Chemicals are integral to many everyday products, from electronics and toys to building materials and household goods. But environmental, health and consumer advocates say the agencies responsible for protecting Americans from exposure to harmful chemicals are allowing too many dangerous substances into the market without testing them for toxicity. Some goods, such as medicines, are tested for safety before they can be sold, but many common products do not go through premarket safety screening. Many concerns focus on infants and young children, who are especially sensitive to toxic hazards. Chemical manufacturers say the existing regulatory system works effectively and can be tightened to address new concerns, but critics argue that a precautionary approach — which would require producers to show that materials are safe before they can be marketed — would protect consumers more fully.