Bridging the gap between standardized laboratory tests and environmental outcomes: investigations of organic ultraviolet filter toxicity to freshwater invertebrates Daphnia magna and Daphnia pulex
Creators: Boyd, Aaron
Publisher: name: University of Alberta Library
Year: 2024

<pre><code>The impacts of anthropogenic activities have been disrupting natural environments at a rate exceeding the capacity of researchers to understand their potential consequences. Standardized research models have become widely adopted to allow for rapid data collection in response to contaminants of emerging concern, including organic ultraviolet filters (UVFs) such as avobenzone, octocrylene and oxybenzone. Through their use in skin care products such as sunscreen, they have been found to ubiquitously contaminate freshwater and marine ecosystems and have consequently been found to cause toxicity to a variety of invertebrate species. To further our understanding of the long-term consequences of contamination in freshwater environments, the toxicity of UVFs were assessed in the model invertebrate, Daphnia magna. Acute 48 h exposures impaired phototactic behaviours and caused latent mortality up to 5 days post-exposure, with recovery possible in surviving organisms. Chronic 21 d exposures resulted in minimal sublethal effects at lower tested concentrations, but complete mortality at higher tested concentrations, suggesting overall that D. magna is among the most sensitive species to these UVFs.
To assess the long-term effects in an exposed population, the standard 21 d chronic toxicity test was repeated to maintain continuous UVF exposures for 5 generations. Mortality and decreased reproduction occurred in the F0 and F1 generations of exposure, with normal physiological function regained by the F3 and F4 generations. Decreased protein abundance was observed in many metabolism and immune functions in the F0 generation, while these same processes were predominantly enriched in the F3 generation, suggesting that physiological adaptations played an important role in the acclimation of D. magna populations. These results suggest that it is incorrect to assume that data generated within a single generation exposure will correlate to long-term outcomes within an exposed population. 
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<p>During this study, it was found that culturing Daphnia in groups can alter their baseline state compared to individual organisms maintained with the same ratio of food and water, including delaying the onset of reproduction and causing the generation of males. While the overall conclusions of toxicity for each UVF were unaffected by the exposure type, subtle changes in development, reproduction, and baseline mortality existed in proportion to the control daphnids across all 5 generations, indicating the importance of considering the context of data when comparing results across studies.<br>
    Most studies measure UVF toxicity to understand the effects of sunscreen pollution, as the inactive ingredients within sunscreen products enter the environment through the same processes as the UVFs. To address the lack of studies comparing the toxicity of UVFs in isolation to those within sunscreen mixtures, five off-the-shelf sunscreens were assessed over 21 d exposures, revealing that sunscreen toxicity was far lower than expected based on the concentration of UVFs within the mixture, indicating that antagonistic interactions between the different components of sunscreens may serve to minimize the toxicity of these complex mixtures. By investigating UVF toxicity in isolation, many studies may overestimate the impacts of sunscreen pollution in natural environments.<br>
    Much biological research is conducted using model species cultured in a laboratory environment for generations to model outcomes in wild populations. Several studies have found differences in stress responses of lab and wild populations; however, many of these studies tested wild organisms in laboratory water without determining if changing the culture water would impact the outcome of the experiments. The toxicity of UVFs was assessed in lab-reared and wild caught Daphnia pulex populations cultured in both laboratory and lake water. It was found that both lab and wild D. pulex were severely weakened when cultured in non-ancestral waters for 3 generations, failing to meet the validity criteria for standard toxicity test guidelines. When cultured in ancestral waters, lab D. pulex were more sensitive to AVO and OXY, while wild daphnids were more sensitive to OCT. These results indicate that culture water can greatly influence the performance of aquatic organisms during experimentation, and that lab populations can deviate from wild counterparts after decades of culturing in a laboratory environment.<br>
    Overall, this thesis highlights several shortcomings of applying standardized research to natural environments and highlights the necessity to understand how methodological decisions impact the data obtained and conclusions drawn in any avenue of biological research.</p>