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Specialty Crops

Thursday, 10 March 2011 15:34

Tobacco Cultivation

Tobacco (Nicotiana tabacum) is a unique plant with its characteristic commercial component, nicotine, contained in its leaves. Although cotton is grown on more surface area, tobacco is the most widely grown nonfood crop in the world; it is produced in approximately 100 countries and on every continent. Tobacco is consumed around the world as cigarettes, cigars, chewing or smoking tobaccos and snuff. However, over 80% of world production is consumed as cigarettes, currently estimated at nearly 5.6 trillion annually. China, the United States, Brazil and India produced over 60% of total world production in 1995, which was estimated at 6.8 million tonnes.

The specific uses of tobacco by manufacturers are determined by the chemical and physical properties of the cured leaves, which in turn are determined by interactions among genetic, soil, climatic and cultural management factors. Therefore, many kinds of tobacco are grown in the world, some with rather specific local, commercial uses in one or more tobacco products. In the United States alone, tobacco is categorized into seven major classes which contain a total of 25 different tobacco types. The specific techniques used to produce tobacco vary among and within tobacco classes in various countries, but cultural manipulation of nitrogen fertilization, plant density, time and height of topping, harvesting and curing are used to favourably influence the usability of the cured leaves for specific products; quality of leaves, however, is highly dependent on prevailing environmental conditions.

Flue-cured, Burley and Oriental tobaccos are the major components of the increasingly popular blended cigarette now consumed worldwide, and represented 57, 11 and 12%, respectively, of world production in 1995. Thus, these tobaccos are widely traded internationally; the United States and Brazil are the major exporters of flue-cured and Burley leaf tobaccos, while Turkey and Greece are the major world suppliers of Oriental tobacco. The world’s largest tobacco producer and cigarette manufacturer, China, currently consumes most of its production internally. Because of increasing demand for the “American” blended cigarette, the United States became the major cigarette exporter in the early 1990s.

Tobacco is a transplanted crop. In most countries, seedlings are started from tiny seeds (about 12,000 per gram) sown by hand on well-prepared soil beds and manually removed for transplanting to the field after reaching a height of 15 to 20 cm. In tropical climates, seed-beds are usually covered with dried plant materials to preserve soil moisture and reduce disturbance of seeds or seedlings by heavy rains. In cooler climates, seed-beds are covered for frost and freeze protection with one of several synthetic materials or with cotton cheesecloth until several days before transplanting. The bed sites are usually treated before seeding with methyl bromide or dazomet to manage most weeds and soil-borne diseases and insects. Herbicides for supplemental grass management are also labelled for use in some countries, but in areas where labour is plentiful and inexpensive, weeds and grasses are often removed by hand. Foliar insects and diseases are usually managed with periodic applications of appropriate pesticides. In the United States and Canada, seedlings are produced primarily in greenhouses covered with plastic and glass, respectively. Seedlings are usually grown in peat- or muck-based media which, in Canada, are steam-sterilized before seeds are sown. In the United States, polystyrene trays are predominantly used to contain the media and are often treated with methyl bromide and/or a chlorine bleach solution between transplant production seasons to protect against fungal diseases. However, only a few pesticides are labelled in the United States for use in tobacco greenhouses, so farmers there depend substantially on proper ventilation, horizontal air movement and sanitation to manage most foliar diseases.

Regardless of the method of transplant production, seedlings are periodically clipped or mowed above the apical meristems for several weeks before transplanting to improve uniformity and survival after transplanting to the field. Clipping is performed mechanically in some developed countries but manually where labour is plentiful (see figure 1).

Figure 1. Manual clipping of tobacco seedlings with shears in Zimbabwe


Gerald Peedin

Depending on availability and cost of labour and equipment, seedlings are manually or mechanically transplanted to well- prepared fields previously treated with one or more pesticides for control of soil pathogens and/or grasses (see figure 2). In order to protect workers from pesticide exposure, pesticides are seldom applied during the transplanting operation, but additional weed and foliar pest management are often needed during subsequent growth and harvesting of the crop. In many countries, varietal tolerance and 2- to 4-year rotations of tobacco with nonhost crops (where sufficient land is available) are widely used to reduce reliance on pesticides. In Zimbabwe, government regulations require seedling beds and stalks/roots in harvested fields to be destroyed by certain dates to reduce the incidence and spread of insect-transmitted viruses.

Figure 2. Mechanical transplanting of flue-cured tobacco in North Carolina (US)


About 4 to 5 hectares per day can be transplanted using ten workers and a four-row transplanter. Six workers are needed for a two-row transplanter and four workers for a one-row transplanter.







Gerald Peedin 

Depending upon tobacco type, fields receive relatively moderate-to-high rates of fertilizer nutrients, which are usually applied by hand in developing countries. For proper ripening and curing of flue-cured tobacco, it is necessary for nitrogen absorption to decrease rapidly soon after vegetative growth is complete. Therefore, animal manures are not routinely applied to flue-cured soils, and only 35 to 70 kg per hectare of inorganic nitrogen from commercial fertilizers are applied, depending on soil characteristics and rainfall. Burley and most chewing and cigar tobaccos are usually grown on more fertile soils than those used for flue-cured tobacco, but receive 3 to 4 times more nitrogen to enhance certain desirable characteristics of these tobaccos.

