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Title: Microbial toxicity testing of inorganic nanoparticles
Author: Widdowson, Alexandra
ISNI:       0000 0004 5368 1583
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2015
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NPs are toxic to a wide range of organisms across trophic levels; gram-positive and gram-negative bacteria (Pseudomonas aeruginosa, Bacillus subtilis, Staphylococcus aureus and Escherichia coli), algae (Pseudokirchneriella subcapitata), crustaceans (Daphnia magna and Thamnocephalus platyurus), fish (rainbow trout, zebrafish, trout) and plants (Lactuca sativa L. and Raphanus sativus L). Due to their lack of target specificity, NPs may pose an environmental risk. The antibacterial properties of Ag and Cu nanoparticles (NP) are enhanced by their large reactive surface area, compared to bulk counterparts. Toxicity of NPs is attributed to their solubility and subsequent release of ions. However, the cytotoxic effects of NPs cannot always be attributed to the free ion fraction. The underpinning objective of this study was to link the response of microbial biosensors to detailed chemical analysis of NP dissolution products. NPs were suspended in Millipore water and in the presence of the steric stabiliser Na citrate and the resulting NP solubility characterised. Using chemical analysis this study quantified the flux of total dissolved metal (total [M]) and free metal ions [M+] from Ag and Cu NPs (Chapter 3). Two bioluminescent biosensors were used to assess the bioavailable metal fraction ([M]bio) of NP dissolution (Chapters 5 and 6). E. coli HB101 pUCD607 (bacterial) and M. citricolor (fungal) were chosen to represent NP toxicity across trophic levels using the same response mechanism. Additionally, the metal-induced bioreporter, P. fluorescens DF57-Cu15, was used to quantify the Cu bioavailability of Cu NP dissolution. By combining chemical and biological analysis this study inferred NP toxicity is not mass dependent, toxicity is dissolution dependent. Dissolution of Ag and Cu NPs in Millipore water was mostly in the [M+] form. This remained the case for Ag NPs in the presence of Na citrate. However, dissolution of Cu NPs in Na citrate was mostly as total [Cu]. This was due to Cu ions complexing readily with citrate. Toxicity of Ag NP dissolution in Millipore water was concentration dependent. Total [Ag] correlated with E. coli HB101 toxicity response. The addition of Na citrate reduced Ag NP dissolution and therefore reduced toxicity to E. coli HB101. M. citricolor was less sensitive than E. coli HB101 to the dissolution products of Ag NPs in Millipore water. However, the sensor was more sensitive to the dissolution of Ag NPs in Na citrate than E. coli HB101. Cu NPs were chemically stable in Millipore water. The bioreporter P. fluorescens DF57-Cu15 was not induced by Millipore suspensions and E. coli HB101 was not inhibited. However, M. citricolor responded to [Cu]bio of Millipore suspensions with a maximum 54% inhibition of bioluminescence. P. fluorescens DF57-Cu15 was induced by the dissolution products of Cu NPs with the addition of Na citrate, only at high NP concentrations (> 500 mg/L). [Cu]bio of the Na citrate suspensions was toxic to E. coli HB101. However, toxicity was greater for M. citricolor with a maximum biosensor inhibition of 83%. There was no correlation between total [Cu], [Cu2+] or [Cu]bio with the response of either biosensors nor the bioreporter. Interpretation of Ag and Cu NP toxicity was made possible by the combining of chemical and biological toxicity assessment. Dissolution of Ag NPs suspended in Millipore water could be attributed as the main factor in toxicity to E. coli HB101 because of the knowledge gained by chemical analysis. It also allowed the conclusion that NP dissolution was a key factor to toxicity in all cases but biological assessment attributed NP assimilation as a contributing factor. Biological assessment is vital as no chemical analysis can quantify [M]bio, especially when [M]bio was perceived differently by biosensors of different trophic levels and modes of action. Combining chemical and biological assessment in this study was essential for interpreting NP toxicity.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Nanoparticles ; Toxicity testing