I did a google search to try and find what the commercial growers use and found a paper which stated that as the commercial organic potato growers rely on copper fungicides that it was permissible for them to use a copper mixture and that the maximum amount of copper that can be applied per hectare is 6kg per year and yet they ban Bordeaux mixture for the general public’s use.
It's one of the great conundrums. Copper is a naturally occurring substance so, technically, it's organic. Yet it's a metal that is known to stay in (well, on top of) the soil so it can build up. Organic growers choose not to use chemicals but use a metal that is known to build up in the soil. And have argued - obviously successfully - that there are no known organic alternatives.
I think the difference for commercial growers is that the authorities have decided they - commercial growers - can be trusted not to poison themselves. Private growers apparently can't.
I don't know what the amount of copper is in the small amount of Bordeaux mixture that I used to spray onto my 8 or 9 rows of spuds was but I reckon that its less than the equivalent of 6kg per hectare each year, I think that the EU believe that we spray the stuff just for fun but I only ever used it sparingly and did pay attention to the potato council blight warnings before spraying.
You can always make your own BM. Copper sulphate, hydrated lime, water. Just get the ratios right.