I the 70's I was attached to an Explosive Ordnance Disposal Squadron, clearing the Maplin Sands, tidal sand flats which were due to be the site of London's Third Airport, but had been a testing target range for over a hundred years, and had also acquired ordnance from the Luftwaffe coming up the Thames, sea mines from the estuary, and being an abort dropping ground for the USAAF during WW2. A lot of stuff out there.
IIRC allied aircraft bombs of that vintage (which form a large part of the ships load) can become unstable because the explosive and inert filler separate out under gravity, so they don't need a functioning fuse mechanism (Allied fuses were [censored]. Looked like the inside of a cuckoo clock)
{German stuff was a standardized aluminium cylinder and electrical. I assumed this meant they were safe 40 years on, but apparently they'd found them still with 3/4 of their original charge level.}
Every now and then we'd send an LCT-full of relatively inert stuff out to be dropped in deep water. I was never on these trips but I'm told they passed quite close to that wreck, following the standard shipping route.
Also there was/is a big petrochemical refinery on Canvey Island (?) which would be within the blast radius. And some tanker traffic.
Quite a lot of theoretically Big Issues around there, though the probabilities are no doubt fairly low.