in downstream parts of the basin, which is fed by two main rivers, the Amu‐Darya and Syr‐Darya. Recent estimates suggest that more than 50% of irrigated soils are salt‐affected and/or waterlogged in Central Asia. Considering the availability of natural and human resources in the Aral Sea Basin as well as the recent research addressing soil and water management, there is cause for cautious optimism. Research‐based interventions that have shown significant promise in addressing this impasse include: (1) rehabilitation of abandoned salt‐affected lands through halophytic plant species; (2) introduction of 35‐day‐old early maturing rice varieties to withstand ambient soil and irrigation water salinity; (3) productivity enhancement of high‐magnesium soils and water resources through calcium‐based soil amendments; (4) use of certain tree species as biological pumps to lower elevated groundwater levels in waterlogged areas; (5) optimal use of fertilizers, particularly those supplying nitrogen, to mitigate the adverse effects of soil and irrigation water salinity; (6) mulching of furrows under saline conditions to reduce evaporation and salinity buildup in the root zone; and (7) establishment of multipurpose tree and shrub species for biomass and renewable energy production. Because of water withdrawals for agriculture from two main transboundary rivers in the Aral Sea Basin, there would be a need for policy level interventions conducive for enhancing interstate cooperation to transform salt‐affected soil and saline water resources from an environmental and productivity constraint into an economic asset.     

Utilization of biosolids during the phytoremediation of hydrocarbon-contaminated soil

Addition of anaerobically digested sewage sludge (biosolids) to soil may improve conditions for phytoremediation of petroleum hydrocarbons (PHCs) through improved soil chemical, biological, and physical properties. A 32-wk greenhouse study investigated three rates of biosolids addition (0, 13.34, and 26.68 g oven-dry biosolids kg(-1) oven-dry soil) and the presence or absence of smooth brome (Bromus inermis Leyss. cv. Carlton) plants on the removal of diesel (3.5 g kg(-1) oven-dry soil) in an industrial, sandy loam soil. Diesel PHCs were divided into two fractions based on equivalent normal straight-chain boiling point ranges (F2: nC10-nC16; F3: nC16-nC34). The addition of biosolids did not increase the extent of PHC degradation but did result in significantly greater first-order decay constants compared to unamended controls. Overall, the presence of plants did not increase the rate or extent of PHC degradation, relative to that observed in unamended, non-vegetated soils. Vegetation was, however, an important factor within the biosolids-amended soils as was observed by a greater extent of PHC degradation. Some of this decrease was attributed to plant-induced removal of biosolids components that were contributing to the F3 fraction. Overall, the low-amendment rate (13.34 g oven-dry biosolids kg(-1) oven-dry soil) was considered to be the most effective treatment because it produced the greatest overall PHC degradation rate (0.226 wk(-1) for total PHCs) and resulted in the greatest recovery of biosolids-derived N by smooth brome (26.6%).     

Agricultural land use and soil degradation in a part of kwara state,Nigeria

Summary Because of the alarming rate of increase in population all over tropical Africa, and the consequent need to grow more food, several writers have suggested the practice of continuous or permanent cultivation in place of the traditional bush fallowing system. This suggestion has been made without recognising the natural vulnerability of tropical soils and the associated problems of actual soil degradation, especially in situations where fertilizer inputs are limited. This study examines the effects of different land use practices on actual soil degradation in a part of Kwara State, Nigeria. This involves comparing the physical and chemical properties of the soils in areas under continuous cultivation, fallow and forests, and using the technique of factor analysis to isolate indices which best describe these phenomena. The results show that the main effects of continuous cultivation in the area examined were to increase the acidity of the soil, that soil organic matter content was likely to double after 10 years of fallow conditions, and that continuous cultivation was capable of reducing the cation-exchange capacity of soils by at least one-third.In general, the soils of the area of study display marked variability, especially with respect to their chemical properties. This is mainly due to variations in soil organic matter content, which in itself is due to differences in agricultural land use practices. Factor analysis of the soil properties generated four main indices of actual soil degradation, of which organic matter is the most important. Some implications of the results are examined, particularly in relation to generating an awareness of actual soil degradation and land use planning.Dr J. Oluwole Ameyan, the senior author, is on the staff of the University of Ilorin. Mr O. Ogidiolu is at the Department of Geography, Ondo State University, Ado-Ekiti, Nigeria.     

