Dissipation pattern and residual levels of boscalid in cucumber and soil using liquid chromatography-tandem mass spectrometry

Abstract

To stipulate the rationale of spraying doses and to determine the safe interval period of boscalid suspension concentrate (SC), the degradation dynamics and residual levels were investigated in cucumber and soil using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Field trials were conducted according to Chinese Guideline on pesticide residue trials. Following application, the degradation kinetics was best ascribed to first-order kinetic models with half-life of 2.67–9.90 d in cucumber. Spraying boscalid SC at 1.5-fold the recommended dosage yield terminal residues, which are clearly lower than the maximum residue limit (MRL) established by China (MRL =5?mg.kg^?1) in cucumber. At variance, the dissipation dynamics in soil did not fit to first-order kinetics and the half-life was more than 17?days, the finding which denotes that the degradation behavior of boscalid in soil proceeds slowly. It has therefore been shown that boscalid is safe for use on cucumbers under the recommended dosage.     

Influence of activated charcoal amendment to contaminated soil on dieldrin and nutrient uptake by cucumbers

Activated charcoal (AC) amendments have been suggested as a promising, cost-effective method to immobilize organic contaminants in soil. We performed pot experiments over two years with cucumber (Cucumis sativus L.) grown in agricultural soil with 0.07 mg kg^?1 of weathered dieldrin and 0, 200, 400, and 800 mg AC per kg soil. Dieldrin fresh weight concentrations in cucumber fruits were significantly reduced from 0.012 to an average of 0.004 mg kg^?1, and total uptake from 2 to 1 μg in the 800 mg kg^?1 AC treatment compared to the untreated soil. The treatment effects differed considerably between the two years, due to different meteorological conditions. AC soil treatments did neither affect the availability of nutrients to the cucumber plants nor their yield (total fruit wet weight per pot). Thus, some important prerequisites for the successful application of AC amendments to immobilize organic pollutants in agricultural soils can be considered fulfilled.     

Biota-sediment metal accumulation and human health risk assessment of freshwater bivalve Corbicula fluminea in Dongting Lake,China

In this study, we analyzed the concentrations of metals in sediments and Corbicula fluminea in China’s Dongting Lake to assess the suitability of C. fluminea as an effective biomonitor of metal contamination in sediments and food safety. We analyzed the biota-accumulation capacity by calculating the biota-sediment accumulation factor (BSAF) and assessed the potential human health risk of metals exposure via consumption of C. fluminea using the target hazard quotient (THQ) and total target hazard quotient (TTHQ). The results showed that the average concentrations of As (31.93 mg kg⁻¹), Cd (5.54 mg kg⁻¹), Cr (105.50 mg kg⁻¹), Cu (32.53 mg kg⁻¹), and Zn (207.89 mg kg⁻¹) in sediments were higher than their respective standard set by the General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China. The sediment metals, which were mainly anthropogenic in origin, were at high levels and pose a relatively high ecological risk. Cadium (Cd) showed very high potential ecological risk levels and should be included in the prior pollutants list in the studied area. The mean levels of As (0.81 mg kg⁻¹) in C. fluminea were 1.62-times higher than that set by the National Health Commission of the People’s Republic of China. BSAF values of the soft tissues of C. fluminea were between 0.05 and 2.14, with higher values for Cu (2.14), Cd (1.77), Zn (1.60), and Ni (1.27). Soft tissues of C. fluminea were able to reflect spatial differences in Sr within sediments around Dongting Lake. The results indicated that C. fluminea could be an potential biomonitor for sediment metals assessment in biomonitoring programs, especially for Cu, Cd, Zn, Ni, and Sr. The mean values for THQ and TTHQ of all the analyzed metals were below 1.0, indicating that the intake of metals via comsumption of C. fluminea does not result in an appreciable risk to human health.

