Toxicological significance of pesticide conjugates

Products formed by the reaction of pesticides and their metabolites with endogenous chemicals (glucose, glucuronic acid, sulfate, glutathione, amino acid, etc.) are referred to as pesticide conjugates. Evidence to date suggests that this is a detoxification process since the resulting products are polar and usually rapidly eliminated from the body. However, very little is known about their acute toxicity, and almost nothing concerning the effects of chronic dietary exposure of animals to these materials. Though conjugates may be formed in vivo by animals administered the parent pesticide, this hardly can be considered an adequate means of assessing their toxic properties. Pesticide metabolites formed by primary metabolic reactions are often evaluated individually in both acute and subchronic toxicity tests, but similar experiments are not conducted with conjugates. To assume that pesticide conjugates are toxicologically insignificant is unsound scientifically, although the rationale for such an assumption is not completely without merit. Many polar compounds are inactive but many, including some conjugates, are biologically active and indeed may be very toxic. While elaborate toxicological investigations of all pesticide conjugates do not appear warranted, there is a clear need to strengthen the data base relative to their potential toxicological significance. Extensive investigations of selected model compounds, representing different pesticide groups and conjugate types, are in order if the issue is to be placed in proper perspective relative to the total safety evaluation of pesticidal chemicals.

Aldicarb and carbofuran transport in a Hapludalf influenced by differential antecedent soil water content and irrigation delay

Pesticide use in agroecosystems can adversely impact groundwater quality via chemical leaching through soils. Few studies have investigated the effects of antecedent soil water content (SWC) and timing of initial irrigation (TII) after chemical application on pesticide transport and degradation. The objectives of this study were to investigate the effects of antecedent soil water content (wet vs dry) and timing of initial irrigation (0h Delay vs 24h Delay) on aldicarb [(EZ)-2-methyl-2-(methylthio)propionaldehyde O-methylcarbamoyloxime] and carbofuran [2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate] transport and degradation parameters at a field site with Menfro silt loam (fine-silty, mixed, superactive, mesic Typic Hapludalf) soils. Aldicarb and carbofuran were applied to plots near field capacity (wet) or near permanent wilting point (dry). Half of the dry and wet plots received irrigation water immediately after chemical application and the remaining plots were irrigated after a 24h Delay. The transport and degradation parameters were estimated using the method of moments. Statistical significance determined for SWC included averages across TII levels, and significance determined for TII included averages across SWC levels. For the dry treatment, aldicarb was detected 0.10 m deeper (P<0.01) on two of the four sampling dates and carbofuran was detected at least 0.10 m deeper (P<0.05) on all of the sampling dates compared to the wet treatment. Pore water velocity was found to be higher (P<0.10) in the dry vs wet treatments on three of four dates for aldicarb and two of four dates for carbofuran. Retardation coefficients for both pesticides showed similar evidence of reduced values for the dry vs wet treatments. These results indicate deeper pesticide movement in the initially dry treatment. For aldicarb and carbofuran, estimated values of the degradation rate were approximately 40-49% lower in the initially dry plots compared to the initially wet plots, respectively. When the initial irrigation was delayed for 24h, irrespective of antecedent moisture conditions, a 30% reduction in aldicarb degradation occurred. This study illustrates the deeper transport of pesticides and their increased persistence when applied to initially dry soils.

Selection of support materials for immobilization of Burkholderia cepacia PCL3 in treatment of carbofuran-contaminated water

This study investigated the utilization of agricultural matrices as the support materials for cell immobilization to improve the technique of bioremediation. Coir, bulrush, banana stem and water hyacinth stem in both delignified and undelignified forms were used to immobilize Burkholderia cepacia PCL3 in bioremediation of carbofuran at 5 mg l(-1) in synthetic wastewater. Undelignified coir was found to be the most suitable support material for cell immobilization, giving the short half-life of carbofuran of 3.40 d (2.8 times shorter than the treatments with free cells). In addition, it could be reused three times without a loss in ability to degrade carbofuran. The growth and degradation ability of free cells were completely inhibited at the initial carbofuran concentrations of 250 mg l(-1), while there was no inhibitory effect of carbofuran on the immobilized cells. The results indicated a great potential for using the agricultural matrices as support material for cell immobilization to improve the overall efficiency of carbofuran bioremediation in contaminated water by B. cepacia PCL3.

