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The GREENLAND project: gentle remediation of trace element contaminated land.

Authors:
  • French National Research Institute for Agriculture Food and Environment
GREENLAND Gentle remediation of trace
element contaminated land
BEST PRACTICE GUIDANCE FOR
PRACTICAL APPLICATION OF GENTLE
REMEDIATION OPTIONS (GRO)
December 2014.
GREENLAND: consortium lead scientists and contact points
Markus Puschenreiter, University of Natural Resources and Life Sciences, Vienna (co-ordinator)
Jaco Vangronsveld, Universiteit Hasselt
Jurate Kumpiene, Luleå tekniska universitet
Michel Mench, Institut National de la Recherche Agronomique
Valerie Bert, Institut National de l’Environnement industriel et des Risques
Andrew Cundy, University of Brighton
Petra Kidd, Consejo Superior de Investigaciones Cientificas
Giancarlo Renella, University of Florence
Wolfgang Friesl-Hanl, Austrian Institute of Technology
Grzegorz Siebielec, Instytut Uprawy Nawozenia I Glebooznawstwa Panstwowy
Rolf Herzig, Phytotech-Foundation
Ingo Müller, Sächsisches Landesamt für Umwelt, Landwirtschaft und Geologie
Jannis Dimitriou, Sveriges lantbruksuniversitet
Xose Quiroga Troncosco, Tratamientos Ecológicos del Noroeste SL
Patrick Lemaitre, Innoveox
Anne Serani Loppinet, CNRS-ICMCB
Other contributors: Paul Bardos, Andrew Church, Jolien Janssen, Silke Neu, Nele Weyens, Nele Witters, Angela
Sessitsch, Rodolphe Gaucher.
Contact points:
Professor Andy Cundy
School of Environment and
Technology, University of Brighton
Lewes Road, Brighton
BN2 4GJ, UK
Tel: + 44 1273 642270
A.Cundy@brighton.ac.uk
Project co-ordinator:
Dr. Markus Puschenreiter
Universität für Bodenkultur
(BOKU); Department für Wald und
Bodenwissenschaften
Peter Jordan Strasse 82
A-1190 Wien
Tel: ++43 1 47654 3126
markus.puschenreiter@boku.ac.at
The views expressed in this guidance are those of the authors, and do not necessarily reflect the views or
policy of their employers, or of the European Commission. Mention of trade names or commercial products
does not constitute endorsement or recommendation for use.
The property rights of the content belong to the GREENLAND consortium. While every effort has been made to
ensure the accuracy and validity of the content, the authors do not make any warranty, express or implied, nor
assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information,
apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned
rights.
The GREENLAND project is financially supported by the European Commission under the
Seventh Framework Programmes for Research (FP7-KBBE-266124, Greenland).
UK
Foreword:
This guidance document presents condensed results from the European Union Framework 7
GREENLAND project, a cross-European multi-partner project focussed on the use of gentle
remediation options (GROs) as practical land remediation and risk management tools. GRO have
been under-utilised as practical remediation strategies in the European contaminated land sector,
despite their capability to provide rapid risk management and generate a range of additional
economic, environmental and social benefits. This guide is intended to encourage wider
consideration and use of GRO as an effective risk management strategy within Europe and in other
geographic regions, and provides:
a context and rationale for the practical application of Gentle Remediation Options as
effective risk management strategies;
examples of successful GRO application within the European contaminated land arena;
an illustration of the potential wider economic, environmental and social benefits that may
be realised during and following GRO application; and
outline operating windows for GRO application.
In addition, we provide a series of technical appendices to support design and implementation of
effective GRO strategies on a site-specific level. The guidance document is aimed at planners,
consultants, regulators, practitioners, scientists, and other brownfields or contaminated land
stakeholders, and is provided with an accompanying decision support tool (DST), in MS Excel format,
which is intended to provide practical decision support when appraising various options for
contaminated site management. The guidance document and the decision support tool are intended
to act as decision support and information guides, not as decision making tools, and should not
replace expert input in common with many remediation strategies GRO are not “off-the-shelf”
tools, and a site specific assessment and testing is required prior to implementation.
