Yes, plastics have harmful effects not only on humans but also the animals specifically wildlife, as well as the environment.
Plastics are known to take a much longer time in order for them to be decomposed. Most plastics are made from harmful chemical which is also deterimental to human health. As the plastic decomposes, it also releases toxins to the environment. When plastics are being burned, they can also contribute to global warming since there is an emission of carbon dioxide (CO2).
The wildlife are affected by its improper disposal because they sometimes accidentally swallow plastics, which eventually might lead to death.