Analysis of mercury in waters using

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A major release of mercury into water and air is through certainindustrial processes, fuel combustion, waste incineration andimproper disposal of mercury containing products.
Once in streams and rivers mercury generally does not remainsuspended in the water column but is deposited in the sediment.
A tiny amount is incorporated into the food chain and undergoesbiomagnification - a natural process whereby contaminants likemercury are found at progressively higher concentrations as theypass from prey to predator up the food chain.
The biomagnification of mercury can lead to concentrations in fishthat exceed the safe levels recommended for human consumption.
The need to monitor and control water sources is paramount evenstill today, despite mercury releases being considerably reducedover recent years, to ensure the continued wellbeing of humans andthe environment in which they exist.
Voltammetry - a brief overview.
Jaroslav Heyrovsky first introduced the concept of polarography circa 1922.
The term voltammetry is applied to designate the current-voltagemeasurement obtained at a given electrode.
Polarography is a special case of voltammetry referring to thecurrent-voltage measurement acquired using a dropping mercuryelectrode with a constant flow of mercury drops.
Stripping voltammetry uses the same instrumentation as traditionalpolarography but a stationary electrode such as the Hanging MercuryDropping Electrode (HMDE) is used.
The voltammetric measurement is performed on a stationary mercurydrop allowing one to achieve considerable increases in sensitivity.
With the Metrohm Multi Mode Electrode (MME) the mercury ishermetically sealed in the reservoir and suffices for around200,000 drops ensuring low laboratory running costs.
For stripping analysis in the region below 1mg/l, Metrohm alsooffers a Rotating Disk Electrode (RDE) with exchangeable tips ofglassy carbon for mercury film techniques and gold fordeterminations of mercury.
RDE are often employed as an alternative to the traditionalmercury-working electrode and offer well defined, reproducibleconditions for voltammetric analysis.
The surface of the solid state electrode is constant throughout theentire analysis allowing low limits of detection.
The jump in sensitivity is made possible by electrochemicalpreconcentration of the metals in question at the surface of thestationary electrode before the current-voltage curve is recorded.
The recorded current is the redissolution (reoxidation) current ofthe preconcentrated metal traces.
Applications of mercury.
Mercury is perhaps best known as the silver liquid present inthermometers but also has over 3000 industrial uses.
Mercury is used in a variety of different industries and iscommonly used in laboratory work for making barometers, diffusionpumps and in analytical instruments such as polarography systemsusing the classic mercury-dropping electrode.
A gaseous form of mercury is used in mercury vapour lamps and foradvertising signs.
It is also used for mercury switches and other electricalapparatus.
Historically, mercury has been used in the manufacture of certainpesticides, anti fouling paints as well as the production ofchlorine and caustic soda although these types of applications havedeclined over recent decades due to the environmental consequencesof their use.
Other uses include catalysts for synthesis and the production ofbatteries or mercury cells.
Mercury will dissolve numerous metals to form amalgams and has beenused in the extraction of gold dust from rocks, as well as withtin, silver and gold in dental fillings.
World-wide dental and medical institutions have previously causedconsiderable mercury contamination to local water supplies butbetter control procedures now require safe and ecologically sounddisposal of the unwanted waste.
Mercury and the environment.
Mercury is an element existing in elemental, inorganic and organic compounds meaning it will always be present in the world around us.
It is possible to remove contaminated solid waste such as soil andsludge and dispose of it elsewhere, such as in a hazardous wastelandfill site but the mercury will still be present.
Mercury is easily vaporised so the air around chlorine-alkaliplants, smelters, waste incineration plants and sewage treatmentplants may contain increased levels of mercury.
The adoption of pollution prevention and recycling schemes formercury bearing waste such as thermometers, fluorescent lights andswitches has led to significant reductions in the amount of mercuryin solid waste streams.
Mercury is being phased out of certain products such as batteriesand industrial permits are becoming ever more stringent in additionto better control technology being developed and adopted for thelikes of industrial or agricultural waste.
As a consequence, mercury discharges into streams and rivers overrecent decades have been greatly reduced.
Historically, there have been few permissible consent levels withregard to contamination by mercury in different water sources.
Today, the Water Supply (Water Quality) Regulations 2000 state thatat the point of the consumers' tap then the maximum concentrationof mercury permitted is 1 mg/l.
Methylation is a product of complex processes that move andtransform mercury.
Atmospheric deposition contains the three principal forms ofmercury but once in surface water, mercury enters a complex cyclein which one form can be converted to another.
Mercury that is attached to particles can settle onto sedimentswhere it can diffuse into the water column and be suspended, buriedor methylated.
Methyl mercury can enter the food chain or it can be released backto the atmosphere by volatilisation.
The concentration of dissolved organic carbon and pH play a strongrole in determining the fate of mercury in a particular ecosystem.
Studies have shown that for a water system with increased acidityor dissolved organic carbon content, then the levels of mercuryobserved are increased due to the enhanced mobility of the mercuryunder these conditions.
The exact mechanism by which mercury enters the food chain islargely unknown and may vary among ecosystems.
It is known that certain bacteria process sulphate in the environment and take mercury up in itsinorganic form before converting it to methyl mercury throughmetabolic processes.