Soudamini Mohapatra

Enhancement of Carbofuran Degradation by Soil Enrichment Cultures, Bacterial Cultures and by Synergistic Interaction among Bacterial Cultures

Suspensions of soil repeatedly treated with carbofuran under glasshouse conditions enhanced the degradation of carbofuran significantly in a mineral salts medium. Ninety-seven per cent of the applied carbofuran degraded in a medium inoculated with soil suspensions treated with carbofuran, compared to 15% in uninoculated medium in 10 days. Out of the seven bacterial cultures isolated from the enrichment culture, two cultures identified as Pseudomonas stutzeri and Bacillus pumilis enhanced carbofuran degradation, resulting in more than 98% loss of the applied carbofuran in 30 days. The other cultures enhanced the degradation up to 70% within the same period. The mixture of all the seven cultures, however interacted synergistically, enhancing the degradation of carbofuran residues to 96% in 10 days.

Behaviour of trifloxystrobin and tebuconazole on grapes under semi-arid tropical climatic conditions

BACKGROUND A mixture of trifloxystrobin and tebuconazole is excellent in controlling both powdery and downy mildew of grapes. The objective of the present work was to study the behaviour of trifloxystrobin and tebuconazole on grape berries and soil following treatment with Nativo 75 WG, a formulation containing both fungicides (trifloxystrobin 250 + tebuconazole 500 g kg(-1)). This study was carried out for planned registration of this mixture for use on grapes in India. RESULTS Initial residue deposits of trifloxystrobin and tebuconazole on grapes were below their maximum residue limit (MRL) of 0.5 and 2 mg kg(-1), respectively, when Nativo 75 WG was applied at the recommended dose of 175 g product ha(-1). The residues dissipated gradually to 0.02 and 0.05 mg kg(-1) by 30 days, and were below the quantifiable limit of 0.01 mg kg(-1) at the time of harvest (60 days after the last treatment). Trifloxystrobin and tebuconazole dissipated at a pre-harvest interval (PHI) of 36 and 34 days, respectively, from the recommended treatment dose. The acid metabolite of trifloxystrobin, CGA 321 113, was not detected in grape berries at any point in time. Soil at harvest was free of any pesticide residues. CONCLUSION Residue levels of both trifloxystrobin and tebuconazole were below MRLs when grapes were harvested 30 days after the last of four applications of 175 g product ha(-1) (trifloxystrobin 44 g AI ha(-1), tebuconazole 88 g AI ha(-1)) under the semi-arid tropical climatic conditions of India.

Persistence and dissipation kinetics of trifloxystrobin and tebuconazole in onion and soil.

The persistence and dissipation kinetics of trifloxystrobin and tebuconazole on onion were studied after application of their combination formulation at a standard and double dose of 75 + 150 and 150 + 300 g a.i. ha−1. The fungicides were extracted with acetone, cleaned-up using activated charcoal (trifloxystrobin) and neutral alumina (tebuconazole). Analysis was carried out by gas chromatograph (GC) and confirmed by gas chromatograph mass spectrometry (GC-MS). The recovery was above 80% and limit of quantification (LOQ) 0.05 mg kg−1 for both fungicides. Initial residue deposits of trifloxystrobin were 0.68 and 1.01 mg kg−1 and tebuconazole 0.673 and 1.95 mg kg−1 from standard and double dose treatments, respectively. Dissipation of the fungicides followed first-order kinetics and the half life of degradation was 6–6.6 days. Matured onion bulb (and field soil) harvested after 30 days was free from fungicide residues. These findings suggest recommended safe pre-harvest interval (PHI) of 14 and 25 days for spring onion consumption after treatment of Nativo 75 WG at the standard and double doses, respectively. Matured onion bulbs at harvest were free from fungicide residues.

Persistence of trifloxystrobin and tebuconazole in banana tissues and soil under the semi-arid climatic conditions of Karnataka, India