The effect of initial concentration of carbofuran on the development and stability of its enhanced biodegradation in top-soil and sub-soil

Carbofuran was incubated in top-soil and sub-soil samples from a pesticide-free site at a range of initial concentrations from 0.1 to 10 mg kg-1. Amounts of the incubated soils were removed at intervals over the subsequent 12 months, and the rate of degradation of a second carbofuran dose at 10 mg kg-1 was assessed. An applied concentration as low as 0.1 mg kg-1 to top-soil resulted in more rapid degradation of the fresh addition of carbofuran for at least 12 months. The degree of enhancement was generally more pronounced with the higher initial concentrations. When the same study was conducted in sub-soil samples from the same site, an initial dose of carbofuran at 0.1 mg kg-1 resulted in only small increases in rates of degradation of a second carbofuran dose. However, degradation rates in the sub-soil samples were, in many instances, considerably greater than in the corresponding top-soil samples, irrespective of pre-treatment concentration or pre-incubated period. Initial doses of 0.5 mg kg-1 and higher applied to sub-soil successfully activated the sub-soil microflora. Application of the VARLEACH model to simulate carbofuran movement through the soil profile indicated that approximately 0.01 mg kg-1 of carbofuran may reach a depth of 70 cm 400 days after a standard field application. The results therefore imply that adaptation of the sub-soil microflora (c 1 m depth) by normal field rate applications of carbofuran is unlikely to occur. In experiments to investigate this in soils exposed to carbofuran in the field, there was no apparent relationship between top-soil exposure and degradation rates in the corresponding sub-soils. The results further confirmed that same sub-soil samples have an inherent capacity for rapid biodegradation of carbofuran. The high levels of variability observed between replicates in some of the sub-soil samples were attributed to the uneven distribution of a low population of carbofuran-degrading micro-organisms in sub-surface soil. There was no apparent relationship between soil microbial biomass and degradation rates within or between top-soil and sub-soil samples.

Behavioral effects of waterborne carbofuran in goldfish

The effects of concentration (1, 10, 100 microg/L) and duration (4, 8, 12 h) of exposure to carbofuran were assessed on the swimming activity, social interactions, and behavioral responses of goldfish to a flow (0.1 L/min) of water, with or without chironomids. Observations were also made on the behavioral responses of unexposed goldfish to a flow (0.1 L/min) of carbofuran-contaminated water. A 4-h exposure of goldfish 1 microg/L carbofuran produced a significant increase in sheltering, burst swimming, and nipping. Responses were enhanced at 100 microg/L. After a 12-h exposure, the behavioral effects of 1 microg/L carbofuran were less apparent. However, burst swimming at 10 microg/L, and sheltering, nipping and burst swimming at 100 microg/L, were still significantly increased after a 12-h exposure to carbofuran. Grouping was not consistently affected by exposure conditions. Chemical attraction to a filtrate of chironomids was significantly reduced after the 4-h exposure to 1 microg/L carbofuran. Decreased attraction to the food extract was less apparent after the 12-h exposure, except at 100 microg/L carbofuran. A significant decrease in attraction to a flow of uncontaminated water was also observed after a 4-h exposure to 10 and 100 microg/L carbofuran. Unexposed goldfish did not show avoidance reaction to a flow of carbofuran-contaminated water, even at a concentration (10 mg/L) exceeding the mean 96-h LC-50 in cyprinids (0.5-1 mg/L). However, at all concentrations tested (0.1, 1, 10 mg/L), goldfish quickly reacted to the introduction of the solution of carbofuran by increased burst swimming and nipping. These results are discussed in the light of the data concerning behavioral and neurotoxic effects of carbamate and organophosphorous insecticides in fish.

