User:Miffyz92/Phenanthrene

Introduction
Phenanthrene, is a potential carcinogenic compound that poses a large toxicity risk to exposed living organisms. Phenanthrene is a polycyclic aromatic hydrocarbon (PAH), PAHs are a large group of organic compounds occurring in groups of two or more. Phenanthrene occurs naturally and is also a man-made chemical. Commonly, humans are exposed to phenanthrene through inhalation from burning fossil fuels and cigarette smoke. Evidence, proven through animal studies, shows that phenanthrene is a potential carcinogen. The EPA has identified 16 PAHs of most concern in regards to environmental toxicity.

Phenanthrene is released during the incomplete combustion of "..coal, oil, gas, and garbage." Incomplete combustion occurs when oxygen or air supplied to the combustion process is small so that carbon monoxide and carbon gases are released instead of carbon dioxide.

Phenanthrene travels through the environment through water runoff, from rivers or other contaminated waterways, and through atmospheric transport.

Haworth Synthesis
The Haworth Synthesis was published in 1932. This reaction involves a Friedel-Crafts acylation between naphthalene and succinic anhydride as well as two Clemmensen reductions and followed by a dehydrogenation with using the metal selenium.

Alternative Synthesis
In addition to the Haworth synthesis, there is an alternative synthesis which involves the dehydration cycloaromatization of an aldehyde. This synthesis involves [1,​1'-​Biphenyl]​-​2-​acetaldehyde reacting with triflic acid and hexafluoroisopropanol as the solvent.

Reactions
Phenanthrene's 9 and 10 bond is reactive and halogenation (i.e the addition of a halogen) easily happens. Shown below is the bromination of phenanthrene upon the 9 and 10 bond.

Physical Characteristics
Phenanthrene is a crystalline compound which appears colorless at room temperature. When dissolved, it exhibits a blue fluorescence. The compound has a faint odor

Do to the molecule being non-polar and consisting of only carbon and hydrogen, phenanthrene is soluble in organic solvents such as carbon tetrachloride and toluene.

Chemical Characteristics
Phenanthrene's enthalpy of combustion and formation are calculated to be -(7048.7 ± 0.9) kJ/mol and (201.7 ± 2.9) kJ/mol, respectively.

Toxicity
Phenanthrene has an octanol water partition coefficient value of 4.57 Kow. This correlates to phenanthrene having the ability to bioaccumulate in an organism. Individual toxicity effects are emphasized over entire ecosystem effects.

Aquatic Toxicity
Phenanthrene has been discovered in contaminated seafood and surface water. As it is is highly lipid-soluble, it is easily metabolized and exerted by fish and invertebrates. Phenanthrene's lipid solubility contributes to it being able to bioaccumulate within the fatty tissues of organisms. Thus, the concentration of phenanthrene within in the organisms tissues will continue to increases as ingestion of the molecule continues. Additionally, with its ability to bioaccumulate, there is an increasing worry about it being accumulated to critical concentrations at high trophic levels. Phenanthrene has been known to cause acute toxicity to aquatic life whether this be inhibition of growth or mortality.

