Susceptibility of Neonatal Rats to Xenobiotics

Current risk assessments of xenobiotics, especially industrial chemicals, are usually based on animal studies. Although many types of toxicity studies are conducted to cover different developmental stages, evaluation for the early postnatal period is not adequate. In this chapter, special attention is directed to the susceptibility of neonatal animals to chemical toxicity. We introduce comparative analysis of the toxic susceptibility of neonatal and young rats to 20 chemicals as examples, and discuss a range of uncertainty factors important in the risk assessment of susceptible groups such as neonates and infants. The results reveal higher susceptibility of neonates to 11 chemicals and lower susceptibility to six chemicals compared with young rats, and one exceptional case of highly specific toxicity in neonates. These phenomena show the importance of studying sensitivity to toxic insults in the early stages of life. It suggests that an uncertainty factor of 10-fold for human variability can be considered appropriate for risk assessment, unless particular toxicity in neonates or infants has been demonstrated, or there is other relevant and credible information regarding the chemical. Keywords: toxic susceptibility; neonates; infants; children; neonatal rats; risk assessment; uncertainty factors; xenobiotics, industrial chemicals