Regional assessment of herbicide sorption and degradation in two sampling years

Sorption and degradation of the herbicide 2,4-D [2,4-dichlorophenoxyacetic acid] were determined for 123 surface soils (0 to 15 cm) collected in 2002 and in 2004 between 49 degrees to 60 degrees north longitude and 110 degrees to 120 degrees west latitude in Alberta, Canada. The soils were characterized by soil organic carbon content (SOC), pH, electrical conductivity, soil texture, cation exchange capacity, carbonate content, and total soil microbial activity. The 2,4-D sorption coefficients, Kd and Koc, were highly variable with coefficients of variation of 89 and 59%, respectively, at the provincial scale. Both Kd and Koc were well described by regression models with SOC and soil pH as variables, regardless of scale. Surprisingly, variations in 2,4-D mineralization were much smaller than variations in sorption. Variability in total 2,4-D mineralization was particularly low, with a coefficient of variation of only 7% at the provincial scale. Average 2,4-D half-lives in ecoregions ranged from 1.7 to 3.5 d, much lower than the field dissipation half-life of 10 d reported for 2,4-D in general pesticide property databases. Regression models describing degradation parameters were generally poor or not significant because 2,4-D mineralization was only weakly associated with measured 2,4-D sorption parameters and soil properties. As such, regional variations in herbicide sorption coefficients should be measured or calculated based on soil properties, to assign distinct pesticide fate model input parameters when estimating 2,4-D off-site transport at the provincial scale. Spatial variations in herbicide degradation appear less important for Alberta as 2,4-D half-lives were similar in soils across the province. The rapid mineralization of 2,4-D is noteworthy because 2,4-D is widely used in Alberta and perhaps adaptation of soil microbial communities allowed for accelerated degradation regardless of soil properties or the extent of 2,4-D sorption by soil.     

Effect of the Prestige oil spill on salt marsh soils on the coast of Galicia (northwestern Spain)

At four estuarine sites on the coast of Galicia (northwestern Spain), all of which were affected by the Prestige oil spill, soil samples were taken from polluted and unpolluted areas and their petroleum hydrocarbon contents, heavy metal contents, and other chemical and physical characteristics were measured. Oil pollution altered both chemical and physical soil properties, aggregating soil particles in plaques, lowering porosity, and increasing resistance to penetration and hydrophobicity. The chromium, nickel, copper, iron, lead, and vanadium contents of polluted soils were between 2 and 2500 times higher than those of their unpolluted counterparts and the background concentrations in Galician coastal sediments. In the cases of Cr, Cu, Ni, Pb, and V, their origin in the polluting oil was corroborated by the high correlation (r >/= 0.74) between the concentrations of these metals and the total petroleum hydrocarbon (TPH) content of the polluted soils. Soil redox potentials ranged from -19 to -114 mV in polluted soils and 112 to 164 mV in unpolluted soils, and were negatively correlated with TPH content (p < 0.01). The low values in the polluted soils explain why the soluble fractions of their total heavy metal contents were very small (generally less than 3%, and in many cases undetectable).     

Biogas production from slaughterhouse wastewaters and use of biofertilizer obtained for biodegradation of aromatic hydrocarbons

The anaerobic digestion of industrial wastes produces a biogas that is an alternative to the use of fossil fuels for energy production. At the end of this process, the stabilized biomass presents high levels of nutrients, which can be used both as biofertilizers in agriculture and for the biodegradation of contaminants in the soil through improvement of the microbiota. Thus, this study aimed to evaluate biogas production by industrial wastes and to use the biofertilizer for the bioremediation of soils previously contaminated with gasoline. The biomass (420 mL) generated approximately 10 liters (L) of methane and 3 L of other gases. Anaerobic incubation reduced total and volatile solids, as well as biochemical oxygen demand, chemical oxygen demand, and the carbon and nitrogen contents of the biomass. The bioremediation experiment showed that 15 days after contamination with gasoline, the addition of the biofertilizer improved the degradation efficiency of monoaromatic hydrocarbons; however, the degradation of polyaromatic hydrocarbons was less time efficient. So, we conclude that the anaerobic incubation of industrial wastes generates a high amount of biogas, and that biofertilizer deposition into contaminated soil does not affect the efficiency of the degradation of aromatic hydrocarbons after 30 days. Novelty or significance : Anaerobic incubation of industrial wastes generates a high calorific value gas, which can be used as an alternative source of energy. And, the resulting biomass, called biofertilizer, can be used to remediate soils contaminated with hydrocarbons.     

