A recent study of lake water in Ada, Okla., before and after annual fireworks displays found that the perchlorate concentration in the water increased by up to a factor of 1,000 in the hours after the show, exceeding several states' maximum allowable levels for drinking water. The levels took between 20 and 80 days to return to normal.This is particularly interesting since so many firework displays are over water. Perchlorate is especially dangerous to developing fetuses and eating fish from these waters may be dangerous. Also present in fireworks are various heavy metals including barium used to make the green colors. I won't recap the whole article but it goes on to talk about greener fireworks that burn cleaner and as a result they actually look brighter because they produce less smoke. Unfortunately, the greener fireworks cost more money and the cheap fireworks produced in China are winning the day.