NEW YORK - Litigation could cost the plastics industry and its insurers US$20 billion (S$28.5 billion) in the United States over the next eight years, according to a report backed by the United Nations and an Australian billionaire.

Companies including petrochemical and consumer goods firms might be liable for the cost of cleaning up plastic pollution, while emerging legal pathways to claim for the harm to society threaten to add to their corporate liabilities. Beyond 2030, legal claims "could be an order of magnitude larger".

The report from Australian mining tycoon Andrew Forrest's non-profit Minderoo Foundation is the first time lawyers and data analysts have modelled how the cost of plastic-related pollution translates into the likely compensation payouts.

The research is supported by the United Nations Environment Programme Finance Initiative, a collaboration between the UN and the finance industry.

An industry trade group, the Plastics Industry Association, responded to the report by arguing that the material outperforms alternatives in cost and sustainability, and litigation could derail clean-up efforts.

"Any litigation will divert funding and resources from the solutions that actually address plastic waste" such as recycling and sorting facilities, said Mr Matt Seaholm, the group's chief executive officer, in an e-mail. The association is looking forward to working with "partners that are more interested in supporting solutions than pointing fingers".

More than 300 million tonnes of plastic are produced every year. At least 14 million tonnes end up in the ocean, where they are ingested by animals and can enter the human food chain, according to the International Union for Conservation of Nature. Like climate change-related risks, plastic pollution can impact the insurance industry through liabilities.

"Similar to fossil-fuel companies and the climate impact of their products, plastic producers are the 'pin-ups' for having created the most extreme externalities ever witnessed in the history of mankind," said Mr Forrest, who is executive chairman and founder of iron ore giant Fortescue Metals Group and Fortescue Future Industries.

The US$20 billion figure is an order of magnitude smaller than losses the insurance industry has suffered from asbestos-related lawsuits. Credit ratings agency AM Best estimates these at US$146 billion, but incurred over decades rather than from the first eight years of claims. Still, the report warns that plastics-related losses could ultimately be comparable in size.

Minderoo enlisted law firm Clyde & Co together with data group Praedicat to calculate the figure by tracing the value of environmental and human health damage, which is estimated to be hundreds of billions of dollars, through the existing legal avenues claimants could take to get compensation. Praedicat's models attached probabilities to successful claims over the effect of chemicals found in plastics.

Some research has linked chemical additives in plastics to health problems such as infertility, early puberty, developmental issues and metabolic disorders. The report estimates that the global social costs associated with these plastic-related chemicals exceeds US$100 billion a year.

Using legal precedents, including some judgments in the recent opioids lawsuits, the researchers calculated expected liabilities of US$20 billion in the United States. Other legal pathways resulted in smaller corporate liabilities.

The large gap between the estimated social cost of plastic pollution and the more than US$20 billion corporate liabilities is partly explained by the relative infancy of plastics litigation and test cases, and the difficulty of linking harms to particular producers of plastic.

Its supply chains include many actors and, unlike with tobacco lawsuits, for example, most people have been exposed to polymers.

Underwriters and risk managers create models to simulate the real world and predict the likelihood of different future outcomes. The report estimates that insurers would need to account for the worst case scenario of losses of US$100 billion when planning for how much capital they need to hold.

But the gap may narrow in the future as case law builds. There is a possibility of a large uptick in successful claims in the medium term, the report says.

The insurance and reinsurance industry make decisions with longer time horizons than investors and companies because they are calculating their exposures to future claims.

"In 10 years' time, the legal cases might be far stronger, the science far more damning," said Mr Dominic Charles, director at the Minderoo Foundation. BLOOMBERG