Allergens and Microorganisms in Cultivating and Handling of Crops - A Review
on Health Hazards and Some Aspects on Exposure Assessment and Exposure
Dan Norbäck and Gunilla
Department of Occupational and Environmental Medicine, University Hospital,
S-753 31 Uppsala, Sweden
Exposure to vegetable dust
from cereals, or other types of crops, may result in both allergic and
non-allergic diseases. Grain dust lung is one of the oldest occupational
diseases described in the literature1. Some crops contain allergens that may
cause various types of allergic manifestations in sensitized workers2-9.
Another hazardous exposure related to crop cultivation and handling is
microbial exposure from mouldy crops and plant materials2. Exposure to
allergens and microorganisms may occur during harvest, but occupational
exposure occurs also during post harvest treatment, e.g. during storage,
refining or preparing of agricultural products. This paper reviews some
literature on occupational health hazard from crops, and discuss aspects on
exposure assessment and exposure control.
Health hazards related to
Plant dust known to cause allergy includes grain (e.g. wheat, rye, oats,
barley), buckwheat, soybeans, coffee beans, tea leaves, herbal tea, cork,
cotton, flax, hemp, jute, tobacco, castor bean (Ricinus Communis), rue (Ruta
graveolens), plant proteases (papain, bromelain), and dust from "Maiko"
(roots from devil's tongue ; Amorphophalus konjak)2-9. These allergic
reactions may include both rhinitis, eye symptoms, and specific allergic
asthma. Non-specific airway obstruction, e.g. decrement in forced expiratory
volume in one second (FEV1) during the workday, may also occur at organic
dust exposure3. Such non-allergic airway obstruction may occur among farm
workers, miller, and grain handler exposure to grain dust, or among
processors, cutters, blenders, and packers handling various types of dusty
The types of cultivated plants differ between different climate zones, and
so do the causes of occupational asthma. Coffee workers may suffer from
asthma caused by dust from green coffee beans6. Workers exposed to
castor-beans, commonly cultivated in Brazil and India, may also develop
allergic asthma6, 8. Cereal dust is another cause of asthma among grain
handlers6, and bakers asthma was described already by Ramazzini1. Besides
allergy to the floor itself, various contaminants in flour may play a role
in baker's asthma, including fungi and arthropod contaminants (e.g. mite
Tyroglyphus farinae or Glycyphagus destructor, and the grain weevil (Sitophilus
granarius)9. In Japan, Maiko, a dust from the tuberous root of devil's
tongue has been reported to cause occupational asthma6, 7. Wheat flour
asthma is reported to be rare in Japan7, but occupational asthma from
buckwheat has been described from both Japan, and other countries7, 10, 11.
Occupational exposure to plant pollen has also been described as causes of
occupational asthma, e.g. strawberry pollen at indoor cultivation of
strawberry7, pollen from sugar beet7, pollen from pyrethrum (Chrysantemum
cinerarieafolium)7, and lycopodium species7. Spore exposure from cultivation
of edible mushrooms may also cause occupational asthma, e.g. from Shiitake
Skin disease account for a large proportion of all occupational illness
within agriculturally related industries12. Contact urticaria is most
frequently caused by skin contact to various citrus fruits, nuts, spices and
grains, containing allergens and vasoactive substances, and food handlers
and gardeners are at particular risk. Certain plants contain compounds
causing phytophototoxic dermatitis, e.g. Umbelliferace family (celery,
parsley, carrots, and coriander, Moraceae family (figs), and Rutaceae family
(lime). Phototoxic eczema from celery may occur among farmers who harvest
it, or among grocery store workers. Bartender may also develop
phytophototoxic eczema on the first and second finger during summertime,
when they squeeze limes outdoors while making cocktails. Exposure to citrus
fruit may also occur in various occupations, and may cause allergic
reactions to terpens (d-limonene, geraniol, and citral)12.
Health hazards related to microbial exposure
Microbial growth may occur in various crops and food, particularly during
damp and humid conditions. Exposure to microorganisms may represent a
potential health hazard, with respect to allergic reactions, asthma,
toxicosis, and airway inflammation13-20. Microorganisms produce a variety of
compounds, including volatile organic compounds21-24, cell-wall toxins such
as endotoxines and 1-3-beta-glucanes13-14, allergens, and specific
mycotoxines. Endotoxines and 1-3-beta-glucanes may cause airway inflammation
at low exposure levels, and may contribute to the development of bronchial
hyperresponsiveness and asthma13-14. Mycotoxines are potent biological
agents, and reports on mycotoxicosis (e.g. ergotism) dates back to 1000
A.D.15. Recently, aflatoxines were classified as human carcinogens by the
International Agency for Research on Cancer (IARC)16. Most studies on
mycotoxines deals with oral exposure through contaminated food, and there
are only few publications on occupational airborne exposure to mycotoxines
in airborne spores. Toxines from Stachybotrys sp., and aflatoxines from
Aspergillus flavus have been shown to cause various types of health
impairments in humans, including immunosupression, dermatitis,
conjunctivitis, upper and lower airway symptoms, fatigue, and headache15.
Inhalation fever (Organic dust toxic syndrome)
Inhalation fever, or organic dust toxic syndrome (ODTS), are terms
describing a noninfectious, febrile illness associated with chills, malaise,
myalgia, a dry cough, dyspnea, headache and nausea that occurs after heavy
organic dust exposure17-19. This syndrome is thought to be an acute febrile
reaction to organic dust exposure distinct from allergic alveolitis. In the
Nordic countries, pulmonary reactions to inhalation of dust from mouldy hay
occasionally occurs among farmers19. Among farmers, ODTS is reported to be
much more common than allergic alveolitis19, the incidence being 10-190
cases / 10000 farmers20.
