PRODUCTS

BRONOPOL

CAS No.: 52-51-7
EC No.: 200-143-0

Synonyms:
bronopol; 2-Bromo-2-nitro-1,3-propanediol; 52-51-7; 2-Bromo-2-nitropropane-1,3-diol; Bronosol; Bronocot; Bronidiol; Bronopolu; Bronotak; Onyxide 500; Lexgard bronopol; 1,3-Propanediol, 2-bromo-2-nitro-; Bronopolum; Bronopolu [Polish]; 2-Nitro-2-bromo-1,3-propanediol; Caswell No. 116A; Bronopolum [INN-Latin]; C3H6BrNO4; Bronopol [INN:BAN:JAN]; bironopol; bronopole UNII-6PU1E16C9W; BRONOPOL; NSC 141021; HSDB 7195; 2-Bromo-2-nitropropane-1,3-diol (Bronopol); Q-200765; Bioban; 2-Bromo-2-nitropropane-1,3-diol [UN3241] [Flammable Solid]; Myacide AS plus; Myacide BT; CAS-52-51-7; Myacide Pharma BP; Canguard 409; BNPD; 2-Bromo-2-nitropropan-1,3-diol; ACMC-1ARSQ; AC1L1DPE; BNPD; BNPK; Bronopol; WLN: Bronopol, PESTANAL(R), analytical standard; 1, 2-bromo-2-nitro-; EC 200-143-0; SCHEMBL23260; Bronopol (JAN/USAN/INN); Bioban BNPD-40 (Salt/Mix); 2-bromo-2nitro-1,3-propanediol; MolPort-002-497-774; 2-b); BNPD; BNPK; Bronopol; 1, 2-bromo-2-nitro-; EC 200-143-0; Bronopol (JAN/USAN/INN); KSC911Q1T; Bioban BNPD-40 (Salt/Mix); 2-bromo-2nitro-1,3-propanediol; MolPort-002-497-774; 200-143-0; 2-bromo-2-nitro-1,3-propandiol; ALBB-031641; HY-B1217; ZINC1088216; Tox21_112079; Tox21_300126; 1,3-Propanediol,2-bromo-2-nitro-; 2-bromanyl-2-nitro-propane-1,3-diol; antimikrobiyal; organik; bromlanma; nitrozamin; hidrojen bromür; Allergens; bronopol; 2-Bromo-2-nitro-1,3-propanediol; 52-51-7; 2-Bromo-2-nitropropane-1,3-diol; Bronosol; Bronocot; Bronidiol; Bronopolu; Bronotak; Onyxide 500; Lexgard bronopol; 1,3-Propanediol, 2-bromo-2-nitro-; Bronopolum; Bronopolu [Polish]; 2-Nitro-2-bromo-1,3-propanediol; Caswell No. 116A; Bronopolum [INN-Latin]; C3H6BrNO4; Bronopol [INN:BAN:JAN]; BRONOPOL; NSC 141021; HSDB 7195; 2-Bromo-2-nitropropane-1,3-diol (Bronopol)

Bronopol

Bronopol (INN; chemical name 2-bromo-2-nitro-1,3-propanediol) is an organic compound that is used as an antimicrobial. It is a white solid although commercial samples appear yellow.

The first reported synthesis of bronopol was in 1897.

Bronopol was invented by The Boots Company PLC in the early 1960s and first applications were as a preservative for pharmaceuticals. Due to its low mammalian toxicity at in-use levels and high activity against bacteria, especially Gram-negative species,[1] bronopol became popular as a preservative in many consumer products such as shampoos and cosmetics. It was subsequently adopted as an antimicrobial in other industrial environments such as paper mills, oil exploration, and production facilities, as well as cooling water disinfection plants.

