Effects of Pyrethroid Insecticides on Aquatic Organisms

Introduction Most aquatic invertebrates and fish are highly susceptible to synthetic pyrethroid insecticides (1, 2). All pyrethroids are potent neurotoxicants that interfere with nerve cell function by interacting with voltage-dependent sodium channels as well as other ion channels, resulting in repetitive firing of neurons and eventually causing paralysis (3, 4). Exposed organisms may exhibit symptoms of hyperexcitation, tremors, convulsions, followed by lethargy and paralysis. Pyrethroids occur mostly as mixtures of stereoisomeric forms, and the toxicity of individual isomers can vary (5). There are two groups of pyrethroids with distinctive poisoning symptoms, type I and type II. Type II pyrethroids are distinguished from type I pyrethroids by an alpha-cyano group in their structure. While type I pyrethroids (e.g. permethrin, cismethrin) exert their neurotoxicity primarily through interference with sodium channel function in the central nervous system, type II pyrethroids (e.g. deltamethrin, esfenvalerate, cypermethrin, bifenthrin) can affect additional ion-channel targets such as chloride