Regarding group B, all AAs and metabolites from the macrolide and lincosamide class were reported in the river Avon. The macrolide AAs, clarithromycin and erythromycin, were reported at 51 ± 4 ng L - 1 and 24 ± 2 ng L -1 , respectively; and metabolites for both were also observed (desmethyl clarithromycin: 95 ± 32 ng L -1 and desmethyl erythromycin 0.88 ± 0.21 ng L -1 ). Several sulfonamides were also reported, including sulfamethoxazole at 33 ± 4 ng L -1 , which is another CEC that has been widely reported in rivers across the world . Sulfapyridine was another of the sulfonamides detected at 75 ± 2 ng L -1 . Whilst sulfapyridine is a major metabolite of sulfasalazine (prescribed as an inflammatory in human medicines), it is also utilized as an AA in veterinary medicine. It is therefore likely that sulfapyridine could be from human consumption of sulfasalazine but also some potential agricultural run-off; particularly as the river in question has a strong surrounding agricultural presence. It is worth mentioning that many AAs used in veterinary medications do have cross-over with those in humans, so AAs could be from a combination of human and animal sources. In comparison, the Olifants River, flowing through pristine environment of Kruger National Park, had less CECs detected with only 13 CECs from group A above quantifiable limits. Whilst very high levels of metformin were reported in the river Avon, this was not detected in the samples collected from Olifants River, as the human contribution to the river is limited. Caffeine was reported in the highest concentration for SA samples, on average 124 ± 104 ng L -1 across the sampling points. Interestingly, whilst pharmaceuticals detection was low in Olifants River, all human indicators investigated in this study were quantifiable. This is likely due to tourists' presence in Kruger Park camps. Carbamazepine has been identified as one of the most readily found CEC in the environment (aus der , and was found in both rivers at concentrations of 51 ± 1 ng L -1 and 1.23 ± 0.79 ng L -1 for Avon and Olifants River, respectively. Interestingly, carbamazepine's metabolite, carbamazepine 10, 11-epoxide, was detected in higher concentrations on average than its parent compound in the Olifants River (2.72 ± 0.90 ng L -1 ); highlighting the importance of monitoring metabolites alongside parent compounds. Table . Average CECs concentrations in river water from the river Avon (UK) and the Olifants River (SA) ecosystems are often exposed to complex cocktails in their environments. It is recognized that mixtures of chemicals exceeds the risk of individual chemicals , highlighting the importance of monitoring a range of CECs in aquatic environments. Due to the large number of CECs present in the environment it will be impossible to screen and monitor them all. It is also important to define the list of surrogate chemicals for monitoring the those that present the highest risk of eco-toxicity.