Occurrence of arsenic species in algae and freshwater plants of an extreme arid region in northern Chile, the Loa River Basin

► Loa River Basin (area of study) presents extreme environmental conditions. ► Arsenic and arsenic compounds were determined in algae and aquatic plants. ► Inorganic arsenic species predominated in all samples. ► Arsenic content in most samples ranged from 20 to 341 mg As kg−1. ► One sample (Cladophora sp.) presented hyperaccumulation of As (11 000 mg As kg−1).