of oxidative stress are frequently found at those biochar doses in E. fetida [191]
and L. terrestris [192], although some studies have reported no oxidative damage
in E. fetida exposed at doses of biochar >2% [193]. Despite these contrasting
results, further research is still needed to know long-term effects of earthworm
inhabiting biochar-amended soils. For example, a 6-month mesocosm study with
A. caliginosa incubated in two different soils evidenced that the synergistic
effects of earthworms and biochar (1% w/w) increased the abundance of other
soil organisms such as springtails and fungi, beside to improve soil fertility and
plant growth [186]. Similarly, a 2-year field experiment examined the impact of
biochar applied on topsoil (10 cm depth) at application rates of 10, 25 and 50 t/ha
(corresponding to 0.6, 1.5 and 3% w/w, respectively) on both soil macrofauna
and mesofauna [194]. The study revealed that, although the abundance of earthworms decreased as the concentration of biochar increased, biochar did not cause
a significant impact on earthworm community structure, and the dose of 0.6% did
not alter earthworm species richness compared to that of control (biochar-free)
soils. Conversely, it was found a significant increase in the abundance of
enchytraeids, mites and collembolans at the highest doses of biochar. In other
field study, researchers observed that biochar applied at 5 and 10 t/ha was no toxic
to macrofauna and also caused an attraction effect to earthworms after 2 years of
application [195], thus recording a twofold density of earthworms in the soils that
received 10 t/ha biochar respect to control (biochar-free) soils. Factors such as
type of biochar and application rate, type of soil, climatic conditions, time of
exposure and microbial community generally modulate the earthworm response
to biochar-amended soils. Taken together these studies encourage biochar application rates of around 1% (w/w) on topsoil to be compatible with fauna diversity
and abundance, and to exploit the potential synergistic effects of earthworms and
biochar to immobilise or degrade APIs.
3. Pharmaceutical toxicity and accumulation in earthworms. To date, most of
toxicity tests with APIs have been performed using E. fetida and E. andrei as
model organisms (discussed in Sect. 4 of the chapter), and data show that these
earthworm species tolerate high API concentrations compared with other soil
organisms (e.g. [87]). Therefore, the use of epigeic earthworms in the
vermicomposting of API-contaminated feedstocks could be a workable strategy.
However, the sensitivity of anecic and endogeic earthworms (Fig. 2) to APIs
should be explored in order to apply them in the in situ vermiremediation strategy
(Fig. 4). In addition, API toxicity has been generally evaluated using a single
chemical, and API mixture or even API molecules mixed with other environmental contaminants commonly detected in agricultural soils have not been
investigated. As discussed in previous sections, a wide variety of APIs is generally found in reclaimed wastewater and biosolids, so exposure of soil fauna to an
API mixture is probably the most real scenario. Similarly, API biodegradation
should be also studied in the context of multiple environmental contaminants
co-existing in agricultural soil.
4. Toxicity of API metabolites. Biodegradation of APIs in soil not necessarily lead to
full mineralization. For example, a laboratory study reported that mineralisation
362
J. C. Sanchez-Hernandez
and L. terrestris [192], although some studies have reported no oxidative damage
in E. fetida exposed at doses of biochar >2% [193]. Despite these contrasting
results, further research is still needed to know long-term effects of earthworm
inhabiting biochar-amended soils. For example, a 6-month mesocosm study with
A. caliginosa incubated in two different soils evidenced that the synergistic
effects of earthworms and biochar (1% w/w) increased the abundance of other
soil organisms such as springtails and fungi, beside to improve soil fertility and
plant growth [186]. Similarly, a 2-year field experiment examined the impact of
biochar applied on topsoil (10 cm depth) at application rates of 10, 25 and 50 t/ha
(corresponding to 0.6, 1.5 and 3% w/w, respectively) on both soil macrofauna
and mesofauna [194]. The study revealed that, although the abundance of earthworms decreased as the concentration of biochar increased, biochar did not cause
a significant impact on earthworm community structure, and the dose of 0.6% did
not alter earthworm species richness compared to that of control (biochar-free)
soils. Conversely, it was found a significant increase in the abundance of
enchytraeids, mites and collembolans at the highest doses of biochar. In other
field study, researchers observed that biochar applied at 5 and 10 t/ha was no toxic
to macrofauna and also caused an attraction effect to earthworms after 2 years of
application [195], thus recording a twofold density of earthworms in the soils that
received 10 t/ha biochar respect to control (biochar-free) soils. Factors such as
type of biochar and application rate, type of soil, climatic conditions, time of
exposure and microbial community generally modulate the earthworm response
to biochar-amended soils. Taken together these studies encourage biochar application rates of around 1% (w/w) on topsoil to be compatible with fauna diversity
and abundance, and to exploit the potential synergistic effects of earthworms and
biochar to immobilise or degrade APIs.
3. Pharmaceutical toxicity and accumulation in earthworms. To date, most of
toxicity tests with APIs have been performed using E. fetida and E. andrei as
model organisms (discussed in Sect. 4 of the chapter), and data show that these
earthworm species tolerate high API concentrations compared with other soil
organisms (e.g. [87]). Therefore, the use of epigeic earthworms in the
vermicomposting of API-contaminated feedstocks could be a workable strategy.
However, the sensitivity of anecic and endogeic earthworms (Fig. 2) to APIs
should be explored in order to apply them in the in situ vermiremediation strategy
(Fig. 4). In addition, API toxicity has been generally evaluated using a single
chemical, and API mixture or even API molecules mixed with other environmental contaminants commonly detected in agricultural soils have not been
investigated. As discussed in previous sections, a wide variety of APIs is generally found in reclaimed wastewater and biosolids, so exposure of soil fauna to an
API mixture is probably the most real scenario. Similarly, API biodegradation
should be also studied in the context of multiple environmental contaminants
co-existing in agricultural soil.
4. Toxicity of API metabolites. Biodegradation of APIs in soil not necessarily lead to
full mineralization. For example, a laboratory study reported that mineralisation
362
J. C. Sanchez-Hernandez