Initial Residue Levels Research Articles

Persistence and Dissipation Kinetics of λ-Cyhalothrin in Okra Fruits and Soil

Understanding pesticide residue levels in food items and soil is crucial for ensuring food safety. In this context, a study on persistence and dissipation kinetics of λ-cyhalothrin residues in okra fruits and soil was conducted for two consecutive years. λ-cyhalothrin was applied in okra at the recommended dose (15 g a.i. ha-¹) and double dose (30 g a.i. ha-¹). Okra fruit and soil samples were collected at different intervals after second spray and the residues were estimated using GC-MS/MS. The initial residue level in okra fruits was higher at double dose and declined gradually falling below the limit of quantification (0.01 mg kg-¹) within 7 to 10 days of application. Dissipation followed first-order kinetics, with half-life of 2.17 to 2.43 days. In soil, the initial residues dropped below the limit of quantification within 3 to 5 days of application. Since the initial residue levels in both okra fruits and soil were below the corresponding EU–MRL (0.2 mg kg-1), λ-cyhalothrin can be safely used in okra cultivation.

Improving pesticide fate models for a simple household food processing: considering multiple crop units.

To understand the fate of pesticides in crops during household cooking processes and human health risks associated with the ingestion of pesticide-contaminated crops, we propose unit-variability-enhanced models, which are capable of evaluating the removal efficiency of pesticides in multiple crop units by soaking in water. The approach integrates the lognormal production model to reveal the modeling mechanics of internal contamination among two crop units in one soaking bowl. The simulated results for 197 pesticides indicate that pesticides with larger unit-to-unit variability factors (VF) at the residue levels and diffusivity rates in water (DW) are more likely to cause internal contamination. Although internal contamination of pesticide residues between two crop units may occur, we find that the overall removal factor ([Formula: see text]) for two crop units is independent of the ratio of initial residue levels between the two crop units. Based on this discovery, we propose the unit-variability-based (UVB) rule to generalize the [Formula: see text] for an n-crop-unit system, where n crop units soak simultaneously in one container. In addition, we demonstrate that under the same consumable and recycling resources, the soaking of two crop units together in one container can yield a maximum mass removal of pesticides if the two units are randomly sampled. Although other factors, such as temperature and the nature of solutions in the cooking process, should be considered in future studies, our models suggest that this soaking method can be conveniently realized in households to reduce negative health effects.

The study of redistribution in residual stresses during fatigue crack growth

Numerical and experimental study was conducted on fatigue crack growth (FCG) of metallic components to investigate the redistribution of mechanical residual stresses during FCG. To this end, the compact tension specimens of an aluminium alloy were used. In addition, mechanical residual stresses were introduced near the crack tip by applying compressive and tensile loads, followed by visually observing the side-surface of the specimens to estimate the crack growth length. In the numerical simulation, cyclic J-integral was used as the crack growth fracture parameter and a good agreement was observed between the numerical and experimental results. The results of the finite element method demonstrated a clear redistribution of mechanical residual stresses during FCG. After a few cycles, the residual stress field around the crack tip reached a lower magnitude value confined in a smaller zone, although this zone was stable during the remaining fatigue process. Finally, present study evaluated the effect of stress ratio, load amplitude, and initial residual stresses level on the redistribution of residual stresses. It was observed that the residual stresses are mainly released during the first steps of fatigue loading.

Determination of Methomyl Residues in Bohe by Ultrahigh-Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS).

The aim of this work is to investigate the presence of methomyl pesticide residue and the rate of disappearance in mint cultivated in the aquaponics system based on the application of UPLC-MS to establish a safety time interval before crop harvesting. Results showed that an effective and sensitive method based on UPLC-MS has been used for the determination of methomyl pesticide residues in mint. The initial residue level was much higher in roots (79.52 μg/kg), and it can be decreased to 16.73 (after 15 days) μg/kg and 3.31 (20 days) μg/kg, while the least was detected on the mix leaves and stems (44.54 μg/kg), and it can be decreased to 15.35 (after 20 days). In our case, we suggest that a safety interval in the range of 15–20 days should be allowed after the detection of methomyl in water, and the concentration of methomyl was lower than the acceptable daily intake (ADI) of the China Food and Drug Administration (CFDA) (20 μg/kg).

Improved analysis of propamocarb and cymoxanil for the investigation of residue behavior in two vegetables with different cultivation conditions.

