Why are fetuses and infants more affected by toxic chemicals?

• A. They eat/drink more per body weight and have less developed immune systems.
• B. They eat less per body weight
• C. They have faster metabolism
• D. They are less exposed to toxins

Answer: (A)

The main idea here is that fetuses and infants are more susceptible because they receive a higher dose per unit of body weight and their defenses against toxicants are not fully developed.

They take in more food and fluid relative to their small body size, so the amount of chemical reaching their bodies per kilogram is larger. In the womb, chemicals can cross the placenta and accumulate in amniotic fluid, exposing the fetus; after birth, breast milk or formula can also deliver substantial amounts relative to body weight. At the same time, their detoxification systems—liver enzymes, kidney function—are immature, so chemicals are cleared more slowly and can reach higher concentrations in developing tissues for longer periods. The blood–brain barrier and other protective barriers are not fully mature, increasing risk of neurotoxic effects. Also, developing organs and tissues are rapidly dividing and differentiating, so disruptions can have lasting, more severe consequences.

So the best explanation is that greater exposure per body weight combined with immature immune and detoxification mechanisms makes fetuses and infants more affected by toxic chemicals.