Cholinesterase inhibition and toxicokinetics in immature and adult rats after acute or repeated exposures to chlorpyrifos or chlorpyrifos-oxon

► Effects of age or dose regimen on cholinesterase inhibition by chlorpyrifos/oxon. ► No age-dependent differences in chlorpyrifos cholinesterase inhibition. ► Pups had lower cholinesterase inhibition at comparable blood chlorpyrifos levels. ► Dose rate caused differential effects on cholinesterase inhibition across tissues. ► Chlorpyrifos-oxon inhibited red blood cell but not brain cholinesterase.