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No. 174: Environmental assessments of sea dumped chemical warfare agents

Hans Sanderson, Patrik Fauser. 2015. Environmental assessments of sea dumped chemical warfare agents. Aarhus University, DCE – Danish Centre for Environment and Energy, 116 pp. Scientific Report from DCE – Danish Centre for Environment and Energy No. 174 http://dce2.au.dk/pub/SR174.pdf


Following the end of the Second World War Germanys approximately 65,000 tonnes stockpiled Chemical Warfare Agent (CWA) munitions were ordered by the allied forces to be destroyed during the second half of 1947 as a result of the Potsdam Conferences. The Russian forces undertook the major part of this task during the summer of 1947 with German barges and crews. The Bornholm basin in the Baltic Sea received more than half of Germanys CWA arsenal with dumping of approximately 11,000 tonnes active CWA chemical substances. There are significant uncertainties and confounding factors to consider when assessing the risk of CWA towards human and environmental health.

Here we assess the potential added indirect human and fish community risks associated with construction of the planned Nord Stream gas pipelines along the S-route in the risk area 3 in the Bornholm basin was modelled using conservative screening level risk methods and assumptions in a desk-top assessment. Risk may arise from perturbation of sediment containing traces of chemical warfare agents (CWA) dumped after the Second World War. Two different risk scenarios (A & B) were developed. In scenario A we assumed a homogeneous distribution of the entire available CWA across the entire area around Bornholm.

Subsequently we found based on measured data that the arsenicals measured along the route do not correlate with total CWA concentrations (r2 = 0.01). Therefore the predominant part of the arsenic in the sediment has other anthropogenic and potential natural sources than CWA. The fish community risk relative to the toxic forms of As is generally low along the S-route. The total As levels found along the S-route are close to the background levels for the Bornholm Deep. Mean arsenic concentrations in sediments range from 5 to 3000 mg/kg, with the higher levels occurring in contaminated areas (IPCS, 2001). The observed average sediment concentration, averaging at 11 mg/kg DM, found by Fauser et al. (2013) is comparable to the average total As in the Bornholm Deep of approximately 20 mg/kg reported by Garnaga et al. (2006). Arsenic concentrations in sediment in the Baltic Sea are quite variable and primarily dependent on the geology and grain size (Emelyanov, 1996).

Further, the statistical analysis suggests that biological abundance is better described by physical parameters than As and CWA contamination levels. There are no strong correlations between the CWA and the biological observations. The ratio between CWA munitions above and below the sediment is unknown; hence special caution should be exercised in connection with laying anchors, since these sink furthest into the sediment and may disturb buried munitions shells when installing the pipelines.

In summary from 2008-2012, re-suspension of CWA-contaminated sediment will cause a maximum added risk corresponding to a risk quotient of 0.0001 at the highest risk location (CWA 22.81) (in comparison to the max. RQs found in 2010 of 0.00107, and 0.003 in 2011), towards the fish community. Compared to the total risk quotient from the prevailing quasi steady-state CWA residues concentrations in the pore water of up to 0.0037 (0.025 in 2010; and 0.17 in 2011), this indicates no significant additional risk from pipe laying activities.

We moreover, collected qualitative data from interviews with local experts and reviewed the historical archives covering the dumping, these suggested low current risk.