Disruptive effects of waste water pollution on aquatic biodiversity

Afusat Jagun Jubril is a climate researcher and environmentalist based at the University of Ibadan in Nigeria, and was a CIRCLE Visiting Fellow at the University of Nairobi in Kenya in 2017. The Climate Impacts Research Capacity and Leadership Enhancement (CIRCLE) Fellowship is a post-doctoral fellowship scheme, that aims to develop the skills and research results of African early career researchers in the field of climate change. CIRCLE is implemented through AESA (the Alliance for Accelerating Excellence in Science in Africa), a funding, agenda setting and programme implementing platform of the African Academy of Sciences and the African Union Development Agency (AUDA-NEPAD). CIRCLE is supported by the Association of Commonwealth Universities (ACU).

Background

Climate change and environmental pollution are considered the most serious human-caused threats to biodiversity and ecosystems. The most pronounced effect of climate change is global warming. Several approaches to help mitigate climate change have been implemented in different regions of the world but more adaptation strategies are essential. Even if emissions were stabilized, global warming and its effects would last many years. For this reason, adaptation will continue to be necessary and requires attention in the context of polluted ecosystems.

Adaptation to heat stress is of great importance to the survival of any species because it facilitates heat tolerance, the absence of which can be lethal and eventually lead to extinction. This CIRCLE research project evaluated the prevalence, anthropogenic sources and effect of selected endocrine disrupting chemicals on water, sediments and tilapia fish in Lake Naivasha, Kenya. The research also sought to draw the attention of the local, regional and international science community to the serious anthropogenic threats to biodiversity and ecosystems through the endocrine system that are caused by the combined effects of climate change and environmental pollution.

Why pollution?  

Global environmental pollution, including water pollution, and ecosystem degradation have been estimated to cause about 13 million human deaths annually. Urban and industrial discharge of untreated effluents are the major source of pollution of surface waters globally  (UNEP, 2012). One‐third of the drinking water necessary to sustain the world’s human population is obtained from surface water sources, which also serve as habitats for many amphibious and aquatic animals. Owing to lack of or improper wastewater treatment facilities before discharge, wastewater contains various chemicals, depending on their source, some of which are known to be Endocrine-Disrupting Chemicals (EDCs).

EDCs have been established to have substantial pathological effects on human and animal endocrine systems that regulate all biological processes in the body (including effects on thyroid hormone, sex steroid hormones and cortisol metabolism). The endocrine system also plays a major role in adaptation to stressors (especially thermal stressors as associated with climate change). EDCs may, therefore, have an effect on the ability of a host organism to respond and adapt to heat stress associated with global warming. Surface waters are polluted by human activity. Pollutants can inhibit the adaptive response of aquatic organisms to climate change, which is presently increasing. The inability of the biological host to adapt to climate change could be a harbinger of the loss of control of thermal tolerance, threatening the survival of various species.

EDCs are components of man-made products originating from industry (dioxins, polychlorinated biphenyls, and alkylphenols), agriculture (pesticides, insecticides, herbicides, phytoestrogens and fungicides), residential sources (phthalates, polybrominated biphenyls, bisphenol A), and pharmaceutical sources (parabens)). All sources can also produce heavy metals such as lead, mercury, and arsenic. The types and prevalence of EDCs in water bodies must be analysed to quantify and distinguish sources of toxicological substances in the water supply.

Awareness of the importance of waste management and advocacy for effective waste management has grown in Africa. However, only a few African countries have standards for effluent discharge into surface waters, and enforcement of standards is poor, therefore pollution is apparent. Levels of EDCs in ecosystems, their sources and implications have received scarce research attention in low-and-middle income countries, especially the effect of EDCs on organisms under stressors such as heat stress from global warming. The trends and impacts of EDCs and global warming on aquatic ecosystems in developing countries require extensive research.

The study

Both field sampling and experimental techniques were used to establish critical parameters to determine environmental exposure and indicate the effects on adaptation of increasing temperatures. Zebra fish were used as a model organism to monitor adaptation to heat stress in the presence of EDCs. Water temperature changes in the lake were also monitored. Field sampling and experimental models were also used to study the combined effect of climate change and environmental pollution with specific endpoints such as heat stress, EDCs and thyroid gland function.

