Complex sentence: On the other hand, the intake of selenium is counteracted by its poor bioavailabilty in the soils of industrialized areas and toxic effects of selenium species may occur at lower concentrations than previously believed.
Split into simpler sentences: On the other hand, the intake of selenium is counteracted by its poor bioavailabilty in the soils of industrialized areas. Furthermore, toxic effects of selenium species may occur at lower concentrations than previously believed.