Are your food container safe?

I recently come across some food container grading. I think it is good to share it here :)
Simply take a container from your kitchen, look at the bottom of the container and check for the grade. Normally, it is located at the bottom with a number (grade) in a triangle.

The grading can tell us what it makes from and whether it is safe or not.

Grade 1 Polyethylene terephthalate (PET or PETE) . Normally we can see this in mineral water bottle. It can be used one time only, shouldn't reuse it because the chemical will be unstable when reusing it.
Grade 2 High-density polyethylene (HDPE) . More rigid and harder than LDPE. This is the best plastic that suitable for food storage.
Grade 4 Low-density polyethylene (LDPE) . Good resistance to most chemicals.
Grade 5 Polypropylene (PP). Good resistance to most chemicals.

Basically, if your food container is grade 2, 4 and 5, you are safe. other grade like 1 (only one time use), 3, 6 and 7 are not recommended to store food in kitchen.