Combined toxicity of pyrethroid insecticides and heavy metals: a review

Co-occurrence of pyrethroid insecticides and heavy metals in the environment may produce combined toxic effects that are higher or lower than toxic effects of single chemicals. Here, we review the interactive effects between various pyrethroid insecticides and metals. Specifically, metals inhibit the microbial degradation of pyrethroids in soil and water environments, but metals facilitate pyrethroids photodegradation. Metals have shown both inhibition and improvement of the detoxification of pyrethroids in living organisms. Exposure to the mixtures of metals and pyrethroids causes enhanced or reduced toxic effects regarding acute toxicity, reproductive and developmental toxicity, hepatotoxicity, immunotoxicity, oxidative stress, biochemical and hematological alterations and genotoxicity, in comparison with those of single chemicals. The few studies that evaluated combined toxicity using specific models revealed both synergistic and antagonistic interactions between pyrethroid insecticides and heavy metals. Limited information is available regarding the underlying mechanisms responsible for the combined toxicity.