Determination of caffeine in treated wastewater discharged in the Nile River with emphasis on the effect of zinc and physicochemical factors

Abstract

The present study aimed to investigate the occurrence of caffeine residues in the Nile River according to drainage of treated wastewater at Assiut, Egypt, and the effects of physicochemical parameters and zinc on its concentration. Four different sites were selected to perform the study: S, wastewater treatment plant (WWTP) canal (source site); J, a junction site between WWTP canal and the Nile; R, a reference site in the Nile before J site; and A, a site located after J site in the Nile. Water and sediment samples were collected in Summer 2022 and Winter 2023. Caffeine and Zn concentrations and physicochemical parameters were measured in the collected samples. The caffeine concentrations in water samples ranged from 5.73 to 53.85 μg L^-1 at S in winter and summer, respectively, while those in sediment ranged from 0.14 mg kg^-1 at R in winter to 1.54 mg kg^-1 at S in summer. Caffeine and Zn concentrations were higher in summer samples. The Water Quality Index (WQI) of the collected samples recorded the lowest values in winter season at S and J sites. The study found that caffeine and zinc concentrations are positively correlated with water temperature and conductivity, while negatively correlated with pH. The association between caffeine and Zn highlights the environmental impact of heavy metals and pharmaceutical residues, and stresses the need for future research on these interactions.

Keywords: Caffeine; Emerging contaminants; Micropollutants; Pharmaceuticals; Water pollution; Water quality; Zinc.

Fig. 1

Maps showing the study sites at Assiut Governorate, Egypt. S, source-of-pollution site, where treated water is discharged from wastewater treatment plant effluent (Arab El-Madabegh WWTP); J, junction site where the water of the wastewater treatment canal meets with water flow of the Nile; R, reference site in the Nile River before the junction site; A, site located after the junction point in the Nile River

Fig. 2

Boxplots of investigated physicochemical parameters at study sites with statistical results (similar letters for each variable show no significant difference at the 0.05 level)

Fig. 3

Boxplots of caffeine and Zn concentrations in water and sediment at study sites with statistical results (similar letters for each variable show no significant difference at the 0.05 level)

Fig. 4

Dendrogram shows the collected samples’ classification at the investigated sites during the summer and winter seasons based on the physicochemical parameters and caffeine and Zn concentrations in water and sediment (after standardizing the collected data)

Fig. 5

Water Quality Index (WQI) for the collected samples of the study sites during the investigated seasons

Fig. 6

Principal component analysis (PCA) for the physicochemical parameters and caffeine and Zn concentrations in water and sediment at study sites during summer and winter seasons (after standardizing the collected data). Notation of variables: AT, air temperature (°C); WT, water temperature (°C); pH, water pH; Cond, conductivity (μS cm⁻¹); TDS, total dissolved solids (ppm); Turb, turbidity (cm); DO, dissolved oxygen (mg L⁻¹); OM, organic matter (%); PO₄, phosphate (mg L⁻¹); NO₃, nitrate (mg L⁻¹); NH₄, ammonia (mg L⁻¹); WCaf, water caffeine (μg L⁻¹); SCaf, sediment caffeine (mg kg⁻¹); WZn, water zinc (mg L⁻¹); SZn, sediment zinc (mg kg⁻¹)