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Apr-2017

The mercury threat is real

Mercury has been elevated to the status of a pollutant of global concern owing to some of its unique toxic properties which pose environmental and health risks.

Roberto Parola and Mike Hayes
Linde HiQ
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Article Summary
An indestructible chemical element, mercury is found both naturally and as an introduced contaminant in the environment, mainly from high-temperature industrial processes such as alkali and metal processing, incineration of coal and oil in electric power stations, foundries, waste combustion and oil and gas processing.

In the past, mining was a substantial source of mercury in some areas. For example, the hydraulic placer-gold mines of the Sierra Nevadas in the United States released several thousand tons of mercury to the environment from the 1860s to the early 1900s. The US Geological Survey believes that high levels of mercury in fish, amphibians and invertebrates downstream of hydraulic mines are a result of historic mercury use.

Current anthropogenic sources are responsible for about 30% of annual mercury emissions into the air. A further 10% comes from natural geological sources and the remaining 60% is from re-emission of previously released mercury that has built up in surface soils and oceans.

Natural sources of atmospheric mercury include volcanoes, geologic deposits of mercury and volatilisation from the ocean. Although all rocks, sediments, water and soils naturally contain small amounts of mercury, some local mineral occurrences and thermal springs are naturally high in mercury.

Long range atmospheric deposition is the dominant source of mercury over aquatic and terrestrial ecosystems. Because it is an element, mercury is not biodegradable and although its form and availability to living organisms may change over time, mercury endures in the environment. Converted by bacterial action in lakes and waterways to a more toxic form known as methylmercury (CH3Hg), it can bioaccumulate in fish and shellfish.  Mercury is so toxic that just one kilogram of mercury is enough to render almost two million kilograms of fish unsafe to eat.

Once it has entered the so-called “global mercury cycle”, methylmercury becomes concentrated as it is transferred up the food chain to birds, animals, marine mammals and humans in a process known as biomagnification. Through this cycle, mercury can contaminate entire food webs, posing a serious threat to ecosystem health and particularly to the higher order species in the food chain, ultimately impacting on human health.

Almost all the mercury in lakes in the European Union has been deposited via atmospheric transport from sources abroad, while the amount being used and released in the world is still increasing. Coal fired power generating plants, owing to the nature of the fossil fuel employed, are the largest man-made source of mercury emissions, while mercury is also found in many everyday household goods, such as lighting and electrical appliances, batteries, medical equipment, older dental fillings, jewellery, paint, thermometers, barometers, manometers, thermostats, pharmaceuticals and pesticides. When these products are discarded, mercury can be released to the environment in a variety of ways during the transport of the waste, its incineration, the post incineration disposal of residuals such as ash, and in landfills.

Although mercury use has gone down in industrialised nations, emissions are growing in other regions, especially in East and Southeast Asia, South America and Sub-Saharan Africa where the use of mercury in artisanal and small scale gold mining operations in remote locations still has a big impact.  All these emissions are likely to increase significantly because of the economic and population growth in these regions.

Mercury has been found to be responsible for a spectrum of adverse human health effects, including permanent damage to the nervous system, in particular the developing nervous system, affecting learning ability and neuro-development in young children. It can be transferred from a mother to her unborn child, making children and women of childbearing age vulnerable populations, especially those living in close proximity to industrial plants. It also affects the kidneys, gastrointestinal complaints and lungs.

UNEP and Minamata Convention
A United Nations Environment Programme (UNEP) report stated that “mercury is a substance that can be transported in the atmosphere and in the oceans around the globe travelling hundreds and thousands of kilometres from where it is emitted. The global environmental threat to humans and wildlife has not receded despite reductions in mercury discharges, particularly in developed countries. Indeed, the problems remain and appear, in some situations to be worsening as demand for energy, the largest source of human made mercury emissions, climbs.”

UNEP has been working to resolve issues around mercury since 2003. Its programme consists of two primary tenants – the first of which is an intergovernmental negotiating committee (INC) which is involved in developing a global legally binding instrument to strengthen global action on mercury. The second - happening simultaneously – is a UNEP Global Mercury Partnership which aims to protect human health and the global environment from the release of mercury by minimising and ultimately eliminating global, anthropogenic mercury releases to air, water and land.

As part of the UNEP initiative, the refining industry agreed to provide information on mercury releases from its activities. In 2012, IPIECA - the global oil and gas industry association for environmental and social issues – published the largest publicly available report on mercury levels, covering 446 crude oils and condensates. IPIECA data indicates the refining sector’s contribution to global mercury emissions as 0.07% of total global mercury releases to air, and less than 0.01% to water.1

Although mercury releases from refining are small, they still need to be managed appropriately and in accordance with local laws and regulations.

On January 2013 140 countries signed the Minamata Convention, the objective of which was to protect human health and the environment from anthropogenic emissions and releases of mercury and mercury compounds. The Convention is named after the Japanese city of Minamata which experienced a severe incidence of mercury poisoning after industrial wastewater was discharged into Minamata Bay. The Convention sets out controls and reductions across a range of products, processes and industries where mercury is used, released or emitted. These range from medical equipment such as thermometers, batteries and energy-saving light bulbs to mining, cement and coal-fired power industry sectors. The treaty also addresses the direct mining of mercury, export and import of the metal and safe storage of waste mercury. At the Intergovernmental Negotiation Committee (INC) 2 session in January, 2011, the INC requested that the UNEP Secretariat prepare a document on the releases of mercury from the oil and gas sector.

Refining plant safety and structural integrity
Although mercury concentrations are less than 2 parts per billion (ppb) in most crudes, mercury has the potential to accumulate and cause operational issues in refining facilities. The two species of mercury that are believed to be prevalent in refineries are elemental mercury and mercury sulphide.

Mercury sulphide, HgS, is the most common form of mercury in nature (USGS, 2003) and is among the least mobile and most stable forms of mercury. However, it decomposes at high temperatures, releasing elemental mercury. It is also converted biologically under anaerobic conditions into organic mercury species. Once mercury enters the biosphere, it becomes part of the mercury cycle.
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