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ReSoil, our patented soil remediation technology is the single commercially available option which efficiently removes Pb and other toxic metals from contaminated soils and sediments, recycles reagent and process waters, generates no liquid wastes, produces no toxic emissions from remediated soil and preserves remediated soil as a natural resource.
Soil contamination with Pb and other toxic metals is ubiquitous
Soils are an omnipresent factor of human existence and valuable, limited resource. They are often contaminated with a number of toxic metals which doesn’t biodegrade or decay, with Pb presenting the most pervasive and persistent risk to human health¹. Urban soils act as an integrator of decades of pollution by Pb-based paint and emissions from the combustion of leaded gasoline. In the USA, exterior Pb paint was used in 89% of residential structures before 1978.² As an example of urban contamination, out of 49 analysed playgrounds in Vilnius, 21 had moderately hazardous to hazardous levels of Pb contamination.³ Both racial/ethnic and income disparities have been documented with respect to exposure to Pb in soils.⁴
Shooting guns at firing ranges is an occupational necessity for military, police officers and security personnel. In the USA alone an estimated 16.000-18.000 firing ranges exist. Following the shooting activity the soil at firing ranges accumulate substantial quantities of Pb.
One of the most important sources of soil Pb is ore mining/smelting: according to a global inventory (late 1980s), about 356-857×10⁶ kg Pb was released annually.⁵ Same of the major miming/smelting locations in Europe are Noyelles-Godault/Auby, Mortagne-du-Nord and Bazoches-les-Gallérandes in France, Pribram in Czech Republic, Olkusz and Bukowno in Poland, Avonmouth in UK, Harjavalta in Finland, Rönnskär in Sweden, Lommel in Belgium, Kuklen in Bulgaria, Kosovska Mitrovica in Kosovo, Veles in Macedonia.⁶ Emissions decreased in western countries over the last 50 years due to the installation of efficient flue gas cleaning systems.⁷ However, the increasing industrial activities on other continents could significantly affect global emissions. For example, up to 2007 cumulative emissions from mining, ore dressing, and smelting in China were about 1.62 ×109 kg Pb.⁸
Pb is highly toxic to humans. Any exposure is considered to be potentially harmful, no threshold for adverse effects has been identified.⁹ In particular children are a highly vulnerable group due to accidental mouth ingestion.¹⁰ Adults take up 10–15% of ingested Pb, whereas children may absorb up to 50% via the gastrointestinal tract.¹¹ Ingestion of soil accounts for more than 80% of the daily Pb exposure.¹² The high gastrointestinal uptake and the permeable bloodbrain barrier make children susceptible to Pb exposure and subsequent brain damage, neurotoxic and developmental effects.¹³ A recent report from the Centres for Disease Control and Prevention (CDC) has found that 535.000 children between one and five years old, in the USA, have a minimum of 5 µg Pb dL ⁻¹ of blood. Not much has changed from the results found in 1990.¹⁴ Arguments are being made to clean up areas where the soil is proven to contain high levels of Pb, especially if children often frequent those areas.
Human population is growing and the world food supply will have to be doubled between 2005 and 2050.¹⁵ The scarcity of soil resources will inevitably force us to cultivate on contaminated areas; metal contaminated land is already exploited for food production to compensate the loss of agricultural surface due to urbanization.¹⁶ All around the world, urban agriculture is booming fulfilling diverse functions including food production, community building, reducing socio-economic tensions and food millage.¹⁷ Urban allotment gardens have recently been offered by local governments to encourage low income citizens to produce their own food.¹⁸ In New York with long history of gardening 71% of the home garden samples exceed respective Soil Clean-up Objective limits for Pb and As.¹⁹ 52% of crop samples from the Berlin inner city vegetable gardens exceeded standards²⁰ for Pb concentration in food crops.²¹ The citywide study showed that Pb contamination of urban soils is raising a major human health concern that may become a major obstacle for the adoption of urban agriculture.²²
Current Remediation methods are ineffective in Pb removal and waste soil
A solution for contamination problems is reclamation and re-use of metal contaminated land by effective, cost-efficientand sustainable (soil preserving) remediation methods. Most countries have made the clean-up and restoration of the contaminated land a priority. Historically, excavation to landfill (dig and dump) has been the solution, offering a quick removal mechanism of a pollution source in the soil. Ever more countries are implementing the legislature with heavy restrictions on landfill. However, other currently available options: soil sealing, separation of contaminated fines, also waste soil. In response, the concept of Gentle Remediation Options (GRO) has emerged. These are techniques that result in no gross reduction of soil functionality as well as risk management.²³ For metal contaminated soils GRO comprises immobilisation and phytoextraction. Up-to-date plant hyperaccumulation of Pb, Cu, Co and Tl remained largely unconfirmed.²⁴ ²⁵ Immobilisation by various additives (phosphates, zeolites, iron and iron oxides etc.) reduces metal plant uptake but does not remove toxic metals from the soil.²⁶ Only a fraction of Pb contaminated soils is treated today due to the lack of efficient and sustainable remediation technologies.
