Preventing or reducing zinc leaching from galvanized steel fishways and grates
There is some concern that the zinc leaching from galvanized steel may impact salmon migration. I've been tasked with finding information on how to "age" or "pickle" the galvanized steel grates prior to installation in a fishway. Does anyone have any thoughts or information on such a process?Tammy Mackey
- Bonneville Dam, Oregon
Hi, Tammy. The galvanizing can be easily and quickly removed by most plating shops by simple immersion in hydrochloric acid. But that would leave you with raw steel that will rust quickly, and consequently the question of what to do to stop the corrosion.
Ted Mooney, P.E. RET
Brick, New Jersey
I have a galvanizer client in Chile. He has found that galvanized steel with lead (about 1%) cages in the ocean lasts only about 2 years, whereas galvanized steel cages with zero lead lasts 10 to 20 years.
In the galvanizing book written by Heinz Bablik it is stated that a galvanized coating containing 0.3% or more tin gives a potable tank lifetime of one year, whereas under 0.3% tin the potable water tank lasts 25+ years.
I was reared in Portland and know all the galvanizers there and in Washington. I expect you may have to get galvanized steel from central California for it to be lead free. Also some galvanizers use bismuth and/or nickel. Most galvanized products do not remain fully IN the water on a continuous basis so corrosion data is limited.
- Hot Springs, South Dakota
Thanks. I don't think anyone had thought of lead leaching from galvanized products, seems they were all more concerned about zinc, but any heavy metal is going to affect a salmon's ability to successfully spawn in their natal stream. Perhaps finding fiberglass grates would be a better option.
Thanks again for the response,
- Bonneville Dam, Oregon
While zinc is toxic to fish, I think it's extremely unlikely that the sort of dissolving you fear could ever cause high enough concentrations to be a problem. Before you go off looking for a solution, find out if you have a problem. Check some water samples for Zinc.
October 10, 2007
you didn't mention if you are speaking of fresh or seawater.
In Scotland there is much salmon farming. Many of the salmon farms have hot dip galvanized walkways, handrails and netholders. Typically these items which are in the splash zone, neither always submerged nor completely dry. Expected (and achieved) life is 10 years after which the steel is stripped of remaining galv and regalvanized.
There's been so suggestion of a problem with Zn for the fish.
In the freshwater scene, its common to have submerged steel (galvanized) in fish ladders round hydro schemes, and at intake grilles (to prevent fish and other items getting sucked into the turbines). The life of these (and therefore the rate at which Zn is dissolved into the water) is very variable, and much less predictable than the saltwater locations. This depends very much on the acidity of the water, some areas of peat runoff causing high acidity. This peat stained (brown) water isn't so good for fishing, but is great from whisky production!
October 10, 2007
Since you are talking about salmon migration, you are talking about flowing water. I seriously doubt if you could find zinc or lead or tin in the very low parts per trillion. If you could, your gate would not last 6 months.James Watts
- Navarre, Florida
April 21, 2009
What about using a galvanized steel tank to keep freshwater fish in, in a backyard aquaponics set-up (filtering fish waste through beds containing vegetables grown in gravel).
The water is going to have 3 ppm NaCl - just pool salt, apparently that keeps the fish healthier, and has no impact on most vegetables (although you can't grow strawberries)
The forum I have been on (backyardaquaponics.com) seems to have a lot of fears around zinc (and lead, potentially from the solder line) killing the fish, but I can't find anyone who actually has had this happen.
A chemist friend has said that the dissolved CO2 in the water from the fish breathing will acidify the water, so this could cause leaching.
Stocking rates will be between 10-20 fish up to 0.5 kg - 1 kg each in a 1800 L gal tank.
I should also say, in Australia, it is common to keep your rainwater in a galvanized tank - many people (including my 7-days-of-work-a-week Dad of 78 years old who made the tank for me) grew up on that water.
- Melbourne, Victoria, Australia
June 6, 2009
Hi, Karen. I don't mean to trivialize my response, but people aren't fish. If you search other threads here you'll find that even very small exposure to zinc kills parrots, and -- while I don't know it to be true -- it is very possible that low concentrations of zinc endangers fish.
October 16, 2009
I am using galvanized brackets in my pond as ledges to put pants on, could the chemicals involved with the metal leak into the water over time and kill my precious fish? thanks!roy galley
- essex, england