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Pyrene
Pyrene
Pyrene
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For other uses, see Pyrene (disambiguation).
Pyrene
Structural formula of pyrene
Ball-and-stick model of the pyrene molecule
Names
Preferred IUPAC name
Pyrene[1]
Other names
Benzo[def]phenanthrene
Identifiers
3D model (JSmol)
1307225
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.004.481 Edit this at Wikidata
84203
KEGG
RTECS number
  • UR2450000
UNII
  • InChI=1S/C16H10/c1-3-11-7-9-13-5-2-6-14-10-8-12(4-1)15(11)16(13)14/h1-10H checkY
    Key: BBEAQIROQSPTKN-UHFFFAOYSA-N checkY
  • InChI=1/C16H10/c1-3-11-7-9-13-5-2-6-14-10-8-12(4-1)15(11)16(13)14/h1-10H
    Key: BBEAQIROQSPTKN-UHFFFAOYAB
  • c1cc2cccc3c2c4c1cccc4cc3
Properties
C16H10
Molar mass 202.256 g·mol−1
Appearance colorless solid

(yellow impurities are often found at trace levels in many samples).

Density 1.271 g/cm3[2]
Melting point 150.62 °C (303.12 °F; 423.77 K)[2]
Boiling point 394 °C (741 °F; 667 K)[2]
0.049 mg/L (0 °C)
0.139 mg/L (25 °C)
2.31 mg/L (75 °C)[3]
log P 5.08[4]
Band gap 2.02 eV[5]
−147·10−6 cm3/mol[6]
Structure[7]
Monoclinic
P21/a
a = 13.64 Å, b = 9.25 Å, c = 8.47 Å
α = 90°, β = 100.28°, γ = 90°
4
Thermochemistry[8]
229.7 J/(K·mol)
224.9 J·mol−1·K−1
125.5 kJ·mol−1
Enthalpy of fusion (ΔfH⦵fus)
 17.36 kJ·mol−1
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 irritant
GHS labelling:[9]
GHS07: Exclamation markGHS09: Environmental hazard
Warning
H315, H319, H335, H410
P261, P264, P271, P273, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
2
1
0
Flash point non-flammable
Related compounds
Related PAHs
 benzopyrene
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Pyrene is a polycyclic aromatic hydrocarbon (PAH) consisting of four fused benzene rings, resulting in a flat aromatic system. The chemical formula is C16H10. This yellow-green solid is the smallest peri-fused PAH (one where the rings are fused through more than one face). Pyrene forms during incomplete combustion of organic compounds.[10]

Occurrence and properties

[edit]

Pyrene was first isolated from coal tar, where it occurs up to 2% by weight. As a peri-fused PAH, pyrene is much more resonance-stabilized than its five-member-ring containing isomer fluoranthene. Therefore, it is produced in a wide range of combustion conditions. For example, automobiles produce about 1 μg/km.[11]

Reactions

[edit]

Oxidation with chromate affords perinaphthenone and then naphthalene-1,4,5,8-tetracarboxylic acid. Pyrene undergoes a series of hydrogenation reactions and is susceptible to halogenation, Diels-Alder additions, and nitration, all with varying degrees of selectivity.[11] Bromination occurs at one of the 3-positions.[12]

Reduction with sodium affords the radical anion. From this anion, a variety of pi-arene complexes can be prepared.[13]

Photophysics

[edit]

Pyrene and its derivatives are used commercially to make dyes and dye precursors, for example pyranine and naphthalene-1,4,5,8-tetracarboxylic acid. It has strong absorbance in UV-Vis in three sharp bands at 330 nm in DCM. The emission is close to the absorption, but moving at 375 nm.[14] The morphology of the signals change with the solvent. Its derivatives are also valuable molecular probes via fluorescence spectroscopy, having a high quantum yield and lifetime (0.65 and 410 nanoseconds, respectively, in ethanol at 293 K). Pyrene was the first molecule for which excimer behavior was discovered.[15] Such excimer appears around 450 nm. Theodor Förster reported this in 1954.[16]

Applications

[edit]
STM image of self-assembled Br4Py molecules on Au(111) surface (top) and its model (bottom; pink spheres are Br atoms).[17]

Pyrene's fluorescence emission spectrum is very sensitive to solvent polarity, so pyrene has been used as a probe to determine solvent environments. This is due to its excited state having a different, non-planar structure than the ground state. Certain emission bands are unaffected, but others vary in intensity due to the strength of interaction with a solvent.

