Neurotoxicity of Chemicals Commonly Used in Agriculture

Nikita B. Katz, Olga Katz, and Steven Mandel

Key words: assessment, wild plants, rodenticides, heavy metals, organochlo-rides, organophosphates

A multitude of chemical agents used in agriculture are known to have significant toxicity, many of them specifically developed to be toxic to animals. This chapter concentrates on the neurological consequences of occupational exposure to these and other common agents, including insecticides, pesticides, heavy metals, and volatile organic and plant toxins.

A physician in rural practice should be acquainted with the strategies for providing emergency care, especially after acute exposure to potent toxins. Acute exposure is suggested by a set of symptoms that include rapidly developing fatigue, dizziness, nystagmus, disorientation, confusion, hallucination, as well as other neurological presentations (e.g., symptoms of intracranial hypertension such as headache, nausea, or vomiting), muscle fasciculations, seizures, or coma (1).

A possibility of occupational exposure must be considered in all agricultural workers and their families; however, those who work in a confined space with little or no means of personal protection, who lack the necessary training or sufficient knowledge of the native language, or lack access to industrial hygiene data should be considered likely candidates for a detailed evaluation.

Often patients provide the best clues by attributing their medical condition to a specific agent or to the possibility of exposure. Patients may complain that their symptoms were preceded by the presence of a chemical smell or a spill of a chemical. They may also note that their symptoms get worse at the end of the shift, workweek, or season. This "undulating" presentation when symptoms are less acute during the weekend or time-off periods may be of special significance as it may allow gauging of personal susceptibility to a specific agent (2,3).

Occupational exposure may be suspected if the patient presents with reversible, static, or progressive neurological symptoms after removal from exposure, symptoms that occur slowly, especially if these symptoms are attributable to central nervous system (CNS) changes such as headache, confusion, disorientation, and behavior or memory changes. Slow onset of peripheral neuropathy, often presenting with numbness in the feet and hands, pain, weakness, or difficulty walking is also highly suggestive of occupation-related toxicity. In the majority of cases, severity of symptoms may be directly related to the length of employment in the field or in processes that expose workers to toxic agents (4,5).

Both clinical and subclinical dysfunction is often noted by abnormal neu-rophysiological, neuropsychological, or neuroimaging testing results. Detailed evaluation of patients whose occupational or environmental history is deemed significant is warranted as it provides a snapshot of the patient's condition against which future changes can be judged.

In all cases strive to achieve unhindered communication with both the patient and the employer. Assistance of qualified interpreters may be needed and chemical names may differ significantly among languages (e.g., nitrogen is "azote" in several European languages). When evaluating the patient, consider both common and rare agents, keeping in mind that what may be rare in an urban/suburban setting may be common in the rural and agricultural setting.

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