The article says nothing about concentrations. There are small concentrations of Arsenic in seawater along with everything else on the periodic chart. Arsenic will kill you in high concentrations. Seawater will not, and it has Arsenic in it. I find the article devoid of rational scientific analysis. It is “scare porn” motivated by politics and not science.
I forgot to add that most of these harmful chemicals are very soluble in di-hydro monoxide. We must ban this dangerous liquid least we all perish.