What it is
Low-density polyethylene is branched polyethylene: soft, flexible, squeezable. Code “4”. Chemically it’s the same backbone as HDPE, just floppier — and its favourite hiding place is as a waterproof film on things that look like paper.
Where you meet it
Cling wrap, bread and freezer bags, squeeze sauce bottles, bin liners — and, invisibly, the plastic lining inside “paper” coffee cups and milk cartons.
What the research shows
The defining measurement comes from NIST: LDPE-lined hot-beverage cups holding 100 °C water for 20 minutes released trillions of nanoparticles per litre, most of them 30–80 nanometres (ES&T, 2022, NIST’s summary) lab. Heat is the trigger; the same film in your freezer is doing very little.
The Australian packaging study applies here too: tearing PE bags open generates microplastics along the tear line (Scientific Reports, 2020) lab. And as polyethylene, LDPE shares the family’s tissue findings — the polymer most commonly found in blood, plaque and brains human obs..
What I do
I treat every takeaway hot cup as a plastic cup, because it is one — my coffee goes in ceramic or steel. Nothing gets microwaved with cling film on it, hot leftovers never meet a plastic bag, and bread comes out of its bag and into the bamboo bread box. Cold and freezer use of PE film I’ve kept: that’s managing dose, not chasing purity.
The honest bit
NIST offered the perspective themselves: those trillions of nanoparticles amount to about 0.1% of the cup lining’s mass — the count is astronomical, the mass is tiny, and no toxicity testing was done in that study. Sit with both halves of that sentence. Also, the same tests found food-grade nylon oven bags shed ~7× more nanoparticles than the cups — the obscure kitchen film out-shed the famous one (see nylon).