The Use of Human Cell Lines to Monitor the Cytotoxicity of Environmental Mixtures in Soil

Author: Dao Swain

Swain, Dao, 2017 The Use of Human Cell Lines to Monitor the Cytotoxicity of Environmental Mixtures in Soil, Flinders University, School of Medicine

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Humans are typically exposed to a multitude of chemical mixtures in the environment with varying impacts on human health. Current guidelines for assessing the human health hazard of environmental mixtures such as agricultural chemicals and bioremediated soil allow for predictions based solely on chemical analysis. However chemical analysis may not detect interactions between chemical compounds or degradation products which may contribute to the toxicity of the soil.

The use of in vitro bioassays may provide a more comprehensive assessment of the risk posed by the mixture to human health. Therefore, the overall aim of this study was to use human cell lines to monitor the cytotoxicity of various environmental mixtures as they degraded in soil. This was achieved by using a range of human cell lines including HepG2 (liver), HaCaT (skin), MRC-5 (lung), JAr (placenta) and WIL2NS (lymphocytes) to monitor the cytotoxicity of environmental mixtures. This thesis also aimed to determine if in vitro cytotoxicity monitoring of environmental mixtures using human cell lines was more sensitive for detecting changes in toxicity compared to chemical analysis. Specific environmental mixtures that were investigated in this thesis included the commercial agricultural product Vitavax 200FF and its active ingredients, carboxin and thiram. The other environmental mixture investigated in this thesis was soil contaminated with total petroleum hydrocarbons (TPH), which was subjected to bioremediation using two different methods.

Cytotoxicity of Vitavax 200FF to cell lines was in the following order; WIL2NS cells > JAr cells > HaCaT cells > MRC-5 cells > HepG2 cells. The cytotoxicity was mainly due to the effects of thiram in the formulation.

The cytotoxicity of Vitavax 200FF and its active ingredients was then monitored during their degradation in soil in simulated laboratory experiments. Both sterile and non-sterile soil was employed to investigate the impact of the presence of microbes on the degradation and cytotoxicity of the product formulation Vitavax 200FF in soil. It was found that high concentrations of Vitavax 200FF could alter the population of soil microorganisms. It was also demonstrated that degradation of the active ingredients of Vitavax 200FF, carboxin and thiram could occur via abiotic catalytic processes as well as via biotic transformation. Degradation products generated from both abiotic and biotic processes were likely to be less toxic than their parent compounds. However, it was found that the soil could remain toxic to human cells for a longer period of time than predicted from chemical testing.

The cytotoxicity of soil contaminated with TPH during bioremediation was then monitored. It was found that the reduction of TPH levels detected via chemical analysis over time did not correlate with a reduction of cytotoxicity over time. It was also found that bioremediation of TPH contaminated soil via the addition of nutrients and microorganisms could potentially be more harmful than allowing the contaminants to degrade in the soil unassisted.

The results of this thesis reinforced the view that assessment using chemical analysis alone is insufficient to determine potential hazards to human health. It was found that a combined approach which includes both chemical and in vitro cytotoxicity testing of chemical mixtures using human cells provided a more comprehensive evaluation of the toxicity posed by complex environmental mixtures.

Keywords: cytotoxicity, soil, degradation, pesticide, bioremediation, petroleum hydrocarbons, cell culture, environmental mixtures, chemical mixtures, toxicity, contaminated soil, in vitro bioassay

Subject: Medical Biotechnology thesis, Medicine thesis

Thesis type: Doctor of Philosophy
Completed: 2017
School: School of Medicine
Supervisor: Dr Lisa Schmidt