Soil washing and removal of toxic metals with chelants preserves basic soil functions.²⁷ ²⁸ In particular soil washing with ethylenediamine tetraacetate (EDTA) as the most effective, benchmark chelant, was intensively studied for the last two decades by research groups worldwide. However, difficulties with cost effective treatment of vast quantities of process solutions²⁹, absence of feasible EDTA recycling and toxic emissions from remediated soil due to poor EDTA biodegradability and environmental persistence has been an unsolved problem – up to now.
ReSoil - cost-efficient, effective, soil preserving and emission free remediation technology
We developed an unique soil-washing technology (patent families US 9108233B2 and EP 3153246B) where EDTA and process waters are recycled in an imposed pH gradient and in a closed process loop (Figure 1). To achieve cost-efficiency the ReSoil technology uses inexpensive and waste materials. The alkalinity imposed by Ca-containing base (i.e. lime) destabilizes EDTA chelates with toxic metals.³⁰ ³¹ Consequently, Pb and other toxic metals (Me) are replaced in the EDTA chelate by Ca and toxic metals participate from the reaction as insoluble hydroxides. The chelant in the recycled Ca-EDTA form is much less soil aggressive than commonly used Na-EDTA.³² To shift the chemical equilibrium further towards product formation, we introduced alkaline adsorption of released toxic metals on polysaccharide materials (i.e. waste paper, R3C-OH) for the substitution/ adsorption/ precipitation reaction:³³
2Ca²⁺ + 4(OH)⁻ + 2Me-EDTA + R3C-OH ↔ 2Ca-EDTA + Me(OH)2(s) + R3C-OH-Me(OH)2-(s)
The alkaline part of the process yields more than 90% of recycled EDTA. The remaining EDTA is recycled in insoluble acidic form (H4EDTA, pK4 = 2.7)after addition of sulfuric acid (H2SO4). Excess SO4²⁻ from the acidic and Ca²⁺ from the alkaline part of the process forms insoluble gypsum (CaSO4) which is removed with the remediated soil. The build-up of salty ions and deterioration of process solutions throughconsecutive batches is thus prevented. Gypsum is a plant nutrient source and beneficial soil conditioner.³⁴ Remediated soil is milled to obtain artificial soil aggregates, and then mixed with the cleansed oversized soil material, fertilized and formulated. The post-remedial toxic emissions from soil are mitigated to the levels close orbellow limits of quantification by effective soil rinsing which reduces toxic metals and EDTA concentration in the downstream process waters (Figure 2) and addition of zero-valent Fe (Fe⁰) into the soil slurry (Patent appl. GB 1720126.0) which enables for fast and permanent adsorption of small residual quantities of EDTA and toxic metals chelates. The process is abiotic; poor EDTA biodegradability is not an issue even if exceedingly high chelant concentrations are used in soil washing. Furthermore, Fe⁰ slurry addition simultaneously immobilize As which is a common soil co-contaminant to soil Pb.
Figure 1. The ReSoil technology flowchart. The recovered EDTA and process waters are reused in a closed cycle. The washed soil is rinsed 3-times with recycled process water and at the end with fresh water to compensate for difference in soil moisture between contaminated soil entering and remediation soil leaving the process.
ReSoil is an ex situ remediation technology – the contaminated soil is excavated and transported to the remediation facility and the remediated soil returned to the site of excavation. Soil washing by EDTA has shown to result in high multimetal (Pb, Zn, Cd, Cu) removal efficiency,³⁵ ³⁶ especially from bioavailable soil fractions.³⁷ ³⁸ Up to 95% of Pb removal from contaminated soils by EDTA has been documented by other research groups.³⁹ The ReSoil process generates less than 1.1% weight of solid wastes, no liquid wastes are produced. The technology was developed from laboratory / pilot-scale to demonstrational remediation plant with the capacity of 6 tons of soil per day in the city of Prevalje in Meza Valley, Slovenia. The cost of remediation is 136-186 $ per ton of soil, without profit.
