The chemical industry is heading for a slowdown as society turns against disposable plastics and the rise of recycling weakens demand, IHS Markit predicted at its annual World Petrochemical Conference.After climbing to multi-year highs, chemical earnings will drop this year and won’t recover until 2023 as environmental issues add to the drag from a downturn in the global economy, according to the global research firm.“Plastic waste I believe is going to be the sustainability issue of our time,” Jim Fitterling, chief executive officer of Dow Inc. and chief operating officer at DowDuPont, said Wednesday at the conference. “It represents not only the biggest risk to our industry,” he said, but also “one of the biggest opportunities.”