Plastics are hydrocarbon.
To explain what this means to the lay man, plastics are gotten from crude-oil; just like your petrol, diesel and engine oil.
When plastics are heated, they release chemicals and these chemicals get into the food that the plastics are used to cook like the beans pudding, moi moi for example. Most of these plastics contain a chemical known as Bisphenol A also known as BPA. When you heat the plastics- as with any stable chemical composition, it becomes unstable and releases these chemicals.
As a rule, DO NOT heat any plastic container with food in it or cause it to become hot e.g by leaving it in the sun.
Although, in advanced countries, there are BPA-free plastics being widely used because of the dangers of ordinary plastics, you can be sure that the plastic used for your moi moi is not BPA-free as BPA-free plastic is not cheap so you cannot buy your moi moi for N250 and expect it to be in BPA-free plastic.
So, as a precaution know these:
There are so many different types of plastics with different uses for each but avoid heating all types of plastics. Including the ones that say on it, “microwave-safe”, “dishwasher safe” etc. Plastics are plastics.
When you want to warm food you kept in plastic in the freezer, put the food in a ceramic bowl, pot or pan before warming it- and that includes the quick warming we do by putting water in a pot and warming the food inside the container that was used to freeze it. (Yes, we know about that)
Take extra care if pregnant as these plastic chemicals affect the unborn child.