IUPAC name
2-Bromo-2-nitropropane-1,3-diol

Identifiers
CAS Number
52-51-7 ☑
3D model (JSmol)
Interactive image
ChEMBL
ChEMBL1408862 ☒
ChemSpider
2356 ☑
ECHA InfoCard 100.000.131
EC Number
200-143-0
KEGG
D01577 ☑
PubChem CID
2450
RTECS number
TY3385000
UNII
6PU1E16C9W ☑
UN number 3241
CompTox Dashboard (EPA)
DTXSID8024652 Edit this at Wikidata
InChI[show]
SMILES[show]
Properties
Chemical formula
C3H6BrNO4

Molar mass    199.988 g·mol-1
Appearance    White solid
Density    1.1 g/cm3
Melting point    130 °C (266 °F; 403 K)
Boiling point    140 °C (284 °F; 413 K) (decomposes)
Pharmacology
ATCvet code
QD01AE91 (WHO)

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Production of bronopol
Bronopol is produced by the bromination of di(hydroxymethyl)nitromethane, which is derived from nitromethane by a nitroaldol reaction.[2] World production increased from the tens of tonnes in the late 1970s to current estimates in excess of 5,000 tonnes. Manufacturing today is the business of low cost producers, mainly in China.

Applications of bronopol
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Bronopol is used in consumer products as an effective preservative agent, as well as a wide variety of industrial applications (almost any industrial water system is a potential environment for bacterial growth, leading to slime and corrosion problems - in many of these systems bronopol can be a highly effective treatment).

The use of bronopol in personal care products (cosmetics, toiletries) has declined since the late 1980s due to the potential formation of nitrosamines. While bronopol is not in itself a nitrosating agent, under conditions where it decomposes (alkaline solution and/or elevated temperatures) it can liberate nitrite and low levels of formaldehyde and these decomposition products can react with any contaminant secondary amines or amides in a personal care formulation to produce significant levels of nitrosamines (due to the toxicity of these substances, the term `significant` means levels as low as 10s of parts per billion).

Manufacturers of personal care products are therefore instructed by regulatory authorities to avoid the formation of nitrosamines which might mean removing amines or amides from the formulation, removing bronopol from a formulation, or using nitrosamine inhibitors.
Bronopol has been restricted for use in cosmetics in Canada.[3]

Physical and chemical properties
Appearance
Bronopol is supplied as crystals or crystalline powder, which may vary from white to pale yellow in colour depending on the grade. The yellow coloration is due to chelation of iron during the manufacturing process.

Melting point of bronopol
As a pure material, bronopol has a melting point of about 130 °C. However, due to its polymorphic characteristics, bronopol undergoes a lattice rearrangement at 100 to 105 °C and this can often be wrongly interpreted as the melting point.
At temperatures above 140 °C, bronopol decomposes exothermically releasing hydrogen bromide and oxides of nitrogen.

Solubility of bronopol
Bronopol is readily soluble in water; the dissolution process is endothermic. Solutions containing up to 28% w/v are possible at ambient temperature.
Bronopol is poorly soluble in non-polar solvents but shows a high affinity for polar organic solvents.

Solubilities at 22-25 °C
Solvent    %w/v
Water    28
Methanol    89
Ethanol    56
Isopropanol    41
Liquid Paraffin    <0.5
Partition coefficient
Study of the solubility data shows that bronopol has a high affinity for polar rather than non-polar environments. In two-phase systems, bronopol partitions preferentially into the polar (usually aqueous) phase.

Partition coefficients at 22-24 °C
Solvent Combination    Partition Co-efficient
Hexanol/Water    0.74
Alkane|Liquid Paraffin/Water    0.043
Chloroform/Water    0.068
Stability in aqueous solution
In aqueous solutions, bronopol is most stable when the pH of the system is on the acid side of neutral. Temperature also has a significant effect on stability in alkaline systems.

Degradation of bronopol
Under extreme alkaline conditions, bronopol decomposes in aqueous solution and very low levels of formaldehyde are produced.[4] Liberated formaldehyde is not responsible for the biological activity associated with bronopol. Other decomposition products detected after bronopol breakdown are bromide ion, nitrite ion, bromonitroethanol and 2-hydroxymethyl-2-nitropropane-1,3-diol.

