Abstract:
Polycyclic Aromatic Hydrocarbons (PAH) are organic compounds made up of carbon and
hydrogen, consisting of two or more connected aromatic rings, produced by the combustion of
carbonaceous compounds. They accumulate in the environment and have an enormous impact on
pollution. Through wet and dry deposition, they accumulate in the biota and invade human
systems via dietary sources, leading to various adverse effects such as carcinogenicity and
genotoxicity. The primary objective of this study is to isolate, identify and select the best soil
inhabiting bacteria from landfills and paddy fields which can degrade lower molecular weight
PAHs, phenanthrene and naphthalene and study their degradation percentages. Bacterial strains
with varying morphology were isolated to identify and evaluate their PAH-degrading potential
and PAH degradation percentages. Plate assay was used as the primary screening test while
spectrophotometric analysis with methylene blue (in 609 nm wavelength) was used as the
confirmation test. For naphthalene, the strains ST1-1, ST1-2, ST2-3, ST3-6, ST3-8, ST3-8/a, SV2-
02, SV3-03, SV4-04 and SV7-07 were capable of a degradation percentage of over 30% with ST1-
1 presenting the highest value at 68.25%. ST1-1 presented a population density of 1x106 CFU/ml.
For phenanthrene, the strains ST1-1, ST1-2, ST2-4, ST3-5, ST3-8, ST3-8/a, SV4-04 and SV6-06
were capable of a degradation percentage of over 20% with ST3-8/a and ST1-1 presenting the
highest value at 46.76% and 41.16%. Both these strains presented a population density of 1x106
CFU/ml. These strains were collected from landfills being used for over 15 years. With the
continuous addition of persistent organic pollutants to the soil, it can be assumed their ability to
degrade prevalent PAHs has been well developed over a long period of time. These selected strains
can be categorized as potential biological agents to degrade PAHs such as phenanthrene and
naphthalene in polluted agricultural soils.