A modified quick, easy, cheap, effective, rugged and safe (QuEChERS) method was developed for the simultaneous determination of highly water-soluble propamocarb and hydrophobic cymoxanil in potato tuber and tomato fruit. Residue behaviors of the fungicides in open field or greenhouse were investigated for the safety evaluation of these two pesticides, and the effects of cultivation conditions, fungicide exposure and fruit size of tomato on residue level are discussed. Vegetable samples were extracted with ammonia-acetonitrile, further purified with multiwall carbon nanotubes and analyzed using high-performance liquid chromatography tandem mass spectrometry. The method was validated with fortified samples at different concentration levels (0.05-2.0 mg kg-1 ). Average recoveries ranged from 84 to 111% with relative standard deviations between 0.3 and 5.5%. Limits of quantification (LOQs) were set at the lowest spiking level of 0.05 mg kg-1 . In tomato and cherry tomato, initial residue level of cymoxanil was below LOQ at recommended good agricultural practices. Propamocarb residues were affected by the cultivation conditions, with highest levels of 0.52 and 0.72 mg kg-1 in open field and greenhouse, respectively. In addition, residues of propamocarb in cherry tomatoes were found to be present at 1.25 mg kg-1 . The field trial results showed that propamocarb and cymoxanil residues in potato tubers were below LOQ due to the tubers not being exposed to sprayed pesticides. The unexpected high residue levels in cherry tomato seem to indicate that cherry tomato with small size presents certain accumulative effects of propamocarb. © 2020 Society of Chemical Industry.

Data collection for the estimation of ecological data (specific focal species, time spent in treated areas collecting food, composition of diet), residue level and residue decline on food items to be used in the risk assessment for birds and mammals

The study described in this report was conducted with the aim of developing an unified database of ecological data and residue data to be used for the risk assessment of plant protection products for birds and mammals. The main sources of data were the information submitted in the context of approval of active substances and authorization of products and and additional information retrieved through a systematic literature review. The data were screened and organised in three Excel databases, one for birds, one for mammals and one for residue studies. The ecological information for birds and mammal risk assessment consisted of data that is used for the determination of focal species, estimation of the proportion of an animal's daily diet obtained in a treated habitat (PT) and assessment of the composition of the diet obtained from a treated area (PD). The information gathered on residues focussed on (initial) residue levels after treatment and on residue decline (the reported half‐life or DT50 and the DT90)

Dissipation of chlorantraniliprole, chlorpyrifos-methyl and indoxacarb\u2014insecticides used to control codling moth (Cydia Pomonella L.) and leafrollers (Tortricidae) in apples for production of baby food

Dissipations of three insecticides: chlorantraniliprole, chlorpyrifos-methyl and indoxacarb in apples were studied following their foliar application on apples intended for production of baby food. The apples were sprayed with formulations for control of codling moth (Cydia Pomonella L.) and leafrollers (Tortricidae). Six experiments were conducted; each insecticide was applied individually on dessert apples. A validated gas chromatography-based method with simultaneous electron capture and nitrogen–phosphorus detection (GC-ECD/NPD) was used for the residue analysis. The analytical performance of the method was satisfactory, with expanded uncertainties ≤36% (a coverage factor, k = 2, and a confidence level of 95%). The dissipations of insecticides were studied in pseudo-first-order kinetic models (for which the coefficient of determination, R2, ranged between 0.9188 and 0.9897). Residues of studied insecticides were below their maximum residue limits of 0.5 mg/kg at an early stage of growth of the fruit. The half-lives of chlorantraniliprole, chlorpyrifos-methyl and indoxacarb were 16–17, 4–6 and 20–24 days, respectively. The initial residue levels declined gradually and reached the level of 0.01 mg/kg in 1 month for chlorpyrifos-methyl, 2 months for chlorantraniliprole and 2.5 months for indoxacarb. To obtain the insecticide residue levels below 0.01 mg/kg, which is the default MRL for food intended for infants and young children, the application of the studied insecticides should be carried out at recommended doses not later then: 1 month before harvest for chlorpyrifos-methyl, 2 months for chlorantraniliprole and 2.5 months for indoxacarb.

