Plastics.

Plastics are made from crude oil. We use them constantly in our daily lives.
We use them to make bottles, cups, boxes and all types of wrappers. school pens , mobile phone cases and bags are just some examples.
As they use to be disposable objects, a large number of them end up in our planet's rivers, seas and oceans, and it takes many years to decompose completely.
This is a serious problem for the environment and for humanity. It has been estimated that, only in the Pacific Ocean, there are about 87,000 tons of plastic!
Plastic can disintegrate into small particles that are later eaten by fish and might even reach our stomachs.
The best solution is to avoid its use as much as possible, reuse each item more than once, just as we do with supermarket bags, and leave it in the yellow container when you are not going to use it any more.