Allergy
Patch test
In 2005-2006, it was the 15th-most-prevalent allergen in patch tests (3.4%) of people with suspected allergic contact dermatitis.[5] It is used as a substitute for formaldehyde, a disinfectant and preservative, in solvents. It is prevalent in skin and personal care products and topical medications.[6]
See also
Bronidox

About Bronopol
Bronopol is manufactured and/or imported in the European Economic Area in 100 - 1 000 tonnes per year.
Bronopol is used by consumers, by professional workers (widespread uses) and in formulation or re-packing.

Biocidal Uses of bronopol
Bronopol is being reviewed for use as a biocide in the EEA and/or Switzerland, for: disinfection, product preservation, preservation of fibres, leather, rubber, or polymers, preservation for liquid systems, controlling slimes, embalming or taxidermy.

Consumer Uses of bronopol
Bronopol is used in the following products: cosmetics and personal care products, perfumes and fragrances, fertilisers and plant protection products.
Other release to the environment of Bronopol is likely to occur from: outdoor use as processing aid and indoor use as processing aid.
Article service life
ECHA has no public registered data on the routes by which Bronopol is most likely to be released to the environment. ECHA has no public registered data indicating whether or into which articles the substance might have been processed.

Widespread uses by professional workers of bronopol
Bronopol is used in the following products: fertilisers, plant protection products, perfumes and fragrances, cosmetics and personal care products and washing & cleaning products.
Bronopol is used in the following areas: agriculture, forestry and fishing and formulation of mixtures and/or re-packaging.
Other release to the environment of Bronopol is likely to occur from: outdoor use as processing aid and indoor use as processing aid.

Formulation or re-packing of bronopol
Bronopol is used in the following products: laboratory chemicals, biocides (e.g. disinfectants, pest control products), fertilisers, plant protection products, perfumes and fragrances, cosmetics and personal care products and washing & cleaning products.
Release to the environment of Bronopol can occur from industrial use: formulation of mixtures and formulation in materials.

Uses at industrial sites of bronopol
ECHA has no public registered data indicating whether or in which chemical products the substance might be used. ECHA has no public registered data on the types of manufacture using Bronopol. ECHA has no public registered data on the routes by which Bronopol is most likely to be released to the environment.

Manufacture of bronopol
ECHA has no public registered data on the routes by which Bronopol is most likely to be released to the environment.

Bronopol, or 2-Bromo-2-nitro-1,3-propanediol, is an inorganic compound with wide-spectrum antimicrobial properties. First synthesized in 1897, bronopol was primarily used as a preservative for pharmaceuticals and was registered in the United States in 1984 for use in industrial bactericides, slimicides and preservatives [F13]. Bronopol is used as a microbicide or microbiostat in various commercial and industrial applications, including oil field systems, air washer systems, air conditioning or humidifying systems, cooling water systems, papermills, absorbent clays, metal working fluids, printing inks, paints, adhesives and consumer products [F13]. Compared to other aliphatic halogen-nitro compounds, bronopol is more stable to hydrolysis in aqueous media under normal conditions [A32792]. The inhibitory activity against various bacteria, including _Pseudomonas aeruginosa_, was demonstrated _in vitro_ [A32792]. Bronopol is approved for use in antibacterial OTC products in Canada.

2-BROMO-2-NITROPROPANE-1,3-DIOL is a white crystals. Ignite easily and burn readily. May detonate under strong shock. Decomposes when heated, evolving toxic gases. Toxic by skin absorption, inhalation or ingestion.

Solubility and miscibility of bronopol:
Bronopol can be easily incorporated into aqueous formulation systems. Concentrated aqueous solutions tend to crystallize at low temperatures. Bronopol dissolves poorly in polar solvents, but organic polar solvents show a high degree of interest.
In non-aqueous systems, it is possible to achieve an effective level of Bronopol by using a suitable carrier solvent with careful selection of the raw materials.

