Add biodegradable bags to the list of take-home carriers that retailers will not be able to distribute to customers at checkout when an Oahu-wide plastic bag bill takes effect next July 1.

Flanked by representatives from several environmental groups, Mayor Kirk Caldwell signed into law Bill 38 during a news conference at Ala Moana Regional Park on Thursday despite lingering questions about allowing compostable plastic bags.

Caldwell said that when he swims laps off Ala Moana, there’s nothing he hates more than feeling his arm getting entangled by a discarded plastic grocery bag.

"They end up going … into the water and they’re eaten by sea life, or they sink to the bottom, or they wrap around coral heads," he said. "They’re bad for the environment."

Bags meeting the definition of "compostable" will still be allowed, as will all nonplastic bags, including paper and cloth.

The original ban on plastic and nonrecyclable bags at the point of sale, approved by the City Council in 2012, exempted biodegradable bags. The original draft of Bill 38 sought to delete the exemption after environmentalists made it clear to Council members that biodegradable bags, when broken down into smaller pieces, can pose a danger to sea creatures.

But business interests including plastic manufacturers, Retail Merchants of Hawaii and the Hawaii Food Industry Association called the measure too draconian because paper and other types of bags cost more money. Council Chairman Ernie Martin pushed out a new version that still allows compostable bags.

To be allowed, the bags must meet the standards of ASTM International, the nonprofit formerly known as the American Society for Testing and Materials. The bill also states compostable bags must be specifically labeled.

"Compostables are better,"Caldwell said. "They break down very quickly."

Biodegradable generally refers to a material that can be broken down by natural processes; compostable means the end product is completely organic and therefore useful to the ecosystem.

Kahi Pacarro, executive director of Sustainable Coastlines Hawaii, said at the news conference that his group would have preferred banning compostable bags but called a ban on biodegradables "a step in the right direction."

Councilman Breene Harimoto, who introduced Bill 38, objected to allowing compostable bags but voted with his colleagues to pass the bill.

The July 1 ban will apply only to bags distributed at checkout. Plastic bags will still be OKto package loose items such as fruits, vegetables, nuts, coffee, candy, or small hardware items, and for frozen foods, meat or fish, flowers or plants, medications, newspaper, laundry and pet items.