     

Evaluation of exposure to fluoride in child population of North Argentina

Fluoride is an important element for humans. It inhibits initiation and progression of dental caries and stimulates bone formation. However, excessive intake may lead to the appearance of dental and/or skeletal fluorosis and a decrease in intellectual coefficient in child populations. This study evaluates exposure to fluoride in the child population of Chaco province (Argentina) by analysis of drinking water, food and its bioaccessible fraction (quantity of fluoride solubilised by gastrointestinal digestion and available for intestinal absorption) and urine as a biomarker of internal dose. The concentration of fluoride in drinking water varied between 0.050 and 4.6 mg L^?1, and 80% of the samples exceeded the WHO drinking-water guideline value (1.5 mg L^?1). Fluoride concentrations in food ranged between 0.80 and 3.0 mg kg^?1 fresh weight (fw), being lower in bioaccessible fraction (0.43–1.9 mg kg^?1, fw). On the basis of the consumption data declared for the young child population, fluoride intake varies between 4.1 and 6.5 mg day^?1, greater than the level recommended for this age group. Moreover, in some cases, concentrations of fluoride found in urine (0.62–8.9 mg L^?1) exceeded those reported in areas with declared fluorosis. All data obtained show the worrying situation of child population in this area of Argentina.

     

Determination of Fungicide Kresoxim-Methyl Residues in Cucumber and Soil by Capillary Gas Chromatography with Nitrogen-Phosphorus Detection

The method of residue analysis of kresoxim-methyl and its dissipation rate in cucumber and soil in a greenhouse were studied. Residues of kresoxim-methyl were extracted from cucumber and soil matrices with acetone, purified by liquid-liquid extraction and Florisil cartridges, and then determined by GC with NP-detector. The limit of detection was estimated to be 9× 10^?12 g, and the minimum determination concentration of kresoxim-methyl in the samples was 0.005 mg kg^?1. The average recoveries ranged from 89.4 to 100.2% with a coefficient variation between 2.4 and 8.9%. Dissipation study showed that the half-lives of kresoxim-methyl in cucumber were approximately 6.5 days at both the recommended and double the recommended dosage. Half-lives for both the treatments were approximately 8 days in soil. The present study revealed that the residues in cucumber were below the MRL (0.05 mg kg^?1, fixed by EU) after 7 days for both treatments.     

Heavy metal bioaccumulation by wild edible saprophytic and ectomycorrhizal mushrooms

Heavy metals cause serious problems in the environment, and they can be accumulated in organisms, especially in the higher fungi. The concentration of Ni, Cr, Pb, Cd, and Hg in 10 species of edible mushrooms in Medvednica Nature Park, Croatia was therefore determined. In addition, the similarity between the studied species was determined by cluster analysis based on concentrations of the aforementioned metals in the fruiting bodies. The contents of nickel, chromium, lead, cadmium, and mercury in the fruiting bodies of mushrooms were obtained by X-ray fluorescence spectrometry. The highest concentrations of Ni (3.62 mg kg^?1), Cr (3.01 mg kg^?1), and Cd (2.67 mg kg^?1) were determined in Agaricus campestris. The highest concentration of Pb (1.67 mg kg^?1) was determined in Macrolepiota procera, and the highest concentration of Hg (2.39 mg kg^?1) was determined in Boletus edulis. The concentration of all heavy metals significantly differed (p?<?0.001) between examined saprophytic and ectomycorrhizal mushrooms. Considering anatomical part of the fruiting body (cap-stipe), a considerably higher concentration of the analyzed elements was found in the cap for all mushroom species. According to calculated bioconcentration factors, all the examined species were found to be bioexclusors of Ni, Cr, and Pb and bioaccumulators of Cd and Hg. Cluster analysis performed on the basis of the accumulation of the studied metals revealed great phenotypic similarity of mushroom species belonging to the same genus and partial similarity of species of the same ecological affiliation.

