Is PVC Safe for Hydroponics?
One of the first questions you may ask before building a hydroponic system is what material can I use? PVC is one of the most popular options due to its ease of use, low cost and wide availability. It can be a controversial material, however, with concerns raised about its potential environmental and health effects. We have several hydroponic systems for growing produce in our home and PVC is one of the primary materials we use, so I did quite a bit of online research to determine whether I was comfortable using it to grow food for my family. I put together this article to summarize what I've found and to point you to sources that I found helpful.
UPDATE: Since writing this article, I sent in a water sample to Simple Lab to test for plastic leachates in my hydroponic setup. I took the water sample from my rail system after the nutrient solution had been in circulation for 2 weeks - just before doing a nutrient change - so that if there was any leaching, it would have adequate time to occur. I've updated this article to include test results for each potential concern. The short summary is that there were no concerning results and I feel very comfortable using PVC in my home hydroponic system.
Disclaimer: This content of this article is for information purposes only. It is a summary of what we've found as we've researched the safety of PVC and plastics for use in hydroponics, but please do your own research and make a decision based on what is comfortable for you. This is not intended to be medical advice of any kind.
From the reading I've done, there are a few primary concerns raised over the use of PVC in consumer goods. I'll give a brief summary of each along with what I've found and why I'm not concerned at this time.
Dioxins are very toxic chemicals and some argue that they are produced when PVC is manufactured or burned. There is debate on how much is actually produced as dioxin emissions have been reduced by 90% since 1987 in spite of the fact that PVC production has increased. But either way, burning PVC is not a situation we should encounter for our purposes with hydroponics. I haven't found any evidence that they are inherently in PVC and could be released into our nutrient solution, so not a concern.
Test Result: Not Tested
Chlorine is a building block of PVC and many point out that it is toxic and should be reason enough to avoid PVC. I haven't found much information on whether it can actually leach out of the PVC, but this doesn't concern me because of our plants. Chlorine is actually a micronutrient required by many plants, but in higher amounts it is toxic to plants. Many plants, such as lettuce, are sensitive to even low concentrations of chlorine (which is why its helpful to treat tap water before putting it into our hydroponic systems). Therefore, if chlorine was being released from PVC into our nutrient solution, it seems the plants would tell us right away.
Test Result: None Detected
Vinyl chloride is a substance made from regular salt and ethylene and is used to manufacture PVC. In large doses it has been correlated with liver issues and is considered a carcinogen. However, it is a gas at room temperature and evaporates out of water rapidly. Primary human exposure has come from workers breathing it in during PVC manufacturing, though in recent years regulations have tightened to protect workers. It is not known to accumulate in plants (see ATSDR website for a helpful overview of vinyl chloride).
Test Result: None Detected
Stabilizers are added to PVC to increase durability or improve other material characteristics. Many different chemical elements have been used, but most concerns are about PVC that is stabilized with lead. Lead was widely used as a stabilizer but has been nearly phased out due to health concerns surrounding lead. It is debated whether these chemicals can even leach out of plastic in the first place, but similar to chlorine, this does not concern me because the plants would tell us if there was a problem. Lead is harmful to plants and there are studies showing that plants defend against lead toxicity with reduced lead uptake, leaving most lead in the roots.
Other potential stabilizers include cadmium, barium and zinc. I have not found any compelling evidence that they leach out of PVC at room temperature. Similar to lead, cadmium is harmful to plants and plant growth is often inhibited by it so it seems the plants would tell us if there was a problem. Barium concentrations need to be relatively high before causing issues for plants or people. Zinc is a required micronutrient for plants and people so it would require a large amount of leaching before we see an issue.
