Thesis project _Phytoremediation as a tool in landscape architecture

Phytoremediation as a tool in landscape architecture design MASTER THESIS PROJECT _Selected parts Alexandros Memetzidis

MASTER THESIS PROJECT: ‘‘Phytoremediation as a tool in landscape architecture’’ Alexandros Memetzidis Supervisors: Mona Chør Bjørn, Morten Ingerslev

Industrial area under the use of Valby Gasværk. ​ One of Denmark’s largest gas work stations with an area of 270.000 m2. ​ The industry produced coal gas which was also stored on the site.

In 1964 a great explosion destroyed the gasworks and resulted in a great catastrophe and the desolation of the area.​ After the explosion, the site was cleaned and reconstructed. Parts of the area were transformed into housing.​ Vigerslev Vænge and Hornemanns Vænge are located on each side of Kulbanevej and the future park area Kulbanepark.

Historical photo (https://www.kristeligt-dagblad.dk/historier/valby)

Studied area

Vigerslev Vænge

Kulbane park Hornemanns Vænge

Plan of the area in 1954 (https://map.krak.dk/?c=55.659208,12.497485&z=17&l=historic)

Plan of the area in 2018 (https://map.krak.dk/?c=55.659208,12.497485&z=17&l=historic) .

The site today The surrounding area includes the Vigerslev Allé train station in the north-east and a green corridor on the south-west. The urban matrix could be characterized as fragmented as there are different and discontinuous axis’s and neighborhoods through the fabric. The train rails create hard boundaries in the area and the traffic arteries segregate the area into different urban planning architectural language.

Fragmented greenery and space Different urban typologies Inaccessibility-strong boarders Lots of playgrounds Variations in the urban net Lack of the human scale in the neighborhood Long stretch but works vertically Connection with the Vigerslev train station Historical area What are the levels of pollution?

Basic traffic arteries Train lines Neighborhood streets Studied area Vigerslev train station

Diagram of infrastructures around the area.

Methodology and analysis Literature review The effectivity of the phytoremediation method lies on the accumulation of the plant and its biomass production. This requires a series of calculations with data that were found in literature with the purpose of creating an estimation as close to reality as possible. This estimation concerns the amounts of heavy metals that will be extracted, the biomass that will be produced and the time this process needs to be completed successfully (McGrath, Zhao and Lombi, 2001).

It was crucial for developing a solution to this question to find literature. Through the literature it was possible to find data which form the variants needed for the calculations. The literature research was separated into the next different stages: Firstly, literature on the soil and heavy metal pollution was studied. Soil properties and concentrations of heavy metals were important for understanding the process of remediation. Moreover, conventional ways of soil remediation were studied, so that it becomes clear how and when phytoremediation excels.

Secondly, research on different heavy metal accumulator species was the next step. Different kinds of metal accumulator species have been found observed and analyzed in scientific reports. The plants that could be used for this thesis project, should also be possible to grow in Denmark and for this purpose the book ‘‘Dansk flora’’ (Barfod et al., 2012) was used to determine which of these heavy metal accumulating species can grow in Denmark.

The third stage was the research of experiments in literature, performed on the specific plants, in order to acquire amounts of heavy metal accumulation in the plant. Different experiments showed different variations in the plant accumulation capacities. For this purpose, these values were taken into consideration in order to show the range of the possible results. The research on this literature aimed in common soil pollution amounts with the case of Kulbanepark in order to acquire more realistic results.

Finally literature for the search of biomass production data for every plant was used. In some cases the biomass production results were also included in the experiments considering the heavy metal accumulation, which produces more accurate results, since in many cases biomass decreases due to soil pollution. Again, different literature showed different biomass productions and different ranges were taken into consideration in order to exhibit the possible deviations.

The data of concentration and biomass production from literature, were applied on the case scenario, as this was the most accurate way to simulate the process. The pollution levels were acquired from the municipality of Copenhagen and was a sampling examination from KMC Nordhavn Laboratories.

Polluted site Pollution data

Evaluate the potential remediation method.