1. Definitions and context what is GRO and how does it work?
1.1 GROs a definition
Gentle Remediation Options (GRO) are risk management strategies or techniques for contaminated
sites that result in a net gain (or at least no gross reduction) in soil functionality as well as risk
management. These strategies and techniques have been successfully applied at sites containing a
range of organic, inorganic and radioactive contaminants. This guidance document, following the EU
Knowledge-Based Bio-Economy research programme GREENLAND, focuses on their application at
trace element (including metal and metalloid) contaminated sites.
1.2 Context
Two broad concepts have emerged in contaminated land management over the past 30 years: the
use of risk assessment to determine the seriousness of problems, and the use of risk management to
mitigate problems found by risk assessment to be significant. For a risk to be present (see Figure 1)
there needs to be a source (of hazardous contamination), one or more receptors (which could be
adversely affected by the contamination) and one or more exposure pathways (linking the source to
the receptors). Receptors might be human health, water resources, a built construction, or the wider
environment. For example, in the UK this combination of a source-pathway-receptor is referred to as
a pollutant or contaminant linkage. Requirements for land and groundwater remediation strictly
depend on risk management needs, whether the intended use of the remediated land is for a “hard”
end use such as a built development or a “soft” end use, where the soil remains unsealed, such as
community parkland. Risk management focuses on breaking the contaminant linkage, either by
controlling the source (e.g. removing or (bio)degrading the contamination); managing the
pathway(s) (e.g. preventing labile contaminant pools and migration of contamination); protecting
the receptor(s) (e.g. planning - institutional - controls to avoid sensitive land uses) or some
combination of these components.
Figure 1: Contaminant Linkage and Risk Management Options (based on DEFRA 2012, after Cundy et
al. 2013).
Conventional approaches to contaminated land risk management have focussed on containment,
cover and removal to landfill (or “dig and dump”). However, since the late 1990s there has been a
move towards treatment-based remediation strategies using in situ and ex situ treatment
Source
Pathway
Receptor
Source “control” Pathway
Management
Receptor protection
technologies (e.g. soil washing). More recently the concept of Gentle Remediation Options (GRO)
has emerged. These are risk management strategies/techniques that result in a net gain (or at least
no gross reduction) in soil functionality as well as risk management. Hence they have particular
usefulness for either maintaining or restoring biologically productive soils. GROs encompass a
number of technologies which include the use of plant (phyto-), fungal (myco-) or bacterial-based
methods, with or without chemical additives, for reducing exposure of local receptors to
contaminants by in situ stabilisation (using biological and / or chemical processes), or extraction,
transformation or degradation of contaminants. GRO includes techniques such as in situ
immobilisation/phytoexclusion, phytovolatilisation, phytostabilisation, rhizofiltration,
rhizodegradation, phytodegradation/phytotransformation and phytoextraction (Table 1). A similar
concept might also exist for groundwater, for example monitored natural attenuation might be
considered a GRO. As a concept GROs are a development of an earlier idea called “extensive”
technologies which sought to distinguish low input longer term remediation approaches from
energy, resource and labour intensive strategies.
Table 1: List of definitions for Gentle Remediation Options used to remediate soils contaminated
by either trace elements or mixed contamination (after Peuke and Rennenberg 2005, Mench et al
2010).
GRO
Definition
Phytoextraction
The removal of metal(loid)s or organics from soils by
accumulating them in the harvestable biomass of
plants. When aided by use of soil amendments, this is
termed aided phytoextraction.
Phytodegradation / phytotransformation
The use of plants (and associated microorganisms
such as rhizosphere and endophytic bacteria) to
uptake, store and degrade organic pollutants.
Rhizodegradation
The use of plant roots and rhizosphere
microorganisms to degrade organic pollutants.
