DT50 Values Research Articles

Isomerization of chlortetracycline in prairie wetland water.

Chlortetracycline (CTC), an antimicrobial administered as a feed additive to cattle, swine, and poultry, is present in the corresponding manure. Land application of raw or processed (composted or stockpiled) manure provides a mechanism by which CTC (and other antimicrobials) enters the environment and becomes available for transport to surface receiving waters via rainfall or snowmelt runoff. Chlortetracycline has been detected in Canadian surface waters, but little has been reported on its fate in aquatic ecosystems. To address this knowledge gap, the dissipation of CTC-enol was monitored in deionized water and water typical of wetlands within the prairie region of Canada. In deionized water, CTC-enol tautomerized to CTC-keto, and both tautomers epimerized to 4-epi-CTC-enol and 4-epi-CTC-keto, respectively. Irreversible isomerization to iso-CTC occurred, which then epimerized to 4-epi-iso-CTC. In wetland water, although tauterization of CTC-enol to CTC-keto occurred, there was no evidence of the formation of the 4-epimers of either CTC-enol or CTC-keto. The major product formed in the wetland water was iso-CTC, some of which epimerized to 4-epi-iso-CTC. Although CTC-enol was shown to tautomerize to CTC-keto, the concentration of CTC-keto remained low in both deionized and wetland water, suggesting that the isomerization of CTC-enol to iso-CTC most likely occurred via CTC-keto. The dissipation of CTC-enol in wetland water was described by pseudo first-order kinetics with a DT50 (time required for 50% dissipation) value of 4.8 h. The short DT50 value of CTC and reduced antimicrobial activity of iso-CTC and 4-epi-iso-CTC suggest a lower probability for selection for CTC-resistant bacteria in Canadian Prairie aquatic ecosystems.

Sorption and degradation of ranitidine in soil: Leaching potential assessment

Pharmaceuticals have been categorized as emerging contaminants that may be hazardous to the environment. To assess their environmental risk, understanding their fate and behaviour is highly needed, particularly in soil where little is known. This study investigated sorption, degradation and mobility potential of ranitidine (RAN) from soil to groundwater in two soils with different physicochemical properties. Sorption resulted in data were found to fit well to isotherm models following the order: linear model > Freundlich > Langmuir with R2 of up to 0.98. RAN showed low sorption affinity to soils with maximum adsorption coefficient (Kd) of 21.47 L kg−1. Physicochemical properties for soil and RAN showed insignificant positive correlation to Kd values except the sand%, which showed significant negative correlation. Degradation of RAN was fitted to the first order exponential decay model with minimum DT50 (time for a 50% dissipation in RAN concentration) values of 31.6 d under non-sterile conditions. Prolonged DT50 of 62.4 d was obtained in soils from sterile treatments indicating the microbial activity role in dissipation of RAN process. To predict potential leaching of RAN in soil, this study experimentally obtained values of Kd, Koc and DT50 were implemented in mathematical screening models. Results showed different but moderate leaching potential of RAN in soils.

Metabolic resistance to S-metolachlor in two waterhemp (Amaranthus tuberculatus) populations from Illinois, USA.

Two waterhemp (Amaranthus tuberculatus) populations from Illinois demonstrating multiple-resistance to acetolactate synthase (ALS)-, 4-hydroxyphenylpyruvate dioxygenase, and photosystem II (PSII)-inhibiting herbicides (designated CHR and SIR) also displayed reduced sensitivity to very-long-chain fatty acid-inhibiting herbicides, including S-metolachlor. We hypothesized that a physiological mechanism, such as enhanced metabolism, could be responsible for the reduced efficacy of S-metolachlor. Metabolism experiments indicated that resistant populations degraded S-metolachlor more rapidly than sensitive populations and equally as rapidly as corn 2-24 h after treatment (HAT). Resistant waterhemp and corn metabolized 90% (DT90 ) of absorbed S-metolachlor in less than 3.2 h whereas DT90 values for sensitive waterhemp exceeded 6 h. The glutathione S-transferase inhibitor 4-chloro-7-nitrobenzofurazon and cytochrome P450-inhibitor malathion decreased the amount of S-metolachlor metabolized in resistant waterhemp at 4 HAT but not in sensitive waterhemp or corn, and altered the abundance of certain metabolites in resistant waterhemp. Results from this research demonstrate that resistance to S-metolachlor in these waterhemp populations is due to enhanced herbicide metabolism relative to sensitive populations. In addition, our results indicate that resistant waterhemp might utilize metabolic pathway(s) more intricate than either sensitive waterhemp or corn based on their metabolite profiles. © 2020 Society of Chemical Industry.

