So, let's continue on with our discussion of plastics for the reef aquarium, Part 3.
Moving along down our list in the table, the next ones are the polyethylenes.
Table courtesy of @Seawitch, ©2019, All Rights Reserved.
PET: polyethylene terephthalate
PEX: cross-linked polyethylene
These are pretty safe. Yes, there are some things that they can leach, but that doesn't mean that they actually do, and it also doesn't mean that they leach these things in amounts that would bother our livestock.
So, I looked at one study that looked at whether PET water bottles were leaching antimony into the water. The study took place in Arizona, where hot weather was expected to exacerbate this process. Yes, they did leach antimony but well below the EPA's maximum contaminant level (MCL) of 6ppb. The numbers the researchers were getting were all under 1ppb. Leaching was significantly affected by time and temperature.
Antimony is a catalyst used in the production of PET, so, we can't avoid the presence of it. Are amounts of less than 1ppb a problem for saltwater livestock? I don't know. We don't typically use a lot of PET products in the reef except as a bristleworm trap. So, it's probably very low risk. PET plastic is also used in 3D printing.
I found one study saying the PE and PEX can leach BPA, but I also found a plastics manufacturer saying that BPA is not used in the manufacture of PE. So, go figure. (18) (31)
I, personally, have some PEX pipe in my home, and I see that it's readily available everywhere. PEX I've been told tends to fail over time and should be replaced eventually. It was fashionable in the 1990's but no longer meets code at least where I live in British Columbia, Canada.
Does PEX leach BPA? I don't know. I found at least one reference that says it does, and others that say it doesn't. The truth is there is not a lot of good research on how plastic pipes affect drinking water. There are three different kinds of PEX, Types A, B, and C. Type B seems to have the least amount of controversy regarding leaching. PEX is, however, highly vulnerable to the degrading effects of UV light. Just sayin'.
An ATO tank made by forum member @dantimdad out of acrylic (PMMA).
This photo is courtesy of @dantimdad, ©2019, All Rights Reserved.
PLA is the only plastic that Dr. Randy Holmes-Farley said we shouldn't use, not because it's toxic--which it isn't--but because it will break down over time into pellets. So, I won't spend time on it here. I know that it's used in 3D-printing.
PMMA: polymethyl methacrylate
PMMA is what we call acrylic, and I'm delighted to report that I couldn't find anything bad to say about mysterious chemicals it might be leaching. Sounds very safe for the reef, which is a good thing since lots of folks have tanks made out of it. I'm going to reinsert my table from Part 1 to remind everyone of the great qualities of acrylic.
Table courtesy of @Seawitch, ©2019, All Rights Reserved.
Next we have polypropylene, and RHF said he believed it to be safe. I did find some references saying it could leach some metals including iron and lead, but how much I don't know. Your buckets are probably made of PP or HDPE. It's commonly found in hard plastic containers like Tupperware.
It's hard, pretty chemical-resistant, rugged, heat-resistant, partially crystalline and cheap. I found one study saying that it did leach metals and another article saying that PP doesn't leach metals.
Yes, PS does appear to leach some nasty things, like benzene and toluene but well under the World Health Organization Guidelines. Of course, those guidelines are written with humans in mind, not shrimp or coral.
I'm not sure what reefers would use PS for. I've heard of frags being mounted on styrofoam, and some people put styrofoam under their tanks. All in all, pretty safe.
A beautiful acrylic (PMMA) display tank.
Photo is courtesy of @ca1ore, ©2019, All Rights Reserved.
PUR seems to be pretty safe, and I didn't find much in the way of articles saying it was leaching things. There is also a long history of reef aquarists--and freshwater aquarists too--using PUR for lots of applications including PUR foam to create "rock" walls inside the aquarium.
So, I'd say this one is very safe *once it's cured*, although it can break down and flake away over time.
PVC: polyvinyl chloride
And last but not least on my list we have PVC. There's a long list of things that PVC may leach into water, but most people use PVC pipe to plumb large systems, and many people have PVC pipe in their homes. Apparently using brass fitting with PVC pipe may make leaching worse in the presence of chlorinated water.
PVC is everywhere, so I don't want to dwell on what it may or may not be leaching into water. The only thing I'll repeat here is that allowing PVC to offgas before using it may help. PVC is even used in blood-collection bags because it's cheap, tough, pliable, and transparent. In fact, 25% of all hospital plastic including IV bags are made of PVC. That's a sobering thought.
Another way to look at classifying plastics.
Screenshot courtesy of @Seawitch. Photo comes from a UK government pdf (30). ©2019, All Rights Reserved.
The fact is that plastic is pretty much inescapable. While preparing this article, @ca1ore reminded me that the DI portion of an RO/DI unit contains plastic beads used in the filtering of water.
So, I'm not sure how much further ahead we are by knowing some of the potential problems of using plastic because it would be very difficult or impossible to have a marine aquarium without ever using plastic.
I certainly wonder if something leaching from plastic could be behind some mysterious tank crashes or tank deaths. Perhaps this series of articles will inspire someone to do some experiments at home with plastic and get their saltwater tested by a professional laboratory.
Special thanks is owed today to @ca1ore, @Brew12, @Greg Gdowski, @PDR, @hdsoftail1065, and @OllieNZ, who all helped me in the preparation of this article often at a moment's notice.
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Author Profile: Cynthia White
Cynthia received her BA in English from NYU a long long time ago. She has been a freelance writer and editor for over 20 years. In 2018, she won the President's Award from the Professional Writers Association of Canada. Now she is a writer and editor on staff at R2R, where her forum nickname is @Seawitch. She lives on Vancouver Island with her husband, three special-needs dogs, and three saltwater aquariums being set up.