Rhizofiltration
The removal of pollutants from aqueous sources by
plant roots and associated microorganisms.
Phytostabilisation
Reduction in the bioavailability of pollutants by
immobilisation in root systems and / or living or dead
biomass in the rhizosphere soil creating a milieu
which enables the growth of a vegetation cover.
When aided by use of soil amendments, this is
termed aided phytostabilisation.
Phytovolatilisation
Use of plants to remove pollutants from the growth
matrix, transform them and disperse them (or their
degradation products) into the atmosphere.
In situ immobilisation / phytoexclusion
Reduction in the bioavailability of pollutants by
immobilizing or binding them to the soil matrix
through the incorporation into the soil of organic or
inorganic compounds, singly or in combination, to
prevent the excessive uptake of essential elements
and non-essential contaminants into the food chain.
Phytoexclusion, the implementation of a stable
vegetation cover using excluder plants which do not
accumulate contaminants in the harvestable plant
biomass can be combined with in situ immobilisation.
Intelligently applied GROs can provide: (a) rapid risk management via pathway control, through
containment and stabilisation, coupled with a longer term removal or immobilisation/isolation of
contaminants; and (b) a range of additional economic (e.g. biomass generation), social (e.g. leisure
and recreation) and environmental (e.g. C sequestration, water filtration and drainage
management, restoration of plant, microbial and animal communities) benefits (which are
encompassed in the generic term “ecosystem services”). These are discussed further in sections 2
and 4 below.
2. Overview of current state of development and risk management
capability.
Despite widespread use of “green” technologies such as landscaping, application of green cover, and
reedbeds and constructed wetlands in remediation or industrial/urban regeneration projects, the
application of GROs as practical remedial solutions is still in its relative infancy, particularly for trace
element-contaminated sites. The barriers to wider adoption, especially in Europe, arise both from
the nature of GROs as remediation techniques, and market and stakeholder perceptions of
uncertainties over whether these methods can achieve effective risk management in the long term.
The majority of remediation work in Europe has been carried out as a result of regulatory demand
for critical risks and/or to stimulate the re-use or development of brownfield land. Hence,
unsurprisingly, most funded remediation and brownfield regeneration projects are in or around
urban environments, and brownfields re-use is strongly driven by economic factors. These projects
are often constrained by pressure on time scale and relatively limited site areas. Both of these
factors have tended to exclude consideration of GROs which are perceived as slow and more suited
to large area problems.
The time taken before prescribed “total” concentration-based risk management targets such as soil
quality thresholds are reached is also seen as a limitation for GROs. This has led to intensive
discussions in particular about phytoextraction, which is perhaps the most well-known GRO, and
which has been widely tested at demonstration scale. Phytoextraction has tended to be seen as a
source management activity which seeks to gradually remove metal(loid)s from soil over time
harvestable biomass. Phytoextraction has poor acceptance as a functional source management tool
because contaminant removal may take decades (when the aim is to clean up to specific levels of
total concentration) and there is some concern over the fate of and contaminant concentration in
harvested biomass. Acceptance of other GROs related to phytostabilisation and in situ
immobilisation is limited because source removal does not take place, and there is a perception that
stabilisation or immobilisation is potentially reversible over time.
Box 1: GRO: Technical Applicability.
GRO are primarily deployed on contaminated soils to remove the labile (or
bioavailable) pool of inorganic contaminants (phytoextraction), remove or degrade
organic contaminants (e.g. phytodegradation), protect water resources (e.g.
rhizofiltration), or stabilise or immobilise contaminants in the subsurface (e.g.
phytostabilisation, in situ immobilisation/phytoexclusion).