Storage stability of bronopol:
When stored at ambient temperature, sealed packaging, Bronopol crystal types are stable for at least 3 years and liquid formulations are stable for at least 2 years. When aqueous solutions of crystalline material are prepared, bronopol is most stable when the pH of the system is acidic. In the presence of buffers, Bronopol`s concentration solutions tend to be self-stabilizing. The best pH for stability is around 4 and the data obtained from studies in dilute solutions of Bronopol show that the lifetime at pH = 4 and room temperature is more than 5 years. At pH and temperature increases, aqueous bronopol solutions become less stable.

Compatibility of bronopol:
Indicates that the concentrated aqueous solutions (20%) of the bronopol solutions (321 type) are compatible with solid PVC, Polyethylene (XDG33), plasticized PVC, silicone rubber, nylon and polypropylene in stainless steel. A diluted aqueous bronopol solution (0.02%) (representative of the level of use); stainless steel (321), aluminum, brass, copper, solid PVC, polyethylene (WJ611) and polyethylene (XD633).
Antimicrobial activity: Bronopol has a complex style of antimicrobial action. It has a broad spectrum against all groups of Bronopol bacteria containing bacteria-reducing anaerobic sulphate. The majority of bacteria are stopped between 6.25 and 50 ppm.

More doses are needed to reduce the activity of Bronopol`s fungi more and more generally. Most yeasts and molds require about 400 to 1600 ppm search. This procedure can not always control bronchopneumic dosages alone. It is not like this, it can be used with other assets. The Bronopol industry has pressure diagnostics:

Paper industry biocides: Processes of water treatment and mill (grinding). Calcium carbonate processing paper mill (grinding) additive preservative.
Water and oil field biocides:
Increasing oil recovery and conditioning cleaning waters such as cooling towers.
Bronopol is capable of controlling microbial contamination (in piercing mud). Tests show that you can clear all levels of contamination.
Industrial product enclosure:
Technical files such as polymer emulsion adhesives and motor materials. Bronopol is a very low level in a multidimensional arrangement.

Pharmacology of bronopol
At concentrations of 12.5 to 50 µg/mL, bronopol mediated an inhibitory activity against various strains of Gram negative and positive bacteria _in vitro_ [A32792]. The bactericidal activity is reported to be greater against Gram-negative bacteria than against Gram-positive cocci [A32792]. Bronopol was also demonstrated to be effective against various fungal species, but the inhibitory action is reported to be minimal compared to that of against bacterial species [A32792]. The inhibitory activity of bronopol decreases with increasing pH of the media [A32792, F13]. Bronopol also elicits an anti-protozoal activity, as demonstrated with _Ichthyophthirius multifiliis_ _in vitro_ and _in vivo_ [A32791]. It is proposed that bronopol affects the survival of all free-living stages of _I. multifiliis_ [A32791].

Health Hazard of bronopol
Excerpt from ERG Guide 133 [Flammable Solids]: Fire may produce irritating and/or toxic gases. Contact may cause burns to skin and eyes. Contact with molten substance may cause severe burns to skin and eyes. Runoff from fire control may cause pollution.
Fire Hazard
Excerpt from ERG Guide 133 [Flammable Solids]: Flammable/combustible material. May be ignited by friction, heat, sparks or flames. Some may burn rapidly with flare-burning effect. Powders, dusts, shavings, borings, turnings or cuttings may explode or burn with explosive violence. Substance may be transported in a molten form at a temperature that may be above its flash point. May re-ignite after fire is extinguished.
Combustible. Gives off irritating or toxic fumes (or gases) in a fire.
Fire Potential
Combustible.
Skin, Eye, and Respiratory Irritations
The substance irritates the eyes, the skin and the respiratory tract.

Safety and Hazard Properties of bronopol
Chemical Dangers
Decomposes on heating and on burning. This produces toxic and corrosive fumes including hydrogen bromide and nitrogen oxides. Reacts with some metals, amines and alkaline compounds.

First Aid Measures of bronopol
First Aid
EYES: First check the victim for contact lenses and remove if present. Flush victim`s eyes with water or normal saline solution for 20 to 30 minutes while simultaneously calling a hospital or poison control center. Do not put any ointments, oils, or medication in the victim`s eyes without specific instructions from a physician. IMMEDIATELY transport the victim after flushing eyes to a hospital even if no symptoms (such as redness or irritation) develop.