Photocatalytic Degradation of Herbicide Orthosulfamuron using Zinc Oxide Nanoparticles in Water

In the present study, the Photocatalysis of Orthosulfamuron, a new class of sulfonyl urea herbicide was investigated using ZnO nano particles in different buffer solutions of pH ranging from 4 to 9. In this study, optimum concentration of the catalyst, initial concentration of the orthosulfamuron and effect of pH of the buffer solution were studied under direct sunlight. The ZnO nano particles were synthesized by sol-gel process and characterized by using SEM, XRD and FT-IR. A commercial formulation of the herbicide having the active strength of 50% was used for the experiment. The rate of reaction followed pseudo first-order kinetics in water. The rate of reaction was 12 folds higher when compared to photolysis. The DT50 values of orthosulfamuron with ZnO nano particles in different buffer solution were 6. 42, 21.68 and 35.22 hours, respectively. The optimum concentration of nano particles to decontamination of orthosulfamuron was observed at 100 mg L-1 and the initial concentration of the orthosulfamuron used in the photocatalysis is 10 mg L-1. The fastest degradation of herbicide orthosulafamuron was observed in pH 4 buffer solution. The degradation products formed during the photocatalysis were identified by using LC-MS/MS which were N-(4,6-dimethoxypyrimidin-2-yl) urea, 2- dimet hyl carbamoyl phenyl sulf amic acid and 1-(4-hydroxy-6-methoxypyrimidin-2-yl)-3-[2-(dimethylcarbamoyl) pheny lsulfamoyl] urea.

Use of Index-Based Screening Models to Evaluate the Leaching of Triclopyr and Fluroxypyr Through a Loam Soil Amended with Vermicompost.

The effect of vermicompost added to a loam soil on the leaching behaviour of two herbicides (triclopyr and fluroxypyr) was examined. Mobility of the herbicides was assessed using disturbed soil columns under laboratory conditions. In both cases, the addition of vermicompost significantly increased the sorption of the compounds. For both, DT50 values were slightly higher in the amended soil, due to the increased adsorption. Rate constants (k) calculated according to pseudo-first order model were significantly lower in the case of triclopyr (very persistent), which led to a much lower degradation rate compared to fluroxypyr (persistent) in both unamended and amended soils. Values calculated for the experimental leaching index (ELI) in unamended and amended soils showed medium and high leachability for fluroxypyr (0.31 and 0.29) and triclopyr (0.72 and 0.70), respectively. Other index-based screening models (GUS, RLPI, LIX) also catalogue both herbicides as potential leachers. Results confirm that triclopyr and fluroxypyr may contaminate groundwater resources.

Persistence of the antimicrobials lincomycin, chlortetracycline, and sulfamethazine in prairie wetlands.

Antimicrobials used in livestock production can be present in manure via excretion in the feces and/or urine. Application of raw or processed (composted or stockpiled) manure to crop and pasture land as a plant nutrient source can result in antimicrobial transport to surface waters via rainfall or snowmelt runoff. Little is known regarding antimicrobial persistence in aquatic ecosystems. Consequently, dissipation of environmentally relevant concentrations of three veterinary antimicrobials (lincomycin, chlortetracycline, and sulfamethazine) was studied in three wetlands on the Canadian Prairies. Study wetlands were fortified in the fall to simulate antimicrobial transport via rainfall runoff from fall manure applications to the wetland catchments. After fortification, water column concentrations of all three antimicrobials decreased through September and October. Plotting natural logarithm values of antimicrobial concentration against time resulted in linear relationships for all three antimicrobials, indicating that the summation of all dissipation processes for each antimicrobial could be described by first-order kinetics. The slopes of the three plots were significantly different, indicating that the order of dissipation was lincomycin<sulfamethazine<chlortetracycline. Consequently, the dissipation DT50 (time required for 50% antimicrobial dissipation) values for lincomycin (14.0d), sulfamethazine (7.0d), and chlortetracycline (3.3 d) were significantly different. The longer DT50 values of lincomycin and sulfamethazine suggest that environmentally relevant concentrations of these antimicrobials may affect bacterial production in prairie wetlands.

