Insecticides have been widely used to control noxious insects in agriculture, forestry, horticulture, public health, and medicine. Their use in agriculture has contributed dramatic increases in crop production and in the quantity and variety of the diet. Insecticides have also played a crucial role in limiting the spread of human and animal vector-borne diseases. The chlorinated hydrocarbon insecticides were heavily used after their introduction, but the disadvantages of using compounds that do not readily degrade under environmental conditions soon became apparent. Their acute toxicity is moderate and less than that of organophosphates and carbamates, but chronic exposure may be associated with adverse health effects. Primarily because of ecological considerations, these compounds have been banned in most countries between 1970 and the 1990s (Mrema et al., 2013). Yet because of their long environmental persistence, biomagnification, and high lipophilicity, exposure to these compounds continues, most notably; through the diet. Dichlorodiphenyltrichloroethane (DDT) and its major metabolite 1,1-bis(p-chlorophenyl)-2,2-dichloroethylene (DDE) are ubiquitous and are found in various tissues of humans throughout the world. Moreover, both DDT and DDE have been consistently found in the follicular fluids and serum of women (Petro et al., 2012; Adlard et al., 2014). It is also known that DDT and its metabolites are potential reproductive toxicants. Furthermore, some insecticides, such as DDT, are still being used in parts of the world for malaria control; hence, toxicity, especially reproductive and developmental toxicity, induced by chlorinated hydrocarbon insecticides is in current discussion (Costa, 2008; Mrema et al., 2013; Wang et al., 2013).
Environmental accumulation of persistent organic pollutants including chlorinated hydrocarbon insecticides has been suggested as a major cause of reproductive dysfunction in humans and animals. Prolonged exposures to chlorinated hydrocarbon insecticides is associated with reproductive abnormalities in several species. High levels of DDE in serum have been associated with shortened menstrual cyclicity (Ouyang et al., 2005), development of polycystic ovaries (Holloway et al., 2007), and longer time to pregnancy (Harley et al., 2008). Significant diet exposure starts early in postnatal life with breastfeeding, as underscored by the evidence that residues of chlorinated hydrocarbon insecticides have been detected in breast milk (Vall et al., 2014; Chávez-Almazán et al., 2016). Findings suggest that serum concentrations of chlorinated hydrocarbon insecticides change across critical windows of human reproduction, signifying the importance of the sampling time (Bloom et al., 2009).
Pyrethroids (synthetic pyrethrins) are one of the important groups of insecticides. As the usage of many chlorinated hydrocarbons has diminished in many parts of the world, synthetic pyrethroids have often served as replacements. Pyrethroids, broad-spectrum insecticides with a nonpersistent nature, low mammalian toxicity, and rapid rate of degradation, are becoming the first choice for use as insecticides both in the house and in agriculture, as well as in medicine for the topical treatment of external parasites. Some pyrethroids, such as permethrin, are used as arthropod contact repellents and can be impregnated into carpets, blankets, uniforms, and mosquito nets (Anadón et al., 2013; Saillenfait et al., 2015). The use of pyrethroids has increased constantly in the recent years. For enhancing their insecticidal activity, most pyrethrins and many pyrethroids are combined with a synergist, such as piperonyl butoxide, N-octylbicycloheptene dicarboximide, sulfoxide, sesamin, sesame oil, sesamolin, and isosafrole, which may also inhibit microsomal oxidation. The most important commercially available pyrethroids are allethrin, bifenthrin, cyfluthrin, lambda-cyhalothrin, cypermethrin, deltamethrin, permethrin, d-phenothrin, resmethrin, and tetramethrin (Anadón et al., 2013; Saillenfait et al., 2015).
Most of the previous research on pesticide-induced developmental and reproductive toxicity is focused on organophosphate and chlorinated hydrocarbon insecticides and very little attention was given to the pyrethroids. However, animal studies on pyrethroids such as cypermethrin, deltamethrin, and fenvalerate demonstrated insecticide-related reproductive untoward effects in both males and fetuses. These studies also showed growth retardation and/or fetal loss due to exposure to pyrethroids to pregnant animals. Pyrethroids have been reported to cause developmental neurotoxicity (Xue et al., 2013) and to affect the semen quality (Radwan et al., 2014) in humans.