Heavy Metals Liu Donghui Department of Applied Chemistry Email: [email protected]
Definition of Heavy Metals • The US EPA’s Terms of Environment defines heavy metals as “Metallic elements with high atomic weights; (e.g. mercury, chromium, cadmium, arsenic, and lead); [that] can damage living things at low concentrations and tend to accumulate in the food chain. ”
INTRODUCTION OF HEAVY METALS
– High atomic weights – Toxicity – Bioaccumulation
Toxicity of heavy metals
Relationship to living organisms • Living organisms require varying amounts of "heavy metals” (Fe, Co, Cu, Mn, Zn, etc.) .
• Damage mental and central nervous function, lower energy levels, and damage to blood composition, lungs, kidneys, liver, and other vital organs.
• Excessive levels can be damaging to the organism.
• Long‐term exposure may result in slowly progressing physical, muscular, and neurological degenerative processes, and some metals (or their compounds) may cause cancer.
• Other heavy metals such as Hg, Pb, As, Cd, and Cr are toxic metals and their accumulation over time in the bodies of animals can cause serious illness. 5
Characteristic of heavy metal
Sources of Heavy metals
• Natural components of the Earth's crust; • Cannot be degraded or destroyed; • Dangerous because of bioaccumulate and biomagnification; • Cannot be destroyed in the environment, it can only change its form, or become attached to or separated from particles.
• • • • • • •
Food，Water，air Purification of metals Nuclear fuels Electroplating Smoking Released as dust on road surfaces Daily necessities
Heavy Metals Pollution
Heavy metals pollution process
Typical heavy metals
What can we do to reduce the risk of exposure? •
Arsenic (a metalloid*)
Beryllium (a very light metal)
Chromium (particularly the hexavalent form)
Antimony (a metalloid*)
Lithium (another very light metal)
Selenium (a metalloid*)
*a metalloid is an element possessing both metallic and non‐metallic properties.
Lead－Sources in the environment • Lead used in paint, batteries, metal products, ceramic glazes, ammunition, medical equipment, scientific equipment and military equipment.
• bluish‐gray metal • no characteristic taste or smell • not dissolve in water and does not burn • can combine with other chemicals to form lead compounds or lead salts
• Some chemicals containing lead, such as tetraethyl lead and tetramethyl lead. • Human activities have spread lead and substances that contain lead to all parts of the environment. • Lead is in air, drinking water, rivers, lakes, oceans, dust, and soil. • Lead is also in plants and animals that people may eat.
Lead－Fate & Transport
Lead－Fate & Transport
• Lead occurs naturally in the environment.
• Once lead goes into the atmosphere, it may travel thousands of miles if the lead particles are small or if the lead compounds easily evaporate.
• Most of the high levels found throughout the environment comes from human activities.
• Lead is removed from the air by rain and by particles falling to the ground or into surface water. • The release of lead to air is now less than the release of lead to land.
• Leaded gasoline, burning fuel, industrial processes, and burning solid waste.
• Sources of lead in surface water or sediment include deposits of lead‐ containing dust from the atmosphere, waste water from industries. • Lead compounds in water may combine with different chemicals. • The levels of lead may build up in plants and animals from areas where air, water, or soil are contaminated with lead.
• by eating foods or drinking water that contain lead • by spending time in areas where leaded paints have been used and are deteriorating • by touching dust or dirt that contains lead. • by working in jobs where lead is used • by using cosmetics • by using health‐care products or folk remedies that contain lead • cigarette smoke also contains small amounts of lead • Lead may also be released from soldered joints in kettles used to boil water for beverages.
• The main target for lead toxicity is the nervous system. • Lead exposure may also cause weakness in fingers, wrists, or ankles. • At high levels of exposure, lead can severely damage the brain and kidneys in adults or children.
Mercury——Fate & Transport • The total amount of mercury in the environment caused by natural processes throughout the world is far greater than the total amount caused by human activities. • Air, water, and soil can contain mercury from both natural sources and human activity. • The mercury in air, water, and soil is thought to be mostly inorganic mercury. • Metallic mercury is a liquid at room temperature. It can evaporate easily into the air and be carried a long distance before returning to water or soil in rain or snow. • Some microorganisms in the water or soil can change inorganic forms of mercury to organic forms. • Organic forms of mercury can enter the water and remain there for a long time. • Small fish and other organisms living in the water can take up the organic forms of mercury. • Plants may also have a greater concentration of mercury.
