Ethylenediaminetetraacetic acid (EDTA) is an
aminopolycarboxylic acid with the formula
2N(CH2CO2H)2">H2N(CH2CO2H)2sub>2. This white, water-soluble solid is widely used to bind to iron (Fe
2+/Fe
3+) and calcium ions (Ca
2+), forming water-soluble
complexes even at neutral pH. It is thus used to dissolve Fe- and Ca-containing scale as well as to deliver iron ions under conditions where its oxides are insoluble. EDTA is available as several salts, notably disodium EDTA,
sodium calcium edetate, and
tetrasodium EDTA, but these all function similarly.
Uses
Textile industry
In industry, EDTA is mainly used to
sequester (bind or confine) metal ions in aqueous solution. In the
textile industry
The textile industry is primarily concerned with the design, production and distribution of yarn, cloth and clothing. The raw material may be natural, or synthetic using products of the chemical industry.
Industry process
Cotton manufac ...
, it prevents metal ion impurities from modifying colours of dyed products. In the
pulp and paper industry
The pulp and paper industry comprises companies that use wood as raw material and produce pulp, paper, paperboard and other cellulose-based products.
Manufacturing process
The pulp is fed to a paper machine where it is formed as a paper web ...
, EDTA inhibits the ability of metal ions, especially
Mn2+, from catalysing the
disproportionation
In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term ca ...
of
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3% ...
, which is used in
chlorine-free bleaching. In a similar manner, EDTA is added to some food as a
preservative
A preservative is a substance or a chemical that is added to products such as food products, beverages, pharmaceutical drugs, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or ...
or stabiliser to prevent catalytic oxidative decolouration, which is catalysed by metal ions.
In
soft drinks containing
ascorbic acid
Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) a ...
and
sodium benzoate, EDTA mitigates formation of
benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen ato ...
(a
carcinogen
A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subst ...
).
Water softener
The reduction of water hardness in laundry applications and the dissolution of scale in boilers both rely on EDTA and related
complexants to bind
Ca2+,
Mg2+, as well as other metal ions. Once bound to EDTA, these metal complexes are less likely to form precipitates or to interfere with the action of the
soap
Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are used ...
s and
detergent
A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are m ...
s. For similar reasons, cleaning solutions often contain EDTA. In a similar manner EDTA is used in the cement industry for the determination of free
lime and free
magnesia in cement and
clinkers.
The solubilisation of
Fe3+ ions at or below near neutral
pH can be accomplished using EDTA. This property is useful in
agriculture
Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled peop ...
including hydroponics. However, given the pH dependence of ligand formation, EDTA is not helpful for improving iron solubility in above neutral soils. Otherwise, at near-neutral pH and above, iron(III) forms insoluble salts, which are less
bioavailable to susceptible plant species.
Scrubbing
Aqueous
e(EDTA)sup>− is used for removing ("
scrubbing")
hydrogen sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The und ...
from gas streams. This conversion is achieved by oxidising the hydrogen sulfide to elemental sulfur, which is non-volatile:
:2
e(EDTA)sup>− +
H2S → 2
e(EDTA)sup>2− +
S + 2 H
+
In this application, the iron(III) centre is
reduced to its iron(II) derivative, which can then be reoxidised by air. In similar manner,
nitrogen oxide Nitrogen oxide may refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds:
Charge-neutral
* Nitric oxide (NO), nitrogen(II) oxide, or nitrogen monoxide
*Nitrogen dioxide (), nitrogen(IV) oxide
* Nitrogen trioxide (), o ...
s are removed from gas streams using
e(EDTA)sup>2−.
The oxidising properties of
e(EDTA)sup>− are also exploited in
photography
Photography is the visual art, art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It i ...
, where it is used to solubilise
silver
Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, whi ...
particles.
Ion-exchange chromatography
EDTA was used in separation of the
lanthanide metals by
ion-exchange chromatography. Perfected by F. H. Spedding ''et al''. in 1954, the method relies on the steady increase in
stability constant of the lanthanide EDTA complexes with
atomic number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
. Using
sulfonated
polystyrene
Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is ...
beads and
Cu2+ as a retaining ion, EDTA causes the lanthanides to migrate down the column of resin while separating into bands of pure lanthanides. The lanthanides elute in order of decreasing atomic number. Due to the expense of this method, relative to
countercurrent solvent extraction, ion exchange is now used only to obtain the highest purities of lanthanides (typically greater than 99.99%).
