Endocrine-disrupting compounds (EDCs) belong to a subclass of so-called emerging organic pollutants and their presence in the environment represents a potential risk to public health (Sauvé and Desrosiers 2014). According to the United States Environmental Protection Agency (USEPA) and the European Chemicals Agency (ECHA), EDCs are exogenous substances or a mixture of substances that alter the structure or function(s) of the endocrine system and cause adverse effects at the level of the organism, its progeny, populations or subpopulations of organisms (EPA 1998; ECHA and EFSA 2018). These compounds are widely distributed in the environment, mainly in aquatic ecosystems, and have attracted special attention due to their potential risk to the health of aquatic organisms and humans, even at very low concentrations such as ng/L (Adeel et al. 2017). Several studies have reported that EDCs may generate different adverse effects on exposed organisms, including feminization and masculinization, deficiencies in the sexual, prostate, brain, and immune development, gonadal atrophy, infertility, precocious puberty, and different types of cancer (prostate, testicles, breast, ovaries, among others) (Roby 2013; Kabir et al. 2015; Wang et al. 2019; Jackson and Klerks 2020). Moreover, it has been reported that EDCs may be associated with a high incidence of obesity and the development of diseases such as diabetes in humans (Hatch et al. 2010).
Among the different EDCs, the estrogens E2 and EE2, the alkylphenols 4NP and 4TOP, as well as the plasticizer BPA, are the most frequently EDCs detected in various aquatic environments such as rivers, lakes, and coastal areas (Ronderos-Lara et al. 2018; Calderón-Moreno et al. 2019; Inam et al. 2019; Salgueiro-González et al. 2019; Jiang et al. 2020; Čelić et al. 2020); due to their high estrogenic potential, these substances are being regulated by the European legislation through the European Water Framework Directive (2000/60/EC). In this sense, 2.0 µg/L has been defined as the maximum admissible concentration for 4NP and 4TOP in surface water (European Parliament 2008). In addition, BPA and E2 were recently proposed for inclusion as priority hazardous substances, recommending 0.01 µg/L and 0.001 µg/L as the maximum allowable concentration in surface water, respectively (European Parliament 2018). Regarding EE2, has been included in the watch list to monitor it and evaluate its possible incorporation as a priority hazardous substance for human health (European Parliament 2013).
In another way, it is known that effluents from WWTPs are one of the main sources of EDCs emissions to aquatic environments, and several studies have reported the detection of EDCs in WWTP effluents around the world, revealing that these substances are partially removed during wastewater treatment processes (Manickum and John 2014; Wee et al. 2019; Jiang et al. 2020; Čelić et al. 2020). For example, Jiang et al. (2020) detected E2 (< LOQ − 50.03 ng/L) and EE2 (4.72–35.03 ng/L) in effluents from 38 WWTPs in China. Similarly, Manickum and John (2014) reported the detection of E2 (4.0–107.0 ng/L) and EE2 (1.0–8.0 ng/L) in the effluent of a WWTP in South Africa. On the other hand, BPA (3.31 ng/L), 4NP (4.62 ng/L), and 4TOP (4.44 ng/L) were detected in a WWTP effluent in Portugal (Carvalho et al. 2016). Furthermore, 4NP (420–2120 ng/L) and 4TOP (5.3–54.8 ng/L) were detected in effluents of nine WWTPs in Iran (Bina et al. 2018). Therefore, the incomplete removal of EDCs in WWTPs contributes to their frequent detection in surface water, which may subsequently impact on the essential activities such as agriculture, livestock, fisheries, drinking water, and domestic and recreational activities (Čelić et al. 2020).
In Mexico, some studies have reported the detection of E2, EE2, and BPA in several WWTPs in a wide concentration range from < LOD – 16,600 ng/L (Díaz-Torres et al. 2013; Estrada-Arriaga et al. 2016; López-Velázquez et al. 2020; Villarreal-Morales et al. 2020). Likewise, other authors such as Calderón-Moreno et al. (2019), and Ronderos-Lara et al. (2018) detected E2, EE2, BPA, 4NP and 4TOP in river water (Morelos, Mexico) at levels from < LOD – 624.3 ng/L, emphasizing EE2 and BPA as the most abundant EDCs.
In particular, the study of EDCs in Monterrey city is of great interest due to it is the second most populated region in Mexico (5,341,171 inhabitants; INEGI 2021), and stands out as one of the most industrialized zone in the country (SEDATU 2015) contributing with the emission of a large number of pollutants into the environment, including some EDCs as was informed by Cruz-López et al. (2020), and Villarreal-Morales et al. (2020). Moreover, is of great interest to evaluate the ecological risk on the aquatic systems due to their high estrogenic potential and the continuous emission of EDCs towards the environment, which may impact directly on the ecosystems of the receiving water bodies such as the urban rivers Pesqueria, Santa Catarina, La Silla, Sabinal, and Topo Chico (Fig. 1),which are tributaries to the Rio San Juan that flows into the Rio Bravo (natural border between Mexico and United States) and the Gulf of Mexico.
Recently, some studies have been focused on evaluating the potential environmental risk through hazard index associated with E2, EE2, BPA, 4NP, and 4TOP in the dissolved phase of surface water (Stasinakis et al. 2012; Peng et al. 2017; Calderón-Moreno et al. 2019) as well as influents and effluents of WWTPs (Yu et al. 2013; Manickum and John 2014; Patrolecco et al. 2015; Ben et al. 2018; Jiang et al. 2020). In these studies, the risk quotients (RQ) have been calculated for several aquatic organisms (i.e. algae, crustaceans, and fish), and it is considered a useful strategy for the evaluation of water resources, which could contribute to improve the wastewater treatment processess, implementing effective strategies of management and control of wastewater discharges, surface, and drinking water, for the health protection of human and aquatic organisms (Xu et al. 2016). Therefore, this study aims to determine the potential environmental risks associated with five dissolved EDCs in four WWTPs from Monterrey City, which to our knowledge, constitutes the first report of this type in WWTPs from Mexico.