Tobacco is a flowering plant with a central meristem which suppresses growth of axillary buds (suckers) by hormonal action until the meristem begins to produce flowers. For most tobacco types, removal of flowers (topping) before seed maturation and control of subsequent sucker growth are common cultural practices used to improve yields by diverting more growth resources into leaf production. Flowers are removed manually or mechanically (primarily in the United States) and sucker growth retarded in most countries with applications of contact and/or systemic growth regulators. In the United States, suckercides are applied mechanically on flue-cured tobacco, which has the longest harvest season of the tobacco types produced in that country. In underdeveloped countries, suckercides are often applied manually. However, regardless of the chemicals and application methods used, complete control is seldom achieved, and some hand labour is usually needed to remove suckers not controlled by the suckercides.

Harvesting practices vary substantially among tobacco types. Flue-cured, Oriental and cigar wrapper are the only types whose leaves are consistently harvested (primed) in sequence as they ripen (senesce) from the bottom to the top of the plant. As leaves ripen, their surfaces become textured and yellow as chlorophyll degrades. Several leaves are removed from each plant in each of several passes over the field during a period of 6 to 12 weeks after topping, depending on rainfall, temperature, soil fertility and variety. Other tobacco types such as Burley, Maryland, cigar binder and filler, and fire-cured chewing tobaccos are “stalk cut”, meaning that the entire plant is cut off near ground level when most of the leaves are judged to be ripe. For some air-cured types, the lower leaves are primed while the remainder of the plant is stalk cut. Regardless of tobacco type, harvesting and preparation of the leaves for curing and marketing are the most labour-intensive tasks in tobacco production (see figure 3).Harvesting is normally accomplished with manual labour, especially for stalk cutting, which has yet to be totally mechanized (see figure 4). Priming of flue-cured tobacco is now highly mechanized in most developed countries, where labour is scarce and expensive. In the United States, about one-half of the flue-cured type is primed with machines, which requires almost complete weed and sucker control to minimize content of these materials in the cured leaves.

Figure 3.  Preparing Oriental tobacco for air-curing soon after hand harvesting


The small leaves are collected on a string by pushing a needle through the central vein of each leaf.









Gerald Peedin 

Figure 4.  Hand harvesting of flue-cured tobacco by a small farmer in southern Brazil


Some farmers use small tractors rather than oxen to pull sleds or trailers. Over 90% of harvesting and other labour is provided by family members,  relatives and/or neighbours.







Gerald Peedin 

Proper curing of most tobacco types requires management of temperature and moisture content within the curing structure to regulate the drying rate of green leaves. Flue-curing requires the most sophisticated curing structures because temperature and moisture control follow rather specific schedules, and temperatures reach over 70 °C in the latter stages of curing, which totals only 5 to 8 days. In North America and Western Europe, flue-curing is accomplished primarily in gas- or oil-fired metal (bulk) barns equipped with automatic or semiautomatic temperature- and humidity-control devices. In most other countries, the barn environment is controlled manually and the barns are constructed of wood or bricks and often fired by hand with wood (Brazil) or coal (Zimbabwe). The initial and most important stage of flue-curing is called yellowing, during which chlorophyll is degraded and most carbohydrates are converted to simple sugars, giving cured leaves a characteristic sweet aroma. The leaf cells are then killed with drier and hotter air to stop respiratory losses of sugars. The products of combustion do not contact the leaves. Most other tobacco types are air-cured in barns or sheds without heat, but usually with some means of partial, manual ventilation control. The air-curing process requires 4 to 8 weeks, depending on prevailing environmental conditions and the ability to control humidity within the barn. This longer, gradual process results in cured leaves with low sugar contents. Fire-cured tobacco, used primarily in chewing and snuff products, is basically air-cured but small, open fires using oak or hickory wood are used to periodically “smoke” the leaves to give them a characteristic wood odour and taste and to improve their keeping properties.

The colours of cured leaves and their uniformity within a lot of tobacco are important characteristics used by buyers to determine the usefulness of tobaccos for specific products. Therefore, leaves with undesirable colours (particularly green, black and brown) are usually manually removed by farmers before offering the tobacco for sale (see figure 5).In most countries, the cured tobaccos are further separated into homogeneous lots based on variations in leaf colour, size, texture and other visual characteristics (see figure 6).In some southern African countries, where labour is plentiful and inexpensive and most of the production is exported, a crop may be sorted into 60 or more lots (i.e., grades) before being sold (as in figure 6).Most tobacco types are packaged in bales weighing 50 to 60 kg (100 kg in Zimbabwe) and delivered to the purchaser in the cured form (see figure 7).In the United States, flue-cured tobacco is marketed in burlap sheets averaging about 100 kg each; however, use of bales weighing over 200 kg is currently being evaluated. In most countries, tobacco is produced and sold under contract between the farmer and the purchaser, with predetermined prices for the various grades. In a few large tobacco-producing countries, annual production is controlled by government regulation or by farmer-buyer negotiation, and the tobacco is sold in an auction system with (United States and Canada) or without (Zimbabwe) minimum established prices for the various grades. In the United States, flue-cured or Burley tobacco not sold to commercial buyers is purchased for price support by grower-owned cooperatives and sold later to domestic and foreign buyers. Although some marketing systems have been substantially mechanized, such as that in Zimbabwe (shown in figure 8),.a great deal of manual labour is still required to unload and present the tobacco for sale, remove it from the sale area and load and transport it to the buyer’s processing facilities.

