Dedman, Craig J. (2021) Nano-pollutants – big impact? Investigating the ecotoxicological effects of nanomaterials in our oceans. PhD thesis, University of Warwick.

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Abstract

Engineered nanomaterials (NMs) used for industrial and commercial applications, represent an emerging contaminant of environmental concern. Due to their widespread use, their entry into the environment is believed inevitable, where the ocean represents the sink for contaminants entered into the aquatic environment. In this thesis new insight is provided on the likely environment risk of engineered NMs towards marine microbial organisms which represent the base of the marine food web and play major roles in global climatic and biogeochemical processes.

Three commonly used NMs with clear pathways into the aquatic environment were selected for study; silver nanoparticles (AgNPs), titanium dioxide (nTiO2) and cerium oxide (nCeO2). Preliminary investigation exposing a natural phytoplankton community to AgNPs identified the marine cyanobacterium Prochlorococcus as particularly sensitive to NMs, and hence the model Prochlorococcus sp. MED4 was selected for use in ecotoxicity assessments. Toxicity testing and subsequent investigation of toxic mechanisms revealed varying impacts of metal-based NMs such as AgNPs, and metal oxide NMs upon Prochlorococcus, largely determined by their respective fate and behaviour upon entry into saline media.

In chapter 2, AgNPs were observed to exert significant cell declines upon Prochlorococcus via the release of toxic silver ions and superoxide. This perturbation was associated with a significant alteration to the cellular proteome and was irreversible in the longer-term. However, cell declines were mitigated by increasing cell density likely due to an increase in production of superoxide dismutase at higher cell numbers. Significant cell declines were observed at concentrations ≥10 μg L-1 under natural conditions, representing the upper limit of AgNPs predicted in the environment. Hence, it is believed that negative impacts of AgNPs upon marine microbial species is only likely in hotspots of contamination.

In chapter 3, the potential impacts of metal oxide NMs (nTiO2 and nCeO2) were investigated. Here, little impact upon Prochlorococcus was recorded in extended exposure (240 h) except at extremely high concentrations (100 mg L-1). Temporary declines were observed in the short-term (≤72 h) and were associated with the heteroaggregation and co-precipitation with nanoparticles which were observed to aggregate rapidly upon entry into seawater, as confirmed by dynamic light scattering (DLS) and fluorescent microscopy. The key role of physical interactions in driving cell declines was further supported by shotgun proteomic analysis of Prochlorococcus exposed to nTiO2 (100 μg L-1), revealing no significant alteration to the cellular or exo- proteome. Effective protocols were established to extract and characterise nTiO2 utilised in consumer products such as cosmetics and sunscreen. Use of nTiO2 extracted from consumer sunscreen in exposures with natural marine microbial communities, found negligible impact upon the structure and diversity of prokaryotic or eukaryotic communities. Hence the current environmental risk of nTiO2 and nCeO2 towards marine microbial species is believed low.

In the final experimental chapter 4, in collaboration with an industrial partner, the effectiveness of novel nCeO2 antifouling surface coatings was examined by use of amplicon sequencing, nutrient analysis and 3D microscopic imaging. Investigation revealed negligible impact of the addition of nCeO2 upon biofilm community structure, however nutrient analysis suggested a slight reduction in biofouling in the presence of nanoparticles.

Item Type:	Thesis (PhD)
Subjects:	G Geography. Anthropology. Recreation > GC Oceanography G Geography. Anthropology. Recreation > GE Environmental Sciences Q Science > QP Physiology Q Science > QR Microbiology T Technology > TA Engineering (General). Civil engineering (General)
Library of Congress Subject Headings (LCSH):	Micropollutants, Marine pollution, Nanostructured materials, Paint, Antifouling
Official Date:	June 2021
Dates:	Date Event June 2021 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	School of Life Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Christie-Oleza, Joseph Alexander ; Davies, Gemma-Louise
Sponsors:	The Central England NERC Training Alliance
Format of File:	pdf
Extent:	xx, 243 leaves : illustrations
Language:	eng

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