It certainly is a problem - both braid and mono have a long life expectancy before it starts to break down ....... when you think that synthetic grass is made to last 10years plus ( braid is made out of the same polymer & contains a lot of the same stabilisers) & if a mono is a nylon 6 base - nylon is inherently UV resistant ...... you have a real environmental problem
So yes - take that old line home with you & put it in the bin
Chris