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.

Bruges

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

Ghent University

Treatment wetlands are used all over the world due to the wide range of effluents that they can treat. Inthe case of effluents containing metals, they are applied as secondary or tertiary treatments. In this workwe 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 primarytreatment and showing a high Cr concentration during 30 days. This work is aimed to assess the plantresponse after an accidental dumping of high Cr concentration in an effluent without the primarytreatment in a treatment wetland. The studied system is a free-water surface wetland located in SantoTomé 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 10m3−1 d 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 partsof leaves, roots, and rhizomes), and sediment were sampled at the inlet and outlet. All samples werecollected in triplicate. Cr bioconcentration (BCF) and translocation factors (TF) were calculated. Besides,plant anatomical measurements and Scanning Electron Microscopy (SEM) X-ray micro-analysis werecarried out. The wetland showed a high Cr percent removal from water indicating that the system wasable to remediate the accidental dumping of this metal. After the accidental dumping, plant tissues fromthe inlet showed Cr concentrations significantly higher than those measured during the normal operationperiod. Death leaves also act as Cr accumulation compartment. Regarding sediment, Cr concentrationsafter the accidental dumping were significantly higher than those obtained during the normal operationperiod. Cr measured in water was not proportional to the Cr measured in tissues and sediment. Thisindicates that once the Cr is discharged into the wetland, it precipitates accumulating on the plant tissuesand bottom sediment. In the mapping obtained under SEM-EDX, Cr accumulation was observed in theroot epidermis. BCFs were higher than 1 in all cases, being the values obtained after the accidentaldumping an order of magnitude larger, indicating that Cr was accumulated in the bottom sediment andthen taken by the roots and accumulated in this organ. During the normal operation period, Cr wastranslocated from roots to rhizomes. However, after the accidental dumping, this metal does nottranslocate, indicating that faced to high Cr availability, this metal is not transported to the aerial partsbeing accumulated in roots as a defense mechanism. After the dumping, the inlet values of root crosssectionalareas (CSA) were significantly higher than that of the outlet. This indicates that one of the plant responses faced to Crexposure 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 withthose of the plants studied in a natural wetland. Faced with an accidental Cr dumping, the studiedtreatment wetland was capable of recovering its performance, demonstrating its robustness. T.domingensis demonstrated tolerance to the high Cr concentrations detected during the accidentaldumping and accumulate this metal in its tissues demonstrating its potential for rhizofiltration andphytostabilization in the studied wetland.