Contamination or Pollution? That’s the Question! Paleoecotoxicological Perspectives
Embargoed until 2024-07-07
Author
Date
2023Type
- Doctoral Thesis
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Abstract
Many lakes in Switzerland are impacted by anthropogenic legacy pollution due to factories and agricultural production often being located near water bodies or in the catchment. The lake sediments then act as a sink for spilled pollutants. With time, the awareness of aquatic ecosystem degradation by anthropogenic pollution increased, and environmental laws for protecting natural resources were created. These laws are based on sediment quality guidelines founded on ecotoxicological tests or computational benchmarks. While these tests can assess short-term adverse effects on a laboratory scale, they fail to encompass the complexity of natural ecosystems, like the synergistic effects of multiple stressors and disentangling their impact.
In this thesis, we researched an intense but localised Sn contamination in the sediments of Lake Zurich. This was caused by a silk factory in Thalwil that used Sn for silk weighting. The Sn contamination started around the same time as eutrophication in Lake Zurich. We thus wanted to characterise the contamination using empirical and historical information. In a next step, we wanted to know if we could disentangle the impact on the ecosystem by eutrophication from the impact of Sn contamination. Finally, we wanted to compare the performance of different bio-indicators and with them extend the scope of traditional ecotoxicological tests. We call this the paleo-ecotoxicological framework.
We applied a multi-proxy approach within this framework, where we used different sedimentological and geochemical proxies, such as qualitative and quantitative Sn measurements, grain size analysis, total organic carbon (TOC) and total nitrogen (TN) contents, among others, as "dose" proxies to describe our contamination. On the other hand, we used bio-indicators as "response" proxies. Response proxies included sedimentary ancient DNA (sedaDNA), which was extracted, amplified, sequenced and annotated using taxonomic databases, and microfossils counts of diatoms and chironomids. As the geochemical analysis of Sn contaminated sediment samples turned out to be challenging, we also improved methods for analysing sediment samples with complex matrices. We improved TN measurement performance using an elemental analyser for different sample matrices. Additionally, we developed an R package as part of this thesis that allows for rapid and reproducible parsing, inspection, visualisation, cleaning and batch processing of Avaatech X-ray fluorescence spectroscopy (XRF) core scanner data.
This thesis revealed that the massive Sn contamination nowadays does not threaten biota or drinking water production and is firmly bound to the sediment, shown by in-situ porewater measurements and ecotoxicological tests with ostracods in ancient contaminated sediment samples alike. We also found that we can disentangle the influence of eutrophication and Sn contamination if we use different "response" proxies together and that these proxies (sedaDNA, diatom and chironomid microfossils and ecotox tests) complement each other. While the Sn contamination in its current form is not toxic anymore to lake biota, we could show that the Sn contamination upon sedimentation did have a poisonous effect on benthic diatoms, indicated by a drop in sedaDNA species richness and abundance. This was confirmed by ostracod tests with an artificial, fresh Sn(IV) contamination, which proved toxic.
We conclude that using different bioindicators within the paleo-ecotoxicological framework is necessary to interpret long-term adverse effects caused by pollution and confounding factors such as eutrophication. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000620419Publication status
publishedExternal links
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Contributors
Examiner: Dubois, Nathalie
Examiner: Lever, Mark A.
Examiner: Eglinton, Timothy I.
Examiner: Domaizon, Isabelle
Publisher
ETH ZurichSubject
Paleolimnology; eDNA; sedaDNA; Paleoecotoxicology; Lake sediments; HEAVY METALS (ENVIRONMENTAL POLLUTANTS)Organisational unit
03868 - Eglinton, Timothy I. / Eglinton, Timothy I.
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