Well, recycling is a good thing, but perhaps the person who decided the time was ripe to leave their 1951 155 millimeter artillery shell at a recycling station in Seattle should have thought another round. Luckily, no one was hurt, and the Army apparently came to save the day.
The trash of war is, as war itself, destructive. The examples are endless, again as war seems to be. Some war trash has direct impact on human security, such as the around 18 million land mines layed down by the British at the battle for El Alamein in 1942, still killing and injuring the Bedouin population living there. But war does not only create weapons trash, it also turns infrastructure and nature into trash, with manifold long-term effects. In short, as if it needed to be stated, war is bad when it happens, and long after.