Trifloxystrobin and tebuconazole are used for control of Sigatoka leaf spot disease of banana. This study was conducted to evaluate residue persistence of the fungicides in/on banana fruit, other edible parts and soil after spray application of the combination formulation, Nativo 75 WG, at the standard dose, 87.5 + 175 and double dose, 175 + 350 g a.i. ha−1. The fungicides were extracted from banana and soil with acetone, partitioned into dichloromethane and cleaned-up using activated charcoal for trifloxystrobin and primary/secondary amine (PSA) for tebuconazole samples. The limit of quantification of the method was 0.05 mg kg−1 for both fungicides. Initial residues of trifloxystrobin were 0.444 and 0.552 mg kg−1 in/on banana with peel (whole fruit), which reached <0.05 and 0.065 mg kg−1 after 30 days from treatment at the standard and double doses, respectively. Tebuconazole residues were 0.636 and 960 mg kg−1 initially and reduced to 0.066 and 0.101 mg kg−1 after 30 days. Trifloxystrobin and tebuconazole degraded with the half-life of about 11 days. Trifloxystrobin or its metabolite was not detected in the fruit pulp. Tebuconazole being systemic in nature moved to the fruit pulp which was highest on the 3rd day (0.103 and 0.147 mg kg−1) and remained for 15 days. Matured banana fruit, flower, pseudostem and field soil were free from fungicide residues. For consumption of raw banana 43 days pre-harvest interval (PHI) is required after treatment of the combination formulation. Therefore application of the fungicides towards maturity stage of the fruits may be avoided.

Dissipation pattern of flubendiamide residues on capsicum fruit (Capsicum annuum L.) under field and controlled environmental conditions

ABSTRACT This investigation was undertaken to compare the dissipation pattern of flubendiamide in capsicum fruits under poly-house and open field after giving spray applications at the recommended and double doses of 48 g a.i. ha−1 and 96 g a.i. ha−1. Extraction and purification of capsicum fruit samples were carried out by the QuEChERS method. Residues of flubendiamide and its metabolite, des-iodo flubendiamide, were analyzed by high-performance liquid chromatography–photodiode array, and confirmed by liquid chromatography–mass spectrometry/mass spectrometry. Limit of quantification of the method was 0.05 mg kg−1, and recovery of the insecticides was in the range of 89.6–104.3%, with relative standard deviation being 4.5–11.5%. The measurement uncertainty of the analytical method was in the range of 10.7–15.7%. Initial residue deposits of flubendiamide on capsicum fruits grown under poly-house conditions were (0.977 and 1.834 mg kg−1) higher than that grown in the field (0.665 and 1.545 mg kg−1). Flubendiamide residues persisted for 15 days in field-grown and for 25 days in poly-house-grown capsicum fruits. The residues were degraded with the half-lives of 4.3–4.7 and 5.6–6.6 days in field and poly-house respectively. Des-iodo flubendiamide was not detected in capsicum fruits or soil. The residues of flubendiamide degraded to below the maximum residue limit notified by Codex Alimentarius Commission (FAO/WHO) after 1 and 6 days in open field, and 3 and 10 days in poly-house. The results of the study indicated that flubendiamide applied to capsicum under controlled environmental conditions required longer pre-harvest interval to allow its residues to dissipate to the safe level.

Residue dynamics of chlorpyrifos and cypermethrin in/on pomegranate (Punica granatum L.) fruits and soil

Study on the residue dynamics of chlorpyrifos and cypermethrin in/on pomegranate (Punica granatum L.) and soil was carried out by conducting supervised field trials as per good agricultural practices. A modified QuEChERS was used to extract the insecticides in pomegranate peel and aril and soil. The limit of quantification (LOQ) of chlorpyrifos and cypermethrin were 0.01 and 0.05 mg kg−1, respectively. Residues of the insecticides remained on the fruit surface and movement to the edible part (aril) was not observed. The residues after treatment on fruit peel were 2.46 and 3.51 mg kg−1 and 2.84 and 4.54 mg kg−1 for chlorpyrifos and cypermethrin, respectively, from recommended and double dose treatments. Chlorpyrifos residues degraded faster compared to cypermethrin. The pre-harvest intervals (PHIs) of chlorpyrifos were 22 and 35 days and those of cypermethrin 50 and 73 days, respectively, at recommended and double dose treatments. In the experimental field soil after the second application chlorpyrifos residues were 0.21 and 0.46 mg kg−1 and cypermethrin residues 0.15 and 0.36 mg kg−1. At harvest, both pesticides showed residues below the LOQ. Based on this study, application of cypermethrin towards harvest may be avoided whereas chlorpyrifos can be applied with 22 days PHI.