Crustaceans
Phenanthrene is toxic to deep-sea crustaceans. The effects of phenanthrene toxicity to deep sea crustaceans was studied by Turner et al. Turner et al. published a study that examined the mortality rate of different deep-sea crustacean species (Janciella spinacauda and Euphausiidae) when exposed to phenanthrene. The studied focused on effects of phenanthrene at different concentrations and varying time lengths. Turner et al. found that the rate of mortality is proportional to the concentration of phenanthrene. As the concentration of phenanthrene Increased, the exposed groups of Janciella spinacauda and Euphausiidae had increasing mortalities. However, visible signs of acute toxicity caused by phenanthrene on Euphausiidae was apparent after only 3 hours of exposure. When Janciella spinacauda is exposed for 48 hours, the rate of mortality is increased. This correlates with the idea that increased exposure time led to increased acute toxicity. For Euphausiidae, they were highly sensitive to phenanthrene. That species had a 100% mortality rate at lower concentrations of phenanthrene than the other studied species. In addition, there is only a slight difference in the mortality rate when Euphausiidae is exposed to phenanthrene for 48 hr instead of 36 hr. Euphausiidae, being severely sensitive to phenanthrene, had the highest mortality rates of 24, 55, and 61% when exposed for 24, 36, and 48 hours, respectively. The LC50 for Euphausiidae and Janciella spinacauda are reported as 81 μg/L and 320 μg/L. As phenanthrene bioaccumulates in fatty tissues, Janciella spinacauda and Euphausiidae had specific critical target lipid body burden (CTLBB) calculated, and both organisms were reported to have phenanthrene in their fatty tissues. For the exposure length of 36 hr, Euphausiidae and Janciella spinacauda had CTLBB levels of 20.1 μmol/g lipid and 62.1μmol/g lipid, respectively. These levels were associated to be the target lipid levels for these organisms because these concentrations of phenanthrene within the deep-sea crustaceans were the cause of death to the crustaceans. Phenanthrene causes major harm to the stability of organisms. Even after the exposure event is done, phenanthrene has accumulated within the fatty tissues of the organisms, and this will lead to greater toxic effects for the organisms as time passes.

Microalgae
In regards to microalgae, phenanthrene has been reported to inhibit the growth of microalgae. Chen et al. published a study in a scientific journal, Scientific Reports, that studied the toxic effects of phenanthrene at varying pHs in regards to the microalgae Chlorella salina. The toxicity of phenanthrene created an environment where the microalgae's growth was unfavorable. The study used two different methods, cell counting and fluorimetric measuring, to determine the amount of Chlorella salina present after being exposed to phenanthrene. The fluorimetric method used the fluorescence properties of chlorophyll within Chlorella salina to measure the amount remaining after being exposed to phenanthrene. The authors reported that there is a correlation between the inhibition of algae growth, the concentration of phenanthrene, and acidity of the water. Within this article, there is a figure that demonstrates the relationship between phenanthrene concentrations and the inhibition rates via the two methods cell count and fluorescence measurements. While demonstrating the effects of phenanthrene concentrations on the algae, the figure also includes how the the inhibition rates vary at different pH levels. As reported within the article, there is a general trend between the increasing concentration of phenanthrene and the inhibition rate of the microalgae. As phenanthrene concentration increases, the inhibition rate increases. Using the cell counting method, after 96-hour exposure to phenanthrene with a concentration of 3.00 mg/L and the water's pH level of 9, there was a 59% inhibitory rate. When exposed to phenanthrene at more acidic pH levels, there was an increase in the inhibition of cell growth of Chlorella salina. After a 96-hour exposure of Chlorella salina to phenanthrene concentration of 3.00 mg/L with the water's pH level of 6, there was a 94% inhibitory rate amongst the microalgae. As the pH level decreased, the EC50 decreased from 1.893 to 0.237 mg L-1. The cell counting method determined that the decrease in pH increased the toxic effects that phenanthrene had on Chlorella salina. Moreover, the fluorimetric method established a heavier reliance on the concentration of phenanthrene to inhibiting the cell growth of Chlorella salina because the fluorimetric method shows an immense increase in inhibition rates as the concentration of phenanthrene increased for every pH levels examined. The two measuring methods produced slightly different results, but there was an agreeance that increasing the concentration of phenanthrene will lead to greater inhibition of growth of the Chlorella salina. Therefore, phenanthrene has drastic negative effects on microalgae and will inhibit their growth.