The constraints on acceptability of GROs are inevitable when remediation success is judged solely
using generic soil concentration targets. While this target-led approach can be attractive to some
because of its simplicity, its inherent conservatism may lead to over-designed risk management
solutions, which are costly, invasive and may not be sustainable. A site-specific approach, that
properly considers source and pathway interventions in a more comprehensive risk management
strategy, allows a more targeted and hence likely more sustainable risk management solution. This
also creates a better rationale for the deployment of plant- and microorganism-based GROs. GROs
may then facilitate land regeneration in circumstances where the case for intervention is
economically marginal by virtue of their lower cost and also, potentially, by their linkage to other
project services such as biomass production, public green space provision, recovery of land values
etc. GRO approaches can be tailored along pollutant linkages (Figure 2), for example:
Source: gradual removal or immobilisation of source term
Pathway: rapid reduction in flux of contaminants to receptors at significant risk
Receptor: using vegetation to manage receptor access to the subsurface.
Figure 2: GRO-based risk management strategy, tailored along contaminant linkage model.
Examples of circumstances which do not favour existing treatment-based remediation solutions, but
which may be highly amenable to this broader risk management approach using GRO, include:
Large treatment areas, particularly where contamination may be causing concern but is not at
strongly elevated levels
Where biological functionality of the soil is required after site treatment
Where other environmental services related to soil quality (e.g. biodiversity, carbon
sequestration) are valued highly
Where there is a need to restore marginal land to produce non-food crops and avoid major land
use changes
Where there are budgetary constraints
Where there are deployment constraints for land remediation process plant (e.g. as a function of
area and location).
Typically these constraints describe sites for which a “soft” end use is envisaged.
Intelligently applied GROs have been shown in a number of cases to provide rapid risk management
via pathway control, through containment and stabilisation, coupled with a longer term removal or
immobilisation of the contaminant source term. Large-scale, long duration, examples of GRO
Source
Pathway
Receptor
Gradual removal or
immobilisation of
source term
Reduction in labile
pool, rapid
reduction in flux of
contaminants to
receptors at
significant risk
Using vegetation to
manage receptor
access to the
subsurface
application at trace element contaminated sites across Europe are given in section 3 in the
GREENLAND case / success stories. In North America, application of GRO is arguably more developed
than in Europe with the US Interstate Technology & Regulatory Council listing 48 sites, largely within
the USA, as hosting “full-scale” phytotechnology trials (as of 2007). GRO application generally in
North America ranges from relatively small-scale phyto- and bio-remediation projects that are driven
and implemented by the local community to larger “green-technology”-based remediation
programmes at Superfund sites which involve tree planting, soft cover etc. GRO can be durable
solutions as long as land use and land management practice does not undergo substantive change
causing shifts in pH, Eh, plant cover etc., suggesting that some form of institutional or planning
control may be required. The use of institutional controls over land use however is a key element of
urban remediation using conventional technologies (e.g. limitation of use for food production), so
any requirement for institutional control and management with GROs continues a long established
precedent.
3. Case / success stories.
Figure 3: The GREENLAND project network of long-term (>5 year) GRO field experiments in Europe
at trace element contaminated sites, covering a range of climatic, soil and contaminant types.
The GREENLAND site network (Figure 3) is a cross-European network of metal(loid) contaminated
sites where phytomanagement efficiency has been tested for long (> 5 year) periods, under different
contaminant types and loadings and soil and climatic conditions, with various plants and cultivars.
Further details of three of these sites are given in the following pages, as examples of cases where
application of phytoextraction, aided phytostabilisation, and in situ stabilisation / phytoexclusion
phytomanagement strategies have led to demonstrable source removal, pathway management or
receptor protection. Further examples are given in the technical appendices which accompany this
guidance.
