The objective of this thesis was to develop new approaches and perspectives in resolving historical information from natural archives. Paleolimnology, the study of past aquatic environments using lake sediment cores, has greatly advanced our understanding of previous environments. This thesis intended to expand the range of historical information that may be used in paleolimnology and for historical reconstructions. Here I used pond sediments and a bat guano deposit as natural archives that recorded a history of events that I interpreted using a combination of chemical and biological measurements. In particular, I applied sterols and stanols as novel approaches for interpreting historical information in natural archives. First, I examined the chemical and biological composition of lake sediments to track the human occupation of Dorset and Thule people in Canada’s High Arctic. As predicted, sterols, stanols, cadmium, copper, and zinc increased in sediments deposited during known periods of human occupation owing to nutrient addition, whereas these increases were absent in reference sites. These methods were further corroborated in a study of 20th century human occupation at Resolute Bay by examining similar constituents in waterbodies that received wastewater discharge. Second, I used δ15N and δ13C to track the agricultural history of Jamaica using a 4,300-year-old bat guano deposit. I then used C/N, δ13C, and sterol and stanol ratios to detect two periods of increased frugivory relative to insectivory-based foraging. Metals normalized to titanium increased during the Industrial Revolution and 206Pb/207Pb values tracked the introduction and subsequent ban of leaded gasoline. I also examined the same chemical constituents in fresh bat guano from frugivorous, insectivorous, and sanguinivorous bats. C/N values decreased and cholestanol, cholesterol, and cholesterol/(cholesterol+sitosterol) values increased in bat guano according to trophic level. This thesis demonstrated the strength of examining several independent lines of evidence to reconstruct historical activities in both High Arctic waterbody sediments and a bat guano deposit. I showed that human activities were traceable within natural archives over several thousand years thus demonstrating that the multi-proxy approach is a powerful tool that can conduct a broad range of analyses in various natural archives.

Nonfat dry milk (NOM) was evaluated to determine the effect of long term storage on its sensory quality, its solubility index and on the development of oxidative derivatives of sterols. Storage variables included the form of the milk, the atmosphere in the storage container, the type of package and the storage temperature. A trained taste panel evaluated the milk for the development of cooked, metallic, and oxidized/stale flavors, mouthfeel and overall acceptability. Gas chromatography was used to determine cholesterol content and the quantity of oxidative derivatives of cholesterol present in the samples. Although long term storage of NOM did not affect the solubility index of the milk, the sensory quality of the milk was affected. Over time storage temperature and type of package had the greatest effect on sensory quality. Milk stored for 30 months at 32 C developed an unacceptable oxidized/stale flavor and at 42 months of storage, milk stored in polybags at 21 C had also developed an oxidized/stale flavor. These results substantiate the importance of controlling storage conditions during long term storage of NOM. NOM stored for four years did not develop harmful quantities of oxidative derivatives of cholesterol. However, certain expected results did occur. NOM stored in polybags developed more oxidative derivatives than samples stored in cans. Samples stored at 32 C developed more oxidative derivatives of cholesterol than any other sample analyzed and 7S-hydroxycholesterol, the only known cytotoxic derivative of cholesterol identified, was present in the samples stored at 32 C. Fresh and control samples of NOM contained similar quantities of oxidative derivatives of cholesterol.

This study assessed the chemical substances that can be used to investigate fecal contamination of surface waters and how they can be used to indicate and trace fecal contamination in oligotrophic rivers of Northern Sweden. It was found that, from previous studies, several chemicals can be used to trace fecal contamination of surface water, and these include pharmaceuticals, personal care products, sterols, stanols and bile acids. Pharmaceuticals have been successfully used to indicate fecal contamination in many tropical countries and some countries in the cold regions and thus can also be applied to oligotrophic rivers. Sterols, stanols and bile acids make it possible to accurately indicate and trace the different sources of fecal contamination and can also be used to distinguish between the different organisms from which those sterols and bile acids emanate. For these groups of chemicals analytical methods such as chromatography and mass spectrometry are used to decipher the different chemicals in the test samples of water or sediment. Overall, these methods can be used concurrently but the sterols and bile acids have more specificity compared to the pharmaceuticals and personal care products / <p>2021-07-06</p>

Sterol is an abundant component of eukaryotic cell membranes and is thought to influence membrane properties such as permeability, fluidity and microdomain formation. Drosophila is an excellent model system in which to study functional requirements for membrane sterol because, although it does not synthesize sterol, it nevertheless requires sterols to complete development. Moreover, Drosophila normally incorporates sterols into cell membranes. Thus, dietary sterol depletion can be used to specifically reduce membrane sterol levels. In contrast, vertebrates do synthesize cholesterol. In this way, sterol depletion in vertebrates demand the use of approaches such as chemical extractions, drug treatments or genetic manipulation which are prone to have side effects. We have controlled the level and type of dietary sterol available to developing Drosophila larvae in order to investigate the requirement for sterol in cell membranes, and to distinguish it from the function of sterol as a precursor for signaling molecules. Strikingly, we show that membrane sterol levels can be reduced 6-fold in most tissues without affecting cell or larval viability. Larvae respond to sterol depletion by arresting their growth and development, and by increasing the level of specific sphingolipid variants that promote survival when sterol is scarce. Thus, non-sterol lipids are able to substitute for sterols in the maintenance of basic membrane biophysical properties required for life. Despite this, Drosophila larvae regulate their growth to maintain membrane sterol levels within tight limits. The existence of this novel membrane sterol-dependent growth control mechanism indicates an important role for bulk membrane sterol in the tissue specific functions of differentiated cells.

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