Due to its relatively low reactivity, it can be found in seawater in large amounts; it is estimated that seawater is approximately 0.14 to 0.25 parts per million (ppm) or 25 micromolar.
dˈuː tʊ ɪts ɹˈɛlətˌɪvli lˈoʊ ɹɪɐktˈɪvᵻɾi, ɪt kæn biː fˈaʊnd ɪn sˈiːwɔːɾɚɹ ɪn lˈɑːɹdʒ ɐmˈaʊnts; ɪɾ ɪz ˈɛstᵻmˌeɪɾᵻd ðæt sˈiːwɔːɾɚɹ ɪz ɐpɹˈɑːksɪmətli zˈiəɹoʊ.fˈoːɹtiːn tə zˈiəɹoʊ.twˈɛnti fˈaɪv pˈɑːɹts pɜː mˈɪliən pˌiːpˌiːˈɛm ɔːɹ twˈɛnti fˈaɪv mˈaɪkɹoʊmˌoʊlɚ.