Example 1: Phytoextraction (DE)
Example 2: Aided phytostabilisation (FR)
Example 3: In situ stabilisation / phytoexclusion (AT)
4. Potential economic, environmental and social benefits.
GROs have potential to deliver a range of additional economic (e.g. biomass generation), social (e.g.
leisure and recreation) and environmental (e.g. C sequestration, water filtration and drainage
management, restoration of plant, microbial and animal communities) benefits (which are
encompassed in the generic term “ecosystem services”), as well as risk management. These wider
benefits have often been only superficially considered during remediation options appraisal in the
past, but present a potentially very important wider value proposition for use of “soft” remediation
strategies such as GRO. Benefits may be in the form of direct revenue generating opportunities (e.g.
biomass revenues), an increase in natural or cultural capital in an area (e.g. soil and water
improvement, provision of green infrastructure, amenity space etc.), or provision of tangible or
intangible economic benefits (e.g. increase in property values, job generation etc.). While economic,
social and environmental benefits will clearly be site and project specific, a number of more generic
qualitative, semi-quantitative and fully quantitative tools and systems are available to enable
identification and quantification of wider benefits arising from application of GRO. Within the
GREENLAND decision support tool (DST), links to three matrices/modules are provided:
(a) The European Union FP7 HOMBRE project (grant 265097, www.zerobrownfields.eu) Brownfield
Opportunity Matrix (BOM). This is an Excel-based qualitative screening tool to help decision
makers identify which services they can obtain from “soft reuse” interventions (including GRO)
at a site, and how these services interact. GREENLAND partners have collaborated with
HOMBRE partners to populate the operating and opportunity windows for GRO within the
Brownfield Opportunity Matrix. The matrix can be used to map the prospective range of
opportunities that might be realised by a remediation or redevelopment project, and the
project’s consequent sources of value.
(b) The SURF indicator sets on sustainability, which outline the various headline indicators that
should be considered during sustainability assessment in land remediation projects. These
indicators provide a semi-quantitative ranking system based on key economic, environmental
and social indicators. In the DST, the user is then referred on to more detailed, external web-
based tools for semi-quantitative and quantitative assessment via Life Cycle Assessment (LCA)
and Cost Benefit and Multi-Criteria Analysis (CBA/MCA)
(c) An outline Cost-Calculator, which has been developed within the GREENLAND project and
incorporates user-entered cost data (including site preparation costs; plant and planting costs;
site costs; biomass costs and revenues; and monitoring costs) to estimate the economic value
proposition of GRO at a particular site. This module has been calibrated” using data from the
GREENLAND site network, which are used to test the cost calculator and give input examples to
the user.
It is important to stress that alongside the more technical aspects of remediation, effective and
sustained engagement strategies with a wide range of stakeholders will be required to ensure that
the full potential benefits of GRO are realised and communicated. Additional support and guidance
for stakeholder engagement, including guidelines for stakeholder engagement when applying GRO
and criteria for the identification of different stakeholders profiles/categories, is provided in the
Greenland project decision support tool and in Appendix 6.
5. Operating windows for GRO.
5.1 High-level (generic) operating windows managing site risk for soft end-use.
Biologically productive soils include those used for agriculture, habitat, forestry, amenity, and
landscaping, and therefore GROs will tend to be of most benefit where a “soft” end use of the land is
intended. Conventionally regeneration of contaminated land for soft end use has involved the use of
cover systems with revegetation and/or removal of contamination hot spots. Remediation (i.e.
mitigation of the effects of contaminants using biological, chemical or physical treatment) has been
largely restricted to returning smaller land areas to hard re-use as these treatments simply tend to
cost too much for soft end uses.
There are many drivers for soft end uses of contaminated land. The site in question may simply not
have a feasible alternative use for reasons of size, location, geotechnical or topographical reasons, or
levels of economic activity, as a result of global shifts in land use and industrial change. There may
be important urban renewal arguments for developing amenity land, particularly in areas of urban
deprivation. In addition, there may also be opportunities for generating renewed economic activity,
for example, through biomass production. Indeed, the EU Renewables Directive (DIRECTIVE
2009/28/EC) points out an enhanced sustainability value for biomass from marginal land, including
contaminated land. The use of GROs can be highly compatible with biomass end use. This creates an
important and expanding role for GROs, as an important part of the value proposition for the
management of degraded land in the future might be an income from biomass-based GRO.
