Bases for pesticide dose expression and adjustment in 3D crops and comparison of decision support systems

Authorities around the world have committed to limiting the use of chemical pesticides by reducing doses, among other strategies. Nevertheless, different dose expression models and decision support systems (DSSs) for dose adjustment coexist for high growing crops (3D crops). Among them, leaf wall area (LWA) and tree row volume (TRV) models have recently been proposed by the European and Mediterranean Plant Protection Organization (EPPO) for pre-registration trials. In this paper, the background and technical bases of six dose adjustment DSSs in fruit crops (PACE, AGMET, DOSA3D, OMAX and PULVARBO) and four in grape orchards (AGMET, OPTIDOSE, DOSAVIÑA and DOSA3D) are described and compared. The discussion leads to the conclusion that LWA and TRV represents a substantial improvement compared to the former crop ground area-based dose expression model. However, total leaf area is the most important parameter for dose adjustment, while sprayer efficiency is also a key factor. Additionally, it is suggested that deposition on leaves (mean values and variability) should be reported in pesticide efficacy evaluations in order to establish the required doses independently from the dose expression mode. The DOSA3D system, based on leaf area index estimation, was found to be the most conservative DSS regarding the spraying volume ratio to TRV because low spraying efficiencies are considered. Instead, AGMET was found to be the most effective for dose adjustment. However, despite the differences between the recommendations, all the analysed DSSs are useful tools for rational decision making about spraying volume rate and pesticide doses at national level. Their use should be promoted by the competent authorities.

Morphological and elemental characterization of leaf-deposited particulate matter from different source types: a microscopic investigation

Particulate matter (PM) deposition on urban green enables the collection of particulate pollution from a diversity of contexts, and insight into the physico-chemical profiles of PM is key for identifying main polluting sources. This study reports on the morphological and elemental characterization of PM_2-10 deposited on ivy leaves from five different environments (forest, rural, roadside, train, industry) in the region of Antwerp, Belgium. Ca. 40,000 leaf-deposited particles were thoroughly investigated by particle-based analysis using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX) and their physico-chemical characteristics were explored for PM source apportionment purposes. The size distribution of all deposited particles was biased towards small-sized PM, with 32% of the particles smaller than 2.5 μm (PM_2.5) and median diameters of 2.80-3.09 μm. The source type influenced both the particles' size and morphology (aspect ratio and shape), with roadside particles being overall the smallest in size and the most spherical. While forest and rural elemental profiles were associated with natural PM, the industry particles revealed the highest anthropogenic metal input. PM_2-10 profiles for roadside and train sites were rather comparable and only distinguishable when evaluating the fine (2-2.5 μm) and coarse (2.5-10 μm) PM fractions separately, which enabled the identification of a larger contribution of combustion-derived particles (small, circular, Fe-enriched) at the roadside compared to the train. Random forest prediction model classified the source type correctly for 61-85% of the leaf-deposited PM. The still modest classification accuracy denotes the influence of regional background PM and demands for additional fingerprinting techniques to facilitate source apportionment. Nonetheless, the obtained results demonstrate the utility of leaf particle-based analysis to fingerprint and pinpoint source-specific PM, particularly when considering both the composition and size of leaf-deposited particles.

Leaf-deposited semi-volatile organic compounds (SVOCs): An exploratory study using GCxGC-TOFMS on leaf washing solutions

Airborne particulate matter (PM) includes semi-volatile organic compounds (SVOCs), which can be deposited on vegetation matrices such as plant leaves. In alternative to air-point measurements or artificial passive substrates, leaf monitoring offers a cost-effective, time-integrating means of assessing local air quality. In this study, leaf washing solutions from ivy (Hedera hibernica) leaves exposed during one-month at different land use classes were explored via comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GCxGC-TOFMS). The composition of leaf-deposited SVOCs, corrected for those of unexposed leaves, was compared against routinely monitored pollutants concentrations (PM₁₀, PM_2.5, O₃, NO₂, SO₂) measured at co-located air monitoring stations. The first study on leaf-deposited SVOCs retrieved from washing solutions, herein reported, delivered a total of 911 detected compounds. While no significant land use (rural, urban, industrial, traffic, mixed) effects were observed, increasing exposure time (from one to 28 days) resulted in a higher number and diversity of SVOCs, suggesting cumulative time-integration to be more relevant than local source variations between sites. After one day, leaf-deposited SVOCs were mainly due to alcohols, N-containing compounds, carboxylic acids, esters and lactones, while ketones, diketones and hydrocarbons compounds gained relevance after one week, and phenol compounds after one month. As leaf-deposited SVOCs became overall more oxidized throughout exposure time, SVOCs transformation or degradation at the leaf surface is suggested to be an important phenomenon. This study confirmed the applicability of GCxGC-TOFMS to analyze SVOCs from leaf washing solutions, further research should include validation of the methodology and comparison with atmospheric organic pollutants.