Diagram showing the numbering and ring fusion locations of pyrene according to IUPAC nomenclature of organic chemistry.

Pyrenes are strong electron donor materials and can be combined with several materials in order to make electron donor-acceptor systems which can be used in energy conversion and light harvesting applications.[14]

Safety and environmental factors

[edit]

Although it is not as problematic as benzopyrene, animal studies have shown pyrene is toxic to the kidneys and liver. It is now known that pyrene affects several living functions in fish and algae.[18][19][20][21]

Its biodegradation has been heavily examined. The process commences with dihydroxylation at each of two kinds of CH=CH linkages.[22] Experiments in pigs show that urinary 1-hydroxypyrene is a metabolite of pyrene, when given orally.[23]

See also

[edit]

References

[edit]

Cited sources

[edit]

Further reading

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Pyrene

View on Grokipedia
from Grokipedia
Pyrene is a (PAH) consisting of four ortho- and peri-fused rings arranged in a flat aromatic system, with the molecular formula C16H10. It exists as a colorless crystalline solid that displays a faint when exposed to . Pyrene has a of 150–152 °C and a of 404 °C at standard pressure, with low in (approximately 0.135 mg/L at 25 °C) but good solubility in organic solvents such as , , and . It is produced primarily through the incomplete of organic materials and occurs naturally in , deposits, and fossil fuels, as well as in environmental samples like tobacco smoke, vehicle exhaust, grilled or smoked foods, and urban . Historically, pyrene has been utilized as a chemical intermediate in the manufacture of dyes, , plastics, and pesticides, often derived from processing. In modern applications, its derivatives are increasingly employed in due to favorable photophysical properties, including high and mobility; notable uses include blue emitters in organic light-emitting diodes (OLEDs), semiconductors in organic field-effect transistors (OFETs), and components in organic photovoltaic cells. Pyrene is classified by the International Agency for Research on Cancer (IARC) as Group 3, meaning it is not classifiable as to its carcinogenicity to humans based on available evidence from showing no tumors in application tests. It acts as a irritant and may cause redness or allergic reactions upon dermal contact, with oral LD50 values in rats around 2,700 mg/kg indicating moderate . Environmentally, pyrene is highly toxic to aquatic life, bioaccumulates in organisms such as fish and crustaceans ( factors up to 4,800), and persists in sediments and water bodies, contributing to from industrial effluents and combustion sources.

Structure and Synthesis

Molecular Structure

Pyrene possesses the molecular \ceC16H10\ce{C16H10} and is structured as four peri-fused rings arranged in a planar configuration, forming a compact (PAH). This peri-fused arrangement involves rings sharing more than one face, resulting in a rigid, flat with high (point group D2hD_{2h}). As the smallest stable peri-fused PAH, pyrene distinguishes itself from linear fused systems like , which features three rings aligned in a straight chain via ortho-fusion. The name "pyrene" originates from the Greek "pyros," meaning fire, as it was first isolated from the products of organic substances by Auguste Laurent in 1837. Pyrene's arises from a delocalized 14 π\pi-electron system in its peripheral circuit, despite a total of 16 π\pi electrons across the four rings, consistent with Platt's perimeter model for PAHs. This electronic arrangement is reflected in the Kekulé structures, which depict alternating single and double bonds but are averaged in reality due to extensive stabilization. Bond lengths vary slightly, with peripheral C-C bonds around 1.40 Å and the central bond approximately 1.42 Å, indicating partial double-bond character throughout the framework.

Synthesis Methods

Pyrene was first isolated in 1837 by the French chemist Auguste Laurent from the of , marking the initial recognition of this as a distinct compound. Subsequent purification efforts, such as those by Carl Graebe in 1871, involved solvent extraction with followed by formation and decomposition of the pyrene picrate complex to yield pure crystalline material. These classical isolation methods typically achieve yields of up to 2% by weight from fractions, often requiring to concentrate the high-boiling components before chromatographic separation. The first laboratory synthesis of pyrene was accomplished in by Friedrich Weitzenböck through a multi-step process starting from o,o'-ditolyl, involving cyclization and dehydrogenation steps to construct the fused ring system. Pyrolytic methods represent another early route, where pyrene forms during the high-temperature decomposition of smaller aromatic precursors, such as or other unsaturated hydrocarbons under atmosphere, mimicking natural processes but adapted for controlled production. These thermal approaches are scalable but produce mixtures requiring extensive purification, with efficiencies improved by optimizing temperature (typically 800–1000°C) and pressure conditions. Modern synthetic strategies emphasize -catalyzed couplings for constructing pyrene oligomers and derivatives, enhancing efficiency and . For instance, palladium-catalyzed cyclization of pyrene-based o-trimethylsilyl triflates enables the formation of higher pyrenylenes, such as 10-membered ring oligomers, through selective C–C bond formation under mild conditions (yields up to 40% for cyclic trimers). Recent advancements focus on direct C–H functionalization of pyrene, avoiding prehalogenation; examples include iridium-catalyzed borylation at the 2,7-positions (68–97% yield) and palladium-catalyzed arylation at the 4- or 10-positions (up to 90% yield with directing groups like picolinamide). These methods, highlighted in regioselective substitutions for functionalized pyrenes, leverage site-specific activation to introduce substituents with high stereochemical control, as reviewed in 2023 analyses of catalysis.