Zebrafish
Within the article by Incardona et al., they reported damage of embryos caused by the toxic effects of phenanthrene. Phenanthrene disrupted cardiac function and eventually caused heart failure of the embryos. The disrupted cardiac function included changes within heart rate and heart rhythm. In reduction of heart rate, phenanthrene had a dose-dependent relationship. In exposure to increased concentrations of phenanthrene, zebrafish had severe bradycardia that eventually amounted to complete atrioventricular blockage. Due to the disrupted cardiac function and heart failures, zebrafish embryos exhibited secondary effects: physical deformities such as smaller eyes and deformed jaws. In the article, Figure 7 compares the exposed group to the control. It was easy to see the deformities caused by the toxic effects from phenanthrene. The exposed group had small eyes, deformed jaws, and accumulated an edema. Overall, exposure of phenanthrene led to cardiac morphogenesis, heart failure, and edema accumulation.

Microplastics
The tendency for microplastics to adsorb toxic contaminants poses a threat for the organisms that may come into contact with a microplastic release pathway. Sorption of contaminants, such as phenanthrene, to different kinds of plastics depends on the pi-pi bond interactions; they have a higher tendency to sorb aromatic compounds. Microplastics are of concern regarding the acute toxicity of phenanthrene and other PAHs because phenanthrene-containing microplastics may be released into an organism’s body following ingestion. A study published in the scientific journal, Ecotoxicology and Environmental Safety, found the distribution coefficients (log Kd) values of phenanthrene to be, “3.07-4.20 (log L/kg)” in relation to microplastic particles. These values are considered to be low and correlate to the sorption ability of a chemical. A low log Kd value correlates to a chemical having the ability to move freely within the particle; here, the particle being a microplastic. The study also found that different kinds of plastics had higher phenanthrene sorption capabilities. Polystyrene has the strongest sorption rate of phenanthrene in comparison to polyethylene, polypropylene and polyvinyl chloride. The log Kd values for phenanthrene decreased as the microplastic particle size decreased. However, when the microplastic decreased to the nanoparticle size, the Kd values increased for phenanthrene because less surface area was available for sorption.

The correlation between toxicity and low sorption values of phenanthrene means that the PAH will more easily detach from whatever substance it has adsorbed to. This can mean that the phenanthrene ingested through an adsorbed substance, such as a microplastic, can more easily interact within the organisms who ingested the microplastic, leading to acute toxicity. Therefore, it is important to understand phenanthrene's adsorption capacity to microplastics as it determines the fate of the PAH toxin within a given ecosystem. Microplastics are of large concern not only regarding their ability to adsorb toxic chemical compounds but due to the fact that they are so small, clean-up efforts are extremely difficult. Understanding the effects microplastics have on ecosystem health will improve efforts to prevent and treat the threats they pose to the health of an ecosystem.

Marine pH Acute Toxicity
In a study published in the journal, Scientific Reports, phenanthrene's toxicity was found to increase alongside a decreasing pH. The effect of toxicity on marine organisms is a stunted growth rate. The EC50 value determines when the expected effects of a toxic compound are 50% of the total expected effect. Alongside lower pH values, from 9 to 6, phenanthrene's EC50 value decreased from "..1.893 to 0.237 mgL^-1.." A lower EC50 value means that a a lower concentration of phenanthrene under increasingly acidic marine ecosystem conditions will reach acute toxicity faster than at higher, more basic pH conditions. Ocean acidification is of high concern regarding decreasing ocean pH levels.

Soil Toxicity
Phenanthrene is a commonly studied PAH due to it being found in high concentrations within PAH mixtures in the environment; it is used as a reference molecule for other PAHs. One of the uses of phenanthrene in bacteria organisms is as a mode of uptake of carbon and energy. The accumulation of phenanthrene in soil is an issue because it will lead to phenanthrene toxicity in the (soil) ecosystem. Phenanthrene toxicity produces effects on functional soil processes, like decreased reproduction of the soil organism, “Folsomia candida (Collembola)..at..concentration of..25 mg/kg soil..” This organism’s ability to reproduce effects “..several molecular pathways" . Other processes affected by phenanthrene toxicity include, “..oxidative stress.” and “..chitin metabolism and protein translation..down-regulated..” It was found that as the toxicity of phenanthrene in a soil ecosystem increased, the effects become more specific on the molecular level. Overall, phenanthrene toxicity affects a soil ecosystem by decreasing reproduction, leading to decreased health of the soil itself.

