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Nail polish
Environmental safety
Regulation and environmental concerns
As previously mentioned, nail polish is a
Dibutyl phthalate
Environmental relevance
Fundamental environmental chemistry
Dibutyl phthalate (DBP) is one of the six phthalic acid esters found on the Priority Pollutant List, which consists of specified chemical pollutants regulated by the
Octanol-Water Partition Coefficient (Log Kow) | |||
Dibutyl Phthalate | 4.11 | 4.31 | 4.46 |
Dissolved organic carbon
DBP is a hydrophobic compound that has a low solubility in water. However, different interactions with dissolved organic carbon (DOC) can have solubilizing effects on DBP and increase its mobility in places it is commonly found, such as in landfills [10]. DOC is known to increase DBP’s water solubility by interacting in two ways: by changing the equilibrium distribution of the solute (DBP) and by direct interaction with DBP. In the first interaction, DBP’s sorption coefficient is lowered when partially water-miscible substances change the equilibrium distribution of DBP between its solid and liquid phase. These partially water-miscible substances are typically alcohols and are also known as cosolvents. The result of this is an increase in DBP’s mobility, but this interaction requires high concentrations of DBP to take place. Increased solubility of DBP is more likely to occur by the second interaction which involves a direct interaction between DBP and other organic compounds. DBP becomes more polar and water soluble after interaction with these typically polar organic compounds found in landfills. DBP can then bind to DOC in a partition-like interaction where the hydrophobic moeitities of DBP and DOC bind each other in a micelle-like structure within an amphiphilic macromolecule. Studies have shown that in some landfill leachates, 85% of phthalate esters are found in their solubilized form due to DOC [11].
Hydrolysis of DBP
DBP and other phthalates found in landfills are known to undergo both acid and base catalyzed hydrolysis. Xenobiotic substances like DBP are commonly degraded by hydrolysis reactions [12]. Metal ions, anions, and organic materials can all serve as catalysts for these acid- or base-catalyzed hydrolysis reactions. In both the acid- and base-catalyzed reactions, DBP is first hydrolyzed to a monoester form that contains a carboxylic acid, and 1-butanol is released. The monoester is then hydrolyzed to form phthalic acid, and a second 1-butanol is released. The overall reaction requires two molecules of H2O and either a base or acid working as the catalyst. This hydrolysis reaction is both pH and temperature dependent in landfills. It occurs readily in the deeper layers of landfills, where temperatures are high and acidic or basic conditions are prevalent. In addition, the reactants tend to mimic their gas-phase structure in these deeper layers, which decreases steric effects during this ester hydrolysis. However, the rate of this reaction is negligible at the surface of landfills due to low temperatures and neutral pH conditions. At pH 7, esters tend to be less electrophilic and less susceptible to hydrolysis [12]. This is one of the primary reasons why DBP concentrations can be elevated on or near the surface of landfills relative to the deeper layers. These elevated concentrations create a cause for concern due to the possibility of the chemical leaching into the surrounding environment.
Photocatalytic degradation of DBP
DBP can also be photochemically degraded with the help of titanium dioxide (TiO2) [13].
TiO2 + hv > 5.13 x 10-19 J TiO2(e-cb/h+vb) e-cb + h+vb (1)
h+vb + OH- (or H2O)surface •OH(+H+) (2)
e-cb + O2 •O2•− + H+ •OOH (3)
TiO2 first absorbs UV light at wavelengths below 3.87 x 10-7 m (or with an energy greater than 5.13 x 10-19 J). This reaction produces electron-hole pairs which will react independently. The conduction band electrons (e-cb) react with dioxygen molecules to produce a superoxide radical anion, ·O2·-. The superoxide radical anion is then protonated to form a
DBP leaching
From the surface film, DBP has a very small tendency to volatilize into the atmosphere due to a
W = (1-f) Wv + f Wp = (1-f) RT/H + f Wp
where Wv is the vapor washout ratio, RT/H is the reciprocal of Henry’s Law constant, Wp is the particle scavenging coefficient, and f is the fraction of chemical on the particulate. Dibutyl phthalate displays a washout ratio (W) of 2.8 x 10-4 with a f of 0.014. Studies have indicated that DBP functions by a “temperature-dependent phenomena” whereby it is in the colder winter months that the vapor pressure of the compound is reduced sufficiently in order to produce an efficient washout ratio. Moreover, because of the hydrophobicity of phthalate esters, their chemical composition permits their sorption into soil and sediment among other environmental components [12]. Upon release into the environment, dibutyl phthalate is able to interact with environmental media in ways that change their chemical behavior [6].