Bronopol is a Standardized Chemical Allergen. The physiologic effect of bronopol is by means of Increased Histamine Release, and Cell-mediated Immunity. The chemical classification of bronopol is Allergens.

Bronopol, or 2-Bromo-2-nitro-1,3-propanediol, is an inorganic compound with wide-spectrum antimicrobial properties. First synthesized in 1897, bronopol was primarily used as a preservative for pharmaceuticals and was registered in the United States in 1984 for use in industrial bactericides, slimicides and preservatives [F13]. Bronopol is used as a microbicide or microbiostat in various commercial and industrial applications, including oil field systems, air washer systems, air conditioning or humidifying systems, cooling water systems, papermills, absorbent clays, metal working fluids, printing inks, paints, adhesives and consumer products [F13]. Compared to other aliphatic halogen-nitro compounds, bronopol is more stable to hydrolysis in aqueous media under normal conditions [A32792]. The inhibitory activity against various bacteria, including _Pseudomonas aeruginosa_, was demonstrated _in vitro_ [A32792]. Bronopol is approved for use in antibacterial OTC products in Canada.

Properties: Biocidal products containing active ingredient Bronopol are used for the preservation of industrial and consumer products and for conditioning industrial and process water. Bronopol is soluble in water and compatible with proteins and non-ionic. Mantarsal activity is poor, poor stability over pH 8, associated with nitrosamine formation, detectable formaldehyde release. Typical usage concentration is between 0,01-0,04%.

Description of bronopol:

Bronopol is a white, odorless crystalline substance that melts at about 130 ºC. It is readily soluble in water, lower alcohols, acetic acid, diethyl ether and ethyl acetate, but poorly soluble in chloroform, acetone and practically insoluble in hydrocarbon solvents. The values of the solubility of bronopol in some solvents are as follows (w / v% at 22-25 ° C): water 28; methyl alcohol 89; ethyl alcohol 56; isopropyl alcohol 41; ethylene glycol 61; methylcarbitol 54; 1,2-propylene glycol 52; dipropylene glycol 48; polyethylene glycol 300; diethyl sebacate 10; isopropyl myristate, mineral oil and vegetable oils less than 0.5. Aqueous solutions of a pure compound have a pH of 5.0-5.5, which is explained by the mobility of hydroxyl hydrogen atoms. Solid compound can be stored for 3 years or longer, it is not influenced by factors such as daylight, humidity (up to 90%) and temperature (up to 45 ° C). However, an aqueous solution of Bronopol is stable only in the cold, provided that the acidity is high enough. An increase in pH and temperature leads to the decomposition of the compound as a result of the decomposition of formaldehyde. The initial process of decomposition of bronopol appears to be a retroaldol reaction with the release of formaldehyde and the formation of bromonitroethanol.

Bromonitroethanol itself is significantly less stable than bronopol, and in the range of conditions studied, its maximum concentration did not exceed 0.5% of the initial concentrations of bronopol. At the same time, a second-order reaction occurs with the participation of bronopol and formaldehyde to obtain 2-hydroxymethyl-2-nitro-1,3-propanediol. The antimicrobial activity of bronopol is mainly due to the presence of electron-deficient bromine atoms in the molecules, which exhibit oxidizing properties, and not the ability to release formaldehyde. The mechanism of the antimicrobial action of bronopol consists of cross-linking of sulfhydride groups of dehydrogenase enzymes that occur on the surface of microbial cells. Disulfide bridges block the metabolism of microorganisms.

Application of bronopol:

Bronopol is used as a preservative in various cosmetic and household products due to its high activity against gram-negative bacteria, especially Pseudomonas aeruginosa and other pseudomonads. These organisms are common water dwellers and can cause pollution and deterioration problems. Bronopol is an effective antibacterial preservative in a wide pH range. It is stable at acidic pH values and is also useful as a labile antibacterial preservative in an alkaline environment. Due to its broad spectrum antibacterial activity, Bronopol can also be used as an active agent, for example in aerosol preparations.