Medicine
Sodium calcium edetate, an EDTA derivative, is used to bind metal ions in the practice of
chelation therapy
Chelation therapy is a medical procedure that involves the administration of chelating agents to remove heavy metals from the body. Chelation therapy has a long history of use in clinical toxicology and remains in use for some very specific medi ...
, such as for treating
mercury and
lead poisoning
Lead poisoning, also known as plumbism and saturnism, is a type of metal poisoning caused by lead in the body. The brain is the most sensitive. Symptoms may include abdominal pain, constipation, headaches, irritability, memory problems, inferti ...
.
It is used in a similar manner to remove excess
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
from the body. This therapy is used to treat the complication of repeated
blood transfusion
Blood transfusion is the process of transferring blood products into a person's circulation intravenously. Transfusions are used for various medical conditions to replace lost components of the blood. Early transfusions used whole blood, but m ...
s, as would be applied to treat
thalassaemia.
Dentistry
Dentist
A dentist, also known as a dental surgeon, is a health care professional who specializes in dentistry (the diagnosis, prevention, management, and treatment of diseases and conditions of the oral cavity and other aspects of the craniofacial co ...
s and
endodontists use EDTA solutions to remove inorganic debris (
smear layer) and lubricate the
root canal
A root canal is the naturally occurring anatomic space within the root of a tooth. It consists of the pulp chamber (within the coronal part of the tooth), the main canal(s), and more intricate anatomical branches that may connect the root ...
s in endodontics. This procedure helps prepare root canals for
obturation. Furthermore, EDTA solutions with the addition of a
surfactant
Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, fo ...
loosen up
calcification
Calcification is the accumulation of calcium salts in a body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. D. Cardiovascular calcification: Orbicular origins. ''Nature M ...
s inside a root canal and allow instrumentation (canal shaping) and facilitate apical advancement of a file in a tight or calcified root canal towards the apex.
Eyedrops
It serves as a
preservative
A preservative is a substance or a chemical that is added to products such as food products, beverages, pharmaceutical drugs, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or ...
(usually to enhance the action of another preservative such as
benzalkonium chloride or
thiomersal
Thiomersal ( INN), or thimerosal ( USAN, JAN), is an organomercury compound. It is a well-established antiseptic and antifungal agent.
The pharmaceutical corporation Eli Lilly and Company gave thiomersal the trade name Merthiolate. It has bee ...
) in ocular preparations and
eyedrops.
Analysis
In evaluating
kidney function, the
chromium(III)
Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal.
Chromium metal is valued for its high corrosion resistance and hardne ...
complex
r(EDTA)sup>− (as radioactive
chromium-51
Naturally occurring chromium (24Cr) is composed of four stable isotopes; 50Cr, 52Cr, 53Cr, and 54Cr with 52Cr being the most abundant (83.789% natural abundance). 50Cr is suspected of decaying by β+β+ to 50Ti with a half-life of (more than) ...
(
51Cr)) is administered
intravenously and its filtration into the
urine
Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra.
Cellular ...
is monitored. This method is useful for evaluating
glomerular filtration rate (GFR) in
nuclear medicine
Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is "radiology done inside out" because it records radiation emit ...
.
EDTA is used extensively in the analysis of blood. It is an
anticoagulant for blood samples for
CBC/FBCs, where the EDTA chelates the calcium present in the blood specimen, arresting the coagulation process and preserving blood cell morphology. Tubes containing EDTA are marked with
lavender
''Lavandula'' (common name lavender) is a genus of 47 known species of flowering plants in the mint family, Lamiaceae. It is native to the Old World and is found in Cape Verde and the Canary Islands, and from Europe across to northern and east ...
(purple) or pink tops.
EDTA is also in tan top tubes for lead testing and can be used in royal blue top tubes for trace metal testing.
EDTA is a slime dispersant, and has been found to be highly effective in reducing bacterial growth during implantation of
intraocular lens
Intraocular lens (IOL) is a lens (optics), lens implanted in the human eye, eye as part of a treatment for cataracts or myopia. If the natural lens is left in the eye, the IOL is known as Phakic intraocular lens, phakic, otherwise it is a pseudop ...
es (IOLs).
Alternative medicine
Some
alternative practitioners believe EDTA acts as an
antioxidant, preventing
free radical
A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing.
