Exploring temporal trends of pesticides in lake sediments by LC-HRMS
A plethora of natural and synthetic chemicals are produced and consumed worldwide. Once those chemicals are consumed and enter the environment, they can reach natural water systems via waste water treatment plant effluents, agricultural run off or other input sources. In case these contaminants are stable enough, they can potentially reach lakes and sorb to sediments. Pollutants which persist over time in the sediment can serve as indicators of past applications and sometimes reveal input patterns. Since the development and establishment of liquid chromatography- high resolution mass spectrometry (LC-HRMS), the analysis of polar organic pollutants was simplified, even for more complex matrices like sediments. Recently, new strategies like the application of target analysis combined with suspect screening and non-target screening are being used to exploit the cocktail of substances present today. Additionally, the risk for organisms exposed to those chemicals can help to understand the individual effects they inherit. Target and suspect screening analysis was conducted at 5 different sampling points, resulting in the detection of 39 target compounds, including 4 transformation products, 16 plant protection products, 7 biocides and 1 corrosion inhibitor, all detected in the pg\gdw to ng\gdw range. Temporal and spatial patterns for the last few decades of pesticides and their metabolites within the catchment of Lake Greifensee was determined for all detected compounds. Diuron and its transformation product diuron-desmethyl showed an almost identical temporal trend across the sediment core. Further, spatial trends across the lake showed a distinct decrease of concentrations for climbazole and
4-&5-methylbenzotriazole, when looking at the top three sediment layers. Temporal and spatial concentration trends of the detected contaminants were linked to their application within the catchment, resulting in explanations for their presence at different locations. Based on these results, a risk assessment was performed using chronic water quality criteria data converted into sediment quality criteria using partition coefficient between organic carbon in the sediment and water as well as the corresponding sediment concentrations of single substances, which led to a risk quotient. The highest RQs were obtained for irgarol, while the remaining compounds show RQs from 0.02 up to approximately 5. The mixture toxicity showed an insufficient to poor evaluation even when excluding the major contributor irgarol from the calculation. Overall, this work showed that temporal and spatial concentration patterns of pesticides within a sediment core can be linked to the applications in the associated catchment. Further, a rough risk assessment was derived for the detected pesticides which showed a relevant risk evaluation for several single substances and the mixture toxicity of sediment layers.