has been shown that their metabolites are actually more toxic than the parent
compounds for aquatic organisms like Hyalella azteca [58, 59]. The increase in
the oxidative stress biomarkers can be ascribed to the biotransformation of paracetamol (i.e., an NASAID present in the effluent) by the subfamily of cytochrome P450,
CYPWC9, that allows the formation of reactive oxygen species (ROS). These ROS
can be OH and oxygenated intermediates like the oxy-cytochrome P450 complex
[P450 (Fe
3+ ) O
2Ã ] as a result of the release of the superoxide anion by reaction
decoupling. In both cases, ROS production is increased, which explains the observed
increases in LPX and HPC. Also, Gómez-Oliván et al. [60] found similar effects
when H. azteca was exposed to paracetamol at 770 mg kg
À1 . This increase may be
due to the formation of N-acetyl p benzoquinonimine which is able to bind to cellular
membranes.
Thus, the results herein presented show that the photo-Fenton process conducted
under pH 8 reduces the toxicity of the pharmaceutical industrial effluent and
therefore the oxidative stress biomarkers are considerably reduced. Therefore, it
can be concluded that the process is effective at achieving both chemical and
biological efficiencies. It is worth pointing out that despite the high mineralization
degree achieved under acid pH, the oxidative stress biomarkers were not reduced,
thus indicating a high degree of toxicity, probably due to the acid condition of the
treated effluent. This implies the need of further addition of chemicals to neutralize
the treated effluent and represents a disadvantage of the process that can be overcome by using the proposed catalyst Fe-pillared clay.
6 Conclusions
An industrial effluent was mineralized by photo-Fenton process catalyzed with an
iron-pillared clay. The use of this catalyst not only facilitates its recovery (e.g., by
magnetism) and reuse after treatment but also allows the use of pH conditions
different to those commonly required acidic for a Fenton process. This treatment
becomes effective when the effluent has an initial TOC of approximately 200 ppm,
otherwise must be diluted. Furthermore, in this process, it is essential to add
hydrogen peroxide (H 2 O 2 ) in a stoichiometric ratio with TOC from effluent to be
treated; otherwise, other less efficient oxidation mechanisms are promoted. This
process leads to a relatively good mineralization degree even without pH modification. A decrease of pH favored Fe leaching and the maximum observed was 4% at a
pH 2.7. The results of oxidative stress biomarkers show that the applied process is
not only chemically effective but also biologically at pH 8.
Acknowledgments A. Mendoza thanks CONACYT for grant 290817 to conduct postgraduate
studies. R. Romero is grateful to CONACYT for their financial support through grant 266149.
CONACYT is also acknowledged for grant 269093. Dr. Uvaldo Hernández, M. Osmín Avilés
Garcia, and M.C.Q. Eduardo Martín del Campo are acknowledged for their support on Fe-PILC
characterization. Citlalit Martinez Soto is also acknowledged for technical support.
256
R. Natividad et al.
compounds for aquatic organisms like Hyalella azteca [58, 59]. The increase in
the oxidative stress biomarkers can be ascribed to the biotransformation of paracetamol (i.e., an NASAID present in the effluent) by the subfamily of cytochrome P450,
CYPWC9, that allows the formation of reactive oxygen species (ROS). These ROS
can be OH and oxygenated intermediates like the oxy-cytochrome P450 complex
[P450 (Fe
3+ ) O
2Ã ] as a result of the release of the superoxide anion by reaction
decoupling. In both cases, ROS production is increased, which explains the observed
increases in LPX and HPC. Also, Gómez-Oliván et al. [60] found similar effects
when H. azteca was exposed to paracetamol at 770 mg kg
À1 . This increase may be
due to the formation of N-acetyl p benzoquinonimine which is able to bind to cellular
membranes.
Thus, the results herein presented show that the photo-Fenton process conducted
under pH 8 reduces the toxicity of the pharmaceutical industrial effluent and
therefore the oxidative stress biomarkers are considerably reduced. Therefore, it
can be concluded that the process is effective at achieving both chemical and
biological efficiencies. It is worth pointing out that despite the high mineralization
degree achieved under acid pH, the oxidative stress biomarkers were not reduced,
thus indicating a high degree of toxicity, probably due to the acid condition of the
treated effluent. This implies the need of further addition of chemicals to neutralize
the treated effluent and represents a disadvantage of the process that can be overcome by using the proposed catalyst Fe-pillared clay.
6 Conclusions
An industrial effluent was mineralized by photo-Fenton process catalyzed with an
iron-pillared clay. The use of this catalyst not only facilitates its recovery (e.g., by
magnetism) and reuse after treatment but also allows the use of pH conditions
different to those commonly required acidic for a Fenton process. This treatment
becomes effective when the effluent has an initial TOC of approximately 200 ppm,
otherwise must be diluted. Furthermore, in this process, it is essential to add
hydrogen peroxide (H 2 O 2 ) in a stoichiometric ratio with TOC from effluent to be
treated; otherwise, other less efficient oxidation mechanisms are promoted. This
process leads to a relatively good mineralization degree even without pH modification. A decrease of pH favored Fe leaching and the maximum observed was 4% at a
pH 2.7. The results of oxidative stress biomarkers show that the applied process is
not only chemically effective but also biologically at pH 8.
Acknowledgments A. Mendoza thanks CONACYT for grant 290817 to conduct postgraduate
studies. R. Romero is grateful to CONACYT for their financial support through grant 266149.
CONACYT is also acknowledged for grant 269093. Dr. Uvaldo Hernández, M. Osmín Avilés
Garcia, and M.C.Q. Eduardo Martín del Campo are acknowledged for their support on Fe-PILC
characterization. Citlalit Martinez Soto is also acknowledged for technical support.
256
R. Natividad et al.