Air pollution deposition on a roadside vegetation barrier in a Mediterranean environment: Combined effect of evergreen shrub species and planting density

Leaf deposition of PM_10-100, PM_2.5-10, PM_0.2-2.5 and of 21 elements was investigated in a roadside vegetation barrier formed by i) two evergreen shrub species (Photinia × fraseri, Viburnum lucidum), with ii) two planting densities (0.5, 1.0 plant m^-2), at iii) three distances from the road (2.0, 5.5, 9.0 m), at iv) two heights from the ground (1.5, 3.0 m), and on v) three dates (Aug, Sep, Oct). The presence of black and brown on-leaf PM_10-100 and their element composition were detected by microscopy and image analysis. Pollutant deposition was also measured using passive samplers at five distances from the road (2.0, 5.5, 9.0, 12.5, 19.5 m) in the area of the barrier and in an adjacent lawn area. V. lucidum had more PM_2.5-10 and PM_0.2-2.5 on leaves than P. × fraseri, while most elements were higher in P. × fraseri. Most pollutants decreased at increasing distances from the road and were higher at 1.5 m from the ground compared to 3.0 m. Higher planting density in P. × fraseri enhanced the deposition of PM_10-100 and PM_2.5-10, while in V. lucidum, the planting density did not affect the depositions. Black PM_10-100 decreased a long distance from the road and was entirely composed of carbon and oxygen, which was thus identified as black carbon from fuel combustion. The vegetation barrier had a higher deposition of most PM fractions at 5.5-12.5 m, while in the lawn area, depositions did not change. At 19.5 m, the PM_10-100 was 32% lower behind the barrier than in the lawn area. In conclusion, the vegetation barrier changed the deposition dynamics of pollutants compared to the lawn area. These results strengthen the role of vegetation barriers and shrub species against air pollution and may offer interesting insights for the use of new road green infrastructures to improve air quality.

Quantifying particulate matter accumulated on leaves by 17 species of urban trees in Beijing, China

Airborne particulate matter (PM) has become a serious environmental problem and harms human health worldwide. Trees can effectively remove particles from the atmosphere and improve the air quality. In this study, a washing and weighing method was used to quantify accumulation of water-soluble ions and insoluble PM on the leaf surfaces and within the wax of the leaves for 17 urban plant species (including 4 shrubs and 13 trees). The deposited PM was determined in three size fractions: fine (0.2-2.5 μm), coarse (2.5-10 μm), and large (> 10 μm). Significant differences in the accumulation of PM were detected among various species. The leaves of Platycladus orientalis and Pinus armandi were the most effective in capturing PM. Across the species, 65 and 35% of PM, on average, deposited on the leaf surface and in the wax, respectively. The greatest PM accumulation by mass on leaves was in the largest PM size fraction, while the accumulation of coarse and fine particle size fractions was smaller. Water-soluble ions accumulated on the leaf surfaces contributed 28% to the total PM mass, on average. This study demonstrated that leaves of woody plants accumulate PM differently, and the most effective plant species should be selected in urban areas for attenuating ambient PM.

Accumulation and variability of maize pollen deposition on leaves of European Lepidoptera host plants and relation to release rates and deposition determined by standardised technical sampling

BACKGROUND

Risk assessment for GMOs such as Bt maize requires detailed data concerning pollen deposition onto non-target host-plant leaves. A field study of pollen on lepidopteran host-plant leaves was therefore undertaken in 2009-2012 in Germany. During the maize flowering period, we used in situ microscopy at a spatial resolution adequate to monitor the feeding behaviour of butterfly larvae. The plant-specific pollen deposition data were supplemented with standardised measurements of pollen release rates and deposition obtained by volumetric pollen monitors and passive samplers.

RESULTS

In 2010, we made 5377 measurements of maize pollen deposited onto leaves of maize, nettle, goosefoot, sorrel and blackberry. Overall mean leaf deposition during the flowering period ranged from 54 to 478 n/cm² (grains/cm²) depending on plant species and site, while daily mean leaf deposition values were as high as 2710 n/cm². Maximum single leaf-deposition values reached up to 103,000 n/cm², with a 95 % confidence-limit upper boundary of 11,716 n/cm².

CONCLUSIONS

Daily means and variation of single values uncovered by our detailed measurements are considerably higher than previously assumed. The recorded levels are more than a single degree of magnitude larger than actual EU expert risk assessment assumptions. Because variation and total aggregation of deposited pollen on leaves have been previously underestimated, lepidopteran larvae have actually been subjected to higher and more variable exposure. Higher risks to these organisms must consequently be assumed. Our results imply that risk assessments related to the effects of Bt maize exposure under both realistic cultivation conditions and worst-case scenarios must be revised. Under common cultivation conditions, isolation buffer distances in the kilometre range are recommended rather than the 20-30 m distance defined by the EFSA.

Particulate Matter deposition on Quercus ilex leaves in an industrial city of central Italy

A number of studies have focused on urban trees to understand their mitigation capacity of air pollution. In this study particulate matter (PM) deposition on Quercus ilex leaves was quantitatively analyzed in four districts of the City of Terni (Italy) for three periods of the year. Fine (between 0.2 and 2.5 μm) and Large (between 2.5 and 10 μm) PM fractions were analyzed. Mean PM deposition value on Quercus ilex leaves was 20.6 μg cm(-2). Variations in PM deposition correlated with distance to main roads and downwind position relatively to industrial area. Epicuticular waxes were measured and related to accumulated PM. For Fine PM deposited in waxes we observed a higher value (40% of total Fine PM) than Large PM (4% of total Large PM). Results from this study allow to increase our understanding about air pollution interactions with urban vegetation and could be hopefully taken into account when guidelines for local urban green management are realized.