Physical and Spectroscopic Properties

Physical Properties

Pyrene is a colorless crystalline solid at , often appearing pale due to trace impurities such as , which can impart the color to otherwise colorless pure material, and exhibiting a slight in both solid form and solutions. Its low volatility is evidenced by a of 4.5 × 10^{-6} mmHg at 25 °C, making it suitable for handling in standard laboratory conditions without significant evaporation. Key thermodynamic properties of pyrene are summarized in the following table:
PropertyValueConditions/Source
Molar mass202.256 g/molComputed (PubChem)
Density1.271 g/cm³23 °C (CRC Handbook, 95th ed.)
Melting point150.62 °C(CRC Handbook, 95th ed.)
Boiling point404 °C760 mmHg (CRC Handbook, 95th ed.)
Vapor pressure4.5 × 10^{-6} mmHg25 °C (Sonnefeld et al., 1983)
These values highlight pyrene's thermal stability, as it remains solid up to near its and can be purified by sublimation under vacuum at approximately 150 °C, where it transitions directly from solid to vapor without intermediate liquid phase. Pyrene demonstrates limited solubility in aqueous environments, with a value of 0.135 mg/L in at 25 °C, contributing to its persistence in environmental matrices. In contrast, it shows good solubility in polar organic solvents such as at 25 °C, facilitating its extraction and use in non-aqueous applications.

Spectroscopic Properties

Pyrene exhibits characteristic ultraviolet-visible (UV-Vis) absorption bands primarily attributed to π-π* transitions in its polycyclic aromatic . The absorption features prominent peaks at 272 nm, 320 nm, and 334 nm, corresponding to the allowed S2 ← S0 transition with vibronic . The molar absorptivity at the 334 nm peak is approximately 50,000 M⁻¹ cm⁻¹, indicating strong absorption suitable for optical applications. These spectral features are observed in non-polar solvents like , providing a baseline for solvent effect studies. In , pyrene displays structured monomer emission centered at 373 nm upon excitation, arising from the S1 → S0 transition. At higher concentrations or in confined environments, formation leads to a broad, red-shifted emission band at approximately 450 nm. The quantum yield is 0.65 in , accompanied by a lifetime of 410 ns at 293 , highlighting pyrene's efficiency as a . These properties enable pyrene's use in probing molecular interactions, including -based designs for detecting analytes. polarity influences the emission, with polar solvents inducing a red-shift due to stabilization of the , as quantified by the Py scale of solvent polarity. The optical of pyrene is 2.02 eV, determined from the onset of the absorption spectrum, reflecting its HOMO-LUMO energy difference. Recent photophysical investigations have extended these properties to pyrene derivatives exhibiting aggregation-induced emission (AIE). For instance, structurally modified pyrene-based luminogens demonstrate enhanced red emission in aggregated states, with applications in anti-counterfeiting materials.

