The first time when I steeped tea, a unknown oily layer made me too hesitated to drink it. Is it the pesticide residues on the tea? Were the tea set dirty?

The first time when I steeped tea, a unknown oily layer made me too hesitated to drink it. Is it the pesticide residues on the tea? Were the tea set dirty?
Just like the storage for the good wine and coffee, it is imperative as well to store your quality tea properly. Accurately, It is quite simple, even though there are different ways to store different type of tea.