     

Concentration and dissipation of chlorantraniliprole and thiamethoxam residues in maize straw,maize, and soil

To study the dissipation rates and final residual levels of chlorantraniliprole and thiamethoxam in maize straw, maize, and soil, two independent field trials were conducted during the 2014 cropping season in Beijing and Anhui Provinces of China. A 40% wettable powder (20% chlorantraniliprole?+?20% thiamethoxam) was sprayed onto maize straw and soil at an application rate of 118 g of active ingredient per hectare (g a.i.ha^?1). The residual concentrations were determined by ultra-high-performance liquid chromatography–tandem mass spectrometry. The chlorantraniliprole half-lives in maize straw and soil were 9.0–10.8 and 9.5–21.7 days, respectively. The thiamethoxam half-lives in maize straw and soil were 8.4–9.8 and 4.3–11.7 days, respectively. The final residues of chlorantraniliprole and thiamethoxam in maize straw, maize, and soil were measured after the pesticides had been sprayed two and three times with an interval of 7 days using 1 and 1.5 times the recommended rate (72 g a.i. ha^?1 and 108 g a.i. ha^?1, respectively). Representative maize straw, maize, and soil samples were collected after the last treatment at pre-harvest intervals of 7, 14, and 28 days. The chlorantraniliprole residue was below 0.01 mg kg^?1 in maize, between 0.01 and 0.31 mg kg^?1 in maize straw, and between 0.03 and 1.91 mg kg^?1 in soil. The thiamethoxam residue concentrations in maize, maize straw, and soil were <0.01, <0.01, and 0.01–0.03 mg kg^?1, respectively. The final pesticide residues on maize were lower than the maximum residue limit (MRL) of 0.02 mg kg^?1 after a 14-day pre-harvest interval. Therefore, a dosage of 72 g a.i. ha^?1 was recommended, as it can be considered safe to human beings and animals.     

Levoglucosan and other cellulose and lignin markers in emissions from burning of Miocene lignites

Levoglucosan (L), mannosan (M), galactosan (G) and other cellulose and lignin markers from burn tests of Miocene lignites of Poland were determined by gas chromatography–mass spectrometry (GC–MS) to assess their distributions and concentrations in the smoke. Their distributions were compared to those in the pyrolysis products of the lignites. Levoglucosan and other anhydrosaccharides are products from the thermal degradation of cellulose and hemicellulose and are commonly used as tracers for wood smoke in the atmosphere. Here we report emission factors of levoglucosan in smoke particulate matter from burning of lignite varying from 713 to 2154 mg kg^?1, which are similar to those from burning of extant plant biomass. Solvent extracts of the lignites revealed trace concentrations of native levoglucosan (0.52–3.7 mg kg^?1), while pyrolysis yielded much higher levels (1.6–3.5 × 10⁴ mg kg^?1), indicating that essentially all levoglucosan in particulate matter of lignite smoke is derived from cellulose degradation. The results demonstrate that burning of lignites is an additional input of levoglucosan to the atmosphere in regions where brown coal is utilized as a domestic fuel. Interestingly, galactosan, another tracer from biomass burning, is not emitted in lignite smoke and mannosan is emitted at relatively low concentrations, ranging from 7.8 to 70.5 mg kg^?1. Thus, we propose L/M and L/(M + G) ratios as discriminators between products from combustion of lignites and extant biomass. In addition, other compounds, such as shonanin, belonging to lignans, and some saccharides, e.g., α- and β-glucose and cellobiose, are reported for the first time in extracts of bulk lignites and of smoke particulate matter from burning these lignites.     

