I've heard selenium can be toxic in high doses. What are the symptoms of toxicity and what is the recommended daily intake?

As a trace mineral, selenium need only be taken in small quantities. In high doses it is extremely toxic. While the recommended maximum allowance for supplemental selenium of 52 mcg per day is a completely safe level, there is a conservative allowance or leeway between this recommendation and reported toxicity levels (well over 200 mcg per day). As soils in Australia are selenium poor, the likelihood of anyone obtaining more than 30-50 mcg per day from food sources is very small.