Hazardous Organic and Inorganic Exposures

Potentially harmful exposures exist in a variety of forms in the farm environment, including solvents, pesticides, paints, welding and combustion fumes, plant toxins, and animal bacteria and viruses. Their possible health effects vary widely and can include acute intoxication, Parkinson’s dis­ease, peripheral neuritis, acute and chronic encephalopa­thy, various cancers, and reproductive problems.

Solvents. A solvent is a liquid used to dissolve other substances, but the most toxic solvents are extracted or manufactured for chemical use. Most solvents are colorless liquids at room temperature that volatilize easily and have strong odors. These compounds may be referred to as volatile organic compounds (VOCs) in reference to their physiochemical properties.

Many commonly used solvents such as gaso­line, kerosene, and jet fuel are mixtures of solvents and other chemicals. They are widely used for manufacturing, degreasing and other cleaning, and as carrying agents in products ranging from insecticides to glues and paints. The most common solvents and solvent mixtures found in the farm environment include pesticides, fuels, paints, and metal degreasers.

There is little information from animal or human studies about the health effects of chronic low-dose expo­sure. Solvents are most commonly inhaled in their vola­tilized form and absorbed via the respiratory track.

Significant doses of solvents may occur through skin exposure and absorption. Most solvents are lipid-soluble but some are water-soluble. Animal studies in the toxicol­ogy literature emphasize the role of solvents as neurotox­ins. The majority of solvents are central nervous system depressants and some have long-term neuropsychological effects, including chronic toxic encephalopathy.

In adults, the following neurobehavioral problems resulting from chronic solvent exposure have been recorded in the literature: memory loss, decreased problem-solving abil­ity, decreased attention span, impaired dexterity and hand-eye coordination, altered reaction time, reduced psychomotor function, and altered personality or mood. In addition to neurotoxic effects, other documented health effects from solvent exposure in adults are pulmonary sensitization, bradycardia, and ventricular fibrillation, defatting of the dermis, chemical burns, and hearing loss.

Pesticides. Agriculture experienced a chemical revolution after the Second World War with the broad-scale introduction of pesticides to control unwanted pests and fertilizers to enhance soil productivity. This revolution brought with it a series of unintended occupational and environmental health consequences, and exposure to pesticides is a seri­ous risk to farmworkers worldwide.

Data from the United States illustrate exposure circumstances for people both working in and living in the agricultural environment. The U.S. Environmental Protection Agency (EPA) esti­mates that as many as 300 000 farmworkers suffer pesticide poisoning each year while the U.S. Natural Resources Defense Council estimates as many as 40 000 physician- diagnosed poisonings occur each year (NRDC, 1998). The International Labour Organization reports that globally 40 000 agricultural workers die annually from exposures to pesticides. Only a small percentage of pesticide-related illnesses are reported to government or health officials.

Pesticides include herbicides to control weeds, insec­ticides to control a range of insects, nematocides to con­trol worms, and fungicides to control molds, fungi, and other mycotoxins. Exposures can happen when workers are mixing, loading, transporting, or applying pesticides and the three main routes of exposure are dermal, inhala­tion, or ingestion. Risk of exposure can be compounded by lack of or improper protective gear, leaking containers, illicit formulations, faulty labeling of the chemical, improper application, and illiteracy. Workers may also be exposed to pesticides if they drink from, wash their hands, or bathe in irrigation canals or holding ponds, where pesticides can accumulate.

While acute pesticide health effects have been well documented, epidemiological investigations continue to evaluate chronic health effects. Toxicologic and epidemi­ologic data reviewed in this section largely originate from adult animal and adult human studies. Infants and children may be exceptionally vulnerable to health complications from exposures due to their developing neurological, immunological, and reproductive systems and due to dif­ferences in their ability to metabolize and excrete toxi­cants (Perry, 2003).

There is evidence that farm families experience ele­vated levels of pesticide residues in their blood and urine. A recent investigation from the U.S. Agricultural Health Study reported that agricultural families could receive an absorbed dose of pesticides after application by a member of the family. The report used indoor air sampling, hand wipe sampling, serum, and urine monitoring to evaluate exposures to the family of a single farm applicator.

The farmer applied the carbamate insecticide carbaryl to pumpkins using a hand-cranked duster. His serum carbaryl levels rose by 3 orders of magnitude following use of the pesticide, and the carbaryl metabolite was detectable in his urine. Urine metabolite measurements taken from his wife and two children showed a doubling of excretion of the carbaryl metabolite following application of the pesticide. These results were seen in the absence of a quantifiable increased carbaryl concentration in indoor air or house dust (Shealy et al., 1997).

Additional preliminary results from the Agricultural Health Study revealed that elevated blood serum pesticide levels were detected in some farm families. The very potent organochlorine insecticide dieldrin, which has been banned in the United States since 1987, was found at significantly elevated levels in the blood of all members of one of the six farm families sampled. Further investigation revealed per­sistently elevated levels of this pesticide in food samples on the farm, although all legal food uses of this pesticide were canceled in 1974. Other persistent organochlorine pesti­cides identified in the blood of farm families included chlordane and trans-nonachlor (Brock etal, 1998).

Residents living near fields sprayed with organophosphate pesticides had small reductions in plasma and whole blood levels of the neurotransmitter enzyme cholinester­ase during the spraying season compared with residents living farther from the fields and with their own cholines­terase levels off-season. At the same time, infirmary records indicated a significant increase in visits for certain symptoms on days when organophosphate pesticides were sprayed.