Ecosystem services of EDTA remediated soil
Realistically tended vegetable gardens with EDTA-remediated soil have supported the growth of vegetables,⁴⁰ grasses and horticultural plants (Figure 3).³⁷ Pb uptake by plants was prevented or significantly reduced (Table 1). Remediation with high EDTA doses affected the soil C and N cycles, soil enzyme activities and the structure and abundance of soil microbial populations, especially arbuscular mycorrhizae.⁴¹ ⁴² However, using simple and inexpensive revitalization measures, e.g., addition of compost, healthy un-polluted soil and commercial or indigenous microbial AM inoculum, restored microbial life.⁴¹ ⁴² ⁴³ The chemical and physical properties of remediated soil were mainly preserved.³⁴ ⁴⁴
The ReSoil technology is fully consistent with criteria set by GRO concept.
1. Cai M, McBride MB, Kaiming L (2016) Bioaccessibility of Ba, Cu, Pb, and Zn in urban garden and orchard soils. Environ Pollut 208A: 145-152.
2. Ryan JA, Scheckl KG, Berti WR, Brown SL, Casteel SW, Chaney RL, Hallfrisch J, Doolan B, Grevatt P, Maddaloni M, Mosby D (2004) Reducing children’s risk from lead in soil. Environ Sci Technol 38: 18-24.
3. Kumpiene J, Brännvall E, Taraskevicius R, Aksamitauskas C, Zinkute R (2011) Spatial variability of topsoil contamination with trace elements in preschools in Vilnius, Lithuania. J Geochem Explor 108: 15-20.
4. Aelion CM, Davis HT, Lawson AB, Cai B, McDermott S (2013) Associations between soil lead concentrations and populations by race/ethnicity and income-to-poverty ratio in urban and rural areas. Environ Geochem Health 35: 1-12.
5. Nriagu JO, Pacyna JM (1988) Quantitative assessment of worldwide contamination of air, water and soils by trace metals. Nature 333: 134-139.
6. Ettler V (2016) Soil contamination near non-ferrous metal smelters: A review. Applied Geochem 64: 56 74.
7. Pacyna JM, Pacyna EG, Aas W (2009) Changes of emissions and atmospheric deposition of mercury, lead, and cadmium. Atmos Environ 43: 117–127.
8. Zhang X, Yang L, Li Y, Li H, Wang W, Ge Q (2011) Estimation of lead and zinc emissions from mineral exploitation based on characteristics of lead/zinc deposits in China. Trans. Nonferrous Met. Soc. China 21: 2513–2519.
9. Miranda ML, Kim D, Galeano MAO, Paul CJ, Hull AP, Morgan SP (2007) The relationship between early childhood blood lead levels and performance on end-of-grade tests. Environ Health Perspect 115: 1242 1247.
10. Kranz BD, Simon DL, Leonardi BG (2004) The behavior and routes of lead exposure in pregrasping infants. J Exp Anal Environ Epidem 14: 300-311.
11. Mohaje R, Salehi MH, Mohammadi J, Emami MH, Azarm T (2013) The status of lead and cadmium in soils of high prevalenct gastrointestinal cancer region of Isfahan. J Res Med Sci 18: 210-214.
12. Clark HF, Hausladen DM, Brabander DJ (2008) Urban gardens: Lead exposure, recontamination mechanisms, and implications for remediation design. Environ Research 107: 312-319.
13. Järup L (2003) Hazards of heavy metal contamination. British Med Bullet 68: 167-182.
14. https://www.pollutionsolutions online.com/news/soi...
15. FAO. Global agriculture towards 2050. High-level expert forum. Rome, 12-13 Oct. 2009.
16. Chen, J. 2007. Rapid urbanization in China: a real challenge to soil protection and food security. Catena. 69: 1-15
17. Alaimo K, Reischl TM, Allen JO (2010) Community gardening, neighborhood meetings, and social capital. J Commun Psychol 38: 497–514.
18. Tei F, Benincasa P, Farneselli M, Caprai M (2010) Allotment gardens for senior citizens in Italy: current status and technical proposals. Acta Hortic 881: 91-96.
19. Cheng Z, Paltseva A, Li I, Morin T, Huot H, Egendorf S, Zulema YR, Singh K, Lee L, Grinshtein M, Liu Y, Green K, Wai W, Wazed B, Shaw R (2015) Trace Metal Contamination in New York City Garden Soils. Soil Sci 180: 167-174.
20. EC No 1881/2006. Commission regulation of 19 December 2006 setting maximum levels for certain contaminants in foodstuffs.
21. Säumel I, Kotsyuk I, Hölscher M, Lenkereit C, Weber F, Kowarik I (2012) How healthy is urban horticulture in high traffic areas? Trace metal concentrations in vegetable crops from plantings within inner city neighborhoods in Berlin, Germany. Environ Pollut 165:124-32.