If moderately polluted and time is not an issue, then phytoremediation is a possible solution.

Choose plants able to grow in the case environment.

Design guidelines Main guidelines for the design process emerge from the results of the previously referred calculations that were performed according to literature. It is important to note that in cases of extreme soil pollution, the phytoremediation process is not successful and hence a physical or chemical remediation should be considered.

Phytoremediation then can be used as a first layer, or else as the net upon which the secondary function of the public use will develop. According to J. Ahern (2012), the multifunctionality of a public space and its efficient use in urban planning is crucial, since space is inherently limited in urban environments. This involves the strategical layout of various ecosystem services on urban land, in order to be achieved.

Moreover, according to J. Ahern, the most common way to to combine the different functions in order to achieve the multifunctionality is the ‘‘spatial stacking’’, analyzed into the efficiently organized functions that can operate independently, or in a complementary manner with each other (Ahern 2012).

What can derive out of this, is that we need space in the city to be available for the public, and their multifunctionality is crucial for servicing different sections of urban life.

Considering the phytoremediation functional layer as the first one, the next layer, or the next ‘‘stacked space’’ would be a space that serves the uses of the society. Society being an inseparable member of the urban ecosystems, is also inseparable from the pollution that has created. However, using phytoremediation process and strategically design the ways a space like this can be used, it could be possible to result in a type of multifunctional space serving for both the environment and the citizens.

Cleaner site Calculate the time span demanded for the execution of the remediation.

Form the strategy dependent on the plants and the time span.

Crop rotations and harvest.

Swap the crops in rotations (if necessary).

Analyzing the area data and pollution The map was acquired from the municipality and refers to sampling tests performed by KMC Nordhavn laboratories in the area. The red dots indicate the holes that the soil samples were examined.

The pollution varies a lot between the sampling holes, with the southern part showing higher amounts of pollution especially in the spots 1, 2 and 3.

Pb: 20 Cd: <0.025 Cu: 7.2 Zn: 22 Ni: 15

Pb: 5.3 Cd: 0.20 Cu: 7.9 Zn: 30 Ni: 19

View from Vigerslevej,

Alexandros Memetzidis, April 2021

Pb: 520 Cd: 1.1 Cu: 120 Zn: 240 Ni: 34

Pb: 200 Cd: 0.79 Cu: 77 Zn: 190 Ni: 25

Pb: 33 Cd: 0.07 Cu: 15 Zn: 100 Ni: 13

View from Vigerslevej junction,

Alexandros Memetzidis,

April 2021

Pb: 83 Cd: 0.22 Cu: 38 Zn: 67 Ni: 28

Pb: 870 Cd: 1.6 Cu: 920 Zn: 360 Ni: 41 Pb: 380 Cd: 1.9 Cu: 260 Zn: 300 Ni: 30

Plan from Laboratoriet A/C Nordhavn

Pb: 1500 Cd: 1.2 Cu: 97 Zn: 230 Ni: 35

View from Retortvej,

Alexandros Memetzidis, April 2021

Handsketching - Basic ideas

Group harvest areas to make strategical harvesting controllable Compartmentalization of harvestable areas, following the terrain and creating barriers towards heavy infrastructure.

Seperation between the harvesting areas can be useful for the harvest.

The flows end on a view point -enjoy the view .

Use of harvest areas as structure blocks to allow the flow in between

Phytoremediation and strategies T. caerulescens

Phytoremediation is a method of removing pollutants from the soil or render them harmless. Moreover, through phytoremediation it is possible to stabilize the soil and prevent pollutants leaching from a contaminated site.

It is a new field of ecological engineering.

F. esc

Phytoremediation can be: • Cost-effective​ • Efficient​ • Environmental friendly​

The table below shows the concentrations of the different heavy metals (in mg/kg dry weigh of the plants biomass), the st

• In situ applicable​ • Does not destroy soil fertility and utility

Pb (Lead)

250

2000 - 8000

Cd (Cadmium)

300

-

Cu (Copper)

-

-

Zn (Zinc)

10.000

-

-

-

Ni (Nickel)

culentum

S. viminalis

Plant species and heavy metal accumulation P. trichocarpa

tudied plants were able to accumulate in their tissue, according to different literature.

