Your body contains about a kilogram of phosphorus. Your bones, teeth, and DNA are made of phosphorus.
And still, White Phosphorus is deadly in doses of less than 1 ppm. Enumerating elements is completely meaningless when talking about toxicity. What matters is the substance which contains the elements. And two chemically closely related substances can be harmless and absolutely toxic. Botulinum toxin, often called Botox for short, is deadly in doses above 2 ppt (or about 150 nanograms for a grown adult), and all it contains are the very same amino acids, which make up about 15% of your body weight.
Copper is necessary for human life.
Same silly argument.
Luckily, posphorus is quite reactive (that's why it was used as an agent in matchsticks), oxidizes fast, and will form phosphoric acid when exposed to air, which indeed is not toxic. It is similar for copper, albeit some copper oxides are themselves toxic.
Germany, which is known for being well organized, had a similar catastrophic flooding in 2021 (184 dead) in the Ahr Valley. Also here, the Weather Service had warned about heavy rainfall and possible catastrophic flooding, but it did not register with the people responsible for civil protection.
That's a real problem with once-in-a-century events. People just can't imagine the possible damage, and are completely unprepared or even consider preparations as wasteful and an obstacle to business, development or personal freedom.
You will lose an important tape file.