Retailers have long considered plastic bags basic to good service. Supermarket clerks toss tofu, eggs and ice cream into individual clear plastic bags to prevent a mess should the products’ own wrapping somehow break. More plastic bags are often provided just in case, then it all goes into bigger shopping bags.

But concerns that the estimated 30 billion plastic shopping bags utilized every year are contributing to global climate change when incinerated have prompted the government to call for restraint.

The April 1 revision to the Containers and Packaging Recycling Law of 1995 requires retailers generating large amounts of plastic waste to cut back. Businesses must report to the government every year on what efforts they have taken toward this end, and face fines if no improvement is made.

Following are some basic facts about plastic bags:

What are plastic shopping bags made of?

Most bags are made of polyethylene, itself a product of nonrenewable crude oil and natural gas. According to the Japan Polyolefin Film Industry Trade Association, each bag requires 18 milliliters of oil.

Is Japan trying to reuse its plastic?

Yes. According to the Environment Ministry, the amount of plastic waste being reused rose by more than three times to 6.1 million tons in the decade to 2004. That represented a little more than 60 percent of total waste plastic.

However, most of that plastic was incinerated as fuel, which releases carbon dioxide into the atmosphere.

Should Japan continue burning, that could become problematic because the country must cut greenhouse gases to 6 percent below 1990 levels by 2012 to comply with its Kyoto Protocol commitment. Instead, Japan is 14.1 percent above the benchmark today and carbon dioxide emissions are still rising.

How much plastic gets recycled?

The Environment Ministry said there are no specific figures for how many bags are recycled. However, of total reused waste plastic in 2004, about 13 percent was not burned but converted into new products. Otherwise, 26 percent of all plastic waste went into landfill and 14 percent was incinerated without being used as fuel, the ministry says.

What party is responsible for recycling plastic?

Local governments are tasked with collecting and separating household garbage, and pay private contractors to incinerate or recycle the refuse. Industrial waste, on the other hand, is the responsibility of corporations, and they can choose whether to recycle.

When Japan recycles plastic, how does the process work?

In the most common method, workers at recycling plants separate plastics made of polyethylene (PE, such as plastic bags) and polypropylene (PP) from those using polystyrene (PS). PP goods include wrappers for stationery, while PS is used for meat and fish trays.

The PE/PP batch gets shredded, washed, filtered, dried and molded into pellets used to make such products as garden stakes and planters. Some plastic bags are converted into new plastic bags, but since separating PE from PP adds to recycling costs, this is rare.

Trash cans are often labeled “moeru gomi” (burnable garbage) and “moenai gomi” (nonburnable garbage).” Where should plastic bags go?

That depends on the local jurisdiction, said Jun Nishimura of the Environment Ministry.

In the past, plastic bags were classified as nonburnable because they released the carcinogen dioxin into the air when incinerated. Now that measures have been taken to drastically cut dioxin emissions, many local governments classify plastic as burnable, Nishimura said.

Does that mean it’s really OK to incinerate plastic bags?

“Because of advances in incineration techniques . . . the only emission raising concern from an environmental perspective is carbon dioxide,” Nishimura said.

But Atsushi Takatori of the Tokyo-based Environmental Research Institute said incineration of plastic releases many other dangerous substances in addition to carbon dioxide. He cited as examples large quantities of nitropolycyclic aromatic hydrocarbons — less carcinogenic than dioxin but emitted in large volumes — and possibly heavy metals as well.

“Everybody says it’s enough to only curb dioxin, but that’s ridiculous. It’s untrue,” he said.

Even Nishimura admitted Japan must do more in regard to climate change, in line with the government’s own “Reduce, Reuse, Recycle” campaign.

Despite progress, he said, “We haven’t achieved much in terms of the ‘reduce’ aspect,” he said. “So with this we’re hoping to cut waste, thus the amount of incinerated matter, and in turn, the amount of carbon dioxide emissions. Plastic bags are the symbol of that effort.”

Will retailers now have to charge for plastic bags?

To the chagrin of environmentalists, the law still does not require retailers to charge for plastic bags. It does encourage businesses to voluntarily charge, to make reusable shopping bags available and to confirm with customers whether they really need a plastic bag. The government proposes that retailers offer gifts as inducements to forgo bags, which ironically could result in new waste.

When it’s absolutely necessary to ask for a bag, is paper or plastic better?

There is debate about that. Nishimura said that overall, paper bags cause less damage to the environment when incinerated. However, according to the Film and Bag Federation, a U.S. plastics industry group, plastic grocery bags consume 40 percent less energy to produce.

But plastic bags take as long as 1,000 years to decompose, while paper bags require only about a month, according to the U.S. Environmental Protection Agency.

How much energy is saved by reusing plastic bags?

When 1 ton of plastic bags is reused or recycled, the energy equivalent of 11 barrels of oil are saved, according to the EPA.

What is being done around the world about plastic bags?

Last week, San Francisco banned plastic bags at large supermarkets in about six months and at big pharmaceutical chains in about a year, The San Francisco Chronicle reported. That follows a move in December by Paris to ban nonbiodegradable plastic bags some time this year.

In Ireland, a 2002 tax imposed on the use of plastic shopping bags cut the use of plastic shopping bags by more than 90 percent, the BBC reported.

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