The agricultural worker can be exposed to a large variety of particle types, the main sources being plants, animals and soil. The particles are classified as inorganic or organic, depending on their source. Since agriculture involves working with living material i.e. plants and animals, the emitted dust will have a high proportion of organic particles. Such particles will show a high content of carbon and often significant amounts of elements like oxygen, sodium, silicon, sulphur, chlorine or potassium. In many cases the particles of organic origin can be identified based on morphology alone. This is the case for pollen grains, trichomes (plant hairs), fibres, animal hairs, dander or plant and insect fragments.
The organic material represented by the crop functions as a substrate for secondary growth of mould and bacteria. These microorganisms will inevitably invade the foliage and seeds. Exoenzymes may break down the biopolymers and use them as nutrition. Favourable conditions cause the mould and bacteria to reproduce and make a multitude of spores in a few hours time. This situation is unfortunate for a corn farmer since he is at high risk for massive exposure to potentially harmful microorganisms when handling the grain, besides getting a product of reduced quality. Bacteria are naturally present in faeces. Handling of manure may give an exposure to microorganisms.
The measurement of microorganisms in air samples is traditionally done by microscopy since the number more correctly than mass reflect the health risk. At NIOH the bacteria are counted in the fluorescence light microscope while mould spores are identified and counted in the scanning electron microscope (SEM).
The soil is often dominated by a mineral fraction. In field samples the inorganic contamination is therefore conspicuous. Air samples taken during tasks like threshing, handling of hay and sorting of potatoes or onions will often show an inorganic portion of 70 wt% or more. Crystalline silica can sometimes dominate the inorganic fraction, but more often there will be a complex mixture of silicate minerals. The combination of SEM and x-ray microanalysis (XRMA) can most often classify the mineral particles to specific groups, sometimes even to species. The reliable identification of individual mineral particles however calls for other methods like polarized light microscopy or transmission electron microscopy with electron diffraction.
More rare are metallic particles or metallic compounds observed in agricultural dust samples. These are likely to originate from welding operations, metal work or from fodder additives.
Please use the following links to search NIOH´s library catalogue for relevant literature about bioaerosols, mycotoxins or mould (keywords: mould or fungi) in agriculture and their influence on the occupational health.
Norwegian keywords: bioaerosol, soppsporer, bakterier, insektdeler, kornstøv, kornlager, hvete, havre, bygg, arbeid med korn