15871
This study evaluates the main essential trace ( Co , Cr , Cu , Fe , I , Mn , Mo , Ni , Se and Zn ) and toxic ( As , Cd , Hg and Pb ) element concentrations in milk from organic and conventional farms in NW Spain ( n = 50 ) .
 Co, Cr, Cu, Fe, I, Mn, Mo, Ni, Se, Zn, As, Cd, Hg, Pb
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 Co, Cr, Cu, Fe, I, Mn, Mo, Ni, Se, Zn, As, Cd, Hg, Pb