Chemical Reactivity

Electrophilic Substitution

Pyrene, as a , exhibits characteristic reactivity in reactions, primarily occurring at the alpha positions (1, 3, 6, and 8) rather than the beta positions (2 and 7). This stems from the higher at the alpha sites, which facilitates the formation and stabilization of the Wheland intermediate during attack. The stabilization arises from better delocalization of the positive charge in the sigma complex at these positions, as determined by computational and experimental analyses of charge distribution in pyrene's . A classic example is , where treatment of pyrene with a mixture of (HNO₃) and (H₂SO₄) predominantly yields 1-nitropyrene as the mononitrated product. This reaction proceeds via the nitronium (NO₂⁺) as the , with the alpha position preference ensuring high selectivity for the 1-site under standard conditions (typically at 0–20°C in mixed acid media). Similarly, reactions favor the alpha positions; for instance, bromination with bromine (Br₂) in or acetic acid solvent results in 1-bromopyrene, reflecting the electrophilic attack by Br⁺ and subsequent proton loss. Sulfonation of pyrene also demonstrates this positional bias, occurring at the 1-position upon reaction with (SO₃) or (H₂SO₄ + SO₃), producing 1-pyrenesulfonic acid. In terms of oxidation, electrophilic pathways lead to formation; (H₂CrO₄, generated from CrO₃ in acetic acid) oxidizes pyrene selectively to pyrene-4,5-dione, involving initial at the K-region followed by further transformation. Kinetic studies indicate that substitution at alpha positions occurs at significantly higher rates compared to beta sites due to the lower for Wheland intermediate formation at electron-rich loci.

Other Reactions

Pyrene undergoes catalytic primarily at the outer rings, yielding 4,5,9,10-tetrahydropyrene as the major product when using (Pd/C) under moderate (3–10 bar) and temperature ( to 90°C) in . Platinum catalysts achieve similar selectivity, with yields up to 96% after chromatographic purification to remove hexahydro impurities. The Birch reduction of pyrene, employing or sodium in liquid with as a proton donor, selectively produces 4,5-dihydropyrene as the initial product, preserving the central aromatic ring while reducing one peripheral bond. This dihydropyrene intermediate can undergo further transformations, such as via of alkyl halides to the enolate-like anion formed under Birch conditions, enabling regioselective functionalization at the 4- and 5-positions. Photochemical reactions of pyrene under (UV) irradiation lead to dimerization via [2+2] cycloaddition, forming cyclobutane-linked dimers such as the head-to-tail or head-to-head , often observed in concentrated solutions or the solid state. These dimers exhibit altered properties, with of the monomer emission due to formation preceding the covalent linkage. Recent advances in C-H activation have enabled direct arylation of pyrene without prefunctionalization, as demonstrated by palladium-catalyzed coupling with arylboroxins using Pd(OAc)₂ and o-chloranil oxidant in at 80°C, yielding C4-arylated products that extend the π-conjugation for . This method achieves high at the 4-position, facilitating the synthesis of extended pyrenes with up to 85% yield for electron-rich aryl groups.

Occurrence and Production

Natural Sources

Pyrene is primarily formed through geological processes in fossil fuels, where it arises from the diagenetic and catagenetic transformation of under heat and pressure over geological timescales. In , a byproduct of , pyrene can constitute up to 2% of the total composition, making it one of the more abundant polycyclic aromatic hydrocarbons in this material. It occurs in minor concentrations in , e.g., 3–14 ppm in various crude oil samples, reflecting its limited formation during kerogen maturation. Similarly, pyrene is present at low levels in , often as part of the broader suite of aromatic compounds extracted from -rich deposits. In extraterrestrial environments, pyrene has been identified in and gas phases, providing evidence of its synthesis in non-terrestrial conditions. The , a CM2 that fell in in 1969, contains pyrene among other polycyclic aromatic hydrocarbons, detected through gas chromatography-mass spectrometry analysis of its organic extracts; isotopic studies further confirm its extraterrestrial origin. Pyrene is also implicated in the , where its presence is inferred from (IR) emission features observed in space. Laboratory measurements of pyrene's IR band strengths match these unidentified emission bands, particularly in regions like the 3–15 μm range, suggesting it contributes to the aromatic inventory of photodissociation regions and reflection nebulae. Recent radio astronomical detections of cyanopyrene isomers (1-, 2-, and 4-cyanopyrene) in the TMC-1 cloud serve as direct proxies for pyrene, with abundances indicating that four-ring polycyclic aromatic hydrocarbons like it may represent a substantial carbon reservoir in cold, dense interstellar clouds. Biogenic traces of pyrene occur at low levels through natural biological and geological processes, though they are negligible relative to sources. In and microorganisms, pyrene can form via slow cyclization of precursors or during the degradation of , as part of broader biogenic synthesis by , , and higher . Volcanic emissions also release trace pyrene during high-temperature eruptions, mimicking of buried organic material but at far lower yields than anthropogenic combustion. Pyrene was first isolated in its impure form in 1837 by French chemist Auguste Laurent from the residue of coal tar produced via destructive distillation, marking the initial recognition of this compound in natural extracts.

