Daphnia as a sentinel species and a bioremediating agent for environmental health protection

Abdullahi, Muhammad ORCID: 0000-0003-2971-6013 (2023). Daphnia as a sentinel species and a bioremediating agent for environmental health protection. University of Birmingham. Ph.D.

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Abstract

Persistent chemicals originating from domestic and industrial activities pose significant risks to environmental and human health due to their toxicity and bioaccumulative potential, even at concentrations below approved regulatory thresholds. Conventional chemical toxicity tests disregard the impact of long-term exposures and use concentrations that organisms rarely encounter in real-world scenarios. Moreover, the potential adverse effect of chemical cocktails of unknown mixtures is rarely assessed because of the current one-chemical-at-time, hazard-focused, siloed approach to environmental and human health protection.
In my thesis, I broadened the use of the sentinel species Daphnia magna as a reliable diagnostic tool for water pollution and as a bioremediation agent to effectively mitigate the risks associated with chemical mixtures in the environment. Through rigorous experiments on four different genotypes of Daphnia magna, each with varying exposure histories to chemical pollution, I was able to quantitatively measure the uptake of four chemical compounds prioritised under the Water Framework Directive (WFD) as well as their mixtures (wastewater). In addition, I delved into the potential mechanisms of toxicity caused by these chemicals both within and across generations. To further support my research, I evaluated the ability of the same Daphnia genotypes to remove and uptake these chemicals and their mixtures under laboratory and semi-natural environmental conditions using mesocosms. The experiments were conducted using high-end concentrations of chemicals based on relevant concentration for surface and wastewater and aimed to evaluate the effectiveness of Daphnia as a remediation agent. At the laboratory scale, the removal efficiencies were 90 % for diclofenac, , 60 % for arsenic, 59 % for atrazine, and 50 % for PFOS. Validation at the prototype scale confirmed the sustained removal efficiency of diclofenac over four weeks. I discovered that previous exposures to chemical stress reduced genome-wide diversity in Daphnia genotypes. This, in turn, leads to reduced tolerance to novel chemical stress across generations. The decreased tolerance is due to reduced gene diversity in detoxification, catabolism, and endocrine genes in experienced genotypes. These genes are important in pathways that are conserved across species and could be potential targets for chemicals in other species, including humans. My preliminary analysis of the impact of these on the gut microbiome in Daphnia suggests the potential role of the bacteria in detoxification. Daphnia plays a crucial role in the food web of aquatic ecosystems and is a key indicator of ecosystem health. Impact of key chemicals on Daphnia can potentially have a cascading effect on other organism in aquatic food-webs. In this thesis, I also completed a proof-of-concept study using Daphnia as a natural filter to remove chemical pollutants from wastewater. Inspired by nature, this solution utilizes Daphnia to absorb and retain persistent chemicals, including pharmaceuticals, pesticide, and industrial chemicals, in a non-discriminatory manner. The technology has the potential to prevent harmful chemicals from entering our waterways. Doing so, it can contribute to a cleaner, more sustainable future by enabling water reuse and preventing environmental pollution.
My future work will investigate the ecotoxicity of chemical pollutants on Daphnia and its microbiome. I will also investigate the mechanisms of biotransformation of chemicals in the Daphnia body following uptake from water and wastewater. This will provide key insights into ecotoxicology using a systems biology approach and will guide the selection of Daphnia genotypes with the highest detoxification ability for applications in bioremediation.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):