The impact of geothermal fluid discharge on drainage water and groundwater quality in terms of toxic contaminants in the agricultural Harran Plain, Turkey

•The Karaali Geothermal field is an important geothermal fluid in (Sanliurfa) southeastern Anatolia of Turkey.•The toxic content of the geothermal fluid was characterized with chemometric techniques.•Al, Fe and Mn values in drainage channels are not suitable for reuse criteria for agricultural irrigation.•Al, B, F, Fe and Mo values measured in groundwater are not suitable for drinkability criteria.•In the pH and metal load diagram, all of the samples are in the "near-neutral-high metal" class. The Karaali Geothermal field located in Harran Plain, which has a great agricultural potential for the development of our country, has a great importance because of being a thermal tourism and greenhouse heating source in Sanliurfa province. In this study, the aim was to determine heavy metal contamination, which has direct and indirect serious effects on human health, due to geothermal causes. In this context, a total of 11 sampling points in the Karaali Geothermal fluid (KG), the closest drainage channels where geothermal water is discharged (DW1, DW2, DW3, DW4 and DW5), and the closest groundwater to these points (GW1, GW2, GW3, GW4 and GW5), were sampled during 8 months between May 2020 and March 2021. Heavy metal concentrations were obtained in the order F>Sr>B>Ba>Al>Li>Fe>Cr>V>Mo>Zn>Cu>Zr>Be>Mn>Cd>Co>Pb>Ag>Ni for groundwater and Al>Fe>Sr>F>B>Mn>Ba>Li>Cu>Zn>Cr>Ni>Co>Mo>Be>Pb>Zr>Cd>Ag>V for drainage water. Al, Fe and Mn values were determined to exceed the acceptable values in terms of suitability of the water in the drainage channels for reuse and agricultural irrigation purposes. In groundwater, the limit values in terms of suitability for drinking water were exceeded for Al, B, F, Fe and Mo parameters. In the diagram of pH and metal load, all the samples were classified as “near neutral–high metal.” The study found that six factors in both drainage and groundwater factor analysis separately explained 86.1% and 81.2% of the total variation in the data, respectively. In the cluster, good results were obtained with three different similarity groups for drainage waters and five different similarity groups for groundwater. These results show that the factors responsible for toxic contamination in the drainage channels and especially in the groundwater are primarily related to the use of geothermal fluid in greenhouse cultivation and spa tourism, excessive use of pesticides and fertilizers in agricultural activities, and geogenic processes.