Anthropogenic Production

Pyrene is primarily generated anthropogenically through the processing of coal tar, a byproduct of coke production in the steel industry, where it constitutes a significant fraction of polycyclic aromatic hydrocarbons (PAHs) present in the tar. Actual environmental releases depend on distillation and application practices such as pavement sealing and creosote treatment. Incomplete combustion from various human activities also contributes substantially to pyrene emissions. In exhaust, pyrene is emitted at rates around 15–20 μg per kilometer traveled, primarily from and diesel engines, making transportation a key diffuse source. smoke releases pyrene at levels of approximately 37 ng per , contributing to indoor and personal exposure, while burning, including residential wood heating and agricultural residue , generates pyrene through of organic matter. Industrial processes beyond coal tar further elevate pyrene releases. Aluminum emits pyrene via anode baking and pitch volatilization, while production involves coke oven operations that liberate PAHs during and refining. Tire wear particles, generated from road friction, contain polycyclic aromatic hydrocarbons including pyrene at total concentrations up to 113 μg per gram of particulate matter, with emissions scaling with vehicle mileage and tire composition. According to the U.S. Agency's 2020 National Emissions , there are significant pyrene emissions from mobile sources in the United States, predominantly from on-road vehicles and non-road equipment.

Applications

Traditional Uses

Pyrene derivatives have been employed in the synthesis of water-soluble fiber-reactive dyestuffs for applications, offering fluorescent properties suitable for marking and materials with enhanced color fastness. A notable example is the development of pyrene-based reactive dyes patented in the early , which exhibit good affinity for fibers and resistance to washing and light exposure. These early formulations leveraged pyrene's inherent to produce brilliant colors in textiles, contributing to their use in industrial processes before more advanced synthetic alternatives dominated. Pyrene has also served as a starting material for producing , plastics, and pesticides. In biochemical and , 1-hydroxypyrene, a primary of pyrene, has served as a key for assessing human exposure to polycyclic aromatic hydrocarbons (PAHs) since the mid-1980s. Urinary levels of 1-hydroxypyrene are measured via techniques like to detect PAH pollution from sources such as occupational settings in coal processing or urban air. This application, first proposed by Jongeneelen et al. in 1985, relies on pyrene's and has become a standard non-invasive probe for PAH due to its specificity and detectability at low concentrations. Pyrene has historically functioned as an in simple donor-acceptor charge-transfer complexes, such as those formed with tetracyanoquinodimethane (TCNQ), which were investigated for their electronic and in early research prior to the 2000s. These complexes facilitated charge separation and were explored in rudimentary photovoltaic devices, leveraging pyrene's ability to donate electrons to strong acceptors like TCNQ for potential energy conversion applications. Such systems provided foundational insights into , though limited by efficiency compared to later developments. Commercially, pyrene is widely available as a high-purity reagent from suppliers including Sigma-Aldrich and Thermo Fisher Scientific, typically in quantities suitable for laboratory organic synthesis kits and custom formulations. This accessibility has supported its use in academic and industrial settings for preparing derivatives in dyes, probes, and electronic materials since the late 20th century.

Advanced Materials and Sensors

Pyrene-based metal-organic frameworks (MOFs) have emerged as versatile platforms for advanced sensing applications due to their tunable and properties. A notable example is HPU-26, a (III)-MOF constructed with a pyrene dicarboxylate linker, which exhibits multi-stimuli-responsive for detecting trace in organic solvents, nitroaromatic explosives, and Fe³⁺ ions through mechanisms. This framework demonstrates high sensitivity to with a of 1.2 × 10⁻⁷ M and selectivity over other interferents, attributed to from the pyrene core to the . Such properties position HPU-26 as a promising candidate for and applications. Covalent organic frameworks (COFs) incorporating pyrene units have similarly advanced thin-film technologies, particularly for vapor detection. Pyrene-derived COF films, synthesized via interfacial , enable rapid and reversible colorimetric sensing of acid vapors such as HCl and HNO₃, with response times under 10 seconds and detection limits in the parts-per-million range. The sensing mechanism relies on protonation-induced changes in the pyrene-based linkages, leading to visible color shifts from yellow to orange-red, while maintaining structural integrity over multiple cycles. These films offer advantages in portability and reusability, addressing challenges in on-site hazardous gas detection. In sensor development, pyrene's has been leveraged for ultrasensitive detection of polycyclic aromatic hydrocarbons (PAHs), crucial for . A 2024 study introduced β-cyclodextrin-functionalized nanowires that restore upon pyrene binding, achieving a of 0.1 nM and a spanning five orders of magnitude (from 1 nM to 10 μM), ideal for quantifying trace PAHs in water samples. This approach outperforms traditional methods by providing real-time, without interference from complex matrices. Additionally, pyrene derivatives serve as efficient photoinitiators in processes, enabling visible-light-triggered radical and cationic polymerizations with high initiation efficiencies under low-intensity , as reviewed in 2020. These systems facilitate the fabrication of advanced composites and hydrogels for sensor encapsulation. Pyrene-fused polyaromatics have gained traction in , particularly for organic light-emitting diodes () and security features. In OLED applications, pyrene-modified emitters with 3,6-substitutions yield deep-blue devices with external quantum efficiencies exceeding 10% and operational lifetimes over 100 hours at 1000 cd/m², due to enhanced charge transport and reduced non-radiative decay. For anti-counterfeiting, red-emitting aggregation-induced emission (AIE) luminogens based on pyrene scaffolds produce inks with tunable emission under UV excitation, exhibiting minimal color migration on paper and enabling multilevel patterns visible only at specific wavelengths. The AIE property, stemming from restricted intramolecular rotations in aggregates, enhances brightness in solid states, making these materials suitable for secure printing. Pyrene's excimer emission further supports such sensing modalities by providing ratiometric signals.

