Over the past twenty years or more, there has been increasing interest in the occurrence and effects of pharmaceuticals in the aquatic environment, particularly in Europe and North America. While the understanding of their occurrence is now relatively well understood in these parts of the world there remains a scarcity of data from many African countries. Thousands of pharmaceuticals are in use worldwide and the effects of these drugs, especially at environmentally relevant concentrations, are still unknown. Moreover, few ecotoxicity test species are recommended by Organisation for Economic Co-operation and Development (OECD) and so a dearth of information exists for many organisms. This PhD was thus carried out to determine the occurrence of pharmaceuticals in Africa rivers (Nigeria) and to seek to improve the understanding of the effects of prolong low-level exposure of Gammarus pulex and Aquaticus aquaticus to pharmaceutical contamination.
The occurrence of 37 pharmaceuticals belonging to 19 therapeutic classes was studied in surface water and effluent in Lagos State, Southwest Nigeria. Samples were collected quarterly between April 2017 and March 2018 from 22 sites, and 27 compounds were detected at least once, many in the microgram per litre range. Maximum concentrations for a range of compounds including sulfamethoxazole, paracetamol, cimetidine, fexofenadine, carbamazepine, metformin and diazepam ranged from 75 g L-1 to 129.5 g L-1. Mean concentrations for 13 compounds were also in the g L-1 order. These values are several orders of magnitude higher than most studies of pharmaceutical occurrence in Europe and North America but similar to some other peak concentrations measured in developing countries such as China and India. Multiple pharmaceutical compounds were found at all monitoring sites and there were no clear spatial patterns. This may indicate that a variety of sources exist throughout the catchment, revealing that there are potentially many contributing sites. Studies in Europe and the US have found that sewage treatment plants (STPs) are the major source of pharmaceutical pollution (Hughes et al., 2013) but in the developing world it seems that there are a greater range of sources contributing to loads in rivers. These may include STPs, pharmaceutical manufacturing plants, urban waste collection areas and disposal of effluent by vacuum trucks. Seasonal trends in the data were complex with some compounds such as fexofenadine, carbamazepine, paracetamol, cimetidine, metformin and sulfamethoxazole being found at higher concentrations in the dry season and conversely, others such as paracetamol, sulfamethoxazole, tramadol and metformin being greater during the wet period. Seasonal usage is unlikely to explain this phenomenon as many compounds would be used equally over the year to treat persistent illnesses, e.g. carbamazepine and metformin. It may be that the multiple sources of pharmaceuticals in the catchment results in this complex picture with some that are associated with continuous effluent discharges (e.g. from STPs and manufacturing facilities) being diluted in the wet season but other sources (e.g. urban waste sites) which see pollutants mobilised in periods of rainfall.
Effect studies focused on the biological effects of erythromycin, diclofenac, ibuprofen and their mixtures on the growth, feeding and mortality of aquatic macro-invertebrates (Gammarus pulex and Asellus aquaticus). It was found that for erythromycin and diclofenac, growth rate decreased, feed intake was reduced, and mortality was significant for G. pulex but not significant for A. aquaticus. For ibuprofen, there was, however, no effect for both test species. For mixtures of erythromycin, diclofenac and ibuprofen growth rate decreased, feed intake was reduced but mortality was not significant for both G. pulex and A. aquaticus. The effects of these pharmaceuticals on the growth, feeding and mortality of the test animals were a result of the actions of the drugs and not attributed to a more general stress response. Although pharmaceuticals are indispensable to human health their usage and discharge to the aquatic environment coupled with their ecotoxicity to aquatic life may lead to ecological problems in the near future. Furthermore, this research confirms the suitability of the test species (G. pulex and A. aquaticus) as ecotoxicological test species that is both amenable to laboratory culture and sufficiently sensitive to provide reliable quantification of environmental risk.
