CHROMIUM REMOVAL USING CONSTRUCTED WETLANDS: METAL ACCUMULATION AND TOLERANCE IN JUNCUS IMBRICATUS

ARÁN, DANIELA S.; MONFERRÁN, MAGDALENA; PIGNATA, M. LUISA; HARGUINTEGUY, CARLOS A.

Río de Janeiro

Congreso; XVI Congresso Brasileiro de Ecotoxicologia - ECOTOX 2021; 2021

ECOTOX y Sociedad Brasilera de Ecotoxicología

Chromium has been detected in freshwater in many regions in Argentina with concentrations of total chromium that exceed the maximum allowed leveles for the protection of the aquatic biota in Argentina ( Harguinteguy et al., 2019; Monferran et al, 2016). Constructed wetlands (CWs) have attracted wide public and scientific interest for the removal of chromium from water and wastewater because it is a cost effective technology owing to its simplicity in operation and high efficiency of removal (Ramírez et al., 2019). The main objective of this study was to investigate the role of Juncus imbricatus in chromium accumulation and tolerance. The native plants Juncus imbricatus used for phytoremediation experiments were collected in ?Los Reartes River? in Cordoba, Argentina. Twelve identical-sized pilot-scale wetland were made in 36L plastic pots and four similarly sized individuals of the specie J. imbricatus were planted in each wetland and acclimatized. After two months a synthetic solution containing Cr prepared from Cr(NO3)3 was added to the wetlands. Three levels of chromium treatment were considered 5 mg, 20 mg and 50 mg per liter. Each treatment was performed in triplicate and the experiment continued for 28 days.Three replicate water samples were collected at the initial time (day 0) and at 1, 3, 7, 14, 21, and 28 days after starting the treatments. Cr in water was determined using a ICP-MS. On the other hand, one plant of Juncus imbricatus was harvested from each wetland and separated into roots, rhizome and stem at 7, 14, 21 and 28 days after starting the treatments. Subsequently samples were used to analize chromium accumulation and physiological parameters suchs as FRAP, MDA, soluble sugars and photosintetic pigments. Finally, the relative growth rate (RGR) was calculated taking into account the variability of the stem biomass during the experiment. Chromium concentration in water decreases during the 28 days of exposure, in all treatments with final removal of 87.46%, 90. 85%, 89.31% for 5 mgL-1 Cr 20 mgL-1 Cr and 50 mgL-1 Cr respectively. The chromium uptake in roots, rhizomes and stems of the macrophyte significantly increased (p < 0.001) with an increase in chromium concentration in the culture medium. J. imbricatus was able to Cr up to 57 mg Cr kg-1in stem, 565 mg Cr kg-1 in rhizome and 2049 mg Cr kg-1 in root when treated at 50 mg Cr L-1. The fact that the plant limits root-to-shoot translocation and maintains relatively low levels in their aboveground tissues over a wide range of metal exposure suggest uggested that the macrophyte acts as a phytostabilizer (Phusantisampan et al., 2016; Rana & Maiti, 2020). Throughout the experimental period, the relative growth rates were positive in all treatments from 0 to 28 days except in wetlands exposed to 50 mgL-1 Cr from the 14th day which showed a decrease. Consistent with these results, a study conducted in a specie of the same genus, Juncus effusus, reported not significative differences in RGR between control and 5 mg L-1 Cr treatment, while the treatments of 10 mg L-1 Cr and higher chromium concentrations reduce the growth rate significatively (Gruber et al., 2008). Regarding physiological parameters, in this study the total chlorophyll, chlorophyll a, chlorophyll b and carotenoids content in J. imbricatus did not differ significantly from the control treatment throughout the experiment. The ferric-reducing antioxidant power (FRAP) provides an indicator of the non-enzymatic antioxidant defense capacity of plant cells and in this research FRAP concentration increases in the stem in the first fourteen days for the 50mg L-1 treatment compared with the control. However it decreases after 28th days of chromium exposure compared with the control and compared with the same treatment at the 14th day. This results suggest a lower antioxidant capacity in the stem after a long exposition to higher Cr concentration. Malondialdehyde (MDA) is an indicator of lipid peroxidation and in this research no significant differences were found between control and Cr group treatments. Finally In J. imbricatus the exposition to chromium was accompanied by a general tendency to increase soluble sugar, which may contribute to maintainosmotic potential, cell turgor and defense of biomolecules and membranes against oxidative stress (Pazcel et al., 2018) Analyzing metal toxicity effects on plant, relative growth rate, visual damage, physiological parameters and metal accumulation are the basis for selecting plant species for phytoremediation. Juncus imbricatus has shown to be a fast-growing plant with a long root system and dense root mat, a tolerant macrophyte to high Cr concentrations, and high metal stabilization potential in the root. All thouse features make the native macrophyte Juncus imbricatus, a promising chromium phytoremediatior plant.