By E Ratshikhopha, A Fourie, O Matuka, T Singh, National Institute for Occupational Health a branch of the National Health Laboratory Service

Biological agents are commercially produced through biotechnological processes to harness their abilities of controlling plant diseases and pests (insect, mites, weeds) or stimulating plant growth.  These renewable resources are increasingly being used as a more eco-friendly and sustainable method of biocontrol and biostimulation.  Their active ingredients can be plants, algae, extracts, microorganisms (bacteria, fungi and viruses) or active metabolites. The controlling mechanisms of biocontrol agents (BCAs) include predation, parasitism, herbivory and pathogenicinity.  Biostimulants contain substances or microorganisms that stimulate natural processes to enhance nutrient uptake and efficiency, tolerance to abiotic stress and crop quality. The use of BCAs is an important development as pesticides are known to be harmful to humans and the environment.  Although there are several important benefits to the application of BCAs and biostimulant agents (BSAs), they could have adverse effects on workers exposed to it without a thorough understanding of the possible consequences.  Therefore, while these biological agents find ready acceptance in agriculture, horticulture, landscaping and production, safety to workers health must be ensured.

Agricultural workers are exposed to high levels of biological agents due to the use of and exposure to BCAs and BSAs which are associated with various occupational diseases.  Exposure to high levels of these agents over a short period is also a health risk to certain workers.  Diseases include allergies, asthma, chronic obstructive pulmonary disease, hypersensitivity pneumonitis and phototoxicity.  The occupational diseases caused by these agents may be dependent on the level of exposure, the concentration of the agent and amount of product used.

Microbial control products can be manufactured as powder, granules and suspensions. These agents become airborne during application of the powder or granular products, leading to occupational exposure.  Individuals applying these products are often exposed to very high levels during their work activities. Exposure can be direct through inhalation of the BCA or indirect by handling treated plants and/or by winds blowing them from or shaking them off surfaces where they are present. Other activities that should be considered when investigating exposure to BCAs and BSAs include production and application of the products and clearing of old plants.

Common biological agents used as BCAs and BSAs include algae (Ascophyllum, Fucus, Laminaria), bacteria (Bacillus subtilis, Ba.Thuringiensis, Rhizobacteria, Streptomyces griseoviridis), fungi/mold (Beauvaria bassiana, Lagenidium giganteum, Paecilomyces lilacinus, P.fumosoroseus, Trichoderma harzianum, T.polysporum, T.viride, Ulocladium atrum, Verticillium lecanii), trees (Lithraea molleoides) and nematodes (Steinernema feltiae).  Reports of exposure to high levels of certain BCAs (B.bassiana, Ba.thuringiensis and Trichoderma species) compared with other agents in environments such as greenhouses are known. It is important to note that some BCAs (e.g. B.basianna and Ba.thuringiensis) have been detected weeks and in some instances several years after application.  This could have been from settled fungal spores or new growth of the fungi on the host, thus soil can act as a reservoir and exposure source.  B.bassiana also poses other challenges as it has numerous antibody proteins, some of which can cross-react with other allergens from other fungi.  Allergy testing was positive for the B.bassiana agent. B.bassianacan also be infectious to individuals with weak immunity; and B.bassiana and Ulocladium atrum has been reported as causal agents of keratitis.  Therefore, sensitised workers may be exposed to the agents long after processes or activities have ended.

The health of a number of workers from different greenhouses workers has been affected from exposure to BCAs (e.g. Ba.thuringiensis (Bactimos^R and Vectobac^R)). Apart from the risk of allergenic sensitisation to exposed workers, the use of Ba.thuringiensis kurstaki (Foray^R48B) also led to increased complaints of gastrointestinal, upper airway and neuropsychiatric symptoms. Allergic sensitisation to V.lecanii was also shown to be high in 35% of farm workers in England and among workers from greenhouses (9 to 21%).  Cases of allergy to a nematode product containing Steinernema feltiae was reported in flower greenhouse and horticulture workers. Paecilomyces, Trichoderma and Ulocladiumhave been implicated in onychomycoses (fungal infection of the nail) cases. The use of Lagenidium giganteum, a watermold as an anti-mosquito control agent has resulted in the emergence of heat-tolerant L.giganteum strains that are pathogenic to lower animals and humans. This poses a public and environmental health concern for countries where diseases caused by mosquitoes are endemic and the BCA is used.

Apart from microbial agents, many essential oils which are natural by-products of plant metabolism show a broad spectrum of insecticidal, anti-feedant, repellent, oviposition deterrent, growth regulatory and anti-vector activities. They thus have great potential for increased use in agriculture.  Essential oils which are so promising for use in agriculture are a good example of natural substances which are a well-known cause of skin allergy or irritation (contact dermatitis) in humans.  Common essential oils that are known to cause skin problems include tea tree, orange, lemon, mandarin and grapefruit oil. These substances can cause outbreaks of occupational contact dermatitis among the crop sprayers or even in the factories producing them. They may also affect individuals where these products are used as insect repellents, flea dips for animals and indoor pesticides.  Another plant, Lithraea molleoides, produced for medicinal purposes also possess antimicrobial, antiviral, cytotoxic and immunomodulatory activities, however, it can also cause allergic sensitivity, skin disease, fever and visual problems in sensitive individuals.

A highly invasive plant, Parthenium hysterophus, causing substantial economic losses in many countries (southern & eastern Africa, Asia, Australia and India) is also known to cause allergic respiratory problems, contact dermatitis and to be mutagenic in humans. Several biocontrol agents have been released in selected areas in South Africa to eradicate this pest.  Care should be taken to ensure that the health of workers involved in the weed management process is not affected by indirect exposure to the BCAs.

While the use of bioproducts as BCAs or BSAs has many advantages such as economic and environmental gains; it also has some limitations as they can affect the health of some workers that are particularly involved in the use of, or are exposed to these agents.  It is essential that hierarchy of controls are implemented to control exposure and where relevant appropriate personal protective equipment is provided for workers. The National Institute for Occupational Health (NIOH) has recognised this as an area that requires more awareness and research in order to protect workers from exposure. Further information can be obtained by contacting the NIOH on +27 (0)11 712 6400 or info@nioh.ac.za

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