• Mercury is a shiny, silver‐white, odorless liquid with a metallic taste. • Mercury can also combine with other elements, such as chlorine, carbon, or oxygen, to form mercury compounds. • In pure form, these mercury compounds are usually white powders or crystals. • All forms of mercury are considered poisonous.
• Because mercury occurs naturally in the environment, everyone is exposed to very low levels of mercury in air, water, and food.
• Long‐term exposure to either inorganic or organic mercury can permanently damage the brain, kidneys, and developing fetus.
• Using skin care and medicinal products
• The most sensitive target of low level exposure to metallic appears to be the nervous system.
• Eating contaminated fish
• The most sensitive target of low level exposure to inorganic mercury appears to be the kidneys.
Arsenic——Fate & Transport
• Classified as a metalloid, having both properties of a metal and a nonmetal;
• Occurs naturally in soil and minerals； • Volcanic eruptions ；
• Steel grey solid material;
• During mining and smelting；
• Used as a preservative for wood, pesticides and additives in animal feed;
• Incinerators； • May enter the air, water, and land from wind‐blown dust and may get into water from runoff and leaching；
• Usually found in the environment combined with other elements( inorganic arsenic, organic arsenic)
• Usually attached to very small particles and transport far away;
• Most inorganic and organic arsenic compounds are white or colorless powders that do not evaporate.
• Most arsenic ends up in the soil or sediment. • Most of arsenic is in an organic form(arsenobetaine) in fish tissues.
• By eating food;
• Most simple organic arsenic compounds are less
– seafood, rice/rice cereal, mushrooms, and poultry
toxic than the inorganic forms.
• By drinking water;
• Arsenic may cause fatigue, abnormal heart rhythm,
• By breathing air;
blood‐vessel damage resulting in bruising, and
• Children may also be exposed to arsenic by eating soil;
impaired nerve function causing a "pins and needles" sensation in your hands and feet.
• By arsenic production; – lead smelting, wood treating, or pesticide application 25
Cadmium——Fate & Transport Cadmium can enter the environment in several ways：
• An element occurs naturally in the earth's crust; • Pure cadmium is a soft, silver‐white metal; • Usually found as a mineral combined with other elements such as oxygen, chlorine , or sulfur;
•Air ：Burning of coal and household waste, metal mining and refining ；
• Not evaporate or disappear from the environment;;
•Water：Disposal of waste water from households or industries.
• Often found as part of small particles in air; • Not have any definite odor or taste;
•Soil：Fertilizers use，Spills and leaks from hazardous waste sites；
• Cadmium has many uses in industry and consumer products, mainly batteries, pigments, metal coatings, and plastics. 27
Cadmium——Fate & Transport
• Cadmium attached to small particles may get into the air and travel a long way before coming down to earth as dust or in rain or snow. • Cadmium does not break down in the environment but can change into different forms.
• Food and cigarette smoke • Air • Drinking water
• Some of the cadmium that enters water will bind to soil but some will remain in the water. • Cadmium in soil can enter water or be taken up by plants. • Fish, plants, and animals take up cadmium from the environment. 29
• A naturally occurring element found in rocks, animals, plants, soil, and in volcanic dust and gases.
Cadmium has no known good effects on your health. •damages the lungs and can cause death； •cause kidney disease； •fragile bones； •have an increased chance of getting lung cancer； •get high blood pressure, iron poor blood, liver disease, and nerve or brain damage.
• No known taste or odor • Steel‐gray solid with a high melting point. • Present in the environment in several different forms. • Chromium(III) occurs naturally in the environment and is an essential nutrient required by the human body. • Chromium(VI) and chromium(0) are generally produced by industrial processes.
Chromium——Fate & Transport • Chromium enters the air, water, and soil mostly in the chromium(III) and chromium(VI) forms as a result of natural processes and human activities.
• Breathing air
• Emissions from burning coal，oil，industry and electric utilities；
• Drinking water
• In air, chromium compounds are present mostly as fine dust particles.