2-40 3,1-20

0,5

1.6 8-15

207

0,59

25 0,3

Root systems and biomass differences

Biomass (kg/ha/y) * HM concentration in plants (mg/kg) = mass HM extracted from the soil (Mc Grath,Zhao and Lombi, 2001)

S. viminalis The plants used for the strategy are both hypperaccumulators and high biomass plants.

Pb

T. caerulescens Cd

Cd

High H.M. accumulation

High biomass production

Low biomass production

Lower H.M. accumulation

Zn Zn

Pb

Cu

Zn

20cm

Ni

Cu

Zn

Ni

Pb Pb

Cd

Pb

50cm Pb

Cd

Benefits of partial harvests

• Landscape does not get drastically transformed.

First harvest on 3years

• The harvest can be strategically planned, to create spaces within the area.

• Smaller organisms like insects can migrate to the rest hosting plants • The whole area should be a closed system concerning the exchange of organic matter - This is one of the biggest challenges.

50% harvest

Next harvest on 4years • The short rotation coppice of willows proposes rotation periods of 3-5 years with optimal conditions for the maximum biomass production, if foliar matter is not harvested from the site. The drifting of leaves to neighboring areas is an important issue and it has to be avoided as it can cause the dispersion of the pollution. This issue has to be assessed in the future (Meers et al., 2005).

• The harvest can be separated in two parts, completing the first one in 3 years and the second one on the 4th year.

Rotation coppice diagram

MASTERPLAN

0

7,5

15

30

Terrain morphology and conceptual diagrams The strategy to be followed begins from the analysis of the area as part of the neighborhood. The important view openings towards the Kulbane park and the high industrial chimney,as well as the flows around and through the plot are the basic compositional directions.

These two space functionalities have to be combined with phytoremediation in order to multifunction as a passage/viewpoint and as a phytoremediation area.

Important views

Flows around and through the site

Section studies

Compartmentalization of the crops

Harvestable crops Strategic harvest and plantation:

The successfull rotation of the plantations results in a successful remediation of the soil. Using the strategy of the compartmentalization of the area, each plantation can be furthermore studied and measured in connectio to the effectivity of the heavy metal accumulation and extraction.

Moreover, in a more realistic situation, areas that contain different excessive amounts of heavy metals can be treated differently. Within these sub-divided areas, there can be different plantation crops for the purpose of dealing with the different amounts of pollution.

The plan diagram on the left shows the different surfaces as plantation crops. There is no actual separation of the surfaces and the boundaries of each surface delimit the different crops. However, a wider passage space is left between these surfaces in order to create space for the workers that harvest the plants in every case.

Hence, sub-dividing the area offers a degree of flexibility in acquiring and monitoring the data as well as the possibility to cope with uneven distributions of pollution, by using different plant densities and different plant spe cies.

On the right side we can observe studies of different harvesting patterns. Every time a surface gets harvested it opens a visual connection to another area. This results in a very dynamic space, which transforms constantly throughout the year.

The studies on the right indicate possible variances in the landscape.

f

on

-

t

r

, e-

Harvesting variations study

Visualization-Through the crops Due to S. viminalis morphology the area will be densely planted. Moreover, in the case of a visitor passing through the site the contact with the soil is important to be avoided. An easy way to create a safe traverse through the polluted space would be to elevate the paths and the viewpoint area. In this way, not only the contact with the soil is excluded, but also plants can grow underneath the path, gaining more space for phytoremediation. Finally, the visitor experiences the space from another perspective than ususally walking on the ground.

Tools and different scenarios: Part of this thesis’ project was the design of a multifunctional space. There are different parameters that can affect a design in a space like this and hence adaptability is demanded in a certain degree. With concern to the different degrees of adaptability in a public space and the need for various possible scenarios, the use of parametric design tools could be an important asset.

