Possible contaminants include: bacterial endotoxins (pyrogens that cause fever and inflammation), residual solvents from manufacturing, heavy metals, other peptides or synthesis byproducts, and in rare cases, bacterial or fungal contamination. This is why the full protocol matters: independent lab testing confirms identity and purity, and sterile filtering through a 0.22μm syringe filter removes bacteria and particulates. Neither step alone is sufficient—testing doesn't remove contaminants, and filtering doesn't verify identity.