Used to be able to prevent this fouling by coating ships and submarines with toxic agents, like heavy metals, but these heavy metals aren't as effective at keeping ships clean as they used to be.
Si era soliti prevenire  questa incrostazione ricoprendo navi e sottomarini  con agenti tossici come metalli pesanti, ma questi metalli pesanti non hanno l' efficacia del mantenere  le navi pulite come una volta.