Soon after the Deepwater Horizon rig exploded into flames and sunk more than three months ago, a chemical called Corexit 9500A was used to disperse the oil. That didn't mean it was gone, just spread out in the water column more so that it is 1) less noticeable, and 2) has a better chance to degrade or to simply dilute further away. But many questioned whether the dispersant chemical itself wasn't a danger to aquatic wildlife.
EPA has been testing Corexit and seven other dispersant chemicals to see if any substitutes are less toxic. Well, it turns out they are all pretty much the same level of toxicity when mixed with Louisiana Sweet Crude Oil. According to EPA, "these results confirm that the dispersant used in response to the oil spill in the gulf, Corexit 9500A, when mixed with oil, is generally no more or less toxic than mixtures with the other available alternatives. The results also indicate that dispersant-oil mixtures are generally no more toxic to the aquatic test species than oil alone."
Some have suggested that the fact EPA had to do testing in the first place, i.e., didn't already have the toxicity data for these chemicals, demonstrates that the Toxic Substances Control Act (TSCA) is totally ineffectual. The 63,000 or so existing chemicals that were grandfathered onto the TSCA Inventory over 30 years ago had no testing done at the time and only the most high volume ones produced during a certain period have had extensive data gathered on them. New chemicals undergo a rigorous review by EPA, but based almost entirely on computer models and comparisons to chemicals of similar structure. Most new chemical notifications include no toxicity testing data, and none is required under the current law unless EPA can show the likelihood of sufficient harm (which is hard to do when you have no data on which to base an assessment of harm).
Congress has started its August recess, after which they will focus mostly on trying to get reelected. So it looks like next year for TSCA reform.