The lack of regulatory standards for degradable plastics in Hong Kong could hamper recycling efforts and cause harm to the environment, a local green group has warned.

The Green Earth also said the SAR is falling "far behind" on policies for biodegradable plastics, and urged officials to act as soon as possible.

The call came after the organisation found all 12 samples of disposable plastic umbrella bags it tested between October and November last year - claimed to be able to break down - contained a non-biodegradable substance called polyethylene (PE).

Thomas Chan, an environmental research associate of the organisation, said the absence of a uniform label on biodegradability means claims on products could be misleading.

"If they [are] only [one percent biodegradable], they can still fulfil their product claim, and that is why when we found out they all have PE... we are worried that they do not have a high standard on their biodegradability," he told RTHK.

The group also found that about one-third of 43 recycling spots it spoke to said they could take degradable plastics, which the government said are not suitable for recycling.

Chan cited a study on mixing recyclable plastics often used for food and beverage packaging, also known as PET, and polylactic acid (PLA), which is biodegradable.

"[In] PET recycling, if there are two to five percent of PLA added into the recycling machine, the machine will break down, as both materials have different melting points that affect the production. The recycling system might not work," he said.

"We recommend to state on the product where to collect biodegradable plastics, to ensure they biodegrade correctly in some facilities, and avoid these products being collected in some recycling facilities."

Chan said the government should reference international standards to formulate policy, adding that the European Union had in 2021 banned plastics that can only break down into smaller pieces but aren't fully biodegradable, something the SAR administration is now considering to phase out.

But without a standard in the meantime, Chan said consumers should not buy or use degradable plastics if they are unsure how well these products break down.

"We purchase these products [out of] goodwill, because we want to be actually environmentally friendly. But if there are no standards, we do not know how these products biodegrade. We have to understand biodegradable plastics are not a solutions to some disposable plastics," Chan said.