Environmental and Health Impacts

Environmental Fate and Remediation

Pyrene's environmental fate is characterized by high persistence due to its low aqueous of 0.135 mg/L at 25°C, which restricts dissolution and in bodies. This hydrophobicity, quantified by a log Kow of 4.88, facilitates strong partitioning into sediments and organic-rich matrices, leading to in benthic organisms and long-term deposition. In aquatic environments, under natural sunlight is relatively rapid, with a near-surface of 0.68–0.85 hours in , primarily through direct photolysis. Microbial transformation represents a key degradation route, initiated by bacterial monooxygenases that perform at the 1-position, yielding 1-hydroxypyrene as a primary intermediate before further ring cleavage via the β-ketoadipate pathway. Transport of pyrene occurs via multiple phases, including volatilization from moist soils, supported by its of 4.5 × 10^{-6} mmHg at 25°C, though this process is limited in dry conditions. Atmospheric dispersion contributes to widespread distribution, with urban air samples showing total PAH levels typically between 1 and 12 ng/m³, often bound to particulate matter from sources. Once deposited, pyrene adsorbs preferentially to sediments, with estimated half-lives for volatilization from model lakes ranging up to 37 days, underscoring its tendency for long-range environmental cycling. Remediation strategies leverage biological and to mitigate pyrene contamination. Bioremediation employing strains effectively degrades pyrene in soils, achieving up to 70% removal over 60 days, often augmented by biosurfactants like rhamnolipids that enhance . Metal-organic frameworks (MOFs) offer promising adsorption-based cleanup, with 2023 studies on pyrene-derived linkers demonstrating selective PAH capture via π-π stacking and hydrophobic interactions, outperforming traditional sorbents in capacity and recyclability. using like removes around 50% of soil pyrene within 60 days through root uptake and microbial activity, providing a cost-effective, option for moderately contaminated sites. Recent research from the 2020s emphasizes pyrene's interactions with , where onto surfaces increases PAH stability and trophic transfer in marine ecosystems, complicating natural attenuation and necessitating integrated removal approaches.

Toxicity and Safety

Pyrene exhibits low , with an oral LD50 greater than 2 g/kg in rats. It is classified as a irritant (GHS H315) and causes serious eye (GHS H319). Chronic exposure to pyrene in rodents leads to kidney and liver damage, including nephropathy, reduced kidney weights, and elevated urea and creatinine levels in rats, as well as enlarged livers with increased hepatic lipid content. Pyrene demonstrates genotoxicity through binding to DNA and formation of adducts, though results from genotoxicity assays are mixed, with mostly negative outcomes in mammalian cells and positive in some bacterial and yeast systems. The International Agency for Research on Cancer (IARC) classifies pyrene as Group 3, not classifiable as to its carcinogenicity to humans, based on limited evidence from animal studies showing no significant tumor induction. The primary metabolite of pyrene, 1-hydroxypyrene, serves as a reliable for () exposure, detectable in urine with levels exceeding 0.5 μmol/mol indicating significant occupational or environmental risk. Safe handling of pyrene requires use in a or well-ventilated area to avoid , as it may cause respiratory irritation (GHS H335). It poses an environmental hazard, being very toxic to aquatic life with long-lasting effects (GHS H410), though can mitigate exposure in certain contexts.

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