The field survey of selected EDCs (polychlorinated biphenyls, bisphenol A (BPA), DDT, lead and cadmium)) in water, sediments and tilapia was carried out to establish their presence at different points of anthropogenic contact in Lake Naivasha. Deposition of EDCs in water, sediment, tilapia fish blood and tissue samples were measured using gas chromatography coupled with mass spectroscopy, and atomic absorption spectrophotometry was used for heavy metal analysis. The physiochemical changes (temperature) in the environment and in water bodies were monitored using primary and secondary remotely-sensed meteorological data. Different points of anthropogenic contact within Lake Naivasha were sampled to determine ecosystem exposure to common EDCs.The associated gross histopathology and haematology changes were also evaluated as biomarkers of exposure using standard methods.

An experimental study was carried out in the laboratory by the exposure of tilapia to some EDCs (heavy metals and DDT) under different heat stresses (temperature change) and monitored for associated pathology and adaptation responses. The expression (PCR) and extent of biomarkers of the thyroid gland of the endocrine system in zebra fish was used as an experimental model.

Outcome of the study

This study was unique in its measurement of how the environment can be impacted by human activities and the effects of such activities by inhibiting the host’s ability to adapt to a changing climate. The occurrence and levels of polychlorinated biphenyls, bisphenol A (BPA), DDT, lead and cadmium above acceptable standards (associated with endocrine disruption) were detected in the water, sediment and tilapia in Lake Naivasha and the levels were associated with different focal points of anthropogenic contact to the Lake. The primary temperature change in the environment and in the water bodies showed an increasing trend, an indication of a continuous warming trend.

Moreover, lesions that are associated with environmental pollutants were observed in the tilapia harvested from the lake. There was also evidence of reduced tolerance to stress in the experimental group of tilapia exposed to heavy metals and DDT under different regimes of temperature stress.

The hidden and unknown impacts of EDCs, which are ubiquitous, appear to have a compounding effect with the potential to become an overwhelming global danger. These data have the potential to guide further research to disaggregate the effects of environmental pollutants such as EDCs on adaptation to global warming. We are further studying the expression (PCR) and extent of biomarkers of the thyroid gland as it relates to its regulation of temperature in zebra fish, used as a model organism to detect quantities of EDCs. The research findings are essential to determine the most effective remediation strategies, early detection of pathological effects associated with exposure to pollutants, and to forestall their detrimental health effects. This is particularly the case as the effects of climate change worsen and are compounded with anthropogenic effects in the environment, such as pollution. Further, the fish farmers stakeholder groups who were supplied with the data and information from this research, were able to understand and discouraged the use of wastewater and waste-contaminated water for fish farming. This work suggests the need for future research on the mechanisms associated with the effect of EDCs on adaptation to climate change, including the elucidation of mechanisms of the action of EDCs as they relate to temperature regulation of the thyroid and other glands in aquatic organisms.

Anticipated impact

• Climate change research in Africa should prioritize adaptation. Africa suffers disproportionate effects of climate change as well as increased pollution by EDCs. An improved understanding of this combined effect would help address local pollution challenges and protect ecosystems and their hosts therein.
• The study has shown that surface water in Lake Naivasha, Kenya, is contaminated with EDCs by anthropogenic influences, and that EDCs can inhibit the adaptive response of temperature tolerance in tilapia fish. This finding is a critical first step in raising awareness and reducing pollution by creating an understanding of the role of pollution in adaptation to global warming.
• Understanding the effects of exposure to EDCs will facilitate approaches to reduction and management of environmental pollution. The findings will further elucidate mechanisms that reduce adaptation and how they relate to environmental pollution and climate change. When fully understood, the combined effects of exposure and warming will facilitate environmental pollution policy.
• The community around Lake Naivasha was impacted by uptake of activities that mitigated the effects of the mechanisms described by these research findings.
• This study has shown that the combined effect of EDC pollution and an increase in temperature are detrimental due to the inhibitory role that EDCs appear to play in adaptation of the host (tilapia fish).
• Recommendations have been made to local and regional authorities to reduce exposure of EDCs in the environment, and to monitor and regulate the disposal of untreated wastewater into the ecosystem.