Transport and Fate
Phenanthrene, along with many other PAH compounds, are considered ubiquitous in the environment, as they have been found in the air, water, soils, and in plants and crops. A majority of phenanthrene ends up in the soil. Wet and dry deposition of PAHs present in urban emissions and wildfire smoke can transport phenanthrene from the atmosphere to soil and surface waters of lakes, rivers, and streams. Phenanthrene in wildfire ash can also be incorporated into the soil or be washed into aquatic ecosystems through water erosion and runoff. In the soil, phenanthrene primarily undergoes either mineralization or is converted to bound residues in the soil matrix. Microbes play a dominant role in converting phenanthrene to non-extractable residues, which can become bioavailable for soil organisms, posing a toxic threat to this ecosystem. From the soil, plants can take up phenanthrene through the roots. A study done on wheat plants showed that phenanthrene is taken up by the plant in two phases: the fast phase, in which phenanthrene diffuses into the roots from the surrounding soil through passive and active uptake, and the slow phase, in which phenanthrene is distributed throughout the plant and accumulates in the tissues.

A majority of the phenanthrene entering aquatic organisms comes from storm water runoff and effluent wastewater discharge from industrial facilities using fossil fuels. Once in freshwater or marine aquatic ecosystems, the phenanthrene partitions between the aqueous and particulate phases. Because PAHs like phenanthrene are extremely insoluble in water, they can remain in the water column as well as sorb onto organic carbon in soil particles and accumulate in benthic sediments. The phenanthrene in these sediments can accumulate in the tissues of benthic organisms, and phenanthrene present in the water column and in crude oil from oil spills on the surface can accumulate in fish and other pelagic organisms. Along with sorption and accumulation, phenanthrene can be lost through biodegradation and photodegradation. Marine bacteria, algae, and other microbes can metabolize PAHs, removing them from aquatic ecosystems. Phenanthrene, along with other PAH compounds, are photosensitive, which also means they can degrade in the presence of UV radiation; however, photodimerisation and photooxidation can create metabolites that are more toxic than the original compounds.

Health Hazards
The most common way in which phenanthrene and other PAHs enter the human body is through inhalation. It can also enter the body if the skin comes into contact with contaminated soils or other products containing phenanthrene, or if contaminated food or water is ingested. Phenanthrene is known to cause irritation to the skin and respiratory track, and can cause the skin to become sensitive in the presence of sunlight. Phenanthrene also produces pungent fumes that may also induce irritation of the respiratory track. Phenanthrene is extremely lipid-soluble and can accumulate readily in the lungs, gut, and fat of humans. Although there are virtually no tests done on human subjects, the toxicity of phenanthrene has been studied in rats and rabbits. According to multiple animal toxicology studies, phenanthrene is a non-carcinogenic compound and was found to not induce the growth of mammary tumors in rats. A study of in utero exposure to PAHs done on rats showed that phenanthrene induced abnormal lipid metabolism through epigenic modification. This is the modification of DNA, resulting in changes of how genes are expressed and regulated. The study also showed that the transcription of genes related to lipogenisis, the metabolic process for fat storage, were upregulated. Blood chemistry has also been performed on rats injected with phenanthrene and ozonized forms of phenanthrene. Phenanthrene injections in the blood led to significant elevations in the rats' serum aspartate aminotransferase (serum AST) and and y-glutamyl transpeptidase levels. Serum AST and y-glutamyl transpetidase are enzymes that are released in the body as a response to liver damage. This indicates that phenanthrene can have the ability to cause kidney and respiratory neoplasms (abnormal growth of cells). The subchronic and chronic effects of phenanthrene have not yet been documented in the literature; however, because people are exposed to phenanthrene in higher amounts relative to other PAHs and its metabolites are easily detected in urine, phenanthrene has been proposed as a good biomarker for general PAH exposure. Although it is not considered to be a carcinogen, phenanthrene is still one of the 16 PAH compounds included on the EPA's Priority Pollutants list.

