Effect of soil improvers on phytoremediation of cadmium and mercury from soil using grass miscanthus x giganteus

Istraživanje prezentirano u ovom radu provedeno je u završnoj godini trogodišnjeg eksperimenta koji se provodio na Agronomskom fakultetu Sveučilišta u Zagrebu u razdoblju od 2018. do 2021. godine. Glavni cilj rada bio je utvrditi utjecaj različitih poboljšivača (čisto tlo – kontrola, otpadni mulj iz bioplinskog postrojenja, mikoriza, pepeo MxG) na fitoremedijaciju tla onečišćenog s kadmijem i živom pomoću trave miskantus (Miscanthus x giganteus – MxG), energetske kulture koja se zbog svojih odlika (višegodišnji rast, visoka produktivnost i otpornost) koristi u proizvodnji biomase. Eksperimentalni dizajn postavljen je u plastičnim posudama prema slučajnom bloknom rasporedu, u četiri tretmana i tri ponavljanja. Tretmani su se međusobno razlikovali po dodanom poboljšivaču, dok je razina onečišćenja bila jednaka (100 mg Cd/kg tla i 20 mg Hg/kg tla). Kemijskim analizama određeni su parametri tla te podzemne (rizomi) i nadzemne biomase miskantusa. Prinos se kretao između 5,0 – 5,5 t ST/ha, sadržaj kadmija između 5,98 – 7,12 mg/kg, a sadržaj žive između 41,78 – 101,79 μg/kg u nadzemnoj biomasi. Sadržaj kadmija u podzemnoj biomasi kretao se između 44,3 – 57,2 mg/kg, a žive između 4,24 – 6,05 mg/kg. Koeficijent obogaćivanja (EC) u nadzemnoj biomasi za Cd kretao se između 0,060 i 0,071, što ukazuje na slabu akumulaciju Cd nadzemnom biomasom; a za Hg između 0,002 i 0,005, što znači da miskantus ne akumulira živu u nadzemnoj biomasi. EC u podzemnoj biomasi za Cd se kretao između 0,44 i 0,57, a za Hg između 0,21 i 0,30 što miskantus svrstava u kategoriju biljaka koje usvajaju umjerene količine Cd i Hg. Faktor translokacije (TF) za Cd kretao se između 0,104 i 0,145, a za Hg između 0,008 i 0,024. Dodani poboljšivači nisu imali značajan utjecaj na fitoremedijaciju kadmija i žive iz jako onečišćenog tla. Utvrđeno je da je onečišćenje visokim koncentracijama Cd i Hg nadjačalo utjecaj dodanih poboljšivača. Onečišćenje teškim metalima negativno je utjecalo na prinos. Pokazalo se da pri onečišćenju kadmijem i živom u ispitivanim koncentracijama miskantus nije najprikladniji izbor za fitoekstrakciju jer nadzemnom biomasom godišnje odnosi niske koncentracije teških metala, a vrijednosti u nadzemnoj biomasi premašuju dozvoljene za njeno sigurno spaljivanje. Prema izračunatom koeficijentu obogaćivanja i faktoru translokacije miskantus je pogodniji za korištenje u procesu fitostabilizacije i proizvodnji biomase na tlima umjereno kontaminiranim teškim metalima.The research presented in this paper was conducted in the last year of a three-year experiment conducted at the Faculty of Agriculture, University of Zagreb, from 2018 to 2021. The main objective of this work was to determine the influence of different amedments (clean soil – control, waste sludge from a biogas plant, mycorrhiza, MxG ash) on phytoremediation of soil contaminated with cadmium and mercury using Miscanthus (Miscanthus x giganteus – MxG), an energy crop used in biomass production due to its characteristics (perennial growth, high productivity and resistance). The experiment was set up in plastic pots as a randomized complete block design with four treatments and three replicates. The treatments differed from each other by the addition of amedments, while the pollutant levels were the same (100 mg Cd/kg soil and 20 mg Hg/kg soil). Soil parameters and below-ground (rhizomes) and above-ground biomass of Miscanthus were determined by chemical analysis. Yield ranged from 5,0 – 5,5 t ST /ha, cadmium content ranged from 5,98 – 7,12 mg/kg, and mercury content ranged from 41,78 – 101,79 μg/kg in aboveground biomass. Cadmium content in belowground biomass ranged from 44,3 – 57,2 mg/kg and mercury content ranged from 4,24 – 6,05 μg/kg. The enrichment coefficient (EC) in the aboveground biomass ranged from 0,060 to 0,071 for Cd, indicating weak enrichment of Cd in the aboveground biomass, and from 0,002 to 0,005 for Hg, indicating that Miscanthus does not enrich mercury in the aboveground biomass. The EC in belowground biomass ranged from 0,44 to 0,57 for Cd and from 0,21 to 0,30 for Hg, placing Miscanthus in the category of plants that accumulate moderate amounts of Cd and Hg. The translocation factor (TF) for Cd ranged from 0,104 to 0,145, and that for Hg ranged from 0,008 to 0,024. The added soil amendments had no significant effect on the phytoremediation of Cd and Hg from heavily contaminated soils. It was found that contamination with high Cd and Hg concentrations overrode the effect of the added soil amendments. Heavy metal contamination had a negative effect on yield. Miscanthus was found not to be the best choice for phytoextraction when contaminated with Cd and Hg at the concentrations tested, because it accumulates and removes low concentrations of heavy metals per year via the aboveground biomass, and the levels in the aboveground biomass exceed those allowed for its safe combustion. According to the calculations of EC and TF, Miscanthus is better suited for phytostabilization and biomass production on soils moderately polluted with heavy metals