In the left picture a possible scenario is shown, of further designing the crossing path of the area with parametric tools. In this scenario, the path is being strongly defined seperating its use from the rest of the environment. Metal and wood can be combined to form the path connection. In this scenario the path is a permanent feature to the whole area and can form an important link for the future design of the area, after the remediation process will be completed. The path becomes part of the functional nature that will inhabit the area.

The shape of the viewpoint becomes part of a reference to the history of the area, resembling the structure of the old gassworks station.

The path will become the main protagonist of the area as the crops will be harvested and regrown. When the crops are at their fullest growth, parts of the path’s entrance will guide the visitor through a densely developed willow pocket forest, while when the crops will be harvested, the path will form the main visual feature. This redefines the relationship between the polluted area and the neighborhood and forms a possible new landmark.

In this way the popularization of the area will bring more people to know about phytoremediation and as a result about pollution and environmental consciousness.

Timeline map of rotations and extractions-Basic modules

3 year rotation 50%

The timeline map shows the rotations as a module that can be repeated until the remediation of the site. The plants that form this strategy are:

S. viminalis, T. caerulescens, F. esculentum.

Extracted: Pb: 0,06kg Cd: 0,06kg Cu: 0,12kg Zn: 3,18kg Ni: 0,01kg

S. viminalis

To be extracted Pb: 3540kg Cd: 2,8kg Cu: 1682kg Zn: 1679kg Ni: 256kg Full harvest

Start of F. esculentum and S. viminalis

Present T. caerulescens

1 year rotation

Cadmium is one of the most toxic heavy metals.

T. caerulescens shows good results in Cd accumulation.

In the first phase the whole site is planted with T. caerulescens. The rotation will keep for 2 years as T. caerulescens is an annual plant, meaning there are going to be 2 rotations in this period.

Extracted: Pb: 2kg Cd: 2,4kg Zn: 80kg

2 Years

Extracted Pb

1 year rotation

After the first harvest of T.Caerulescens , next metal that should be targeted is Lead. F. esculentum is a good hypperaccumulator of Lead. This proposal consists of the simultaneous use of F. esculentum and S. viminalis, as a deeper root system and biodiversity variances should be established.

F. esculentum

5 Years

Swap crops

4th year rest 50% Extracted: Pb: 0,08kg Cd: 0,08kg Cu: 0,16kg Zn: 4,2kg Ni: 0,02kg

Walking

F. esculentum crops

Future

S. viminalis crops

Walking

S. viminalis crops

F. esculentum crops

Extracted Pb

1 year rotation

Fagopyrum Salix-3 years harvest

F. esculentum and S. viminalis have different rotation cycles according to their biomass production. Hence, the landscape is constantly going to be transforming. F. esculentum will be harvested every year while S. viminalis will be harvested every 3 years for the first 50% and on the 4th year the rest 50%.

6 Years

Salix-4 years harvest

Axonometric diagrams of the 2 different plantations. After each plantation reaches the desired extractions, they swap positions.

Biomass filters

A dyn

As reported above, according to Meers et al., 2005 the issue of foliar biomass escaping the area has to be assessed. To solve this, another functional layer should be added in the composition. It is crucial for the area under phytoremediation to be confined at its periphery so that polluted biomass will not escape. Possible confining element could be metal or plastic railings, densely positioned, so that foliar masses can be retained within the site.

This can also prove useful during the harvesting of the plantations.

The lan As the public landsc from it and p

Basic view

B

B

Basic view

Biomass barriers

Biomass barriers

Pathway

namic landscape - Adaptive design

4.Viewpoint

ndscape space that derives out of phytoremediation is a dynamic space. e process moves forward in time there can be a gradual restitution of the space back to the society. This graduality can be the base for an adaptive cape design strategy that develops as time passes and receiving feedack tself. This also practically means that this landscape has to be monitored processed constantly in order to be effective.

