If there’s one line in the 1967 classic film The Graduate that has aged poorly, it might be Mr McGuire’s advice to a young Dustin Hoffman to find his future in plastics.

Now, just over 50 years later, plastics are more commonly cast as retro at best, and an environmental menace otherwise.

The Royal Society’s report last week on plastics and the environment then makes for interesting reading.

The report’s press release highlights badly managed plastic waste that finds its way into the ocean. It is a real and substantial problem. But the report’s evidence suggests perhaps a few heretical conclusions are hidden between the lines.

The worst place for plastic to wind up is in the ocean. Before it breaks down, plastic waste can harm or kill large marine animals; after it breaks down into microparticles, it enters the food chain. Neither is good. The report suggests that by 2050, the ocean will contain more plastic than fish, by weight. Keeping plastic out of the ocean matters. But how much New Zealand waste winds up there?

Unfortunately, while the report tells us a lot about the global problem, it doesn’t offer enough data on the situation here at home.

The report tells us that about a fifth of the ocean’s plastic waste originates from marine activities like fishing and shipping, with about 640,000 tonnes of fishing equipment discarded at sea each year.

But it does not tell us about the relative contributions from New Zealand.

The report points to research published in 2015 showing the largest contributors to marine plastic waste. Countries contributing substantially to the overall problem either have a high proportion of mismanaged waste, or a small proportion of mismanaged waste combined with high overall volumes of waste. In 10 of the 20 countries estimated as the source of the largest volumes of plastic waste reaching the ocean, more than 80 percent of all waste was considered ‘mismanaged’.

Obviously, New Zealand does not make that list, as waste here is better managed than in places like China, Indonesia, the Philippines, Vietnam and Sri Lanka – the top five countries who together contribute more than half of the world’s total mismanaged plastic waste. Old landfills, like the abandoned landfill that spilled into Fox River during flooding, could here count as mismanaged – but that is hardly representative of New Zealand’s newer landfills.

But New Zealand does contribute to those poor-performing countries’ problems by sending our waste overseas for processing: more than 41,000 tonnes of plastic waste was exported from New Zealand in 2017.

Why does New Zealand plastic waste make its way overseas?

Recycling a lot of plastics simply is not economical here: It costs more to turn many categories of waste plastics into new materials than to create new material. The report does a good job of explaining the basic economics. When that waste is sent overseas for processing, it can too easily wind up in the oceans. The report notes that since China’s ban on such imports, plastic waste in New Zealand has been stockpiling here and now presents fire hazards.

The report presents data on the kinds of plastic waste on beaches internationally – often things that can make their way to the beach as litter washed down through storm drains. The report notes that storm water in New Zealand is discharged directly into the ocean or into rivers but presents no comprehensive statistics on waste found in New Zealand, largely because the numbers here do not exist.

Twenty-year-old data from the Chathams and Stewart Islands was cited to provide evidence that discarded fishing equipment formed a substantial part of the waste then-found – but we don’t know whether that data tells us anything useful about the situation today. The Ministry for the Environment’s consultation document on the plastic bag ban hoped that by 2021, a national litter database might provide some help. Until then, we are flying blind.

Overall, the report tells a compelling story about the international plastic burden imposed on the oceans and the need for improvement. But it is difficult to take the leap from that evidence to the report’s suggestion that New Zealand should focus on reducing plastic use.

The report identifies a few relevant gaps in the local knowledge base. In short, we do not know where, how, and how much local plastic enters the environment, and we do not know the country of origin of the plastics that do show up in New Zealand waters. It is rather difficult to make suggestions of cost-effective policy around reducing plastic use in the absence of good information.

Another alternative remains almost heretical, but consistent with the case presented in the report: Modern New Zealand landfills are the safest place for plastics and we should make greater use of them. Too many materials put into the recycling stream simply cannot be cost-effectively recycled and risk either stockpiling here in less-suitable facilities or being sent abroad and risking outcomes worse than a well-managed New Zealand landfill.

Modern landfills are constructed to deal with any leachate from the disposal of plastics. Fees charged at the tip are designed to ensure that the landfill covers its costs. When those fees are set properly, all of the costs of waste disposal are incorporated into the price each of us pays for a council rubbish bag or for a trip to the dump – including the cost of the land purchased for the tip.

Contrary to the usual stories of shortages of land for landfill, fairly simple back-of-the-envelope calculations show it would take thousands and thousands of years before lack of land for landfill became anything close to a problem. The more relevant problem is ensuring that tips are properly constructed – land is a small part of the overall cost of a new site. And at the end of their useful lives, landfills do not have to be a blight. Hamilton’s superb gardens, for example, are built over its old rubbish dump.

Rather than using the waste disposal levy to encourage waste minimisation, we might instead use it to help councils deal with legacy issues from ancient landfills built to inadequate standards with insufficient provision for whole-of-life contingencies, and to improve the filtration of storm-water outflows to keep litter from flowing out to the sea.

Mr McGuire’s advice from The Graduate might not be quite so outdated; plastics feature in the composite materials in the most advanced aircraft. But we do have to make sure plastic waste does not wind up in places it does not belong. That requires better evidence about the extent and nature of the problem in New Zealand, and about cost-effective solutions. In the meantime, landfills are both retro and effective.