Ohio State University Extension Bulletin

Pesticide User's Guide

Bulletin 745

How Pesticides Affect Humans

All pesticides must be considered potentially toxic to humans and animals. The hazard in the use of pesticide materials lies in failure to follow precautions and directions for use as indicated on the label or unexpected accidents such as the bursting of spray hoses, breakage or rusting of pesticide containers and careless storage or improper disposal of containers.

Man may be exposed to pesticides through various routes such as ingestion (swallowing), inhalation (breathing), skin contact and eye contact. Skin absorption is the most common route of exposure for the sprayman. Different areas of the body exhibit different degrees of resistance to penetration of the pesticide through the skin (see diagram). Open lesions in the skin or conditions of dermatitis, as well as higher temperatures, enhance the absorption of pesticides. Dermal exposure from pesticides is often prolonged and magnified because in normal spraying operations the applicator may delay the self decontamination procedures, may wear the same clothing beyond one day's use without laundering, or may use inadequate procedures to remove contamination from the skin and clothing.

Exposure to some pesticides, particularly the organophosphates, destroys important enzymes in the nervous system. Repeated exposure may, without producing symptoms, progressively increase susceptibility to poisoning. Applicators using phosphate pesticides should get a preexposure check (usually a blood test for cholinesterase enzyme activity) and periodic checking during the spray season to determine the extent of exposure.

You should get medical advice quickly if you or your fellow workers have unusual or unexplained symptoms while at work or later in the day. Do not allow yourself or anyone else to become dangerously ill before calling a doctor or going to a hospital. It is better to be too cautious than too late. If you believe that you may have been poisoned, be sure to take the pesticide container (or label) with you to the emergency room or to your family doctor.


The organophosphates are involved in more cases of occupational poisoning and deaths than any other single group of pesticides. The symptoms of poisoning by organophosphates progress through several stages.

The usual sequence of symptoms of mild poisoning is as follows: fatigue, headache, dizziness, numbness in the arms or legs, nausea and vomiting, excessive sweating and salivation, and abdominal cramps or diarrhea.

In moderate poisoning, the symptoms listed for mild poisoning become more severe. Additional symptoms for moderate poisoning include inability to walk, generalized weakness, difficulty in talking, muscular twitches, and contraction of the pupil of the eye.

The symptoms for severe poisoning are unconsciousness, severe contraction of the pupil of the eye, muscular twitches, secretions from the mouth and nose, and respiratory difficulty. If victims of severe poisoning are not treated immediately, death will usually result.

Illness is frequently delayed several hours, and an applicator may first become sick at home after supper. If symptoms begin more than 12 hours after the last known exposure to the pesticide, illness is probably due to some other cause.


The carbamates likely to cause illness through occupational exposure act in the same way as the organophosphates, and produce the same type of poisoning symptoms. The illness caused by carbamates is usually not as severe or as enduring, however, and they are generally considered safer than the highly toxic organophosphates.

Pyrethrins and Synthetic Pyrethroids

Pyrethrin is extracted from the flowers of chrysanthemum plants. Synthetic pyrethroids, which are chemically similar to pyrethrins, are manufactured in pesticide laboratories. Both of these insecticides are highly toxic to insects and fish but less toxic to humans than most insecticides. Pyrethrins and synthetic pyrethroids affect the central nervous system, and extremely high exposure results in convulsions, lack of coordination, and a tetanic-like condition. Because of their low level of toxicity, however, pyrethrins and synthetic pyrethroids usually cause only irritation to the skin and eyes.

Chlorinated Hydrocarbons

Only a few organochlorines have caused occupational poisoning. Several of them are regularly stored in the body tissues, however, and may accumulate in considerably higher concentrations in pesticide applicators than in the general population.

Early symptoms of poisoning include headache, nausea, vomiting, general discomfort, and dizziness. With more severe poisoning, convulsions follow or may appear without these early warning symptoms. Coma may follow the convulsions. Excessive excitability and irritability are common symptoms.

Metals and Metalloids

The metallic pesticides that cause the most poisonings in the United States are those containing arsenic. Large single doses of most heavy metal pesticides cause vomiting and stomach pain. The exact nature of the symptoms varies with the metal, but in all cases the illness is chronic.


Cyanide is one of the fastest-acting poisons. Massive doses results in unconsciousness and death without warning. Smaller doses may result in the odor of bitter almonds on the breath, salivation, nausea, anxiety, confusion and dizziness. Illness may last one or more hours, terminating with unconsciousness, convulsions, and death from respiratory failure.


The injurious effects of anticoagulants are due to loss of blood, mainly into the body tissues. For example, the initial symptoms in chronic warfarin poisoning are back pain and abdominal pain.


Poisoning from fluoroacetates (1080, for example), causes stimulation of the central nervous system resulting in convulsions and abnormal heart rhythm.


The symptoms of poisoning by one or a few relatively large doses of the dinitrophenols (Elgetol, for example) include headache, nausea, gastric distress, restlessness, a sensation of heat, flushed skin, sweating, deep and rapid respiration, fast beating of the heart, fever, ashen color, collapse and coma. Acute poisoning with DNOC usually runs a rapid course. Death or almost complete recovery within 24 to 48 hours is the general rule.


Symptoms of excessive exposure to fumigants are similar to drunkenness (poor coordination, confusion, sleepiness and unconsciousness). Methyl bromide is extremely dangerous because a toxic or even fatal dose can be absorbed before symptoms appear. Many fumigants can also cause severe chemical burns when trapped against the skin. Do not wear tight clothing or jewelry (even watches or rings) when using liquid fumigants.


Pyridylium herbicides (paraquat, for example) may be harmful if inhaled or absorbed through the skin and may be fatal if swallowed. Lung fibrosis can develop if paraquat is swallowed or inhaled. The symptoms of injury may be delayed. Prolonged skin contact will cause severe irritation.

Back | Forward | Table of Contents