SEASONAL VARIATIONS IN THE OCCURRENCE AND DISTRIBUTION OF PHARMACEUTICALS IN THE ODO-IYA ALARO RIVER, LAGOS STATE SOUTHWEST NIGERIA

Abstract

The occurrence and seasonal variations of 37 pharmaceuticals belonging to 19 therapeutic
classes in a sewage treatment plant (Alausa STP) and surface water in Lagos, Southwest
Nigeria was investigated. Water samples were collected quarterly from April 2017 to January
2018. Among the targeted analytes, 26 compounds were detected. The ten most frequently
detected compounds across the sampling locations were fexofenadine, carbamazepine,
paracetamol, metformin, diazepam, cimetidine, codeine, sulfamethoxazole, atenolol and
trimethoprim. The highest concentrations was observed for antibiotic and analgesic:
sulfamethoxazole (129474 ngL-1
) had the highest maximum concentration followed by
paracetamol (111374 ngL-1
). Over all, paracetamol had the highest mean concentration
(18178 ngL-1
) while sulfamethoxazole had the second highest mean concentration (11160
ngL-1
). Cimetidine had the third highest maximum concentration of (95689 ngL-1
) and mean
concentration (10458 ngL-1
). There were no specific spatial trends observed in this
investigation and concentrations of pharmaceuticals in the study locations were high
throughout the catchment revealing that there are potentially many contributing sites. So
there were statistically significant differences between the different site categories
(Pharmaceutical manufacturing sites (PME), Alausa STP site (SE), Semi- Urban and Urban
sites (GLM: χ2
(3) = 883.32, p <0.001). There are seasonal variations in the number of
analytes detected in each sampling station. The mean and median concentrations of all the
pharmaceuticals detected in the Odo-Iya Alaro River are extremely higher in the peak of the
dry season than any other season. Hence, there were statistically significant differences
between the dry season, peak of dry season, the wet season and peak of the wet season
((GLM: χ
2
(3) = 8.63), p<0.001). More pharmaceuticals were detected in the peak of the wet
season (22) than the other seasons. 17 analytes were each found in the wet and dry seasons
while 16 pharmaceuticals were detected at the peak of the dry season. Pharmaceuticals are
indispensable to human health although their usage and discharge into the aquatic
environment may lead to ecological problems and antibiotic resistance. This investigation
showed that pharmaceutical pollution of the aquatic environment is a major challenge in
Nigeria and management efforts are needed to address this issue