BP resumed spraying dispersants into the Gulf of Mexico today, according to The Associated Press. The company started using the chemicals a week after the spill first occurred, but had halted their use in order to test their environmental impact.

As we've reported, the chemicals -- which are intended to thin out the oil -- contain harmful toxins of their own. Their exact makeup is kept secret, but they do contain a compound "associated with headaches, vomiting and reproductive problems at high doses."

They're also called dispersants for a reason. The chemicals break up the oil and then disperse it, so instead of having the oil collect at the surface, dispersed droplets of oil can spread more quickly and in more directions. This means the droplets linger longer in the water, collecting on the seabed and harming the ecosystem offshore

Using dispersants involves a trade-off, according to a 2005 National Academy of Sciences report. It's a choice between diluting oil droplets more broadly and invisibly in the ocean and seeing thick gobs of it coating seabirds and beaches.

Nonetheless, the Environmental Protection Agency has given BP approval to move ahead with the chemicals, BP spokesman Mark Proegler told the AP.

The EPA has said that the federal government will regularly analyze the effect of dispersants on "the environment, water and air quality, and human health."