Dissipation of difenoconazole in apples used for production of baby food

ABSTRACTDissipation of fungicide difenoconazole (3-chloro-4-[(2RS,4RS;2RS,4SR)-4-methyl-2-(1H-1,2,4-triazol-1-ylmethyl)-1,3-dioxolan-2-yl]phenyl 4-chlorophenyl ether) was studied following its application on apples intended for production of baby food. The apples (varieties: Jonagold Decosta, Gala and Idared) were sprayed with the formulation to control pathogens causing fungal diseases: powdery mildew (Podosphaera leucotricha ELL et Ev./Salm.) and apple scab (Venturia inaequalis Cooke/Aderh.). A validated gas chromatography-based method with simultaneous electron capture and nitrogen phosphorus detection (GC-ECD/NPD) was used for the residue analysis. The analytical performance of the method was highly satisfactory, with expanded uncertainties ≤ 19% (a coverage factor, k = 2, and a confidence level of 95%). The dissipation of difenoconazole was studied in pseudo-first-order kinetic models (for which the coefficients of determination, R2, ranged between 0.880 and 0.977). The half-life of difenoconazole was 12–21 days in experiments conducted on three apple varieties. In these experiments, the initial residue levels declined gradually and reached the level of 0.01 mg kg−1 in 50–79 days. For the residue levels to remain below 0.01 mg kg−1 (the maximum acceptable concentration for baby foods), difenoconazole must be applied approximately 3 months before harvest, at a dose of 0.2 L ha−1 (50 g of an active ingredient per ha).

Usage of the relationship between the application rates of the active ingredient of fungicides and their residue levels in mature apples to creating a coherent system of MRLs

Setting of maximum residue levels (MRLs; tolerances in the USA) in crops requires a big amount of data concerning residues from a number of supervised field trials for each pesticide/crop combination. This task is time-consuming, costly and fairly complicated. Therefore, we initiated a study on the utilization of the interpolation method in supporting and facilitating of assessing the value of the MRLs which are now being in use, and in creating their consistent system in the future. A mathematical formula for predicting the initial pesticide residue level in mature apples was developed by establishing the relationship between application rates and residue levels of the pesticide active ingredients in mature apples. This dependence was described by a linear equation R 0 = 1.2593 × D, with coefficient of determination r 2 = 0.984, where D is an application rate of a given substance. This relationship makes it possible to predict a residue level of other substances of fungicidal activity. Thus, residue levels (both predicted by the formula and obtained in the frame of Polish National Monitoring Program) of fungicides now used in apple orchards, in mature apples were typically lower than those of the statutory MRLs. Bearing in mind that the European Union policy is directed towards substantial reduction in pesticide use, the MRLs might be reconsidered in order to be set at lower values.

Effects of processing on carbendazim residue in Pleurotus ostreatus

Samples of Pleurotus ostreatus were exposed to fungicide carbendazim to study the effect of processing on the residues. In most cases, processing operations led to a significant decrease in residue levels in the finished products, particularly through washing, drying, and cooking processes. The results indicated that rinsing under running tap water led to more than 70.30% loss in carbendazim residues. When dried under sunlight could remove more than 70.30% residues. There was a 63.90–97.14% reduction after steaming, with processing time extending, the removal rates increased especially for lower initial residue level samples. The residue was almost completely removed by frying combined with microwave heating. Furthermore, boiling the mushrooms reduced the residue in the mushroom and no carbendazim residues were determined in the broth.

Distribution and dissipation of deltamethrin, dimethomorph, imidacloprid, mepanipyrim, and metalaxyl applied to chili peppers

Field trials were carried out to investigate the dissipation rates of pesticides as well as to measure the terminal residues in chili peppers. Deltamethrin, dimethomorph, imidacloprid, mepanipyrim, and metalaxyl were applied to chili peppers 15 days prior to harvest. Chili pepper samples were collected at specified intervals and were subjected to residue analysis and dislodgeable residue study. In most cases, initial residue levels were rapidly dissipated with time. The dissipation pattern of pesticide residues fits well to first-order kinetics. Biological half-lives, as calculated from regression curves, of most pesticides were estimated to be <4 days. In the fast growing chili pepper, a dilution effect was considerably involved in the rate of dissipation. As a result, it was possible to predict the terminal residue at harvested crops from the initial residue level and declining curve of pesticides.

