run away as fast as you can if you do not know the risk.

Imagine, one year after your tenant live in the house, he sue you for two millions for headace cuased by the contamination, and you knowingly let them live in contaminated house, how do you think the court will rule.

On the other hand, if you know and can mitigate risk, this could be a sweet deal, if you can get the house for 50% of the market value.