Along the Belgian coast, a narrow submerged sand-bank called ‘Paardenmarkt’ (Horse Market) extends from the Port of Zeebrugge to the Dutch border. Few people are aware that this sand-bank is one of the largest World War I ammunition dump sites in the North Sea. In fact, the figures are perplexing: at least 35.000 tons of German ammunition, at least a third of which are chemical shells, located just at about 500 meters off the Knokke-Heist beach, a main touristic attraction. Only since 1988, the area has been marked on nautical charts. The official sea map shows an average depth of from 1.2 to at the most 4 meters. Five dotted lines are drawn on this sand-bank that form a pentagon. Neither fishing nor anchoring are allowed in this two square kilometers area. It is also forbidden for swimmers, divers and surfers. However, there are no warning signs and the area is only indicated by a few orange buoys.

Chemical weapons dumped at sea: an international problem

The Paardenmarkt ammunition dump site is far from unique. War creates an enormous amount of waste, which has to be disposed of somehow. Military waste is generally toxic and costly to dispose of safely, so the solution has usually been to dump it, and the sea seemed to be a convenient place. In the decades following World War I, and even more so after World War II, the major powers disposed of massive quantities of captured, damaged, and obsolete chemical warfare material by dumping them in the seas and oceans. Some dumping operations were carefully undertaken, including the keeping of records of where the dumping occurred, a listing of the material that was dumped, and the quantities of dumped material. Other dumping was done haphazardly with no or minimal records being written and kept. The total quantity of chemical warfare material discarded at sea will never be known precisely, but most likely is on the order of several hundreds of thousands of tons. The American Center for Nonproliferation Studies (CNS) has been able to identify at least 127 dumping sites globally.

The Paardenmarkt dumping

Paardenmarkt: A Toxic Legacy of the Great WarVery large amounts of explosives were left behind all over Belgium after the Great War. Their collection and preliminary storage in ammunition depots created extremely dangerous situations, resulting in many fatal accidents. As the situation gradually became intolerable and the disposal of ammunition on land still involved too many risks, the Belgian government decided to dump the ammunition in sea in late 1919. This received hardly any attention and was soon forgotten. Even today, there still is a great deal of uncertainty about the dumping operations at Paardenmarkt. No reports or hard evidence has been available so far. The Belgian interwar military archives, which were located in Moscow until recently, may shed some light on the matter in the future.

Nobody knows exactly how much ammunition has been dumped at Paardenmarkt. Most estimates are in the 35.000 tonne range. For the most part unused German ammunition, usually packed in wooden crates. So far, it has been generally assumed that about one third of the dumped ammunition consists of chemical warfare material. However, there are indications suggesting that this share may be much more. It comprises mustard gas, and other WW I chemical warfare agents, like chloropicrin, phosgene, diphosgene and (extremely toxic) arsenic compounds, so-called 'Clark'. The ratio between these substances is unknown, but in all probability mustard gas shells do not exceed one third of the chemical ammunition at Paardenmarkt.

A toxic legacy

In the early 70s, ammunition was found during dredging operations east of the Port of Zeebrugge. Extensive investigations revealed a number of chemical shells on 17 different sites on or just below the seabed. Hence, the Paardenmarkt dumping site was saved from oblivion. The first exploratory seismic and magnetic investigation of the dump site was conducted in 1988. By then, the shells had been largely covered by a layer of sediment, as the current pattern had radically changed since the extension of the Port of Zeebrugge. This had resulted in significant sedimentation in the dump area. Recent topographical studies seem to indicate a stagnation in this process.

So far it is unclear what the evolution of the site will be over the coming years. The condition of the shells brought to the surface in 1972 was ‘remarkably’ good. The low-oxygen environment in the seabed had slowed down corrosion to a considerable extent. The current state of the shells is unknown since no ammunition has been brought to the surface ever since. I seems plausible that the ammunition has not corroded very much at this moment, but we should keep in mind that even slow corrosion cannot prevent the shells from leaking in the long run.

Corrosion of the shells will cause the chemical agents to be released only very slowly, so that the chemicals are very likely to get diluted. Most chemical agents will probably not pose much of a threat to the marine environment or human life ashore. There are two exceptions: ‘Clark’ and mustard gas, which are both extremely toxic and break down only very slowly. Furthermore, their degradation products are often equally toxic as well. Due to the present sediment cover it is unlikely that shells will be washed ashore. The biggest threat seems to come from commercial fishing in the immediate area and from possible shipping disasters, as Paardenmarkt is located near one of the busiest ports of Northwestern Europe, within a stone’s throw of the principal shipping routes.

Long-term strategy

Salvaging the ammunition seems technically feasible, but that is a very costly and hazardous undertaking. If there were indications that the ammunition would surface partial or complete containment of the site could be considered. However, there are no indications at the moment that there is immediate danger. Consequently, the best option is to let the Paardenmarkt dump site be. A thorough long-term strategy for the dump site will be of vital importance. In view of the short distance to the coast and the shallow water depth, frequent monitoring of the area remains highly important.

Current Belgian government policy provides for this frequent monitoring. The country fully meets the requirements of current international agreements: do not touch anything, but keep monitoring. Belgium has ratified the Chemical Weapons Convention, which entered into force in 1997, but this convention is silent with respect to the remediation of chemical agents and munitions dumped at sea prior to 1972. Nevertheless, the countries that in the past chose to take the easy way out by disposing their chemical warfare material by ocean dumping are now realizing the unpleasant fact that this material, although out of sight, is not out of mind because it presents threats to public health and the environment as discussed above.

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