3.Path

Basic view

2.Biomass filters

Pathway

Biomass barriers

Elevated path

Biomass barriers

2.Harvesting areas

1.Subdivision

Elevated path

Axonometric diagram of the layers composing the landscape

Visualization-Entering the phytoremediation area The transformation of the contaminants becomes a visual experience, by staging of phytoremediation as landscape typologies (Sleegers 2010). When the path functions as a landmark it also attracts people which results in further education and information of the polluted areas. People can know more and use the polluted spaces too. The area can be framed with elements in order to keep the foliar matter within the plot. These frames that work as a filter for the area, minimizing the chance that the plant biomass escapes, should be also part of the composition.

Discussion Phytoremediation is based on plants and one of its greater assets is the use of hypperaccumulators and metal tolerant plants. What was crucial for this study and possibly for other similar studies, was the use of existing literature. The data should be extracted from the literature in order to perform all the calculations explained above. However, it was quite a difficult task to find different data for different aspects of a plant’s attributes and correlate them in a way to describe and calculate the phenomenon of phytoremediation, as different variants were affecting every report’s results.These variants include the different climate, different soil characteristics and pollution, and different plants. This practically means that there is the need of an official database of registered hypperaccumulators and their capabilities for remediation purposes. The need for this database is very important, not only so that we can study more in detail and take advantage of their unique abilities, but also to protect them as many metal tolerant plants and hypperaccumulators that live in metalliferous soils, suffer from habitat loss (Reeves et al., 2017).

Considering the above, the calculations of the extraction of Pb with F. esculentum could have been more accurate and show the extraction amounts, if more correlated literature was found. This could give a more precise estimation of the time span and hence the visual and practical impact this would have on the landscape.

Furthermore, it needs to be mentioned that another important variable that is connected to the whole process is the biodiversity attributes that is a natural consequence of the plant cultures. For example S. viminalis is associated with many invertebrates, which populate, feed and dwell on the plant (BRC - Database of Insects and their Food Plants, 2021). This issue creates a whole new variation of aspects to the whole subject, that confirms even more the required inderdisciplinary oversight.

An important challenge that should be taken into consideration, is the handling of foliar biomass of the area (Meers et al., 2005). It is crucial for the foliar matter to not escape the area, as the dispersion of pollution to neighboring areas creates another problem while trying to solve one.

Finally, it is also important to mention that different pollution can generate different plant ‘‘pallete’’ and landscape formation. The way plants are being used throughout the space, creates a visual impact on the landscape and this could work as an inspiration to landscape architects, in order to use plants to create ‘‘space’’. Additionally, the urban equipment can play an important role in the way this space is being displayed and connected with the surrounding infrastructures. Lighting equipment and ways to stage the whole site under remediation, could be one of the potential, studies that could take part in a further developement of this project.`

i_ Conclusions

This thesis aimed in exploring ways, that the phytoremediation process could be implemented into the landscape architecture design process. Phytoremediation is a process that is based on living organisms and any attempts to control and predict possible future developments of a similar project, result in estimations. It could be considered as a process that has an input- a polluted area, and an output-a cleaner remediated area. Throughout the in-between phases this process demands inderdisciplinary collaboration between scientists, designers and planners, as well as long periods of time (Sleegers 2010). As calculated above, the cleaning process can take between decades to hundreds or thousands of years.

However, if the time span of the process extends within a few decades, which in many cases is possible, then it would be sensible to say that it could be a completely possible method for remediation.

Phytoremediation, offers a decentralized in situ solution over a problem that demands great energy consumption and is coped with no attractive solutions until this day (Sleegers 2010). The non-natural remediation techniques that are used today either postpone the problem or have serious repercussions on the soil and its properties.

Spaces under phytoremediation could gradually be included in the green infrastructures of a city. From the isolation and confinement of the polluted areas, phytoremediation may allow the strategic connectivity between them and the city while visibly performing their remediation. Whole districts that are confined due to the hazard of pollution can be revitalized and updated (Sleegers 2010). In this case Kulbanepark’s transformation, is an upcoming revitalization of the area and the area studied in this thesis is an extention space connecting Kulbanepark with the Vigerslev train station and the north-east part of the whole neighborhood.

