Sprouts like brassicas, including broccoli sprouts, put out tiny root hairs when they're thirsty and looking for water. You may notice this happen when you pick the sprouting jar up in the morning and see their tails look white and fuzzy. Please give them a rinse so they can have a good drink, drain them well and you should notice the fuzz disappear. If the fuzz doesn't fade away, there's a good chance it's mould so throw them out and begin again.