• Eating food
• Rain and snow help remove chromium from air. • A small amount may dissolve in the water. Soluble chromium compounds can remain in water for years before settling to the bottom. • Fish do not accumulate much chromium in their bodies from water. • Most of the chromium in soil does not dissolve easily in water and can attach strongly to the soil.
• Skin contact • People who work in chromium industries can be exposed to higher‐than‐normal levels of chromium.
What can we do to reduce the risk of exposure?
• Chromium(III) is an essential nutrient that helps the body use sugar, protein, and fat. • An intake of 50 to 200 ug of chromium(III) per day is recommended for adults. • Long‐term exposure to chromium has been associated with lung cancer. • Caused stomach upsets and ulcers, convulsions, kidney and liver damage, and even death. 35
ANALYSIS OF HEAVY METALS
Pretreatment for Heavy Metals
Dry Ashing Method Procedure: •The samples were placed in a muffle furnace and heated consecutively at 180 °C for 3 h, at 220 °C for 1 h, at 260 °C for 1h, at 300°C for 1h, and at 400°C for 1h, and were further ashed overnight at 500 °C (16 h). •The ash residue was dissolved in 5 mL of HCl (37%) and quantitatively transferred to 50 mL volumetric flasks. The flasks were sonicated for 10 min (Bransonic 52, Branson, Danbury, CT) and placed in a hot‐water bath (95 °C) for 1 h. •The resulting matrix solutions were filtered (DG2M, Microgon, Laguna Hills, CA) and diluted 10‐fold before they were injected. • EPA‐Health & Environmental Research Online (HERO) 40
Wet Digestion Method •
EPA METHOD 3050B‐‐ACID DIGESTION OF SEDIMENTS, SLUDGES, AND SOILS
SUMMARY OF METHOD
Microwave Digestion Method
– For the digestion of samples, a representative 1‐2 gram (wet weight) or 1 gram (dry weight) sample is digested with repeated additions of nitric acid (HNO3) and hydrogen peroxi de (H2O2). – For GFAA or ICP‐MS analysis, the resultant digestate is reduced in volume while heating and then diluted to a final volume of 100 mL. – For ICP‐AES or FLAA analyses, hydrochloric acid (HCl) is added to the initial digestate and the sample is refluxed. In an optional step to increase the solubility of some me tals(see Section 7.3.1: NOTE), this digestate is filtered and the filter paper and residues are rin sed, firswith hot HCl and then hot reagent water. Filter paper and residue are returned to the digestion flask, refluxed with additional HCl and then filtered again. The digestate is then diluted to a final vol ume of 100 mL.
• • • •
EPA METHOD 3015A Microwave Assisted Acid Digestion Of Aqueous Samples And Extracts SUMMARY OF METHOD A representative aqueous sample is extracted with concentrated nitric acid or, optionally, concentrated nitric acid and concentrated hydrochl oric acid, using microwave heating with asuitable laboratory microwav e unit. The sample and acid(s) are placed in a fluorocarbon polymer (such as PFA or TFM) or quartz microwave vessel or vessel line r. The vessel is sealedand heated in the microwave unit for a specified period of time. After cooling, the vesselcontents are filtered, centrifug ed, or allowed to settle and then diluted to volume and analyzedby the appropriate determinative method.
– If required, a separate sample aliquot shall be dried for a total percent solids determination.
Detection Methods for Heavy Metals •
EPA METHOD 3052
MICROWAVE ASSISTED ACID DIGESTION OF SILICEOUS AND
ORGANICALLY BASED MATRICES
SUMMARY OF METHOD
A representative sample of up to 0.5 g is digested in 9 mL of concentrated nitric acid and usually 3 mL hydrofluoric acid for 15 minutes using microwave heating with a suitable laboratory microwave system. The method has several additional alternative acid and reagent combinations including hydrochloric acid and hydrogen peroxide. The method has provisions for scaling up the sample size to a maximum of 1.0 g. The sample and acid are placed in suitably inert polymeric microwave vessels. The vessel is sealed and heated in the microwave system. The temperature profile is specified to permit specific reactions and incorporates reaching 180 ± 5 ºC in approximatel y less than 5.5 minutes and remaining at 180 ± 5 ºC for 9.5 minutes for the completion of specific reactions (Ref. 1, 2, 3, 4). After cooling, the vessel contents may be filtered, centrifuged, or allowed to settle and then decanted, diluted to volume, and analyzed by the appropriate SW‐846 method.
