Environmentalists warned that Honolulu’s municipal government would diminish the effectiveness of Oahu’s so-called plastic bag ban by including exceptions and alternatives that allow windblown rubbish to proliferate. Little more than a week after the ban took effect on July 1, it seems obvious these critics were correct.

Some retailers simply replaced thin plastic bags with paper or thicker plastic ones, which comes as no surprise given the loopholes in the law, but does not further the goal of reducing disposable packaging at retail checkouts.

The City Council and mayor should act swiftly to tighten the ordinance, and not leave Oahu — the biggest polluter in the island chain — with the weakest law in the state.

Retailers who are following the letter of the law by offering customers thicker plastic bags at checkout should think better of this tactic. The spirit of the law is to reduce the use of single-use plastic bags altogether, not to replace them with longer-lasting plastic bags on the claim that the new ones will be used more than once.

Neither is the spirit of the law to encourage retailers to simply substitute paper for plastic. Although paper is recyclable and not a threat to marine life in the same way as lightweight plastic bags, the goal is to reduce the number of disposable bags consumers use to carry out their purchases.

The best approach encourages customers to bring their own sturdy totes for groceries and other purchases, not for retailers to substitute one throw-away for another.

The city government diluted the clarity of that goal and the efficacy of law itself by inserting compromise language in an ordinance that purports to ban plastic checkout bags while still allowing certain types on the claim that they are reusable or compostable.

Retailers who have exploited those loopholes should instead trust that their customers can adapt to bringing their own durable carryalls — and encourage them to do so.

To be sure, many retailers are observing not only the letter of the law but also its spirit. Some are offering a premium to shoppers who bring their own bags, while others are charging a reasonable price for durable reusable bags.

While consumers may reward these retailers with greater loyalty, and spurn those who thwart the law’s central intent, as one environmental petition urges, it’s not enough for consumers to try to shame stores into doing the right thing. The City Council and mayor must do their jobs, and strengthen the law so that Oahu sees the same benefits as neighbor islands that have enacted stricter measures. Those benefits include a measureable decrease in the amount of plastic rubbish blowing around, improving the general appearance of the islands and reducing the threat to marine life that occurs when plastic products enter the ocean and are ingested by creatures large and small.

There is a financial incentive, too, for businesses and customers to wean themselves from the overreliance on disposable checkout bags. The flimsy plastic checkout bags now banned on Oahu were the cheapest to manufacture, at about 2 cents a bag. Bags legal under the overly broad compromise law cost about 10 to 14 cents a bag to make, an expense that surely will be passed on to the customer.

Before the ban took effect, the city government surveyed Oahu businesses to see how they intended to comply with the ban, and the results only intensified the environmental concerns now proved valid. Of those retailers who intended to keep offering bags, 44 percent planned to offer recyclable paper bags, 25 percent planned to offer compostable bags (even though there is no commercial composting facility on Oahu, and the city has advised residents to dispose of such bags as general waste) and 31 percent planned to offer reusable bags, including a thicker plastic variety allowed under the law.

Oahu’s municipal government gave retailers too many outs, and, not surprisingly, some stores took them. The standard to follow, though, is those businesses that have welcomed the law in letter and spirit, and encourage customers to bring their own durable, reusable totes.

The city government should act swiftly to ensure that this becomes the norm on Oahu, if we are to reduce the litter that mars the island from mauka to makai.