Based on their chemical properties, pesticides are classified as: organochlorine pesticides (OCPs);
organophosphate pesticides (OPPs); carbamate pesticides;
synthetic pyrethoids; and nicotinoids.
Pesticides are also grouped as synthetic pesticides or biological pesticides. The classification of pesticides according to the manner of use can be listed as (Table 6.1): acaricides; algicides; antifouling agents; antimicrobials; attractants; avicides;
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bactericides; biocides;
defoliants (cause leaves or other foliage to drop from a plant); desiccants (promote drying of living tissues);
fungicides; fumigants; herbicides; insecticides;
insect growth regulators (disrupt the molting, maturity from pupal stage); miticides/acaricides;
microbial pesticides; molluscicides; nematicides; ovicides;
plant growth regulators (alter the expected growth, flowering, or reproduction rate of plants); repellents; and rodenticides. table 6.1 groups of Pesticides Pesticide uses
Algicide Control algae in lakes, canals, swimming pools, water tanks, and other sites Antifouling agent Kill or repel organisms that attach to underwater surfaces, such as boat bottoms Antimicrobial Kill microorganisms (such as bacteria and viruses)
Attractant To attract pests—for instance, to lure an insect or a rodent to a trap Avicide Control of unwanted birds
Bactericide Pesticides derived from such natural materials as animals, plants, bacteria, and certain minerals
Biocide Kill microorganisms
Fumigant Produce gas or vapor intended to destroy pests in buildings or soil Fungicide Kill fungi, blights, mildews, molds, fungal diseases, and rusts Herbicide Kill weeds and other plants that grow where they are not wanted Insecticide Kill insects and other arthropods
Microbial pesticide
Microorganisms that kill, inhibit, or outcompete pests, including insects or other microorganisms
Miticide/acaricide Kill mites that feed on plants and animals Molluscicide Kill snails and slugs
Nematicide Kill nematodes (microscopic, worm-like organisms that feed on plant roots) and eelworms
Ovicide Kill eggs of insects and mites
Pheromones Biochemicals used to disrupt the mating behavior of insects Piscicide Control of fish
Repellent Repel pests, including insects (such as mosquitoes) and birds Rodenticide Control mice and other rodents
Herbicides share common signs and symptoms. In general, herbicides cause irri- tation to the skin, eyes, and respiratory tract. However, they are also known to impart low levels of systemic toxicity to animals and humans. Herbicides prevent or elimi- nate weeds and thus replace or reduce manual and mechanical weeding. Because they reduce the need for cultivation, they can also prevent soil erosion and water loss. Herbicides can be divided into two categories: selective herbicides, which can be applied directly on specific crops without damaging them, and nonselective her- bicides, which destroy or eliminate all plants. Weeds are undesirable plants growing within a crop that compete for resources such as nutrients, water, and light. It is well known that without weed control, crop yields suffer a significant loss. The discovery of selective herbicides in the twentieth century offered a boon for the control and elimination of weeds. These products contributed to substantial increases in yield and consistency of crop production.
Bipyridyl herbicides include alachlor, amitrole, atrazine, bromacil, bromoxynil, butylate, cyanazine, dalapon, dicamba, diuron, linuron, fluometuron, hexazinone, molinate, metolachlor, oryzalin, pendimethalin pronamide, propanil, propazine, simazine, terbacil, triallate, and triclopyr. In addition to these herbicides, the most common bipyridyls are diquat and paraquat. Paraquat is more toxic than diquat and produces chronic abnormal cell growth in the lungs, cornea and lens of the eye, nasal mucosa, skin, and fingernails. Diquat affects the eye lens and intestinal tract lining, but does not usually produce the frequently fatal lung changes characteristic of paraquat.
Ingesting diquat or paraquat causes severe irritation to the mucous membranes of the mouth, esophagus, and stomach. Repeated vomiting generally follows. Large doses of diquat also produce restlessness and reduced sensitivity to stimulation. Dermal exposure to paraquat and diquat concentrates may cause severe skin irrita- tion and burning. Contact with dilute liquids and diquat dusts may cause slight to moderate irritation. Dermal absorption of paraquat apparently is slight, but diquat is absorbed and after repeated contact will produce symptoms similar to those follow- ing ingestion. Exposure to paraquat and diquat spray mist may produce skin irrita- tions, nasal bleeding, irritation and inflammation of the mouth and upper respiratory tract, coughing, and chest pain. Exposure to paraquat concentrates may cause black- ening of the nails and abnormal nail growth.
Chlorophenoxy herbicides include 2,4-D and MCPA. Human exposure to these chemical substances causes moderate irritation to skin and mucous membranes. Inhalation may cause burning sensations in the nose, sinuses, and chest; and cough- ing. Prolonged inhalation leads to dizziness. Further, irritation of the stomach usu- ally leads to vomiting soon after ingestion, pain in the chest and abdomen, diarrhea, headache, mental confusion, and bizarre behavior—early signs and symptoms of severe poisoning leading to unconsciousness.
Arsenical herbicides such as Ansar and Montar cause very rapid, acute poi- soning. The symptoms include inflammation of the mouth and esophagus, burning abdominal pain, thirst, vomiting, “rice water” or bloody diarrhea, headache, dizzi- ness, muscle weakness and spasms, low body temperature, sluggishness, delirium, coma, and convulsions. The arsenical herbicides also cause liver damage, yellowness
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of the skin, reduction in red and white blood cells and blood platelets, circulatory failure, and death. In contrast, chronic arsenic poisoning causes prominent dermal manifestations. These include overgrowth of the cornea or epidermis; scaling off of dead skin; excessive fluids under the skin of the face, eyelids, and ankles; white streaks across the nails; loss of nails or hair; and brick-red coloration of visible mucus membranes. For more information on herbicides, refer to the literature.1–6
Rodenticides include coumarins, zinc phosphide, and strychnine.
Synthetic pyrethroids are synthetic compounds that mimic the structure of natu- rally occurring pyrethrins. The systemic toxicity by inhalation or dermal absorption is low. There have been very few systemic poisonings of humans by pyrethroids. Dermal contact may result in skin irritation such as stinging, burning, itching, and tingling progressing to numbness. The group of synthetic pyrethroids includes allethrin, cyfluthrin, cypermethrin, esfenvalerate, fenvalerate, flucythrinate, fluvali- nate, permethrin, resmethrin, tetramethrin, and tralomethrin.
Fungicides are extensively used in industry, agriculture, the home, and the garden. They vary enormously in their potential for causing adverse effects in humans. Most fungicides currently in use are unlikely to cause frequent or severe poisonings. Apart from poisonings that affect the body generally, fungicides have probably caused dis- proportionate numbers of irritant injuries to skin and mucous membranes, as well as some dermal sensitization. The fungicides cover a great variety of chemical com- pounds differing widely in their toxicity. Highly toxic compounds are used as fumi- gants of foods and in warehouses and for seed dressing and soil disinfection. Cases of poisoning have been described with organomercurials, hexachlorobenzene, and pentachlorobenzene, as well as with the slightly toxic dithiocarbamates. More infor- mation can be found in the literature.1–5a