Bioremediation of Soil Degraded by Sewage Sludge: Effects on Soil Properties and Erosion Losses

Soils in the Mediterranean area are very prone to erosion due to the loss of organic matter and the consequent lack of protective vegetation. In this experiment a Mediterranean degraded soil with a 15% slope was amended at a rate of 250 t ha^–1 wet weight with sewage sludge and with a mixture of sewage sludge and barley straw (70% carbon from sewage sludge and 30% from the straw) in order to study their influence on soil structure recovery and hence the soilss resistance to erosion processes. Both types of organic amendment led to an improvement in several soil properties (physical, biological, and microbiological) as a result of the spontaneous growth plant covering that became evident three months after amendment. This vegetation remained throughout the two years of the experiment and prevented the water erosion processes that normally precede soil degradation. Amendment by sewage sludge alone reduced soil loss by 80% compared with the control soil, while the mixture that included both sewage sludge and barley straw reduced losses by 84%, both reducing runoff by 57%. The amended soils showed increases in the percentage of stable aggregates, the levels of the total and water-soluble C fractions, microbial biomass C, basal respiration, and the activity of the different enzymes involved in the biogeochemical cycles of C, N, and P. The results confirm the usefulness of sewage sludge as an organic amendment for recovering damaged soils.     

施用污泥堆肥对滩涂土壤理化性质的影响

污泥堆肥中富含有机质营养成分，可改良土壤，同时要防止重金属和病原菌等可能引起的污染。为评价污泥堆肥作为土壤改良基质的可能性，本试验系统进行了上海曲阳水质净化厂污泥堆肥／滩涂土混配土的理化性质分析。研究结果表明，污泥堆肥与滩涂土混配后，土壤pH、电导率、阳离子交换量等理化指标得到改善；营养得到补充，肥力提高明显；混配土中未见病原菌污染问题，污泥堆肥施加比例控制在30％（干重计）以内时，也不存在重金属污染风险，混配土可以满足农用要求。     

Soil fate of agricultural fumigants in raised-bed, plasticulture systems in the southeastern United States

Soil concentrations and degradation rates of methyl isothio-cyanate (MITC), chloropicrin (CP), 1,3-dichloropropene (1,3-D), and dimethyl disulfide (DMDS) were determined under fumigant application scenarios representative of commercial raised bed, plastic mulched vegetable production systems. Five days after application, 1,3-D, MITC, and CP were detected at concentrations up to 3.52, 0.72, and 2.45 μg cm, respectively, in the soil atmosphere when applications were made in uniformly compacted soils with a water content >200% of field capacity and covered by a virtually impermeable or metalized film. By contrast, DMDS, MITC, and CP concentrations in the soil atmosphere were 0.81, 0.02, and 0.05 μg cm, respectively, 5 d after application in soil containing undecomposed plant residue, numerous large (>3 mm) clods, and water content below field capacity and covered by low-density polyethylene. Ranked in order of impact on the persistence of fumigants in soil were soil water content (moisture), soil tilth (the physical condition of soil as related to its fitness as a planting bed), the type of plastic film used to cover fumigated beds, and soil texture. Fumigants were readily detected 13 d after application when applied in uniformly compacted soils with water contents >200% of capacity and covered by a virtually impermeable or metalized film. By contrast, 1,3-D and MITC had dissipated 5 d after application in soils with numerous large (>3 mm) clods and water contents below field capacity that were covered by low-density polyethylene. Soil degradation of CP, DMDS, and MITC were primarily attributed to biological mechanisms, whereas degradation of 1,3-D was attributed principally to abiotic factors. This study demonstrates improved soil retention of agricultural fumigants in application scenarios representative of good agricultural practices.     

Concrete grinding residue characterization and influence on infiltration

Concrete grinding residue (CGR) is a slurry byproduct created by concrete pavement maintenance operations. Disposal of CGR slurry is presently regulated on the basis of very minimal information. The least immediate expense is incurred by spreading CGR slurry directly on vegetated roadway ditches and embankments. The direct disposal impacts to environmental quality in terms of soil physical or chemical properties are not known. Five CGR materials from widely dispersed sites in the United States were analyzed for particle size distribution and evaluated with a suite of USEPA physical and chemical analyses. Values found for the parameters examined are not considered harmful. An infiltration column study was also conducted in which two CGRs were mixed at 8 and 25% by weight and also surface applied 2.5 mm deep with two contrasting (relatively fine and coarse textured) soils. With the finer soil, statistically (p < 0.05) significant decrease in infiltration time (increased infiltration rate) was associated with the 25% and surface-applied CGR treatments, compared with the untreated control soil. The results indicate that excessive application of CGR may increase water infiltration into soil in the short-term. This should be kept in mind, but does not appear to be generally detrimental.     

