A replacement-first approach to toxicity testing is necessary to successfully reauthorize TSCA.

The Toxic Substances Control Act is the principal US law governing industrial chemicals. Over the past three and one half decades, it has become clear that a considerable toxicological information gap exists about chemicals in commerce. The current provisions of the US TSCA law have failed to fill, and perhaps even exacerbated, that gap. For at least the past 5 years, bills have been introduced before the US Congress to reauthorize TSCA.Filling the toxicological information gap has been one of the driving forces for this call for substantial change. This article describes efforts to modernize TSCA, with an emphasis on the new provisions that would be put into place if the legislation became law. The article shows that only by implementing a "replacement-first" strategy - a strategy that is not currently incorporated into TSCA reauthorization efforts - can TSCA modernization efforts potentially fill the toxic data voids.