Kids who romp around on wooden structures in playgrounds could face a higher risk of contracting lung or bladder cancer than those who don’t come into contact with the equipment, the head of the federal Consumer Product Safety Commission said on Friday. Nearly all wooden playground equipment in the U.S. has been treated with the pesticide chromated copper arsenate, which can leave arsenic residue on kids’ hands — and, kids being kids, the residue can too easily end up in their mouths. The agency is considering a ban on the arsenic-based preservative in playground equipment; consumer groups petitioned for such a ban in 2001.