[jeroen79]

reusability is mainly done for cost instead of environment, but you need to launch a lot to re-cup the costs, and esa is not a commercial org like spacex.

I do think the ESA rockets use a more eco friendly fuel then others, that is probably more important then some metal on the seabed.

[perihelions]

Solid rocket fuel is one of the less eco-friendly things that exists. A fully-stacked Ariane 6 is, by mass, 11% chlorine.