Tasker eller skraldespande? Når det kommer til genbrug, er svaret kompliceret

Det virkede som et ligetil spørgsmål til biologiprofessor Paul Mensink:Er plastikposer, der indeholder genanvendelige genstande, bedre eller værre for miljøet end blå kasser?

Men spørgsmålet er blevet til en kompliceret gåde.

"Det korte svar er:'Det afhænger af'," sagde Mensink, direktør for kandidatmiljøprogrammer ved Det Naturvidenskabelige Fakultet, efter at hans team offentliggjorde en omfattende undersøgelse af Ontario kommuners politikker og praksis for indsamling og sortering af genanvendeligt materiale.

Hans forskning, offentliggjort i Environmental Challenges , viser mere end 40 % af kommunerne tillader brug af plastikgenbrugsposer. Han ønskede at undersøge begrundelsen for at tillade eller forbyde poser ved kantstenen.

"Det forekommer mig, at hvis man skal tillade eller forbyde det ene eller det andet, så har man brug for noget god videnskab bag. Jeg ville virkelig gerne have et solidt svar på, hvilken vej det skal gå. Og det gør vi bare ikke. ved godt."

Uklarheden falder ikke i god jord hos Mensink. Det er et markant hul, sagde han, fordi omkostningerne ved genanvendelse, der nu er delt 50/50 mellem industri og kommuner, snart vil blive båret af industrien alene.

I blot ét kvarter fandt hans team ud af, at næsten et ud af 10 hjem brugte mindst én plastikgenbrugspose, med et gennemsnit på 1,65 poser pr. hus. Ekstrapoleret til kun 160 hjem, kan det beløbe sig til mere end 10.000 genbrugsposer til engangsbrug om året, eller omkring 380 kg plast, der bruges til at aflede plast fra lossepladsen. Hvis alle i London brugte poser i samme hastighed som dette ene kvarter, ville det beløbe sig til 1,4 millioner poser om året.

Based on those numbers alone, Mensink was prepared to dismiss bags as environmental folly.

Until he and a team of environmental science students dug more deeply.

Some of the bags held shredded paper or easily dispersable plastics, they found. On windy days, the bags could prevent those items from becoming street litter as open-topped blue boxes couldn't.

Waste handlers can also pick up and sling bags into a recycling truck more quickly than they can sort through blue-box plastics and paper at curbside, and that can mean less tailpipe emissions.

On the other hand, there is the environmental cost of extracting the oil and manufacturing the bags in the first place, plus the cost of shipping them to a store and the cost a homeowner would have in driving to a store to buy them.

Then there's the question of what happens to the bags when they arrive at a recycling facility. Some municipalities have automatic debagging machines. At other facilities, someone has to rip them apart manually, at additional staffing costs and potential safety concerns for workers. Some facilities will send the bags back into the recycling stream, he found. At others, they are trashed.

"Initially I thought, 'Why use bags in the first place?' Single-use plastic bags sound like a bad idea because there are other, reusable options. However, when you take all the variables into account—it becomes a mind puzzle," Mensink said.

And if there's a single takeaway from their research so far, it would be that being environmentally responsible is a complex matter.

"I get that this is an overlooked issue, especially when our big aim here is to capture recyclables and keep them out of the landfill and waterways," said Mensink.

But consumption is costly. There is always a trade-off.

And calculating the true bottom line of any one solution always requires a deeper dive, he said. "Trying to measure the environmental impact of what we produce and consume is as complex as it is important."