Ageing
Ailments of unknown cause
Biogerontology
Biological processes
Causes of death
Cellular processes
Gerontology
Life extension
Metabo ...
s from injuring
blood vessel
Blood vessels are the structures of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away from ...
walls, therefore reducing
atherosclerosis
Atherosclerosis is a pattern of the disease arteriosclerosis in which the wall of the artery develops abnormalities, called lesions. These lesions may lead to narrowing due to the buildup of atheromatous plaque. At onset there are usually ...
. These ideas are unsupported by scientific studies, and seem to contradict some currently accepted principles. The
U.S. FDA has not approved it for the treatment of atherosclerosis.
Cosmetics
In
shampoo
Shampoo () is a hair care product, typically in the form of a viscous liquid, that is used for cleaning hair. Less commonly, shampoo is available in solid bar format. Shampoo is used by applying it to wet hair, massaging the product into th ...
s, cleaners, and other personal care products, EDTA salts are used as a sequestering agent to improve their stability in air.
Laboratory applications
In the laboratory, EDTA is widely used for scavenging metal ions: In
biochemistry
Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology ...
and
molecular biology
Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and phys ...
, ion depletion is commonly used to deactivate
metal-dependent enzymes, either as an assay for their reactivity or to suppress damage to
DNA,
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...
s, and
polysaccharide
Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with ...
s. EDTA also acts as a selective
inhibitor
Inhibitor or inhibition may refer to:
In biology
* Enzyme inhibitor, a substance that binds to an enzyme and decreases the enzyme's activity
* Reuptake inhibitor, a substance that increases neurotransmission by blocking the reuptake of a neurotra ...
against dNTP hydrolyzing enzymes (
Taq polymerase,
dUTPase, MutT), liver
arginase and
horseradish peroxidase independently of metal ion
chelation. These findings urge the rethinking of the utilisation of EDTA as a biochemically inactive metal ion scavenger in enzymatic experiments. In analytical chemistry, EDTA is used in
complexometric titrations and analysis of
water hardness
Hard water is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, ...
or as a
masking agent to sequester metal ions that would interfere with the analyses.
EDTA finds many specialised uses in the biomedical labs, such as in
veterinary
Veterinary medicine is the branch of medicine that deals with the prevention, management, diagnosis, and treatment of disease, disorder, and injury in animals. Along with this, it deals with animal rearing, husbandry, breeding, research on nutri ...
ophthalmology
Ophthalmology ( ) is a surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders.
An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a med ...
as an
anticollagenase to prevent the worsening of
corneal ulcers in animals. In
tissue culture EDTA is used as a chelating agent that binds to
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
and prevents joining of
cadherins between cells, preventing clumping of cells grown in liquid suspension, or detaching adherent cells for
passaging. In
histopathology
Histopathology (compound of three Greek words: ''histos'' "tissue", πάθος ''pathos'' "suffering", and -λογία '' -logia'' "study of") refers to the microscopic examination of tissue in order to study the manifestations of disease. Sp ...
, EDTA can be used as a decalcifying agent making it possible to cut sections using a
microtome once the tissue sample is demineralised.
EDTA is also known to inhibit a range of
metallopeptidases, the method of inhibition occurs via the
chelation of the metal ion required for catalytic activity. EDTA can also be used to test for
bioavailability of heavy metals in
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...
s. However, it may ''influence'' the bioavailability of metals in solution, which may pose concerns regarding its effects in the environment, especially given its widespread uses and applications.
EDTA is also used to remove crud (corroded metals) from fuel rods in nuclear reactors.
Side effects
EDTA exhibits low acute toxicity with (rat) of 2.0 g/kg to 2.2 g/kg.
It has been found to be both
cytotoxic
Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are an immune cell or some types of venom, e.g. from the puff adder (''Bitis arietans'') or brown recluse spider (''Loxosceles reclusa'').
Cell physiology
Treating ...
and weakly
genotoxic in laboratory animals. Oral exposures have been noted to cause reproductive and developmental effects.
The same study
also found that both dermal exposure to EDTA in most cosmetic formulations and inhalation exposure to EDTA in
aerosol
An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas. Aerosols can be natural or anthropogenic. Examples of natural aerosols are fog or mist, dust, forest exudates, and geyser steam. Examples of ant ...
ised cosmetic formulations would produce exposure levels below those seen to be toxic in oral dosing studies.
