Editing Creosote (section)

==Chemical reactions with sediment and organisms==
Once the soluble compounds from the creosote preservative leach into the water, the compounds begin reacting with the external environment or are consumed by organisms. The reactions vary depending on the concentration of each compound that is released from the creosote, but major reactions are outlined below:

===Alkylation===
[[Alkylation]] occurs when a molecule replaces a hydrogen atom with an alkyl group that generally comes from an organic molecule.<ref>{{cite web |title=Alkylation |website=Dictionary.com |url=https://www.dictionary.com/browse/alkylation |access-date=October 29, 2016}}</ref> Alkyl groups that are found naturally occurring in the environment are [[organometallic chemistry|organometallic]] compounds.<ref name="Connell 2005"/> Organometallic compounds generally contain a methyl, ethyl, or butyl derivative which is the alkyl group that replaces the hydrogen.<ref name="Connell 2005"/> Other organic compounds, such as [[methanol]], can provide alkyl groups for alkylation.<ref name=Bolognini2002/> Methanol is found naturally in the environment in small concentrations, and has been linked to the release from biological decomposition of waste and even a byproduct of vegetation.<ref name=Howard311/> The following reactions are alkylations of soluble compounds found in creosote preservatives with methanol.

====m-Cresol====
[[File:M-cresol reaction with methanol.png|frameless|upright=2.25]]

The diagram above depicts a reaction between m-cresol and methanol where a c-alkylation product is produced.<ref name=Bolognini2002/> The c-alkylation reaction means that instead of replacing the hydrogen atom on the -OH group, the methyl group (from the methanol) replaces the hydrogen on a carbon in the benzene ring.<ref name=Bolognini2002/> The products of this c-alkylation can be in either a para- or ortho- orientation on the molecule, as seen in the diagram, and water, which is not shown.<ref name=Bolognini2002/> [[Isomer]]s of the dimethylphenol (DMP) compound are the products of the para- and ortho-c-alkylation.<ref name=Bolognini2002/> Dimethylphenol (DMP) compound is listed as an aquatic hazard by characteristic, and is toxic with long lasting effects.<ref>{{cite web |title=2,3-Dimethylphenol |website=PubChem Database |publisher=National Center for Biotechnology Information |url=https://pubchem.ncbi.nlm.nih.gov/compound/2_3-dimethylphenol |access-date=April 7, 2019}}</ref>

====Phenol====
[[File:Phenol reaction with methanol.png|frameless|upright=1.5]]

This diagram shows an o-alkylation between phenol and methanol. Unlike the c-alkylation, the o-alkylation replaces the hydrogen atom on the -OH group with the methyl group (from the methanol).<ref name="Balsama et al 1984"/> The product of the o-alkylation is methoxybenzene, better-known as [[anisole]], and water, which is not shown in the diagram.<ref name="Balsama et al 1984"/> Anisole is listed as an acute hazard to aquatic life with long-term effects.<ref>{{cite web |title=Anisole |website=PubChem Database |publisher=National Center for Biotechnology Information |url=https://pubchem.ncbi.nlm.nih.gov/compound/anisole |access-date=April 7, 2019}}</ref>

