Phytoremediation as effective clean-up approach: its ...

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Phytoremediation as effective clean-up approach: its perspectives of use in practice

ZANE VINCEVICA-GAILE4, JURIS BURLAKOVS, KARINA STANKEVICA Department of Environmental Science, University of Latvia, Raina Blvd. 19, Riga, Latvia

ABSTRACT

Environmental contamination is a widespread global problem. Among other clean-up technologies, phytoremediation is a costeffective environmentally friendly clean-up approach which uses plants and their associated microorganisms in rhizosphere as soil and groundwater treatment agents. Many plants in action with microbial communities are enhancing degradation of organic pollutants and by accumulation can improve remo­ val of inorganic contaminants from soil and water. Plants can be used for remediation of soil and water polluted with hydrocarbons, chlorinated substances, pesticides, metals, explosives, radionuclides, as well as for the reduction of excess of nutrients. Selection of plant species for phytoremediation treatment processes are based on their evapotranspiration potential, presence of degradative enzymes, growth rate, yield and depth of root zone, and ability to bioaccumulate contaminants. For soils polluted with metallic elements the most commonly used phytoremediation methods are phytoextraction and phytostabilization, but for organic contaminants phytodegradation

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Corresponding author (e-mail: [email protected]; phone: +371 26523248)

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Phytoremediation as effective clean-up approach: its perspectives of ...

is more appropriate. Phytoextraction is a biological method when certain plant species can uptake and accumulate contaminants from soil as hyperaccumulators, while phytostabilization means that plant species are able to immobilize contaminants of soil and groundwater through accumulation and sorption by roots, onto roots’ epidermis or by precipitation in the root zone. Innovative approaches involve phytoremediation in combination with soil amendment applications, electrokinetics and bioremediation. Hydrocarbons and metallic elements are well known contaminants commonly found in soils and ground­ water in Latvia. The aim of this study is to summarize advantages and disadvantages of phytoremediation, and to provide short directions for planning the phytoremediation in cases of environmental contamination by metals and hydrocarbons. Keywords: environmental contamination, remediation technologies, phytoremediation, soil pollution, Latvia. 1. INTRODUCTION

Worldwide development of industry, global population growth and so called ‘business-as-usual’ have lead the modern society to seek for the new solutions due to growing concern on environmental problems connected with pollution of soil, water and air. From the 1960s, when the environmental philosophy outlined new type of development on thinking based on nature and industrial coexistence, the society reali­ zed the importance of environmental protection and remediation of polluted areas. Therefore, former industrial areas nowadays are recognized as brownfields and contaminated sites, and they are managed under the rules of national guidelines (Carson, 1965; Hardin, 1968; Ellis and Hadley, 2009). According to the statements of the US EPA (United States Environmental Protection Agency), the term ‘contaminated site’ refers to a specific spatial area with defined amount of pollution exceeding legislative norms (Superfund, 2015). Superfund program (the USA federal government’s program to clean-up the uncontrolled hazardous waste sites) includes many thousands of areas in the USA waiting for clean-up which are different by contamination level and character, costs and other factors. But in Europe the European

