PROBLEMS OF IRRIGATION WITH POLLUTED WATERS IN GREENHOUSES

The effects of heavy metal environmental pollution on natural soilplant systems are complex and must be investigated by steps. Selection of sources of irrigation waters for greenhouse cultures should be carefully studied, particularly in industrialized areas where pollution normally reaches high levels. This study was carried out in order to learn more about metal uptake mechanisms by plants.

Rye-grass cultures on perlite, an artificial soil, were performed in the laboratory with individual additions of Cu, Zn, Na, Co, Ni, Cd, As and Pb after the plant had developed with a basic nutrient solution. Dry weights, moisture and components contents were determined in all samples previously divided into roots and tops.

Results show growth reductions in all cases, especially in tops associated with a decrease in moisture. Added elements concentrations increase and uptake would presumably continue in longer periods of cultivation. Added elements are accumulated in roots with the exceptions of As and Na.

Essential macronutrients equilibria in the plant seem to be disturbed only with the addition of As, the most toxic element in these experiences. Micronutrients contents show variations that could be related to perturbation of uptake and transport processes, and suggest, in some cases, the development of a defense mechanism.