Synthesis
The compound was first described in 1935 by
Ferdinand Münz
Ferdinand Münz (1888-1969) was an Austrian chemist who first synthesized EDTA (ethylenediaminetetraacetic acid) at the IG Farben in 1935, patented both in Germany (anonymously) and in the USA (with his name), with the aim of producing a citric ...
, who prepared the compound from
ethylenediamine
Ethylenediamine (abbreviated as en when a ligand) is the organic compound with the formula C2H4(NH2)2. This colorless liquid with an ammonia-like odor is a basic amine. It is a widely used building block in chemical synthesis, with approximately ...
and
chloroacetic acid. Today, EDTA is mainly synthesised from
ethylenediamine
Ethylenediamine (abbreviated as en when a ligand) is the organic compound with the formula C2H4(NH2)2. This colorless liquid with an ammonia-like odor is a basic amine. It is a widely used building block in chemical synthesis, with approximately ...
(1,2-diaminoethane),
formaldehyde
Formaldehyde ( , ) ( systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section ...
, and
sodium cyanide
Sodium cyanide is a poisonous compound with the formula Na C N. It is a white, water-soluble solid. Cyanide has a high affinity for metals, which leads to the high toxicity of this salt. Its main application, in gold mining, also exploits its h ...
. This route yields the tetrasodium EDTA, which is converted in a subsequent step into the acid forms:
:H
2NCH
2CH
2NH
2 + 4
CH2O + 4
NaCN + 4 H
2O → (NaO
2CCH
2)
2NCH
2CH
2N(CH
2CO
2Na)
2 + 4
NH3
:(NaO
2CCH
2)
2NCH
2CH
2N(CH
2CO
2Na)
2 + 4
HCl → (HO
2CCH
2)
2NCH
2CH
2N(CH
2CO
2H)
2 + 4
NaCl
This process is used to produce about 80,000 tonnes of EDTA each year. Impurities cogenerated by this route include
glycine
Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid ( carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinog ...
and
nitrilotriacetic acid; they arise from reactions of the
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogeno ...
coproduct.
Nomenclature
To describe EDTA and its various
protonated forms, chemists distinguish between EDTA
4−, the
conjugate base
A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid donates a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as in the reverse reaction it loses a ...
that is the
ligand
In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's ele ...
, and H
4EDTA, the
precursor to that ligand. At very low pH (very acidic conditions) the fully protonated H
6EDTA
2+ form predominates, whereas at very high pH or very basic condition, the fully deprotonated EDTA
4− form is prevalent. In this article, the term EDTA is used to mean H
4−''x''EDTA
''x''−, whereas in its complexes EDTA
4− stands for the tetraanion ligand.
Coordination chemistry principles
In
coordination chemistry
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ''ligands'' or complexing ...
, EDTA
4− is a member of the
aminopolycarboxylic acid family of ligands. EDTA
4− usually binds to a metal cation through its two amines and four carboxylates, i.e., it is It a
hexadentate
A hexadentate ligand in coordination chemistry
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn k ...
("six-toothed")
chelating agent. Many of the resulting
coordination compounds adopt
octahedral geometry. Although of little consequence for its applications, these octahedral complexes are
chiral. The
cobalt(III) anion
o(EDTA)
O, or o, is the fifteenth letter and the fourth vowel letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''o'' (pronounced ), plu ...
sup>− has been resolved into
enantiomer
In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical ant ...
s. Many complexes of EDTA
4− adopt more complex structures due to either the formation of an additional bond to water, ''i.e.'' seven-coordinate complexes, or the displacement of one carboxylate arm by water. The
iron(III) complex of EDTA is seven-coordinate. Early work on the development of EDTA was undertaken by
Gerold Schwarzenbach in the 1940s. EDTA forms especially strong complexes with
Mn(II),
Cu(II), Fe(III),
Pb(II) and Co(III).
Several features of EDTA's complexes are relevant to its applications. First, because of its high
denticity, this ligand has a high affinity for metal cations:
:
2O)6">e(H2O)6sup>3+ + H
4EDTA
e(EDTA)sup>− + 6 H
2O + 4 H
+ ''K''eq = 10
25.1
Written in this way, the
equilibrium quotient shows that metal ions compete with protons for binding to EDTA. Because metal ions are extensively enveloped by EDTA, their
catalytic properties are often suppressed. Finally, since complexes of EDTA
4− are
anion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
ic, they tend to be highly soluble in water. For this reason, EDTA is able to dissolve deposits of
metal oxide
An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...
s and
carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonat ...
s.
