Ovrednotenje izvedljivosti remediacije s kelatnimi ligandi in ocena tveganj remediiranih tal

Jež, Erika (avtor), Leštan, Domen (mentor)

Namen doktorske disertacije je bil ovrednotiti izvedljivost remediacije s kelatnim ligandom etilendiamintetraocetno kislino (EDTA) ter oceniti tveganja zaradi remediiranih tal, če bi jih vnesli v okolje. Za ovrednotenje izvedljivosti remediacijske metode z EDTA smo analizirali 268 vzorcev tal iz Mežiške doline. Vzorce tal smo ekstrahirali s 60 mmol EDTA kg-1 in v povprečju odstranili 63 ± 11 % Pb ter 22 ± 16 % Zn. Prikaz podatkov v prostoru (analiza Baysian kriging) pred ekstrakcijo vzorcev z EDTA in po njej dokazuje, da ima remediacijska metoda potencial za zmanjšanje prostora, kjer je vsebnost Pb in Zn nad kritično mejo. Z in vitro metodo SOP EPA (angl. Standard operating procedure for an in vitro bioaccessibility assay for lead in soil) smo 79 mežiškim vzorcem v naseljih določili biodosegljivost Pb in ugotovili, da imajo tla, ekstrahirana z EDTA, v primerjavi z neremediiranimi nižjo biodosegljivost Pb za 2,6-krat v Mežici, 3,2-krat v Žerjavu in 2,9-krat v Črni na Koroškem. Za iste vzorce smo poleg podatkov o skupni vsebnosti Pb v tleh in biodosegljivega Pb v tleh pred ekstrakcijo z EDTA in po njej pridobili tudi podatke o vsebnosti Pb v pitni vodi ter vsebnosti Pb v zraku in jih vnesli v napovedovalni model IEUBK (angl. Integrated exposure uptake bio-kinetic model). Z modelom IEUBK smo ocenili, da bi se povprečna vsebnost Pb v krvi triletnikov znižala pod 10 µg dL-1 le v Mežici in Črni na Koroškem, v Žerjavu pa bi bila ocenjena povprečna vsebnost tudi po ekstrakciji z EDTA nad 10 µg dL-1. Ker napovedovalni modeli vrednotijo remediacijsko metodo kot izvedljivo, smo se v disertaciji podrobneje posvetili potencialnim tveganjem remediiranih tal (ostanek EDTA/emisije EDTA v okolje). Za ta namen smo izvedli ekstrakcijo tal z EDTA na 20 vzorcih iz Slovenije, Avstrije, Češke in ZDA z različnimi lastnostmi tal in smo s spektrofotometrično metodo ugotovili, da je EDTA ostala v tleh v različnih deležih. Največ EDTA je ostalo v tleh po ekstrakciji s H4EDTA (64 ± 17 %), najmanj pa po ekstrakciji s CaNa2EDTA (14 ± 8 %). 60 kg tal iz Podkloštra (Avstrija) smo remediirali s CaNa2EDTA v pilotni remediacijski napravi in izmerili, da se v kislih pogojih iz sveže remediiranih tal lahko sprosti 5 % EDTA (od 120 mmol kg-1). Tla smo za namen določanja sekundarnih emisij starali 18 mesecev pri sobni temperaturi, stresno situacijo smo simulirali s ponavljanjem odmrzovanja in zamrzovanja ter vnesli deževnike (Lumbricus rubellus). Iz remediiranih tal s simulacijo abiotskih in biotskih dejavnikov se v kislih pogojih sprošča 3 % EDTA. Ker EDTA v okolju hitro tvori komplekse s potencialno strupenimi kovinami, ki so nevarni za zdravje ljudi in okolje, moramo vsako emisijo iz remediiranih tal obravnavati kot nevarnost.

• Jezik: Slovenski jezik
• Ključne besede: remediacija tal, EDTA, zemljevid onesnaženosti, svinec v krvi otrok, biodosegljivost svinca, ostanek EDTA, sekundarne emisije EDTA
• Vrsta gradiva: Doktorsko delo/naloga
• Organizacija: BF - Biotehniška fakulteta
• Leto izida: 2019
• PID: 20.500.12556/RUL-107607
• Datum objave v RUL: 07.05.2019

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Fisibility evaluation of remediation with chelants andrisk assesment of remediated soil

Izvleček

The aim of the doctoral thesis was to evaluate the feasibility of remediation with chelant ethylenediaminetetraacetic acid (EDTA). Soil samples from 268 locations in the Meza Valley were extracted with 60 mmol EDTA kg-1 with the average removal rate of Pb and Zn of 63 ± 11% and 22 ± 16%, respectively. The use of Baysian kriging method predicted that applying EDTA-based soil extraction has potential for spatial reduction of soil contamination with Pb and Zn below the critical regulatory threshold limit. EDTA extractions of 79 soil samples taken from populated area in cities of Mezica, Žerjav and Črna na Koroškem reduced the in vitro bio-accessibility of soil Pb assessed using Standard operating procedure for an in vitro bioaccessibility assay for lead in soil (SOP EPA) method by 2.6-, 3.2- and 2.9-times, respectively. Data on soil total Pb concentrations and data on in vitro Pb bio-accessible concentrations in both contaminated and remediated soils, and data on Pb concentration in airborne dust and Pb in drinking water were fed into Integrated Exposure Uptake Bio-kinetic model (IEUBK). The IEUBK model predicted that after EDTA soil extraction the mean blood Pb level in 3-year-old children in cities of Mežica and Črna na Koroškem would decrease bellow the targeted value of 10 µg dL-1; only in city Žerjav the expected mean blood Pb level would remain above the value stipulated by legislation. Since models (kriging and IEUBK) predicted the remediation by EDTA as a potentially feasible, the focus of the doctoral work shifted to examination of potential risks posed by the remediated soil (EDTA retention/EDTA emissions). We assessed EDTA in 20 remediated soil samples with diverse soil properties from contaminated sites in Slovenia, Austria, Czech Republic and USA. Results proved that applied EDTA was partly retained in remediated soils. Spectrophotometric analysis showed that EDTA retention was the largest when the chelating agent was used in form of H4EDTA (64 ± 17%) and the smallest when CaNa2EDTA was applied (14 ± 8 %). Sixty kg of contaminated acidic soil from Arnoldstein (Austria) was washed in a pilot remediation plant using 120 mmol kg-1 of CaNa2EDTA. Up to 5% of the total applied chelating agent was detected in emissions (acidic conditions) from freshly remedied soil. Remediated soil was further aged under room conditions for 18 months, environmental abiotic stressors were simulated by repeating soil freezing and thawing and soil biotic factors by soil inoculation with Lumbricus rubellus earthworms. The emissions of EDTA from soil exposed to various abiotic and biotic factors reached up to 3 %. Emissions of EDTA chelated with toxic metals are hazardous for humans and environment and must be prevented.

• Ključne besede: Soil remediation, EDTA, soil pollution map, children lead poisoning, lead bio-accessibility, EDTA retention, secondary emissions of EDTA