===Bioaccumulation===
[[Bioaccumulation]] is the process by which an organism takes in chemicals through ingestion, exposure, and inhalation.<ref name="Clarke"/> Bioaccumulation is broken down into bioconcentration (uptake of chemicals from the environment) and biomagnification (increasing concentration of chemicals as they move up the food chain).<ref name="Clarke"/> Certain species of aquatic organisms are affected differently from the chemicals released from creosote preservatives. One of the more studied organisms is a mollusk. Mollusks attach to the wooden, marine pilings and are in direct contact with the creosote preservatives.<ref name=Weitkamp2011/> Many studies have been conducted using [[polycyclic aromatic hydrocarbon]]s (PAH), which are low molecular hydrocarbons found in some creosote-based preservatives. In a study conducted from Pensacola, Florida, a group of native mollusks were kept in a controlled environment, and a different group of native mollusks were kept in an environment contaminated with creosote preservatives.<ref name="Elder"/> The mollusks in the contaminated environment were shown to have a bioaccumulation of up to ten times the concentration of PAH than the control species.<ref name="Elder"/> The intake of organisms is dependent on whether the compound is in an ionized or an un-ionized form.<ref name="Neff 2002"/> To determine whether the compound is ionized or un-ionized, the pH of the surrounding environment must be compared to the pKa or acidity constant of the compound.<ref name="Neff 2002"/> If the pH of the environment is lower than the pKa, then the compound is un-ionized which means that the compound will behave as if it is non-polar.<ref name="Neff 2002"/> Bioaccumulation for un-ionized compounds comes from partitioning equilibrium between the aqueous phase and the lipids in the organism.<ref name="Neff 2002"/> If the pH is higher than the pKa, then the compound is considered to be in the ionized form.<ref name="Neff 2002"/> The un-ionized form is favored because the bioaccumulation is easier for the organism to intake through partitioning equilibrium.<ref name="Neff 2002"/> The table below shows a list of pKas from compounds found in creosote preservatives and compares them to the average pH of seawater (reported to be 8.1).<ref>{{cite web |title=Ocean Acidification |website=Pristine Seas |publisher=National Geographic |url=https://www.nationalgeographic.org/society/our-programs/pristine-seas/ |url-status=dead |archive-url=https://web.archive.org/web/20150829013542/http://ocean.nationalgeographic.com/ocean/explore/pristine-seas/critical-issues-ocean-acidification/ |archive-date=2015-08-29}}</ref>
{| class="wikitable"
!Compound
!pKa
!pH of Seawater
!Form (Ionized or Un-Ionized)
|-
|m-cresol
|10.09
| rowspan="6" |8.1
|Un-ionized
|-
|o-cresol
|10.29
|Un-ionized
|-
|p-cresol
|10.30
|Un-ionized
|-
|2-ethylphenol
|10.20
|Un-ionized
|-
|guaiacol
|9.98
|Un-ionized
|-
|phenol
|9.99
|Un-ionized
|}

Each of the compounds in the table above is found in creosote preservatives; all are in the favored un-ionized form. In another study, various species of small fish were tested to see how the exposure time to PAH chemicals affected the fish.<ref name="United States Environmental Protection Agency-2008"/> This study showed that an exposure time of 24–96 hours on various shrimp and fish species affected the growth, reproduction, and survival functions of the organisms for most of the compounds tested.<ref name="United States Environmental Protection Agency-2008"/>

===Biodegradation===
It can be seen in some studies that biodegradation accounts for the absence of creosote preservatives on the initial surface of the sediment.<ref name="Elder"/> In a study from Pensacola, Florida, PAHs were not detected on the surface on the aquatic sediment, but the highest concentrations were detected at a depth of 8-13 centimeters.<ref name="Elder"/> A form an anaerobic biodegradation of m-cresol was seen in a study using sulfate-reducing and nitrate-reducing enriched environments.<ref name="Ramanand"/> The reduction of m-cresol in this study was seen in under 144 hours, while additional chemical intermediates were being formed.<ref name="Ramanand"/> The chemical intermediates were formed in the presence of [[bicarbonate]]. The products included 4-hydroxy-2-methylbenzoic acid and acetate compounds.<ref name="Ramanand"/> Although the conditions were enriched with the reducing anaerobic compounds, sulfate and nitrate reducing bacteria are commonly found in the environment. For further information, see [[sulfate-reducing bacteria]]. The type of anaerobic bacteria ultimately determines the reduction of the creosote preservative compounds, while each individual compound may only go through reduction under certain conditions.<ref name="Phelps"/> [[BTX (chemistry)|BTEX]] is a mixture of benzene, toluene, ethylbenzene, and xylene, that was studied in the presence of four different anaerobic-enriched sediments.<ref name="Phelps"/> Though the compound, BTEX, is not found in creosote preservatives, the products of creosote preservatives' oxidation-reduction reactions include some of these compounds. For oxidation-reduction reactions, see the following section. In this study, it was seen that certain compounds such as benzene were only reduced under sulfate-enriched environments, while toluene was reduced under a variety of bacteria-enriched environments, not just sulfate.<ref name="Phelps"/> The biodegradation of a creosote preservative in an anaerobic enrichment depends not only on the type of bacteria enriching the environment, but also the compound that has been released from the preservative. In aerobic environments, preservative compounds are limited in the biodegradation process by the presence of free oxygen.<ref name="Aronson et al 1999"/> In an aerobic environment, free oxygen comes from oxygen saturated sediments, sources of precipitation, and plume edges.<ref name="Aronson et al 1999"/> The free oxygen allows for the compounds to be oxidized and decomposed into new intermediate compounds.<ref name="Aronson et al 1999"/> Studies have shown that when BTEX and PAH compounds were placed in aerobic environments, the oxidation of the ring structures caused cleavage in the aromatic ring and allowed for other functional groups to attach.<ref name="Aronson et al 1999"/> When an aromatic hydrocarbon was introduced to the molecular oxygen in experimental conditions, a dihydrodiol intermediate was formed, and then oxidation occurred transforming the aromatic into a catechol compound.<ref name="Aronson et al 1999"/> Catechol allows for cleavage of the aromatic ring to occur, where functional groups can then add in an ortho- or meta- position.<ref name="Aronson et al 1999"/>