The
p''K''a values of free EDTA are 0, 1.5, 2, 2.66 (
deprotonation of the four
carboxyl groups) and 6.16, 10.24 (deprotonation of the two
amino groups).
[Hans Peter Latscha: ''Analytische Chemie.'' Springer-Verlag, 2013, , p. 303.]
Environmental fate
Abiotic degradation
EDTA is in such widespread use that questions have been raised whether it is a
persistent organic pollutant
Persistent organic pollutants (POPs), sometimes known as "forever chemicals", are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. They are toxic chemicals that adverse ...
. While EDTA serves many positive functions in different industrial, pharmaceutical and other avenues, the longevity of EDTA can pose serious issues in the environment. The degradation of EDTA is slow. It mainly occurs
abiotically in the presence of sunlight.
The most important process for the elimination of EDTA from surface waters is direct
photolysis at wavelengths below 400 nm. Depending on the light conditions, the photolysis
half-lives of iron(III) EDTA in surface waters can range as low as 11.3 minutes up to more than 100 hours. Degradation of FeEDTA, but not EDTA itself, produces iron complexes of the triacetate (ED3A), diacetate (EDDA), and monoacetate (EDMA) – 92% of EDDA and EDMA biodegrades in 20 hours while ED3A displays significantly higher resistance. Many environmentally-abundant EDTA species (such as
Mg2+ and
Ca2+) are more persistent.
Biodegradation
In many
industrial wastewater treatment plants, EDTA elimination can be achieved at about 80% using
microorganisms. Resulting byproducts are ED3A and
iminodiacetic acid (IDA) – suggesting that both the backbone and acetyl groups were attacked. Some microorganisms have even been discovered to form nitrates out of EDTA, but they function optimally at moderately alkaline conditions of pH 9.0–9.5.
Several bacterial strains isolated from sewage treatment plants efficiently degrade EDTA. Specific strains include ''
Agrobacterium radiobacter'' ATCC 55002 and the sub-branches of
Pseudomonadota
Pseudomonadota (synonym Proteobacteria) is a major phylum of Gram-negative bacteria. The renaming of phyla in 2021 remains controversial among microbiologists, many of whom continue to use the earlier names of long standing in the literature. The ...
like BNC1, BNC2,
and strain DSM 9103. The three strains share similar properties of
aerobic respiration
Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...
and are classified as
gram-negative bacteria
Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...
. Unlike photolysis, the chelated species is not exclusive to iron(III) in order to be degraded. Rather, each strain uniquely consumes varying metal–EDTA complexes through several enzymatic pathways. Agrobacterium radiobacter only degrades Fe(III) EDTA
while BNC1 and DSM 9103 are not capable of degrading iron(III) EDTA and are more suited for
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
,
barium,
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...
and
manganese(II) complexes. EDTA complexes require dissociation before degradation.
Alternatives to EDTA
Interest in environmental safety has raised concerns about biodegradability of
aminopolycarboxylates left, 120px, a metal complex with the EDTA anion
120px, Aspartic acid is an aminodicarboxylic acid and precursor to other ligands.
An aminopolycarboxylic acid (sometimes abbreviated APCA) is a chemical compound containing one or more nitrogen at ...
such as EDTA. These concerns incentivize the investigation of alternative aminopolycarboxylates.
[ Candidate chelating agents include nitrilotriacetic acid (NTA), iminodisuccinic acid (IDS), polyaspartic acid, ''S,S''-ethylenediamine-''N'',''N''′-disuccinic acid (EDDS), methylglycinediacetic acid (MGDA), and L-Glutamic acid ''N'',''N''-diacetic acid, tetrasodium salt (GLDA).
]
Iminodisuccinic acid (IDS)
Commercially used since 1998, iminodisuccinic acid (IDS) biodegrades by about 80% after only 7 days. IDS binds to calcium exceptionally well and forms stable compounds with other heavy metal ions. In addition to having a lower toxicity after chelation, IDS is degraded by '' Agrobacterium tumefaciens'' (BY6), which can be harvested on a large scale. The enzymes involved, IDS epimerase
IDS may refer to:
Computing
* IBM Informix Dynamic Server, a relational database management system
* Ideographic Description Sequence, describing a Unihan character as a combination of other characters
* Integrated Data Store, one of the first da ...
and C−N lyase, do not require any cofactors
Cofactor may also refer to:
* Cofactor (biochemistry), a substance that needs to be present in addition to an enzyme for a certain reaction to be catalysed
* A domain parameter in elliptic curve cryptography, defined as the ratio between the orde ...
