Assessment of passive sampling for the monitoring of explosive residues in surface water

Between 1920 and 1967, approximately 8’200 tons of ammunition waste were dumped into several Swiss lakes. Previous studies based on grab sampling revealed traces of HMX, RDX and PETN in the water column of three studied lakes; however, these researches showed that the ammunition waste at the lake bottom was likely not involved in that contamination. On the contrary, external sources (tributaries contaminated by hot spots) might be the main cause. The goal of this study is to assess whether explosive monitoring by passive sampling is feasible in the affected lakes and rivers, and whether integrative sampling confirms results obtained by grab sampling. As a first step, two kinds of passive samplers (adsorbent covered by a diffusion membrane) were calibrated in a channel system supplied with continuously refreshed lake water spiked with HMX, RDX, PETN and six nitroaromatics (including TNT). Exposure parameters in the system were kept as close as possible to the ones expected in the studied lakes. Sampling rate (RS) of HMX, RDX and PETN were in the range of 30 to 130 mL day 1. RS of nitroaromatics were up to 10 times lower because of the high accumulation of these compounds in the diffusion membrane. This latter was thus used as receiving phase for nitroaromatics, leading to Rs higher than 150 mL day 1. As a second step, the samplers were deployed on lake-bottom sediments (200m depth) with the aid of a remotely operated vehicle. Samplers were also deployed in rivers by fixing iron bars in the riverbed. In lakes, HMX, RDX and PETN were found at very low concentrations (