There are certain words in our vocabulary that make our hair stand up and cause palpitations of the heart. They include polluting and hazardous chemicals like benzene, PCBs asbestos, lead, cadmium, cyanide, chromium and mercury.
If all the current claims against some of the above (asbestos, chromium, lead and mercury) were true, this writer should be already dead many times over. I can recall, as a laboratory assistant at Tioxide, that the most common chemical test involved shaking a titanium solution with mercury-zinc amalgam in a reductor. There were numerous spills on the floor, between the bench tiles - everywhere - and we scooped it up, played with it etc. for years and without any harmful effects with scores of workers involved on a regular basis. Probably over half of the adult population has a mouthful of mercury amalgam as teeth fillings and not many of us suffer from those, possibly over-rated mercury poisoning effects.
Commonly Encountered Dangerous Materials
Some potentially dangerous chemicals can be rendered harmless to ourselves and the environment by careful use and total recovery and recycling - these include 111 tri-chloro ethane solvent and hexavalent chromium (used in hard chromium plating). We should also consider that many substances appear on the scene as secondary or attached materials - mercury in gold and other ores, cadmium in phosphate rock from Nauru, etc.
So, when it comes to mercury, let's look at both sides of the equation and give it a fair assessment.
Mercury – Properties and Occurrence
Mercury, a silvery liquid metal at room temperature, is one of the ‘heavy metals’. Like water, it can evaporate and become airborne and stable in its elemental form. It occurs naturally in cinnabar (Spain, Algeria, China) as well as a by-product of gold and zinc mining.
Applications of Mercury
Mercury is a highly efficient metal that adds product life and efficiencies to several commonly used items such as fluorescent tubes, mercury vapour lamps, long life batteries, electrical switch gear , thermometers, barometers, blood pressure gauges, diffusion pumps, vacuum pumps, electric rectifiers, electrodes for electrolytic processes, anti-fouling paints and dental amalgam.
Mercury combines with most common metals (except iron or platinum), to form extremely stable amalgams that have various uses including gold and silver extraction from ores, carrier for redox reactions and dental amalgams.
It also forms monovalent and divalent Compounds including mercuric sulphide, mercurous chloride, mercuric chloride, medicinals and mercury fulminate.
Mercury In Thermometers
Mercury has an almost constant coefficient of expansion, i.e. the change in volume for each degree rise or fall in temperature is almost the same and it is this unique property that provides the reliability and accuracy of thermometers.
Mercury in Lights
Mercury vaporizes in lamps, fluorescent tubes and ultra-violet ray lamps for sterilizing uses. Efforts have been made to decrease the quantity of mercury in modern fluorescent tubes but this is usually at the expense of a shorter, effective, operating life. Some mercury is still critical for fluorescent lighting.
Mercury in Batteries
The consistent performance and long life of mercury-based batteries is of vital importance to many applications, including medical and defence.
Other Applications of Mercury
Looking at the above list, we can see that several of the uses are essential and others are not. It can be strongly argued that mercury should not be used in the 21st century for pigments, for the production of chlorine for paper bleaching or for fulminate in blasting caps. Some may argue that use in dental amalgams should also be stopped. A typical dental amalgam contains approximately 50% mercury, 25% silver and the remainder being copper, tin and a trace of zinc. However, the mercury in amalgams is very, very stable.
The Effect of Mercury on the Humans and Exposure Levels
Mercury is classified by the EPA as a Schedule A ‘priority toxic waste’.
- It has a TLV in air of 0.05 mg per cubic metre (0.05 ppb)
- For OSHA the air limit is 0.1 mg per cubic metre (0.1 ppb)
- It affects the gastro intestinal tract (GIT)
- It affects the central nervous system (CNS) - nerve poison
- Mercury and its compounds are equivocal tumorigenic agents (ETA)
In drinking water, the limit is 0.001 mg per litre (1 ppb). Breathing too much mercury fumes will cause ‘mercurialism’ tremors, salivation, stomatitis, loosening of teeth.
Mercury and Water Pollution Effects
Mercury is absorbed by sharks, fish and crabs which can then become more dangerous dead than alive. Recent levels in shark’s fins in Thailand, those caught in Hong Kong harbour, were 42 times the maximum limit. Methyl mercury is the typical form and it is very dangerous for pregnant women and young babies as it blocks nerve cell formation and causes neurological deficiencies. There was a recent scare about high levels of mercury in dolphins in South Australia (446 ppm highest in the world).
Sources of Mercury Pollution
Overseas studies have shown that a significant proportion of total mercury discharged comes from dental surgeries (Seattle USA 1990 - 14%, Denmark 1987 - 60%). All dental surgeries should now have absorbent filters fitted (new ISO Std DIS 11143) but most do not. So, next time the dentist tells you to ‘spit in here’, ask him/her where it ‘ends up’ and ‘do you have a filter system?’.