Symptoms included respiratory problems, head­ache, and eye irritation (Richter et al., 1986). These data suggested that exposures to organophosphate pesticide drift might result in quantifiable cholinesterase inhibition and symptoms requiring medical treatment in residents living nearby application fields.

In adults, acute pesticide exposures resulting in poi­soning symptoms have been well documented. The chronic health effects from pesticide exposures that have been reported include neurobehavioral problems, Parkinson’s symptoms, various cancers, and problems in reproduction including sterility.

The problem of unintended consequences of pesticide exposures globally is compounded by poor public health protections for workers and a lack of comprehensive reg­ulations focused on controlling exposures for citizens. The World Health Organization (Dinham and Malik, 2003) estimates that 20 000 women, men, and children die of accidental pesticide poisonings each year; three million are nonfatally poisoned, and nearly three-fourths of a million new people each year experience chronic effects from exposure.

Some industrializing countries in Asia and Africa are either importing pesticides that are banned elsewhere or are producing them locally. Com­pounds known to have considerable toxicity and that are environmentally or biologically persistent such as organochlorines remain in use in over 20 different countries today, while the long-term ecological and public health consequences of continued use remain unknown.

Microbes and Their Toxins. Grain dusts, molds, and fungi are among several plant- based irritants that abound in the agricultural environ­ment and that cause a host of respiratory problems in adult farmers. The clinical features of adult illnesses caused by these irritants should be considered with regard to the potential for child exposures as well. As with other chronic diseases, chronic respiratory diseases are likely to originate during early exposures, with damage accumu­lating over time until eventual clinical symptoms appear. Preventing such exposures early may be the key to reduc­ing respiratory disease in adulthood.

Grain dust is a complex substance composed of plant debris, insect parts, silica, chemical residues, molds, fungi and bacteria and their metabolites, including endotoxins. Approximately 40% of its particles are less than 5 pm in mean diameter and represent a respirable piece that can penetrate the terminal bronchioles.

Exposure to antigens from organic dusts may be responsible for hypersensitiv­ity pneumonitis, which has a reported prevalence of 0.1-15% among adult farmers. Hypersensitivity pneumo­nitis is difficult to diagnose in adult farmers because it has an insidious course and appears as recurrent influenza­like episodes or nonspecific respiratory symptoms and may result in chronic respiratory problems that look like pulmonary fibrosis.

The organic-dust toxic syndrome is an acute response to inhaling organic dust, usually characterized by a delayed onset of fever, malaise, and chest tightness that does not evidence immunologic involvement and has an apparently benign course without long-term respiratory impairment. Possible mechanisms include a toxic reaction to endotox­ins, mycotoxins, or proteinase enzymes of moldy plant materials.

It is related to dust level and can be reproduced in laboratory subjects exposed to high concentrations of grain dust. Exposures responsible for the related condition extrinsic allergic alveolitis (farmer’s lung) are actinomycetes such as Micropolyspora faeni, fungi, and animal pro­teins present in many agricultural environments.

Working in confined spaces such as silos or manure pits can pose risks for exposure to toxic gases such as nitrogen dioxide from fermented grain or methane gas emitted from manure. Both of these gases can be fatal when inhaled and proper ventilation of enclosures is critical for mitigating acute exposures.

Carcinogens. While the epidemiologic data are not conclusive enough to demonstrate causality for any one agricultural expo­sure, a number of increased cancer risks have been asso­ciated with either farming or specifically with pesticide exposure, including non-Hodgkin’s lymphoma, leukemia, multiple myeloma, soft tissue sarcoma, Hodgkin’s disease, and cancer of the prostate, pancreas, ovary, breast, and testis.

Currently only arsenic-containing insecticides are recognized as known human carcinogens by the Interna­tional Agency for Research on Cancer, but many other pesticides are suspected. Agricultural workers are also at excess risk for developing skin cancer, which is most often caused by chronic exposure to ultraviolet radiation from the sun.

Skin Irritants. Data from studies of adult farmers indicate that skin irritation starts soon after employment commencement and increases to involve more than 60% of workers after 4 years of employment in the grain industry (Zejda et al, 1993). Skin cancers, dermatophyte infections, and pesti­cide-related skin diseases are common in farmers.

The impact of microscopic fungi on farmers’ health seems to be greater than originally understood. The infec­tion may be transmitted from infected humans, animals, plants, or soil. To date, little epidemiological data on fungal skin disease in farmers are available. Epidemiologi­cal studies from Poland suggest that mycoses are the most prevalent skin diseases in farmers and may be present in over 20% of the population (Spiewak, 1998).

Working conditions on farms directly contribute to the develop­ment of fungal infections. Farmers may spend extended periods working in humid conditions and long hours wear­ing rubber boots or gloves. Besides infection, fungi may also cause noninvasive forms of skin disease, such as dermato-mycotoxicosis professionalis or alternariosis.

Most pesticide-related dermatoses are contact dermatitis, both allergic and irritant. Rare clinical forms also occur, includ­ing urticaria, erythema multiforme, ashy dermatosis, para­keratosis variegata, porphyria cutanea tarda, chloracne, skin hypopigmentation, and nail and hair disorders.