Silver Hilton said it best; lead (pencil lead/slinkies etc.) isn't a real problem to salmon because of its non-solubility. Lead restrictions in National Parks are Federal regulations to protect migratory birds under the Migratory Birds Protection Act.

Resident salmon caught near Todd Shipyards and other industrial facilities likely accumulated those heavy metals from industrial effluents that contain dissolved metals. It's my understanding that resident blackmouth have shown levels elevated above background, but only sporadically, and at levels that are not harmful to fish or humans. As for non resident migrants, this is generally not a problem because of their relatively short exposure; they generally migrate past these areas relatively quickly on their way in or out. I happen to think that habitat degradation in these highly developed lower river areas has done more harm to salmon populations than the pollutants. Juvenile salmon cannot rear in these areas anymore, which affects the total carrying capacity of the river.

Places like Commencement Bay, Elliot Bay, Harbor Island, Eagle Harbor, etc. are still highly polluted and are just now beginning clean-up phases. I really wouldn't eat bottom fish caught in developed areas because these are residents that live in close association with the bottom sediments where these pollutants accumulate. However, fish that don't live in these areas generally come up clean in testing. This includes Puget Sound blackmouth and the forage fish species that they feed on (herring, surf smelt, sand lance). These species just don't seem to spend that much time in highly polluted areas so exposures are minimized. It wouldn't surprise me though to see accumulations above normal; just not at consistently dangerous levels.

Given these findings, the thing about using steel or aluminum as an alternative is the greater volume you would use because of its lighter density. The tradeoff is putting more of the stuff in the river because you use more. And like was mentioned, its not likely to bury as deeply, whether it be in the next drift down or in the lower river after it blasts downstream from winter storms. River mouths are generally depositional, and the excess lead gets deposited and buried in the lower rivers like sand, rocks, and other debris. And as it works its way downstream, the denser stuff will be deposited in deeper sediment layers.

I guess my opinion is that pencil lead and such is just another form of litter that should be minimized while on the river. Practice good fishing techniques. If your consistently dragging bottom (instead of bouncing), take some of it off. If your constantly hanging up, move, or switch to a float. And if you pull up that loooong piece of line attached to the bottom, take a minute to pull it out and stick it in a small trash bag (a must for the back of the vest).