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Commission estimated about a half of million sites defined as contaminated sites and up to five million of potentially contaminated sites (Vanheusden, 2009). Individual countries usually set principles and legislation thresholds distinctively, e.g., in Russia the Law on Environmental Protection is focused mainly on the environmental prevention setting maximum permissible concentration levels for chemicals in soil (No.52-FZ, 1999; No.7-FZ, 2002). In the Republic of South Africa the legislator announced the act for norms defining appropriate criteria and methods for the assessment of contaminated land (No.59, 2008). Specific aspects on legislation defining contamination and recommending remediation techniques worldwide are summarized in the book written by D.E. Ellis and P.W. Hadley (2009). Legislation in Latvia regarding environmental pollution management and control (Law on Pollution, 2001) promoted the establishment of the National Register of Contami­nated Territories (NRCT) which includes areas subdivided into three categories: 244 contaminated sites (where contamination exceeds the permissible level by 10 times or more) are included in the 1st category; the 2nd category involves the list of 2,642 potentially contaminated sites; and the 3rd category consists of 684 sites that are removed from the first and second category listing after remediation or detailed assessment (NRCT, 2015). In overall, environmental contamination is a widespread global problem and remediation technologies applicable for treatment of soils, groundwater and surface waters have to be developed and modernized to gain more environmental benefits (Kabata-Pendias and Pendias, 2001; Vanheusden, 2009). However, the real economic situation in the world shows that available resources for remedial operations in both, developed and developing countries, are rather limited; therefore, the aims of treatment actions must be addressed to achieve the best available results by least necessary means, i.e., a technology chosen for environmental remediation should be effective and feasible at the same time (Sas-Nowosielska et al., 2005). The aim of this study is to discuss the feasibility of phytoremediation in polluted, contaminated or degraded territories, to summarize advantages and disadvantages of phytoremediation, as well as to provide a brief overview of the most frequent problems regarding planning and implementation of environmental remediation and

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landscape improvement in the areas of concern for planning the phytoremediation actions in cases of environmental contamination by metals and hydrocarbons, 2. CHOICE OF PHYTOREMEDIATION AS A REMEDIATION TECHNOLOGY

Remediation is a clean-up, mitigation, correction, abatement, reduction, elimination, control and containment or prevention of release of contamination thereby protecting human and animal health and environment (Powter, 2002; Superfund, 2015). Clean-up technologies are developed also with the aim to improve environmental quality, to eliminate historically and actually contaminated sites minimizing loss of land as a resource (No.2008/1/EC, 2008). Low consumption of energy and resources, low waste production, minimized footprint and innovations are recommended characteristics for feasible remediation technologies (Schrenk et al., 2007). Decision on choice of remediation technologies should take into account: a) Short-term and/or long-term effectiveness; b) Effectiveness of contaminant reduction at the site; c) Toxicity reduction of contaminant; d) Cost-effectiveness of remediation. Remediation technologies can be divided as in situ and ex situ technologies; according to the scope of application – vadose and saturated zone technologies; taking into account the processes used – as biological, physical separation, chemical, physical-chemical, thermal and containment techniques (Prokop et al., 2000). Among known clean-up technologies, phytoremediation is a cost-effective environmentally friendly clean-up approach which uses plants and their associated microorganisms in rhizosphere as soil and groundwater treatment agents. Many plants in action with microbial communities are enhancing degradation of organic pollutants and by accumulation can improve removal of inorganic contaminants from soil and water. Plants can be used for remediation of soil and water polluted with hydrocarbons, chlorinated substances, pesticides, metals, explosives, radionuclides as well as for the reduction of excess of nutrients (Black, 1995; Schnoor, 1997; Belz, 1998; Eweis et al., 1998; Blumberga

