There is a lack of data on the occurrence of pharmaceuticals in estuaries worldwide, with little understanding of their temporal and spatial variations globally. Ibuprofen, paracetamol, diclofenac, trimethoprim and citalopram were measured in twelve estuaries in the UK. Initially, these compounds were monitored in the Humber Estuary, where samples were taken every two months over a twelve month period in order to assess their spatial and temporal variations. Ibuprofen was found at some of the highest concentrations ever measured in an estuary globally (18-6297ng l-1), with paracetamol also measured at relatively high concentrations (4-917 ng l-1) in comparison to the other compounds. In terms of spatial distribution, a pattern was observed where the highest concentrations were found at a site at which wastewater is discharged, whilst compound concentrations were often lower upstream and downstream of this site. The downstream profile of pharmaceuticals differed temporally with concentrations highest downstream when input from wastewater effluent was highest. Eleven further estuaries were sampled around the UK in order to put the occurrence of pharmaceuticals in the Humber Estuary into a wider context. Pharmaceutical concentrations in the other estuaries sampled were less than 210 ng l-1 but, again, ibuprofen and paracetamol were found at concentrations higher than other compounds, whereas diclofenac and citalopram were absent in many estuaries. The 2 Humber, which is the receiving environment for the sewage effluent of approximately 20% (13.6 million people) of the population of England, was observed to have the highest overall concentration of pharmaceuticals in contrast to the other estuaries sampled, thereby representing a worst case scenario for pharmaceutical pollution.

Only a small proportion of pharmaceuticals available for commercial use have been monitored in the aquatic environment, and even less is known about the effects on organisms. With thousands of pharmaceuticals in use, it is not feasible to monitor or assess the effects of all of these compounds. Prioritisation schemes allow the ranking of pharmaceuticals based on their potential as environmental contaminants, allowing resources to be appropriately used on those which are most likely to enter the environment and cause greatest harm. Many different types of prioritisation schemes exist in the literature and those utilising predicted environmental concentrations (PECs), the fish plasma model (FPM), critical environmental concentrations (CECs) and acute ecotoxicological data were assessed in the current study using the 50 most prescribed drugs in the UK. PECs were found to be overestimates of mean measured environmental concentrations but mainly underestimations of maximum concentrations. Acute ecological data identified different compounds of concern to the other effects assessments although the FPM and CECs methods were more conservative. These schemes highlighted antidepressants, lipid regulators, antibiotics, antihypertensive compounds and ibuprofen as priority compounds for further study and regulation. Electronic supplementary material The online version of this article (10.1007/s11356-018-3834-9) contains supplementary material, which is available to authorized users.