I have read a few treads on this subject before, and I have a couple of points to make:
Dumping the lead on the take has become a fad/fashion with many "Carp anglers?" because they read this is the way forward (of coarse the tackle sponsors want to see this at 1.50 quid per lead!) without understanding why it is an advantage to lose the lead!
So the said "Carp angler" buys the lead release systems as the "comics advise" because they know no better! Where infact unless your water is packed with dense weed there is no need to dump the lead at all !!!
Some anglers claim that dumping the lead brings Carp to the surface and out of the weed, I'm not convinced of this as I can't understand how a 2-4oz lead will keep an angry 20-30lbs Carp down in the water?
As for damaging the water quality of a water I have read that once the lead has oxidized (which happens in air and water, becomes dull grey and not silver in colour) it becomes inert, also if is buried in silt ect??? Not 100% on this but that’s what I have read, if wrong please correct me! So to finish I see it as a waste of money for the anglers that use this and great marketing from the tackle firms!