Removal from Environmental Systems
PAHs can be classified as high or low in molecular weight depending on how many aromatic rings they contain. High molecular weight PAHs contain 4 or more aromatic rings and low molecular weight PAHs contain 2 or 3 aromatic rings. As the number of aromatic rings increases, the PAH molecules hydrophobicity increases and the molecule will have a stronger resistance to microbial degradation. A higher molecular weight and increased hydrophobicity also means that increasingly, the compound is less soluble in water; phenanthrene's molecular weight is lower than most PAHs.

Removal in a Marine Ecosystem
PAHs are known for being difficult to remove from the environment due to their hydrophobic properties, they do not dissolve in water; making PAHs a persistent pollutant. Dissolution increases the ease by which a contaminant moves through an ecosystem. If a contaminant does not dissolve in water, then it stays in the system until toxin-specific processes dominate degradation. In regards to PAHs, their degradation pathway is not completely understood; it is known that bacteria play a large role in degradation processes. Specifically, the bacteria Cycloclasticus, degrades, “..naphthalene, phenanthrene, pyrene, and other aromatic hydrocarbons”, in marine environments. Cycloclasticus are found globally in many aquatic ecosystems including, “..estuaries, coastal areas, deep-sea sediments, and polar oceans.” The degradation pathway of PAHs separate from external factors begins with, “..dihydroxylation mediated by a ring-hydroxylating dioxygenase.” Little is known about the rest of the pathway and the difference in pathways of specific PAHs. Apart from being able to degrade phenanthrene, cycloclasticus can use phenanthrene as a carbon and/or energy source. The degradation pathway transforms each PAH into an intermediate and further, degradation through mineralization.

Sorption
One of the techniques identified to remove PAHs from aquatic ecosystems is adsorption. Toxins bind to solid materials present in a system such as “..activated carbon, biochar, and modified clay minerals..” These solid materials have the ability to remove up to 100% of the contaminate in aqueous solutions or immobilize them in a soil. In a review published in the journal, Chemosphere in 2015, the recorded sorption rates of activated carbon, biochar, and modified clay minerals from 1934 to 2015 were summarized. The study found that the sorption rate depends on, "..particle size, temperature, pH, contact time, salinity.." Some of the results for phenanthrene adsorption include, a wheat straw biochar material adsorbed, "71-88%" of phenanthrene present. Powder activated carbon (PAC) adsorbed "95%" of phenanthrene and a soybean stalk based carbon adsorbed, "99.89%."

Sepiolite
Ground sepiolite was studied to determine its capability to adsorb phenanthrene in a study published in the journal of Ecological Engineering in 2014. Application was centered around the use of sepiolite to bind phenanthrene and another PAH, pyrene, in groundwater systems. Sepiolite was chosen as a sorbent material because it is a low-cost option; activated charcoal is the most effective material used to adsorb pollutants but its high-cost increases the need for the exploration of low-cost options. Sepiolite was examined due to its "..high sorption capacity and selectivity because of..high porosity and molecular sieving properties." The sorption capacity of a PAH is dependent upon their hydrophobic properties; if a PAH is less hydrophobic then, it will possess less of an ability to bind to an adsorbent materials, including sepiolite. Although, when the phenanthrene and pyrene were studied as a mixture, the less hydrophobic phenanthrene had a higher adsorption capacity. Overall, sepiolite was determined to be a low-cost and efficient material to adsorb PAHs such as phenanthrene and pyrene. Adsorption is the most common removal process for PAHs. The mechanism for adsorption is summarized as: first, a mass transfer. Second, a physical or chemical adsorption by the molecule to the adsorbent material’s surface, and then, molecule diffusion to an adsorption site by "..a pore diffusion process..or..a solid surface diffusion mechanism."