Alternatives to Mercury Amalgam Fillings
In this case, we have already solved the problem by introducing new plastic composite fillings free of mercury but even these new plastic composites are also still under some cloud as some experts believe that they interfere with estrogen production and can cause sterility in males. In Denmark and Sweden, pregnant women and young children are encouraged not to use mercury fillings as a precautionary measure only but attempts to widen this have been stalled by the estrogen/sterility scare and other unproven issues.
Trends Associated with Mercury and Dentistry
Whatever happens, there will still be a lot of dental mercury in the system for a great number of years which we must prevent entering the environment. The mercury filling business seems to be continuing in Australia with over 20 tonnes of mercury imported annually for use in dental amalgam. There is a general global transfer to plastic composites based mainly on environmental, not health reasons. The case against tried and true mercury (over 150 years) is far from proven.
Mercury and Air Pollution
Air pollution from mercury comes from two main sources, namely the highest concentrations in air have been found at ‘crematoriums’ (from the volatilisation of teeth fillings) while the other main source is methyl mercury that comes from landfills. Typical products to blame for the latter include thermometers, fluorescent tubes, batteries and coal burning. Methane typically generates in landfills and specific bacteria can modify the reaction to form both mono and di methyl mercury. Rain will condense this gas and it is then absorbed or dissolved into the water streams.
What Approach Should we Take Regarding Mercury?
In mercury we have a very important and useful metal that comes to us with both the high cost of pollution and associated health hazards.
If we cannot stop mercury, its compounds or by-products entering the environment, then we should cause its use to be banned. If we can keep it from entering the environment, by such methods as ‘closed loop recycling’, then we should accept this as legitimate, at least until environmentally superior materials are found or synthesised. This latter approach is a second tier ‘cleaner production or pollution prevention’ approach.
What Happens to our Mercury Wastes Now?
Fluorescent tubes and mercury vapour lamps are generally thrown directly into landfills (where the transition to dimethyl mercury can occur). Some mercury wastes are wet crushed, mixed with concrete and landfilled (with EPA approval but not as EPAs preferred option). This technique is not recommended because it simply hides rather than solves the problem. Other wet crusher systems are sometimes used but most of these do not recover mercury. Other mercury wastes, such as button batteries are collected and exported to Europe for recovery, although in theory, export of any toxic waste is prohibited.
What Happens to Mercury Dental Wastes?
Dental amalgam is collected, to a degree, and a lot of it is then stored at ‘no fixed address’ premises for export or backyard (unapproved) distillation recovery. A lot of dental mercury waste goes directly to sewer and into the waterways. More responsible dentists separate their mercury wastes and have it collected.
Closed Loop Recovery
Is closed loop recovery available commercially? Yes! Many countries in the Northern Hemisphere have been operating recovery systems for over 15 years, often with government regulation and financial assistance (e.g. Denmark and Sweden).
The dry crush, separation and vacuum distillation systems are well proven and operate commercially for fluorescent tubes, mercury lamps, batteries, dental amalgam, thermometers, switch gear etc. Materials recovered include mercury, glass phosphor powder, aluminium, other metals. All of them go back to the trade for re-use.
Closed Loop Recovery of Mercury in Australia
EPA Vic approved this system back in 1992 but it was not established here commercially until October 2000 (EPA licensed and approved). The system is very clean and no mercury can escape to the atmosphere or to waterways.
Now we have to educate the public and the relevant industries to use this system in a comprehensive manner - so please, pass the message on! Companies with ISO 14001 environmental management system accreditation are leading the way, insisting that their wastes be recovered rather than dumped.
Eco-Recycle Vic is encouraging landfill operators and local councils to adopt and use this recovery systems approach.
EPA Vic, NSW and SA are encouraging the use of this recovery, recycling system and soon will ban mercury wastes from landfill.
Suggestions for Those Dealing with Mercury Wastes
The dental industry should fully adopt the ISO Standard and force all members to install fully recyclable amalgam separators in their surgeries.
As a radical suggestion, maybe all crematoriums should have a 'prep room' where all teeth with mercury fillings are removed and collected.
Product manufacturers that use mercury should adopt the ‘total product stewardship’ approach and insist on the recovery route. It is understood that the lighting industry in Australia is now seriously considering this approach.
So, we can ‘eliminate the curse’ and enhance ‘the blessing’ of this wonderful material/metal - Mercury - without environmental defects.
This information has been sourced, reviewed and adapted from materials provided by LECO Corporation.
For more information on this source, please visit LECO Corporation.