Considering the question of if there can be landscapes under remediation with the adjunct functionality of recreation, the thesis’s conclusion answer is that under the correct strategy and set of the variants eg. plantations and manipulation of the users’s flow through the site, then the multifunctionality in this space is possible. Its limitations though reside in the fact that the landscape cannot be experienced as other landscapes, as there is always the boundary of keeping a distance between the visitor and the polluted soil.

The functions can operate in separate layers, which can be complementing each other, but cannot intersect, due to the pollution.

ii_ Conclusions

The flow of the visitors should be elevated to avoid contact with the soil and the main additional use could play a role in engaging people into the process of phytoremediation as a means of supporting environmental education (Sleegers 2010).

This means that this landscape should be publicly known for its fundamental use and its history, so that visitors can be educated about pollution, learn about the area and more importantly learn that the remediation processes are not an easy task.

The landscape space that derives out of phytoremediation is a dynamic space. The transformation of the contaminants becomes a visual experience, by staging of phytoremediation as landscape typologies (Sleegers 2010). As the process moves forward in time there can be a gradual restitution of the public space back to the society. This graduality can be the base for an adaptive landscape design strategy that develops as time passes and receiving feedack from itself. This also practically mean that this landscape has to be monitored and processed constantly in order to be effective.

Phytoremediation is a newly studied scientific area and there is a big effort from scientists, trying to decode the functions that take place throughout the whole process, as a lot of these functions are still unknown eg. the function of accumulating toxic heavy metals without showing toxicity effects. As a possible future scenario, it could be that there is the possibility of creating genetically modified plants that are tolerant in the toxicity of the pollutants-in this case heavy metals- and furthermore render them capable of accumulating large amounts of them in their tissue.

This could end up possibly in a very succesful phytoremediation scenario but this is only a speculation for the future.

Finally, as mentioned above phytoremediation’s process is an estimation of possible outcomes, rendering the whole process theoretical and stochastic.

However, Jack Ahern’s adaptive design implementing ‘‘safe to fail’’ design experiments, may prove very useful in this case, as adaptive design is based on the available knowledge, but is taking into consideration the uncertainty of success. This means that design proposals can acquire similar structures to scientific experiments to explore the undetermined outcome. This can be succeded through monitoring the project’s performance in a smaller scale and thus while in the process of developing it, the possibility of failure is minimized (Ahern 2013).

References Ahern, J., 2012. Urban landscape sustainability and resilience: the promise and challenges of integrating ecology with urban planning and design. Landscape Ecology, 28(6), pp.1203-1212.

Algreen, M., Trapp, S. and Rein, A., 2013. Phytoscreening and phytoextraction of heavy metals at Danish polluted sites using willow and poplar trees. Environmental Science and Pollution Research, 21(15), pp.8992-9001.

Ali, H., Khan, E. and Sajad, M., 2013. Phytoremediation of heavy metals—Concepts and applications. Chemosphere, 91(7), pp.869-881.

Andersen, L., Holm, P., Lehmann, N., Petersen, L., Jørgensen, U. and Mortensen, J., 2000. Phytooprensning af metaller. [online] Miløministeriet Miljøstyrelsen. Available at: <https://www2.mst.dk/udgiv/publikationer/2000/87-7944-097-5/pdf/87-7944-098-3.pdf> [Accessed 28 May 2021].

Assunção, A., Schat, H. and Aarts, M., 2003. Thlaspi caerulescens , an attractive model species to study heavy metal hyperaccumulation in plants. New Phytologist, 159(2), pp.351-360.

Baker, A., McGrath, S., Sidoli, C. and Reeves, R., 1994. The possibility of in situ heavy metal decontamination of polluted soils using crops of metal-accumulating plants. Resources, Conservation and Recycling, 11(1-4), pp.41-49.

Barfod, A., Seberg, O., Rasmussen, F. and Frederiksen, S., 2012. Dansk flora. Kbh.: Gyldendal.

Borggaard, O., Holm, P. and Strobel, B., 2019. Potential of dissolved organic matter (DOM) to extract As, Cd, Co, Cr, Cu, Ni, Pb and Zn from polluted soils: A review. Geoderma, 343, pp.235-246.

