111: Fumigants

INTRODUCTION

Proper use of pesticides can have a beneficial role in human health by increasing the quality and quantity of crops. Alternatively, their improper use can lead to a variety of acute and chronic poisonings.⁵⁶ Pesticide ­poisoning is a global public health problem,⁵⁴ and each year approximately 300,000 deaths occur worldwide due to pesticides.⁵³

Fumigants are nonspecific pesticides applied to kill and control rodents, nematodes, insects, weed seeds, and fungi anywhere in soil, on structures, crops, grains, and commodities.⁴⁹ They represent a diverse group of xenobiotics that are dissimilar in their chemical structures, physical properties, and mechanisms of toxicity (Tables 111–1 and 111–2). Many fumigants, particularly the halogenated solvents, have been largely abandoned because of their toxicity. In the 1987 Montreal Protocol, an international agreement was adapted to phase out ozone-depleting chemicals, such as methyl bromide, which was scheduled to be discontinued in 2005. ­Unfortunately, many agricultural companies received exemptions, as satisfactory substitutes for some of its uses have not emerged.

Since fumigants exist as solids that can release toxic gases on reacting with water (zinc phosphide, aluminum phosphide) or with acids (sodium or calcium cyanide), as liquids (ethylene dibromide, dibromochloropropane, formaldehyde) that can vaporize at ambient temperature, or as gases (methyl bromide, hydrogen cyanide, ethylene oxide), inhalation is the most common route of exposure (Table 111–1). In their gaseous forms fumigants are generally heavier than air and will stay concentrated just above the ground surface and lower floors of buildings.

Their exposure risk is enhanced by their general lack of good warning properties, non–species-selective effects, and high potency. Although chemicals from many different classes were used in the past as fumigants, only a few remain in use ...