The Influence of Sulphur and Oxigen Additions in Mg-Treated Iron on the Cooling Curves Parameters

The main objectiv of this experimental reserch is a comparative analysis of sulphur and oxygen effects on the cooling curves parameters at different iron melt modifying potential (residual Mg content). For the experiment, three irons with different modifying potential (0.0014, 0.0213 and 0.033 wt % residual Mg content respectively) were developed. After Ca-Ba inoculation, the three irons were additional treated by stoichiometric equivalent additions of sulphur or oxygen as FeS2 and Fe2O3 respectively. Both FeS2 and Fe2O3 sources were placed on the bottom of standard Quik-Cup moulds,usualy used for iron melt thermal analysis. The effect of sulphur and oxygen on the standard and nonconventional cooling curves parameters were evaluated to a more deep understanding of the cast iron solidification mechanism. The cooling curves parameters are strongly influenced both by the initial residual Mg level of iron melt and afterwords sulphur/oxygen additions. A very complex and sometimes confused variation of the cooling curves parameters was recorded because of different actions of the three factors (iron melt modifying potential, sulphur and oxygen). As a previous paper highlighted, sulphur addition has a strong graphite decompactizing effect while oxygen addition has mostly an inoculant effect.

Residue behaviour of six pesticides in button crimini during home canning

The effect of home canning (including washing, boiling, cooling, adding solution and sterilisation) on residue levels of imidacloprid, diflubenzuron, abamectin, pyriproxyfen and β-cypermethrin and chlorothalonilin on button crimini was assessed. Residues of imidacloprid, diflubenzuron, abamectin and pyriproxyfen were measured by UPLC-MS/MS; the residues of β-cypermethrin and chlorothalonil were measured by GC. Results showed that washing resulted in a 3.8% reduction of the initial residue level of imidacloprid (p ≤ 0.05). From washing to sterilisation the processing effect was significant compared with raw crimini (p ≤ 0.05), but processing through cooling and adding solution had no effect. For diflubenzuron, from raw crimini to sterilisation the processing effect was significant by comparison with the initial level (p ≤ 0.05); the processing effect was not obvious between two sequential steps, and the sequential steps have list: washing and boiling, boiling and cooling, boiling and adding of solution, cooling and adding solution. The changes in abamectin levels were also significant from raw crimini to sterilisation compared with raw crimini (p ≤ 0.05), but the changes were not obvious from boiling to adding solution and amongst them. For pyriproxyfen, washing resulted in a 39% reduction, but changes were not obvious from washing to sterilisation, p ≤ 0.05 between two consecutive steps. The whole procedure could significantly decrease residues of β-cypermethrin (p ≤ 0.05); washing could significantly reduce residues of β-cypermethrin; the effects of last procedures were complicated, and p ≤ 0.05 between two consecutive steps. Washing resulted in an 80% reduction of chlorothalonil; after washing there were no detectable residues. After the whole process, the processing factors for imidacloprid, diflubenzuron, abamectin, pyriproxyfen, β-cypermethrin and chlorothalonil were 0.40, 0.22, 0.04, 0.85, 0.28 and 0, respectively.

Fatigue crack propagation into the residual stress field along and perpendicular to laser beam butt‐weld in aluminium alloy AA6056

ABSTRACTLaser beam butt welds in Al‐alloys are very narrow and are accompanied by steep residual stress gradients. In such a case, how the initial crack orientation and the distance of the notch tip relative to the weld affect fatigue crack propagation has not been investigated. Therefore, this investigation was undertaken with two different crack orientations: along the mid‐weld and perpendicular to the weld. Fatigue crack propagation ‘along the mid‐weld’ was found to be faster in middle crack tension specimens than in compact tension specimens. For the crack orientation ‘perpendicular to the weld’, the relative distance between the notch tip and the weld was varied using compact tension specimens to generate either tensile or compressive residual stresses near the notch tip. When tensile residual stresses were generated near the notch tip, fatigue crack propagation was found to be faster than that in the base material, irrespective of the difference in the initial residual stress level and whether the crack propagated along the mid‐weld or perpendicular to the weld. In contrast, when compressive weld residual stresses were generated near the notch tip, fatigue crack arrest, slow crack propagation, multiple crack branching and out of plane deviation occurred. The results are discussed by considering the superposition principle and possible practical implications are mentioned.

