Parecía una pregunta sencilla para el profesor de biología Paul Mensink:¿las bolsas de plástico que contienen materiales reciclables en la acera son mejores o peores para el medio ambiente que las cajas azules?

Pero la pregunta se ha convertido en un enigma complicado.

"La respuesta corta es:'Depende'", dijo Mensink, director de programas ambientales de posgrado en la Facultad de Ciencias, luego de que su equipo publicara un estudio exhaustivo de las políticas y prácticas de los municipios de Ontario para la recolección y clasificación de materiales reciclables.

Su investigación, publicada en Environmental Challenges , muestra que más del 40% de los municipios permiten el uso de bolsas plásticas de reciclaje. Quería examinar la justificación para permitir o prohibir las bolsas en la acera.

"Me parece que si va a permitir o prohibir uno u otro, necesita algo de buena ciencia detrás. Realmente quería obtener una respuesta sólida sobre el camino que debería seguir. Y simplemente no lo hacemos". saber."

La ambigüedad no le sienta bien a Mensink. Esa es una brecha significativa, dijo, porque el costo del reciclaje, ahora dividido 50/50 entre la industria y los municipios, pronto será asumido solo por la industria.

En solo un vecindario, su equipo descubrió que casi uno de cada 10 hogares usaba al menos una bolsa de reciclaje de plástico, con una media de 1,65 bolsas por casa. Extrapolado a solo 160 hogares, eso podría equivaler a más de 10,000 bolsas de reciclaje de un solo uso por año, o alrededor de 380 kilogramos de plástico que se usan para desviar plásticos del vertedero. Si todo el mundo en Londres utilizara bolsas al mismo ritmo que este barrio, ascendería a 1,4 millones de bolsas al año.

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."