Dissipation and persistence behaviour of fipronil and its metabolites in clay soil under laboratory condition

A laboratory experiment was conducted at Food Quality Testing Laboratory, Navsari Agricultural University, Navsari to study the dissipation behaviour of fipronil and its metabolites in clay soil under laboratory condition. In method verification, acetonitrile based extraction and dispersive clean-up approach adopted to quantify the residues of fipronil and its metabolites with gas chromatography (GC-ECD) from soil was accurate, precise and sensitive enough. The soils were spiked at the rate of 1.0 and 2.0 mg/kg level for single and double dose, respectively. Soil was extracted at 5, 10, 20, 30, 60, 90 and 120 days after incubation for residues and quantified on GC-ECD. The residues of total fipronil in soil were quantified upto 90 days after their incubation in both single and double dose. The DT50 values of sum total of fipronil and its metabolites recorded at single and double dose were found to be 28.3 and 31.9 days, respectively.

Culex quinquefasciatus Egg Membrane Alteration and Ovicidal Activity of Cipadessa baccifera (Roth) Plant Extracts Compared to Synthetic Insect Growth Regulators.

BackgroundInsecticide resistance among mosquito vectors for synthetic insecticides still remains a major problem for control efforts. This study assessed the ovicidal potential of crude solvent extracts from the medicinal plant Cipadessa baccifera comparatively to standard registered synthetic insect growth regulators (IGR) on freshly laid eggs of Culex quinquefasciatus.MethodFive plant extracts were prepared using different solvents. The batches of eggs were exposed to different concentrations of each solvent extract comparatively to synthetic IGR. The hatched eggs of Cx. quinquefasciatus were subjected to different concentrations. The first instars that emerged from the eggs were counted daily. The egg hatching inhibition was observed 24, 48 and 72 hrs post treatment. The desiccation median time (DT50 and DT90) was calculated.ResultsThe percent egg hatching inhibition was inversely proportional to the concentration of extracts. The morphological damage to the eggs was observed. Among five solvent extracts, acetone extracts showed the highest ovicidal activity. The changes in eggshell morphology were observed. The maximum ovicidal activity was observed in acetone extracts with DT50 value of 1.70 hrs (0.91–2.22). The methanol plant extract using gas chromatography-mass spectrometry identified 14 compounds.ConclusionThese results suggest that the acetone extracts of C. baccifera have the potential to be used as an ovicidal agent for controlling mosquito populations in aquatic stages. The biodegradability of the extracts has the advantage of being eco-friendly.

Co-composting of oil-based drilling cuttings by bagasse.

The feasibility of using a locally abundant bulking material (sugarcane bagasse) in Khuzestan province, Iran, to remove petroleum hydrocarbons from oil-based drill cuttings (OBDCs), using composting process, was investigated. OBDCs were collected from the discharge point of a drilling rig and bagasse was collected from a sugarcane agro-industry near Ahwaz. Experiments were performed in the dark and at room temperature, using different bagasse to OBDCs ratios. Degradation extent and kinetics of total petroleum hydrocarbons (TPHs) and poly aromatic hydrocarbons (PAHs), as well as dehydrogenase and urease enzymes activities and number of heterotroph bacteria during the co-composting of OBDCs and bagasse were studied and measured. Highest PAHs and TPH removals were observed when OBDCs were composted with 15% bagasse. After 70days of incubation, PAHs and TPH were removed up to 24.8% and 67.5%, respectively. Studying the enzymes activities and number of heterotrophs with TPH and PAHs concentrations over time suggests that biodegradation is the main mechanism in the degradation process. The first-order kinetic model was fitted to the TPH and PAHs degradation data and contaminants half-lives were estimated to be in the range of 40-80 and 170-240days respectively. DT90 values for TPH and PAHs were in the range of 120-260 and 560-1260days, depending on the bagasse content.

