@misc{10481/97619,
year = {2024},
url = {https://hdl.handle.net/10481/97619},
abstract = {Soil pollution by potentially toxic elements (PTEs) (e.g., Pb, As, Zn, Cu, Cd, and
Sb) is a significant environmental problem worldwide, mainly associated with
anthropogenic sources and activities, including the mining industry. These
elements, while naturally occurring in the environment, can reach toxic
concentrations and persist for long periods, causing severe damage to
ecosystems and posing serious risks to human health.
In scenarios where extensive and severe soil pollution occurs, active soil
remediation actions are needed to mitigate environmental damages and
protect humans and other living organisms health. The Guadiamar Green
Corridor (GGC) (Seville, SW Spain) represents an exemplary scenario of a
natural ecosystem severely damaged over the long term by anthropogenic
activities, and more specifically by PTEs pollution. This area was severely
affected by the Aznalcóllar mining spill occurred in 1998, which resulted in
high levels of persistent soil pollution despite initial cleanup efforts. Still
nowadays, 25 years after the accident, residual polluted areas remain evident
along the GGC by the existence of bare highly acidic soil patches with elevated
PTEs concentrations. These residual polluted soils represent a risk not only to
the environment but also to human health, requiring continuous monitoring
and the development of comprehensive protocols and effective and feasible
remediation strategies.
This thesis addresses the need to develop sustainable and effective strategies
for remediation PTE-polluted soils, using the GGC as a case study. The
research is focused on the valorization of wastes and by-products from
anthropogenic activities and the application of symbiotic microorganisms as
viable strategies for remediation of soils polluted by PTEs. The aim of this
thesis is to evaluate the effectiveness and feasibility of a set of cost-effective
and environmentally friendly soil remediation techniques and strategies for
the ecological remediation of PTE-polluted soils. For this purpose, various soil
remediation treatments, including inorganic liming amendments (gypsum
mining spoil and marble sludge), organic amendments (vermicompost and
biotransformed dry olive residue (DOR) by saprobic fungi), and physical
techniques such as landfarming and biopiles, were applied in situ to polluted
soils in the GGC. Furthermore, a soil bioremediation approach based on
arbuscular mycorrhizal fungi (AMFs) was implemented under greenhouse
conditions to evaluate the potential of this bioremediation strategy to
enhance the effectiveness of the physicochemical treatments. The thesis evaluates the impact of the treatments applied on the main soil
properties and pollution levels over time, as assessed in chapters 2, 3, and 4.
Liming treatments, based on gypsum mining spoil and marble sludge, were
highly effective in neutralizing the strong acidity of the polluted soils,
particularly marble-based treatments, which led to complete pH
neutralization. Water-soluble and EDTA-extractable fractions of the PTEs
were measured to assess the changes in soil mobility and bioavailability of
PTEs following the application of the treatments to the polluted soil (PS).
Liming treatments were also the most effective in reducing both fractions of
these elements. This was associated with a significant increase in soil pH,
resulting in the effective immobilization of highly mobile elements such as Cu,
Zn, and Cd. However, excessively high pH levels could limit the immobilization
of other PTEs such as As, thus increasing its bioavailability. Resolubilization of
As and Pb could also occur in the presence of organic matter by competing
mechanisms for sorption sites in the soil. Therefore, the doses of liming and
organic amendments should be accurately estimated to effectively control
the mobility of PTEs in polluted soils.
In chapter 2, an ecotoxicological assessment of soil pollution in the treated
soils was carried out using a variety of bioassays selected as indicators of
PTEs stress in polluted soils, to evaluate the effectiveness of the remediation
treatments applied to the PS. A set of ecotoxicological tests were performed
using both the solid and liquid phase of the soil, involving target organisms
from different taxonomic groups and trophic levels, including
microorganisms, plants, and invertebrates. The results showed that marblebased
treatments were the most effective in reducing soil toxicity, primarily
due to their strong pH neutralization, which reduced PTEs solubility and
minimized toxicity risks. Moreover, bioassays using the liquid phase showed
higher sensitivity to toxicity compared to those using the solid phase, thus
providing a better estimation of soil toxicity.
