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No. 302: Prospective added environmental risk assessment from re-suspension of chemical warfare agents following the installation of the Nord Stream 2 pipelines

Sanderson, H. & Fauser, P. 2019. Prospective added environmental risk assessment from re-suspension of chemical warfare agents following the installation of the Nord Stream 2 pipelines. Nord Stream 2 added CWA environmental risk assessment. Aarhus University, DCE – Danish Centre for Environment and Energy, 122 pp. Scientific Report No. 302 http://dce2.au.dk/pub/SR302.pdf

Summary

The sampling campaigns included in this report are the latest of the Nord Stream (2008–2012) and Nord Stream 2 (2015–2016) campaigns and cover the planned extension of the Nord Stream pipeline system. The samplings were conducted in October 2015 and March 2016. They comprised the preferred route (ES) and two alternative pipeline route options (FS and RA) that were developed based on bathymetric and geological data together and other factors (DHI, 2015). Two pipeline paths (ES and FS) are outside the dumpsite and one (RA) is going through the secondary dumpsite on a number of sampling stations. 17 sediment samples from a total of 121 were therefore taken within the known dump site where there are currently activity restrictions of e.g. anchoring and fishing.

Improved analytical methods resulted in higher detection frequencies and concentrations found than during the previous investigations (Sanderson et al., 2014). It is notable that novel compounds were detected, i.e. cyclic dissipation products of mustard gas as well as parent mustard gas. The former are unknown to the field of environmental toxicology and risk assessment. Hence, an investigation of their environmental toxicity following OECD and GLP test guidelines were commissioned. The most hazardous compound 1-Oxa-4,5-dithiepane was used in chronic tests for algae and daphnia, respectively, to derive an assessment factor of 500 resulting in a PNEC of 0.0165 mg/L.

The risk quotient (RQ) for single chemical warfare agents (CWAs) and for the sum of CWAs was calculated as the CWA concentration divided by the toxicity threshold value. The risk from the inherent, i.e. present and undisturbed CWA concentrations in sediment and bulk water, were quantified together with the added risk from sediment agitation in different distances from the pipeline. Added sediment concentrations in the lower bulk water layer arise from sweeping that occurs along the entire pipeline on all three routes, trenching that occurs at three sections and involves only some sampling stations, and rock placement that takes place near one sampling station.

In summary, the mean and maximum added RQs from pipeline installation for the sum of chemicals are below one (< 0.003) for all three routes indicating a negligible environmental risk, and the two routes ES and RA have approximately the same maximum added RQs, whereas the value for route FS is a factor of approximately 20 lower. Clearly, the route RA with the highest single finds of parent and degradation CWA is less favourable relative the ES route from a CWA exposure point of view. Hence, in conclusion the FS or ES route is recommended from a CWA exposure avoidance perspective.