Atomic Absorption Spectrophotometer（AAS） • Atomic absorption spectroscopy (AAS) is a spectroanalytical procedure for the quantitative determination of chemical elements employing the absorption of optical radiation (light) by free atoms in the gaseous state.
Atomic Fluorescence Spectrometry（AFS） • AtomicFluorescence spectroscopy is a type of electromagnetic spectroscopy which analyzes fluorescence from a sample.
• In analytical chemistry the technique is used for determining the concentration of a particular element in a sample to be analyzed. • AAS can be used to determine over 70 different elements in solution or directly in solid samples. 45
Inductively Coupled Plasma‐Atomic Emission Spectrometry（ICP‐AES）
X Ray Fluorescence（XRF） • X‐ray fluorescence (XRF) is the emission of characteristic "secondary" (or fluorescent) X‐rays from a material that has been excited by bombarding with high‐ energy X‐rays or gamma rays.
• Inductively coupled plasma atomic emission spectroscopy (ICP‐AES), also referred to as inductively coupled plasma optical emission spectrometry (ICP‐OES), is an analytical technique used for the detection of trace metals.
• The phenomenon is widely used for elemental analysis and chemical analysis, particularly in the investigation of metals, glass, ceramics and building materials, and for research in geochemistry, forensic science and archaeology.
• It is a type of emission spectroscopy that uses the inductively coupled plasma to produce excited atoms and ions that emit electromagnetic radiation at wavelengths characteristic of a particular element.
ICP atomic emission spectrometer.
Inductively Coupled Plasma‐Mass Spectrometer（ICP－MS）
Inductively Coupled Plasma‐Mass Spectrometer（ICP－MS）
• An ICP‐MS combines a high‐temperature ICP (Inductively Coupled Plasma) source with a mass spectrometer.
ICP‐MS has many advantages over other elemental analysis techniques such as atomic absorption and optical emission spectrometry, including:
The ICP source converts the atoms of the elements in the sample to ions. These ions are then separated and detected by the mass spectrometer.
• ICP‐MS is an analytical technique used for elemental determinations.
•Detection limits for most elements equal to or better than those obtained by Graphite Furnace Atomic Absorption Spectroscopy (GFAAS) •Higher throughput than GFAAS •The ability to handle both simple and complex matrices with a minimum of matrix interferences due to the high‐temperature of the ICP source •The ability to obtain isotopic information.
UltraViolet‐Visible Spectrophotometer （UV‐VIS）
Chromatographic methods • Gas Chromatography (GC) • High Performance Liquid Chromatography （HPLC）
• Ultraviolet–visible spectroscopy or ultraviolet‐visible spectrophotometry (UV‐Vis or UV/Vis) refers to absorption spectroscopy or reflectance spectroscopy in the ultraviolet‐visible spectral region. • It uses light in the visible and adjacent (near‐UV and near‐infrared (NIR)) ranges.
Rapid detection technique of heavy metals
Comparison of the methods ICP‐MS, ICP‐AES, AAS
• • • •
•Linearity •Sensitivity •Operability •Cost
Biosensor ELISA Immunoassay Dipstick method
Heavy Metal Detectors • • • • • • • • •
Heavy metals analysis • Correct measurement results are a prerequisite for compliance with limit values, which are always specified as total metals.
Lead Thallium Mercury Cadmium Colbalt Aluminum Iron Nickel Zinc
• Matrix factors (e.g. interference ions, colour, turbidities, etc.) may have a negative impact on the measurement and cause false results to be obtained. • If the sample preparation is inadequate, frequently used complexing agents such as EDTA, NTA and citric acid may also cause low‐bias results to be obtained, as they bind the metal ions and thus inhibit the detection reaction. In practice it is necessary to carry out a sample digestion before the metals are analyzed.
Heavy metals analysis
Heavy metals analysis
Homogenisation •Turbid samples must be homogenised prior to the digestion step, to ensure that the contents are evenly distributed before sampling. •The appropriate sample volume must then be pipetted off while stirring continues.
