An active biomonitoring approach using three-spined stickleback (Gasterosteus aculeatus, L.) to assess the efficiency of a constructed wetland as tertiary treatment of wastewater
Graphical abstract
Introduction
Human activities generate large volumes of wastewater that must be treated before being released into the environment in order to limit the potential negative effects on ecosystems and human health. However, for several decades, the presence of micropollutants in aquatic environments has become a widespread problem of increasing concern. These micropollutants, also known as “emerging contaminants”, include many different molecules such as pharmaceuticals, personal care products, natural and synthetic hormones, pesticides, and industrial chemicals such as polychlorinated biphenyl (PCB) or polycyclic aromatic hydrocarbons (PAH) (Luo et al., 2014). Wastewater treatment plants (WWTPs) are not designed to treat all these contaminants and WWTPs effluents concentrate these molecules which are released into the natural environment where they can be found in concentrations ranging from ng/L to µg/L (Blum et al., 2018). This complex mixture of xenobiotics may have deleterious effects on living organisms downstream of effluents discharge area. Indeed, many studies highlight estrogenic effects, induction of oxidative stress, modification of immune system parameters and histological damage in caged fish downstream of WWTPs (Cazenave et al., 2014, Jasinska et al., 2015, McGovarin et al., 2018, Pérez et al., 2018).
To improve wastewater treatment of WWTPs, new technologies have emerged such as membrane bioreactors, activated carbon absorption, ultra- or nano- filtration, reverse osmosis, ozonation or other advanced oxidation processes (Gorito et al., 2017). However, even if these technologies are effective, they are often expensive. Another alternative may be to set constructed wetland (CW) downstream of WWTPs. CW allows self-purification of water through natural process involving wetland vegetation, soil, and their associated microbial assemblage to treat effluent or other water source (US EPA 2000). This solution has the advantage of being financially more accessible, both in terms of implementation and maintenance (Ayaz and Akca, 2000).
Several authors have studied the efficiency of some different types of CW to improve physicochemical parameters. Their results have shown that efficiency depends on the installation type and the season. However, in all cases, CWs are efficient to decrease suspended solids, nitrogen concentration, chemical and biological oxygen demand and water contamination by some pathogens such as coliforms (removal higher than 90%) (Ahmed et al., 2008). Other studies have also highlighted the effectiveness of CWs in reducing pesticides (Anderson et al., 2013), human and veterinary drugs (Anderson et al., 2013, Hsieh et al., 2015), industrial chemicals (Síma et al., 2013, Toro-Vélez et al., 2016) as well as antibiotics and antibiotic-resistant bacteria (Chen et al., 2015). Some authors have also focused on the effects of endocrine disruption in fish and reported a decrease in estrogenic effects downstream of the CW in male fathead minnow (Pimephales promelas) (Hemming et al., 2001, Bringolf and Summerfelt, 2003).
All studies conducted to assess CWs efficiency used chemical or physicochemical parameters. However, chemical analyses do not consider the bioavailability of compounds and the real exposure and risk for living organisms. Moreover, physicochemical analyses do not allow the assessment of health status of living organisms in theses ecosystems. Over the past decades, some tools have been proposed to link chemical contamination to biological responses of exposed individuals. Among them, biomarkers are defined as observable and measurable changes on organisms (ranging from molecular to individual level and from biochemical to behavioral responses) following a pollution exposure or an environmental modification (Van der Oost et al., 2003). The biomarker approach is particularly useful to assess environmental impact of local pollution point source (Sanchez et al., 2012) and, by extension, to assess the effectiveness of process that improves the water quality.
The present work aims to assess for the first time the effects of a constructed wetland built downstream of a wastewater treatment plant using a multi-biomarker approach in three-spined stickleback (Gasterosteus aculeatus) with an active biomonitoring strategy. Caged fish are increasingly used in environmental risk assessment, especially in case of WWTP’s effluent contamination (Cazenave et al., 2014, McGovarin et al., 2018, Pérez et al., 2018). Caging is particularly useful when the sentinel species is absent in a study site. Even if the species is present, this approach prevents the risk associated with the capture of endangered species. Moreover, the stress caused by predation is reduced and the sampling is facilitated compared to passive sampling (Oikari, 2006). Several biotic (number of individuals, size, sex, age, etc.) and abiotic parameters (distance with the pollution source, exposure duration, etc.) can be standardized through caging approach (Oikari, 2006). The use of well calibrated individuals allows a thorough biomarker comparison between sites according to the chemical contamination. In this study, the three-spined stickleback was chosen as sentinel species because of its large geographical repartition in northern Europe and its resistance to pollution and environmental changes (temperature, salinity), which allows caging in many hydrosystems. Moreover, sticklebacks have a small size (from four to eight centimeters) (Wootton, 1984) and are easy to handle which facilitates caging (Le Guernic et al., 2016). Biomarkers measured in this study are representative of some important physiological functions frequently assessed in organism downstream WWTP such as innate immune responses, antioxidant system, biotransformation enzymes, reproduction parameters and synaptic transmission (Cazenave et al., 2014, Jasinska et al., 2015, McGovarin et al., 2018, Pérez et al., 2018). The assessment of a great number of physiological functions allow to integrate the effect of a complex mixture of contaminants as in a WWTP’s effluent. Finally, biomarkers were integrated in an Integrated Biomarker Response index (IBRv2) developed by Sanchez et al. (2013) that will be used to synthetize the global biomarker response of fish.
Section snippets
Description of the study area
The city of Sacy-le-Grand is located inside a huge wet and peaty area of 1000 ha which includes a Natura 2000 and Ramsar site with a surface area of 245 ha (i.e. Les Marais de Sacy). The WWTPs of Sacy-le Grand is a small plant that collects and treats wastewater from this town and surrounding villages and is designed for 10,000 population equivalents. In addition to the primary treatment, this WWTP is equipped with a phosphate and nitrate removal treatment. The CW is located downstream the WWTP
Water physical and chemical parameters
Results of physicochemical parameters are presented in Table 1. Significant differences were highlighted for water temperature between the three sites with warmer water at Ladrancourt and cooler water at the exit of the wetland. Conductivity and oxygen rate at the entrance of the wetland were respectively higher and lower compare to Ladrancourt but these differences disappeared at the exit of the wetland.
Stickleback biomarkers
No mortality was observed during the whole experiment. Sticklebacks showed no external sign
Discussion
The improvement of the water quality is highlighted and summarized by the Integrated Biomarker Response index which was equal to 25.2 at the entrance of the constructed wetland and decreased to 17.4 at the exit of the constructed wetland. Considering the entrance of the CW as the theorical maximum IBR, the IBR at Ladrancourt was reduced by 31% which attests the efficiency of the CW in improving the water quality on a biological point of view. The seeming induction/inhibition of some biomarkers
Conclusion
In the present study, the efficiency of the constructed wetland of Sacy-le-Grand to improve the water quality was investigated by using an active biomonitoring approach with three-spined sticklebacks. Some physiological functions were assessed such as antioxidant and innate immune systems, metabolic detoxication, synaptic transmission and reproduction parameters. The integration of all the biomarker results in an integrated biomarker response index (IBRv2) has highlighted the benefic effect of
Acknowledgments
This research was funded by the INTERREG DIADeM program and the French Ministry of Ecology Ecotoxicology programs. The authors thank the European Regional Development Fund (ERDF). The authors are grateful to Tony Rulance (Oise County) and to Sacy-le-Grand town council for an easily access to the sites. The authors are also grateful to Dr. Antoine Le Guernic for his scientific advice.
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