Metabolism of carbofuran by Aspergillus niger and Fusarium graminearum

Metabolism of carbofuran in pure liquid cultures of A. niger and F. graminearum was investigated. Carbofuran and its metabolites were analyzed by HPLC and TLC. The average recoveries of carbofuran, 3-hydroxycarbofuran, 3-ketocarbofuran, and 3-ketocarbofuran phenol from fungi media were found to be 88.65, 86.19, 75.48, and 80.48%, while their detection limits were 0.035, 0.031, 0.015 and 0.140 ppm, respectively. The data showed that A. niger was capable of degrading carbofuran more faster than F. graminearum. Carbofuran disappeared biexponentially from the liquid culture media of both fungi. The terminal half-life values of carbofuran were 10.4 and 12 days in the media of A. niger and F. graminearum, respectively. The amounts of carbofuran reached 15.56 and 19.71% of the applied dose after 21 days in case of A. niger and F. graminearum, respectively. Carbofuran was biotransformed to 3-hydroxycarbofuran, 3-ketocarbofuran, and 3-ketocarbofuran phenol. The percentages of the major metabolite, 3-hydroxycarbofuran were 47.72 and 7.77% in case of A. niger and F. graminearum after 21 days, respectively.

Dermal pharmacokinetics of the insecticide furathiocarb in rats

The pharmacokinetics of furathiocarb were studied in vivo in male Sprague-Dawley rats following dermal treatment. HPLC and post-column derivatization were used for the analysis of furathiocarb and its metabolites (carbofuran, 3-hydroxycarbofuran and 3-ketocarbofuran). Carbofuran and 3-hydroxycarbofuran were detected in plasma and urine rather than furathiocarb. 3-Ketocarbofuran, another potential metabolite, was not observed in any sample. The concentration of carbofuran was higher than that of 3-hydroxycarbofuran in plasma, but the reverse was the case in urine. The corresponding area under the plasma concentration-time curve, Tmax, and Cmax values of carbofuran and 3-hydroxycarbofuran for 1500 mg kg-1 doses were 2.4-8.0 mg equiv hml-1, 12 h and 0.1-0.4 mg equiv ml-1, respectively. T1/2 was calculated only for 3-hydroxycarbofuran (28 h). Two metabolites were excreted in a dose-dependent manner without saturation.

Persistence and metabolism of carbofuran in the soil and sugarcane plant

Persistence and metabolism of carbofuran in the soil and sugarcane plant were studied under tropical sugarcane ecosystem. Residues of carbofuran and its metabolites in the soil, sugarcane leaf, and juice were determined by employing matrix-specific sample preparation methods and gas chromatography equipped with mass spectrometry. The recoveries of carbofuran, 3-keto carbofuran, and 3-hydroxy carbofuran were in the range of 88.75 ± 2.58-100.25 ± 2.38, 90.38 ± 2.61-98.24 ± 4.78, and 89.25 ± 3.11-98.10 ± 3.19%, respectively, at three levels of fortification across the three matrices involved in the study. At recommended dose (carbofuran 3% CG at 2 kg a.i./ha), the initial deposit of carbofuran in the soil was 14.390 ± 1.727 μg/g. The total residues comprising both carbofuran and 3-hydroxy carbofuran were detected up to 105 days after treatment with the half-life of 10.83 days. The parent compound and its metabolite were detected and quantified in the sugarcane plant (leaves and juice) from 14 days after application of carbofuran in the soil. The total residues (carbofuran and 3-hydroxy carbofuran) were detected in the leaves and cane juice up to 75 and 30 days after treatment, respectively.

