Microbial community and ecotoxicity analysis of bioremediated, weathered hydrocarbon-contaminated soil

Abstract

Bioremediated soils are usually disposed of after meeting legislated guidelines defined by chemical and ecotoxicity tests. In many countries including Australia, ecotoxicity tests are not yet mandatory safety requirements. This study investigated the biotreatment of weathered hydrocarbon-contaminated soils in 12-week laboratory-based microcosms. Monitored natural attenuation resulted in ~43% reduction of total petroleum hydrocarbon contaminant to 5503 mg/kg (C16–C35), making the soil suitable for disposal as waste under current guidelines (pesticide and metal contents within safe limits). 16S rDNA (universal and AlkB) and ITS-based DGGE fingerprints showed stable and adapted microbial communities throughout the experimental period. However, ecotoxicology assays showed 100% mortality of earthworms (Eisena fetida) in potting soils containing ≥50% (≥2751 mg/kg, legally safe in situ concentrations) contaminated soil over 14 days. Up to 70% reduction in radish (Raphanus sativus) seed germination was observed in potting soils containing ≥10% contaminated soil (≥550 mg/kg, legally safe ex situ concentrations for soil disposal into residential areas). The results indicate the toxicity of these soils to soil biota despite meeting legislated Australian safe levels and guidelines for disposal or use in residential areas.

Remediation of saline soils by a two-step process: Washing and amendment with sludge

“…Germination assays R. sativus L. seeds (radish) were used in the germination tests to evaluate the remediation of treated soils (Sheppard et al, 2011) and studies of waste phytotoxicity (Andreozzi et al, 2008).…”

Phytoremediation

“…One of these alternate methods is termed bioaugmentation: in this case the addition of hydrocarbon degraders (mostly bacteria and to a lesser extent fungi) which are generally isolated or enriched in the laboratory from samples taken from contaminated sites (Perelo 2010 ;Sarkar et al 2005 ). Although the application of bioaugmentation to environments contaminated with petrogenic hydrocarbons has been extensively studied in both marine and terrestrial systems (Kadali et al 2012 ;Makadia et al 2011 ;Sheppard et al 2011 ;Simons et al 2012 ;, there exists potential question or concern relating to the introduction of exogenous organisms and the potential negative impacts of this introduction on the diversity and functionality of the natural ecosystem (Iwamoto and Nasu 2001 ).…”

Exploiting the intrinsic hydrocarbon-degrading microbial capacities in oil tank bottom sludge and waste soil for sludge bioremediation

“…Using previously bioremediated soils which usually have enhanced microbial degrading capacity should be beneficial to the oil tank bottom degradation. Recent reports Sheppard et al 2011) have shown that under conditions of monitored natural attenuation, such soils were as equally effective as the application of microbe-nutrient formulation for TPH reduction in contaminated soils. The use of the fungus nutrient formulation and previously bioremediated (treated) waste soil was beneficial to TPH reduction in this study especially between days 0 and 49.…”

“…TPH contents of replicate samples were determined in samples using the modified standard protocol of International Organization for Standardization (ISO2004), ISO/DIS 16703 GC. The soil TPH content was estimated as described by Sheppard et al (2011). Standard calibration curves were made from hydrocarbon mixture (RTW solution) dilutions.…”

“…However when detoxified, such soils should be suitable candidates for treating oil wastes. In Australia, the levels of total petroleum hydrocarbon (TPH) and other residual hydrocarbon fractions such as benzo (a) pyrene and aromatic fractions and metals permissible in treated waste soils prior to landfill disposal are defined by the National Environmental Protection Council (NEPC) (NEPC 1999;Sheppard et al 2011). Waste soils which have satisfied the legislated safety threshold (such as having TPH levels of B10,000 mg kg -1 ) can possess substantial microbial hydrocarbon-degrading potential which can be successfully harnessed for treating new hydrocarbon contaminants Sheppard et al 2011).…”