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After collecting sediment cores from the Paardenmarkt surroundings, VLIZ researchers started analysing them for a range of sedimentological properties in order to improve our understanding of the environment in which microbes are producing biogenic gases. These sedimentological properties include grain size, water content, organic content, depositional structure, and a set of geophysical characteristics such as density and magnetic susceptibility (a measure of how much a material becomes magnetised in an applied magnetic field).

 

 

 

The dumped munition at the Paardenmarkt contains a large amount of explosive compounds such as 2,4,6-trinitrotoluene (TNT) and chemical warfare agents such as Yperite (mustard gas). If released into the environment, these compounds could be very harmful to the marine ecosystem. In terms of managing these chemicals, the crucial research question is: are they biodegradable?

 

 

 

As TNT is susceptible to microbial degradation, some of the metabolites are on the list of target compounds. Although TNT is well-known as explosive, it is a very toxic compound as well, and some of the degradation products are even more toxic. Moreover, the presence of TNT in the surrounding sediment and water, originally well-hidden in the housing of the explosive device, is an indication of the corrosion or so-called “loss of integrity”, not surprising for metal capsulations in a seawater environment.

 

 

Previous research has shown that the shallow subbottom sediments in the Paardenmarkt area contain a substantial amount of gas, either adsorbed onto sediment particles, dissolved in pore water or as bubbles in pore space. This phenomenon is not exceptional, and can be observed in many shallow seas throughout the world. The source of the gas is believed to be biogenic and a result of bacterial degradation of organic matter. The composition, concentration and fluxes of the gas, and its variability with depositional depth, however, have barely been studied and are poorly understood. Potential interactions between gas and buried munition shells may significantly influence corrosion velocity and the eventual release and spread of toxins into the environment. Hence, it is of great importance to conduct a thorough study of shallow gas in the Paardenmarkt area -in the sediment and water column- to better understand its entailments.

The core task of the Antwerp Maritime Academy Corrosion Team (Amacort) is to assess the present and future (corrosion) condition of the munition at the Paardenmarkt dumpsite. Since we are not allowed to bring any shells to the surface and determine their state by observation and measurement, we have to rely on an experimental approach, statistical analysis and modelling.