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u.c., 2010). Plant species are selected regarding geographical circumstances, evapotranspiration potential, yield, enzymes, growth rates, root characteristics and bioaccumulation properties. For the extraction of metallic elements from soils the most common processes used are phytoextraction and phytostabilization (Sas-Nowosielska et al., 2005), but for organic contaminants – phytodegradation (Langer et al., 2010). Process of phytoextraction means accumulation of contaminants from soil by plants-hyperaccumulators (Wang et al., 2013), but phytostabilization is applied when contaminants in soil and groundwater can be immobilized by sorption on roots or precipitation within the root zone (Wenzel, 2009). 2.1. Components of phytoremediation Processes of plant metabolism and their interaction with microorganisms of rhizosphere can directly and indirectly destroy petroleum hydrocarbons by degrading them to other substances such as alcohols, acids, carbon dioxide and water. These substances are less persistent in the environment and usually less toxic, unlike the initial substances and compounds (Eweis et al., 1998). The efficiency of phytoremediation depends on a choice of plant species, e.g., many plants including oilseed rape Brassica napus L., oat Avena sativa L. and barley Hordeum vulgare L. are able to accumulate metallic elements and metalloids such as selenium, copper, cadmium and zinc (Brown et al., 1994; Bañuelos et al., 1997; Ebbs et al., 1997). It should be considered that soil can be treated only up to a certain depth, as plants can clean up soil and groundwater to a depth the roots are growing. However, there are species of trees and shrubs, e.g., greasewood (saltbush) Sarcobatus vermiculatus and prosopis Prosopis juliflora Sw., roots of which are able to extend into the ground down to a depth of 18 m or deeper, but these species are not present in Europe (Landmeyer, 2012). In case of shallow contamination in temperate climate, as it is in the Baltic States, species of willows (e.g., common osier Salix viminalis L.) can be used for phytoremediation due to their deployed root system and ability to grow fast (Blumberga u.c., 2010). Five main processes that dominate in phytoremediation (Figure 1) are rhizofiltration, phytodegradation, phytostabilization, phytoextraction and phytovolatilization (Salt et al., 1998).

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Figure 1. Principal components of phytoremediation process (after Salt et al., 1998).

During the process of rhizofiltration, terrestrial or aquatic plants absorb pollutants through the root system; as a result, substances concentrate and precipitate. Thereby it is possible to remediate sites contaminated by pollution from industrial waste leachate, drained agricultural land and sites of mining waste pollution. Plant roots can absorb metallic elements such as Pb, Cd, Cu, Ni, Zn and Cr (Chaudhry et al., 1998). Known rhizofiltrators of Pb are Indian mustard Brassica juncea Czern. and common sunflower Helianthus annuus L., but studies indicate that Indian mustard in aquatic environment accumulate also Cd, Cr, Cu, Ni, and Zn (Dushenkov et al., 1995). Phytodegradation is based on plant metabolic pathways that contribute to reduction of organic matter, transformation, degradation, stabilization or evaporation of contaminant from soil or groundwater (Chaudhry et al., 1998). Plants contain enzymes that are able to disrupt and convert chlorine solvents such as trichlorethylene and other herbicides, and even explosives (Black, 1995). Rhizodegradation is a kind of phytodegradation when organic matter is degraded in the soil rhizosphere (root zone) due to the microbiological processes promoted by fungi, yeasts, bacteria and other microorganisms that can recycle organic substances as a source of energy and carbon found, e.g., in fuel and solvents (Ghosh and Singh, 2005). Two basic principles of phytostabilization are based on mechanical stabilization of contaminated soil by reducing erosion and transfer of

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pollution to other areas, as well as by immobilization through sorption, precipitation and complexation. Commercial stabilization of Pb, Zn and Cu containing compounds in contaminated soils can be done, e.g., by plant species such as common bent Agrostis tenuis Sibth. and red fescue Festuca rubra L. (Prasad and Freitas, 2003). Phytoextraction is the most known principal component of the phytoremediation technology (Prasad and Freitas, 2003). After the metal accumulation occurs in plants, the plants have to be harvested, collected and taken away from the area – the process may require long time (up to 20 years) of practicing and this reason is considered as one of disadvantages for this technology. Studies showed that Indian mustard Brassica juncea Czern. for accumulation of Zn is much more efficient than Alpine Penny-cress Thlaspi caerulescens (which is known as an hyperaccumulator of Zn) due to the reason that B. juncea produces 10 times more biomass than T. caerulescens (Blaylock and Huang, 2000). During phytovolatilization plants are extracting substances from soil and/or groundwater reworking them to gaseous state (e.g., As, Hg) and releasing into air. This is considered as controversial method as harmful gaseous compounds are released into the atmosphere (Prasad and Freitas, 2003). However, this method has an advantage as it does not require severe maintenance, not disrupts natural processes, reduces soil erosion, as well as there is no need to remove the contaminated plant material (Heaton et al., 1998; Rugh et al., 2000). 2.2. Advantages and disadvantages of phytoremediation Phytoremediation is a relatively universal approach to remove contaminants from the environment. Furthermore, with lower efficiency, this methodology can function even in a passive way as plants are able to remove, destroy or sequester hazardous substances during their natural lifecycle. However, plants that are tolerant to environmental contaminants often produce low amount of biomass in the presence of a contaminant (Glick, 2003; Khan et al., 2000). Advantages and disadvantages of phyto­ remediation are summarized in Table 1.

