It can take some plastic items hundreds of years to biodegrade.
Helium balloons in particular are a hazard to seas and to cattle. In exchange for a short and ‘beautiful’ release, the balloons return to earth to pollute even the most remote of places. There is currently no ban in this country, but some counties are considering it.
In the UK many plastic bags are now biodegradable and thanks to single-use bag tax, the use of them has declined by 86% (stat from UK Department for Environment, Food & Rural Affairs , Dec 2018).