Is selenium harmful ? does it lead to death or any other disorders ?

Trace element: You need a certain amount of selenium in your diet, and most people probably do not need to supplement. At various times, the "natural healing" community has taught that "selenium is very good for you" and "selenium is very bad for you." The NIH is pretty good: https://ods.od.nih.gov/factsheets/Selenium-healthProfessional/#h6 An evidence-based holist can guide you through questions like this.