Fallen Shipping Containers

In a typical year, how many shipping containers fall off container ships at sea? The answer is here.

Each year, an estimated 10,000 shipping containers fall off container ships at sea. Although many of these containers float at the surface for months, most eventually sink to the seafloor. No one knows what happens to these containers once they reach the deep seafloor.

That seems like a lot.
The article describes a research program to study the effects of these containers.

Shortly after midnight on February 26, when the Med Taipei was directly offshore of Monterey Bay, stacks of containers began to break free of their lashings and topple sideways. Fifteen of the 40-foot-long containers fell overboard into the churning sea. Yet the ship continued south. By the time the ship reached the Port of Los Angeles, nine more containers had fallen overboard, and another 21 lay crumpled on deck.
Marine biologists will count the number of deep-sea animals on and around the container, and collect samples of sediment at various distances from the container for biological and chemical analysis. By comparing animal communities close to and away from the container, the researchers hope to determine what effects (if any) the container has had on seafloor life.
According to the U.S. Customs manifest, the container discovered by MBARI holds 1,159 steel-belted tires. Other containers that fell overboard held cyclone fencing, leather chairs, and mattress pads.

And this:

Approximately 90 percent of worldwide non-bulk cargo travels by container ship, and between five and six million containers are in transit at any given moment. To make matters worse, not all container cargo is inert. Perhaps 10 percent of shipping containers carry household and industrial chemicals that could be toxic to marine life.