permafrost
... that there are at least 13,000 sites containing toxic materials that are frozen in permafrost, many of which are expected to start thawing and releasing their pollutants in the near future?
... that there are at least 13,000 sites containing toxic materials that are frozen in <b id="mwAaU"><a href="./Permafrost" id="mwAaY" rel="mw:WikiLink" title="Permafrost">permafrost</a></b>, many of which are expected to start thawing and releasing their pollutants in the near future?