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Ece - Pollutant and Risk of Pollution

The phosphoric acid (H3PO4) transported by the Ece came from the OCP (Office chérifien des phosphates) one of the world leaders in crude phosphate production, exporting crude phosphate, phosphoric acid and solid fertilisers to around 40 different countries. The phosphoric acid onboard the Ece was an acid with a low concentration of heavy metals.

Phosphoric acid is used in the manufacture of fertiliser (superphosphates), the protection of metals, the pharmaceutical industry, water treatment, cleaning, paint and certain food products.

Phosphoric acid is one of the most bulk transported basic chemicals. Phosphoric acid holds ninth position on the American coastguards' list of the most spilled chemicals.

Cedre edited an intervention and response guide about the risk of phosphoric acid spills in their series of chemical mini guides, published in the early 1990s (French only). This document provides information on the evolution of the product in the case of an accidental spill in water. It includes accidental spill scenarios in the sea, in rivers and in lakes, with recommendations about intervention (personal safety) and pollution response.

In this incident, no major spill of fuel or cargo was observed. However iridescences of hydrocarbon surfaced and exploration of the wreck may confirm the hyphothesis that phosphoric acid may seep out via cracks in the hull, piping, or tank vents. The leakage could reach 25 m³/hour. There were therefore no major pollution risks, but a risk of progressive leakage remained. The product was, as far as we know, colourless or nearly colourless, with a refractive index close to that of water. Leaks were therefore difficult to detect by video observation.

Phosphoric acid is, like all acids, a corrosive liquid. It is non volatile and does not produce vapour. It has a higher density than that of seawater (density of 1.53 at 20 °C for a solution of ~50% P2O5 ou ~75% H3PO4) and therefore sinks when spilled. It is totally soluble in water and does not build up in the food chain.

The main risk for humans is essential linked to contact with the skin or mucus membranes, causing irritation or even burns in the case of prolonged contact with a concentrated solution. The same risk applies to marine animals. Phosphoric acid leaking from the wreck would mix with water and acidify the immediate surroundings. Once the leaking stopped, the neutralising power from the seawater would quickly raise the pH back to its original value (around 8) in the affected zone. The environmental impact would be too temporary and localised to be quantifiable.

The GESAMP, a group of experts selected by OMI (the International Maritime Organisation) to study the scientific aspects of pollution at sea, gave the pollution 0, on a scale of 0 to 5, for persistance in the environment, 1, on a scale of 0 to 6, for acute aquatic toxicity and 3, on a scale of 0 to 4, for toxicity to aquatic mammals due to contact ot ingestion.

The 1973 MARPOL convention divided transported products into 4 categories (A, B, C, D), according to the risks they involved for marine resources, human health and the accreditation of the sites. Category D is the classification for the least dangerous products. This includes harmful liquids which, when spilled in water, present a "discernible risk for marine resources and human health or may slightly harm the site or other legitimate uses of the sea and therefore lead to certain precautionary measures concerning the conditions of use".

There was therefore no immediate major pollution risk from the phosphoric acid. However the question which came to light, as with all wrecks, was the question of whether to remove the potential pollutants (acid and fuel) trapped in the wreck.

To help decide what observation operations should be carried out and what action should be taken, a series of dilution tests in Cedre's laboratory were carried out using coloured phosphoric acid and water acidity measurements. The first results showed that the acid spread out at the bottom, before diluting in a matter of a few minutes without any currents. When strong currents were simulated, the acid diluted rapidly as soon as it touched the water. It progressively decomposed into hydrogen ions (H+), responsible for the decrease in pH, and into phosphate ions (PO4--).

Cedre was asked about the possible fertilising effect of the phosphate ions, which could lead to an anarchical development of green algae in the event of a major spill. This question is IFREMER's domain. However in this case the pollution did not involve a major spill and the availability of phosphate ions in February is not a key factor in the developmant of green algae.



Photo source: Cedre
Last update: April 2006