bark) represents a source of nutrients also for the autochthonous soil microbiota.
Even if the addition of nutrients positively impacts on the bioremediation efficiency
(Lang et al. 2000; Steffen et al. 2007; Federici et al. 2012), the growth-inhibition and
mycophagy phenomena could still occur as a result (de Boer et al. 2005; Baldrian
2008).
Other constraints for the application of fungal technologies at field scale are the
strict growth conditions required by most WRFs. For example, 37 and 30
C
represent the optimum temperatures for P. chrysosporium growth and ligninolytic
enzymes production, respectively. These conditions are not easily maintained under
actual environmental conditions due to daily and seasonal fluctuations (Hestbjerg
et al. 2003). Contrary to P. chrysosporium, P. ostreatus is less affected by temperature changes: the degradation of organic pollutants by this WRF was demonstrated
even at very low temperatures (up to 8
C) (Eggen and Sveum 1999; Lang et al.
2000; Hestbjerg et al. 2001). Furthermore, Pleurotus sp. is highly competitive with
soil microbiota and thus more successful to colonize the contaminated matrix than
other fungi (in der Wiesche et al. 1996; Lang et al. 1997, 1998; Stella et al. 2017).
Another parameter that deeply influences the effectiveness of bioremediation is
the bioavailability of contaminants, which depends on soil organic matter content,
soil texture and structure, soil aging, and hydrophobicity of the contaminants. For
instance, historically contaminated matrices are characterized by a significant
non-bioavailable fraction of compounds and the complete biodegradation of recalcitrant pollutants, such as PAHs and PCBs, is hardly reached. Nonetheless, several
authors asserted that bioavailability should be the underlying basis for risk assessment and in setting the remediation goals at contaminated sites (Latawiec et al. 2010;
Naidu et al. 2015; Stella et al. 2013). This concept is more and more readily accepted
by decision makers and regulatory organizations (Naidu et al. 2015). Therefore, the
efficiency of certain bioremediation applications at field scale should be evaluated by
the estimation of both concentration and bioavailability of the target contaminants.
Moreover, the feasibility of applying a mycoremediation strategy, as well as other
bio-based remediation technologies, should be evaluated performing accurate
compound-specific and ecotoxicological analyses to assess if the oxidized and
more water-soluble products exert a higher toxicity than parent molecules themselves. In case polar metabolites are formed, as in the case of oxidized HMW-PAHs,
it is of utmost importance to determine the presence of other microorganisms that are
able to cooperate with fungi in the complete mineralization of contaminants.
Another important parameter to take into account when a mycoremediation
approach is selected for the restoration of contaminated sites is the formulation
and the amount of inoculum carrier. Indeed, ligninolytic fungi are not able to grow
in soil unless an external substrate is provided. Therefore, the selection and the
pre-colonization of the lignocellulosic carrier by the fungus is crucial to support an
efficient and long-lasting fungal growth into soil. However, using a large amount of
lignocellulose-immobilized fungi is not always economically feasible and would
significantly increase the volume of the soil after treatment. A valid alternative to
bypass the high costs associated with the production of fungal inoculum is the reuse
of SMS, which is a cheap and readily available source of both fungal mycelia and
22 Mycoremediation of Contaminated Soils
457
Even if the addition of nutrients positively impacts on the bioremediation efficiency
(Lang et al. 2000; Steffen et al. 2007; Federici et al. 2012), the growth-inhibition and
mycophagy phenomena could still occur as a result (de Boer et al. 2005; Baldrian
2008).
Other constraints for the application of fungal technologies at field scale are the
strict growth conditions required by most WRFs. For example, 37 and 30
C
represent the optimum temperatures for P. chrysosporium growth and ligninolytic
enzymes production, respectively. These conditions are not easily maintained under
actual environmental conditions due to daily and seasonal fluctuations (Hestbjerg
et al. 2003). Contrary to P. chrysosporium, P. ostreatus is less affected by temperature changes: the degradation of organic pollutants by this WRF was demonstrated
even at very low temperatures (up to 8
C) (Eggen and Sveum 1999; Lang et al.
2000; Hestbjerg et al. 2001). Furthermore, Pleurotus sp. is highly competitive with
soil microbiota and thus more successful to colonize the contaminated matrix than
other fungi (in der Wiesche et al. 1996; Lang et al. 1997, 1998; Stella et al. 2017).
Another parameter that deeply influences the effectiveness of bioremediation is
the bioavailability of contaminants, which depends on soil organic matter content,
soil texture and structure, soil aging, and hydrophobicity of the contaminants. For
instance, historically contaminated matrices are characterized by a significant
non-bioavailable fraction of compounds and the complete biodegradation of recalcitrant pollutants, such as PAHs and PCBs, is hardly reached. Nonetheless, several
authors asserted that bioavailability should be the underlying basis for risk assessment and in setting the remediation goals at contaminated sites (Latawiec et al. 2010;
Naidu et al. 2015; Stella et al. 2013). This concept is more and more readily accepted
by decision makers and regulatory organizations (Naidu et al. 2015). Therefore, the
efficiency of certain bioremediation applications at field scale should be evaluated by
the estimation of both concentration and bioavailability of the target contaminants.
Moreover, the feasibility of applying a mycoremediation strategy, as well as other
bio-based remediation technologies, should be evaluated performing accurate
compound-specific and ecotoxicological analyses to assess if the oxidized and
more water-soluble products exert a higher toxicity than parent molecules themselves. In case polar metabolites are formed, as in the case of oxidized HMW-PAHs,
it is of utmost importance to determine the presence of other microorganisms that are
able to cooperate with fungi in the complete mineralization of contaminants.
Another important parameter to take into account when a mycoremediation
approach is selected for the restoration of contaminated sites is the formulation
and the amount of inoculum carrier. Indeed, ligninolytic fungi are not able to grow
in soil unless an external substrate is provided. Therefore, the selection and the
pre-colonization of the lignocellulosic carrier by the fungus is crucial to support an
efficient and long-lasting fungal growth into soil. However, using a large amount of
lignocellulose-immobilized fungi is not always economically feasible and would
significantly increase the volume of the soil after treatment. A valid alternative to
bypass the high costs associated with the production of fungal inoculum is the reuse
of SMS, which is a cheap and readily available source of both fungal mycelia and
22 Mycoremediation of Contaminated Soils
457