Qualitative and quantitative analysis of agricultural dust in working environment

ABSTRACT 
 
The presented quantitative and qualitative analysis of dust in agricultural working environment is a continuation of the process of recognizing the exposure to dust among private farmers. The study covers the following: determination of respirable fraction of dust in the respiratory zone (on the background of total dust) while performing individual farming activities which constitute an annual work cycle, organic and mineral components of settled dust for basic groups of farming activities, and the main mineral pathogenic component - free silica in airborne and settled dust. The study was conducted on 5 farms specialising in: cultivation of cereals, root plants, vegetables, dairy cattle and swine breeding and mixed production. The analysis of settled dust covered 17 types of dust accompanying field work and farm/indoor activities. Studies of airborne dust were conducted on farmers while performing 40 main work activities which contributed to the annual work cycle. Results of the study confirmed the following: agricultural work activities are accompanied by a high level of dustiness and showed the presence of a respirable fraction in airborne dust of up to 25%, a higher level of pathogenic free silica SiO2 in settled dust samples in the working environment of a farmer, compared to dust in respiratory zone, a comparable level of SiO2 in total and respirable airborne dust, and a high level of organic component in settled dust at work activities with plant material. These results indicated that the evaluation of farmers’ exposure to dust should be based on the examination of samples taken in the respiratory zone while performing individual work activities.


METHODS

Standardised methods were applied in field and laboratory studies. The level of airborne dust - total and respirable - was determined by a weighing method and personal equipment: AP-2-aspirators, ORMED, Lodz, Poland, and SKC/224-PCEX7 aspirators, SKVC Ltd, Dorset, UK. In both fractions of airborne dust the contents of free silica was determined by colorimetric method, with the use of the following spectrophotometers: Specol 11, Carl-Zeiss, Yena, Germany, and Marcel Mini Eco, MARCEL Sp. Z.o.o, Warsaw, Poland. The same method was applied for the determination of this component in settled dust. The contents of organic and mineral components in settled dust was also analysed by the method of total combustion of organic components contained in the sample (total ash) at a temperature of approximately 900ºC. In studies of settled dust, the sample for analysis was the fraction below 100 micrometers. For organic agricultural dust particles, the density of which remains within 1–2 g cm-3 , this fraction possesses the potential of respirable dust. This means that the particles of this fraction may occur in airborne dust in the respiratory zone long enough to get into the stream of the air inhaled by a farmer at work. Studies of each type of settled dust were based on analysis of the composition of 3 samples. The determinations of the level of free silica in the ash - residues after the combustion of settled dust - were performed 3 times for each ash sample. The level of this component in airborne dust was determined in joint dust samples due to too small weighed portions of dust in individual samples. Dust in the respiratory zone was collected in 2 series covering 2 measurements of total dust concentration each and 2-6 measurements of the level of respirable dust.

RESULTS

The following 7 groups of work activities were distinguished which contribute to the typical technologies applied on farms carrying out basic plant and animal production:

• cultivation and treatment activities: spring ploughing, post-harvest ploughing, harrowing, cultivation, disk harrowing, work with deep plough, cultivation with aggregate, rolling of soil, mechanical and manual cultivation of crops.
• fertilizing: sowing of mineral fertilizers, fertilizing with natural fertilizers;
• sowing, planting: sowing seeds with a grain drill, potato planting, manual sowing and planting;
• plant treatment: chemical spraying of crops, treatment of seed-grain;
• plant harvesting: harvesting of cereals with combine or cutter, collecting and pressing straw, cutting of plants with Orkan, harvesting of leguminous plants and sweet corn with a combine, cutting leaves or tops, digging of potatoes and beetroots, manual harvesting and vegetable sorting, manual harvesting of fruits;
• farming activities: care of animals (cattle and swine), grain threshing, bean threshing, sorting and packing of potatoes, crushing of grain, cleaning of grain, mixing of fodder, cutting of wood with chain and circular saws, cleaning activities;
• other activities: manual reloading, work with Cyklop and Tur loaders, repair, transport.

Settled dust. 

The studies of settled dust covered 17 types of dust accompanying the above-mentioned work activities. Table 1 and Figure 1 present the results of study of these types of dust. The mineral fraction constitutes the main component of dust settled on a tractor during cultivation and treatment activities and harvesting of root crops, also of dust settled on potato sorting machine and packer - from 90.0–98.9%. The greatest percentage of organic fraction was noted in dust settled on grain mill, corn cleaner and mixer - from 93.6–97.7%. Combine harvesting of cereals is a source of dust with similar percentages of both fractions, the organic component being dominant. However, dust settled on the surface of a thresher during stationary grain threshing in a farm room contained up to 1/4 mineral component. Here, we should expect the presence of a considerable number of microbes, especially during threshing performed in winter, when the conditions of storage of the crops (sheaves of cereals, bean haulms) are conducive to the development of microorganisms. The analysis of ash in order to determine the contents of free silica showed the presence of this component in various samples - from 30–66% of the ash mass. For the mass of the whole ash sample, SiO2 constituted from 0.9% in settled dust on fodder mixer to 64.6% in dust settled on a tractor and beets combine harvester during harvesting of beetroots. The spread of the results obtained resulted from a non-uniform morphology of the collected samples of settled dust, which, in turn, is associated with the heterogeneous character of dust, both in airborne and settled phases

Airborne dust. 

Table 2 presents results of the measurements of the concentration of total and repirable dust, as well as results of determinations of the level of free silica SiO2 in this dust. The considerable spread of values obtained is noteworthy. This is associated primarily with non-stable release of dust in the course of work, changeable conditions accompanying work at the subsequent measurement cycles, and finally, with the previously mentioned heterogeneous character of airborne previously mentioned heterogeneous character of airborne dust, especially in a space not isolated from external conditions. In the mass of inhaled total dust, respirable dust occurs in the quantity of 5.0–25.1%, and most often constitutes up to 10% of total dust. The lowest percentage of respirable dust was observed during manual sowing and planting, work with a loader, cutting plants with Orkan, and cutting leaves and tops, whereas the highest percentage of this dust was noted during transport, sweet corn combine harvesting, and manual reloading. The compilation of results of measurements of airborne dust concentrations, presented in Figure 1, confirms that the highest risk caused by dust occurs at farm/indoor, cultivation and treatment activities.

Studies of the level of free silica in airborne dust showed the greatest amounts of this mineral component in dust accompanying mechanical and manual treatment of crop, spring ploughing and beets digging. A relatively low level of SiO2 was noted in dust during reloading and animal care activities. The analyses indicated that the levels of free silica generally remained on a similar level in both fractions examined. Slightly greater levels of silica were noted in respirable dust during chemical plant protection and fertilizing - work activities performed in a closed cabin, which resulted in a greater amount of fine particles penetrating into the interior of the cabin through leaks (Fig. 3). Figure 4 presents the range of concentrations of free silica dust - total and respirable - obtained for 7 groups of agricultural activities. The highest values of concentrations and the greatest spread of these values were noted in the group of cultivation and treatment activities, as well as household activities. The comparison of the levels of SiO 2 in settled and airborne dust (Fig. 5) showed that greater amounts of these components were present in settled dust. This is due to thicker silica fractions which do not occur in the airborne phase in the respiratory zone. Due to a higher density of SiO2 particles (ρ quartz is 2.645 g cm-3) the level of this component in airborne dust is smaller than that of a lighter organic component, compared to static settled dust.
