n 2006, they said that five chemicals — lead, methylmercury, arsenic, PCBs and toluene — should be considered toxic to the developing brain. The doctors did not conduct new studies on these substances, but now, based on a reading of new research, which has been exploding in recent years, they've added six more:• Manganese, a natural chemical found in drinking water in places like Bangladesh.• Fluoride, in high concentrations, which has caused problems in China, though the low levels added to American drinking water are presumed safe.• Chlorpyrifos, an insecticide used on golf courses and in agriculture among other places.• Dichlorodiphenyltrichloroethane (DDT), an insecticide banned in the U.S. in the 1970s, but still used in some countries.• Tetrachloroethylene (PERC), a solvent used in dry cleaning and metal degreasing.• Polybrominated diphenyl ethers (PBDE), also known as flame retardants and often found in furniture, electronics and clothing, including children's pajamas.