Lead author of a study into firework smoke, Teresa Moreno, Institute of Environmental Assessment and Water Research, IDAEA, Barcelona, Spain, suggests that many of the metals used to produce particular colors when a firework explodes are bioactive.

When a pyrotechnic display takes place it releases a lot of smoke, liberating minute metallic particles of lead, copper, strontium, potassium and magnesium, just micrometers or smaller in size, which can be inhaled deep into the lungs. In the absence of a ban on fireworks, spectators should stay well back in a
place not affected by the smoke and pay attention to the wind direction to reduce their exposure, the team says.

• Effect of fireworks events on urban background trace metal aerosol concentrations: Is the cocktail worth the show?,
  Teresa Moreno, Xavier Querol, Andrés Alastuey, Fulvio Amato, Jorge Pey, Marco Pandolfi, Nino Kuenzli, Laura Bouso, Marcela Rivera y Wes Gibbons,
  J. Haz. Mater. 2010, 183 (1-3): 945-949.
  DOI: 10.1016/j.jhazmat.2010.07.082