Setting the pH •The pH setting before and after the digestion is especially important for precise metal analysis. The necessary pH of less than 1 before the digestion is obtained by adding the sulphuric acid. •If, in exceptional cases, the correct value is not reached (e.g. when the sample has a high buffering capacity), additional sulphuric acid must be added. 57
Heavy metals analysis
Heavy metals analysis‐‐ICPMS
• Sample digestion • Undissolved and complexed heavy metals are dissolved by heating in an acid environment in the presence of an oxidising agent (either 1 hour at 100 °C in a LT 200 thermostat or 15 minutes in a HT 200S high temperature thermostat).
• Typical detection limits for ICPMS are 0.01‐1 ug/L (ppb) in solution. Sample preparation usually consists of simply diluting the sample in 1% nitric acid although we offer a variety of digestion techniques.
• A comparison of the results obtained before and after the digestion shows whether the digestion is necessary.
Analysis of Lead & its Compounds
Analysis of Mercury & its Compounds
• Pretreatment (Similar to that for Cd and Pb)
– Ashing using sulphuric acid; – Closed‐vessel digestion under pressure such as microwave digestion method EN 13346:2000 or EPA 3052:1996; – Nitric acid and hydrogen peroxide such as EPA 3050B Rev. 2:1996 – Sulphuric acid, Nitric acid, hydrogen peroxide wet decomposition method such as BS EN 1122:2001 etc; – By ICP‐AES/ICP‐OES, such as EN ISO 11885:1998 – By AAS such as EN ISO 5961:1995 – By ICP‐MS
– Closed‐vessel microwave digestion method such as EPA 3052:1996; – Commercially available Mercury Analyzer (inclusive of sample pretreatment and analysis); – Cool Condensing Digestion vessel (Kjeldahl), using sulphuric and nitric acid wet Decomposition Method;
Maximum permissible level for Pb is 100 mg/Kg(ppm) Cadmium can also be analyzed together when ICP‐OES and ICP‐ MS is used
• Analysis Method for low Concentrations: – By cold vapour Hydride Generation AAS Method or Hydride attachment to ICP‐OES/ICP‐MS
EN‐1122: 2001 Method B – Procedure
EN‐1122: 2001 Method B – Total Cd Analysis
• 1. Add 10 mL of H2SO4 to accurately‐weighed 0.500gm of sample in a beaker; • 2. Heat for about 20 minutes until char; • 3. Cool for about 5 minutes; • 4. Add 5 mL of H2O2 to the residues, heat for a further 10 minutes for the reaction to complete; • 5. Repeat steps 3‐4 until a pale clear yellow solution is obtained. • 6. Cool the solution for about 5 minutes; Add 5 mL of HNO3, until reaction is complete. • 7. Dilute to volume(100 mL) and filtered.
Total Cd analysis •Applicable Area: All plastics, except teflon •Concentration ranges of 10 to 3,000 mg/Kg(ppm) •Samples Types: •At least 2 g of homogeneous samples cut using sharp blades in small pieces of less than 0.1 g each piece. •Digestion Procedure: •Weigh about 0.5 g to the nearest mg, digested in appropriate digester( In duplicates)
EPA 3052 ‐ Microwave Digestion Method
EPA 3050B‐1 Analysis of Pb • Weighed accurately about 1g of sample in a beaker • Add 2.5 mL (65%) HNO3 10 mL(37%) HCl • Heat at 95°C ± 5°C for 15 minutes • Collect the clear filtrate in a 100 mL volumetric flask Wash the residue and filter paper with 5mL hot HCl & 5 mL hot D.I. water • Collect the wash in the same volumetric flask • Digest the residue with 5 mL HCl • Combine the above digestate with the filtrate in the same volumetric flask • Make up the total filtrates to volume ‐ 100 mL 65
Variation Between Open Digestion & Microwave Digestion
Sony Environmental Monitored Substances SS‐00259 3rd Edition • Analysis of hexavalent Chromium, Cr 6+ • Pretreatment – Using hot water extraction
• Analysis Method: – By UV‐VIS Spectrometry;
• Maximum permissible level for Total Chromium is 5 mg/Kg(ppm) •
NB: 1. Total concentration for Hg