sulfamethoxazole [177]. This high sorption ability was corroborated in soil column
tests (2% w/w biochar), which led to propose those biochars as soil amendments to
reduce API leaching potential. Researchers of that study also postulated that the
occurrence of functional groups on the biochar surface would explain the high
sorption capacity of the biochars produced at 450
C.
The pH is another environmental variable that facilitates API sorption onto
biochar surface. Sorption of triclosan and ibuprofen significantly increased in solution of pH between 4.0 and 7.0 [178]. Furthermore, the occurrence of humic substances in the aqueous phase reduced the sorption of APIs to biochar because of two
reasons: the binding of APIs to the dissolved humic substances and/or blockage of
the open pores of biochar by humic substances, thus hampering the interaction
between biochar and APIs [178]. These observations suggest that in alkaline soils
or soil with a high organic matter content, biochar may fail in its capacity of binding
APIs. Despite these interfering factors, what it seems clear is that pH <7.0 favours
adsorption of APIs to biochar surface, irrespectively of the soil type [179].
Biochars produced at low pyrolysis temperatures (<450
C) are more appropriated for soil fertilisation. They generally contain non-pyrolysed organic matter
susceptible to be foraged by soil microorganisms; therefore its application causes
an increase of soil microbial activity and biomass [175]. This type of biochars has a
low specific surface area and porosity, which reduces its capacity to retain agrochemicals such as herbicides [180], therefore not compromising the agronomic
purpose of pesticide treatment [181].
The scope of adding biochar to API-contaminated soils is decreasing API bioavailability and toxicity to plants. Indeed, bioaccumulation of APIs by plants is
substantially reduced in biochar-amended soils. For example, the application of
biochar produced at 700
C to soil (5% w/w) reduced a 86% and 63% the uptake
of 5 and 50 mg/kg sulfamethazine, respectively, by lettuce (Lactuca sativa)
[182]. Similarly, carbamazepine and propranolol concentrations were markedly
lower in Lolium perenne grown in API-spiked soils amended with biochar produced
at 450–520
C than plants grown in biochar-free, API-spiked soils [183]. However,
the adsorption of APIs on the biochar surface could have two side-effects: (1) an
enhanced toxicity on soil microorganisms because of progressive accumulation of
APIs on the biochar surface [177] and (2) the failure of API biodegradation because
of limited bioaccessibility for microbial degradation [80]. One strategy that could
partially solve these biochar-linked side-effects could be the co-application of
earthworms and biochar.
Past studies have reported no clear synergistic effects from co-application of
earthworms and biochar on soil microbial communities [184] or soil enzyme activities and plant growth [185]. However, a recent investigation evidenced beneficial
effects of the co-application of A. caliginosa and willow chip-derived biochar on the
abundance of springtails and soil fungal biomass after 6 months of incubation (1%
w/w biochar in 2.65 L of soil holding 4 adult earthworms), although such positive
interactions depended on the soil type [186]. Moreover, some studies have shown
that incubation of earthworms (L. terrestris and A. caliginosa) in the presence of pine
needle- or spent coffee ground-derived biochar caused a significant increase of soil
360
J. C. Sanchez-Hernandez
tests (2% w/w biochar), which led to propose those biochars as soil amendments to
reduce API leaching potential. Researchers of that study also postulated that the
occurrence of functional groups on the biochar surface would explain the high
sorption capacity of the biochars produced at 450
C.
The pH is another environmental variable that facilitates API sorption onto
biochar surface. Sorption of triclosan and ibuprofen significantly increased in solution of pH between 4.0 and 7.0 [178]. Furthermore, the occurrence of humic substances in the aqueous phase reduced the sorption of APIs to biochar because of two
reasons: the binding of APIs to the dissolved humic substances and/or blockage of
the open pores of biochar by humic substances, thus hampering the interaction
between biochar and APIs [178]. These observations suggest that in alkaline soils
or soil with a high organic matter content, biochar may fail in its capacity of binding
APIs. Despite these interfering factors, what it seems clear is that pH <7.0 favours
adsorption of APIs to biochar surface, irrespectively of the soil type [179].
Biochars produced at low pyrolysis temperatures (<450
C) are more appropriated for soil fertilisation. They generally contain non-pyrolysed organic matter
susceptible to be foraged by soil microorganisms; therefore its application causes
an increase of soil microbial activity and biomass [175]. This type of biochars has a
low specific surface area and porosity, which reduces its capacity to retain agrochemicals such as herbicides [180], therefore not compromising the agronomic
purpose of pesticide treatment [181].
The scope of adding biochar to API-contaminated soils is decreasing API bioavailability and toxicity to plants. Indeed, bioaccumulation of APIs by plants is
substantially reduced in biochar-amended soils. For example, the application of
biochar produced at 700
C to soil (5% w/w) reduced a 86% and 63% the uptake
of 5 and 50 mg/kg sulfamethazine, respectively, by lettuce (Lactuca sativa)
[182]. Similarly, carbamazepine and propranolol concentrations were markedly
lower in Lolium perenne grown in API-spiked soils amended with biochar produced
at 450–520
C than plants grown in biochar-free, API-spiked soils [183]. However,
the adsorption of APIs on the biochar surface could have two side-effects: (1) an
enhanced toxicity on soil microorganisms because of progressive accumulation of
APIs on the biochar surface [177] and (2) the failure of API biodegradation because
of limited bioaccessibility for microbial degradation [80]. One strategy that could
partially solve these biochar-linked side-effects could be the co-application of
earthworms and biochar.
Past studies have reported no clear synergistic effects from co-application of
earthworms and biochar on soil microbial communities [184] or soil enzyme activities and plant growth [185]. However, a recent investigation evidenced beneficial
effects of the co-application of A. caliginosa and willow chip-derived biochar on the
abundance of springtails and soil fungal biomass after 6 months of incubation (1%
w/w biochar in 2.65 L of soil holding 4 adult earthworms), although such positive
interactions depended on the soil type [186]. Moreover, some studies have shown
that incubation of earthworms (L. terrestris and A. caliginosa) in the presence of pine
needle- or spent coffee ground-derived biochar caused a significant increase of soil
360
J. C. Sanchez-Hernandez