Receiving of bronopol:

The method for producing bronopol includes loading the reaction vessel with water, bromopicrin, nitromethane and paraformaldehyde, gradually supplying the base to the reaction vessel with stirring, bringing the reaction to completion and separating bronopol from the aqueous reaction mixture.

Bronopol products are currently registered for use in oilfield systems, air purification systems, industrial water treatment systems, laboratory water baths, coatings, emulsions, air conditioning / humidification systems, pulp and paper industry systems, metalworking cutting fluids, and also consumer / institutional products.

Action on the body of bronopol:

Bronopol (2-bromo-2-nitropropane-1,3-diol) is a bactericide with limited effectiveness against fungal organisms. It is active against Pseudomonas species and should be used at a pH of 5 to 8.8, below the application temperature of 45 ° C. Bronopol has a complex mechanism of action that attacks thiol groups in cells, suppressing respiration and cellular metabolism.

Research indicates that bronopol is a corrosive eye irritant and moderate to severe skin irritant in rabbits. The fate of the environment and the ecological consequences of the use of Bronopol are moderately highly toxic for estuarine / marine invertebrates; slightly toxic to marine fish; slightly toxic to birds with acute oral ingestion. However, no quantitative risk assessment has been carried out. The risk to the aquatic environment is being addressed under the NPDES permitting program by the Water Resources Authority. It is now required that labels on all products containing Bronopol meet NPDES requirements.

The mechanism of the antimicrobial action of bronopol is quite complex, and, as a rule, it is not associated with the release of formaldehyde. That is why it is considered that it is a mistake to classify this preservative as a typical formaldehyde donor. Nevertheless, it cannot be denied that formaldehyde is nevertheless formed during the decomposition of bronopol, and the presence of cross-sensitivity to bronopol with an established allergy to formaldehyde takes place. However, the release of formaldehyde does not occur at the same rate and in the same amount under different conditions.

The main factors affecting the destruction of bronopol are pH, sunlight and temperature. It was found that with the addition of citric acid, which lowers the pH, the decomposition of bronopol in aqueous solutions slows down, which is quite natural, and an increase in temperature and exposure to sunlight increases the rate of decomposition. These facts are taken into account when formulating recipes.

There are few quantitative data on the destruction of bronopol - much less than for typical formaldehyde donors, but they are still there; the highest concentration of formaldehyde in alkaline compounds, which is quite natural, but they are not so high as to cause concern or put a warning about the presence of formaldehyde in the marking. The pH range from 5 to 6 can be considered quite favorable for the preservative's behavior and for the skin.

Bronopol, like other preservatives, can cause the development of symptoms of contact dermatitis, but in most cases it does not belong to the leaders, but rather an outsider. A different situation is observed only in case of serious skin diseases, such as chronic eczema or atopic dermatitis, in which the normal barrier function of the skin is disrupted, and the frequency of using special cosmetics designed to relieve symptoms is increased, which leads to an increased risk of developing sensitization. But the specificity of allergic reactions to bronopol is not due to formaldehyde, but to other products of its decay, such as 2-bromoethanol, 2-bromo-2-nitroethanol and bromonitromethane.

The connection between the use of bronopol in cosmetics and the potential for the formation of carcinogenic nitrosamines theoretically exists (and if the established precautions are not followed, it can be realized in practice), but for this, restrictions are introduced to minimize these risks [1]... Nitrosamines are found almost everywhere in the environment; moreover, they are formed in the human digestive tract as a result of the reaction between secondary amines or amides and nitrite ions. Bronopol itself is not a nitrosating agent, but under conditions under which it decomposes (alkaline environment and / or elevated temperature), it can release nitrite ions, potentially capable of producing nitrosamines - if anything, because for this reaction there is only nitrite is not enough. Accordingly, bronopol is not used where there is a risk of formation of nitrosamines, and cosmetic raw materials, which may contain trace amounts of secondary amines or amides, undergo thorough cleaning and strict control