Allergic alveolitis (hypersensitivity pneumonitis)
This disease has been described mainly among farmers that have been exposed
to high concentrations of mouldy organic dust ("farmers lung")17-19. It is
characterized by acute recurrent pneumonia with fever, cough, chest
tightness, and lung infiltrates. There are diagnostic criteria to be
fulfilled for the diagnosis of extrinsic allergic alvolitis25. Allergic
alveolitis is a rare disease, among farmers the incidence rate is estimated
to be 2-30 cases / 10000 farmers20. In Japan, the most prevalent form of
allergic alveolitis is reported to be summer-type hypersensitivity
pneumonitis, caused by indoor moulds during summer26.
One of the major problems in occupational epidemiology is the estimation of
the exposure. Exposure measurements are needed to identify sources of
exposure, to evaluate the effect of environmental improvements, and to be
able to compare the exposure in different types of occupations, or in
different countries. For allergens, it is not obvious that there is a
dose-response relationship. Another problem in studies on immunodepression
and antibody formation is the control for other factors (e.g. viral
infections, tobacco smoking, exposure to irritants) modifying the effect of
the allergen exposure27. Exposure measurements of airborne allergens have
not been applied until recently, mainly because of a lack of analytical
methods capable of detecting low levels of airborne allergens. Quantitative
and specific allergen measurements in settled dust have been applied in some
studies on indoor animal allergens, e.g. monoclonal antibodies from cats,
dogs and house dust mites28-29. It is, however, unclear to what extent
allergen contents in settled dust reflects the relevant airborne exposure to
Because of the difficulties in quantifying airborne allergens, personal
exposure measurements of airborne total dust, respirable dust, or organic
dust have been applied, by conventional hygienic methods5. Total dust can be
sampled on cellulose acetate filter, and determined by gravimetric
analysis5, 30. If both inorganic dust and organic dust is present in the
air, organic dust concentration can be determined as the weight difference
before and after low-temperature ashing of the total dust samples collected
on the filters30. Respirable dust can also be determined by direct reading
instruments (e.g. SIBATA PH5), based on the measurement of Rayleight light
scattering by a lase diod31. Such direct reading instruments may have a
lower accuracy than gravimetric methods for dust measurements. They are,
however, particularly useful as a tool to identify emission sources, and to
evaluate the effects of measures aiming to reduce the dust exposure.
Measurements of microorganisms and microbial exposures
There are various types of exposures related to microbial growth. By
tradition, microbiologists have measured only viable spores in air samples,
by cultivation and identification of mould species. In many types of
occupational environments, however, only a small proportion of the airborne
microorganisms are viable. Biological effects of nonpathogenic
microorganisms are similar for viable and non-viable organisms. In addition,
there are cases when bacteria, and not only moulds, should be included in
the exposure assessment. One method capable of detecting both viable and
non-viable moulds and bacteria is the CAMNEA method. This method utilizes
pumped air sampling on plycarbonate filters (Nucleopore, Pleasanton,
California, USA), followed by acridine orange staining, and counting of
microorganisms by epiflourescence microscopy32. The CAMNEA method has been
demonstrated to be a simple and accurate mean to measure microbial exposure
in highly contaminated occupational environments33.
There are also chemical and biological methods available to quantify
specific compounds related to microbial exposure. Endotoxines are toxic
constituents to the cellwall of gram negative bacteria, and
(1-3)-beta-glucanes are constituents of the cellwall of microfungi. Both
endotoxines and (1-3)-beta-glucanes can be detected by the Limulus assay, a
biological method34, 35. Because of possible interaction between these
toxins, and the nonspecificity of the Limulus system, there is a need to
develop new sensitive and specific analytical methods for these cell-wall
toxines, e.g. by means of gas chromatography and mass-specrometry.
Microorganisms may also emit volatile organic compounds (VOC). Some of these
VOC's are specific compounds produced exclusively by microorganisms (e.g.
geosmin or 1-octen-3-ol)21-24. It has recency been shown in Sweden that
measurements of MVOC can be used also as a rapid and economical indicator of
mould growth in stored cereals24. The most commonly occuring metabolites
from grain-detoriating Aspergillus sp. and Penicillium sp. were found to be
3-methylfuran, 2-methyl-1-propanol, and 3-methyl-1-butanol. It was therefore
concluded that these are the best indicators of mould growth in stored
cereals. One particular advantage of MVOC analysis, as compared to
cultivation of mould spores, is possibility to get a representive air sample
from the whole batch of cerials in the store, and the possibility to get the
analytic results within one day.
Conclusions and recommendations
Exposure to organic vegetable dust from cereals, or other types of crops may
cause various allergic and non-allergic health disturbances, including
asthma, dermal disorders, fever reactions, and airway obstruction and
inflammation. In occupations where dust exposure to vegetable dust occurs,
it is important to minimize the exposure to the workers. This is
particularly important if the work process generates a large proportion of
respirable dust, and if the dust is contaminated by moulds or bacteria, or
contains known allergens.
Exposure control could be done by encapsulation of the process, use of local
exhaust ventilation, or by use of personal airway protection devices, e.g.
disposable dust filters. Mould growth in the crop should be avoided, and
special precaution is neeed when mouldy plant material is handled. The
measurement of microbial volatile organic compounds (MVOC) as a rapid and
ecconomical indicator of microbial growth in stored crops should be further
evaluated. If possible, the exposure to potential occupational biohazards
should be quantified by exposure measurements. It is also important to
evaluate the effects of measures taken aiming to reduce the dust exposure,
by repeated exposure measurements.
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Current Advances in Buckwheat Research (1995) : 957 - 964
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