Cadmium accumulation in and tolerance of rice (Oryza sativa L.) varieties with different rates of radial oxygen loss

Cadmium (Cd) uptake and tolerance were investigated among 20 rice cultivars based on a field experiment (1.2 mg Cd kg⁻¹ in soil) and a soil pot trial (control, 100 mg Cd kg⁻¹), and rates of radial oxygen loss (ROL) were measured under a deoxygenated solution. Significant differences were found among the cultivars in: (1) brown rice Cd concentrations (0.11-0.29 mg kg⁻¹) in a field soil, (2) grain Cd tolerance (34-113%) and concentrations (2.1-6.5 mg kg⁻¹) in a pot trial, and (3) rates of ROL (15-31 mmol O₂ kg⁻¹ root d.w. h⁻¹). Target hazard quotients were calculated for the field experiment to assess potential Cd risk. Significant negative relationships were found between rates of ROL and concentrations of Cd in brown rice or straw under field and greenhouse conditions, indicating that rice cultivars with higher rates of ROL had higher capacities for limiting the transfer of Cd to rice and straw.     

Arsenic contamination and potential health risk implications at an abandoned tungsten mine, southern China

In an extensive environmental study, field samples, including soil, water, rice, vegetable, fish, human hair and urine, were collected at an abandoned tungsten mine in Shantou City, southern China. Results showed that arsenic (As) concentration in agricultural soils ranged from 3.5 to 935 mg kg⁻¹ with the mean value of 129 mg kg⁻¹. In addition, As concentration reached up to 325 μg L⁻¹ in the groundwater, and the maximum As concentration in local food were 1.09, 2.38 and 0.60 mg kg⁻¹ for brown rice, vegetable and fish samples, respectively, suggesting the local water resource and food have been severely contaminated with As. Health impact monitoring data revealed that As concentrations in hair and urine samples were up to 2.92 mg kg⁻¹ and 164 μg L⁻¹, respectively, indicating a potential health risk among the local residents. Effective measurements should be implemented to protect the local community from the As contamination in the environment.     

The dissipation rates of trichlorfon and its degradation product dichlorvos in cabbage and soil

The residual levels and dissipation rate of trichlorfon, and its degradation product, dichlorvos, in cabbage crops and the soil in which these were grown, were determined by gas chromatography at two geographically distant experimental sites, one in Kunming and one in Beijing, China. Trichlorfon was applied at two dosages (900 g ai ha⁻¹ and 1350 g ai ha⁻¹). Maximum final residues of trichlorfon in soil and cabbage were 1.23 mg kg⁻¹ and 1.81 mg kg⁻¹ respectively at Kunming, and 0.35 mg kg⁻¹ and 0.70 mg kg⁻¹ respectively at Beijing. However, the final residues of dichlorvos in both cabbage and soil was only 0.04 mg kg⁻¹ at Kunming, and only 0.03 mg kg⁻¹, or “not detectable”, at Beijing. The mean half-life of trichlorfon in cabbage was 1.80 d with a dissipation rate of 90% over 5 d, while that in soil was 3.05 d with a dissipation rate of 90% over 14 d at one experimental site. The dissipation rates of trichlorfon and its degradation product dichlorvos at the two experimental sites were different, suggesting that degradation of these pesticides was affected by local soil characteristics and climate. When applied at both the recommended dosage and at 1.5 times this, no detectable residues of either trichlorfon or dichlorvos were found in soil or cabbage at harvest. Although trichlorfon can easily degrade into dichlorvos, which is highly toxic to humans and other animals, the observed low residual levels of dichlorvos suggest that trichlorfon is safe when applied at the recommended dosage.     

Distribution, speciation and availability of antimony (Sb) in soils and terrestrial plants from an active Sb mining area

Here, we present one of the first studies investigating the mobility, solubility and the speciation-dependent in-situ bioaccumulation of antimony (Sb) in an active Sb mining area (Xikuangshan, China). Total Sb concentrations in soils are high (527-11,798 mg kg⁻¹), and all soils, including those taken from a paddy field and a vegetable garden, show a high bioavailable Sb fraction (6.3-748 mg kg⁻¹), dominated by Sb(V). Elevated concentrations in native plant species (109-4029 mg kg⁻¹) underpin this. Both chemical equilibrium studies and XANES data suggest the presence of Ca[Sb(OH)₆]₂, controlling Sb solubility. A very close relationship was found between the citric acid extractable Sb in plants and water or sulfate extractable Sb in soil, indicating that citric acid extractable Sb content in plants may be a better predictor for bioavailable Sb in soil than total acid digestible Sb plant content.     

