Comparing different techniques to assess the risk of dust drift from pesticide-coated seeds.

BACKGROUND: Although considered as a safe pesticide application method, treated seeds can pose environmental risks when abraded pesticide-laden seed particles are expelled during sowing. This dust drift risk is clearly linked with seed coating quality. Seed coating quality is traditionally assessed with Heubach dust meters, and guidelines are established in terms of the 'Heubach value'. This technique may, however, not take all drift-sensitive particles into account. In this study, results of the Heubach test are compared with two alternative set-ups: mechanical sieving and the individual sowing element. RESULTS: The abrasion potential assessed with the Heubach dust meter was much lower than the total dust fraction generated by mechanical sieving and the individual sowing element. The amount of dust produced and the dust particle size distribution of both the other techniques were comparable. CONCLUSION: It looks as if the Heubach dust meter underestimates the risk of dust drift. Using one of the alternative methods might be a more appropriate way to assess the abrasion potential of seeds. Given the low investment cost required, mechanical sieving seems to be a good approach for non-specialised labs. The individual sowing element set-up is the most realistic simulation of in-field dust drift generation but requires a higher initial investment. Therefore, this set-up is most suitable for specialised labs and is recommended for further research in this area. © 2017 Society of Chemical Industry.

Characteristics of dust particles abraded from pesticide treated seeds: 1. Size distribution using different measuring techniques.

BACKGROUND: Particle size is one of the most important properties affecting the driftability and behaviour of dust particles abraded from pesticide dressed seeds during sowing. Three particle sizing techniques were used determine the particle size distribution of dust abraded from seeds from six different species. RESULTS: Important differences in dust particle size distribution between species were observed with the finest dust for rapeseed and the coarsest dust for barley. Wet laser diffraction and sonic sieving particle size results correlated well while micro-CT is able to deliver three-dimensional information and additional physical particle properties (shape, porosity). CONCLUSION: All particle sizing techniques have their (dis)advantages and none of them is able to perfectly describe the real size distribution of non-spherical particles. The particle size information gathered can be used in dust drift prediction models, risk assessment tools and will help to better understand the dust drift phenomenon. © 2017 Society of Chemical Industry.

Characteristics of dust particles abraded from pesticide treated seeds: 2. Density, porosity and chemical content.

BACKGROUND: Apart from particle size, drift of abraded seed particles during sowing is mainly affected by two other physical properties, viz. particle shape and envelope density. The impact of these abraded seed particles on the environment is highly dependable on their active ingredient content. In this study, the envelope density and chemical content of dust abraded from seeds was determined as a function of particle size for six seed species. RESULTS: Envelope density and active ingredient content both change as a function of particle size. Important differences in these physico-chemical properties were observed between the six species. Functions were fitted to the collected data to describe the physico-chemical properties as a function of particle size. CONCLUSION: The gathered physico-chemical information is essential for the computational fluid dynamics (CFD)-based dust drift prediction models and can be useful for other prediction models as well as for the ongoing risk assessment of active ingredients used for seed treatment on ecosystems and ecosystem-services. In addition, the results can help to better understand the dust drift phenomenon and to develop mitigation strategies. © 2017 Society of Chemical Industry.

Assessment of the abrasion potential of pesticide-treated seeds using the Heubach test.

During sowing of pesticide-treated seeds, pesticide-laden dust and abraded seed particles may be emitted to the environment, possibly leading to environmental contamination and posing health risks. In many countries there is currently no legislation concerning the acceptable amount of dust of treated seeds. This study aimed to gain insight in the abrasion potential of available pesticide-treated seeds and its associated factors. The abrasion potential of 45 seed samples of 7 different species (viz. sugar beet, oat, barley, wheat, spelt, pea, and maize) was determined using the Heubach test and amounts of dust were expressed as g 100 kgseeds-1, g 100,000 seeds-1, and g ha-1. The abrasion potential fell generally within the boundaries of maximum permissible values adopted by different countries. Species, seed treatment company, number of active ingredient (AIs) and combination of AIs had significant effects on the abrasion potential, whereas little or no effect of agitation and conservation was found. However, species were situated differently with respect to each other depending on the unit in which the abrasion potential was expressed. A standard unit that takes into account the species' seed rate is suggested to give the fairest assessment of dust drift risk and would allow international comparison.

Quantitative 3D shape description of dust particles from treated seeds by means of X-ray micro-CT.

Crop seeds are often treated with pesticides before planting. Pesticide-laden dust particles can be abraded from the seed coating during planting and expelled into the environment, damaging nontarget organisms. Drift of these dust particles depends on their size, shape and density. In this work, we used X-ray micro-CT to examine the size, shape (sphericity) and porosity of dust particles from treated seeds of various crops. The dust properties quantified in this work were very variable in different crops. This variability may be a result of seed morphology, seed batch, treatment composition, treatment technology, seed cleaning or an interaction of these factors. The intraparticle porosity of seed treatment dust particles varied from 0.02 to 0.51 according to the crop and generally increased with particle size. Calculated settling velocities demonstrated that accounting for particle shape and porosity is important in drift studies. For example, the settling velocity of dust particles with an equivalent diameter of 200 µm may vary between 0.1 and 1.2 m s(-1), depending on their shape and density. Our analysis shows that in a wind velocity of 5 m s(-1), such particles ejected at 1 m height may travel between 4 and 50 m from the source before settling. Although micro-CT is a valuable tool to characterize dust particles, the current image processing methodology limits the number of particles that can be analyzed.

Pesticide-laden dust emission and drift from treated seeds during seed drilling: a review.

Dressing seeds with pesticides to control pests is a widespread practice with important advantages. Recent incidents of bee losses, however, have directed attention to the emission of abraded pesticide-coated seed particles to the environment during sowing. This phenomenon of drift of pesticide dust can lead to pesticide contamination of air, water and other natural resources in crop-growing areas. This review article presents the state of the art of the phenomenon of dust emission and drift from pesticide seed dressing during sowing and its consequences. Firstly, pesticide seed treatment is defined and its pros and cons are set out, with the focus on dust, dust emission and dust drift from pesticide-coated seed. The factors affecting emission of pesticide dust (e.g. seed treatment quality, seed drilling technology and environmental conditions) are considered, along with its possible effects. The measuring techniques and protocols and models currently in use for calculating the behaviour of dust are reviewed, together with their features and limitations. Finally, possible mitigation measures are discussed, such as improving the seed quality and the use of modified seed drilling technology, and an overview of regulations and stewardship activities is given.