Agencies have begun to delve into implementing affordable and resourceful methods of treating water supplies to decrease the concentration of the plasticizer components in rivers and lakes. First, adsorption to remove organic compounds has been extensively researched by the EPA whereby activated carbon is used to treat water consumed by humans. Another method under current investigation is the biological avenue which utilizes populations of microorganisms to degrade the esters. For example, Enterobacter species can biodegrade municipal solid waste—where the DBP concentration can be observed at 1500 ppm—with a half-life of 1.04 x 105 seconds. In comparison, the same species can break down 100% of dimethyl phthalate after a span of six days. However, this treatment method varies significantly depending on temperature, anaerobic and aerobic conditions, and more [14].
Toluene toxicity
Environmental relevance
Fundamental environmental chemistry
Toluene, also known as
Toluene and photochemically-produced hydroxyl radicals
Hydroxyl radicals are formed via a two-step reaction (reactions 1 and 2). The first step is the photolysis of gaseous ozone which employs solar energy and results in diatomic oxygen gas and an oxygen atom in its excited state. The electronically excited oxygen atom has sufficient excitation energy to now react with water vapor, producing hydroxyl radicals [17][18].
Reaction (1): O3 + hv O(1D) + O2
Reaction (2): O(1D) + H2O 2OH•
The initial reaction of toluene with a hydroxyl radical includes direct OH addition to the ortho position of the benzene ring and results in an ortho OH-toluene adduct (also known as methylhydroxycyclohexadienyl radical). The adduct subsequently reacts with atmospheric O2 via three possible pathways, however, the third will not be discussed as it has been proven to be thermodynamically and kinetically inhibited. The first pathway, upon reaction with O2, forms a primary organic peroxy radical (RO2) via O2 addition. The second pathway, upon reaction with O2, forms the phenolic compound O-cresol and hydroperoxy radicals (HO2) via hydrogen abstraction [19].
Both RO2 (reaction 3) and HO2 (reaction 4) products generated react with nitric oxide (NO) to form nitrogen dioxide (NO2) which subsequently undergoes photodissociation to produce ground-state oxygen atoms that recombine with molecular oxygen to produce tropospheric ozone (reactions 5 and 6) .
Reaction (3): RO2 + NO RO + NO2
Reaction (4): HO2 + NO OH + NO2
Reaction (5): NO2 + hv NO + O·
Reaction (6): O· + O2 + M O3 + M
Toluene and nitrate radicals
Nitrate radicals are formed when anthropogenic NO2 gas, commonly emitted by industrial sources, reacts with atmospheric ozone (reaction 7). Nitrate radicals are known as a “night-time oxidizer” as its nighttime concentration is nearly twice the concentration of the hydroxyl radical during the daytime [24].
Reaction (7): NO2 + O3 NO3• + O2
Nitrate radicals oxidize toluene either by the abstraction of the alpha-hydrogen atom, shown on top, or by the transfer of an electron, shown on bottom. These reactions result in nitric acid (HNO3) and nitrate (NO3-) (i.e. a strong acid and its conjugate base) [25].
Nitric acid exists in the atmosphere in its gas phase and can react with gaseous ammonia to form particulate or aerosol nitrate. Nitric acid is highly corrosive, and if concentrated in the environment, it can react rapidly with other natural or anthropogenic environmental compounds. These reactions can occur so rapidly that they result in a chemical fire or explosion [26]. Nitrate is highly soluble in the environment which enables the compound to easily move with soil water towards plant roots and to inhabit surface water and ground water. The pollution of bodies of water with excess nitrate from the atmosphere may lead to hypoxia. The compound promotes rapid algae growth, which then results in reduced oxygen water levels making it difficult for marine species to survive [27].
See also
References
- ^ "Household Hazardous Waste | Pacific Southwest: Solid Waste | US EPA". www3.epa.gov. Retrieved 2017-11-28.
- ^ "U.S.: Usage of nail polish and nail care products 2016 | Statistic". Statista. Retrieved 2017-11-28.
- .
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- PMID 28716940.
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- doi:10.17226/19914.
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- ^ ISBN 9781461458814.
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- ^ Pubchem. "toluene". pubchem.ncbi.nlm.nih.gov. Retrieved 2017-11-27.
- ^ "Explore Nature (U.S. National Park Service)". www.nps.gov. Retrieved 2017-11-27.
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- ISSN 0022-4936.
- ^ "Nitric acid | National Pollutant Inventory". www.npi.gov.au. Retrieved 2017-11-27.
- ^ PG, Mr. Brian Oram,. "Water Research Center - Nitrogen effects on surface and groundwater quality". www.water-research.net. Retrieved 2017-11-27.
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