Dissipation of fomesafen in fumigated, anaerobic soil disinfestation-treated, and organic-amended soil in Florida tomato production systems.

Fumigated, anaerobic soil disinfestation-treated (ASD), and organic-amended soil management strategies have been investigated as potential methyl bromide (MBr) alternatives for controlling diseases, nematodes, and weeds in soil. Nutsedge and broadleaf weed control using fomesafen has been reported to be comparable to MBr in normal cropping systems. There is no information on the fate of fomesafen used in combination with alternative practices. In this study, the fate of fomesafen in these alternative systems was measured byliquid chromatography-tandem mass spectrometry (LC/MS-MS) following extraction using a modifiedQuick Easy Cheap Effective Safe (QuEChERS) method. The reported half-life (DT50 ) values for fomesafen in the top 15 cm of soil were from 62.9 to 107.3 days. The DT50 values in organic-amended soil were higher than in ASD-treated soil in the top 15 cm. For all treatments, reductions in concentrations were positively correlated with lower redox potentials and organic matter content. Some leaching of fomesafen into the 16-30 cm zone was observed in all treatments. The DT50 values in this study were generally higher than those reported in previous studies performed at different locations. Due to increased losses of the herbicide and subsequent reduction in weed control, fomesafen is likely not to be suitable for effective weed control in systems using ASD techniques employing composted poultry litter and molasses. Integration of fomesafen using composted yard waste 1 (CYW1) and Soil Symphony Amendment (SSA) may result in acceptable weed control. Given that the soil was very sandy and the pH was higher than the pKa, fomesafen might leach deeper than 30 cm, particularly with the use of chemical soil fumigants (CSFs). © 2019 Society of Chemical Industry.

Degradation studies of dimethachlor in soils and water by UHPLC-HRMS: putative elucidation of unknown metabolites.

Degradation of dimethachlor was evaluated in soils and water, detecting metabolites in incurred samples. Putative elucidation was performed using HRMS and software tools, detecting new possible metabolites of dimethachlor.

Antibiotics in the Soil Environment-Degradation and Their Impact on Microbial Activity and Diversity.

Antibiotics play a key role in the management of infectious diseases in humans, animals, livestock, and aquacultures all over the world. The release of increasing amount of antibiotics into waters and soils creates a potential threat to all microorganisms in these environments. This review addresses issues related to the fate and degradation of antibiotics in soils and the impact of antibiotics on the structural, genetic and functional diversity of microbial communities. Due to the emergence of bacterial resistance to antibiotics, which is considered a worldwide public health problem, the abundance and diversity of antibiotic resistance genes (ARGs) in soils are also discussed. When antibiotic residues enter the soil, the main processes determining their persistence are sorption to organic particles and degradation/transformation. The wide range of DT50 values for antibiotic residues in soils shows that the processes governing persistence depend on a number of different factors, e.g., physico-chemical properties of the residue, characteristics of the soil, and climatic factors (temperature, rainfall, and humidity). The results presented in this review show that antibiotics affect soil microorganisms by changing their enzyme activity and ability to metabolize different carbon sources, as well as by altering the overall microbial biomass and the relative abundance of different groups (i.e., Gram-negative bacteria, Gram-positive bacteria, and fungi) in microbial communities. Studies using methods based on analyses of nucleic acids prove that antibiotics alter the biodiversity of microbial communities and the presence of many types of ARGs in soil are affected by agricultural and human activities. It is worth emphasizing that studies on ARGs in soil have resulted in the discovery of new genes and enzymes responsible for bacterial resistance to antibiotics. However, many ambiguous results indicate that precise estimation of the impact of antibiotics on the activity and diversity of soil microbial communities is a great challenge.

