Monitoring of Endocrine Disruptors in Surface Waters of the Mekong Delta in Vietnam

Abstract

This study monitors estrogenic-Endocrine Disruptors (e-EDs) in surface waters in the Mekong Delta in Vietnam, one of the most populated agricultural areas in the world. e-ED is a subclass of Endocrine Disruptors (EDs), which are chemicals with the potential to elicit negative effects on endocrine systems of humans and animals. The feminisation of male fish caused by e-EDs, i.e. 17β-estradiol (E2) and estrone (E1), ethinyl estradiol (EE2), and nonylphenol (NP) is probably the most typical example about the effects of EDs. Since e-EDs can be either natural or synthetic chemicals, their sources to the environment vary differently such as domestic discharge, industrial discharge and agricultural runoff. A comprehensively review on e-EDs in the literature and related studies in aquatic environment in Vietnam shows that different e-EDs possess different estrogenic potency, and their potency varies widely. The analytical method used contributes to the variability. However, regardless of the analytical methods estrogens are, in general, estrogenically more potent than xenoestrogens. Therefore, estrogens usually contribute predominantly in the total estrogenic activity of environmental samples although they normally occur at lower concentration as compared to that of xenoestrogens. In addition, the review shows that in Vietnam although data on estrogens are lacking of, there are some data on xenoestrogens and these chemicals ubiquitously occurred in water bodies at considerable concentrations. In many cases they exceeded the Predicted No Effect Concentration (PNEC) for freshwater life, especially in urban areas. Without contribution from estrogens, estrogenic activity caused by xenoestrogens was generally low due to their weak potency. However, in some cases, their estrogenic activity occurred at considerable levels due to their high concentration in the environment, which may cause an estrogenic risk for aquatic fauna. <br /> The estrogenic activity in the surface waters of Can Tho City (CTC), a mid size city located in the Mekong Delta in Vietnam, was monitored. Water samples from the urban, industrial and suburban areas were analysed by the Yeast Estrogen Screen (YES) assay. Additionally, estrogenic activity was analysed for samples at the upstream and downstream stations out of CTC to estimate the estrogenic discharge of the city. The estrogenic activity was frequently detected (100% in the urban and industrial areas, 86% in the suburban area). The concentrations in the urban (range 0.03 to 33.99 ng E2 equivalent (EEQ)/L, median 0.72 ng EEQ/L) and industrial (range 0.08 to 11.8 ng EEQ/L, median 1.08 ng EEQ/L) areas were significant higher (p < 0.05) than the suburban area (range ND (not detected) to 2.99 ng EEQ/L, median 0.256 ng EEQ/L). In the Hau River (Bassac River), the estrogenic activity was lower at the upstream (range 0.015 to 1.09 ng EEQ/L, median 0.333 ng EEQ/L) as compared to the downstream station (range 0.04 to 1.57 ng EEQ/L, median 0.485 ng EEQ/L). In the urban area, 37.5% of the detected samples had a higher concentration than the PNEC of 1 ng/L. In the industrial and suburban areas, 56% and 9% exceeded the PNEC, respectively. The results indicate a potential estrogenic risk for aquatic fauna in all the sampling areas. Using the data, it is estimated that CTC discharged an amount between 44 to 88 g EEQ/day, which is in the same order of magnitude to a modeled result of 37 g EEQ/day. Human and animal discharges seemed to be the major estrogenic sources in this city.<br /> To compare estrogenic activity in the surface waters of different agro-ecosystems in CTC, and Dong Thap Province (DTP), two representative areas in the Mekong Delta in Vietnam, water samples from irrigation canals, agricultural fields, fishponds in the suburban and rural areas in CTC and DTP were analysed on estrogenic activity, respectively. In CTC estrogenic activity (range ND to 3.62 ng EEQ/L, median 0.28 ng EEQ/L) was detected in 68% of all the samples, from those, 17% of the samples had a higher estrogenic activity than the PNEC value. Whereas in DTP estrogenic activity (range ND to 4.97 ng EEQ/L, median 0.2 ng EEQ/L) was detected in 59% of all the samples and it was significantly (p < 0.05) lower than in CTC. From those estrogenic activity in 13% of the samples exceeded the PNEC value. Domestic discharge is likely to be the reason for the observed estrogenic activities in both CTC and DTP. <br /> In both areas, in the effluent of fishponds the estrogenic activity (in DTP: range ND to 0.75 ng EEQ/L, median 0.14 ng EEQ/L, in CTC: range 0.05 to 2.66 ng EEQ/L, median 0.69 ng EEQ/L) tended (p > 0.05) to be higher as compared to the inflowing water (in DTP: range ND to 1.6 ng EEQ/L, median 0.08 ng EEQ/L, in CTC: range 0.29 to 1.35 ng EEQ/L, median 0.56 ng EEQ/L). Although in DTP the estrogenic activity in agricultural runoff was low (range 0.02 to 0.58 ng EEQ/L, median 0.16 ng EEQ/L), it was elevated in CTC (range ND to 3.6 ng EEQ/L, median 0.3 ng EEQ/L). Direct discharge of domestic wastewater into the fields in CTC could be the reason. Except for the canal category (in DTP: range ND to 2 ng EEQ/L, median 0.19 ng EEQ/L, in CTC: range ND to 2.99 ng EEQ/L, median 0.256 ng EEQ/L) the estrogenic activities obtained in the fields and the fishponds in CTC were significantly higher than those in their respective categories in DTP (p < 0.05). <br /> About one third of the samples caused a cytotoxic effect to the yeast cells in both areas CTC and DTP (in CTC: 35% in urban area; 42% in industrial area; 24.7% in suburban area (canal, fishpond, agricultural field), in DTP: 33.3% (canal, fishpond, agricultural field, national park)). This effect either completely killed the yeast cells or inhibited yeast cell growth; as a consequence, these cytotoxic samples did not generate estrogenic activity.<br /> In CTC, the cytotoxic effect mainly occurred in all sampling categories (i.e. urban area, industrial area, canals and agricultural fields) except in the fishponds. The measured water quality parameters of the cytotoxic samples significantly differed to those of the normal samples, i.e. DO or EC values in the cytotoxic samples were lower or higher than those in the normal samples, respectively. However, the reason for the cytotoxic effect in CTC is unknown. In DTP, this effect mainly occurred in the rice fields and in the canals, and rarely in other sampling categories, i.e. the national park and the fishponds. There was no significant difference between the measured water quality parameters (i.e. DO, EC and pH) of the cytotoxic samples and those of the normal samples. Pesticides could be responsible for the observed cytotoxic effects in DTP although sometimes these effects occurred as well at the upstream station. <br /> In Vietnam, human and animal wastes are not properly treated, and in many cases they are directly discharged into water bodies. Most likely, the rather frequent detection of estrogenic activity in surface waters in the Mekong Delta is related to these discharges. Additionally, elevated estrogenic activity as compared to the PNEC value indicates an estrogenic risk to the aquatic fauna, especially in the urban and industrial areas. Considering these facts, estrogenic activity in the environment in Vietnam certainly deserves further studies to elucidate potential sources and to assess estrogenic risk in detail. In any case, domestic discharges, especially human and animal wastes need to be sufficiently treated in order to reduce estrogenic activity in water bodies in Vietnam.