substitution
... that substitution of a hazardous chemical can backfire if it turns out to be a "regrettable substitution" that unwittingly introduces a new hazard?
... that <b id="mwBVA"><a href="./Hazard_substitution" id="mwBVE" rel="mw:WikiLink" title="Hazard substitution">substitution</a></b> of a <a href="./Chemical_hazard" id="mwBVI" rel="mw:WikiLink" title="Chemical hazard">hazardous chemical</a> can backfire if it turns out to be a "regrettable substitution" that unwittingly introduces a new hazard?