Burning plastic raises a stink

时间:2019-02-27 01:03:05166网络整理admin

By Debora MacKenzie THE plastics industry is coming under increasingly determined fire worldwide for claiming that incinerating its products does not significantly increase emissions of the deadly chemical dioxin. In a new report timed to spearhead a campaign to ban the production of PVC, the US arm of the international environmental group Greenpeace rejects the industry’s assertion that there is no correlation between the quantity of chlorine from plastics burnt in incinerators and their emissions of dioxin. And a leading member of the US Environmental Protection Agency’s (EPA) scientific advisory panel on dioxin backs Greenpeace’s conclusions. Dioxin is a toxic organic chemical that contains chlorine. It is produced when chlorine and hydrocarbons are burnt at high temperatures. The biggest source of chlorine in incinerated waste is PVC, a hydrocarbon that also contains chlorine. This has led many scientists to argue that it is the main culprit in causing dioxin emissions from incinerators. But factors such as the burn temperature and the supply of oxygen can also affect the production of dioxin, and this has made it hard to demonstrate whether there is a correlation between burning PVC and dioxin emissions. The plastics industry has lobbied hard against proposals to restrict the use of PVC. In 1995, the Vinyl Institute, an American industry association, commissioned a study into dioxin emissions from the consultancy firm Rigo and Rigo Associates in Cleveland, Ohio. The report, which was published by the American Society of Mechanical Engineers (ASME), found no links between burning PVC and dioxin emissions. It has since been heavily cited in industry campaigns-for example, to block limits on PVC packaging in Spain and Sweden. Greenpeace’s scientists question the methods used in the Rigo report. They note that it used only indirect measures of the input of chlorine and output of dioxin from incinerators. For example, to estimate chlorine input, the Rigo team noted the type of waste and the average percentage of chlorine in that waste type. Greenpeace also complains that the Rigo team looked for correlations between chlorine input and dioxin emissions within the data for different types of incinerator, rather than looking for a correlation across all types of incinerator. Valerie Thomas of Princeton University in New Jersey agrees that Rigo’s analysis was unlikely ever to reveal a correlation between chlorine input and dioxin output. Within categories of incinerator, she says, differences in dioxin emissions due to differences in chlorine input will be swamped by other sources of variation. “But if you compare different classes of incinerator, you can see an effect,” says Thomas. Indeed, in 1995 Thomas published a study comparing the dioxin emissions of different types of incinerator burning waste with widely different chlorine contents, in which she reported a significant correlation between dioxin output and the input of chlorine (Toxicological & Environmental Chemistry, vol 50, p 1). Ellen Silbergeld of the University of Maryland, who sits on the EPA’s dioxin advisory panel, also supports the Greenpeace analysis. She says that it is “appalling that the ASME was not more critical” of the Rigo report before endorsing it. However, a statement from the Vinyl Institute rejects the Greenpeace report. The Rigo study was “more sophisticated”,