Interactions of Paraoxonase-1 with Pharmacologically Relevant Carbamates

Mammalian paraoxonase-1 hydrolyses a very broad spectrum of esters such as certain drugs and xenobiotics. The aim of this study was to determine whether carbamates influence the activity of recombinant PON1 (rePON1). Carbamates were selected having a variety of applications: bambuterol and physostigmine are drugs, carbofuran is used as a pesticide, while Ro 02-0683 is diagnostic reagent. All the selected carbamates reduced the arylesterase activity of rePON1 towards the substrate S-phenyl thioacetate (PTA). Inhibition dissociation constants (Ki), evaluated by both discontinuous and continuous inhibition measurements (progress curves), were similar and in the mM range. The rePON1 displayed almost the same values of Ki constants for Ro 02-0683 and physostigmine while, for carbofuran and bambuterol, the values were approximately ten times lower and two times higher, respectively. The affinity of rePON1 towards the tested carbamates was about 3-40 times lower than that of PTA. Molecular modelling of rePON1-carbamate complexes suggested non-covalent interactions with residues of the rePON1 active site that could lead to competitive inhibition of its arylesterase activity. In conclusion, carbamates can reduce the level of PON1 activity, which should be kept in mind, especially in medical conditions characterized by reduced PON1 levels.

A laboratory study of the persistence of carbofuran and its 3-hydroxy- and 3 keto-metabolites in sterile and natural mineral and organic soils

In a laboratory study, the persistence of carbofuran and its 3-hydroxy- and 3-keto-metabolites was examined separately over 16 wk in sterile and natural organic (muck) and mineral (loam) soils. Carbofuran was relatively persistent in sterile soils; at 8 wk 77% remained in the sterile muck and about 50% remained in the sterile loam. In the natural muck 25% of initial carbofuran remained at wk whereas in the natural loam carbofuran had completely disappeared by that time. The 3-ketocarbofuran was very short-lived even in the sterile muck where only 50% remained at 1 wk. The 3-hydroxycarbofuran degraded appreciably on zero day in the natural soils (with conversion to 3-keto-carbofuran) and about 90% had disappeared in 1 wk. A more detailed study of the persistence of 3-hydroxycarbofuran in the natural soils showed complete disappearance in 2 days in loam and in 3 days in muck. The 3-ketocarbofuran produced from the 3-hydroxy-carbofuran reached a maximum concentration in 1 day and then disappeared within 4 days in loam and about 1 wk in muck.

Transgenerational effects of co-exposure to cadmium and carbofuran on zebrafish based on biochemical and transcriptomic analyses

The combined toxicity of heavy metals and pesticides to aquatic organisms is still largely unexplored. In this study, we investigated the combined impacts of cadmium (Cd) and carbofuran (CAR) on female zebrafish (F0 generation) and their following F1 generation. Results showed that mixtures of Cd and CAR induced acute synergistic effects on both zebrafish adults of the F0 generation and embryos of the F1 generation. Combined exposure to Cd and CAR could obviously alter the hepatic VTG level of females, and the individual exposures increased the relative mRNA levels of vtg1 and vtg2. Through maternal transmission, co-exposure of Cd and CAR caused toxicity to 4-day-old larvae of the F1 generation, evidenced by the significant changes in T4 and VTG levels, CYP450 activity, and the relative transcriptional levels of genes related to the hormone, oxidative stress, and apoptosis. These effects were also reflected by the global gene expression pattern to 7-day-old larvae of F1 generation using the transcriptomic analysis, and they could also affect energy metabolism. Our results provided a more comprehensive insight into the transgenerational toxic impacts of heavy metal and pesticide mixtures. These findings highlighted that it was highly necessary to consider transgenerational exposures in the ecological risk assessment of chemical mixtures.

Determination of aldicarb, carbofuran and some of their main metabolites in groundwater by application of micellar electrokinetic capillary chromatography with diode-array detection and solid-phase extraction

This paper describes a UV detection method for the pesticides aldicarb and carbofuran, and some of their main metabolites, aldicarb-sulfoxide, aldicarb-sulfone and 3-hydroxy-carbofuran, in ground waters. Micellar electrokinetic chromatography (MEKC) with diode-array detection was developed for their determination at 210 nm. The experimental study was performed using sodium dodecyl sulfate (SDS) at a concentration level of 140 mM, and a buffer of borax/HCl 20 mM at pH 8 which gives the best resolution with an analysis time of less than 20 min. Different instrumental parameters such as voltage (23 kV), injection time (12 s) and temperature (25 degrees C) were optimized. The detection limits were in the range 2-7.4 microg glitre(-1) by solid-phase extraction (SPE) with a subsequent evaporation step. Groundwater spiked samples were pre-concentrated off-line with graphite carbon and subsequently analyzed by MEKC with diode-array detection yielding average recoveries between 77 and 97% (n = 4) with RSD between 2-7%.

