Farmer weed crop International Institute of Tropical Agriculture/Flickr

Cómo las sustancias seguras se vuelven peligrosas

PALO ALTO – Desde el desarrollo de la ciencia de la toxicología en el siglo XVI, su principio rector ha sido que "la dosis hace el veneno". Es una regla que se aplica a las medicinas utilizadas por pacientes en todo el mundo muchos miles de millones de veces por día. La dosis correcta de aspirina puede ser una bendición terapéutica, pero consumirla en exceso puede resultar letal. El principio incluso se aplica a los alimentos: grandes cantidades de nuez moscada o regaliz son notoriamente tóxicas.

El riesgo que plantea una sustancia depende ampliamente de dos factores: su capacidad inherente para causar daño y nuestra exposición a ella. Es una idea simple, pero inclusive algunos profesionales razonables parecen incapaces de entenderla -como lo demuestra la decisión de la Agencia Internacional para la Investigación del Cáncer (IARC por su sigla en inglés), que forma parte de la Organización Mundial de la Salud, de clasificar el herbicida de uso frecuente 2,4-D como "posiblemente cancerígeno para los seres humanos".

Cuando se trata de herbicidas, la IARC parece estar en una mala racha. La organización recientemente clasificó el glifosato, otro herbicida popular, como "probablemente" cancerígeno, una conclusión en desacuerdo con las de agencias regulatorias en todo el mundo.

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