Are Galvanized Steel Planters Safe

Yes, using galvanized steel for planting is considered safe. Zinc is one of the most widely used metals in the world. In galvanized metal, the zinc alloy coating protects the underlying steel from corrosion and extends the life of the steel.

Learn more: What is zinc plated steel? Does zinc rust? How long does galvanized steel last?

In small amounts, zinc is an essential element needed by the body and is one of the most abundant elements in the human body (12 p.175). Therapeutically zinc is used in human medicine to treat zinc deficiency and strengthening immunity. Zinc oxide is an ointment ingredient used to treat burns and infectious and skin diseases. Humans, plants, and animals depend on zinc.

Related: The importance of zinc and The function of zinc in the body.

National Academy of Sciences (NAS) established the Recommended Dietary Allowances (RDAs) for zinc at 11 mg/day for men and 8 mg/day for women (12 p.175). Harmful effects generally begin at levels 10-15 times higher than the amount needed for good health

How readily do our bodies absorb zinc from our environment?
More than one study, reviewed in the Toxicological Profile for Zinc, has shown zinc can be absorbed into the human body following inhalation (breathing it), ingestion (eating it), or dermal contact (skin). No estimates of the bioavailability of zinc after inhalation of zinc particles in air, ingestion from water and soil, or skin contact with bath water or soil were located. If zinc is partly present in an irreversibly adsorbed state in soil, this part is not available for skin absorption. (12 p.184)

Zinc in food?
Zinc is present in pretty much all of the foods we eat. Zinc is found in high concentrations in animal products, especially some seafoods. Fruits and vegetables were found to have lower concentrations of zinc. A diet of dairy products, meat, fish, poultry, grains, and cereals provides approximately 77% of the daily zinc intake.

Food Average zinc/kg
Meats, fish, poultry 24.5 mg zinc/kg
Grains (cereal products) 8 mg zinc/kg
Potatoes 6 mg zinc/kg
Wheat 41 mg zinc/kg
Rye 13 mg zinc/kg
Rice 8-20 mg zinc/kg
Vegetables 4.31 mg zinc/kg
Fruit 1.66 mg zinc/kg
Mushrooms 9.7 mg zinc/kg
Cocoa 35 mg zinc/kg
Tea 35 mg zinc/kg
Coffee 6.7 mg zinc/kg
Peas 3.3-3.5 mg zinc/kg
Onions 3.4 mg zinc/kg

(table above from 12 p.176-177)

Does zinc bioaccumulate in the food chain?
Zinc bioconcentrates moderately in aquatic creatures, and bioconcentrates higher in crustaceans and bivalve species than in fish. Zinc may concentrate in plants grown in industrially contaminated soil, but it does not biomagnify and accumulate through the terrestrial food chain. (12 p.184) The concentration of zinc in plants depends on the plant species, soil pH, and the composition of the soil. Plant species do not concentrate zinc above the levels present in soil. (12 p.159)

Does zinc get recycled into the soil?
Biological degradation of zinc complexes in soil is necessary for the normal operation of ecosystems to facilitate the recycling of zinc from litter, feces, and dead organisms. In some environments, bacteria and fungi are able to oxidize zinc sulfide producing zinc sulfate, which will solubilize in the soil solution (12 p.161)

Although there is risk to children of exposure to zinc in their environment, a 2005 report by the Agency for Toxic Substances explains, "the zinc found in and exposed to children in home products such as paint, ointments, galvanized metals, coins, and dietary supplements, should be low and will not disproportionately affect children." (12 p.185)

At the normal rate of galvanized steel corrosion, soil concentrations of zinc inside a galvanized steel container garden will remain well below harmful levels.

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