Radioprotection of 4-hydroxy-3,5-dimethoxybenzaldehyde (VND3207) in culture cells is associated with minimizing DNA damage and activating Akt

Vanillin is a naturally occurring compound and food-flavoring agent with antioxidant and antimutagenic activities. In present study, we explored the radioprotective effect of a novel vanillin derivative VND3207 (4-hydroxy-3,5-dimethoxybenzaldehyde). VND3207 has a much higher potential in scavenging hydroxyl radical and superoxide radical than vanillin as indicated in the ESR spin-trapping measurement, and it can effectively protect plasmid DNA against 10–50 Gy γ-ray induced breaks in vitro at the concentrations as low as 10–20 μM. Using human lymphoblastoid AHH-1 cells and human fibroblastoid HFS cells, we demonstrated that VND3207 at 5–40 μM concentrations significantly attenuated the inhibition of proliferation and occurrence of apoptosis produced by 1–8 Gy γ-irradiation. In the cultured cells, VND3207 significantly decreased the initial production and residual level of DNA double-strand breaks (DSBs) induced by 2 or 8 Gy irradiation. Treatment of VND3207 enhanced the level of DNA-PKcs protein, a critical component of DNA DSB repair pathway in the cells with or without γ-irradiation. Consistently, the phosphorylation of Akt protein, a mediator of survival signal, as well as its substrate GSK3β was concurrently increased by VND3207. Our results suggest that VND3207 has radioprotection effect through its capabilities as a powerful antioxidant, in minimizing DNA damage, and activating survival signal Akt pathway, and it may be of value in the development of radioprotective compounds.

Row cleaners enhance reduced tillage planting of corn in Iran

Seed placement and failure to establish a uniform plant stand are critical problems associated with conservation tillage production of corn ( Zea mays) following wheat ( Triticum aestivum) in Iran. Our objectives were to evaluate the performance of a conventional corn planter (with runner type openers) equipped with row cleaners and to demonstrate for local farmers an affordable method for reduced tillage corn production. The reduced tillage system studied consisted of disking followed by chisel plowing and another disking ahead of planting. A ground-driven row cleaner was fabricated and mounted to each unit of a common pneumatic single seed planter and used to plant at three forward speeds (4, 7, and 10 km h −1) into no- (NR), half- (HR), and whole- (WR) residue plots. This compares to a typical system of complete removal or burning the previous wheat residue in the region. The amount of residue retained in the row, depth of seed placement, emergence rate and three indices of uniformity in seed spacing were determined. Row cleaners performed best at the highest forward speed, retaining an average residue cover of 920 kg ha −1 compared to 1350 kg ha −1 for plots planted without using row cleaners. This 430 kg ha −1 more residue removal was a significant improvement with regard to soil–seed contact. For the HR and WR plots, residue removal averaged 45% and 70% of that present before planting, suggesting that the row cleaners will work more effectively at high residue conditions. Without row cleaners, initial residue levels resulted in a shallow planting depth, but when row cleaners were used, planting depth was maintained near the target depth (5 cm). The desired planting depth was also obtained at 7 km h −1 in the HR plots. Row cleaners significantly increased plant emergence rate with the maximum (3.5 plants d −1 m −1) being observed for seeds planted at 4 km h −1 in the HR plots. This agrees with others who showed high residue reduces plant emergence and grain yield. Planting with row cleaners into HR plots at 7 km h −1 resulted in the lowest miss and precision indices comparable to those of a no-residue plot (16.5% and 17.5%, respectively), and a quality of feed index as high as 69% was obtained at similar conditions. Our results indicate that equipping available planters with row cleaners can result in a successful reduced tillage corn production system and thus satisfy both farmers and authorities promoting conservation tillage. In addition to the environmental benefits of the proposed system, it is expected that the savings in time, fuel and labor would offset the cost of row cleaners.

Numerical evaluation of residual stress relaxation by cyclic load

The aim of this work is to evaluate by numerical simulation the real stress state of a welded component subjected to a sinusoidal external load. In particular, the relaxation process of the residual stress, due to the application of a cyclic external load, has been studied. Longitudinal welded joints, laser welded and 3 mm thick, are analysed in this work following the residual stress evolution during a fatigue test. A numerical procedure, implemented by the ABAQUS code, carries out the residual stress field originated by a welding process and it is taken as a pre-stress condition in the present ABAQUS simulations. In order to evaluate the influence of the amplitude level on the residual stress relaxation, eight different sinusoidal loads at the load ratio R = 0.1 are applied to the model. The results show a significant reduction in the initial residual stress level, even after the first load cycle. They offer a very precise explanation of the fatigue behaviour of this kind of welded joints, confirming the behaviour experimentally observed.