Analysis of 28 insecticides in curry leaves (Murraya koenigii L.) by gas chromatography and gas chromatography–mass spectrometry

ABSTRACT A simple and efficient method was developed for analysis of 28 insecticides (organochlorines, organophosphates and synthetic pyrethroids) in curry leaves (Murraya koenigii L.). The extraction of the analytes was carried out with acidified acetonitrile and purification with magnesium sulphate, primary secondary amine along with graphitised carbon black to remove excess chlorophyll content in curry leaves. Acetonitrile extracts were changed into hexane + acetone (9 + 1) and hexane + toluene (9 + 1) in the final step. In another method ethyl acetate was used for extraction and purification was carried out as above. The analytes in the samples were determined by gas chromatography (GC) and confirmed by gas chromatography–mass spectrometry (GC–MS). Use of ethyl acetate increased the recovery of the analytes, but co-extractive interference led to higher GC maintenance. Acidified acetonitrile was found to be a better extraction solvent compared with ethyl acetate. The use of hexane:toluene (9:1) as exchange solvent increased the recovery of organochlorine insecticides compared with hexane:acetone (9:1). The limit of quantification (LOQ) of the method was 0.01 mg kg−1 for organochlorine insecticides and 0.05 mg kg−1 for organophosphates and synthetic pyrethroids. The recoveries of organochlorines were within 70.36–82.45%; organophosphates, 82.54–90.93% and synthetic pyrethroids, 88.45–90.71% at the LOQ level. The method developed was found suitable for analysis of real samples of curry leaves. The pesticides detected in curry leaves collected from the retail market were mainly organophosphates and synthetic pyrethroids.

Persistence and dissipation of fluopicolide and propamocarb on cabbage and soil under semi-arid climatic conditions

ABSTRACT Persistence and dissipation of fluopicolide and propamocarb were studied on cabbage and soil as per good agricultural practices over a period of 2 years. A modified QuEChERS analytical method in conjunction with gas chromatography (GC) and GC–mass spectrometry was used for analysis of fluopicolide and its metabolite, 2,6-dichlorobenzamide, and propamocarb in cabbage and soil. The results of the method validation were satisfactory with recoveries within 74.5–100.81% and relative standard deviations 4.8–13.9% (n = 6). The limit of detection (LOD) and limit of quantification (LOQ) of both fluopicolide and 2,6-dichlorobenzamide were 0.003 µg mL−1 and 0.01 mg kg−1, respectively. The LOD and LOQ of propamocarb were 0.03 µg mL−1 and 0.1 mg kg−1, respectively. During 2013, the initial residue deposits of fluopicolide on cabbage were 0.60 and 1.48 mg kg−1 from treatments at the standard and double doses of 100 and 200 g a.i. ha−1 which dissipated with the half-life of 3.4 and 3.7 days. During 2014, the residues were 0.49 and 1.13 mg kg−1 which dissipated with the half-life of 4.2 and 5.1 days. Propamocarb residues on cabbage were 5.36 and 12.58 mg kg−1 in the first study (2013) and 4.85 and 10.26 mg kg−1 in the second study (2014) from treatments at the standard and double doses of 1000 and 2000 g a.i. ha−1, respectively. The residues dissipated with the half-life of 4–5.5 days. The preharvest interval, the time required for fluopicolide + propamocarb residues to dissipate below the maximum residue limits (notified by EU) at the standard dose, was 11.8 and 14 days during 2013 and 2014. Residue of 2,6-dichlorobenzamide was always

Dissipation kinetics and risk assessment of fluopyram and tebuconazole in mango (Mangifera indica)

ABSTRACT The combination formulation of fluopyram and tebuconazole is used for control of fungal diseases and post-harvest disease management of mango. Dissipation study of the fungicides on mango was carried out after giving applications of fluopyram +tebuconazole at the standard and double doses of 150 + 150 and 300 + 300 g active ingredient hectare−1 (g a.i. ha−1), respectively. Fluopyram residues on mango were 0.8 and 0.9 mg kg−1 and tebuconazole residues, 0.308 and 0.4 mg kg−1 after three and four applications at the standard dose. At double dose treatment the residue levels for fluopyram were 1.266 and 1.453 mg kg−1 and tebuconazole, 0.681 and 0.853 mg kg−1, respectively. Residue dissipation in mango fruits followed first order rate kinetics and the half-life (DT50) were 4.3–5.4 days for fluopyram and 3–3.8 days for tebuconazole. Faster dissipation of the fungicides was observed after the fourth treatment which directly correlated to higher rainfall during that period. The combined residues of fluopyram+tebuconazole reduced to below their maximum residue limits (MRLs) within 36–38 days. Dietary risk assessment on human health indicated that fluopyram and tebuconazole application to mango is unlikely to pose risk to human beings. This study gives valuable information on the judicious use of this combination formulation on mango, especially towards harvest.