Abstract
Temporal trends of industrial organic contaminants can show how environmental burdens respond to changes in production, regulation, and other anthropogenic and environmental factors. Numerous studies have documented such trends from the Northern Hemisphere, while there is very limited data in the literature from sub-Saharan Africa. We hypothesized that the temporal trends of legacy and contemporary industrial contaminants in sub-Saharan Africa could greatly differ from the regions in which many of these chemicals were initially produced and more extensively used. For this purpose, a dated sediment core covering six decades from a floodplain system in urban Dar es Salaam, Tanzania, was analysed. The samples were analysed for selected legacy persistent organic pollutants (POPs) [polychlorinated biphenyls (PCBs) and polybrominated biphenyl ethers (PBDEs)] and chemicals of emerging concern (CECs) [alternative brominated flame retardants (aBFRs), chlorinated paraffins (CPs), and dechloranes]. All groups of chemicals showed a steep increase in concentrations towards the uppermost sediment layers reflecting the more recent years. Concentrations of the individual compound groups in surface sediment were found in the order CPs >> aBFRs ∼ ∑25PBDEs > dechloranes ∼ ∑32PCBs. Time trends for the individual compounds and compound groups differed, with ∑32PCBs showing presence in sediments since at least the early 1960s, while some CECs first occurred in sediments corresponding to the last decade. Investigations into potential drivers for the observed trends showed that socioeconomic factors related to growth in population, economy, and waste generation have contributed to increasing concentrations of PBDEs, aBFRs, CPs, and Dechlorane Plus. Further monitoring of temporal trends of industrial organic contaminants in urban areas in the Global South is recommended.
Highlights
Legacy persistent organic pollutants (POPs), like polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), have physicochemical properties which makes them persistent, bioaccumulative, toxic, and have a potential for long-range environmental transport
The trend in organic matter (OM) content is not likely to be the main driver for the observed temporal trends. These findings suggest that the increasing trends in legacy POPs and chemicals of emerging concern (CECs) in sediment layers corresponding to the late 2010s are mainly a consequence of increased primary emissions from products and waste in connection with the rapid socioeconomic development in the region
This study showed that concentrations of both legacy POPs and CECs, chlorinated paraffins (CPs) and DBDPE, have increased notably in sediment layers corresponding to the late 2010s
Summary
Legacy persistent organic pollutants (POPs), like polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), have physicochemical properties which makes them persistent, bioaccumulative, toxic, and have a potential for long-range environmental transport. International regulation ensured an end to production of PCBs by the 1990s and PBDEs by the 2010s (Breivik et al, 2002; UNEP, 2017; Abbasi et al, 2019), while the CECs largely remain unregulated at an international level and production remains high or is increasing (Glüge et al, 2016; Xiong et al, 2019; Hansen et al, 2020). Both legacy POPs and CECs have been and are still used extensively in consumer products with different functions and user lifetimes. Emissions to the environment may occur during production, and during use of products containing legacy POPs and CECs, and from their disposal and recycling when these products reach their end of life
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