Prediction of Cadmium uptake by brown rice and derivation of soil–plant transfer models to improve soil protection guidelines

Cadmium (Cd) levels in paddy fields across Taiwan have increased due to emission from industry. To ensure the production of rice that meets food quality standards, predictive models or suitable soil tests are needed to evaluate the quality of soils to be used for rice cropping. Levels of Cd in soil and rice grains were measured in 19 paddy fields across the western plains in Taiwan. Cadmium levels in soil range from less than 0.1 mg kg^?1 to 30 mg kg^?1. Measured Cd levels in brown rice were predicted very well (R² > 0.8) based on Cd and Zinc in a 0.01 M CaCl₂ extract or a soil–plant transfer model using the reactive soil Cd content, pH, and cation exchange capacity. In contrast to current soil quality standards used in Taiwan, such models are effective in identifying soils where Cd in rice will exceed food quality standards.     

PM10 emission factors for non-exhaust particles generated by road traffic in an urban street canyon and along a freeway in Switzerland

Recent studies have shown clear contributions of non-exhaust emissions to the traffic related PM10 load of the ambient air. These emissions consist of particles produced by abrasion from brakes, road wear, tire wear, as well as vehicle induced resuspension of deposited road dust. The main scope of the presented work was to identify and quantify the non-exhaust fraction of traffic related PM10 for two roadside locations in Switzerland with different traffic regimes. The two investigated locations, an urban street canyon with heavily congested traffic and an interurban freeway, are considered as being typical for Central Europe. Mass-relevant contributions from abrasion particles and resuspended road dust mainly originated from particles in the size range 1–10 μm. The results showed a major influence of vehicle induced resuspension of road dust. In the street canyon, the traffic related PM10 emissions (LDV: 24 ± 8 mg km^?1 vehicle^?1, HDV: 498 ± 86 mg km^?1 vehicle^?1) were assigned to 21% brake wear, 38% resuspended road dust and 41% exhaust emissions. Along the freeway (LDV: 50 ± 13 mg km^?1 vehicle^?1, HDV: 288 ± 72 mg km^?1 vehicle^?1), respective contributions were 3% brake wear, 56% resuspended road dust and 41% exhaust emissions. There was no indication for relevant contributions from tire wear and abrasion from undamaged pavements.     

Triclosan affects the microbial community in simulated sewage-drain-field soil and slows down xenobiotic degradation

Effects of the common antibacterial agent triclosan on microbial communities and degradation of domestic xenobiotics were studied in simulated sewage-drain-field soil. Cultivable microbial populations decreased 22-fold in the presence of 4 mg kg⁻¹ of triclosan, and triclosan-resistant Pseudomonas strains were strongly enriched. Exposure to triclosan also changed the general metabolic profile (Ecoplate substrate profiling) and the general profile (T-RFLP) of the microbial community. Triclosan degradation was slow at all concentrations tested (0.33-81 mg kg⁻¹) during 50-days of incubation. Mineralization experiments (¹⁴C-tracers) and chemical analyses (LC-MS/MS) showed that the persistence of a linear alkylbenzene sulfonate (LAS) and a common analgesic (ibuprofen) increased with increasing triclosan concentrations (0.16-100 mg kg⁻¹). The largest effect was seen for LAS mineralization which was severely reduced by 0.16 mg kg⁻¹ of triclosan. Our findings indicate that environmentally realistic concentrations of triclosan may affect the efficiency of biodegradation in percolation systems.     

