Additionally, PhACs in soil can be transformed by biotic or abiotic reactions,
leading to transformation products that can be more stable, more toxic, and persistent
than their parent compounds [75, 76]. Among abiotic processes, photodegradation
[77] and hydrolysis [78] are known to transform PhACs in aquatic media. The antiinflammatory drugs diclofenac, naproxen, ibuprofen, and the diuretic agent
amiloride were found to be transformed to hydroxyl metabolites, presenting higher
toxicity, after a photocatalytic treatment [79–84]. Additionally, studies from Yamamoto et al. [85] reported a slow rate in sunlight photodegradation of acetaminophen,
mefenamic acid, as well as ibuprofen and carbamazepine. In soils, photodegradation
was observed for sulfonamides and tetracycline antibiotics which spread on the soil
surface and pig slurry following first and biphasic kinetics, respectively [86].
Biotic transformation of PhACs is mainly achieved by microorganisms, which
have developed during their long-lasting evolution an impressive enzymatic array
able not only to detoxify their environment but also to get access to nutrients for their
growth. PhACs biodegradation is achieved by two types of microbial guilds catalyzing two types of transformation: one the one hand, co-metabolic transformation is
catalyzed by non-specific enzymes (such as P450 monooxygenase also involved in
the biodegradation of other xenobiotics such as pesticides) [74, 87–96]. On the other
hand, metabolic transformation is catalyzed by specific enzymes leading to partial or
full mineralization of PhACs that are used as nutrients and energy sources for the
growth of the degrading microbial guild [87, 90, 97–112]. From this point of view,
transformation of PhACs by fungi and bacteria is a key process for their dissipation
in the environment [113–116]. Since PhACs are designed to remain active after
ingestion, most of them are relatively recalcitrant to biodegradation. However, it was
shown that chronic or punctual exposure of soil microbial communities to PhACs
can enhance their degrading capacities toward them [109, 117]. Biodegradation of
PhACs in soils has been reported for naproxen [38, 74, 118]; ibuprofen [38, 114,
119, 120]; diclofenac [74, 114, 121–123]; paracetamol [39]; carbamazepine [62];
antibiotics such as sulfamethazine [109] and sulfadiazine [124]; triclosan [51, 125–
133]; antifungals such as fluconazole, clotrimazole, and miconazole [25, 131, 134–
136]; and caffeine [113].
3 Impact of PhACs on in Soil Living Microorganisms
Residues of human and veterinary PhACs enter terrestrial environments as complex
liquid or solid biomixtures applied to crop as organic fertilizer or for watering. Like
other active ingredients used for plant protection (pesticides), PhACs are relatively
recalcitrant to biodegradation, active at rather low concentrations, and target key
enzymes involved in essential biological functions that are widespread in the tree of
life. During the last decades, the presence of pharmaceutical residues in the aquatic
environment has raised special attention, and numerous studies have reported their
effects on the aquatic living organisms and supported ecosystem services [137–
140]. However, little is known regarding the effect of antibiotics and other PhACs on
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leading to transformation products that can be more stable, more toxic, and persistent
than their parent compounds [75, 76]. Among abiotic processes, photodegradation
[77] and hydrolysis [78] are known to transform PhACs in aquatic media. The antiinflammatory drugs diclofenac, naproxen, ibuprofen, and the diuretic agent
amiloride were found to be transformed to hydroxyl metabolites, presenting higher
toxicity, after a photocatalytic treatment [79–84]. Additionally, studies from Yamamoto et al. [85] reported a slow rate in sunlight photodegradation of acetaminophen,
mefenamic acid, as well as ibuprofen and carbamazepine. In soils, photodegradation
was observed for sulfonamides and tetracycline antibiotics which spread on the soil
surface and pig slurry following first and biphasic kinetics, respectively [86].
Biotic transformation of PhACs is mainly achieved by microorganisms, which
have developed during their long-lasting evolution an impressive enzymatic array
able not only to detoxify their environment but also to get access to nutrients for their
growth. PhACs biodegradation is achieved by two types of microbial guilds catalyzing two types of transformation: one the one hand, co-metabolic transformation is
catalyzed by non-specific enzymes (such as P450 monooxygenase also involved in
the biodegradation of other xenobiotics such as pesticides) [74, 87–96]. On the other
hand, metabolic transformation is catalyzed by specific enzymes leading to partial or
full mineralization of PhACs that are used as nutrients and energy sources for the
growth of the degrading microbial guild [87, 90, 97–112]. From this point of view,
transformation of PhACs by fungi and bacteria is a key process for their dissipation
in the environment [113–116]. Since PhACs are designed to remain active after
ingestion, most of them are relatively recalcitrant to biodegradation. However, it was
shown that chronic or punctual exposure of soil microbial communities to PhACs
can enhance their degrading capacities toward them [109, 117]. Biodegradation of
PhACs in soils has been reported for naproxen [38, 74, 118]; ibuprofen [38, 114,
119, 120]; diclofenac [74, 114, 121–123]; paracetamol [39]; carbamazepine [62];
antibiotics such as sulfamethazine [109] and sulfadiazine [124]; triclosan [51, 125–
133]; antifungals such as fluconazole, clotrimazole, and miconazole [25, 131, 134–
136]; and caffeine [113].
3 Impact of PhACs on in Soil Living Microorganisms
Residues of human and veterinary PhACs enter terrestrial environments as complex
liquid or solid biomixtures applied to crop as organic fertilizer or for watering. Like
other active ingredients used for plant protection (pesticides), PhACs are relatively
recalcitrant to biodegradation, active at rather low concentrations, and target key
enzymes involved in essential biological functions that are widespread in the tree of
life. During the last decades, the presence of pharmaceutical residues in the aquatic
environment has raised special attention, and numerous studies have reported their
effects on the aquatic living organisms and supported ecosystem services [137–
140]. However, little is known regarding the effect of antibiotics and other PhACs on
270
S. Gallego and F. Martin-Laurent