Lead: None Detected
Cadmium: None Detected
Barium: 0.0015 ppm (much lower than EPA goal of 2 ppm for drinking water)
Zinc: 0.0322 ppm (expected in nutrient solution)
Phthalates seem to be one of the most controversial and least understood component of plastics. Phthalates are compounds added to many plastics (especially PVC) to give them improved material properties such as flexibility, weather resistance or transparency. At the microscopic level, phthalates are mixed in with the plastic, but aren't fully bonded with it, so they can leach out. With hydroponics, the concern is that phthalates exist in the rails or piping of our hydroponic systems, leach out into our nutrient solution, can be absorbed by plants and then consumed by us. Each of these steps must occur for there to be any issue so I'll look at each step individually.
First, phthalates must exist in the PVC we are using. Since phthalates are primarily used for making plastic flexible (they are also called "plasticizers"), some rigid PVC does not contain phthalates at all. However, I have not found any way to know for sure which PVC contains phthalates and which does not. I've noticed that the PVC we use, particularly the square rails, will dent instead of crack when impacted, so I'm guessing there are plasticizers at work to give it slight flexibility and durability (PVC by itself is brittle). If I'm wrong and the PVC we use doesn't contain phthalates, we can stop here.
Assuming there are phthalates in our hydroponic PVC, the next question is will they leach out into our nutrient solution? Phthalates have a weak solubility in water, but that solubility is driven by a variety of factors including the type of phthalate, temperature and lipid content of the solution. Of most importance to us, the rate of leaching increases greatly with greater temperatures. Many studies I've come across start their analysis at 30 C (86 F) and go up from there. I haven't found any evidence that phthalates leach out into water at room temperatures and one study of PVC IV bags used for infants showed no leaching into a non-lipid solution at 32 C. High temperatures are already bad for hydroponics for other reasons (disease, plant comfort, etc.) so high temperatures are not something we are likely to encounter. So my concern about phthalates ends here.
However, for the sake of completeness, what if trace amounts of phthalates did leach into the water? The phthalates then must be absorbed by the plants and transported to the leaves or fruit. This has not been widely studied, especially with hydroponics, but I did find a study done on hydroponic tomato plants where phthalates were added to the nutrient solution and the concentration of phthalates in the roots, leaves and fruits were measured. Even after adding large amounts of phthalates directly to the nutrient solution, they determined that 0.01% of the phthalates added to the solution ended up in the leaves of the plant and no measurable amount were in the fruit. There are several studies measuring phthalates absorbed by plants in soil and some show a small amount of uptake from the soil to the leaves and others show none, with only measurable amounts of phthalates present in the roots. So can phthalates be absorbed by plants? Seems like it is possible, though in extremely small amounts and an even smaller portion actually makes it to the leaves and fruit.
So then if phthalates do make it to our food and we eat it, is it harmful? This is a large debate with arguments on both sides. There are some studies on animals that showed reproductive issues from exposure to large amounts of phthalates, but there seems to be little conclusive evidence on their effects on humans (see US CDC factsheet and US FDA Q&A on phthalates). One thing that does seem agreed on is that we are regularly exposed to phthalates from lots of sources. They can be in drinking water, air, soil, food, children's toys, medical IV bags, medical devices, cosmetic products, food storage, etc.
So in summary, it seems highly unlikely that there are significant amounts of phthalates in the food we grow hydroponically compared to what we are already exposed to day-to-day.
Test Result: None Detected
Another reason I'm comfortable with PVC is based on how widely it is used. Large portions of municipal and residential water supplies use PVC. As mentioned previously, PVC is also used in a variety of industries including medical applications. Additionally, commercial and hobby hydroponic growers have used it for decades.
Also, an important thing to keep in mind is that dirt is not 100% food safe. Dirt and traditional irrigation can contain very harmful bacteria. For example, in 2018 there was an outbreak of E. coli on Romaine Lettuce that hospitalized 96 people and killed 5. As we continue to innovate in food production I think it's important to remember that we don't currently have a way of growing 100% safe food. Home hydroponics can be a step in the right direction.
In summary, I am comfortable using PVC to grow produce hydroponically based on the research I've done. This does not mean that I'm opposed to working to find even better materials. Let's keep working towards safer, healthier and widely accessible produce!