LAST MARCH, during a scavenger hunt at the Ocean Shores Beachcombers’ Fun Fair, contestants found something new: Thermos-size aluminum canisters holding white powder residues.

Tide and time had scoured their labels, but contest judge Curt Ebbesmeyer, an oceanographer and freelance flotsam-ologist, recognized the canisters from his own Beachcombers’ Alert newsletter, which investigates worldwide flotsam findings. In 2003 a Dutch beachcomber identified similar beached canisters as pest bombs used to fumigate shiploads of grain. The white powder inside, aluminum phosphide, goes in the hold; rats and roaches don’t come out.

Ebbesmeyer and the beachcombers alerted state and Coast Guard officials. More canisters have been reported, from Long Beach to Ozette. The Washington State Department of Ecology has traced them to a Brazilian manufacturer and suspects the canisters fell or got tossed off a grain ship fumigated in Canada—but says there’s no chance of finding the offending vessel.

Ebbesmeyer has traced the oceanic paths of everything from sneakers and bathtub duckies lost off freighters to severed heads and bodies in death inquests (and full disclosure: I’m writing a book with him), so he’s not deep-sixing the canister case yet. He sees a clue in the dates scribbled in pencil on the bottoms of some canisters. And his army of beachcombers stands ready to look for more.