Effects of municipal reclaimed wastewater on the macro- and micro-elements status of soil and of Brassica oleracea var. Italica, and B. oleracea var. Gemmifera

An experiment was conducted in a greenhouse, located in Agrinion, Greece, where the effect of treated municipal wastewater (TMWW), compared to the ordinary irrigation water, was studied by means of a randomized block statistical design, on the macro- and micro-element and heavy metal content of Brassica oleracea var. Italica (Broccoli), and B. oleracea var. Gemmifera (Brussels sprouts) plants, as well as on the physical and chemical properties of the clay loam (CL) soil, and its inorganic composition, in order to examine the possibility of TMWW reuse for the irrigation of the above vegetables. The transplanting was done on December 2005, and harvesting of the heads and sprouts 16 weeks later, i.e. at the end of April. Ordinary irrigation water, TMWW, soil, and plant samples, were analyzed, and the data obtained were statistically processed. The following were found: applied TMWW increased significantly, in comparison to control, the content of some macro- and micro-elements in the soil, but the concentrations of most of them were generally within the accepted critical levels, except for P and Zn and Cd whose concentration varied as follows: in Brocoli soil P 18.36–41.16 mg/kg, Zn 3.61–4.64 mg/kg, and Cd 0.065–1.20 mg/kg, while in Brussels sprouts soil P 20.6–36.32 mg/kg, Zn 2.87–4.83 mg/kg and Cd 0.06–1.45 mg/kg. These results showed that TMWW had a residual effect with respect to these elements. Similarly, the TMWW increased significantly the heavy metal content in the dry matter of the roots as follows: in Brussel sprouts Cd varied from 0.0083 to 0.78, Co 0.029 to 3.38 and Ni from 4.83 to 7.27 μg/g, respectively, and in Broccoli Ni varied from 4.20 to 10.13 μg/g. TMWW also increased the accumulation of Fe in the roots of Broccoli from 379.5 to 1022.0 mg/kg. However, the levels of the heavy metals in the edible plant parts (heads and sprouts) were very high, varying as follows: in Broccoli Ni 3.91–4.15 μg/g, and Pb 9.82–10.40 μg/g, while in Brussels sprouts Cd 0.8–1.17 μg/g, Co 2.35–2.70 μg/g, and Ni 5.70–6.17 μg/g. These increased heavy metal contents in the edible plant parts, and the heavy FC and E. coli load of the TMWW, constitute a high health risk factor, and therefore the TMWW studied, cannot be used at the present time for the irrigation of these vegetables, unless it is subjected in the future, to a secondary or advanced primary treatment (APT).