Although numerous studies have shown toxic effects of paracetamol on aquatic
organisms [234–236], little information is available regarding its ecotoxicity toward
microorganisms. Paracetamol has antibacterial properties on isolated Gram-positive
strains [179]. In combination with doxycycline, it was found to inhibit the activity of
nitrifying, denitrifying, and anaerobic ammonium oxidation (anammox) bacteria
involved in N cycle from different batch reactors [237]. The microbial toxicity of
paracetamol was assessed using the MARA (microbial assay for risk assessment),
the Microtox, and the Ames microplate assay [96]. Gram-negative bacilli and
Serratia were the most sensitive bacteria, while the most resistant were Enterococcus
and yeast Pichia anomala. According to MARA performed with 11 different strains,
the mean value of microbial toxic concentration (MTC equivalent of EC50) was
3,435.00 Æ 129.90 mg/L, and the EC50 estimated values using Microtox with
Aliivibrio fischeri were 7,923 mg/L and 9,487 mg/L after 5 and 15 min of paracetamol exposure, respectively. Ames assay concluded that paracetamol was
non-mutagenic, according to the EPA standards [96].
3.3 Antidepressants: Fluoxetine (Prozac) and Citalopram
Hydrobromide (Celexa)
Antidepressants are medications that can help ease symptoms of depression, anxiety,
and affective disorders. Among them, selective serotonin reuptake inhibitors (SSRI)
are the most commonly prescribed. They increase the levels of serotonin in the brain
and block the reabsorption of serotonin into neurons. Examples of SSRI antidepressants are citalopram and fluoxetine, commonly marketed with diverse trade names
such as Prozac and Celexa, respectively.
Citalopram is a chiral compound sold as a racemic mixture, but only the
S-enantiomer (sold as Escitalopram) has the desired antidepressant effect. Similarly,
fluoxetine is commercialized as a racemic mixture, with the S-enantiomer approximately 1.5 more potent than the R-enantiomer. In the human body, fluoxetine is
metabolized to norfluoxetine. Several studies have found citalopram, fluoxetine, and
its major metabolite norfluoxetine in different environmental matrices [222, 238–
242]. Under laboratory conditions, citalopram and fluoxetine are relatively recalcitrant to hydrolysis, photolysis, and microbial degradation [243, 244]. Nonetheless,
the biodegradation of fluoxetine by a single bacterium (preferably the R-enantiomer)
[105] or microbial consortium has been reported [245, 246]. Fluoxetine biodegradation applied at 1 μg/L was reported in estuarine and coastal seawaters with halflives ranging from 6 to 10 days [247]. Similarly, in activated sludge the biodegradation of citalopram was reported with 60% and 40% elimination rates under aerobic
and anoxic conditions, respectively [248, 249]. In activated sludge [250], similar
elimination rates (70%) of citalopram were observed under aerobic conditions, and
this biotic transformation led to the formation of 14 different transformation
products.
Impact of PhACs on Soil Microorganisms
275
organisms [234–236], little information is available regarding its ecotoxicity toward
microorganisms. Paracetamol has antibacterial properties on isolated Gram-positive
strains [179]. In combination with doxycycline, it was found to inhibit the activity of
nitrifying, denitrifying, and anaerobic ammonium oxidation (anammox) bacteria
involved in N cycle from different batch reactors [237]. The microbial toxicity of
paracetamol was assessed using the MARA (microbial assay for risk assessment),
the Microtox, and the Ames microplate assay [96]. Gram-negative bacilli and
Serratia were the most sensitive bacteria, while the most resistant were Enterococcus
and yeast Pichia anomala. According to MARA performed with 11 different strains,
the mean value of microbial toxic concentration (MTC equivalent of EC50) was
3,435.00 Æ 129.90 mg/L, and the EC50 estimated values using Microtox with
Aliivibrio fischeri were 7,923 mg/L and 9,487 mg/L after 5 and 15 min of paracetamol exposure, respectively. Ames assay concluded that paracetamol was
non-mutagenic, according to the EPA standards [96].
3.3 Antidepressants: Fluoxetine (Prozac) and Citalopram
Hydrobromide (Celexa)
Antidepressants are medications that can help ease symptoms of depression, anxiety,
and affective disorders. Among them, selective serotonin reuptake inhibitors (SSRI)
are the most commonly prescribed. They increase the levels of serotonin in the brain
and block the reabsorption of serotonin into neurons. Examples of SSRI antidepressants are citalopram and fluoxetine, commonly marketed with diverse trade names
such as Prozac and Celexa, respectively.
Citalopram is a chiral compound sold as a racemic mixture, but only the
S-enantiomer (sold as Escitalopram) has the desired antidepressant effect. Similarly,
fluoxetine is commercialized as a racemic mixture, with the S-enantiomer approximately 1.5 more potent than the R-enantiomer. In the human body, fluoxetine is
metabolized to norfluoxetine. Several studies have found citalopram, fluoxetine, and
its major metabolite norfluoxetine in different environmental matrices [222, 238–
242]. Under laboratory conditions, citalopram and fluoxetine are relatively recalcitrant to hydrolysis, photolysis, and microbial degradation [243, 244]. Nonetheless,
the biodegradation of fluoxetine by a single bacterium (preferably the R-enantiomer)
[105] or microbial consortium has been reported [245, 246]. Fluoxetine biodegradation applied at 1 μg/L was reported in estuarine and coastal seawaters with halflives ranging from 6 to 10 days [247]. Similarly, in activated sludge the biodegradation of citalopram was reported with 60% and 40% elimination rates under aerobic
and anoxic conditions, respectively [248, 249]. In activated sludge [250], similar
elimination rates (70%) of citalopram were observed under aerobic conditions, and
this biotic transformation led to the formation of 14 different transformation
products.
Impact of PhACs on Soil Microorganisms
275