Suspect and non-targeted screening of chemical pollutants in Botswana's aquatic environments

Chemical pollution in the aquatic systems of Botswana has been sparsely studied despite its potential ecological importance. Here, we perform a study of water samples collected from 13 locations distributed across Botswana to obtain the first overview of the nature and distribution of chemical contaminants across the country's aquatic environment. High resolution mass spectrometry was applied using non-targeted and suspect screening methods to qualitatively analyse samples. A total of 114 contaminants of emerging concern (CECs) were identified including 68 (59.6 %) pharmaceuticals and pharmaceutical metabolites; 16 (14.2 %) pesticides; 13 (11.4 %) psychoactive compounds and metabolites; 11 (9.7 %) industrial chemicals and intermediates and lastly, 5 (4.4 %) personal care products. Allopurinol, 3,4-dimethylmethcathinone, and diazolidinyl urea represented the most commonly detected pharmaceutical, psychoactive drug and personal care product, respectively. The pesticide dodemorph and three industrial chemicals (stearamide, pthalic acid and bis(2-ethylhexyl) phthalate) were detected in all samples obtained. 90 CECs were detected in receiving water (from 7 sample locations), 75 in wastewater (from 3 sample locations) and 60 in surface water (from 9 sample locations). Of the compounds detected, only 8 had been identified in environmental samples acquired in Botswana previously. We discuss the variations in the nature and frequency of chemical pollutants detected in this work in a geographical context. The results indicate that Botswana's aquatic systems are subject to pollution, despite wastewater treatment and that in order to mitigate potentially harmful effects on both human and aquatic ecosystems, more investigations are required to correctly identify, track and tackle the sources of pollution.