6 Challenges and Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
6.1 Determining the Current States and Effects of CNPs in the Environment . . . . . . . . . . 194
6.2 Identifying the Toxicological Risk Factors of CNPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
6.3 Characterizing and Identifying the Potentially Safe Applications of CNPs
in the Future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
Abstract Increasing production and utilization of cerium oxide nanoparticles
(CNPs) in recent years have raised wide concerns about their toxicity. Numerous
studies have been conducted to reveal the toxicity of CNPs, but the results are
sometimes contradictory. In this review, the most important factors in mediating
CNPs toxicity are discussed, including (1) the roles of physicochemical properties
(size, morphology, agglomeration condition, surface charge, coating and surface
valence state) on CNPs toxicity; (2) the phase transfer and transformation process of
CNPs in various aqueous, terrestrial, and airborne environments; and (3) reductive
dissolution of CNPs core and their chemical reactions with phosphate, sulfate/S
2À ,
and ferrous ions. The physicochemical properties play key roles in the interactions of
CNPs with organisms and consequently their environmental transformations, reactivity and toxicity assessment. Also, the speciation transformations of CNPs caused
by reactions with (in)organic ligands in both environmental and biological systems
would further alter their fate, transport, and toxicity potential. Thus, the toxicity
mechanisms are proposed based on the physical damage of direct adsorption of
CNPs onto the cell membrane and chemical inhibition (including oxidative stress
and interaction of CNPs with biomacromolecules). Finally, the current knowledge
gaps and further research needs in identifying the toxicological risk factors of CNPs
under realistic environmental conditions are highlighted, which might improve predictions about their potential environmental influences. This review aims to provide
new insights into cost-effectiveness of control options and management practices to
prevent environmental risks from CNPs exposure.
Keywords Cerium oxide nanoparticles · Environmental transformation · Redox
reactions · Surface properties · Toxicity
Abbreviations
AA
Acrylic acid
Alg
Alginate
AS
Artificial soil solution
ATP
Adenosine triphosphate
CA
Citric acid
C-CNPs
Cubic cerium oxide nanoparticles
CEC
Cation exchange capacity
CNPs
Cerium oxide nanoparticles
156
G. You et al.
6.1 Determining the Current States and Effects of CNPs in the Environment . . . . . . . . . . 194
6.2 Identifying the Toxicological Risk Factors of CNPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
6.3 Characterizing and Identifying the Potentially Safe Applications of CNPs
in the Future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
Abstract Increasing production and utilization of cerium oxide nanoparticles
(CNPs) in recent years have raised wide concerns about their toxicity. Numerous
studies have been conducted to reveal the toxicity of CNPs, but the results are
sometimes contradictory. In this review, the most important factors in mediating
CNPs toxicity are discussed, including (1) the roles of physicochemical properties
(size, morphology, agglomeration condition, surface charge, coating and surface
valence state) on CNPs toxicity; (2) the phase transfer and transformation process of
CNPs in various aqueous, terrestrial, and airborne environments; and (3) reductive
dissolution of CNPs core and their chemical reactions with phosphate, sulfate/S
2À ,
and ferrous ions. The physicochemical properties play key roles in the interactions of
CNPs with organisms and consequently their environmental transformations, reactivity and toxicity assessment. Also, the speciation transformations of CNPs caused
by reactions with (in)organic ligands in both environmental and biological systems
would further alter their fate, transport, and toxicity potential. Thus, the toxicity
mechanisms are proposed based on the physical damage of direct adsorption of
CNPs onto the cell membrane and chemical inhibition (including oxidative stress
and interaction of CNPs with biomacromolecules). Finally, the current knowledge
gaps and further research needs in identifying the toxicological risk factors of CNPs
under realistic environmental conditions are highlighted, which might improve predictions about their potential environmental influences. This review aims to provide
new insights into cost-effectiveness of control options and management practices to
prevent environmental risks from CNPs exposure.
Keywords Cerium oxide nanoparticles · Environmental transformation · Redox
reactions · Surface properties · Toxicity
Abbreviations
AA
Acrylic acid
Alg
Alginate
AS
Artificial soil solution
ATP
Adenosine triphosphate
CA
Citric acid
C-CNPs
Cubic cerium oxide nanoparticles
CEC
Cation exchange capacity
CNPs
Cerium oxide nanoparticles
156
G. You et al.