San Francisco will soon have the most extensive ban on Styrofoam in the country.

On Tuesday, the Board of Supervisors unanimously passed legislation by Supervisor London Breed that bans the product in food packaging such as meat trays, packing peanuts, ice chests, dock floats and mooring buoys.

The legislation goes into effect Jan. 1. Breed gave grocers a six-month waiver to phase out meat trays made of Styrofoam, which is technically known as polystyrene foam.

The legislation also gives the city Department of the Environment the power to make exceptions for categories of polystyrene use. The department’s spokesman has said that it will probably allow companies that ship medicines at prescribed temperatures to continue using polystyrene for at least a few more years.

Polystyrene has been a mainstay in the packing industry because it’s inexpensive, lightweight, effective and doesn’t disintegrate if it touches water. But it also takes centuries to decompose, clogging landfills and, when it gets into the water, contaminating the food chain and ecosystem.

Breed hailed the legislation’s passage.

“We just passed the toughest anti-Styrofoam law in the country, and we did it unanimously! This is a huge step for our environment and health. San Francisco is on our way to leading the country on environmental policy — again!”

— Emily Green

Play nice? After a state Senate primary race with relatively few negative attacks, the race between San Francisco Supervisors Scott Wiener and Jane Kim was expected to get rougher this fall.

Unless it doesn’t. In a letter Wednesday, Kim called on Wiener to sign a positive campaign pledge, essentially barring his campaign from running defamatory advertisements. In fact, one stipulation is that Wiener doesn’t mention Kim in his campaign at all — in addition to sharing copies of his ads with her before they are mailed or broadcast.

In return, Kim promised to do the same. All they had to do is sign on the dotted line. The election is “too important to not focus on solutions” and instead attack each other, Kim said in a letter.

But Wiener isn’t keen on pulling out a pen just yet. In a response letter, campaign spokesman Jeffrey Sparks expressed surprise and accused Kim of running an “intensely negative, false and misleading campaign” in the primary.

“It’s odd, at best, that your campaign, after engaging in such negative and defamatory campaigning would then turn around and insist that we not engage in factually accurate campaigning about each other’s record and not even mention each other’s names,” he said.

Sparks stipulated that if she apologized, he would consider signing the agreement.

That sparked another letter from Kim’s campaign. In a note to Wiener, Kim spokeswoman Julie Edwards defended their campaign, saying they made no negative or false comments during the primary.

“The only false statements we are aware of in the primary campaign came from your campaign, including the ridiculous attack a few weeks ago that Jane Kim was somehow responsible for the election of George W. Bush,” Edwards wrote.

She added, “The fact that even this simple request ... was met with a string of invective is not a good sign.”

Then she asked again for Wiener to sign the promise to run a positive campaign. But it looks as if neither candidate will be putting pen to paper any time soon.

— Lizzie Johnson

Housing fire victims: The victims of recent fires in the Mission and elsewhere in the city could get help finding new housing.

Supervisor Scott Wiener wants to give people displaced by the fires preference in applying for below-market housing units. Like other tenants who have been evicted or displaced, people who have lost their homes because of the fires would have a better chance at the units.

“Victims of fire have no time to prepare for their displacement — fires are sudden and merciless,” Wiener said in a statement. “By giving them a real shot at an affordable housing unit, we will make a real difference in keeping them in San Francisco and in their community.”

The legislation doesn’t specify when the fires had to occur — within the past 18 months is one option.

The ordinance will next go to the Land Use and Transportation Committee for a hearing.

— Emily Green

Email: cityinsider@sfchronicle.com, egreen@sfchronicle.com, ljohnson@sfchronicle.com Twitter: @sfcityinsider, @emilytgreen, @lizziejohnsonnn