Carbofuran pesticide toxicity to the eye

Pesticide exposure to eyes is a major source of ocular morbidities in adults and children all over the world. Carbofuran (CF), N-methyl carbamate, pesticide is most widely used as an insecticide, nematicide, and acaricide in agriculture, forestry, and gardening. Contact or ingestion of carbofuran causes high morbidity and mortality in humans and pets. Pesticides are absorbed in the eye faster than other organs of the body and damage ocular tissues very quickly. Carbofuran exposure to eye causes blurred vision, pain, loss of coordination, anti-cholinesterase activities, weakness, sweating, nausea and vomiting, abdominal pain, endocrine, reproductive, and cytotoxic effects in humans depending on amount and duration of exposure. Pesticide exposure to eye injures cornea, conjunctiva, lens, retina, and optic nerve and leads to abnormal ocular movement and vision impairment. Additionally, anticholinesterase pesticides like carbofuran are known to cause salivation, lacrimation, urination, and defecation (SLUD). Carbofuran and its two major metabolites (3-hydroxycarbofuran and 3-ketocarbofuran) are reversible inhibitors of acetylcholinesterase (AChE) which regulates acetylcholine (ACh), a neurohumoral chemical that plays an important role in corneal wound healing. The corneal epithelium contains high levels of ACh whose accumulation by AChE inhibition after CF exposure overstimulates muscarinic ACh receptors (mAChRs) and nicotinic ACh receptors (nAChRs). Hyper stimulation of mAChRs in the eye causes miosis (excessive constriction of the pupil), dacryorrhea (excessive flow of tears), or chromodacryorrhea (red tears). Recent studies reported alteration of autophagy mechanism in human cornea in vitro and ex vivo post carbofuran exposure. This review describes carbofuran toxicity to the eye with special emphasis on corneal morbidities and blindness.

Transformation and ecotoxicity of carbamic pesticides in water

BACKGROUND

N-methylcarbamate insecticides are widely used chemicals for crop protection. This study examines the hydrolytic and photolytic cleavage of benfuracarb, carbosulfan and carbofuran under natural conditions. Their toxicity and that of the corresponding main degradation products toward aquatic organisms were evaluated.

METHODS

Suspensions of benfuracarb, carbosulfan and carbofuran in water were exposed to sunlight, with one set of dark controls, for 6 days, and analyzed by 1H-NMR and HPLC. Acute toxicity tests were performed on Brachionus calyciflorus, Daphnia magna, and Thamnocefalus platyurus. Chronic tests were performed on Pseudokirchneriella subcapitata, and Ceriodaphnia dubia.

RESULTS AND DISCUSSION

Under sunlight irradiation, benfuracarb and carbosulfan gave off carbofuran and carbofuran-phenol, while only carbofuran was detected in the dark experiments. The latter was degraded to phenol by exposure to sunlight. Effects of pH, humic acid and KNO3 were evaluated by kinetics on dilute solutions in the dark and by UV irradiation, which evidenced the lability of the pesticide at pH 9. All three pesticides and phenol exhibited acute and higher chronic toxicity towards the aquatic organisms tested.

CONCLUSION

Investigation on the hydrolysis and photolysis of benfuracarb and carbosulfan under natural conditions provides evidence concerning the selective decay to carbofuran and/or phenol. Carbofuran is found to be more persistent and toxic.

RECOMMENDATIONS AND OUTLOOK

The decay of benfuracarb and carbosulfan to carbofuran and the relative stability of this latter pesticide account for many papers that report the detection of carbofuran in water, fruits and vegetables.

Pesticide detoxifying functions of N-halamine fabrics

Halamine structures incorporated on polyester/cotton fabrics were able to detoxify oxime carbamate pesticides that contain thio bonds rapidly upon contact. The reaction was endothermic, and the detoxification rate was in first order to concentrations of the pesticides. Aldicarb was degraded in a much faster rate than that of methomyl by the halamine fabrics. The reactivity of halamine structures was different, and imide halamine was more reactive than amine halamine. The detoxification was an oxidative reaction on the sulfur atom existing in both aldicarb and methomyl. The same halamine structures were unable to effectively react with carbaryl and carbofuran, which are aromatic carbamates and do not contain any thio bonds.

