The assessment of Namibian water resources for endocrine disruptors

Abstract

Namibia is the driest sub-Saharan country in Africa and it is characterised by low and variable rainfall. As a result, potable water in this mostly semi-arid country is considered an extremely valuable resource. Given the variety of anthropogenic and natural chemicals released into the environment by a growing human population, many water resources worldwide present health risks to both man and wildlife. Many of these chemicals are classified as endocrine disruptors which are chemicals with the ability to adversely affect the physiological systems regulated by the endocrine systems of organisms. These include, among others, reproductive, neurological and immunological effects. Endocrine disrupting chemicals include: natural and synthetic hormones such as estrogen, estrone, estriol and testosterone; heavy metals such as tri-butyltin, lead and cadmium; pesticides such as organophosphates and organochlorides; and a number of compounds such as polycyclic aromatic hydrocarbons and polychlorinated biphenyls. Windhoek, the capital city of Namibia, has for long been at the forefront of water reclamation by being the first town in the world to reclaim sewage for direct potable re-use. Presently, reclaimed sewage contributes approximately a third of the potable water utilised in Windhoek, with the remaining water being sourced mainly from a three-dam system: the S von Bach, Swakoppoort and Omatako dams, as well as from boreholes tapping into the Windhoek aquifer. Prior to the research conducted for this thesis, no studies have been undertaken to determine the endocrine disrupting potential of the reclaimed sewage in Windhoek. Likewise, no such studies have been performed on any of the surface water sources in this country, including the three-dam system supplying Windhoek. During 2010 and 2011, raw sewage, treated sewage and reclaimed sewage samples from Windhoek were collected at different stages of the wet and dry season. These samples were analysed for cytotoxicity using a lactate dehydrogenase (LDH) assay, for neurotoxicity using an acetylcholinesterase (AChE) inhibition assay, for inflammatory activity using enzyme-linked immunosorbent-assays (ELISAs) to determine interleukin-6 (IL-6) and interleukin-10 (IL-10) concentrations, as well as for the presence and quantification of three selected steroid hormones: estradiol, estrone and testosterone using ELISAs. Simultaneously, surface water from nine dams in Namibia were collected and analysed for the same parameters. High estradiol, estrone and testosterone levels were detected in the raw sewage. The sewage treatment plant process significantly reduced the concentration of these hormones, but levels were still in the range where adverse effects can be expected in organisms exposed to this water. The reclamation process successfully removed these residual hormones. The AChE inhibition and inflammatory activity of the treated sewage was also significantly lower than in the raw sewage and were completely removed in the reclaimed water. Cytotoxicity was only present in the raw sewage. In all the dam waters, no samples showed cytotoxicity. Estrone was the only hormone detected at low levels, once in the Avis dam water sample and once in the Goreangab dam water sample. The highest acetylcholinesterase inhibition was noted in the Goreangab dam water. Water from all the dams induced high IL-6 production with the highest levels being in the Goreangab and Swakoppoort dam water. IL-10 was lower than IL-6 concentrations in all samples, but was also highest in the Goreangab and Swakoppoort as well as the Avis dam water samples. During 2017 the efficiency of the reclamation process of treated sewage in Windhoek was assessed using a range of immunotoxicological bioassays on the water samples. This again included LDH and AChE inhibition assays as well as IL-6 and IL-10 production. In addition interferon-γ (IFN-γ) and macrophage inflammatory protein (MIP) -1β production were also determined using ELISAs. As a broad screen for immunotoxicity, proteome profiling was performed to test for 36 different chemokines and cytokines. This is the first time that proteome profiling is used for determining the immunotoxicity of treated sewage reclaimed for direct potable water use. For the 2017 assays, no cytotoxicity was detected in treated sewage or reclaimed water. Based on the ELISAs, treated sewage induced IL-6, MIP-1β and IL-10 production, but not IFN-γ. The corresponding test results for the reclaimed water were negative. The proteome profile indicated the presence of interleukin-1ra (IL1ra), Monocyte Chemoattractant Protein-1 (MCP-1), MIP-1α/MIP-1β, IL-6 and interleukin-1β (IL-1β) in culture supernatants exposed to treated sewage, but not to the reclaimed water. In conclusion, the results of the studies indicated the usefulness of the in vitro bioassays to test the endocrine disrupting potential of water sources. Results indicated that intake water at the reclamation plant in Windhoek contains contaminants that can adversely affect human health. The reclamation process however successfully removed these. However, routine monitoring is required to ensure continued delivery of safe potable water. The study further indicated the usefulness of proteome profiling as a quick, cost-effective screen for the immunotoxicity of water sources. The proteome profile can be followed up with cytokine-specific ELISAs to better quantify the inflammatory potential of water sources.