Author: Aqua Gardening

Plastic Types in Hydroponics and Aquaponics

Plastic Type Numbers

Plastic types in Hydroponics and Aquaponics

Plastics are used extensively in Hydroponics and Aquaponics, and as there can be some nasty chemicals present inside them we should know the different types and how they could affect our health. Read on to find out which types of plastics exist, and click here to find out more about their effects.

In 1988, to assist recycling of disposable items, the Plastic Bottle Institute of the Society of the Plastics Industry devised a now-familiar scheme to mark plastic bottles by plastic type. A plastic container using this scheme is marked with a triangle of three "chasing arrows", which encloses a number giving the plastic type:

  1. PET (PETE), polyethylene terephthalate
  2. HDPE, high-density polyethylene (safe)
  3. PVC, polyvinyl chloride
  4. LDPE, low-density polyethylene (safe)
  5. PP, polypropylene (safe)
  6. PS, polystyrene
  7. Other plastic types

In addition to these plastic types, plastics may have UV stabilisers added to their composition. All of these types and variations are described below.

1 Polyethylene terephthalate (PET or PETE)

Used to make soft drink, water, sports drink, ketchup, and salad dressing bottles, and peanut butter, pickle and jam jars.

GOOD: Not known to leach any chemicals that are suspected of causing cancer or disrupting hormones.

2 High density polyethylene (HDPE) *food safe*, commonly blue barrels

Milk, water, and juice bottles, yogurt and marge tubs, cereal box liners, and grocery, trash, and retail bags.

GOOD: All food grade buckets are made of HDPE #2 but not all HDPE #2 containers are food grade. Check container is marked food grade or USDA/FDA/NSF approved. Plastic type #2 containers that are not food grade will have been manufactured with a non-food-grade 'mold release agent'. This agent is used to help get the newly shaped plastic off of the hard mold that it was shaped from during manufacturing. Without the release agent, the new plastic shape will likely stick to the mold. Some mold release agents enable much faster production than others, but may be toxic to your health if later used with food stuffs.

3 Polyvinyl chloride (V or PVC)

Most cling-wrapped meats, cheeses, and other foods sold in delicatessens and groceries are wrapped in PVC.

BAD: To soften into its flexible form, manufacturers add 'plasticizers' during production. Traces of these chemicals can leach out of PVC when in contact with foods. According to the National Institutes of Health, di-2-ethylhexyl phthalate (DEHP), commonly found in PVC, is a suspected human carcinogen. PVC piping is often used in hydroponics and aquaponics and will leach chemicals over time when it ages and also when exposed to the sun.

4 Low-density polyethylene (LDPE) food safe

Some bread and frozen food bags and squeezable bottles.

OK: Not known to leach any chemicals that are suspected of causing cancer or disrupting hormones, but not as widely recycled as plastic types #1 or #2.

5 Polypropylene (PP)  food safe

Some ketchup bottles and yogurt and margarine tubs.

OK: Hazardous during production, but not known to leach any chemicals that are suspected of causing cancer or disrupting hormones. Not as widely recycled as plastic types #1 and #2.

6 Polystyrene (PS)

Foam insulation, floating rafts, and also for hard applications (e.g. cups, some toys)

BAD: Benzene (material used in production) is a known human carcinogen. Butadiene and styrene (the basic building block of the plastic) are suspected carcinogens. Energy intensive and poor recycling properties.

7 Other (usually polycarbonate)

Baby bottles, microwave ovenware, eating utensils, plastic coating for metal cans

BAD: Made with biphenyl-A, a chemical invented in the 1930s in search for synthetic estrogens. A hormone disruptor. Simulates the action of estrogen when tested in human breast cancer studies. Can leach into food as product ages.

UV Stabilisers also known as UV absorbers

UV stabilisers prevent the long term degradation of plastic exposed to the sun. There are different types of stabilisers used depending on their use and intended service life. Typically, the UV stabiliser absorbs UV light and thereby protects the plastic it is molded with. Chemicals that may be present in UV stabilisers include oxanilides for polyamides, benzophenones for PVC, benzotriazoles and hydroxyphenyltriazines for polycarbonate (Wikipedia).

What to use?

At Aqua Gardening, we focus on Plastic type #2 (food safe) for use in Aquaponics, and Plastic types #2 or #5 for Hydroponics. Generally, there is more exposure of Aquaponics systems to UV light and damage from the weather, so these systems must be safe even after they are damaged and scratched. On the other hand, most Hydroponic systems are located indoors or inside greenhouses, so they are generally more protected from the elements and do not get exposed to as much UV. Saying that, all of our NFT channels are made using #2 Food Safe plastic as the majority are exposed to the sun. Many customers favour the savings which come from choosing #5 over the food grade #2.

Want to know more? Check out the Plastic in Hydroponics page.

References: Wikipedia -