Prediction of environmental concentrations of glucocorticoids: The River Thames, UK, as an example

Synthetic glucocorticoids (GCs) are consumed in large amounts as anti-inflammatory and immunosuppressive drugs worldwide. Based on what has been learnt from studies of other human pharmaceuticals, they are likely to be present in the aquatic environment. However, to date, information on the environmental concentrations of GCs is very limited. The situation is complicated by the fact that a considerable number of GCs are in everyday use in most developed countries. Hence, obtaining a full picture of GC concentrations in the aquatic environment using the traditional analytical chemistry approach would be time-consuming and expensive. Thus, we took a modelling approach to predict the total environmental concentration of all synthetic GCs (consisting of 28 individual GCs) in the River Thames, as a first step in risk assessment of these drugs. Using reliable data on consumption, the LF2000-WQX model predicts mean concentrations up to 30ng/L of total GCs in surface water as a best case scenario when the lowest excretion and highest removal rates in sewage treatment works were used, whereas mean concentrations up to 850ng/L were predicted when the highest excretion and lowest removal rates are considered. We also present the 10th and 90th percentile concentrations (which indicate the likely range of concentrations seen from high flow to low flow conditions in the river) of the highest and lowest consumed GCs, to show the spatial and temporal variations of the concentrations of individual GCs. These data probably provide reliable estimates of the likely range of concentrations of GCs in a typical river impacted by effluent from many sewage treatment plants. Results also identify the hot spots where field studies on fish could be focused. To determine if aquatic organisms face any threat from GCs, laboratory toxicity studies should be conducted using concentrations similar to those reported here.