The box was not empty before the food

What they found

In a survey published in 2023, a lab in Zhejiang, China, rinsed 354 unused polystyrene takeout boxes from restaurants in 28 cities and counted the plastic particles that washed off. The surprise was the pattern. Boxes with more particles tended to hold a bigger share of fibres and a smaller share of polystyrene, the plastic the boxes are made of.

Each box was shaken twice in 95 °C water, then twice in 30 °C water. The rinse was filtered, and every suspect particle was checked with an infrared scan (FTIR, which identifies a material by the light it absorbs). Taiyuan had the highest city average, 86 particles per box, and 90% of them were fibres. Fuzhou had the lowest, 18, with 53% of them fragments and the highest polystyrene share of any city, 90%. Higher counts also went with a bigger combined share of polyethylene, polypropylene and polyester. The authors suspect plastic fibres from the air settled on the boxes while they were made, stored and transported.

Evidence: Emerging

Why it matters

No box came out clean. The same lab also rinsed 210 unused polypropylene boxes from 7 cities. All 564 boxes carried particles about 0.05 mm or larger that an infrared scan matched to plastic: 3 to 43 per polypropylene box and 5 to 173 per polystyrene box, before any food went in. Test runs without a box found fewer than 2. Wherever the particles came from, they were in the box the food goes into.

The swap

Order in plastic less, and skip foam

Each box adds a little, so ordering food in plastic less often is the simplest cut. Where you have a choice, favour places that don't use polystyrene foam: an earlier rinse test found the most particles in rough polystyrene boxes, though that evidence is thin and not from these surveys, where boxes with more particles tended to hold more fibres. Reheat leftovers on a plate or in a glass dish rather than in the tub, and heat them as thoroughly as you normally would. No need to buy anything.

Cost: Free · Swap rating: Likely

What we don't know yet

These were empty 2019-2020 Chinese restaurant boxes; no study here measured what reaches the food. Both surveys used 95 °C water, then filtered the rinse, which EFSA, Europe's food safety agency, warns can make additive specks pass for plastic. One counted rayon and cellophane as plastic. EFSA logged both, discussed neither on its own, and judges real release much lower than many studies report.