Predicting Chlorine Residuals and Formation of TTHMs in Drinking Water

Chlorination is the most widely practiced form of disinfection in the United States. It is highly effective against most microbiological contaminants. However, there is concern that the disinfection by-products (DBPs) formed by the use of chlorine might be carcinogenic. One class of DBPs that are formed and the only class of DBPs that currently are regulated are total trihalomethanes (TTHMs). Therefore, much effort is being expended in developing models that can be used to predict both TTHMs and chlorine residual levels in treated drinking water. This paper presents a model that predicts both TTHMs and chlorine residuals based on the consumption of chlorine and can be used to assist in evaluating the complex balance between microbial and DBP risks associated with disinfecting drinking water with chlorine. The parameters of the model have been found to be functions of total organic carbon, pH, temperature, and initial chlorine residual level. Bromide and the subsequent formation of brominated by-products were not considered in this paper.

Volatile and Dislodgeable Residues Following Triadimefon and MCPP Application to Turfgrass and Implications for Human Exposure

Volatilization can be a major route of pesticide loss following application to turfgrass areas. Consequently, a significant portion of applied pesticide may be available for human exposure via volatile and dislodgeable residues. In this study, volatile and dislodgeable residues were determined following application of triadimefon [1‐(4‐chlorophenoxy)‐3,3‐dimethyl‐l‐(1H‐1,2,4‐triazol‐l‐yl) butanone], and MCPP [( +/−)‐2‐(4‐chloro‐2‐methylphenoxy) propionic acid], to established plot of ‘Penncross’ creeping bentgrass (Agrostis palustris Huds.). For each application, a 10‐m radius plot was sprayed and the Theoretical Profile Shape (TPS) method of Wilson was used to estimate volatile flux. Dislodgeable residues were concurrently determined by wiping treated turfgrass with a water dampened piece of cheesecloth. Less than 8% of the total applied triadimefon was measured as volatile residues with nearly all volatilization loss occurring within 5 to 7 d of application. Diurnal patterns of triadimefon volatilization were evident. Mid‐day (1100–1500 h) triadimefon volatile flux on Days 2 (4.6 g ha−2 h−1 ) and 3 (2.4 g ha−2 h−1) was 2 and 1.4 times, respectively, greater than the average of morning and late afternoon volatile flux on these respective days. Less than 1% of the total applied MCPP was measured as volatile residue. Volatile MCPP residues decreased over time to nondetectable levels by Day 5. Both triadimefon and MCPP dislodgeable residues were greatest on Day 1 following application and dissipated over time. By Day 5, triadimefon dislodgeable residues decreased to 0.04% of the initial residue level immediately following application and MCPP dislodgeable residues were nondetectable. Inhalation and dermal exposures to humans were estimated from measured air concentrations and dislodgeable residues, respectively. Hazard quotients (HQs) were calculated for both volatile and dislodgeable residues of each pesticide. Exposures (i.e., doses) divided by reference doses (Rfds) resulted in hazard quotients (HQs). Triadimefon and MCPP volatile and dislodgeable residues resulted in HQs below 1.0 throughout the entire 15‐d experimental period indicating that exposures were below any level expected to cause adverse health effects.

Distribution and decay of phosmet residues in the canopy of “T-bar” trellised kiwifruit

Abstract Phosmet was applied in mid season to “T-bar” trellised kiwifruit (Actinidia deliciosa) by airblast sprayer at 112.5 g a.i/100 litres and 2250 litres/ha. Residue levels on the upper and lower surfaces of leaves from two canopy zones and two shoot types were assessed by chemical and biological assays. Chemical assays used a brief solvent wash of a fixed area of the separate leaf surfaces. In the bioassays neonate Epiphyas postvittana (Walker) larvae were cagedon each surface. These procedures were repeated 1, 3, 8, 14, and 29 days after spray application in mid summer. Mean initial residues ranged from 2.1 μg/cm2 to 9.0 μg/cm2, with levels 2–3 times greater on lower surfaces than upper surfaces. Residue half-lives calculated for lower leaf surfaces ranged from 6 to 20 days. The half-life for upper surface residues was estimated graphically at 3 days. Differences in the initial residue levels between canopy zones and shoot types tended to be offset by subsequent decay rates. Chemical assays and mort...