Abstract
The occurrence of emerging organic contaminants within the aquatic environment in Africa is currently unknown. This study provides early insights by characterising a broad range of emerging organic contaminants (n > 1000) in groundwater sources in Kabwe, Zambia. Groundwater samples were obtained during both the dry and wet seasons from a selection of deep boreholes and shallow wells completed within the bedrock and overlying superficial aquifers, respectively. Groundwater sources were distributed across the city to encompass peri-urban, lower cost housing, higher cost housing, and industrial land uses. The insect repellent DEET was ubiquitous within groundwater at concentrations up to 1.8 μg/L. Other compounds (n = 26) were detected in less than 15% of the sources and included the bactericide triclosan (up to 0.03 μg/L), chlorination by-products – trihalomethanes (up to 50 μg/L), and the surfactant 2,4,7,9-tetramethyl-5-decyne-4,7-diol (up to 0.6 μg/L). Emerging contaminants were most prevalent in shallow wells sited in low cost housing areas. This is attributed to localised vulnerability associated with inadequate well protection, sanitation, and household waste disposal. The five-fold increase in median DEET concentration following the onset of the seasonal rains highlights that more mobile compounds can rapidly migrate from the surface to the aquifer suggesting the aquifer is more vulnerable than previously considered. Furthermore it suggests DEET is potentially useful as a wastewater tracer in Africa. There was a general absence of personal care products, life-style compounds, and pharmaceuticals which are commonly detected in the aquatic environment in the developed world. This perhaps reflects some degree of attenuation within the subsurface, but could also be a result of the current limited use of products containing emerging contaminants by locals due to unaffordability and unavailability. As development and population increases in Africa, it is likely a wider-range of emerging contaminants will be released into the environment.
Highlights
Organic compounds previously not known to be significant in freshwater, in terms of distribution and/or concentration, are being more widely detected as analytical techniques improve (Farre et al, 2012)
There were relatively few detections, presumably since Kabwe is not industrialised on any scale. This is the first study to provide an insight into the occurrence of a broad range of emerging contaminants (ECs) in the aquatic environment in Africa, with a focus on groundwater beneath Kabwe, Zambia
A total of 27 compounds were identified including the omnipresent DEET, at a median concentration greater than that observed in other groundwater studies across the globe
Summary
Organic compounds previously not known to be significant in freshwater, in terms of distribution and/or concentration, are being more widely detected as analytical techniques improve (Farre et al, 2012) These compounds, which have the potential to cause known or suspected adverse ecological or human health effects, are often collectively referred to as emerging contaminants (ECs). ECs include newly synthesised substances as well as ones that have long been present in the environment but whose presence and significance are only being elucidated (Daughton, 2004) They include a wide array of different compounds and their transformation products: pharmaceuticals, personal care products, pesticides, veterinary products, industrial compounds/by-products, food additives, and engineered nano-materials (Murray et al, 2010; Pal et al, 2010; Schriks et al, 2010; Hughes et al, 2012; Lapworth et al, 2012; Postigo and Barcelo, 2014). When used in combination with groundwater residence time tracers, such as chlorofluorocarbons (CFCs) or sulphur hexafluoride (SF6), these could be powerful techniques for understanding contaminant processes and groundwater vulnerability
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