Farmer weed crop International Institute of Tropical Agriculture/Flickr

Come una sostanza sicura diventa pericolosa

PALO ALTO – Sin dal suo sviluppo nel XVI secolo, il principio ispiratore della tossicologia è stato che “il veleno è nelle dosi”, una regola che vale per i medicinali assunti miliardi di volte al giorno da pazienti in tutto il mondo. Una giusta dose di aspirina può essere una benedizione dal punto di vista terapeutico, ma un consumo eccessivo può rivelarsi fatale. Lo stesso principio si applica anche agli alimenti, infatti è noto che la noce moscata o la liquirizia assunte in dosi massicce diventano tossiche.

Il rischio legato a una sostanza dipende, in linea di massima, da due fattori: la sua nocività intrinseca e l’esposizione ad essa. Il concetto è semplice, ma sembra che persino alcuni presunti professionisti del settore siano incapaci di afferrarlo – come dimostra la decisione dell’Agenzia internazionale per la ricerca sul cancro (IARC), un organismo dell’Organizzazione mondiale della sanità, di classificare il comune erbicida 2,4-D come “potenzialmente cancerogeno per l’essere umano”.

Per quanto riguarda gli erbicidi, la IARC sembra collezionare un errore dietro l’altro. L’organizzazione ha recentemente classificato il glifosato, un altro erbicida comune, come “probabilmente” cancerogeno, una conclusione che contrasta con quella di altri enti regolatori nel mondo.

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