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Phytoremediation as effective clean-up approach: its perspectives of ...

Table 1. Advantages and disadvantages of phytoremediation (after Schnoor, 1997; Belz, 1998; US EPA, 2008; Landmeyer, 2012). Advantages

Disadvantages

Esthetical and energy efficient method

Relatively slow clean-up of contamination In situ clean-up is efficient at depth 1–2 m; as plant roots do not extend deeply in the aquifer 3–5 m deep treatment possible only with a special design Plants may contaminate food chain Less efficient for direct degradation of hydrophobic contaminants bound to soil Volatilization can create air pollution problem

Stimulates bioremediation in symbiosis with microorganisms

Relatively cheap method Immobilizes metallic elements and hydrophobic substances in soil Vegetation at contaminated sites also reduces erosion caused by wind and water

Considerable limitation of phytoremediation method is a narrow range of contaminant concentrations or plant toxicity potential within it can be applied. Weather aspects, climatic factors, hazardous waste and toxic by-products are also among the considerable factors that should be taken in account. In the temperate climatic zone, more to the North, there is limited choice of plant species applicable for phytoremediation; and much shorter seasonal period of biomass production can also limit application of phytoremediation. Understanding the plant physiology, biochemistry, extraction properties and other factors is crucial for the success of phytoremediation as a remediation method in practice (Gonzaga et al., 2006). Phytoremediation requires plants to be isolated from wildlife and agricultural lands – once contaminated, plants must be disposed away in an appropriate way. Plant disposal ways include incineration, gasification, drying pyrolysis, acid extraction, an­ aerobic digestion, extraction of oil, chlorophyll, fibres from plants etc. (Bolenz et al., 1990; Sas-Nowosielska et al., 2005). Correctly chosen plant species, improved root systems and use of appropriate soil amendments can enhance decontamination process during phytoremediation. Genetic breeding of plants can improve bioavailability and metal uptake in order to cultivate specific plant species for removal of certain contaminants in various climatic zones. Phytoremediation mitigates environmental prob-

lems without the need for soil excavation. More than 750 terrestrial

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and aquatic plants are applicable for reduction of metallic elements and metalloids in soil and groundwater (Sarma, 2011). Estimated costs of phytoremediation methods can be much lower compared to conventional remediation methods (Table 2).

Table 2. Comparison of estimated costs of several remediation technologies (after ITRC, 1997; Schnoor, 1997; recalculated according to Measuring Worth, 2012). Remediation technology Phyto-remediation Fixation

Estimated costs (EUR/m3) 20–50

Required time (months) 15–40

100–220

6–9

Landfilling

120–480

Conventional extraction Electro-kinetics

250–600

8–12

210–420

12–36

Additional factors Other related or expenses problems Time/land commitment Transport/excavation Long-term monitoring Long-term monitoring 5,000 m3 minimum Chemical recycling Time/land commitment

Residue disposal Leaching

Residue disposal

Chelating agents (e.g., EDTA) can be used to increase efficiency of phytoextraction but environmental impact of organics-metal compounds should be carefully assessed to avoid subconscious contamination. Phytoextraction is mainly used for removal of Pb, and also for other metals such as Ni, Zn, Cd. Phytostabilization does not remove contaminants from soil, but reduces mobility of contaminants, thus further distribution of pollution and contamination of food chain is prevented. Vegetation reduces erosion of soil decreasing water percolation and preventing direct contact with the soil-immobilized contaminants by controlling the pH, volatiles and redox conditions of soil (Vangronsveld et al., 1995; US EPA, 2008). In cases of high level contamination, it is advisable to create plant cover at the site in combination with soil amendments, especially if the level of contamination can affect endurance of selected plant species. Reduction of environmental hazards is the measure of the method’s efficiency (SasNowosielski et al., 2005; Greenland Project, 2014).