Competitive degradation between the fumigants chloropicrin and 1,3-dichloropropene in unamended and amended soils

The mixture of 1,3-dichloropropene (1,3-D) and chloropicrin (CP) is used as a preplant soil fumigant. In comparison with individual fumigants, application of a mixture may affect the environmental dissipation and fate of each chemical, such as emission and degradation. We investigated the degradation of CP, 1,3-D, and their mixture in fresh soils and sterile soils, and evaluated the competitive characteristic of fumigants in the mixture. The degradation of low concentrations of CP in fresh soil was accelerated at early times in the presence of 1,3-D, whereas the addition of CP reduced the degradation rate of trans-1,3-D, possibly by inhibiting the activity of trans-1,3-D degrading microorganisms. The potential of applying amendments to the soil to increase the rate of CP and 1,3-D degradation was also illustrated. The degradation of both fumigants was significantly enhanced in soils amended with ammonium thiosulfate (ATS) and sodium diethyldithiocarbamate (Na-DEDTC) compared with unamended soil. Competitive degradation was observed for CP in amended soils in the presence of 1,3-D. The degradation of cis-1,3-D in amended soils spiked as a mixture of 1,3-D and CP was repressed compared with the rate of degradation in samples spiked with 1,3-D only. This implied that in abiotic degradation, CP and cis-1,3-D competed for a limited number of reaction sites in amended soil, resulting in decreased degradation rates. No significant influence of fumigant mixtures was observed for trans-1,3-D in amended soil.     

Biochar and earthworm effects on soil nitrous oxide and carbon dioxide emissions

Biochar is the product of pyrolysis produced from feedstock of biological origin. Due to its aromatic structure and long residence time, biochar may enable long-term carbon sequestration. At the same time, biochar has the potential to improve soil fertility and reduce greenhouse gas (GHG) emissions from soils. However, the effect of biochar application on GHG fluxes from soil must be investigated before recommendations for field-scale biochar application can be made. A laboratory experiment was designed to measure carbon dioxide (CO) and nitrous oxide (NO) emissions from two Irish soils with the addition of two different biochars, along with endogeic (soil-feeding) earthworms and ammonium sulfate, to assist in the overall evaluation of biochar as a GHG-mitigation tool. A significant reduction in NO emissions was observed from both low and high organic matter soils when biochars were applied at rates of 4% (w/w). Earthworms significantly increased NO fluxes in low and high organic matter soils more than 12.6-fold and 7.8-fold, respectively. The large increase in soil NO emissions in the presence of earthworms was significantly reduced by the addition of both biochars. biochar reduced the large earthworm emissions by 91 and 95% in the low organic matter soil and by 56 and 61% in the high organic matter soil (with and without N fertilization), respectively. With peanut hull biochar, the earthworm emissions reduction was 80 and 70% in the low organic matter soil, and only 20 and 10% in the high organic matter soil (with and without N fertilization), respectively. In high organic matter soil, both biochars reduced CO efflux in the absence of earthworms. However, soil CO efflux increased when peanut hull biochar was applied in the presence of earthworms. This study demonstrated that biochar can potentially reduce earthworm-enhanced soil NO and CO emissions. Hence, biochar application combined with endogeic earthworm activity did not reveal unknown risks for GHG emissions at the pot scale, but field-scale experiments are required to confirm this.     

四川盆地丘陵区紫色土退化研究——Ⅱ.紫色土退化的微形态特征

采用比较研究法和辅以定点追踪观测,研究了四川盆地丘陵区几种主要紫色土退化的微形态特征。根据土壤退化的某些微形态诊断特征,将紫色土退化问题归纳为土壤物理性退化、土壤构造性退化和土壤营养性退化等类;在此基础上,评价了本区几种主要紫色土的退化状况,并提出应重点治理典型紫色土的退化和紫色土普遍存在的构造性退化问题。     

