A whole package of Quaker Quick Oats with iron, which are the most iron-rich cereals i could find in a quick search, has about 20mg iron per serving * 13 servings = 290 mg iron. So no, there's no risk of injury at 4 boxes of cereals per gram of iron. We humans don't need to replenish iron that much (if we don't suffer from major blood loss), we are pretty good at internal recycling.