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Phytostabilization can be performed by use of phosphate amendments if cations are target contaminants. However, contaminated soils often contain a portion of inorganic and organic pollutants that require complex approach of decontamination. Innovative pilot studies are performed by combining electrokinetic and phytoremediation methodologies which compiles advantages of both technologies in order to overcome the limitations of each other (Cameselle et al., 2013). C.L. Reddy with colleagues (2006) described improved remediation at a manufactured gas plant area by use of surfactants, co-solvents and cyclodextrin for degradation of polycyclic aromatic hydrocarbons (PAHs), but significant removal of metallic elements was not detected in this study. Phytoremediation in combination with electrokinetics, applications of soil amendments and other bioremediation improvements for immobilization and extraction of metals-containing compounds requires additional research. 3. APPLICATION OF PHYTOREMEDIATION IN LATVIA

Decision support. Preliminary research, sampling and fate of contaminants must be predicted before the choice of appropriate phytoremediation technology; historical information and data from previous investigations can promote establishing a set of potential options and criteria (Figure 2).

Figure 2. Basic steps of decision support in the choice of remediation technologies.

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The main concerns of application of phytoremediation methods in Latvia are related to costs and legislation which often contradicts the business interests. Decision-makers and stakeholders should be strict on need of preliminary studies and allow some flexibility in order to avoid too high costs and stagnation of the remediation process (SUMATECS Project, 2008; Greenland Project, 2014). Financial feasibility, market situation, environmental quality demands and recovery of the land resources are also among the important factors for decision making. Applicability. Phytoremediation techniques are recommended if the contamination level is at low or medium level in comparison to guidelines and legislation acts (SUMATECS Project, 2008; Ellis and Hadley, 2009; Greenland Project, 2014). Until current time, no full scale phyto­remediation applications have been performed in Latvia; however, several trials were done and some cases are described in this paper as follows. Table 3 summarized contaminated sites and type of contamination where phytoremediation can be applicable as effective remediation technology. Case studies. One of the sites where phytoremediation of area conta­minated by a complex of pollutants has been realised at Jaunmilgravis industrial territories (Vega Stividors, Ltd. and BLB, Ltd.; No.01964/611 and No.01964/629, based on NRCT, 2015; Table 3). The areas are situa­ted in the northern part of Riga City, approximately 5 km from the estuary of the River Daugava in the Gulf of Riga. Soil pollution source in these areas was superphosphate production slag where were detected Pb, Cu, Zn and As in high concentration. The territories are still used for industrial purposes, but preliminary studies have shown the parcels of the area with low to medium contamination of metallic elements, metalloids and hydrocarbons where phytoremediation appli­cations are recommended as appropriate remediation technology (Burlakovs and Vircavs, 2012). The pilot study area was chosen based on the results of the preliminary research. Economic reasons were among the determinant to choose this territory – the selected parcel was not exploited by industry. Obtained results and applied multi-criteria analysis revealed that phytoremediation can be the best feasible option for clean-up in 3–5 ha of the total industrial area (21 ha).

