Figure 2.1 Selected properties of pharmaceuticals.

2.1.2 Reported or Potential Metabolites and/or Transformation Products

During the last two decades many studies have been performed in order to evaluate their sources, occurrence, fate and effects on human health and other organisms [1, 2, 4–10]. Many different sources of their presence have been pointed out, including their inefficient removal in the wastewater treatment plants, husbandry, aquacultures, inappropriate drugs disposal, pharmaceutical industry etc. [1, 2, 4–10]. In general, after their application in human medicine or in veterinary use, pharmaceuticals undergo different processes leading to the excretion of their metabolites, which should usually be less active and more polar than native forms [1, 2]. In some cases, however, metabolism may lead to more active compounds, such as metabolites of carbamazepine, diclofenac, acetaminophen [11–14] or tamoxifen (hydroxyl-desmethyltamoxifen and 4-hydroxytamoxifen), which (these last two) can be up to 100 times more potent and active than the parent compound [15]. This in turn leads to the occurrence in the environment not only of their parent forms but also of their metabolites [11–14, 16]. However, it must also be taken into account that pharmaceuticals and their metabolites may undergo many different transformation processes in the waste water treatment plant, drinking water treatment processes or being present in the environment (such as hydrolysis, photodegradation and biodegradation), which can also lead to the production of many new additional degradation products of pharmaceuticals [11]. For example, glucuronide- and sulfate-conjugates (phase II metabolites) have been observed to be readily deconjugated during biological wastewater treatment to the active form of the pharmaceutical or its corresponding phase I metabolite [11]. All of these compounds, including metabolites and degradation products, are usually referred to as “transformation products (TPs)” in the scientific literature [11, 12, 14].

It must also be highlighted that the environmental fate of TPs can be different from the parent compound, meaning that the environmental compartments that are exposed to the parent compound may not be exposed to a TP [11]. While some of the TPs are known and have already been detected in the aquatic environment in concentrations higher than their parent compounds, the majority of TPs present there have not been identified yet [11]. The current state of knowledge on the presence of TPs in the environment has been quite recently presented [11–14, 16]. Based on these data, selected TPs have been presented in Table 2.1. Taking into consideration these data, it might be concluded that human and the environment are exposed to a highly variable and still not fully known cocktail of pharmaceuticals and their TPs.

2.1.3 Occurrence

In 2019 the German Environmental Agency (Umwelt Bundesamt) published the Final report on The database “Pharmaceuticals in the Environment” – Update and new analysis (Texte 67/2019). This is a summary of the state of knowledge on this problem [17]. It is based on the data published all over the world in 1,519 publications from peer-reviewed journals and 240 review papers from 1987 up to 2016. The analysis of these data revealed that pharmaceuticals and their transformation products have been detected in 75 countries, and in 54 different matrices worldwide. It was proved that 771 active pharmaceutical substances and their TPs have been measured globally, and 596 substances in the European Union. It must also be noted that