GROs therefore offer a cost effective treatment alternative for managing risks for soft end uses,
rather than simply containing or transferring contamination. GROs should be attractive alternatives
to conventional clean-up methods in these situations owing to their relatively low capital costs and
the inherently aesthetic nature of planted or “green” sites. In addition, “greening” of contaminated
or marginal land may have additional wider benefits in terms of educational and amenity value, C
sequestration, resource deployment (i.e. for re-use of organic matter/compost and technosols) and
providing a range of ecosystem services see also section 4.
5.2 Detailed operating windows.
As discussed above, and illustrated by the case/success stories in section 3, GRO can be effectively
used as part of a wider risk management strategy at contaminated sites, while promoting additional
economic, environmental and social benefits. GRO can be implemented in a range of soil types and
climates, across a range of site and contaminant types. As with other remediation strategies
however they are not a simple “off-the-shelf” solution that can be applied to every site situation and
type, and a site specific assessment and testing is required prior to implementation. Further details
on GRO design and implementation are given in the technical appendices which accompany this
guidance, but here we provide quick reference tables on GRO applicability, and a link to three MS
Excel-based operating window matrices which allow the user to check the outline applicability of
GRO (grouped as phytoextraction, phytostabilisation, and immobilisation/phytoexclusion) to a
specific site, in terms of local soil pH, site plant toxicity, climate, soil type, and depth of
contamination. The purpose of these tables and matrices is to highlight the potential applicability of
GRO at a site, NOT to confirm that GRO will be a successful risk management tool at that site.
Further technical and design input and expertise will be required to effectively design and
implement a GRO strategy that effectively manages contaminant risk, and delivers wider benefit.
Contact points and further literature to support this is given in section 6, in the appendices, and on
page 1 of this guidance.
Quick reference: Are GRO applicable to your site?
Key questions:
If YES, are GRO potentially applicable?
Does the site require immediate
redevelopment?
Unlikely (except immobilisation / phytoexclusion
which can show immediate positive effects)
Are your local regulatory guidelines based on
total soil concentration values?
Unlikely for phytoextraction but possibly for some
other GRO
Is the site under hard-standing, or has buildings
under active use?
Unlikely (there is a need to remove the hard-
standing or buildings and to establish a soil layer
enabling plant growth).
Do you require biological functionality of the soil
during and after site treatment?
YES
Is the treatment area large, and contaminants
are present but not at strongly elevated levels?
YES (even where soil ecotoxicity is high, use of soil
pretreatments and amendments may enable GRO
application)
Are the contaminants of concern present at
depths within 5 10m of the soil surface?
YES (depending on soil porosity, if contamination is
present within 1m of the soil surface then treatment
is possible by most plants. Deeper contamination may
be addressed using trees, with interventions where
necessary to promote deeper rooting).
Is the economic case for intervention and use of
"hard" remediation strategies marginal?
YES
Are you redeveloping the site for soft end-use
(biomass generation, urban parkland etc)?
YES
Quick reference: Which metal(loid) contaminants can GRO treat?
Link to MS Excel-based operating window matrices allowing the user to check the outline
applicability of GRO (grouped as phytoextraction, phytostabilisation, and immobilisation /
phytoexclusion) to a specific site can be accessed via the GREENLAND project decision support tool