Effect of EDTA and NTA on cadmium distribution and translocation in Pennisetum purpureum Schum cv. Mott

The primary objective of this research was to investigate the cadmium (Cd) distribution in Pennisetum purpurem (Napier grass) in the presence of 30 mg/L of Cd and different types and concentrations of chelating agents (ethylenediaminetetraacetic acid disodium dihydrate (EDTA), nitrilotriacetic acid (NTA), and EDTA-NTA mixtures). Plant samples were collected every 15 d during a 105-d experimental period. Accumulation of Cd in each part of the plant was determined using atomic absorption spectrometer (AAS), and the distribution of Cd was determined by laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) and synchrotron radiation micro X-ray fluorescence (SR-micro-XRF). The highest concentrations of Cd accumulation of 889?±?53 mg kg^?1 in the underground part (roots) and 265?±?26 mg kg^?1 in the aboveground part (stems and leaves) in the presence of 1:1 M ratio of Cd:EDTA after 30 d of exposure were observed. Plants grown in the presence of either NTA or EDTA-NTA mixtures showed significant lower Cd accumulation levels. The LA-ICP-MS analysis showed that Cd was primarily accumulated in the aboveground part (stems and leaves), especially in the xylem and intercalary meristem. In addition, translocation factor was very low. Thus, P. purpurem could be considered as a candidate plant for cadmium phytostabilization.

     

Dry and wet deposition of water-insoluble dust and water-soluble chemical species during spring 2007 in Tsukuba,Japan

Dry and wet depositions were sampled daily in Tsukuba, Japan, in spring 2007. Temporal variations in the dry and wet deposition fluxes of dust and water-soluble chemical species were controlled largely by air mass origin, the water vapor mixing ratio, and Asian dust events. The contribution of local sources to dry deposition of dust was large when the wind speed was high. Dry deposition fluxes of water-soluble chemical species were larger in humid air masses than in dry air masses. Wet deposition fluxes of dust and water-soluble chemical species indicated that air masses that passed over dust source regions and industrial regions became mixed with the maritime air masses over the coastal site of the Asian continent and western part of the Japanese islands. The total deposition of dust was 4220 mg m^?2 month^?1, and that of water-soluble chemical species ranged from 10 to 636 mg m^?2 month^?1. Wet deposition fluxes of the total deposition flux of dust accounted for 72% and those of water-soluble chemical species was for 72–96%. In particular, the largest wet deposition occurred during a single Asian dust event on 3 April. This event accounted for 23% (950 mg m^?2 month^?1) of the monthly dust deposition flux and for 2–28% (0.43–51 mg m^?2 month^?1) of the monthly deposition flux of water-soluble chemical species. This result implies that the wet deposition flux associated with even one sporadic Asian dust event can have extensive impacts on both terrestrial and oceanic ecosystems in East Asia.     

Concentrations of organochlorine pesticides (OCPs) residues in foodstuffs collected from traditional markets in Indonesia

A total 23 of organochlorine pesticides (OCPs) residues were determined in five groups of foodstuffs, i.e.: vegetables (carrot, potato, cucumber, corn, and onion), rice, pulses (green bean and soybean), nuts (peanut), and fish (milkfish), which collected from traditional markets in three big cities of Indonesia; Jakarta, Bogor, and Yogyakarta. OCPs were only detected in fatty foodstuffs, such as soybean, peanut, and milkfish. The concentration of HCB (expressed as ng g^?1 on a whole basis), ΣDrins, ΣDDTs, ΣHeptachlors, and ΣHCHs were in the range of <0.3–0.74 ng g^?1, <0.03–0.42 ng g^?1, <0.02–0.41 ng g^?1, <0.03–0.14 ng g^?1, and <0.03–0.06 ng g^?1, respectively, which were far below the maximum residue limits (MRLs) as established by FAO/WHO. These very low concentrations of OCPs residues in foodstuffs indicated that OCPs were used only in past time and no recent input into the environment. Furthermore, the estimated daily intake (EDI) of HCB, ΣDDTs, ΣDrins, ΣHeptachlors, and ΣHCHs in five group foodstuffs, which were 60% of total daily diet of Indonesian, were 0.09 ng kg^?1 bw d^?1, 0.04 ng kg^?1 bw d^?1, 0.01 ng kg^?1 bw d^?1, 0.003 ng kg^?1 bw d^?1, and 0.002 ng kg^?1 bw d^?1, respectively. These results were far below the acceptable daily intake (ADI) as established by FAO/WHO, which indicated that consumption of foodstuffs from Indonesia were at little risk to human health in term of OCPs at present.     

