This is a question we are absolutely not qualified to answer. While your safety suits are designed to keep you safe and protected from harmful materials, I am not qualified to say whether or not you will be 100% safe having locked hair and working in and around such hazardous materials.
Dreadlocks do tend to hold onto smells, powders, debris, and other things more strongly than brushable hair. If you feel you are at any risk of hazardous materials becoming trapped in your hair, I would say that this is an instance where you have to make a priority decision.
Is your hairstyle more important, or the potential risk to your health?
I strongly you suggest to contact your supervisors about this matter and read the safety material information on the materials you are working with.