(DST), downloadable from: http://www.greenland-project.eu/
6. Selected further information sources.
Phytoremediation for trace element
contaminated sites: the Greenland
project
http://www.greenland-project.eu/
ITRC Phytotechnologies guidance
http://www.itrcweb.org/Guidance/GetDocument?documentID=64
USEPA Phytotechnologies factsheet
(including links to success stories)
http://www.epa.gov/tio/download/remed/phytotechnologies-
factsheet.pdf
Application at US Superfund sites
(USEPA, 2014)
http://www.epa.gov/superfund/accomp/news/phyto.htm
CLU-IN phytotechnologies overview
https://www.clu-
in.org/techfocus/default.focus/sec/Phytotechnologies/cat/Overview/
Further examples of full-scale
phytotechnology application
http://www.clu-in.org/products/phyto/search/phyto_list.cfm
Phytoremediation of Contaminated
Soil and Ground Water at Hazardous
Waste Sites
http://www.clu-in.org/download/remed/epa_540_s01_500.pdf
Phytoremediation of contaminated
soils and groundwater: lessons from
the field
http://www.au-plovdiv.bg/cntnr/fiziologia/statii/Vassilev/23.pdf
Willows for energy and
phytoremediation in Sweden
http://www.fao.org/docrep/008/a0026e/a0026e11.htm
Stakeholder engagement guidance for
GRO and case studies
http://www.ncbi.nlm.nih.gov/pubmed/23973957,
http://www.greenland-project.eu/
Thesis
Full-text available
GENERAL BACKGROUND : As a result of anthropogenic activities, soil resources remain contaminated with heavy metals and petroleum hydrocarbons. The high frequency of occurrence of multi-contaminated soils in the environment brings to light the necessity to find remediation solutions adequate in such complex scenarios, which besides have seldom been studied. Phytoremediation is a biologically based remediation technology, which takes advantage of the intrinsic physiological abilities of plants to remediate contaminated media. Plants and their associated microorganisms perform phytoremediation processes (e.g. phytoextraction and rhizodegradation), which can bring about the clean-up of multi-contaminated soils. However, a major constraint which hinders the success of phytotechnologies is low bioavailability of pollutants in soil. As a result, chemically- and biologically-assisted phytoremediation are possible strategies used to overcome this limitation and improve the remediation efficiency. The chemical approach presented in this study involves the addition of biodegradable soil amendments to increase the ability of contaminants to be transferred from a soil compartment to plants and microorganisms. The biological strategy explored herein consists of inoculating contaminated soils with bacteria (bioaugmentation) able to improve remediation of pollutants and/or promote plant features.MAIN OBJECTIVES: a) To investigate the phytoremediation potential of alfalfa (Medicago sativa) in multi-contaminated soils b) To study the effects of the low molecular weight organic acid citric acid and the surfactant Tween® 80 on the phytoremediation process c) To assist phytoremediation with a bioaugmentation approach using Pseudomonas aeruginosa bacteria. METHODOLOGIES: Determination of germination and mortality rates, assessment of plant physiological parameters. Quantification of plant biomass, heavy metals in plants, total petroleum hydrocarbons (TPH) in soil, soil microbiological indicators. Calculation of phytoremediation parameters. REMARKABLE RESULTS : Alfalfa presented low tolerance to TPH contaminated soil at 8400 mg kg-1 soil, which was improved when TPH were present at lower concentration (3600 mg kg-1 soil). Alfalfa was able to take up metals to a limited extent (<100 mg kg-1 dry matter), while had a positive effect in promoting microbial number of alkane degraders and lipase activity in the rhizosphere. Moreover, the combined application of citric acid and Tween® 80 resulted in a greater improvement of these parameters. Bioaugmentation with P. aeruginosa had a promoting effect on alfalfa biomass (71% increase of plant total dry biomass). In addition, the highest TPH removal rates (68%, after 90 days of experiment) were obtained in soils vegetated with alfalfa and bioaugmented with P. aeruginosa.OVERALL CONCLUSION: Alfalfa could tolerate a heavy metal and petroleum hydrocarbon co-contaminated soil (subject to TPH levels), which is an essential characteristic for any plant species to be used in phytoremediation. Alfalfa could not be considered as an actively heavy metal removal species as it was not able to phytoextract significant amounts of heavy metals (still in the presence of soil amendments or bioaugmentation). Nevertheless, the enhancement of microbial number and activity in the rhizosphere encouraged the potential of this plant species to be successfully used in the remediation of petroleum hydrocarbons. These effects were additionally enhanced by the joint application of soil amendments. Finally, the combination of phytoremediation and bioaugmentation seems a promising approach to achieve the remediation of petroleum hydrocarbons, when present in multi-contaminated soils
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