Walid Chmingui 1 , Olfa Mahjoub 1 , Monica Brienza 2 , Amel Jemai 1 , Marwa Rmili 1 , Serge Chiron 2
In arid and semi-arid countries, biotic and abiotic stressors are increasingly threatening natural water resources either by jeopardizing their quantity or/and their quality. In Tunisia, preserving natural water resources has become one of the most important challenges in addition to reusing non-conventional water resources. The reuse of treated wastewater (TWW) for irrigation in agriculture and for aquifer recharge were among the adopted strategies despite the low quality of the produced TWW and their outdated and inexistent guidelines, respectively. Besides, secondary biological treatment of urban wastewater does not degrade emerging compounds like pharmaceutical active compounds (PACs). Meanwhile, the reuse of TWW for irrigation is associated with an environmental and health impacts linked to the exposure of users and the groundwater (GW) to chemical compounds and pathogens. This study deals with the impact of TWW reuse on GW quality of Hammamet-Nabeul aquifer, a costal aquifer in the North-east of Tunisia subjected jointly to over-exploitation by farmers, marine intrusion, and infiltration during irrigation with TWW.
The work consisted in sampling of irrigation water (TWW and GW), determining conventional water quality parameters, and analyzing selected PACs in these water samples using liquid chromatography coupled to mass spectrometry (LC-MS). The results showed that TWW was exceeding the threshold values set by the Tunisian quality standard (NT-106.03) for reuse in agriculture, especially, COD, BOD5, and total suspended solids (TSS). For GW samples, a high mineralization was observed in the aquifer in addition to the impact of agricultural practices (irrigation and fertilization). Indeed, electrical conductivity ranged between 4.4 and 7.6 mS/cm thus exceeding the threshold value recommended by FAO for irrigation water (2 mS/cm). Additionally, nitrates concentrations in GW samples ranged between 40 and 162 mg/L; beyond the values recommended by FAO (30 mg/L). The screening mode of LC-MS allowed the identification of 38 PACs; 30 PACs were detected in GW samples. The quantification of ofloxacin, carbamazepine, and caffeine revealed high concentrations ranging from ng/L to μg/L. The concentrations in TWW, varied between 0.39 and 13.32 μg/L while in GW they varied between 0.02 and 3.23 μg/L.
The risk quotients calculated for each of the selected compound detected in TWW showed a very high ecological risk to the environment. Based on PACs distribution in the aquifer, the use of GW for the irrigation could pose potential environmental and sanitary risks to humans and animals.