Editing Creosote (section)

===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"/>