The route and rate of thiamethoxam soil degradation in laboratory and outdoor incubated tests, and field studies following seed treatments or spray application

BACKGROUNDThe route and rate of degradation of thiamethoxam in the laboratory and field was investigated. The effect of dark incubation versus light/dark cycles, seed treatment versus spray, and watering‐in for spray application was explored in side‐by‐side trials.RESULTSGeometric mean DT50 values were 75.4 days in OECD307 studies, and 18.3 (spray) and 16.5 (seed treatment) days in the field. In laboratory soil core studies DT50 values were 24.9 to 43.5 days, with the lowest value from the light/dark incubated soil core. Mean clothianidin formation was 19.7% applied thiamethoxam [mol/mol] in OECD307 studies and 17.5 (spray) and 3.4% (seed) in field trials.CONCLUSIONSoil DT50 values decreased with increasingly realistic tests (laboratory OECD307 to soil cores to soil cores with a light/dark cycle to field trials). The majority of the differences were associated with the soil treatment in OECD307 studies which destroys soil structure and retards the degradation rate; and from the impact on soil pore water movement in light/dark conditions. Degradation rates in the field were comparable between spray application and seed treatments. Maximum clothianidin concentrations were four‐fold lower for seed treatments than for spray application in field studies. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Influence of different agricultural management practices on soil microbial community over dissipation time of two herbicides

Soil microbiology could be affected by the presence of pesticide residues during intensive farming, potentially threatening the soil environment. The aim here was to assess the dissipation of the herbicides triasulfuron and prosulfocarb, applied as a combined commercial formulation, and the changes in soil microbial communities (through the profile of phospholipid fatty acids (PLFAs) extracted from the soil) during the dissipation time of the herbicides under field conditions. The dissipation of herbicides and the soil microbial structure were assessed under different agricultural practices, such as the repeated application of herbicides (twice), in unamended and amended soils with two organic amendments derived from green compost (GC1 and GC2) and with non-irrigation and irrigation regimes. The results obtained indicate slower dissipation for triasulfuron than for prosulfocarb. The 50% dissipation time (DT50) decreased under all conditions for the second application of triasulfuron, although not for prosulfocarb. The DT50 values for both herbicides increased in the GC2 amended soil with the highest organic carbon (OC) content. The DT50 values decreased for prosulfocarb with irrigation, but not for triasulfuron, despite its higher water solubility. The herbicides did not have any significant effects on the relative population of Gram-negative and Gram-positive bacteria during the assay, but the relative abundance of Actinobacteria increased in all the soils with herbicides. At the end of the assay (215 days), the negative effects of herbicides on fungi abundance were significant (p < 0.05) for all the treatments. These microbiological changes were detected in non-irrigated and irrigated soils, and were more noticeable after the second application of herbicides. Actinobacteria could be responsible for the modification of herbicide degradation rates, which tend to be faster after the second application. This study makes a useful contribution to the evaluation of the soil environment and microbiological risks due to the long-term repeated application of herbicides under different agricultural management practices.

Dissipation of herbicides after repeated application in soils amended with green compost and sewage sludge

Certain agricultural practices, such as the repeated application of herbicides or organic amendments to soil, can influence herbicide dissipation. This research has studied the effects of two repeated applications of mesotrione, pethoxamid, and triasulfuron on their dissipation rates in unamended soil (S) and soil amended with green compost (S+GC) or sewage sludge (S+SS). The dissipation experiment has also included an evaluation of the adsorption of the three herbicides by soils and of changes in soil dehydrogenase activity (DHA). The adsorption of the three herbicides by amended soils (Kf range 0.83–2.98) was higher than by unamended soil (Kf range 0.20–0.64). The adsorption coefficients (Kd) of mesotrione and triasulfuron were higher for S+SS, while that of pethoxamid was higher for S+GC, but no relationship between values for the time to 50% degradation (DT50) and adsorption coefficients could be determined. The repeated application of mesotrione decreased its dissipation rate in unamended soil (DT50 increased from 4.75 to 8.15 days) and amended soils (DT50 increased from 11.7 to 28.2 days in S+GC and from 17.7 to 37.9 in S+SS), whereas the repeated application of pethoxamid increased its dissipation rate in all the treatments, and the rate for triasulfuron increased only in amended soils. The highest DT50 values for pethoxamid (12.3 days) and triasulfuron (57.1 days) were in S+GC, and the lowest in S+SS (8.35 and 24.7 days). Soil DHA was stimulated by the presence of GC in the soil and by the first application of mesotrione. The second application of mesotrione and pethoxamid positively affected soil DHA, but this did not occur for triasulfuron. The repeated applications of herbicides and soil organic amendments have different effects on herbicide dissipation, adsorption, and soil DHA, and they should be taken into account when assessing soil quality and other potential environmental implications of pesticide use.