Figure 5.  Manual removal of cured Burley leaves from the stalks


Gerald Peedin


Figure 6.  Manual separation of cured flue-cured tobacco into homogeneous grades in Zimbabwe.


Gerald Peedin


Figure 7.  Loading tobacco bales for transport from the farm to a marketing centre in southern Brazil


Gerald Peedin


Figure 8.  Unloading a farmer’s tobacco bales at the auction centre in Zimbabwe, which has the most mechanized and efficient flue-cured marketing system in the world.


Gerald Peedin


Hazards and Their Prevention

The manual labour required to produce and market tobacco varies greatly around the world, depending primarily on the level of mechanization used for transplanting, harvesting and market preparation. Manual labour involves risks of musculoskeletal problems from activities such as transplanting seedlings, application of suckercides, harvesting, separation of the cured tobacco into grades and lifting of tobacco bales. Training in proper lifting methods and provision of ergonomically designed tools can help prevent these problems. Knife injuries may occur during cutting, and tetanus may arise in open wounds. Sharp, well-designed knives and training in their use can reduce the number of injuries.

Mechanization can reduce these risks, but carries risks of injury from the machinery used, including transportation accidents. Well-designed tractors with safety cabs, properly guarded machinery and adequate training can reduce the number of injuries.

Spraying of pesticides and fungicides can involve the risk of chemical exposures. In the United States, the Environmental Protection Administration (EPA) Worker Protection Standard requires farmers to protect workers from pesticide-related illness or injury by (1) providing training on pesticide safety, specifically those pesticides used on the farm; (2) providing personal protective equipment (PPE) and clothing and assuming responsibility for their proper use and cleaning, plus ensuring that workers do not enter treated fields during specific time intervals after pesticide application; and (3) providing decontamination sites and emergency assistance in case of exposure. Substitution of less hazardous pesticides should also be done where possible.

Field labourers, usually those not accustomed to working in tobacco fields, sometimes become nauseous and/or dizzy soon after direct contact with green tobacco during harvesting, perhaps because nicotine or other substances are absorbed through the skin. In the United States, the condition is called “green tobacco sickness” and affects a small percentage of workers. Symptoms occur most often when sensitive individuals are harvesting wet tobacco and their clothing and/or exposed skin is in almost continuous contact with green tobacco. The condition is temporary and not known to be serious, but causes some discomfort for several hours after exposure. Suggestions for sensitive workers to minimize exposure during harvesting or other tasks requiring prolonged contact with green tobacco include not starting work until the leaves have dried or wearing lightweight rain gear and waterproof gloves when the leaves are wet; wearing long trousers, long-sleeve shirts and possibly gloves as precautions when working in dry tobacco; and leaving the field and washing immediately if symptoms occur.

Skin diseases may occur in workers handling tobacco leaf in warehouses or barns. Sometimes workers in these storage areas, especially new workers, may develop conjunctivitis and laryngitis.

Other preventive measures include good washing and other sanitary facilities, provision of first aid and medical care, and proper training.



Thursday, 10 March 2011 15:43

Ginseng, Mint and Other Herbs

There is no standard definition for the term herb, and the distinction between the herbs and spice plants is unclear. This article provides an overview of general aspects of some herbs. There are more than 200 herbs, which we are here considering to be those plants originally grown mainly in temperate or Mediterranean climates for their leaves, stems and flowering tops. The primary use for herbs is to flavour foods. Important culinary herbs include basil, bay or laurel leaf, celery seed, chervil, dill, marjoram, mint, oregano, parsley, rosemary, sage, savory, tarragon and thyme. The major demand for culinary herbs comes from the retail sector, followed by the food processing and food service sectors. The United States is by far the major consumer of culinary herbs, followed by the United Kingdom, Italy, Canada, France and Japan. Herbs are also used in cosmetics and pharmaceutical products to impart desirable flavours and odours. Herbs are used medicinally by the pharmaceutical industry and in the practice of herbal medicine.


Ginseng root is used in the practice of herbal medicine. China, the Republic of Korea and the United States are major producers. In China, most operations have historically been plantations owned and run by the government. In the Republic of Korea, the industry is made up of more than 20,000 family operations, most of which are smallholdings, family operations that plant less than an acre each year. In the United States, the largest proportion of producers work on smallholdings and plant less than two acres per year. However, the largest proportion of the US crop is produced by a minority of growers with a hired workforce and mechanization that allows them to plant as much as 60 acres per year. Ginseng is usually grown in open field plots covered by artificial shade structures that simulate the effects of the forest canopy.