The remediation treatments evaluated aimed to facilitate and accelerate
natural ecological succession in areas of the GGC where it was hindered by the
extremely limiting conditions. The success of these treatments in triggering
succession and facilitating the recovery of biological communities in the
highly degraded soil was assessed by analyzing the status of these
communities at various levels. In chapter 3, the vegetation status and
spontaneous recolonization of the reference and treated soils by native plants
were measured. In general, the treatments were effective in promoting spontaneous vegetation growth by improving soil properties and reducing
PTEs availability. Among them, those based on vermicompost showed the
greatest vegetation cover and species richness, approaching the conditions of
the adjacent naturally recovered soils (RS). These treatments significantly
increased soil organic carbon content and improved water retention capacity,
essential for facilitating plant recolonization and growth in polluted soils. In
the studied soils, two native plant species, Lamarckia aurea and Spergularia
rubra, acted as pioneer species colonizing the soil, exhibiting remarkable
ability to accumulate Pb and As in their roots. They can be considered key
species in the area, as they not only serve as pioneers in recolonizing the
degraded soils but also facilitate the subsequent recolonization by other
species less tolerant to high levels of pollution. Thus, the success of the
remediation strategy can be promoted by the early recolonization of the soil
by these highly pollution-tolerant species, which enhance further evolution of
the soil physical, biological, and chemical conditions.
The presence of pioneer plant species in treated soils can enhance microbial
activity by providing soil microbial communities with suitable habitat, along
with essential organic carbon and nutrient contents, which are crucial for key
soil processes and overall ecosystem functioning at the local scale. For this
reason, when evaluating the rate of ecological succession driven by
remediation treatments, it is important to take into account not only
aboveground processes, such as vegetation response, but also those
occurring belowground. In this regard, the soil microbiological status of both
reference and treated soils was evaluated in chapter 4. The results showed
that PS had low total abundances, community structure, and diversity of
microbial communities, confirming that microbial biomass and taxonomic
diversity of soil communities were significantly affected by the PTEs
concentrations. On the other hand, the soil treatments evaluated for their
microbiological status, specifically marble sludge and biopile, showed
effectiveness in restoring soil quality. The abundance and structure of
microbial populations under both treatments were restored to levels
proximate to those found in RS.
The application of the remediation treatments to PTE-polluted soils in the GGC
led to significant improvements in soil quality, reducing the mobility and
toxicity of PTEs, and allowing the establishment of vegetation. However,
despite these improvements, the conditions and quality of the treated soils
remained less favorable compared to the RS, with a persistent potential risk of PTEs remobilization that requires to be monitored over time. This highlights
that physicochemical techniques for the remediation of polluted soils alone
may not be enough to permanently alleviate pollution risks. Consequently, soil
bioremediation processes could be implemented in parallel to promote the
remedial effects of other techniques. In this sense, Chapter 5 explores the
addition of a biological element, AMFs inoculation, to the soil remediation
treatment that showed the highest overall effectiveness in the field-based insitu
remediation approach (marble sludge), combined with organic
amendments. Biotransformed DOR showed high effectiveness in improving
soil physicochemical and biological status when combined with marble
sludge, promoting plant growth and survival, and reducing PTEs toxicity and
plant uptake. Thus, DOR biotransformed by saprobic fungi can represent an
efficient organic amendment for remediating PTE-polluted soils.
Furthermore, the combined application of marble sludge and DOR along with
AMF inoculation, further enhanced PTEs immobilization in polluted soils by
stimulating the phytostabilization process induced by AMFs. This
bioremediation approach improved plant protection and significantly
increased the overall effectiveness of the remediation process, showing
potential as a sustainable bioremediation strategy for restoring soil functions
and reducing toxicity in areas polluted by PTEs.
In conclusion, this thesis provides valuable insights into the remediation of
PTE-polluted soils. Overall, the results demonstrated that combining
physicochemical treatments with a bioremediation approach, incorporating
AMF inoculation and organic amendments, significantly enhanced the
effectiveness of soil remediation processes. This approach not only improves
soil health and reduces PTEs mobility, but also supports the re-establishment
of vegetation and microbial communities in the degraded soils. These findings
contribute to the development of more effective and sustainable soil
remediation strategies that can be applied to similar polluted sites worldwide.
Moreover, the results emphasize the importance of a holistic approach to soil
remediation that considers not only the soil physicochemical status but also
its biological health and capacity for ecological recovery.},
organization = {Tesis Univ. Granada.},
organization = {Project RTI 2018-094327-B-I00 (Spanish Ministry of Science, Innovation and Universities)},
publisher = {Universidad de Granada},
title = {Remediation of soils polluted by metal(loid)s based on waste valorization and bioremediation by symbiotic and saprobic microorganisms},
author = {Paniagua López, Mario},
}