Removal of Two Neonicotinoid Insecticides and Mineralization of 14C-Imidacloprid in Biomixtures.

Environmental contamination with neonicotinoid insecticides represents an issue of wide concern due to their negative effects on pollinators. The goal of this work was to evaluate the potential use of biomixtures employed in biopurification systems (BPS) to remove two neonicotinoid pesticides, imidacloprid and thiamethoxam, from wastewater of agricultural origin. The removal was assayed by quantification of the parent compounds andthe detection of putative transformation products of imidacloprid by means of LC-MS/MS,and mineralization of radiolabeled imidacloprid. Two biomixtures (B1, B2) were prepared using coconut fiber, compost and two soils pre-exposed to imidacloprid (volumetric composition 50:25:25). After spiking of neonicotinoids and 228days of treatment, the removal ranged from 22.3%-30.3% and 38.6%-43.7% for imidacloprid and thiamethoxam, respectively. Transformation products imidacloprid-urea, desnitro-imidacloprid and desnitro-olefin-imidacloprid were detected in both biomixtures. The mineralization of 14C-imidacloprid revealed DT50 (mineralizationhalf-lives) values of 3466 and 7702days in the biomixtures B1 and B2, respectively, markedly lower than those in the soil used in their preparation (8667 and 9902days, respectively). As demonstrated by these findings, the high persistence of these compounds in the BPS suggests that additional biological (or physicochemical) approaches should be explored in order to decrease the impact of neonicotinoid-containing wastewater of agricultural origin.

Dissipation of terbuthylazine, metolachlor, and mesotrione in soils with contrasting texture

ABSTRACTThis study evaluates the dissipation of terbuthylazine, metolachlor, and mesotrione at different depths in soils with contrasting texture. The field trial was conducted at the Padua University Experimental Farm, north-east Italy. The persistence of three herbicides was studied in three different soil textures (clay soil, sandy soil, and loamy soil) at two depths (0–5 and 5–15 cm). Soil organic carbon content was highest in the clay (1.10%) followed by loam (0.67%) and sandy soil (0.24%); the pH of soils was sub-alkaline. Terbuthylazine, metolachlor, and mesotrione were applied on maize as a formulated product (Lumax®) at a dose of 3.5 L ha−1. Their dissipation in the treated plots was followed for 2 months after application. The concentrations of herbicides were analyzed by liquid chromatography-mass spectrometry. The dissipation of terbuthylazine, metolachlor, and mesotrione could be described by a pseudo first-order kinetics. Terbuthylazine showed the highest DT50, followed by metolachlor and mesotrione. Considering the tested soil, the highest DT50 value was found in clay soil for terbuthylazine and metolachlor, whereas for mesotrione there was no difference among soils. Significant differences were found between the two soil depths for terbuthylazine and metolachlor, whereas none were found for mesotrione. These results suggest that soil texture and depth have a strong influence on the dissipation of terbuthylazine and metolachlor, whereas no influence was observed on mesotrione because of its chemical and physical properties.

Vancomycin and/or Multidrug-Resistant Citrobacter Freundii Altered the Metabolic Pattern of Soil Microbial Community.