Boroș, M. and Micle, V., 2021. Study on soil decontamination by phytoremediation in the case of former industrial sites.. [online] Cabdirect.org.

Available at: <https://www.cabdirect.org/cabdirect/abstract/20163066119> [Accessed 27 May 2021].

Bradshaw, H., Ceulemans, R., Davis, J. and Stettler, R., 2000. Emerging Model Systems in Plant Biology: Poplar (Populus) as A Model Forest Tree. Journal of Plant Growth Regulation, 19(3), pp.306-313.

Brc.ac.uk. 2021. BRC - Database of Insects and their Food Plants. [online] Available at: <http://www.brc.ac.uk/dbif/hostsresults.aspx?hostid=4996> [Accessed 29 May 2021].

Campbell, C., 1997. Buckwheat, Fagopyrum esculentum Moench. Rome, Italy: IPGRI, pp. 26, 54.

De Oliveira, V. and Tibbett, M., 2018. Tolerance, toxicity and transport of Cd and Zn in Populus trichocarpa. Environmental and Experimental Botany, 155, pp.281-292.

Dunlap, J. and Stettler, R., 1998. Genetic variation and productivity of Populus trichocarpa and its hybrids. X. Trait correlations in young black cottonwood from four river valleys in Washington. Trees, 13(1), pp.28-39.

References Edwardson, S. 1996. Buckwheat: Pseudocereal and nutraceutical. p. 195-207. In: J. Janick (ed.), Progress in new crops. ASHS Press, Alexandria, VA. Ernst, W., 1996. Bioavailability of heavy metals and decontamination of soils by plants. Applied Geochemistry, 11(1-2), pp.163-167.

Holm, PE 2001, Soil remediation. in Edited by Hans Chr. Bruun Hansen (ed.), Environmental Soil Chemistry. Matej Bel University, Banská Bystrica, Leonardo da Vinci Programme, pp. 170-191.

Jensen, J., Holm, P., Nejrup, J., Larsen, M. and Borggaard, O., 2009. The potential of willow for remediation of heavy metal polluted calcareous urban soils. Environmental Pollution, 157(3), pp.931-937.

Københavns Stadsarkiv. 2021. Før eksplosionen. [online] Available at: <https://kbharkiv.dk/udforsk/historier-om-koebenhavn/eksplosionen-paa-valby-gasvaerk/ foer-eksplosionen> [Accessed 29 May 2021].

McCutcheon, S. and Jørgensen, S., 2008. Phytoremediation. Encyclopedia of Ecology, pp.568-582.

McGrath, S., Zhao, F. and Lombi, E., 2001. Phytoremediation of metals, metalloids, and radionuclides.

Meers, E., Lamsal, S., Vervaeke, P., Hopgood, M., Lust, N. and Tack, F., 2005. Availability of heavy metals for uptake by Salix viminalis on a moderately contaminated dredged sediment disposal site. Environmental Pollution, 137(2), pp.354-364.

Mleczek, M., Gąsecka, M., Waliszewska, B., Magdziak, Z., Szostek, M., Rutkowski, P., Kaniuczak, J., Zborowska, M., Budzyńska, S., Mleczek, P. and Niedzielski, P., 2018. Salix viminalis L. - A highly effective plant in phytoextraction of elements. Chemosphere, 212, pp.67-78.

Nord-Larsen, T., Sevel, L. and Raulund-Rasmussen, K., 2014. Commercially Grown Short Rotation Coppice Willow in Denmark: Biomass Production and Factors Affecting Production. BioEnergy Research, 8(1), pp.325-339.

Olejniczak, A., Cyganiuk, A., Kucinska, A. and P., J., 2021. Energetic Willow (Salix viminalis) – Unconventional Applications. [online] Academia.edu. Available at: <https://www.academia.edu/28881136/Energetic_Willow_Salix_viminalis_Unconventional_Applications> [Accessed 22 May 2021].

Pulford, I., 2003. Phytoremediation of heavy metal-contaminated land by trees—a review. Environment International, 29(4), pp.529-540.

