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Abstract Band 64

Nguyen, Dang Giang Chau (2015): Risk assessment for drinking water quality (pesticides and antibiotics) in the Mekong Delta, Vietnam. Bonner Bodenkundliche Abhandlungen 64, 101 S.



The reliance on pesticides and antibiotics to control and prevent pest infestation or diseases is inevitably connected with risks for humans and environment. I evaluated the potential risk associated with the occurrence of pesticides and antibiotics in different water sources utilized for drinking (surface-, ground- , harvested rain-, piped-, chemically treated surface-, and bottled water) in the Mekong Delta, Vietnam. Five study sites were selected in Can Tho City and An Giang Provinces, representing different land-use systems, as well as fish hatcheries (in Can Tho) and mature catfish production (in An Giang). After detailed assessment of exposure pathways, I monitored the occurrence of fifteen pesticides (isoprothiolane, fenobucarb, fipronil, butachlor, pretilachlor, propiconazole, hexaconazole, difenoconazole, cypermethrin, fenoxapro-p-ethyl, tebuconazole, trifloxystrobin, azoxystrobin, quinalphos, and thiamethoxam) as well as four antibiotics (sulfamethoxazole, sulfadiazine, trimethoprim, and enrofloxacin) in the above mentioned water sources, using solid phase extraction for water samples, accelerated solvent extraction for sediment samples, gas chromatography–mass spectrometry for pesticide analysis, and liquid-state tandem mass spectrometry for antibiotic analysis. In addition, I performed semi-field experiments in mesocosms under tropical condition to investigate the dissipations of sulfadiazine, trimethoprim and enrofloxacin.

The survey results revealed that improper pesticide application, storage and waste disposal prevailed at the study sites. As a result, annual median concentrations of the fifteen target pesticides ranged from 0.15 to 1.10 µg L-1 in surface water samples. Since surface water is often used for drinking without adequate treatment (survey result), the results were compared with the European Comission guideline value for total pesticides in drinking water (0.5 µg L-1). This value was exceeded in 95.6 % of surface water samples (n = 181), in all harvested rainwater samples (n = 6), in all chemically treated canal water samples (n = 6), and even in 12.5 % of bottled drinking water samples (n = 48). Overall, we failed to identify a clean water source in the Mekong Delta with respect to pesticide pollution. The studied antibiotics were also detected in the surface water samples, with maximum concentrations of 0.10 to 0.11 µg L-1 for the sulfonamides, of 0.33 µg L-1 for trimethoprim, and of 0.06 µg L-1 for enrofloxacin. These concentrations were lower than the predicted no-effect concentrations for aquatic organisms and minimum inhibitory concentrations for bacteria, suggesting limited antibiotic related risk to human and aquatic ecosystems in the monitored systems. None of these antibiotics were detected in the groundwater and piped water samples. In part, this is caused by rapid dissipation under ambient conditions of the Mekong Delta as shown by the dissipation models developed in this study. In summary, the measured concentrations of the investigated antibiotics are unlikely to cause risks to the aquatic environment; yet, the frequent occurrence of these antibiotics is of concern and might lead to chronic exposure of aquatic organisms as well as humans.

In conclusion, my research shows that agrochemicals pose a risk to human and ecosystem health in the Mekong Delta. A combination of improper handling and high application rates are threatening all investigated drinking water sources for the delta´s population. I therefore proposed recommendations to reduce the likelihood of exposure in which reducing the amount of pesticides and antibiotics introduced to the environment from agricultural and aquacultural activities is the priority.