What Materials are Safe?
How does one choose system components that are safe? Do we choose Stainless Steel or Brass. Of all the different plastics, which ones are safe? Or are there any of them, that are truly safe?
We will divide this discussion into three sections; metal, plastic, and concrete.
316 Stainless Steel is the optimum choice for pipes and fittings for aquaponics. However it is also the most expensive. People sometimes substitute lower grades of stainless steel, brass, copper, black or galvanized iron, and PVC pipe. In aquaponics systems, a good quality 304 Stainless is a good replacement for 316 stainless. If a person goes online and does their home work, they can save considerably over 316 stainless. Imported stainless quality ranges from excellent to poor. Personally we try to avoid stainless steel from India.
Most pipe and fittings are usually used for water or air. Since the air in an inside aquaponics operation is usually somewhat humid, even air lines need to resist corrosion. A large percentage of Brass fittings have some lead in its alloy. Lead is poisonous. Also brass has copper in it. If copper is not oxidized it does not present a problem. However copper is considered an active metal, meaning it readily reacts with many other substances. Most people have seen copper or brass items that have a blue corrosion on it. That blue is poisonous. We recommend not using brass or copper pipe fittings if at all possible. Doing so will slowly poison your fish.
We also do not recommend using black iron or galvanized pipe or fittings. Black pipe often has oil residue on it, even if it looks clean. That oil is poisonous to fish. So is the soap residue that remains if you try to clean it. Fish are very sensitive. Galvanized pipe is coated with Zinc, and zinc is also not good for fish.
Plastics are one of those tradeoffs, due to cost and ease of use, that every farmer has to consider. Our experience is that PVC and Polyethylene are the two safest plastics to use at room temperature. If heated to what we would call hot to the touch or hotter, that changes. The government allows different plastics to be used around food and food processing. If you are using a tank heater, do not place it next to the wall of a plastic tank.
Some equipment and packaging is made of different plastics and if you are going to use them, you will have exposure to those plastics. We have tried to eliminate plastics where ever we can, but in our modern world, it is just about impossible to eliminate plastics.
Fiberglass tanks are often used in aquaculture because of their great strength and their ability to mold into jus about any shape. Our personal preference is to not use fiberglass, as we have been on many older boats and the fiberglass is still off gassing what we consider an unacceptable smell. Many fish hatcheries use fiberglass tanks.
Our recommendation is to stay away from any epoxies, even ones NSF rated or FDA approved. Epoxy has BPA in it.
BPA is used to make certain plastics and epoxy resins; it has been in commercial use since 1957. BPA-based plastic is clear and tough, and is used to make a variety of common consumer goods (such as baby and water bottles, sports equipment, and CDs and DVDs) and for industrial purposes, like lining water pipes. Epoxy resins containing BPA are used as coatings on the inside of many food and beverage cans. It is also used in making thermal paper such as that used in sales receipts.
It is part of the bisphenols group of chemical compounds with two hydroxyphenyl functionalities. It is a colorless solid that is soluble in organic solvents, but poorly soluble in water. Bisphenol A has a vapor pressure of 5×10−6 Pa.
BPA exhibits hormone-like properties at high dosage levels that raise concern about its suitability in consumer products and food containers where exposure is orders of magnitude lower. Since 2008, several governments have investigated its safety, which prompted some retailers to withdraw polycarbonate products. A 2010 report from the United States Food and Drug Administration (FDA) identified possible hazards to fetuses, infants, and young children. Since that time numerous studies performed at the National Center for Toxicological Research have been performed that addressed many of those issues.
The United States FDA has removed the use of BPA in baby bottles, sippy cups and infant formula packaging based on market abandonment, not safety. The European Union and Canada have banned BPA use in baby bottles.
(Source: http://en.wikipedia.org/wiki/Bisphenol_A, 2013)
Concrete for fish tanks and grow beds is a cheaper option. Yet straight concrete has issues in affecting pH. There are ways to correct this issue. We are currently researching this and will add more later as information comes available.
Which materials do we use?
We use stainless steel, polyethylene, PVC, and in limited applications, polypropylene. In future expansions, we will concentrate on making the grow beds and fish tanks out of concrete.