Reeves, R., Baker, A., Jaffré, T., Erskine, P., Echevarria, G. and van der Ent, A., 2017. A global database for plants that hyperaccumulate metal and metalloid trace elements. New Phytologist, 218(2), pp.407-411.

Schwartz, C., Echevarria, G. and Morel, J., 2003. Plant and Soil, 249(1), pp.27-35.

References Sleegers, F., 2010. Phytoremediation as Green Infrastructure and a Landscape of Experiences, Proceedings of the Annual International Conference on Soils, Sediments, Water and Energy: Vol. 15 , Article 13. Available at: https://scholarworks.umass.edu/soilsproceedings/vol15/iss1/13 [Accessed 29 May 2021] Suman, J., Uhlik, O., Viktorova, J. and Macek, T., 2018. Phytoextraction of Heavy Metals: A Promising Tool for Clean-Up of Polluted Environment?. Frontiers in Plant Science, 9.

Tamura, H., Honda, M., Sato, T. and Kamachi, H., 2005. Pb hyperaccumulation and tolerance in common buckwheat (Fagopyrum esculentum Moench). Journal of Plant Research, 118(5), pp.355-359.

Vysloužilová, M., Tlustoš, P. and Száková, J., 2011. Cadmium and zinc phytoextraction potential of seven clones of Salix spp. planted on heavy metal contaminated soils. Plant, Soil and Environment, 49(No. 12), pp.542-547.

Wang, L., Zheng, B., Yuan, Y., Xu, Q. and Chen, P., 2020. Transcriptome profiling of Fagopyrum tataricum leaves in response to lead stress. BMC Plant Biology, [online] 20(1). Available at: <https://doi.org/10.1186/s12870-020-2265-1.

Www2.mst.dk. 2001. 6 Soil, Danish Environmental Protection Agency. [online] Available at: <https://www2.mst.dk/udgiv/Publications/2001/87-7944-519-5/html/kap06_eng.htm> [Accessed 29 May 2021].

WEBSITES Andersen, L., Holm, P., Lehmann, N., Petersen, L., Jørgensen, U. and Mortensen, J., 2000. Phytooprensning af metaller. [online] Miløministeriet Miljøstyrelsen. Available at: <https://www2.mst.dk/udgiv/publikationer/2000/87-7944-097-5/pdf/87-7944-098-3.pdf> [Accessed 28 May 2021].

Boroș, M. and Micle, V., 2021. Study on soil decontamination by phytoremediation in the case of former industrial sites.. [online] Cabdirect.org.

Available at: <https://www.cabdirect.org/cabdirect/abstract/20163066119> [Accessed 27 May 2021].

Brc.ac.uk. 2021. BRC - Database of Insects and their Food Plants. [online] Available at: <http://www.brc.ac.uk/dbif/hostsresults.aspx?hostid=4996> [Accessed 29 May 2021].

Olejniczak, A., Cyganiuk, A., Kucinska, A. and P., J., 2021. Energetic Willow (Salix viminalis) – Unconventional Applications. [online] Academia. edu. Available at: <https://www.academia.edu/28881136/Energetic_Willow_Salix_viminalis_Unconventional_Applications> [Accessed 22 May 2021].

Sleegers, F., 2010. Phytoremediation as Green Infrastructure and a Landscape of Experiences, Proceedings of the Annual International Conference on Soils, Sediments, Water and Energy: Vol. 15 , Article 13. Available at: https://scholarworks.umass.edu/soilsproceedings/vol15/iss1/13 [Accessed 29 May 2021] Københavns Stadsarkiv. 2021. Før eksplosionen. [online] Available at: <https://kbharkiv.dk/udforsk/historier-om-koebenhavn/eksplosionen-paa-valby-gasvaerk/foer-eksplosionen> [Accessed 29 May 2021].

Www2.mst.dk. 2001. 6 Soil, Danish Environmental Protection Agency. [online] Available at: <https://www2.mst.dk/udgiv/Publications/2001/87-7944-519-5/html/kap06_eng.htm> [Accessed 29 May 2021].

Alexandros Georgios Memetzidis Copenhagen May 2021