Lover's Bridge - Love Locks Paris

In Paris, there is a bridge over the Seine where lovers attach a lock with their marks - initials, a date, or a quote.  After locking onto the bridge, the keys are heaved into the Seine. After a few months, when the locks have completely filled a panel, the panel holding the locks is removed and wood is affixed in place of the panel, until the new panel arrives days later.  Here we have a missing panel with some graffiti scrawled across the wood placeholder.  Soon this will be replaced with a new iron panel, and people will fill it up with locks again.

But a question, where do the locks go after they are removed?