Root morphometrical response in plants growing in a wetland constructed for the treatment of a metallurgical effluent.

HADAD H. R.; MUFARREGE, M. M.; DI LUCA, G. A.; DENARO, A.C.; NOCETTI, E.; MAINE, M.A.

Simposio; 10th International Symposium on Wetland Pollutant Dynamics and Control, WETPOL.; 2023

Treatment wetlands are used all over the world due to the wide range of effluents that they can treat. In the case of effluents containing metals, they are applied as secondary or tertiary treatments. In this work we studied a free-water surface wetland that treat the effluent containing Cr from a metallurgical factory. However, during the monitoring occurred an unintentional dumping of effluent without the primary treatment and showing a high Cr concentration during 30 days. This work is aimed to assess the plant response after an accidental dumping of high Cr concentration in an effluent without the primary treatment in a treatment wetland. The studied system is a free-water surface wetland located in Santo Tomé city, Santa Fe province, Argentina (31º39’45” S, 60º48’58” W). It is 20 m long, 7 m wide, and 0.3– 0.7 m deep, and is waterproofed with a geomembrane. Mean wastewater discharge is approximately 10 m3 d−1 and water residence time is 7–10 days. The wetland was planted with Typha domingensis. Samples were taken shortly after the unintentional dumping of effluent. Water, plants (aerial and submerged parts of leaves, roots, and rhizomes), and sediment were sampled at the inlet and outlet. All samples were collected in triplicate. Cr bioconcentration (BCF) and translocation factors (TF) were calculated. Besides,plant anatomical measurements and Scanning Electron Microscopy (SEM) X-ray micro-analysis were carried out. The wetland showed a high Cr percent removal from water indicating that the system was able to remediate the accidental dumping of this metal. After the accidental dumping, plant tissues from the inlet showed Cr concentrations significantly higher than those measured during the normal operation period. Death leaves also act as Cr accumulation compartment. Regarding sediment, Cr concentrations after the accidental dumping were significantly higher than those obtained during the normal operation period. Cr measured in water was not proportional to the Cr measured in tissues and sediment. This indicates that once the Cr is discharged into the wetland, it precipitates accumulating on the plant tissues and bottom sediment. In the mapping obtained under SEM-EDX, Cr accumulation was observed in the root epidermis. BCFs were higher than 1 in all cases, being the values obtained after the accidental dumping an order of magnitude larger, indicating that Cr was accumulated in the bottom sediment and then taken by the roots and accumulated in this organ. During the normal operation period, Cr was translocated from roots to rhizomes. However, after the accidental dumping, this metal does not translocate, indicating that faced to high Cr availability, this metal is not transported to the aerial parts being accumulated in roots as a defense mechanism. After the dumping, the inlet values of root cross- sectional areas (CSA) were significantly higher than that of the outlet. This indicates that one of the plantresponses faced to Cr exposure in the TW was to increase the size of roots to tolerate this metal. Crtolerance was determined by significantly higher parameters of the root morphometry in comparison with those of the plants studied in a natural wetland. Faced with an accidental Cr dumping, the studied treatment wetland was capable of recovering its performance, demonstrating its robustness. T. domingensis demonstrated tolerance to the high Cr concentrations detected during the accidental dumping and accumulate this metal in its tissues demonstrating its potential for rhizofiltration and phytostabilization in the studied wetland.