Complex sentence: Some heavy metals are either essential nutrients (typically iron, cobalt, and zinc), or relatively harmless (such as ruthenium, silver, and indium) but can be toxic in large amounts or certain forms.
Split into simpler sentences: Some heavy metals are essential nutrients (typically iron, cobalt, and zinc). Others are relatively harmless (such as ruthenium, silver, and indium) but can be toxic in large amounts or certain forms.