22. Delbecque N, Verdoodt A (2016) Spatial patterns of heavy metal contamination by urbanization. J Environ Qual 45: 9-17.
23. Cundy AB, Bardos RP, Church A, Puschenreiter M, Friesl-Hanl W, Muller I, Neu S, Mench M, Witters N, Vangronsveld J (2013) Developing principles of sustainability and stakeholder engagement for “gentle” remediation approaches: The European contex. J Environ Managem 129: 283-291.
24. Robinson BH, Anderson CWN, Dickson NM (2015) Phytoextraction: Where is the action? J Geochem Explor 151: 34-40.
25. Van der Ent A, Baker AJM, Reeves RD, Pollard AJ, Schat H (2013) Hyperaccumulators of metal and metalloid trace elements: Fact and fiction. Plant Soil 362: 319-334.
26. Friesl-Hanl W, Platzer K, Horak O, Gerzabek MH. (2009) Immobilizing of Cd, Pb, and Zn contaminated arable soils close to a former Pb/Zn smelter: a field study in Austria over 5 years. Environ Geochem Health 31: 581-594.
27. Ferraro A, Fabbricino M, van Hullebusch ED, Esposito G, Pirozzi F (2016) Effect of soil / contamination characteristics and process operational conditions on aminopolycarboxylates enhanced soil washing for heavy metals removal: A review. Rev Environ Sci Biotechnol 15: 111-145.
28. Udovic M, Lestan D (2012) EDTA and HCl leaching of calcareous and acidic soils polluted with potentially toxic metals: Remediation efficiency and soil impact. Chemosphere 88: 718-724.
29. Voglar D, Lestan D (2014) Chelant soil-washing technology for metal-contaminated soil. Environ Technol 35: 1389-1400.
30. Pociecha M, Lestan D (2012) Novel EDTA and process water recycling method after soil washing of multi-metal contaminated soils. J Hazard Mater 201-202: 273-279.
31. Pociecha M, Lestan D (2012) Washing of metal contaminated soil with EDTA and process water recycling. J Hazard Mater 235-236: 384-387.
32. Papassiopi N, Tambouris S, Kontopoulos A (1999). Removal of heavy metals from calcareous contaminated soils by EDTA Leaching. Water Air Soil Pollut 109: 1-15.
33. Lestan D (2017) Novel chelant-based washing method for soil contaminated with Pb and other metals: A pilot-scale study. L Degrad Dev 28: 258 –2595.
34. Watts DB, Warren AD (2014) Sustainable uses of FDG gypsum in agricultural systems: Introduction. J Environ Qual 43: 246-252.
35. Voglar D, Lestan D (2013) Pilot-scale washing of Pb, Zn and Cdcontaminated soil using EDTA and process water recycling. Chemosphere 91: 76-82.
36. Voglar D, Lestan D (2010) Electrochemical separation and reuse of EDTA after extraction of Cu contaminated soil. J Hazard Matter 180: 152-157.
37. Jelusic M, Lestan D (2015) Remediation and reclamation of soils heavily contaminated with toxic metals as a substrate for greening with ornamental plants and grasses. Chemosphere 138: 1001-1007.
38. Udovic M, Lestan D (2009) Pb, Zn and Cd mobility, availability and fractionation in aged soil remediated by EDTA leaching. Chemosphere 74: 1367-1373.
39. Nowack B, Schulin R, Robinson BH (2006) Critical assessment of chelant-enhanced metal phytoextraction. Env Sci Technol 40: 5225-5232.
40. Jelusic M, Vodnik D, Macek I, Lestan D (2014) Effect of EDTA washing of metal polluted garden soils. Part II: Can remediated soil be used as a plant substrate? Sci Total Environ 475: 142-52.
41. Jelusic M, Vodnik D, Lestan D (2014). Revitalization of EDTA-remediated soil by fertilization and soil amendments. Ecol Eng 73: 42 –438.
42. Kaurin A, Cernilogar Z, Lestan D (2018) Revitalisation of metal-contaminated, EDTA-washed soil by addition of unpolluted soil, compost and biochar: Effects on soil enzyme activity, microbial community composition and abundance. Chemosphere 193: 726–736.
43. Maček I, Šibanc N, Kavšček M, Lestan D (2016)Diversity of arbuscular mycorrhizal fungi in metal polluted and EDTA washed garden soils before and after soil revitalization with commercial and indigenous fungal inoculum. Ecol Eng 95: 330–339.
44. Zupanc V, Kastelec D, Lestan D, Grcman H (2014) Soil physical characteristics after EDTA washing and amendment with inorganic and organic additives. Environ Pollut 186: 56–62.