Ginseng is also grown in intensively cultivated forest plots. A few per cent of the world’s production (and most organic ginseng) is gathered by wild collectors. The roots take 5 to 9 years to reach marketable size. In the United States, bed preparation for either forest plot or open field methods is typically accomplished by a tractor-towed plow. Some hand labour may be required to clear ditches and give the beds their final shape. Mechanized planters pulled behind a tractor are often used for seeding, although the more labour-intensive practice of transplanting nursery seedlings into beds is common in the Republic of Korea and China. Constructing the 7- to 8-foot-high pole and wood lath or cloth shade structures over open field plots is labour intensive and involves considerable lifting and overhead work. In Asia, locally available woods and thatch or woven reeds are used in the shade structures. In mechanized operations in the United States, mulching the plants is accomplished with straw shredders which are adapted from machines used in the strawberry industry and pulled behind a tractor.

Depending on the adequacy and condition of machine guarding, contact with the tractor PTO shaft, the straw shredder’s intake or other moving machinery parts can present a risk of entanglement injury. For each year until harvest, three hand weedings are required, which involve crawling, bending and stooping to work at crop level and which place high demands on the musculoskeletal system. Weeding, especially for the first- and second-year plants, is intensive work. One acre of field-grown ginseng may require more than 3,000 total hours of weeding over the 5 to 9 years preceding harvest. New chemical and non-chemical weed control methods, including better mulching, may be able to reduce the musculoskeletal demands posed by weeding. New tools and mechanization also hold promise for reducing the demands of weeding work. In Wisconsin, US, some herb growers are testing an adapted pedal cycle that allows weeding in a seated posture.

Artificial shade creates an especially humid environment susceptible to fungus and mould infestation. Fungicides are routinely applied at least monthly in the United States with tractor-towed application machinery or backpack garden sprayers. Insecticides are also spray applied as needed, and rodenticides put out. The use of lower-toxicity chemicals, improvements in application machinery and alternative pest management practices are strategies for reducing the repeated, low-dose pesticide exposures experienced by employees.

When the roots are ready for harvest, the shade structures are disassembled and stored. Mechanized operations utilize digging machinery adapted from the potato industry which is towed behind a tractor. Here again, inadequate machine guarding of the tractor PTO and moving machinery parts may present a risk of entanglement injuries. Picking, the last step in harvesting, involves hand labour and bending and stooping to gather roots from the soil surface.

On smaller holdings in the United States, China and the Republic of Korea, most or all of the steps in the production process are typically done by hand.

Mint and Other Herbs

There is considerable diversity in herb production methods, geographical locations, work methods and hazards. Herbs can be collected in the wild or grown under cultivation. Cultivated plant production has the advantages of greater efficiency, more consistent quality and timing of the harvest, and the potential for mechanization. Much of the mint and other herb production in the United States is highly mechanized. Soil preparation, planting, cultivation, pest control and harvesting are all done from the seat of a tractor with towed machinery.

Potential hazards resemble those in other mechanized crop production and include motor vehicle collisions on public roads, traumatic injuries involving tractors and machinery and agricultural chemical poisonings and burns.

More labour-intensive cultivation methods are typical in Asia, North Africa, the Mediterranean and other areas (e.g., mint production in China, India, the Philippines and Egypt). Plots are ploughed, often with animals, and then beds are prepared and fertilized by hand. Depending on the climate, a network of irrigation trenches is excavated. Depending on the type of herb produced, seeds, cuttings, seedlings or rhizome portions are planted. Periodic weeding is especially labour intensive and the day-long shifts of stooping, bending and pulling place high demands on the musculoskeletal system. Despite extensive use of manual labour, weed control in herb cultivation is sometimes inadequate. For a few crops, chemical weeding with herbicides, sometimes followed by manual weeding, is used, but herbicide use is not widespread since herb crops are often herbicide sensitive. Mulching crops can reduce weeding labour needs as well as conserve soil and soil moisture. Mulching also generally aids plant growth and yield, since mulch adds organic matter to soils as it decomposes.

Aside from weeding, labour-intensive soil preparation methods, planting, construction of shade or support structures, harvesting and other operations can also result in high musculoskeletal demands for prolonged periods. Modifications in production methods, specialized hand tools and techniques, and mechanization are possible directions to explore for reducing musculoskeletal and labour demands.

The potential for pesticide and other agricultural chemical burns and poisonings can be a concern on labour-intensive operations since backpack sprayers and other manual application methods may not prevent adverse exposures via the skin, mucous membranes or breathing air. Work in greenhouse production poses special hazards due to the confined breathing atmosphere. Substituting lower toxicity chemicals and alternative pest management strategies, improving application equipment and application practices, and making better PPE available may be ways to reduce risks.

The extraction of volatile oils from the harvested crop is common for certain herbs (e.g., mint stills). Cut and chopped plant material is loaded into an enclosed wagon or other structure. Boilers produce live steam which is forced into the sealed structure through low-pressure hoses, and the oil is floated and extracted from the resulting vapour.