Environmental fate of rice pesticides in California

Each of the pesticides reviewed is reported to dissipate from field water after application. Carbofuran is hydrolyzed rapidly under the alkaline conditions usually found in the rice field environment, and its hydrolysis products are also degraded rapidly. The longest half-life reported (18-26 d) was in water that overlaid soil treated with Furadan granular formulation. Generally, carbofuran dissipation ranged from 36 hr to 3 d. Under field application, bensulfuron methyl showed a half-life of 1-3 d, but others have recovered all of the "dissipated" herbicide in the soil compartment. MCPA applied to rice fields is reportedly degraded by the joint action of sunlight and microbial action with a half-life of 3-5 d. Methyl parathion showed a maximum half-life of 9-17 d in a model aquatic ecosystem, but other reports found more rapid dissipation. The half-life of molinate has been observed by numerous researchers to be less than 5 d, with volatility the major route of loss. A half-life as short as 5-7 d has been reported for thiobencarb applied to rice fields, but others report much longer periods; volatility again is expected to be a significant route of loss. Microbial degradation takes place with each of the subject pesticides. Numerous authors have reported enhanced degradation of carbofuran under conditions of repeated application, and this probably holds true for the others. A specialized segment of the microbial population (Pseudomonas spp.) is purported to carry out most of the degradation but is inefficient at degrading the hydrolysis product, carbofuran phenol. Biodegradation of bensulfuron methyl has been observed with actinomycetes, fungi, and bacteria, and takes place primarily by oxidation and hydrolysis. Methyl parathion is biodegraded primarily by nitro reduction to aminomethyl parathion. A fungus, an actinomycete, and a bacterium were shown to biodegrade molinate, primarily by oxidation at the sulfur atom and the azepine ring. Thiobencarb is biodegraded in anaerobic sediments at a slow rate; the dechlorinated thiobencarb was shown to cause dwarfing of rice in some fields. Otherwise, its aerobic biodegradation is rapid and follows the same routes as with molinate. Carbofuran is a systemic insecticide that is rapidly absorbed and translocated to aerial parts of the plant. Carbofuran is metabolized in rice plants to the corresponding phenol, which is irreversibly bound into the plant, as well as to 3-hydroxycarbofuran and other minor components; it is depurated through leaf exudate, from which it volatilizes. Rice plants were observed to take up more bensulfuron methyl through shoots than roots and to metabolize it to the 4-hydroxy analog. The half-life of methyl parathion in Hydrilla verticulla, an aquatic macrophyte, was 1 wk, but little has been reported on methyl parathion in plants. Barnyardgrass was found to absorb greater amounts of molinate than did rice, and it produced larger proportions of basic metabolites, which may form the basis for its selective toxicity. Thiobencarb has been shown to be rapidly absorbed, translocated, and metabolized in rice plants, barnyardgrass, and the broadleaved wild amaranth, smartweed, and lambsquarters. Translocation was more rapid and extensive in barnyardgrass than in rice, and most of the 14C radiolabel was recovered as metabolites. Its terminal metabolite, chlorobenzoic acid, was taken up into lignin-like plant constituents. It is apparent that information on plant uptake and biodegradation is limited--none exists for woody species--but the fact that some species appear resistant to the herbicides suggests that biodegradative ability is general. (ABSTRACT TRUNCATED)

Impact of oxytetracycline and bacterial bioaugmentation on the efficiency and microbial community structure of a pesticide-degrading biomixture