Growing season methane budget of an Inner Mongolian steppe

We present a methane (CH₄) budget for the area of the Baiyinxile Livestock Farm, which comprises approximately 1/3 of the Xilin river catchment in central Inner Mongolia, P.R. China. The budget calculations comprise the contributions of natural sources and sinks as well as sources related to the main land-use in this region (non-nomadic pastoralism) during the growing season (May–September). We identified as important CH₄ sources floodplains (mean 1.55 ± 0.97 mg CH₄–C m^?2 h^?1) and domestic ruminants, which are mainly sheep in this area. Within the floodplain significant differences between investigated positions were detected, whereby only positions close-by the river or bayous emitted large amounts of CH₄ (mean up to 6.21 ± 1.83 mg CH₄–C m^?2 h^?1). Further CH₄ sources were sheepfolds (0.08–0.91 mg CH₄–C m^?2 h^?1) and pasture faeces (1.34 ± 0.22 mg CH₄–C g^?1 faeces dry weight), but they did not play a significant role for the CH₄ budget. In contrast, dung heaps were not a net source of CH₄ (0.0 ± 0.2 for an old and 0.0 ± 0.3 μg CH₄–C kg^?1 h^?1 for a new dung heap). Trace gas measurements along two landscape transects (volcano, hill slope) revealed expectedly a mean CH₄ uptake (volcano: 76.5 ± 4.3; hill: 28.3 ± 5.3 μg CH₄–C m^?2 h^?1), which is typical for the aerobic soils in this and other steppe ecosystems. The observed fluxes were rarely influenced by topography.The CH₄ emissions from the floodplain and the sheep were not compensated by the CH₄ oxidation of aerobic steppe soils and thus, this managed semi-arid grassland did not serve as a terrestrial sink, but as a source for this globally important greenhouse gas. The source strength amounted to 1.5–3.6 kg CH₄–C ha^?1 during the growing season, corresponding to 3.5–8.7 kg C ha^?1 yr^?1.     

Application of indoxacarb for managing shoot and fruit borer of eggplant (Solanum melongena L.) and its decontamination

Indoxacarb was applied at 75 and 150 g a.i. ha^{? 1} for two years to an eggplant (Solanum melongena L.) crop grown in the field plots in order to evaluate its efficacy for management of the lepidopteron pest, shoot and fruit borer. The residues of the insecticide were quantified by high-pressure liquid chromatography (HPLC). The mean initial deposits of indoxacarb on eggplant fruits were found to be 2.60–2.634 mg kg^{? 1} and 3.64–3.68 mg kg^{? 1} from the two rates of applications, respectively. They declined with time and reached to non-detectable (< 0.02 mg kg^{? 1}) after 15–20 d. Residues dissipated with a half-life of 3.0–3.8 d from both first and second-year application. A 3 d waiting period for harvest of fruits after insecticide application and processing resulted in the residue levels that were below the Codex maximum residue limit (MRL) of 0.5 mg kg^{? 1} thereby achieving a maximum safety and minimum risk to consumers. The best combination of chemicals for decontamination of indoxacarb was found to be by washing with a mixture of alkali and potassium permanganate (KMnO₄) thereby resulting in the removal of 67.5% and 59.2 % residues for 5 and 10 μ g g^{? 1} spiking doses, respectively. Major products formed on reaction of indoxacarb with alkali were identified by electron spray ionization chromatography/mass spectrometry (ESI/MS). The per cent reduction on the weight and number basis of treated eggplant plots were compared to those observed in control plots to demonstrate the effectiveness of indoxacarb treatment on shoot and fruit borer population.