Possible hazards associated with the process include burns from live steam and, less frequently, boiler explosions. Preventive measures include regular inspections of boilers and live steam lines to ensure structural integrity.

Herb production with low levels of mechanization may require prolonged close contact with plant surfaces and oils and, less often, associated dusts. Some reports are available in the medical literature of sensitization reactions, occupational dermatitis, occupational asthma and other respiratory and immunological problems associated with a number of herbs and spices. The available literature is small and may reflect underreporting rather than a low likelihood of health problems.

Occupational dermatitis has been associated with mint, laurel, parsley, rosemary and thyme, as well as cinnamon, chicory, cloves, garlic, nutmeg and vanilla. Occupational asthma or respiratory symptoms have been associated with dust from Brazilian ginseng and parsley as well as black pepper, cinnamon, cloves, coriander, garlic, ginger, paprika and red chillies (capsaicin), along with bacteria and endotoxins in dusts from grains and herbs. However, most cases have occurred in the processing industry, and only a few of these reports have described problems arising directly from exposures incurred in herb cultivation work (e.g., dermatitis after parsley picking, asthma after chicory root handling, immunologic reactivity after greenhouse work with paprika plants). In most reports, a proportion of the workforce develops problems while other employees are less affected or asymptomatic.

Processing Industry

The herb and spice crop processing industry represents a higher order of magnitude exposure to certain hazards than herb crop cultivation. For example, the grinding, crushing and mixing of leaves, seeds and other plant materials can involve work in noisy, extremely dusty conditions. Hazards in herb processing operations include hearing loss, traumatic injuries from inadequately guarded moving machinery parts, dust exposures in breathing air, and dust explosions. Closed processing systems or enclosures for machinery can reduce noise. Feed openings of grinding machines should not permit the entry of hands or fingers.

Health conditions including skin diseases, irritation of the eyes, mouth and gastrointestinal tract, and respiratory and immunological problems have been linked to dusts, fungi and other air contaminants. Self selection based on ability to tolerate health effects has been noted in spice grinders, usually within the first 2 weeks of work. Segregation of the process, effective local exhaust ventilation, improved dust collection, regular mopping and vacuuming of work areas, and personal protective equipment can help reduce risks from dust explosions and contaminants in breathing air.



Thursday, 10 March 2011 15:48


The world’s most widely cultivated edible fungi are: the common white button mushroom, Agaricus bisporus, with an annual production in 1991 of approximately 1.6 million tonnes; the oyster mushroom, Pleurotus spp. (about 1 million tonnes); and the shiitake, Lentinus edodes (about 0.6 million tonnes) (Chang 1993). Agaricus is mainly grown in the western hemisphere, whereas oyster mushrooms, shiitake and a number of other fungi of lesser production are mostly produced in East Asia.

The production of Agaricus and the preparation of its substrate, compost, are for a large part strongly mechanized. This is generally not the case for the other edible fungi, although exceptions exist.

The Common Mushroom

The common white button mushroom, Agaricus bisporus, is grown on compost consisting of a fermented mixture of horse manure, wheat straw, poultry manure and gypsum. The materials are wetted, mixed and set in large heaps when fermented outdoors, or brought into special fermentation rooms, called tunnels. Compost is usually made in quantities of up to several hundred tonnes per batch, and large, heavy equipment is used for mixing heaps and for filling and emptying the tunnels. Composting is a biological process that is guided by a temperature regime and that requires thorough mixing of the ingredients. Before being used as a substrate for growth, compost should be pasteurized by heat treatment and conditioned to get rid of the ammonia. During composting, a considerable amount of sulphur-containing organic volatiles evaporates, which can cause odour problems in the surroundings. When tunnels are used, the ammonia in the air can be cleaned by acid washing, and odour escape can be prevented by either biological or chemical oxidation of the air (Gerrits and Van Griensven 1990).

The ammonia-free compost is then spawned (i.e., inoculated with a pure culture of Agaricus growing on sterilized grain). Mycelial growth is carried out during a 2-week incubation at 25 °C in a special room or in a tunnel, after which the grown compost is placed in growing rooms in trays or in shelves (i.e., a scaffold system with 4 to 6 beds or tiers above each other with a distance of 25 to 40 cm in between), covered with a special casing consisting of peat and calcium carbonate. After a further incubation, mushroom production is induced by a temperature change combined with strong ventilation. Mushrooms appear in flushes with weekly intervals. They are either harvested mechanically or hand-picked. After 3 to 6 flushes, the growing room is cooked out (i.e., steam pasteurized), emptied, cleaned and disinfected, and the next growing cycle can be started.

Success in mushroom cultivation depends heavily on cleanliness and prevention of pests and diseases. Although management and farm hygiene are key factors in disease prevention, a number of disinfectants and a limited number of pesticides and fungicides are still used in the industry.

Health Risks

Electrical and mechanical equipment

A pre-eminent risk in mushroom farms is the accidental exposure to electricity. Often high voltage and amperage is used in humid environments. Ground fault circuit interrupters and other electrical precautions are necessary. National labour legislation usually sets rules for the protection of labourers; this should be strictly followed.

