Are Nano-sized Catalysts used for Environmental Remediation Ecotoxicologically Safe?

Nanotechnology plays a critical role in driving the industrial revolution by manipulating matter at the atomic/molecular scale to produce new materials, electronics and clinical breakthroughs. Despite their multiple benefits, nanomaterials including nano-sized catalysts are released into the environment during synthesis and use, requiring their critical evaluation in terms of ecological, environmental and health-related negative effects. Based on their physicochemical properties, nanomaterials exist in various forms and are extensively used by various industrial sectors and for environmental remediation. Despite significant advances, there is ongoing research about the long-term effects and biological/ecotoxicological risks caused by nano-sized catalytic materials. Safer (so-called “green”)-production strategies as well as surface functionalization/modification can minimize potential risk hazards thereby keeping their performance.

The role of several physicochemical and environmental factors affecting the toxicological properties of nano-sized catalytic materials used in environmental remediation applications will be reviewed. Within this scope, firstly different nanomaterials used as environmental remediation catalysts will be evaluated based on their ecotoxicological properties thereby focusing on modes of toxic action, toxicity testing as well as major factors affecting their toxic response. In the second part of this review, examples will be given based on our own experimental work with nano-catalytic materials (home-made MoS₂ nanosheets and their bulk MoS₂ precursor; a home-made Zn-Fe nanolayered double hydroxide) using battery tests conducted with four different test organisms (the marine photobacterium V. fischeri, the freshwater crustacean D. magna; the freshwater micro-alga P. subcapitata and the greater duckweed S. polyrhiza) for high sensitivity multi-level ecotoxicological data gathering. It was concluded that battery bioassays serve as more detailed, sensitive and reliable tools to question the ecotoxicological safety of nano-catalytic materials. The present study highlights the importance of combining biotests with chemical analysis to provide a more complete picture of the ecotoxicological effects of engineered nanomaterials considering structure-toxicity relationships.