Here's one I haven't heard of before. Mermaid's tears. Apparently this term is used to describe the tiny pieces of plastic which litter our oceans. Often this plastic comes from industry, domestic use or shipping but usually ends up in tiny fragments, often the size of fish eggs but sometimes smaller than a grain of sand. These so-called mermaid's tears have been found throughout the world's oceans and the evidence suggests they're on the increase.
So what harm do they cause? Well, many plastics do not biodegrade and so can last for centuries in the world's oceans. They can then leach chemicals which are consumed by marine creatures. It's already been discovered the many species unknowingly consume these tiny pieces of plastic and there's a strong suspicion that they will be passed on throughout the food chain. Research is continuing into the impact such chemicals may have on marine life.