OR/18/052 Conclusions and recommendations

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Lapworth, D J, Crane, E J, Stuart, M E, Talbot, J C, Besien, T, and Civil, W. 2018. Micro-organic contaminants in groundwater in England: summary results from the Environment Agency LC-MS and GC-MS screening data. British Geological Survey Internal Report, OR/18/052.

This is the first study to assess robust summary statistics, using non-detects methods, for top 50 compounds for groundwater samples in England analysed by the target screening by GC-MS and LC-MS. Due to the high proportion of censored results in this type of data set, this approach is essential for future assessments to estimate summary statistics.

Targeted screening methods are particularly useful for surveillance purposes, i.e. assessing the occurrence of a broad range of emerging substances in groundwater, and are being (and should to continue to be) used to help prioritise ongoing monitoring activates in England and elsewhere in Europe.

The dominance of different groups of compounds differs for the GC-MS and LC-MS screen, and this reflects to a large extent the methodological differences, however, there are several frequently detected groups of compounds that are present in both suites including pesticides and pharmaceuticals. Five pesticides were detected in the top 50 for both screens.

The GC-MS results for the top 50 compounds are characterised by low frequency of detection (up to 1–10%), however max concentrations are high and are typically at 10–100 mg/L concentrations. LC-MS results for the top 50 compounds are characterised by much higher frequency of detections (10–65%), however, maximum concentrations are typically at the sub mg/L concentrations. This difference to a large extent reflects the much lower LOD for the LC-MS method compared to the GC-MS method, and possibly the more limited spatial data coverage for the LC-MS method.

Spatially coherent results for many groups of compounds are found and can be related to different land use and/or sources of pollution as well as hydrogeological characteristics of aquifers in England, i.e. the degree of aquifer confinement as well as more karstic features in parts of the Chalk in England.

Pesticides, halogenated solvents and industrial compounds dominate the top 50 compounds for both LC-MS and GG/MS results, however, several emerging substances such as pharmaceuticals are represented in the top 50 in terms of frequency of detections and concentrations.

There is a much more limited LC-MS database so far compared to GC-MS data. The high frequency of detects are noteworthy, particularly for the LC-MS data set, >10% for top 50 compounds. This suggests that it would be beneficial to extend the spatial and temporal coverage of groundwater samples analysed in England, as well as Wales, Scotland and NI using this type of targeted approach.

A key priority for future work is assessing the potential risk to groundwater and groundwater dependant (eco)systems from hazardous substances.

Further work should be prioritised to assess the results for particular groups of emerging substances with high persistence and hazardous properties such as perfluorinated substances, pharmaceuticals — particularly anti-microbial substances, as well as neonicotinoids.

Further work to compare targeted screen data with results from dedicated suites, where there is an overlap in substances, is needed to fully understand the utility of the targeted screen data.