.
Polyaspartic acid
Polyaspartic acid, like IDS, binds to calcium and other heavy metal ions. It has many practical applications including corrosion inhibitors, wastewater additives, and agricultural polymers. A Polyaspartic acid-based laundry detergent was the first laundry detergent in the world to receive the EU flower ecolabel. Calcium binding ability of polyaspartic acid has been exploited for targeting of drug-loaded nanocarriers to bone. Preparation of hydrogel
A hydrogel is a crosslinked hydrophilic polymer that does not dissolve in water. They are highly absorbent yet maintain well defined structures. These properties underpin several applications, especially in the biomedical area. Many hydrogels ar ...
s based on polyaspartic acid, in a variety of physical forms ranging from fiber
Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorpora ...
to particle
In the physical sciences, a particle (or corpuscule in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass.
They vary greatly in size or quantity, fro ...
, can potentially enable facile separation of the chelated ions from a solution. Therefore, despite being weaker than EDTA, polyaspartic acid can still be regarded as a viable alternative due to these features as well as biocompatibility, and biodegradability.
''S'',''S''-Ethylenediamine-''N'',''N''′-disuccinic acid (EDDS)
A structural isomer
In chemistry, a structural isomer (or constitutional isomer in the IUPAC nomenclature) of a compound is another compound whose molecule has the same number of atoms of each element, but with logically distinct bonds between them. The term met ...
of EDTA, ethylenediamine-''N'',''N''′-disuccinic acid (EDDS) is readily biodegradable at high rate in its ''S'',''S'' form.
Methylglycinediacetic acid (MGDA)
Trisodium dicarboxymethyl alaninate
Trisodium ''N''-(1-carboxylatoethyl)iminodiacetate, methylglycinediacetic acid trisodium salt (MGDA-Na3) or trisodium α-DL-alanine diacetate (N-(2-Carboxyethyl)iminodiacetic acid, α-ADA), is the trisodium anion of ''N''-(1-carboxyethyl)iminodiac ...
, also known as methylglycinediacetic acid (MGDA), has a high rate of biodegradation at over 68%, but unlike many other chelating agents can degrade without the assistance of adapted bacteria. Additionally, unlike EDDS or IDS, MGDA can withstand higher temperatures while maintaining a high stability as well as the entire pH range. MGDA has been shown to be an effective chelating agent, with a capacity for mobilization comparable with that of nitrilotriacetic acid (NTA), with application to water for industrial use and for the removal of calcium oxalate
Calcium oxalate (in archaic terminology, oxalate of lime) is a calcium salt of oxalic acid with the chemical formula . It forms hydrates , where ''n'' varies from 1 to 3. Anhydrous and all hydrated forms are colorless or white. The monohydrate ...
from urine from patients with kidney stone
Kidney stone disease, also known as nephrolithiasis or urolithiasis, is a crystallopathy where a solid piece of material (kidney stone) develops in the urinary tract. Kidney stones typically form in the kidney and leave the body in the urine ...
s.
Methods of detection and analysis
The most sensitive method of detecting and measuring EDTA in biological samples is selected reaction monitoring capillary electrophoresis mass spectrometry
Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a '' mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is u ...
(SRM-CE/MS), which has a detection limit of 7.3 ng/mL in human plasma and a quantitation limit of 15 ng/mL. This method works with sample volumes as small as 7–8 nL.
EDTA has also been measured in non-alcoholic beverages using high performance liquid chromatography (HPLC) at a level of 2.0 μg/mL.
In popular culture
In the movie Blade (1998), EDTA is used as a weapon to kill vampires, exploding when in contact with vampire blood.
References
External links
EDTA: Molecule of the Month
EDTA Determination of Total Water Hardness
*
{{DEFAULTSORT:Ethylenediaminetetraacetic Acid
Acetic acids
Amines
Antidotes
Chelating agents
Photographic chemicals
Preservatives
E-number additives
Hexadentate ligands
Ophthalmology drugs