I mean that refer your comment in paragraph one ,as you need me to change from agents to micro-organisms
Undesirable substances" - more commonly known as contaminants – in EU legislation on animal nutrition means any substance or product, with the exception of pathogenic agentsmicro-organisms, present in and/or on the product intended for animal feed which presents a potential danger to human health, animal health or the environment or do not adversely affect livestock production.3