Being synthetic, they also release microplastics into our freshwater when you wash them. I do my mountainbike trailriding in jeans. Have never experienced much of a downside. Also, big plus: jeans look rad when you patch and mend and dirty them!
A pair of trail pants that lasts you 20 years compared to a pair of jeans that lasts 4 and has to be replaced 5 times is probably a net win for microplastics when you factor in the amount of plastic used when manufacturing and shipping both items.