Volatilization and degradation of soil-applied dimethylselenide

Dimethylselenide (DMSe) is a highly volatile gas that is produced by indigenous microorganisms in seleniferous soils and sediments; however, little is known about the soil conditions that affect the persistence of DMSe and its transport to the atmosphere. In this study we investigated the effect of moisture content, temperature, and organic amendments on the degradation of soil-applied DMSe. The degradation of DMSe was entirely a result of biological mechanisms, but changes in temperature (20-40 degrees C) and soil moisture content (30-70% of the maximum water holding capacity) had little influence on the degradation rate. In contrast, amending soil with either 1% casein or gluten (by weight) had an inhibitory effect on the degradation of DMSe. After 18 d, 2.1 times more DMSe was present in the casein-amended soil and 2.6 times more DMSe was present in the gluten-amended soil. The transport of DMSe in packed soil columns was also investigated. Increasing the depth to soil surface was found to significantly decrease the amount of DMSe transported to the air. After 6 d, 57% of DMSe injected 10 cm below the soil surface was volatilized. At an injection depth of 20 cm the cumulative emissions were reduced by 38% and at 30 cm the cumulative emissions were reduced by 51%. In columns containing 1% casein or gluten in the top 5 cm of soil the cumulative loss of DMSe was about 9% higher than in unamended soil. Increasing our understanding of the soil conditions that influence the gaseous diffusion of DMSe should help in determining the feasibility of using Se volatilization as a remediation technique.     

Laboratory degradation studies of bentazone, dichlorprop, MCPA, and propiconazole in Norwegian soils

Laboratory degradation studies were performed in Norwegian soils using two commercial formulations (Tilt and Triagran-P) containing either propiconazole alone or a combination of bentazone, dichlorprop, and MCPA. These soils included a fine sandy loam from Hole and a loam from Kroer, both of which are representative of Norwegian agricultural soils. The third soil was a highly decomposed organic material from the Froland forest. A fourth soil from the Skuterud watershed was used only for propiconazole degradation. After 84 d, less than 0.1% of the initial MCPA concentration remained in all three selected soils. For dichlorprop, the same results were found for the fine sandy loam and the organic-rich soil, but in the loam, 26% of the initial concentration remained. After 84 d, less than 0.1% of the initial concentration of bentazone remained in the organic-rich soil, but in the loam and the fine sandy loam 52 and 69% remained, respectively. Propiconazole was shown to be different from the other pesticides by its persistence. Amounts of initial concentration remaining varied from 40, 70, and 82% in the reference soils after 84 d for the organic-rich soil, fine sandy loam, and loam, respectively. The organic-rich soil showed the highest capacity to decompose all four pesticides. The results from the agricultural soils and the Skuterud watershed showed that the persistence of propiconazole was high. Pesticide degradation was approximated to first-order kinetics. Slow rates of degradation, where more than 50% of the pesticide remained in the soil after the 84-d duration of the experiment, did not fit well with first-order kinetics.     

Influence of pyrene combination state in soils on its treatment efficiency by Fenton oxidation

Interactions of hydrophobic organic compounds (HOCs) with soil organic matter (SOM) determine their combination state in soils, and therefore strongly influence their mobility, bioavailability, and chemical reactivity. Contact time (aging) of an HOC in soil also strongly influences its combination state and environmental fate. We studied Fenton oxidation of pyrene in three different soils to reveal the influences of SOM, contact time, and combination state on the efficiency of vigorous chemical reactions. Pyrene degradation efficiency depended strongly on the dose of oxidant (H(2)O(2)) and catalyst (Fe(2+)); the greatest degradation was achieved at an oxidant to catalyst molar ratio of 10:1. Pyrene degradation differed among the three soils, ranging from 65.4% to 88.9%. Pyrene degradation efficiency decreased with increasing SOM content, and the aromatic carbon content in SOM was the key parameter. We hypothesize that pyrene molecules that combine with the compact net structure of aromatic SOM are less accessible to Fenton oxidation. Furthermore, pyrene degradation efficiency decreased considerably after aged for 30 days, but further aging to 60 and 180 days did not significantly change degradation efficiency. The Fenton oxidation efficiency of pyrene in both unaged and aged soils was greater than the corresponding desorption rate during the same period, perhaps because Fenton reaction can make pyrene more accessible to the oxidant through the enhancement of HOCs' desorption by generating reductant species or by destroying SOM through oxidation.     