Despite many studies, our knowledge on the impact of antibiotics and antibiotic-resistant bacteria on the metabolic activity of soil microbial communities is still limited. To ascertain this impact, the community level physiological profiles (CLPPs) and the activity of selected enzymes (dehydrogenase, urease, and phosphatases) in soils treated with vancomycin (VA) and/or multidrug resistant Citrobacter freundii were determined during a 90-day experiment. A multivariate analysis and the resistance (RS)/resilience (RL) concept were used to assess the potential of native microorganisms to maintain their catabolic activity under exposure of VA and/or a high level of C. freundii. In addition, the dissipation rate of VA was evaluated in non-sterile (nsS) and sterile (sS) soils. The results revealed a negative impact of VA on the metabolic activity of soil microorganisms on days 1, 15, and 30 as was showed by a decrease in the values of the CLPP indices (10–69%) and the enzyme activities (6–32%) for treated soils as compared to the control. These observations suggested a low initial resistance of soil microorganisms to VA and/or C. freundii but they were resilient in the long term. Considering the mean values of the RS index, the resistance of measured parameters was categorized in the following order: alkaline phosphatase (0.919) > acid phosphatase (0.899) > dehydrogenase (0.853) > the evenness index (0.840) > urease (0.833) > the Shannon-Wiener index (0.735) > substrate richness (0.485) > the AWCD (0.301). The dissipation process of VA was relatively fast and independent of the concentration used. The DT50 values for VA applied at both concentrations were about 16 days. In addition, the dissipation of VA in nsS was three times faster compared to the dissipation of antibiotic in sS. In conclusion, both CLPP and enzyme activities assays appeared to be useful tool for the determination of disturbances within soil microbial communities and used together may be helpful to understand the changes in their catabolic features. The entry of large quantities of VA and/or C. freundii into soil may temporarily change microbial activity thus pose a potential risk for soil functioning.

Effects of temperature, water content, pH and soil sterilization on the degradation of CP4-EPSPS protein released from herbicide-tolerant corn leaves in the soil

Determining the influence of soil environmental factors on the degradation of CP4-EPSPS protein from herbicide-tolerant (HT) corn residue is crucial for assessing the ecological risks of commercialized transgenic crops. We investigated the effects of soil temperature (15 °C, 25 °C, 35 °C), soil water content (20%, 33%, 50%), pH (5.0, 7.0, 9.0) and soil treatment (not sterilized, sterilized) on the degradation of CP4-EPSPS protein released from the leaves of the HT corn variety CC-2. An exponential model (first order) was fitted to the degradation dynamics of CP4-EPSPS protein and used to estimate the time required for 50% degradation (DT50) and for 90% degradation (DT90). The results showed that CP4-EPSPS protein released from CC-2 leaves presented similar degradation features in all treatments: a sharp decrease in the early stage followed by a slow decline in the middle and late stages was observed. In the late stage (more than 120 d after the experiment started), CP4-EPSPS protein released from CC-2 leaves was not detected in the soil using enzyme-linked immunosorbent assay (ELISA) tests. The DT50 values of CP4-EPSPS protein released from CC-2 leaves ranged from 0.92 d to 11.32 d, and the DT90 values ranged from 3.11 d to 36.59 d. The results suggest that soil temperature and soil sterilization significantly affected the degradation of CP4-EPSPS protein. Faster degradation rates were observed at higher temperature under non-sterilized conditions, but soil water content and pH did not clearly affect the degradation of CP4-EPSPS protein. These findings suggest that under appropriate soil temperature conditions, CP4-EPSPS protein from HT corn residue will not persist or accumulate in the soil.

Role of soil physicochemical properties in quantifying the fate of diuron, hexazinone, and metribuzin.

The physicochemical properties of soil are fundamental to quantification of the fate of herbicides. Thus, the aim of this research was to evaluate the fate of diuron, hexazinone, and metribuzin in five soils (Clay-1, Clay-2, Loam-1, Loam-2, and Sand), presenting variation in clay content, cation exchange capacity (CEC), pH, and organic carbon (OC). Herbicides radiolabeled with 14C were applied, and the 14C-CO2 released from mineralization was trapped in 0.2molL-1 sodium hydroxide solution. The degradation ratio, as well as herbicide-bound residues (non-extractable), transformation products, and residues extractable from soil, was also evaluated. Average 14C-CO2 evolution accumulated for diuron mineralization was higher (22.24%) than hexazinone (7.73%) and metribuzin (3.20%). The degradation time half-life (DT50) values for hexazinone correlated with soil OC content. Although no correlation between soil properties and DT50 values was found for metribuzin, the degradation rate and total degree of mineralization were low in sand soil for metribuzin. Regarding diuron, OC content and CEC value appear to be related to mineralization and degradation rate, respectively. Differences in soil properties can influence the persistence and fate of herbicides, affecting their impact on the environment, weed control, and possible effects on subsequent crops.