What do I do about work?!

Hi all, just looking for some advice on telling work that I'm pregnant. So if I had an office job I'd probably leave it until about 12 weeks, but I work in a workshop with tractors...so like a mechanic. So on a daily basis I'm exposed to chemicals, fumes, heavy lifting and tools. Im also out on people's farms a lot. I've only just found out and I'm early on but has anyone been in a similar situation of having a high risk job? I'm wondering if I should tell them right away or leave it a few weeks? It's my first baby.