The effects of the treated municipal wastewater (TMWW) on the essential nutrients interactions in the various plant parts of Brassica oleracea var. Italica (Broccoli) was studied, in comparison to the fresh irrigation water, denoted as "control". The experiment was based on a randomized block design, and it was conducted in a greenhouse of the Department of Environmental and Natural Resources Management, University of Ioannina, Agrinion, Greece. It included two treatments, i.e. (a) TMWW and (b) control, in six replications, with a total number of 2 x 6 = 12 plots of 2.5 m x 1.8 = 4.5 m(2) size. The plants were transplanted in rows 0.8 m apart from each other, while the distance between the plants in the row was 0.5 m. During the growth period, thirteen applications of TMWW and control, respectively, were made, each one being equal to 30 L/4.5 m(2). In total, 390 L/4.5 m(2) or 867 m(3)/ha were applied. The following were found: 1) The TMWW reuse favored and intensified the synergetic interactions: Ca x Fe, K x P, Fe x Ni in the roots. As a result, higher levels of Fe, P and Ni were accumulated in comparison to the corresponding levels under the control. 2) The following interactions studied, were functioning simultaneously in: a - roots, leaves and heads (N x Zn, P x Zn), b -roots and]caves (Ca x Ni, K x B and P x K) and c - roots and heads (Fe x Ni, Mn x B, and Fe x Ca), thus, suggesting their importance in the plant nutrition and growth processes. 2) The broccoli root system, in comparison to leaves and heads accumulated in general, higher levels of nutrients, especially Fe (1200 mu g/g) suggesting that this vegetable is a Fe accumulator. The lowest nutrient accumulation, as a result of the interactions under the TMWW effect, was found in the edible plant part, i.e. in the broccoli heads.