FUMIGANTS, which kill insects in more or less enclosed spaces, have different degrees of hazards. Fumigants that present minimum hazards, such as ethylene dichloride-carbon tetrachloride mixture, may be used safely by farmers to treat stored grain. Others, which require greater precautions, like carbon disulfide, should be used only by commercial pest-control operators. The most hazardous fumigants, such as hydrocyanic acid gas, should never be used by the novice. The pest-control operator is trained to handle them and knows the proper precautions. Any fumigant that is toxic to insects is also toxic to human beings.

Before any fumigant is used, the various sources of information should be consulted and labels should be carefully read. Antidotes and first-aid treatments should be noted.

Two principal precautions that should be taken when a fumigant is used, regardless of its degree of toxicity, are to avoid exposure to a heavy concentration or inhalation of vapors for a long time and to avoid spilling the fumigant on the skin or clothing.

A farmer who may be using a limited amount to treat one or two grain bins and who is using a fumigant recommended for farm use is exposed to it only for a short time. Protection from breathing the fumes is usually not necessary, as he can avoid prolonged inhalation. When the fumigant is used repeatedly over a long period and in enclosed spaces, protection against inhalation is necessary. If there is exposure to high concentrations, a full-face mask should be worn. The mask should have a canister suitable for the fumigant used; not every canister will afford protection against all gases. Because the life of a canister is limited, new ones must be supplied whenever those in use show signs of weakness. Gas masks are not designed for protection against prolonged exposure to heavy gas concentrations, and exposure should be limited to the short period necessary to release the fumigant and to open the building for airing.

Many fumigants readily penetrate the skin and may be taken up by the blood stream. Gloves resistant to the fumigant should be worn, particularly if large quantities are involved. If material is spilled on the skin or work clothes, a bath with soap and water should be taken and the clothing changed. This precaution should be followed immediately with the most dangerous fumigants.

Persons not actually engaged in applying the fumigant should be protected from drift or leakage or from gaining entrance to the enclosed space during the fumigation. The buildings should be locked and posted. Keeping watchmen on duty during the exposure period is desirable.

Some fumigants, such as carbon disulfide, have a fire or explosion hazard, and care should be taken to avoid any spark or flame near the vapors.

Contamination of food products being fumigated directly or when stored in warehouses receiving a general fumigation must be avoided. Certain fumigants, such as hydrocyanic acid gas and methyl bromide, are absorbed, especially in moist materials, and therefore such products should not be used as food until thoroughly aired and found to contain no appreciable residue. Damp mattresses and clothing may absorb the gas and thorough airing before they are used is important.

DRIFT OF INSECTICIDES outside of the area being treated may create a danger, especially if extremely poisonous materials are being applied. People living or working in the line of drift may be made seriously ill in extreme cases. A few insecticides, such as hexaethyl pyrophosphate and parathion, present hazards because of their vapors or dusts. They might cause serious consequences if large quantities drifted over areas where human beings, domestic animals, or fowl might be subjected to concentrations of the vapor or dusts for considerable time. Areas to be treated should be vacated until after the vapors or dusts have dissipated, unless one is certain that no hazard would exist.

Sprays are less likely to drift than dusts. Certain insecticides are stomach poisons of low solubility in water. If they should drift to gardens of leafy vegetables or small fruits the residue might be dangerous. Some insecticides might remain on the plants for sometime and be difficult to wash off. It would not be safe to eat products from such gardens soon afterwards. Drift of such insecticides over pastures might create a hazard to grazing stock more because of the amount they take in with their food than because of actual contact of the material with their bodies. Similar drift to fields of hay crops may leave deposits sufficient to make the resulting hay injurious to livestock or indirectly to the public through the contamination of milk or meat.

Obviously one has to consider the general situation before starting to apply the insecticides. If possible, the application should be made at a time when hazards from drift will not be created, regardless of the kind of insecticide used. Applications from the air are more likely to contaminate adjacent fields, gardens, and pastures than ground applications. Therefore only competent and reliable pilots should be employed to do such work, fields should be posted, and the owner should be on hand to supervise the operation. Canopies or hoods on ground equipment help to keep the materials from drifting and so add to the effectiveness of the application.

INSECTICIDES OR REPELLENTS often are applied to livestock and household pets.

Pyrethrum and rotenone, for example, present no hazards if kept out of the animal's eyes, but solutions and emulsions containing toxaphene, benzene hexachloride, and chlordane may be harmful if the concentration is too high. Formulations containing parathion and hexaethyl pyrophosphate should never be used on animals, regardless of the formulation. Solvents such as oils and xylene in themselves are irritating and may cause loss of hair and scaling of the skin. They may also facilitate the penetration of the insecticide into the animal's body. For those reasons only insecticides and formulations recommended by proper authorities and labeled with specific instructions should be used on livestock or pets. Precautions on the label should be observed.

Because some crops may be injured by insecticides, labels should indicate susceptible crops and the insecticide concentration that should be employed against pests. Solvents or other ingredients may be safe on one crop but injure another. For example, it has been shown that cucumbers and squash are likely to be injured by DDT insecticides, although the same strength and dosage would be perfectly safe on most crops. Even certain varieties of a given vegetable may be easily injured by an insecticide that would not affect others.

SOME INSECTICIDES are poisonous to fish, toads, lizards, and snakes. For example, DDT and most of the new chlorinated materials, particularly toxaphene, kill fish at a very low concentration. Care must be taken to avoid insecticidal treatments or drift over open water, such as wide rivers and lakes, since wind may concentrate the material along a margin in sufficient quantity to kill fish. Remnants of spray from tanks and spray equipment should be drained and washed into a hole in the earth where they will not gain access to streams and ponds. Insecticides should never be mixed on or near wells.

Awareness of hazards and adoption of safeguards in using and storing pesticides are urgently needed. The object of instructions to that end is not to frighten people so that they will not use pesticides but to get them to observe proper precautions. The intelligent use of pesticides will enable users to derive the greatest good with the least chance of adverse effect.

F. C. BISHOPP is an assistant chief of the Bureau of Entomology and Plant Quarantine.

JOHN L. HORSFALL, a graduate of the State University of Iowa, is chief entomologist of the American Cyanamid Company. He has been engaged in research and development of chemicals for pest control since 1920.