Biomarkers of pyrethroid toxicity in fish

Pesticides contribute to human welfare by reducing vector-borne diseases and protecting crops against pests. Insecticides are the most widely employed pesticides for agricultural, domestic, and industrial pest control. However, some insecticides such as synthetic pyrethroids, analogs of the natural pyrethrin, persist in the environment and result in different hostile effects on nontarget organisms. Due to a continuous increase in the use of pyrethroids and their widespread application, different generations and types of pyrethroids have been frequently reported from environmental media, biota, and residential areas. Synthetic pyrethroids are observed to be less toxic to mammal and birds, relatively toxic to amphibians, and highly toxic to aquatic organisms including fish. Here, we review the occurrence, fate, biotransformation, and bioavailability of pyrethroids in waters. We also present biomarkers used to evidence toxicological effects of pyrethroids on fish. Toxic effects include oxidative stress and damage such as production of reactive oxygen species and lipid peroxidation; neurological behavioral inconsistencies; developmental effects such as delayed development and signaling; biochemical alterations of protein, glucose, and enzymes; hematological changes in white blood cells, red blood cells, and hemoglobin; physiological effects on metabolism and heart function; histopathological changes in the brain, liver, and gills; molecular toxicity including DNA damage, micronuclei induction, and altered gene or mRNA expression; and reproductive or endocrine disruption, e.g., disrupted pathways and signaling. Mechanisms of toxicity and control measures are also discussed.