Mercury in Malta’s seas exceeds EU parameters

The amount of potentially harmful mercury in Malta’s coastal waters has exceeded the levels laid down in the EU’s Environmental Quality Standards Directive, an assessment carried out by the Malta Environment and Planning Authority (MEPA) has revealed. 

The report is based on samples taken by different monitoring stations at nine coastal bodies during 2015, all of which registered a “poor chemical status” for mercury.

When ingested in seafood in large quantities, mercury can pose a threat to human health, especially to the development of the child in the womb and early in life.

The report was published in the MEPA website in September as one of a series of reports related to Malta’s Water Catchment Management Plan, an EU requirement aimed at improving the status of Malta’s inland and coastal waters.

Mercury in seafood

Another report recently issued by MEPA – related to the implementation of the Marine Strategy Framework Directive – reveals that there were “a few occasions where mercury exceeded the permissible levels” stipulated by EU directives in muscle meat of sampled fresh dogfish, chilled tuna and fresh and frozen swordfish. 

This emerged from tests on samples of fish undertaken by the Department of Environmental Health, which regularly undertakes chemical monitoring of fish and other seafood destined for human consumption. 

In 2011 the Times of Malta had reported that a high concentration of mercury in seafood was the main public health hazard found during “market surveillance” among the 27 cases reported by Malta to the EU’s Rapid Alert System for Food and Feed (RASFF).

Mercury sources to be investigated

One of the measures proposed by the newly published Water Catchment Management Plan is the establishment of a Mercury Management Plan to enable the investigation of possible sources of mercury and find ways of reducing its presence in Maltese waters. 

But Malta has already declared that it will not be able to achieve the parameters set by EU directives before 2021 since it has first to investigate the possible sources of this contaminant, a source which may well be related to industrial activity taking place in other countries.

While confirming Malta’s “poor chemical status” when it comes to mercury, the MEPA assessment describes mercury as Malta’s “only failure” when it comes to the good chemical quality of its coastal waters.

Sediments in eight out of nine water bodies around the Maltese coast did not exceed the permissible amount of mercury. The only one exception being the coastal body in the north east of Malta, which includes St Paul’s Bay and Mellieha.

Various potential sources for the high levels of mercury in Maltese waters are mentioned in the MEPA report. One potential source is the old coal-fired power station which emitted mercury. But this is deemed to be an unlikely source because of low levels of mercury in the sediment except for an area in the north east.

The report states that “transboundary sources” from other countries also need to be investigated, together with untreated sewage formerly released at Xghajra.

How toxic is mercury?

Mercury is a naturally occurring metal found in the general environment even in the absence of human activities.  But fossil fuel combustion, especially that of coal, mining, smelting, waste incineration, fertilizers, fungicides, sewage and other human activities also release mercury in the sea or the air. 

All forms of mercury can enter the body and are potentially toxic to humans, depending on the level consumed.

In the sea mercury is transformed by bacteria into methylmercury which can accumulate in fish and shellfish. 

Large predatory fish like swordfish are more likely to have high levels of mercury as a result of eating many smaller fish that have acquired mercury through the ingestion of plankton.

People may be exposed to mercury in any of its forms but exposure mainly occurs through consumption of fish and shellfish contaminated with methylmercury.

A significant example of mercury exposure affecting public health occurred in Minamata, Japan, between 1932 and 1968, where a factory producing acetic acid discharged waste liquid into Minamata Bay. The discharge included high concentrations of methylmercury. The bay was rich in fish and shellfish, providing the main livelihood for local residents and fishermen from other areas. 

For many years, no one realised that the fish were contaminated with mercury, and that it was causing a strange disease in the local community and in other districts. At least 50,000 people were affected to some extent and more than 2,000 cases of Minamata disease were certified. Minamata disease peaked in the 1950s, with severe cases suffering brain damage, paralysis, incoherent speech and delirium.

What could be the reason for a poor status in mercury?

Prof. Alfred Vella, Chemist

Mercury sources are multiple and controlling the dispersion of this heavy metal is a vexing issue.

Coal-burning, cement making, solid waste incineration, smelting of metals and mining are significant sources of atmospheric mercury, ending up in sea water and eventually in the tissue of fish.

This means that consuming large fish such as tuna and swordfish, that would have been in longer contact with contaminated water than small fish, would present a risk to human health from the effects of mercury.

In the Mediterranean mercury pollution is exacerbated by the presence of cinnabar (mercury ore) deposits in Sicily, which are believed to contribute significantly to pollution of coastal waters.

Mercury and its compounds are used in a wide variety of applications (dental fillings, marine antifouling paints, thermometers, batteries), so municipal solid waste sites would also be heavy sources of mercury and its compounds.

I suspect that for Malta, the most significant sources of mercury would be the landfills: however, our coastal waters are also likely to be subject to effects from trans boundary aerial mercury contamination and trans boundary mercury in the water column.