Toxic element in half of this garlic? (8)
I believe the answer is:
thallium
'toxic element' is the definition.
'thallium' can be an answer for 'element' (thallium is a kind of element). I'm not certain of the 'toxic' bit.
'half of this garlic?' is the wordplay.
'half of' indicates taking half.
'garlic?' becomes 'allium' (I can't explain this - if you can you should believe this answer much more).
'this' with half the letters taken is 'th'.
'th'+'allium'='THALLIUM'
'in' is the link.
Can you help me to learn more?
(Other definitions for thallium that I've seen before include "Metallic element, Tl" , "Metallic element used in rat poison" .)