If you take a good look at your plastic water bottle, there'd be a number enclosed inside a triangle made of arrows. Not all plastics belong to the same grade. The plastic used in a mineral water bottle will be different from the one used in a computer keyboard. We don't pay attention to these unique identification numbers on plastic items, but they help us understand the grade of plastic we are using and whether it is safe or food grade. Here's what each of those numbers mean.
#1: Polyethylene Terephthalate (PET, PETE). PET is a clear and tough plastic used in the manufacture of containers for soft drinks, water, beer, ketchup, microwavable food trays, etc. It is recyclable and generally considered safe for food. However, there are some reports of PET plastics leaching the heavy metal antimony into food.
#2: High Density Polyethylene (HDPE) is used to make different types of bottles and is food grade. This grade of plastic is well suited for packaging products with a short shelf life like milk, water and juice. It is also used for cosmetics, shampoo and detergents. But like PET, HDPE was also shown to leach oestrogenic compounds like BPA into food.
#3: Polyvinyl Chloride (PVC, Vinyl) is not food grade despite having good chemical resistance and stability. It's mainly used for non food-related packaging like blister packs and clamshell packs. It can also be used in making pipes, window frames, cable insulation, carpets and flooring. Never eat or serve anything in #3 grade plastic.
#4: Low Density Polyethylene (LDPE) is a tough kind of plastic, which is also flexible. It is mainly used in heat sealing and also in the manufacture of flexible lids, bottles, dry cleaning bags, newspapers, shrink wrap, coatings for paper milk cartons, hot and cold beverage cups, toys and squeezable bottles. Never reuse this plastic or subject it to heat while cooking.
#5: Polypropylene (PP) is used to make containers for yoghurt, margarine, takeout meals and deli foods. It's also used in the manufacture of medicine bottles, bottle caps etc. It's considered a safe plastic but avoid microwaving food in it or reusing it.
#6: Polystyrene (PS) It is a versatile plastic also known as Styrofoam or thermocol. It is used to manufacture cups, plates, bowls and takeout containers. Other uses include protective packaging for delicate items, compact disc cases and medicine bottles. Styrofoam or styrene exposure is also tied to cancer risks.
#7: Every other plastic that doesn't fit into the 1-6 bracket is number as 7. This code applies to things made out of resin or more than one resin, used in a multi-layer combination. It's not wise to use #7 grade plastic for storing or serving food because there is no saying what it is made out of. It could contain toxic chemicals such as BPA that could leach into the food.