effect on contaminant degradation rate. The most reliable explanation for this effect
is the change in soil organic matter content and quality (humification) by earthworm
activity. However, earthworms exert a positive effect on soil microbial activity and
exoenzyme production even in the presence of environmental contaminants
[48]. Taken together these studies suggest that inoculation of agricultural soils
with earthworms could be a suitable strategy to remove or immobilise APIs, thus
reducing the risk of being available to plants.
To date, remediation technology aimed to remove APIs is focused on the
treatment of wastewater [2]. In soil remediation, only physical and chemical engineering systems have been tested in API-contaminated soils. For example, the
electrokinetic technique, which consists of applying an electric field using two or
more electrodes introduced in soil, has been used to remediate soils spiked with a
mixture of sulfamethoxazole, ibuprofen, triclosan and caffeine [132]. The soil
physicochemical alterations induced by the electric field, mainly on soil pH, caused
a significant API degradation (13–85% of initial concentration) within 7 days of
continual electrokinetic treatment (10 mA of current intensity). Among the chemical
remediation methods, the use of the oxidant chemical persulfate alone or in combination with activating agents (iron), heat, alkaline chemicals or electrokinetic is
widely used in the degradation of a variety of environmental contaminants such as
PCBs, PAHs, pesticides, phthalates and APIs [133]. For example, ibuprofen
(46–48 μM/kg soil) was fully removed from soils after a 60-min treatment with
persulfate (20 mM/kg soil) activated by thermal treatment of soil (60
C) [134]. In a
similar laboratory study, the antibiotic sulfamethoxazole was almost fully degraded
(87.6% of initial concentration) in agricultural soils incubated for 4 h at 30
C
with persulfate activated with nanoscale zero-valent iron (nZVI) nanoparticles
[135]. However, persulfate-assisted remediation technologies have three main drawbacks: (1) alterations in the soil physicochemical and biological properties with
potential adverse consequences to soil quality, (2) the need of external energy supply
(e.g. electrokinetic technique and heating-activated persulfate treatment) and (3) the
high costs associated with the application of these remediation techniques in realfield scenarios [132]. For example, remediation of ibuprofen-contaminated soils
using both Fenton oxidation and nZVI nanoparticle methodologies led to toxic
soils showing phytotoxicity [136].
Bioremediation of API-contaminated soils has not been extensively investigated.
As with other organic pollutants, API dissipation is mainly due to microorganisms
[23]. Additionally, aerobic conditions largely facilitate their degradation [137, 138].
Because anecic and endogeic earthworms continually aerate soil via the creation of
burrows, they should be excellent “bioreactors” of API degradation. Table 2 summarises the main advantages and limitations of using soil-dwelling earthworms in
the bioremediation of API-contaminated soils as well as some uncertainties that
demand further research. The effect of earthworms on API degradation must be seen
not only as a biodegradation process but also as a strategy of chemical
immobilisation leading to reduce bioavailability and toxicity of these pollutants.
Many studies have documented that the earthworm feeding activity and cast deposition on the soil surface and the burrow walls contribute to decrease the degradation
Vermiremediation of Pharmaceutical-Contaminated Soils and Organic Amendments
355
is the change in soil organic matter content and quality (humification) by earthworm
activity. However, earthworms exert a positive effect on soil microbial activity and
exoenzyme production even in the presence of environmental contaminants
[48]. Taken together these studies suggest that inoculation of agricultural soils
with earthworms could be a suitable strategy to remove or immobilise APIs, thus
reducing the risk of being available to plants.
To date, remediation technology aimed to remove APIs is focused on the
treatment of wastewater [2]. In soil remediation, only physical and chemical engineering systems have been tested in API-contaminated soils. For example, the
electrokinetic technique, which consists of applying an electric field using two or
more electrodes introduced in soil, has been used to remediate soils spiked with a
mixture of sulfamethoxazole, ibuprofen, triclosan and caffeine [132]. The soil
physicochemical alterations induced by the electric field, mainly on soil pH, caused
a significant API degradation (13–85% of initial concentration) within 7 days of
continual electrokinetic treatment (10 mA of current intensity). Among the chemical
remediation methods, the use of the oxidant chemical persulfate alone or in combination with activating agents (iron), heat, alkaline chemicals or electrokinetic is
widely used in the degradation of a variety of environmental contaminants such as
PCBs, PAHs, pesticides, phthalates and APIs [133]. For example, ibuprofen
(46–48 μM/kg soil) was fully removed from soils after a 60-min treatment with
persulfate (20 mM/kg soil) activated by thermal treatment of soil (60
C) [134]. In a
similar laboratory study, the antibiotic sulfamethoxazole was almost fully degraded
(87.6% of initial concentration) in agricultural soils incubated for 4 h at 30
C
with persulfate activated with nanoscale zero-valent iron (nZVI) nanoparticles
[135]. However, persulfate-assisted remediation technologies have three main drawbacks: (1) alterations in the soil physicochemical and biological properties with
potential adverse consequences to soil quality, (2) the need of external energy supply
(e.g. electrokinetic technique and heating-activated persulfate treatment) and (3) the
high costs associated with the application of these remediation techniques in realfield scenarios [132]. For example, remediation of ibuprofen-contaminated soils
using both Fenton oxidation and nZVI nanoparticle methodologies led to toxic
soils showing phytotoxicity [136].
Bioremediation of API-contaminated soils has not been extensively investigated.
As with other organic pollutants, API dissipation is mainly due to microorganisms
[23]. Additionally, aerobic conditions largely facilitate their degradation [137, 138].
Because anecic and endogeic earthworms continually aerate soil via the creation of
burrows, they should be excellent “bioreactors” of API degradation. Table 2 summarises the main advantages and limitations of using soil-dwelling earthworms in
the bioremediation of API-contaminated soils as well as some uncertainties that
demand further research. The effect of earthworms on API degradation must be seen
not only as a biodegradation process but also as a strategy of chemical
immobilisation leading to reduce bioavailability and toxicity of these pollutants.
Many studies have documented that the earthworm feeding activity and cast deposition on the soil surface and the burrow walls contribute to decrease the degradation
Vermiremediation of Pharmaceutical-Contaminated Soils and Organic Amendments
355