[ErnBatavia]

They are also a sobering reminder that about 10,000 containers fall off cargo ships each year, creating all manner of flotsam and jetsam.

If the writer means the standard truckbound 20 or 40 footers, I highly doubt this number

[KarlInOhio]

They are also a sobering reminder that about 10,000 containers fall off cargo ships each year, creating all manner of flotsam and jetsam.

If the number is accurate, most probably fall off the ships in port into the hands of organized crime.

[Question_Assumptions]

If the writer means the standard truckbound 20 or 40 footers, I highly doubt this number

It's plausible. During a storm, a whole column of them can peel off the side of a ship. A man who worked with me years ago had a wife who worked in shipping for a consumer electronics company and this was apparently a big enough concern for her that she'd always schedule her containers to arrive first and leave last so that they'd be stacked near the middle of the ship. I can't imagine her going through all that trouble if this didn't happen very often. There is also no telling how many containers get "lost" somewhere closer to the docks.