Thavamani Palanisami (PhD Student)
University of South Australia

Project Title
Remediation of mixed contaminated soils with special reference to MGP sites.

Biography
Thavamani is undertaking his PhD in the Centre for Environmental Risk Assessment and Remediation (CERAR), UniSA. He is a CRC CARE and IPRS funded student. He completed his Bachelor degree in agriculture, and Masters in environmental sciences at Tamilnadu Agricultural University, India. His Masters thesis was on ‘Evaluating textile effluent sludge as a soil ameliorant for problem soils’. Before he came to Australia he worked as a senior research fellow for three years in the project entitled ‘Bioremediation of nitrate contaminated groundwater’ in India. He has had 5 years of experience in bioremediation research. His main areas of interest are environmental microbiology, toxicology and soil chemistry.

Start Date
February 2006

Project Details
Soil ecosystems are subject to contamination from a variety of hazardous chemicals such as heavy metals and toxic organic compounds. Soil is a medium of life, and one of the most valuable natural resources on earth. Anthropogenic pollutants hardly occur in the environment as single constituents. Hazardous substances present even in water and air ultimately reside in soil matrix. This situation often creates a soil system which receives more than one type of contaminant, which referred to as mixed contamination.

Mixed contaminant soils are the complex, multi-component systems with a range of different types of contaminants, such as PAHs, phenols, pesticides, BTEX and metals, co-existing in different physical and chemical forms. The intra- and interspecific interaction and binding of mixed contaminants reduce the bioavailability, and become low/unavailable to the native microbial populations. 

Previous studies have shown that the focus of remediation works throughout the last twenty years have been single contaminants, although the majority of contaminated sites contain a heterogeneous mixture of organic and inorganic contaminants. Presumably, the presence of such a toxic mixture of chemicals is one reason for the lack of progress in the remediation of such contaminated sites. Manufactured gas plant (MGP) sites are the typical example of mixed contaminant sites. MGP sites have more than one hundred species of PAHs and oxy-PAHs, and coexist with heavy metals such as cadmium, chromium, cyanide, arsenic and zinc etc.

This research will focus on studying the toxicity and remediation methods for mixed contaminant MGP sites.

Thesis Abstract - Summary
Mixed contaminated soils are the complex, multi-component systems with a range of different types of organic and inorganic co-existing in different physical and chemical forms. Polycyclic aromatic hydrocarbons (PAHs), characterised by their high hydrophobicity, resistance to natural degradation and carcinogenic properties, often co exist with metals at many contaminated sites around the world. Previous and current research on remediation technologies has focused on either organic compounds or metals, with very little focused on mixed contaminants. Given this unexplored area, this thesis underpins the science of mixed contaminant remediation with special reference to PAHs and metals that are very common in manufactured gas plant (MGP) sites.

In this study, a model mixed contaminated soil collected from 100-year-old former MGP site was subjected to detailed characterisation including effect of PAHs and metals on soil biological activities. The site characterisation based on metal speciation provided better understanding of the risk than traditional physico-chemical characterisation alone. The combined effect of PAHs and metals was well pronounced by dehydrogenase activity. Even though the microbial diversity in PAHs and metals contaminated soil was reduced, a few adapted species survived as confirmed by the molecular analysis of MGP sites soils.