filtering roof runoff prior to going into pond

I guess this is ultimately a soil question...I am in my "pond era," in the process of going pond-crazy, digging clay-lined ponds and mini-pond/swales all over the place to try to retain as much water as I can on my fairly steeply-sloped property. The house has a new asphalt roof (3 years) and I haven't wanted to collect any water from it while it's so new, although the preexisting diversion system deposits it close to an orchard area anyway. (Those trees are very happy, albeit perhaps mildly toxic!) As I plot ponds closer to the house, however, I am wondering about redirecting that runoff accordingly into those ponds. Has anyone experimented with a pre-groundwater roof runoff filter that is somehow built into a moving system, not just a catchment? The closest I found searching the forums was this thread: https://permies.com/t/150382/safely-rainwater-collected-asphalt-shingle ...William's comment there about a living filter is very intriguing but I don't know what I could do that could work outside year-round here in zone 6b. Maybe a rain garden of heavy-metal accumulating plants around the pond? I'm also not sure how big a worry it is and how much the issue diminishes in time. Of course I eventually will want to switch to a metal roof, but that isn't an option anytime soon.

Letting the water percolate through a bed of biochar would be a good low-tech approach. This would filter out organic contaminants and heavy metals leaching from the roofing material and bind them safely out of harm's way.

Thanks Phil—that's just the sort of thing I'm wondering about! I haven't been making biochar but I should get into it. I have no idea of how much I would need and how long it would last but I will look into it. My very rough estimate of water potential from the whole roof is around 20,000 gallons a year, although I might only redirect from half of it to start.