Degradation of methyl isothiocyanate and chloropicrin in forest nursery soils

Recent studies have observed enhanced degradation of methyl isothiocyanate (MITC) from repeated fumigation in agricultural soils. Little is known about fumigant degradation in forest and nursery soils. This study was conducted to determine degradation rates of MITC and chloropicrin (CP) in two forest soils and the impacts of nursery management on degradation of MITC and CP. The half-life values of MITC and CP were evaluated in the laboratory under isothermal conditions (22 +/- 2 degrees C). Three rates representing 0.5x, 1x, and 2x field application rates for each fumigant were used in laboratory incubations. Effect of microbial degradation was determined by conducting incubations with both fresh and sterilized soils. Soil moisture effects were also studied. There was no difference in MITC or CP degradation between fumigated and nonfumigated forest nursery soils. Soil sterilization and high soil moisture content (15% by wt.) reduced MITC and CP degradation. The degradation rates of MITC and CP varied with factors such as nursery history, fumigant application rates, and freshness of tested soils.     

Sorption and stability of the polycyclic nitramine explosive CL-20 in soil

The polycyclic nitramine CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) is being considered for use as a munition, but its environmental fate and impact are unknown. The present study consisted of two main elements. First, sorption-desorption data were measured with soils and minerals to evaluate the respective contributions of organic matter and minerals to CL-20 immobilization. Second, since CL-20 hydrolyzes at a pH of >7, the effect of sorption on CL-20 degradation was examined in alkaline soils. Sorption-desorption isotherms measured using five slightly acidic soils (5.1 < pH < 6.9) containing various amounts of total organic carbon (TOC) revealed a nonlinear sorption that increased with TOC [K(d) (0.33% TOC) = 2.4 L kg(-1); K(d) (20% TOC) = 311 L kg(-1)]. Sorption to minerals (Fe(2)O(3), silica, kaolinite, montmorillonite, illite) was very low (0 < K(d) < 0.6 L kg(-1)), suggesting that mineral phases do not contribute significantly to CL-20 sorption. Degradation of CL-20 in sterile soils having different pH values increased as follows: sandy agricultural topsoil from Varennes, QC, Canada (VT) (pH = 5.6; K(d) = 15 L kg(-1); 8% loss) < clay soil from St. Sulpice, QC, Canada (CSS) (pH = 8.1; K(d) = 1 L kg(-1); 82% loss) < sandy soil provided by Agriculture Canada (SAC) (pH = 8.1, K(d) = approximately 0 L kg(-1); 100% loss). The faster degradation in SAC soil compared with CSS soil was attributed to the absence of sorption in the former. In summary, CL-20 is highly immobilized by soils rich in organic matter. Although sorption retards abiotic degradation, CL-20 still decomposes in soils where pH is >7.5, suggesting that it will not persist in even slightly alkaline soils.     

Degradation of endosulfan in a clay soil from cotton farms of western Queensland.

The persistence and degradation of endosulfan isomers and their primary degradation product, endosulfan-sulfate, were studied in a clay soil from cotton farms of western Queensland. Endosulfan degradation in relation to soil moisture, temperature, day and night temperature fluctuation, waterlogging and re-application were studied. The results show that the degradation rates of both endosulfan isomers were greatly affected by changes in soil water content and temperature. Under a high water content-high temperature regime the concentration of alpha-endosulfan in the soil fell rapidly during the first 4 weeks of application, followed by a prolonged period of slower rate of degradation. Alpha endosulfan showed a bi-exponential form of degradation for all water content-temperature experiments except for extremes in both these two factors. In the submerged soils (and also in low-water content, low temperature, non-submerged experiments) no such rapid initial degradation of alpha-endosulfan was observed, and a single first-order rate equation describes the data. Degradation of beta-endosulfan was significantly slower than for the alpha-isomer under all conditions studied. A half-life of more than a year was recorded for the beta-isomer when both water content and temperature were low. The degradation of beta-endosulfan showed no sign of the bi-exponential function observed for alpha-isomer, and a single first order rate equation described the data obtained for each factor studied. Endosulfan-sulfate was the major degradation product in all non-submerged experiments. Its build up in the soil very closely followed the disappearance of alpha-endosulfan. Its highest build-up was in the high water content-low temperature experiments, but its persistence was primarily influenced by soil temperature. Both alpha and beta-isomers, and endosulfan sulfate, persisted longer in the submerged soil. Re-application of endosulfan, and day and night fluctuation of temperature had contrasting effects on the degradation of the two isomers. Both factors slowed down the degradation of alpha-endosulfan and enhanced that of beta-endosulfan, but their net effect was to prolong the overall persistence of this chemical in the soil. Submerged conditions reduced the net formation of endosulfan-sulfate and enhanced its degradation rate.