Also, mechanical equipment may pose dangerous threats by its damaging weight or function, or by the combination of both. Composting machines with their large moving parts require care and attention to prevent accidents. Equipment used in cultivation and harvesting often has rotating parts used as grabbers or harvesting knives; their use and transport require great care. Again, this holds for all machines that are moving, whether they be self-propelled or pulled over beds, shelves or rows of trays. All such equipment should be properly guarded. All personnel whose duties include handling electrical or mechanical equipment in mushroom farms should be carefully trained before work is started and safety rules should be adhered to. Maintenance ordinances of equipment and machines should be taken very seriously. A proper lockout/tagout programme is needed as well. Lack of maintenance causes mechanical equipment to become extremely dangerous. For example, breaking pull chains have caused several deaths in mushroom farms.

Physical factors

Physical factors such as climate, lighting, noise, muscle load and posture strongly influence the health of workers. The difference between ambient outside temperature and that of a growing room can be considerable, especially in the winter. One should allow the body to adapt to a new temperature with every change of location; not doing so may lead to diseases of the airways and eventually to a susceptibility to bacterial and viral infections. Further, exposure to excessive temperature changes may cause muscles and joints to become stiff and inflamed. This may lead to a stiff neck and back, a painful condition causing unfitness for work.

Insufficient lighting in mushroom-growing rooms not only causes dangerous working conditions but also slows down picking, and it prevents pickers from seeing the possible symptoms of disease in the crop. The lighting intensity should be at least 500 lux.

Muscle load and posture largely determine the weight of labour. Unnatural body positions are often required in manual cultivation and picking tasks due to the limited space in many growing rooms. Those positions may damage joints and cause static overload of the muscles; prolonged static loading of muscles, such as that which occurs during picking, can even cause inflammation of joints and muscles, eventually leading to partial or total loss of function. This can be prevented by regular breaks, physical exercises and ergonomic measures (i.e., adaptation of the actions to the dimensions and possibilities of the human body).

Chemical factors

Chemical factors such as exposure to hazardous substances create possible health risks. The large-scale preparation of compost has a number of processes that can pose lethal risks. Gully pits in which recirculation water and drainage from compost is collected are usually devoid of oxygen, and the water contains high concentrations of hydrogen sulphide and ammonia. A change in acidity (pH) of the water may cause a lethal concentration of hydrogen sulphide to occur in the areas surrounding the pit. Piling wet poultry or horse manure in a closed hall may cause the hall to become an essentially lethal environment, due to the high concentrations of carbon dioxide, hydrogen sulphide and ammonia which are generated. Hydrogen sulphide has a powerful odour at low concentrations and is especially threatening, since at lethal concentrations this compound appears to be odourless because it inactivates human olfactory nerves. Indoor compost tunnels do not have sufficient oxygen to support human life. They are confined spaces, and testing of air for oxygen content and toxic gases, wearing of appropriate PPE, having an outside guard and proper training of involved personnel are essential.

Acid washers used for removal of ammonia from the air of compost tunnels require special care because of the large quantities of strong sulphuric or phosphoric acid that are present. Local exhaust ventilation should be provided.

Exposure to disinfectants, fungicides and pesticides can take place through the skin by exposure, through the lungs by breathing, and through the mouth by swallowing. Usually fungicides are applied by a high-volume technique such as by spray lorries, spray guns and drenching. Pesticides are applied with low-volume techniques such as misters, dynafogs, turbofogs and by fumigation. The small particles that are created remain in the air for hours. The right protective clothing and a respirator that has been certified as appropriate for the chemicals involved should be worn. Although the effects of acute poisoning are very dramatic, it should not be forgotten that the effects of chronic poisoning, although less dramatic at first glance, also always require occupational health surveillance.

Biological factors

Biological agents can cause infectious diseases as well as severe allergic reactions (Pepys 1967). No human infectious disease cases caused by the presence of human pathogens in compost have been reported. However, mushroom worker’s lung (MWL) is a severe respiratory disease that is associated with handling the compost for Agaricus (Bringhurst, Byrne and Gershon-Cohen 1959). MWL, which belongs to the group of diseases designated extrinsic allergic alveolitis (EAA), arise from exposure to spores of the thermophilic actinomycetes Excellospora flexuosa, Thermomonospora alba, T. curvata and T. fusca that have grown during the conditioning phase in compost. They can be present in high concentrations in the air during spawning of phase 2 compost (i.e., over 109 colony-forming units (CFU) per cubic metre of air) (Van den Bogart et al. 1993); for causation of EAA symptoms, 108 spores per cubic metre of air are sufficient (Rylander 1986). The symptoms of EAA and thus MWL are fever, difficult respiration, cough, malaise, increase in number of leukocytes and restrictive changes of lung function, starting only 3 to 6 hours after exposure (Sakula 1967; Stolz, Arger and Benson 1976). After a prolonged period of exposure, irreparable damage is done to the lung due to inflammation and reactive fibrosis. In one study in the Netherlands, 19 MWL patients were identified among a group of 1,122 workers (Van den Bogart 1990). Each patient demonstrated a positive response to inhalation provocation and possessed circulating antibodies against spore antigens of one or more of the actinomycetes mentioned above. No allergic reaction had been found with Agaricus spores (Stewart 1974), which may indicate low antigenicity of the mushroom itself or low exposure. MWL can easily be prevented by providing workers with powered air-purifying respirators equipped with a fine dust filter as part of their normal work gear during spawning of compost.

