Kate, I,too, am glad you started this thread. When Steve got diagnosed, part of the process was heavy metal testing. Many other things too like vitamin defiencies, immune markers, etc. If you really have concern about this, get the reports from your doctor who used an accredited lab for the results.
One thing many have found is doctors, nurses, healthcare providers dont know als. Naturopathy becomes something we all look at as a means to help our pals. Keep looking for the right doctors, they are invaluable. If you attend clinic ask there for recommendations on things to try. They will have a deeper knowledge of als and what helps more than most.