Insecticides have the highest toxicity ratings for human exposures. Most insecticides work by affecting the nervous system. According to the USDA Chemical Use Survey, insecticides were applied to 21% of Iowa’s soybean crop in 2012. In 2010, insecticides were applied to 12% of acres planted to corn nationwide. (PDF) Common classes of insecticides currently in use include Organophosphates, Pyrethroids and Neonicotinoids.
Organophosphates are a class of chemicals that contain phosphorus. Common active ingredients in organophosphate insecticides are chlorpyrifos, malathion, acephate and Naied. The EPA classifies organophosphate insecticides as moderately to highly toxic. They work by interfering with the nervous system, inhibiting the enzyme that halts nerve impulses (acetylcholinesterase). Chlorpyrifos (known by many trade names, including Dursban and Lorsban) was the most common insecticide sprayed on Iowa soybeans in 2012 (14% of total planted acres).
Symptoms of acute exposure include nausea, headaches, twitching, trembling, excessive salivation and tearing of the eyes, difficulty breathing, convulsions and, at higher doses, death. Worker restricted-entry interval: 24 hours (Chlorpyrifos).
Pyrethroids are a class of synthetic chemicals that mimic the insecticidal properties of chrysanthemum flowers (pyrethrins). Bifenthrin and Lambda-cyhalothrin, both pyrethroid insecticides, were applied to 8% of Iowa’s soy crop in 2012. Toxicity by inhaling or skin absorption is low. The most common symptom resulting from dermal exposure to Bifenthrin are itching, tingling, burning and numbness of the skin. Field workers have reported skin irritation and burning sensations when working with lambda-cyhalorthrin. In some cases, symptoms lasted up to 72 hours. Worker Restricted-entry interval: 12 hours (Bifenthrin) and 24 hours (Lambda-Cyhalothrin)
Neonicotinoids are modeled after nicotine and affect the central nervous system of insects. These are a relatively new class of pesticides, becoming available in the early 1990s in the U.S. Neonicotinoids are more toxic to insects than mammals. Ingestion and inhalation are the most likely mechanisms for poisoning. In agricultural contexts, neonicotinoids are usually applied directly to seeds and do not drift. Symptoms resemble acute nicotine poisoning and may include disorientation, confusion, agitation, headache, drowsiness, dizziness, weakness, tremor, unconsciousness. Imidacloprid is the most common active ingredient in neonicotinoid insecticides. Worker restricted-entry interval: 12 hours (imidacloprid).