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Table 3. List of contaminated sites in Latvia where phytoremediation is feasible option for full or part-scale clean-up (according to NRCT, 2015). No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

Name, location and type of contaminated site JSC Lokomotive in Daugavpils (industrial area) Tank polygon in Zvarde (former military area) Former pesticides warehouse in Vilani Bangas, former Soviet Army missile base (former military area) Mekora, Ltd. in Riga (former military factory) Russo-Balt, Ltd. in Riga (former military factory) JSC Latvijas Krasmetali in Riga (brownfield)

Number in NRCT list

Type of contamination

05004/1046

HM1, OP2

84988/1437

OP, HM

78175/3584

DDT3, HM

98788/3471

OP, HM

01924/585

OP, COD4, HM (Ni, Zn, Cu, Pb)

01934/638

HM (Pb, Zn, Cd), OP

01934/623

HM, OP

Former “Alfa” area in Riga (2 sites, former industrial area)

01944/675 01944/677

Trichlorethylene, COD, SAS, OP, alcohols, phenols, HM

01954/669

COD, OP, N, HM (Cu)

01954/609

Phenols, N, HM (Pb, Zn)

01964/4411

OP, HM

01964/5418

OP, HM

01964/629

HM, As

01964/611

HM, OP, HM (As)

01964/627

OP, HM (Pb)

01964/626

OP, HM (Pb, Cu)

01964/625

COD, HM (Pb)

–

OP

Biekengravis in Riga (former hazardous waste dump) Viva Color, Ltd. in Riga (brownfield) Eko Osta, Ltd. in Riga Port (former Soviet Army fuel base) Former gardening pesticide warehouses in Riga Vega Stividors, Ltd. in Riga Port (industrial area) BLB, Ltd. in Riga Port (industrial area) Magnats, Ltd. in Riga Port (industrial area) Grand, Ltd. in Riga (former light bulb factory, brownfield) JSC Starts in Riga (industrial area) Venstpils (8 sites)

HM – heavy metals and their compounds OP – oil products 3 DDT – dichlorodiphenyltrichloroethane, 1,1,1-trichloro-2,2-di(4-chlorophenyl)ethane 4 COD – contamination with organic substances creating a high level of chemical oxygen demand 1 2

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Phytoremediation of several areas contaminated by hydrocarbons was partly applied in technical projects, mainly these were the sites where spill accidents were located, e.g., Polotsk-Ventspils pipeline ruptures, industrial areas of Ventspils port, also some railway accident locations (at Krauja, Vecumnieki, Mangali railway stations). In these sites natural (passive) phytoremediation has occurred (Figure 3).

a

b

Figure 3. Practical application of natural (passive) phytoremediation: a) pyrocondensate leaching site at Vecumnieki railway station; b) site (Udeka, Ltd.) contaminated with hydrocarbons at the Ventspils port (photos by J. Burlakovs).

a

b

c

Figure 4. Willow species applied in phytoremediation project at AS Ventspils Nafta area: a) Salix hyprid ‘Ingers’, b) Salix acutifolia, c) Salix purpurea (photos by I. Ruksane).

During the summer of 2014, a phytoremediation project started at “Ventspils Nafta” Ltd. with the aim to reduce soil contamination of hydrocarbons and increase the esthetical value of the industrial landscape. Plants used in this phytoremediation project are hybrid willows Salix hybrid ‘Tora’ and Salix hybrid ‘Ingers’, long-leaved violet willow Salix acutifolia, purple willow Salix purpurea L. and white willow Salix alba L. ‘Sericea’ (Figure 4), as well white clover Trifolium repens L. additionally

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was used as lower stage of vegetation. The phytoremediation trial was performed at area of about 0.1 ha at the Ventspils port territory. Regular monitoring at the Ventspils port territory is still continuing with sampling and analysis of soil. Calculations based on the phyto­remediation trial will allow determination of clean-up speed and effi­ciency at the site. Remediation work is performed with the involvement of landscape architects in order to guarantee the quality of landscape esthetical performance. Hydrocarbons and metals are known contaminants commonly found in soils and groundwater in Latvia. However, performed phyto­ remediation actions during these case studies lacked profound analysis of disadvantages from the scientific point of view – fast results, public acceptance and clean-up progress were considerably more important for main stakeholders (customers). Volatilization of pollution and possible contamination of food chain was not taken into account during the technical planning. Phytoremediation provides significant aesthetic improvement of landscape if applied in the city environment, but prior the application it has to be planned correctly by various stakeholders – decisionmakers, landscape architects, biologists, environmental experts, with participation of NGOs and population. The Sarkandaugava Armlet (in the north part of Riga) is an armlet of the River Daugava, which before the World War II was nice-looking and relatively clean water basin with low but regular stream (Figure 5). Nowadays it is a pond polluted by excess of nutrients and the size of the armlet is reduced due to overgrowing (SDS, 2013).