Some pickers have been found to suffer from damaged skin of finger tips, caused by exogenous glucanases and proteases of Agaricus. Wearing gloves during picking prevents this.


Mushroom growing has a short and complicated growing cycle. Thus managing a mushroom farm brings worries and tensions which may extend to the workforce. Stress and its management are discussed elsewhere in this Encyclopaedia.

The Oyster Mushroom

Oyster mushrooms, Pleurotus spp., can be grown on a number of different lignocellulose-containing substrates, even on cellulose itself. The substrate is wetted and usually pasteurized and conditioned. After spawning, mycelial growth takes place in trays, shelves, special containers or in plastic bags. Fructification takes place when the ambient carbon dioxide concentration is decreased by ventilation or by opening the container or bag.

Health risks

Health risks associated with the cultivation of oyster mushrooms are comparable to those linked to Agaricus as described above, with one major exception. All Pleurotus species have naked lamellae (i.e., not covered by a veil), which results in the early shedding of a large number of spores. Sonnenberg, Van Loon and Van Griensven (1996) have counted spore production in Pleurotus spp. and found up to a billion spores produced per gram of tissue per day, depending on species and developmental stage. The so-called sporeless varieties of Pleurotus ostreatus produced about 100 million spores. Many reports have described the occurrence of EAA symptoms after exposure to Pleurotus spores (Hausen, Schulz and Noster 1974; Horner et al. 1988; Olson 1987). Cox, Folgering and Van Griensven (1988) have established the causal relation between exposure to Pleurotus spores and occurrence of EAA symptoms caused by inhalation. Because of the serious nature of the disease and the high sensitivity of humans, all workers should be protected with dust respirators. Spores in the growing room should at least partially be removed before workers enter the room. This can be done by directing the circulation air over a wet filter or by setting ventilation at full power 10 minutes before workers enter the room. Weighing and packing of mushrooms can be done under a hood, and during storage the trays should be covered by foil to prevent release of spores into the working environment.

Shiitake Mushrooms

In Asia this tasty mushroom, Lentinus edodes, has been grown on wood logs in the open air for centuries. The development of a low-cost cultivation technique on artificial substrate in growing rooms rendered its culture economically feasible in the western world. The artificial substrates usually consist of a wetted mixture of hardwood sawdust, wheat straw and high-concentration protein meal, which is pasteurized or sterilized before spawning. Mycelial growth takes place in bags, or in trays or shelves, depending on the system used. Fruiting is commonly induced by temperature shock or by immersion in ice-cold water, as is done to induce production on wood logs. Due to its high acidity (low pH), the substrate is susceptible to infection by green moulds such as Penicillium spp. and Trichoderma spp. Prevention of the growth of those heavy sporulators requires either sterilization of the substrate or use of fungicides.

Health risks

The health risks associated with the cultivation of shiitake are comparable with those of Agaricus and Pleurotus. Many strains of shiitake sporulate easily, leading to concentrations of up to 40 million spores per cubic metre of air (Sastre et al. 1990).

Indoor cultivation of shiitake has regularly led to EAA symptoms in workers (Cox, Folgering and Van Griensven 1988, 1989; Nakazawa, Kanatani and Umegae 1981; Sastre et al. 1990) and inhalation of spores of shiitake is the cause of the disease (Cox, Folgering and Van Griensven 1989). Van Loon et al. (1992) have shown that in a group of 5 patients tested, all had circulating IgG-type antibodies against shiitake spore antigens. Despite the use of protective mouth masks, a group of 14 workers experienced a rise in antibody titres with increased duration of employment, indicating the need for better prevention, such as powered air-purifying respirators and appropriate engineering controls.

Acknowledgement: The view and results presented here are strongly influenced by the late Jef Van Haaren, M.D., a fine person and gifted occupational health physician, whose humane approach to the effects of human labour was best reflected in Van Haaren (1988), his chapter in my textbook that formed the basis of the present article.



Thursday, 10 March 2011 15:50

Aquatic Plants

Adapted from J.W.G. Lund’s article, “Algae”, “Encyclopaedia of Occupational Health and Safety,” 3rd edition.

Worldwide aquaculture production totalled 19.3 million tonnes in 1992, of which 5.4 million tonnes came from plants. In addition, much of the feed used on fish farms is water plants and algae, contributing to their growth as a part of aquaculture.

Water plants that are grown commercially include water spinach, watercress, water chestnuts, lotus stems and various seaweeds, which are grown as low-cost foods in Asia and Africa. Floating water plants that have commercial potential are duckweed and water hyacinth (FAO 1995).

Algae are a diverse group of organisms; if the cyanobacteria (blue-green algae) are included, they come in a range of sizes from bacteria (0.2 to 2 microns) to giant kelps (40 m). All algae are capable of photosynthesis and can liberate oxygen.

