Pick up a plastic container and turn it over. On the bottom you will find a number from 1 to 7 inside a triangle of arrows. That symbol was not born in a health ministry. It is the industrial standard ASTM D7611, devised by the Society of the Plastics Industry in 1988 to make waste sorting easier. It does not certify food safety.
This article checks three numbers—3, 6 and 7—on which EFSA, ECHA and peer-reviewed studies have documented migration profiles. The documents exist. The number on the bottom, alone, does not replace them.
What the number on the bottom actually means
The SPI code divides polymers into seven categories for recycling plants. No health authority has ever linked these digits to a food-suitability judgement.
| Number | Abbreviation | Polymer | Common use |
|---|---|---|---|
| 1 | PET | Polyethylene terephthalate | Bottles, trays |
| 2 | HDPE | High-density polyethylene | Bottles, milk jugs |
| 3 | PVC | Polyvinyl chloride | Films, tubing |
| 4 | LDPE | Low-density polyethylene | Bags |
| 5 | PP | Polypropylene | Microwave containers |
| 6 | PS | Polystyrene | Disposable cups |
| 7 | Other | Polycarbonate, nylon | Flasks, coatings |
Realising that these are logistics labels for waste changes how you read the bottom of a bottle.
Number 3: PVC contains phthalates that migrate
Polyvinyl chloride is rigid. To make it flexible, industry adds phthalates such as DEHP, DBP and DINP. These molecules are not chemically bound to the plastic matrix. When the container meets fats or oils, they migrate into the food.
ECHA, under the REACH Regulation, classifies DEHP, DBP, DIBP and BBP as toxic to reproduction (Repr. 1B) and endocrine disruptors. Restrictions have been in force since July 2020. EFSA confirmed in 2019 that cumulative dietary exposure, although below the safe group level, has tighter margins for children and pregnant women. If the container bears the number 3, phthalates are not a hypothesis. They are a physical property of the material.
Number 6: styrene monomer migrates from polystyrene
Polystyrene is the material of disposable cups. It contains residues of styrene monomer, classified by the International Agency for Research on Cancer (IARC) as a possible human carcinogen (Group 2B).
In 2023, Guazzotti et al. published a study in Foods on 25 dairy products in PS packaging. Styrene was detected in 60 % of samples, with peaks at 135 ng/g. Standard tests using food simulants at 40 °C did not detect migration; real supermarket samples did. Fats and heat accelerate migration. A boiling coffee in a polystyrene cup is not the same thing as an in-vitro test.
Number 7: where BPA ends up
Number 7 is the residual bin. It includes polycarbonate, which contains bisphenol A (BPA), but also unclassified polymers. The problem is twofold: some polymers are documented as problematic, others are unidentified.
In 2023, EFSA revised its BPA assessment. The tolerable daily intake (TDI) dropped from 4 µg/kg to 0.2 ng/kg body weight: a twenty-thousand-fold reduction. The agency concluded that current dietary exposure exceeds this limit by two or three orders of magnitude for all population groups. On 19 December 2024, Regulation (EU) 2024/3190 banned BPA in all food-contact materials.
But 7 also means "other plastic". If the polymer is not specified, the consumer does not know what is inside. And EU Regulation 10/2011 requires assessment of non-intentionally added substances (NIAS) only when the polymer is known. With number 7, that assessment is impossible.
Number 1: when the most common is not the most neutral
PET is the most widely used polymer worldwide for bottles. It is considered safe for single use and cold storage, but it is not inert.
A 2016 study by Chapa-Martinez et al., published in Science of the Total Environment, measured antimony migration—a PET catalyst—in commercial water bottles. Levels increased with storage time and temperature. In 2025, EFSA confirmed that microplastics migrate from food-contact materials, albeit at lower levels than earlier studies suggested. PET does not have the risk profile of 3, 6 or 7. But reusing it for months or leaving it in the sun is not a neutral choice.
How to use plastic in contact with food
Practical lines emerge from the documents. They are not moral rules; they are options consistent with the data.
If you want to reduce exposure to migrating substances, you would avoid numbers 3, 6 and 7 for any food use. You would not use PVC or polystyrene for hot liquids, fatty foods or microwaves: heat and lipids accelerate the documented migration of phthalates and styrene. For PET #1, you would keep it to single use and cold storage, without leaving it in the sun or reusing it indefinitely. Polypropylene #5 is considered the most suitable for microwaves, but "most suitable" does not mean "one hundred percent safe". For storage and reheating, glass, stainless steel and ceramics have lower migration profiles.
The numbers on the bottom are industrial recycling codes. They are not safety seals. Numbers 3, 6 and 7 have documented chemical migration profiles—phthalates, styrene, BPA—assessed by EFSA, ECHA and studies in journals such as Foods and Science of the Total Environment. The documents exist. The number on the bottom, alone, does not.
If 7 can hide BPA or unidentified polymers, and if 3 only certifies that the recycler knows where to throw it, how much do you trust a symbol that certifies nothing about safety? The answer is not in this article. It is in the label you read, or in the one you decide to have read by someone with no interest in hiding anything from you.
