its not about telling other colleagues Im concerned, its about still having a job
The first thing I would do is consult the HR person in the organisation and find out exactly what their policies are. THen I would arm myself with the relevant information about your legal entitlements under Australian law. It is unlawful to sack someone because they are pregnant - that said, employers can be quite tricky about finding other excuses. So document, document, document, and make sure you can let them know when you tell them that you are quite aware of your rights.

While heavy lifting won't harm your baby in early pregnancy, your ligaments are softening already, and you may injure yourself - but your employer needs to know that they shouldn't be asking *anyone* to do VERY heavy lifting - workplace safety requires adequate lifting equipment.

The magnetic field would concern me as much as the lifting.