Algae are nearly all aquatic, but they may also live as a dual organism with fungi as lichens on drier rocks and on trees. Algae are found wherever there is moisture. Plant plankton consists almost exclusively of algae. Algae abound in lakes and rivers, and on the seashore. The slipperiness of stones and rocks, the slimes and discolourations of water usually are formed by aggregations of microscopic algae. They are found in hot springs, snowfields and Antarctic ice. On mountains they can form dark slippery streaks (Tintenstriche) that are dangerous to climbers.

There is no general agreement about algae classification, but they are commonly divided into 13 major groups whose members may differ markedly from one group to another in colour. The blue-green algae (Cyanophyta) are also considered by many microbiologists to be bacteria (Cyanobacteria) because they are procaryotes, which lack the membrane-bounded nuclei and other organelles of eukaryotic organisms. They are probably descendants of the earliest photosynthetic organisms, and their fossils have been found in rocks some 2 billion years old. Green algae (Chlorophyta), to which Chlorella belongs, has many of the characteristics of other green plants. Some are seaweeds, as are most of the red (Rhodophyta) and brown (Phaeophyta) algae. Chrysophyta, usually yellow or brownish in colour, include the diatoms, algae with walls made of polymerized silicon dioxide. Their fossil remains form industrially valuable deposits (Kieselguhr, diatomite, diatomaceous earth). Diatoms are the main basis of life in the oceans and contribute about 20 to 25% of the world’s plant production. Dinoflagellates (Dinophyta) are free-swimming algae especially common in the sea; some are toxic.


Water culture can vary greatly from the traditional 2-month to annual growing cycle of planting, then fertilizing and plant maintenance, followed by harvesting, processing, storage and sale. Sometimes the cycle is compressed to 1 day, such as in duckweed farming. Duckweed is the smallest flowering plant.

Some seaweeds are valuable commercially as sources of alginates, carrageenin and agar, which are used in industry and medicine (textiles, food additives, cosmetics, pharmaceuticals, emulsifiers and so on). Agar is the standard solid medium on which bacteria and other micro-organisms are cultivated. In the Far East, especially in Japan, a variety of seaweeds are used as human food. Seaweeds are good fertilizers, but their use is decreasing because of the labour costs and the availability of relatively cheap artificial fertilizers. Algae play an important part in tropical fish farms and in rice fields. The latter are commonly rich in Cyanophyta, some species of which can utilize nitrogen gas as their sole source of nitrogenous nutrient. As rice is the staple diet of the majority of the human race, the growth of algae in rice fields is under intensive study in countries such as India and Japan. Certain algae have been employed as a source of iodine and bromine.

The use of industrially cultivated microscopic algae has often been advocated for human food and has a potential for very high yields per unit area. However, the cost of dewatering has been a barrier.

Where there is a good climate and inexpensive land, algae can be used as part of the process of sewage purification and harvested as animal food. While a useful part of the living world of reservoirs, too much algae can seriously impede, or increase the cost of water supply. In swimming pools, algal poisons (algicides) can be used to control algal growth, but, apart from copper in low concentrations, such substances cannot be added to water or domestic supplies. Over-enrichment of water with nutrients, notably phosphorus, with consequent excessive growth of algae, is a major problem in some regions and has led to bans on the use of phosphorus-rich detergents. The best solution is to remove the excess phosphorus chemically in a sewage plant.

Duckweed and a water hyacinth are potential livestock feeds, compost input or fuel. Aquatic plants are also used as feed for noncarnivorous fish. Fish farms produce three primary commodities: finfish, shrimp and mollusc. Of the finfish portion, 85% are made up of noncarnivorous species, primarily the carp. Both the shrimp and mollusc depend upon algae (FAO 1995).


Abundant growths of freshwater algae often contain potentially toxic blue-green algae. Such “water blooms” are unlikely to harm humans because the water is so unpleasant to drink that swallowing a large and hence dangerous amount of algae is unlikely. On the other hand, cattle may be killed, especially in hot, dry areas where no other source of water may be available to them. Paralytic shellfish poisoning is caused by algae (dinoflagellates) on which the shellfish feed and whose powerful toxin they concentrate in their bodies with no apparent harm to themselves. Humans, as well as marine animals, can be harmed or killed by the toxin.

Prymnesium (Chrysophyta) is very toxic to fish and flourishes in weakly or moderately saline water. It presented a major threat to fish farming in Israel until research provided a practical method of detecting the presence of the toxin before it reached lethal proportions. A colourless member of the green algae (Prototheca) infects humans and other mammals from time to time.

There have been a few reports of algae causing skin irritations. Oscillatoria nigroviridis are known to cause dermatitis. In freshwater, Anaebaena, Lyngbya majuscula and Schizothrix can cause contact dermatitis. Red algae are known to cause breathing distress. Diatoms contain silica, so they could pose a silicosis hazard as a dust. Drowning is a hazard when working in deeper water while cultivating and harvesting water plants and algae. The use of algicides also poses hazards, and precautions provided on the pesticide label should be followed.



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