Old newspapers are not safe for mulch or compost, because of the composition of their ink (which included toxic cadmium, lead and chromium). But most newspaper inks of the 21st century are soy-based and regarded as safe. To make sure, call up the newspapers in question and find out if they use a soy-based ink. If they do, the newspapers are safe for mulch and compost. If you wish to be a real stickler about it, ask a separate question regarding their colored pages (if any), the inks for which may or may not contain harmful ingredients.