Bioavailability of weathered hydrocarbons in engine oil-contaminated soil: Impact of bioaugmentation mediated by Pseudomonas spp. on bioremediation.

Heavier fraction hydrocarbons (C15-C36) formed in soil after biotic and abiotic weatherings of engine oil are the continuing constraints in the bioremediation strategy, and their bioavailability remains a poorly quantified regulatory factor. In a microcosm study, we used two strains of Pseudomonas, P. putida TPHK-1 and P. aeruginosa TPHK-4, in strategies of bioremediation, viz., natural attenuation, biostimulation and bioaugmentation, for removal of weathered total petroleum hydrocarbons (TPHs) in soil contaminated long-term with high concentrations of engine oil (39,000-41,000 mg TPHs kg-1 soil). Both the bacterial strains exhibited a great potential in remediating weathered hydrocarbons of engine oil. Addition of inorganic fertilizers (NPK), at recommended levels for bioremediation, resulted in significant inhibition in biostimulation/enhanced natural attenuation as well as bioaugmentation. The data on dehydrogenase activity clearly confirmed those of bioremediation strategies used, indicating that this enzyme assay could serve as an indicator of bioremediation potential of oil-contaminated soil. Extraction of TPHs from engine oil-contaminated soil with hydroxypropyl-ß-cyclodextrin (HPCD), but not 1-butanol, was found reliable in predicting the bioavailability of weathered hydrocarbons. Also, 454 pyrosequencing data were in accordance with those of bioremediation strategies used in the present microcosm study, suggesting the possible use of pyrosequencing in designing approaches for bioremediation.

Earthworm Comet Assay for Assessing the Risk of Weathered Petroleum Hydrocarbon Contaminated Soils: Need to Look Further than Target Contaminants.

Earthworm toxicity assays contribute to ecological risk assessment and consequently standard toxicological endpoints, such as mortality and reproduction, are regularly estimated. These endpoints are not enough to better understand the mechanism of toxic pollutants. We employed an additional endpoint in the earthworm Eisenia andrei to estimate the pollutant-induced stress. In this study, comet assay was used as an additional endpoint to evaluate the genotoxicity of weathered hydrocarbon contaminated soils containing 520 to 1450 mg hydrocarbons kg-1 soil. Results showed that significantly higher DNA damage levels (two to sixfold higher) in earthworms exposed to hydrocarbon impacted soils. Interestingly, hydrocarbons levels in the tested soils were well below site-specific screening guideline values. In order to explore the reasons for observed toxicity, the contaminated soils were leached with rainwater and subjected to earthworm tests, including the comet assay, which showed no DNA damage. Soluble hydrocarbon fractions were not found originally in the soils and hence no hydrocarbons leached out during soil leaching. The soil leachate's Electrical Conductivity (EC) decreased from an average of 1665 ± 147 to 204 ± 20 µS cm-1. Decreased EC is due to the loss of sodium, magnesium, calcium, and sulphate. The leachate experiment demonstrated that elevated salinity might cause the toxicity and not the weathered hydrocarbons. Soil leaching removed the toxicity, which is substantiated by the comet assay and soil leachate analysis data. The implication is that earthworm comet assay can be included in future eco (geno) toxicology studies to assess accurately the risk of contaminated soils.

Microbial diversity and hydrocarbon degrading gene capacity of a crude oil field soil as determined by metagenomics analysis.

Soils contaminated with crude oil are rich sources of enzymes suitable for both degradation of hydrocarbons through bioremediation processes and improvement of crude oil during its refining steps. Due to the long term selection, crude oil fields are unique environments for the identification of microorganisms with the ability to produce these enzymes. In this metagenomic study, based on Hiseq Illumina sequencing of samples obtained from a crude oil field and analysis of data on MG-RAST, Actinomycetales (9.8%) were found to be the dominant microorganisms, followed by Rhizobiales (3.3%). Furthermore, several functional genes were found in this study, mostly belong to Actinobacteria (12.35%), which have a role in the metabolism of aliphatic and aromatic hydrocarbons (2.51%), desulfurization (0.03%), element shortage (5.6%), and resistance to heavy metals (1.1%). This information will be useful for assisting in the application of microorganisms in the removal of hydrocarbon contamination and/or for improving the quality of crude oil. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:638-648, 2016.

Toxicity and oxidative stress induced by used and unused motor oil on freshwater microalga, Pseudokirchneriella subcapitata.

Although used motor oil from automobiles is one of the major pollutants through storm water in urban environments leading to contamination of water bodies, very little information is available on its toxicity towards growth of microalgae. Also, to our knowledge, there are no data on the used motor oil-induced oxidative stress in microalgae. We therefore investigated the toxicity of used and fresh motor oil on growth and antioxidant enzymes of a microalga, Pseudokirchneriella subcapitata. In general, used oil was more toxic to the alga than fresh oil. Used oil at 0.20 % inhibited algal growth, measured in terms of chlorophyll a, by 44 % while fresh oil was nontoxic up to 2.8 %. Water-accommodated fraction (WAF) of the used oil at >50 % concentration exhibited significant toxicity while WAF from fresh oil was nontoxic even up to 100 %. Used oil and its WAF, even at lower concentrations, increased the levels of antioxidant enzymes indicating algal response to the toxicity stress. When the alga was exposed to WAF from fresh motor oil, no alterations in the antioxidant enzyme levels were evident. The present investigation suggests that contamination of aquatic systems with used oil could potentially affect the ecosystem health via disruption of primary producers that are located at the base of the food chain.