It is proposed that bronopol generates biocide-induced bacteriostasis followed by a growth at an inhibited rate in bacteria, via two distinct reactions between bronopol and essential thiols within the bacterial cell [A32790]. Under aerobic conditions, bronopol catalyzes the oxidation of thiol groups, such as cysteine, to disulfides. This reaction is accompanied by rapid consumption of oxygen, where oxygen acts as the final oxidant. During the conversion of cysteine to cystine, radical anion intermediates such as superoxide and peroxide are formed from bronopol to exert a direct bactericidal activity. The oxidation of excess thiols alters the redox state to create anoxic conditions, leading to a second reaction involving the oxidation of intracellular thiols such as glutathione to its disulfide. The resulting effects are inhibition of enzyme function, and reduced growth rate following the bacteriostatic period [A32790]. Under the anoxic conditions, the reaction between thiol and bronopol decelerates without the involvement of oxygen and the consumption of bronopol predominates. Bronopol is ultimately removed from the reaction via consumption and resumption of bacterial growth occurs [A32790].

The half-life of bronopol in the biological systems is not reported in the literature. The half-life value reported for bronopol reflects the environment fate of the compound. When released into the air as vapours, bronopol is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals where the half life for this reaction is approximately 11 days [L2578]. The photolysis half-life is 24 hours in water but may be up to 2 days under natural sunlight [L2578].

Transformation products usually differ in environmental behaviors and toxicological properties from the parent contaminants, and probably cause potential risks to the environment. Toxicity evolution of a labile preservative, bronopol, upon primary aquatic degradation processes was investigated. Bronopol rapidly hydrolyzed in natural waters, and primarily produced more stable 2-bromo-2-nitroethanol (BNE) and bromonitromethane (BNM). Light enhanced degradation of the targeted compounds with water site specific photoactivity. The bond order analysis theoretically revealed that the reversible retroaldol reactions were primary degradation routes for bronopol and BNE. Judging from toxicity assays and the relative pesticide toxicity index, these degradation products (i.e., BNE and BNM), more persistent and higher toxic than the parent, probably accumulated in natural waters and resulted in higher or prolonging adverse impacts. Therefore, these transformation products should be included into the assessment of ecological risks of non-persistent and low toxic chemicals such as the preservative bronopol.

Bronopol undergoes degradation in aqueous medium to form bromonitroethanol from a retroaldol reaction with the liberation of an equimolar amount of formaldehyde [A32793]. Formaldehyde is a degradation product of bronopol, which may cause sensitization [L2578]. Bromonitroethanol further decomposes to formaldehyde and bromonitromethane. Bromonitroethanol may also break down to release a nitrite ion and 2-bromoethanol [A32793].

An aqueous solution of bronopol degrades in the presence of cupric and ferric ions as well as aluminum and tin metals.

Environmental Fate/Exposure Summary
Bronopol's production and use as a preservative for cosmetics and pharmaceuticals may result in its release to the environment through various waste streams; its use as an agricultural bacteriostat will result in its direct release to the environment. If released to air, a vapor pressure of 1.26X10-5 mm Hg at 20 °C indicates bronopol will exist in both the vapor and particulate phases in the atmosphere. Vapor-phase bronopol will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 11 days. Particulate-phase bronopol will be removed from the atmosphere by wet and dry deposition. Bronopol rapidly photodegrades at pH 4 exhibiting a photolysis half-life of 24 hours in water; under natural sunlight, a photolysis half-life of 2 days is expected. Therefore, bronopol may be susceptible to direct photolysis. If released to soil, bronopol is expected to have very high mobility based upon an estimated Koc of 1. Volatilization from moist soil surfaces is not expected to be an important fate process based upon an estimated Henry's Law constant of 1.3X10-11 atm-cu m/mole. Bronopol is not expected to volatilize from dry soil surfaces based upon its vapor pressure. Utilizing the Japanese MITI test, 0% of the theoretical BOD was reached in 4 weeks indicating that biodegradation is not an important environmental fate process. If released into water, bronopol is not expected to adsorb to suspended solids and sediment based upon the estimated Koc. Volatilization from water surfaces is not expected to be an important fate process based upon this compound's estimated Henry's Law constant. An estimated BCF of 3 suggests the potential for bioconcentration in aquatic organisms is low. At 20 °C, the hydrolysis half-life was extrapolated to be about 18 years at pH 4, about 1.5 years at pH 6, and approximately 2 months at pH 8. Occupational exposure to bronopol may occur through inhalation of dust and dermal contact with this compound at workplaces where bronopol is produced or used. Use data indicate that the general population may be exposed to bronopol via dermal contact with this compound or other consumer products containing bronopol.

