phobos13013 writes "Here's an article just in time for 4th of July fireworks shows! The ACS's Chemical and Engineering News provides a fairly technical discussion about the hazardous chemicals in modern fireworks displays. Perchlorate is currently the oxidizer of choice in fireworks, but it is also known to be a thyroid blocker. Since perchlorates are water-soluble anions, they dissolve into groundwater quickly. A study performed last summer over a lake in Ada, Oklahoma showed that less than a day after a fireworks display, the lake's chlorate levels jumped by a factor of 1,000. It took weeks for the levels to drop back down to their baseline. On the other hand, heavy metals are used to produce the pretty colors typically associated with the best fireworks. The trend is to start using nitrogen-based oxidizing fireworks; they produce less smoke, which means a smaller amount of colorizing agents can be used in displays."