===Oxidation-reduction===
Even though many studies conduct testing under experimental or enriched conditions, [[redox|oxidation-reduction reactions]] occur naturally and allow for chemicals to go through processes such as biodegradation, outlined above. Oxidation is defined as the loss of an electron to another species, while reduction is the gaining of an electron from another species. As compounds go through oxidation and reduction in sediments, the preservative compounds are altered to form new chemicals, leading to decomposition. An example of the oxidation of p-cresol and phenol can be seen in the figures below:

====p-Cresol====
[[File:P-cresol degradation to benzoate.png|frameless|upright=2.25]]

This reaction shows the oxidation of p-cresol in a sulfate-enriched environment.<ref name="Smolenski"/> P-cresol was seen to be the easiest to degrade through the sulfate-enriched environment, while m-cresol and o-cresol where inhibited.<ref name="Smolenski"/> In the chart above, p-cresol was oxidized under an anaerobic sulfate reducing condition and formed four different intermediates.<ref name="Smolenski"/> After the formation of the intermediates, the study reported further degradation of the intermediates leading to the production of carbon dioxide and methane.<ref name="Smolenski"/> The p-hydroxylbenzyl alcohol, p-hydroxylbenzaldehye, p-hyrdoxylbenzoate, and benzoate intermediates all are produced from this oxidation and released into the sediments.<ref name="Smolenski"/> Similar results were also produced by different studies using other forms of oxidation such as: iron-reducing organisms,<ref name=Lovley1990/> Copper/Manganese Oxide catalyst,<ref name=wang2004/> and nitrate- reducing conditions.<ref name=Bossert1986/>

====Phenol====
[[File:Phenol reaction with iron and peroxide.png|frameless|upright=1.5]]

This reaction shows the oxidation of phenol by iron and peroxide.<ref name="Zazo et al 2005"/> This combination of iron, which comes from iron oxide in the sediment, and the peroxide, commonly released by animals and plants into the environment, is known as the [[Fenton reaction|Fenton Reagent.]]<ref name="Zazo et al 2005"/> This reagent is used to oxidize phenol groups by the use of a radical hydroxide group produced from the peroxide in the p-benzoquinone.<ref name="Zazo et al 2005"/> This product of phenol's oxidation is now leached into the environment while other products include iron(II) and water. P-benzoquinone is listed as being a very toxic, acute environmental hazard.<ref>{{cite web |title=Quinone |website=PubChem Database |publisher=National Center for Biotechnology Information |url=https://pubchem.ncbi.nlm.nih.gov/compound/p-benzoquinone |access-date=April 7, 2019}}</ref>