Based on a classification scheme(1), an estimated Koc value of 1(SRC), determined from a structure estimation method(2), indicates that bronopol is not expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is not expected(3) based upon an estimated Henry's Law constant of 1.3X10-11 atm-cu m/mole(SRC), derived from its vapor pressure, 1.26X10-5 mm Hg(4), and water solubility, 2.5X10+5 mg/L(5). Bronopol is stable to hydrolysis under normal environmental conditions. At 20 °C, the hydrolysis half-life was extrapolated to be about 18 years at pH 4, about 1.5 years at pH 6, and approximately 2 months at pH 8(6). Bronopol rapidly photodegrades at pH 4 exhibiting a photolysis half-life of 24 hours in water(6). According to a classification scheme(7), an estimated BCF of 1(SRC), from an estimated log Kow of -0.64(2) and a regression-derived equation(2), suggests the potential for bioconcentration in aquatic organisms is low(SRC). Bronopol was not biodegraded using a mixed culture sewage sludge test(8); therefore, biodegradation is not expected to be an important fate process in the aquatic environment(SRC).

The rate constant for the vapor-phase reaction of bronopol with photochemically-produced hydroxyl radicals has been estimated as 1.3X10-12 cu cm/molecule-sec at 25 °C(SRC) using a structure estimation method(1). This corresponds to an atmospheric half-life of about 11 days at an atmospheric concentration of 5X10+5 hydroxyl radicals per cu cm(1). Bronopol is stable to hydrolysis under normal environmental conditions. At 20 °C, the hydrolysis half-life was extrapolated to be about 18 years at pH 4, about 1.5 years at pH 6, and approximately 2 months at pH 8. At elevated temperatures (>30 °C) or high pH, rapid hydrolysis may occur producing formaldehyde and to a lesser extent tris(2-hydroxymethyl-2-nitropropane-1,3-diol), 2-bromo-2-nitroethanol, and other polymeric and aliphatic nitro compounds(2). Bronopol rapidly photodegrades at pH 4 exhibiting a photolysis half-life of 24 hours in water. Degradation products identified included tris(2-hydroxymethyl-2-nitropropane-1,3-diol). Under natural sunlight (assuming 12 hours of light and dark), a half-life of 2 days is expected(2).

Using a structure estimation method based on molecular connectivity indices(1), the Koc of bronopol can be estimated to be 1(SRC). According to a classification scheme(2), this estimated Koc value suggests that bronopol is expected to have very high mobility in soil.

The Henry's Law constant for bronopol is estimated as 1.3X10-11 atm-cu m/mole(SRC) derived from its vapor pressure, 1.3X10-5 mm Hg(1), and water solubility, 2.5X10+5 mg/L(2). This Henry's Law constant indicates that bronopol is expected to be essentially nonvolatile from moist soil and water surfaces(3). Bronopol is not expected to volatilize from dry soil surfaces(SRC) based upon its vapor pressure(1).

According to the 2006 TSCA Inventory Update Reporting data, the number of persons reasonably likely to be exposed in the industrial manufacturing, processing, and use of bronopol is 100 to 999; the data may be greatly underestimated(1).

NIOSH (NOES Survey 1981-1983) has statistically estimated that 5,176 workers (4,904 of these were female) were potentially exposed to bronopol in the US(1). Occupational exposure to bronopol may occur through inhalation of dust and dermal contact with this compound at workplaces where bronopol is produced or used. Use data indicate that the general population may be exposed to bronopol via dermal contact with this compound or other consumer products containing bronopol(SRC).