a

b

Figure 5. The Sarkandaugava Armlet in 1930s (a) and in 2013 (b); the width and depth of the channel eighty years ago allowed the entrance of ships, while nowadays the channel became shallow, steady dead-end oxbow pond with excessive nutrient amount and oxygen deficient environment (photos from SDS, 2013).

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In cooperation with the Riga City Council in 2011 the technical project was worked out planning pilot program on planting works in order to improve the situation near the Sarkandaugava Armlet with further proceeding of revitalization works. The main emphasis from the environ­mental point of view should be put on the treatment of nutrient pollution and recovery of natural processes that is possible through clean-up of channel sediments, extracting of nutrients by phytoremediation using aquatic and terrestrial plants on the coastline. The first work was done by designing the project, distribution of information and pilot planting of common sunflower Helianthus sp. plants. However, currently the future of this landscape and environmental improvement project is unknown as the Riga City Council has not defined, if this area will be transformed to larger size infrastructure object or not. Case studies and plans of phytoremediation projects in Latvia mentioned and briefly characterized above can help to understand the main problems related to the environmental remediation issues. 4. FUTURE PERSPECTIVES

Phytoremediation practice in Latvia reveals that several pilot projects are realized or planned in urban and rural territories of the country to reduce environmental pollution. However, more serious environmental management on problem analysis should be performed as commercial enterprises rarely are interested in complete recovery of pollution and benefits-creating for the community, but the respon­sible authorities do not have systematic approach in feasibility analysis and territorial planning aspect. Positive feedback and communication during the performance and participation in case study projects were gained from NGOs and community representatives. Obtained information revealed broad perspectives for use of phytoresources in, so called, environmentally friendly gentle remediation when environmental contamination in polluted territories is reduced using plants. Analysis of case studies revealed indicative directions and steps of performance and problems arising through the implementation of phytoremediation practice. Involvement of scientific environmental and landscape experts and mutual collaboration with stake-holders, including responsible authorities and enterprises with right attitude

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to decision-making, will lead to positive outcomes in delivery of sustainable results from clean-up projects and practical implementation of more environmentally friendly technologies with close to zero emissions that is crucial in a scope of minimizing climate change problems. CONCLUSIONS

Historical information and preliminary studies on environmental situation in planned for clean-up areas should be performed by decision-making stakeholders and experts; if the phytoremediation can help solve both, environmental and landscape improvement, goals, it should be evaluated from feasibility aspect and compared to other applicable gentle remediation technologies. Phytoremediation is significant aesthetic landscape improvement measure if planned correctly. Case studies in Latvia revealed broad perspectives for use of this remediation technology in future as environmentally friendly and less costly method compared to conventional remediation technologies. Certain problems should be solved for risk analysis of potential negative aspects such as volatilization of contaminants and contamination of food chain as this aspect never has been taken into account in case studies performed in Latvia. ACKNOWLEDGEMENTS

This study was supported by the European Social Fund Project “Interdisciplinary Team of Young Scientists for Assessment and Restoration of Soil Quality and Usage Potential in Latvia” No.2013/ 0020/1DP/1.1.1.2.0/13/APIA/VIAA/066. Special thanks to Ilze Ruksane for consultations on the phytoremediation case studies in Sarkandaugava and “Ventspils Nafta” Ltd.

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