Experimental determination of the upper critical levels for Cd, Pb, Mo and Cu in adventitious roots of onion bulbs, Allium cepa L.

Patricio Álvarez V.1, Jorge Cortés M.1, Donatila Ferrada T.1, Cecilia Leyton M.1 y Jorge Sans P.1

The maximun concentration of heavy metal aliowed in irrigator water established by the Chilean official norm NCh 1333. Of 1978, (INN 1987) are not based in studies performed in Chile, country with a great mine industries. Thus, the rules of others countries may be too restrictive for certain metals and permisive for others. For this reason, it is important to develop biological models in order to precísily define the concentration of heavy metals in water to be tolerated by living systems. The purpose of this work was to determine the absolute upper critical level for two non essential heavy metals, Cd and Pb, and two essential metals, Mo and Cu, in adventitious roots of onion bulbs cultured directly in tap water. For this purpouse, we studied separatly the effect of different concentration of each one of the four metals on root growth, oxidative metabolism and the accumulation of then in several parts of the plants. The results show that upper critical level (metal concentration present in water capable to inhibit 20% of root growth) obtained after 96 hr of treatment, for Cd, Pb, Mo and Cu was 1.08, 2.40, 75.70 and 0.09 mg/L, respectively. The obtained upper critical level for Cd and Mo are 108 and 7.570 time fold higher to the Chilean norm, respectively. In contrast, for Pb and Cu the upper critical level obtained correspond approximately to the half of the Chilean official norm. These results show that the Chilean norm for Cd and Mo in irrigator water is too restrictive. On the contrary, fur Cu and Pb is surpass. The significan ce and projection of these results by using this bioassy is discussed.

Keywords: upper critical level, biological toxicity, root growth, cadmiun, molybdenum, lead, copper.
1 Laboratorio de Fitobiologia Celular y Molecular, Departamento de Biologia Celular y Genética, Facultad de Medicina, Universidad de Chile, Casilla 70061, Correo 7. Santiago, Chile.