Spoiler alert: it isn’t.
But so you don’t have to take our word for that, the most accurate, accessible source of information on runoff from copper in architecture in the English language of which we are aware can be found on the Copper Development Association’s website. Read about them here: https://www.copper.org/about/cda_mission.html
Researching this issue can get convoluted as copper and other pollutants can come from many sources, so it is best to compare apples to apples when discussing runoff. We want to concern ourselves only with ARCHITECTURE based studies, and the one most people cite when discussing this issue comes from the 1997 study in Connecticut where scientists evaluated runoff from 5 different buildings and determined what effect it might cause to the environment. Here it is in its entirety on the CDA site: https://www.copper.org/environment/impact/NACE02225/nace02225b.html
(Note the hyperlinks on the left under “Environment” to quickly jump to specific study sections.)
You can fast forward to the conclusions page here if you like: https://www.copper.org/environment/impact/NACE02225/nace02225e.html
That’s a lot to read and possibly misconstrue, so here is a link to the general overview and consensus:
https://www.copper.org/applications/architecture/water_runoff_overview.html
Initially there might be higher concentrations of copper in runoff water on new builds. If water runoff from gutters, downspouts, or driveways directly discharges onto a paved surface that is connected to the storm drain system, you can retrofit them to redirect runoff onto grassy areas, into a rain garden, collection tank, etc., or best, directly to the sewer / ground drainage. As shown in the study, once the runoff hits the ground or the drain systems, any potential toxins are rendered benign.
As the study discusses, the ionic copper (more potentially toxic) coming off the roof does not want to remain in the ionic state and readily binds to the cast iron and concrete piping of drainage systems. The same goes for soil which is incredibly effective at reducing ionic copper concentration.
When properly planned, and water properly directed, there should be zero concern for any interference with local biospheres, marine or otherwise.
Finally, consider that all high end, modern buildings are planned with copper pipes for plumbing. We drink water from those pipes. We water our lawns from those pipes. We bathe in water from those pipes. Restaurants are required to have copper pipes for sanitation purposes as they are naturally antimicrobial and keep our food and drinks safe.
If you or any members on your design build team require further answers
to this end, reach out to us so everyone can feel confident about using copper in this manner.