An experimental study evaluating the effect of bioaugmentation and antibiotic (oxytetracycline) application on pesticide degradation and microbial community structure of a biomixture used in a biopurification system (BPR) was conducted. The bioaugmentation employed a carbofuran-degrading bacterial consortium. The non-bioaugmented biomixture showed excellent performance for removal of atrazine (t_1/2: 9.9 days), carbendazim (t_1/2: 3.0 days), carbofuran (t_1/2: 2.8 days), and metalaxyl (t_1/2: 2.7 days). Neither the addition of oxytetracycline nor bioaugmentation affected the efficiency of pesticide removal or microbial community (bacterial and fungal) structure, as determined by DGGE analysis. Instead, biomixture aging was mainly responsible for microbial population shifts. Even though the bioaugmentation did not enhance the biomixtures' performance, this matrix showed a high capability to sustain initial stresses related to antibiotic addition; therefore, simultaneous elimination of this particular mixture of pesticides together with oxytetracycline residues is not discouraged.

Mechanism insights into the transformation of carbosulfan during apple drying processes

The transformation of carbosulfan (CSN) in apples was investigated during oven-drying, microwave drying, and sun-drying. CSN transformed primarily into carbofuran (COA) during these drying processes. The conversion kinetics of CSN and COA was fitted by curve regression and mainly conformed to quadratic models (R² = 0.70-0.97). Oven-drying promoted the transformation of CSN into COA. Microwave drying resulted in the highest scavenging capacity against CSN and COA (41%-100%). Moreover, a transformation mechanism was proposed on the basis of density functional theory (DFT) calculation. The COA originated from a series of chemical reactions involving hydroxyl substitution, cleavage, and oxidation; this result was further confirmed on the basis of molecular electrostatic potential (MEP) and molecular orbital theory. Furthermore, the toxicity and stability of CSN and COA were evaluated with the T.E.S.T. program. COA was less toxic than CSN to aquatic organisms but more toxic than CSN to rats. Therefore, COA production should be avoided during drying. Microwave drying was found to be the optimum choice for drying apples.

Biodegradation of carbofuran in soils within Nzoia River Basin, Kenya

Carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate) has been used within the Nzoia River Basin (NRB), especially in Bunyala Rice Irrigation Schemes, in Kenya for the control of pests. In this study, the capacity of native bacteria to degrade carbofuran in soils from NRB was investigated. A gram positive, rod-shaped bacteria capable of degrading carbofuran was isolated through liquid cultures with carbofuran as the only carbon and nitrogen source. The isolate degraded 98% of 100-μg mL(-1) carbofuran within 10 days with the formation of carbofuran phenol as the only detectable metabolite. The degradation of carbofuran was followed by measuring its residues in liquid cultures using high performance liquid chromatography (HPLC). Physical and morphological characteristics as well as molecular characterization confirmed the bacterial isolate to be a member of Bacillus species. The results indicate that this strain of Bacillus sp. could be considered as Bacillus cereus or Bacillus thuringiensis with a bootstrap value of 100% similar to the 16S rRNA gene sequences. The biodegradation capability of the native strains in this study indicates that they have great potential for application in bioremediation of carbofuran-contaminated soil sites.

Microbial degradation of carbosulfan by carbosulfan--and carbofuran-retreated rice soil suspension

The role of microorganisms in the degradation of carbosulfan (2,3-dihydro-2,2-dimethyl-7-benzofuranyl-(di-n-butyl)-aminosulfenyl++ + methyl carbamate), an analogue of carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl-N-methyl carbamate) was studied by selective enrichment of microorganisms degrading either or both insecticides by repeated application of the insecticides, individually or in combination to flooded soil. Soil suspension from the pots treated with carbosulfan and carbofuran, individually or in combination collected after two applications, effected distinctly more rapid hydrolysis of carbosulfan than did the suspension from untreated pots or the uninoculated medium. The rate of hydrolysis was further accelerated by soil suspensions collected after six applications of the insecticides in the order carbosulfan treated > carbofuran treated > carbosulfan + carbofuran treated. The ability of treated and untreated suspension to degrade carbofuran was also studied. The rate of degradation of carbofuran by the suspension was in the order carbofuran retreated > carbosulfan + carbofuran retreated > carbosulfan retreated soil. Further involvement of microorganism in the rapid degradation of carbosulfan was confirmed by testing the degradation in sterilized and nonsterilized enrichment culture.