Selenium, copper, and zinc are all essential to good health in small amounts, and toxic in excess. Personally I doubt that they cause ALS, and am guessing that their excretion is due to a disease process. An environmental toxin called β-Methylamino-L-alanine (BMAA) from cyanobacteria has been linked to significantly increased occurrence of sporadic ALS in populations with frequent dietary consumption of food sources containing high levels of BMAA — including the Chamorro population of Guam where ALS incidence is approximately 100 times greater than other populations https://pubmed.ncbi.nlm.nih.gov/19929726/ .
Wowser. What's their diet consist of?