I did not know that fireworks contained plastic (although I should have). However, please be aware that the health impacts of microplastics aren't really well known, which places this article in the "mostly scare-mongering" rather than "actual risk we should care about"; this is typical of the BBC these days. Of all the things that Americans do that are unhealthy, plastic pollution by fireworks is pretty low on the list of enumerable, measureable harms. While, fireworks and firecrackers are quite dangerous on their own for explosive reasons.

A better source would probaly be this observational study (https://www.sciencedirect.com/science/article/pii/S0025326X2...) and I was unable to find any high quality studies that showed any strong evidence of direct harm.

It (BBC) is just a low quality source for information impacting our lives, with an emphasis on dire-sounding, but poorly understood harms.