Soil Foodweb Inc.
Dr. Elaine Ingham

Current Bibliographic References on Bioremediation

SUMMARY: Heavy Metals Bioremediation of Soil

L. Diels, M. De Smet, L. Hooyberghs, and P. Corbisier (1999). Heavy metals bioremediation of soil. Molecular Biotechnology, Vol.12, Issue 2, pp. 149-158.

Abstract

Historical emissions of old nonferrous factories lead to large geographical areas of metals-contaminated sites. At Least 50 sites in Europe are contaminated with metals like Zn, Cd, Cu, and Pb. Several methods, based on granular differentiation, were developed to reduce the metals content. However, the obtained cleaned soil is just sand. Methods based on chemical leaching or extraction or on electrochemistry to release a soil without any salts and with an increased bioavailability of the remaining metals content. In this review a method is presented for the treatment of sandy soil contaminated with heavy metals. The system is based on the metal solubilization on biocrystallization capacity of Alcaligenes eutrophus CH34. The bacterium can solubilize the metals (or increase their bioavailability) via the production of siderophores and adsorb the metals in their biomass on metal-induced outer membrane proteins and by bioprecipitation. After the addition of CH34 to a soil slurry, the metals move toward the biomass. As the bacterium tends to float quite easily, the biomass is separated from the water via a flocculation process. The Cd concentration in sandy soils could be reduced from 21 mg Cd/kg to 3.3 mg Cd/kg. At the same time, Zn was reduced from 1070 mg Zn/kg to 172 mg Zn/kg. The lead concentration went down from 459 mg Pb/kg to 74 mg Pb/kg. With the aid of biosensors, a complete decrease in bioavailability of the metals was measured.

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SUMMARY: Bioremediation of Lead


Chen, H. Pan, S. (2005). Bioremediation potential of spirulina: toxicity and biosorption studies of lead. Journal of Zhejiang University SCIENCE, 6B(3):171-174

Abstract 
This study examines the possibility of using live spirulina to biologically remove aqueous lead of low concentration (below 50 mg/L) from wastewater. The spirulina cells were first immersed for seven days in five wastewater samples containing lead of different concentrations, and the growth rate was determined by light at wavelength of 560 mm. The 72 h-EC50 (72 h medium effective concnetration) was estimated to be 111.46 mg/L (lead). Afterwards, the lead adsorption by live spirulina cells was conducted. It was observed that at the initial stage (0-12 min) the adsorption rate was so rapid that 74% of the metal was biologically adsorbed. The maximum biosorption capacity of live spirulina was estimated to be 0.62 mg lead per 10alga cells.

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SUMMARY: Uptake of Lead by a Ciliate

A. Rehman, S. Ashraf, J. I. Qazi, & A. R. Shakoori (2005). Uptake of Lead by a Ciliate, Stylonchia mytilus, isolated from Industrial Effluents: Potential Use in Bioremediation of Wastewater. Bulletin of Environmental Contamination and Toxicology, Vol. 75, Issue 2, pp. 290-296.

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Asphalt and Toxins in Soil
Answer from Dr. Ingham to an email question 


With respect to the asphalt, and indeed any toxins in soil, the methods you use in dealing with them is critically important. 

So, an explanation of the steps to help you understand the situation.    

If you add just a single species, or even a couple species, to the soil to deal with this problem area, problems will be made worse.  Any one species of bacteria, or fungi, are limited in the set of metabolic functions they can perform.  Thus, an amendment with just one to 6 species will probably contain a few species that can begin the job of breaking down the asphalt, or diesel or oil, or whatever.  But, that first step typically does only step one in a thousand step process to detoxify and build soil organic matter.  

And unfortunately, the compound released after that first step will likely be more toxic than the asphalt itself.  

Thus, addition of a limited set of organisms will be worse than doing nothing.  Except that natural processes will begin to add the organisms to break these things down, and thus the toxic steps are going to happen.

So, what to do....... I suspect you can see how to deal with this already.  

Add the maximum diversity of all beneficial life that you possibly can.  You will likely need to add that max diversity life more than once, maybe several times in the first year, and perhaps every year for the next ten years.  

Max diversity of bacteria, fungi, protozoa, nematodes, microarthropods that you need will be found in aerobically managed compost.  Critical to check that compost as it finishes, or when you buy it, to make sure that diversity is present.  

So, how long will it take to break down the asphalt ---- well, how big are the chunks?  Can you till the compost into the soil as deep as the asphalt is found, plus a little lower?  If any initial steps in decomposition have started, the toxic compounds that will be released will have begun movement downward in the soil.  

You said people told you that asphalt is inert?  Apparently they have only worked with dirt, where there is no life.  Either that  
or they have never read work on soils below parking lots.  anyway, the answer is max diversity, so ALL the remaining 999 metabolic steps needed to deal with all the nasty compounds released and processed will happen in a short period of time.   

For a time, however, I would avoid growing non-mycorrhizal plants in that area with the asphalt chunks and the solidified oil residues.  Grow only plants that require mycorrhizal fungi to help them, and make sure the mycorrhizal fungi are present and colonizing the root systems.  Thus, getting hold of local source of good mycorrhizal fungi would be a good idea.  Perhaps contacting Mycorrhizal Applications (www.mycorhizae.com) for some help in this area would be good.   

There have been some good studies on the ability of mycorrhizal fungi to prevent uptake of toxics such as are released from materials like oil, asphalt, etc.  The mycorrhizal fungus apparently will take up the toxic materials, but the plant will not accept the toxics, so the hyphae outside the plant accumulate the toxics.  Just make sure to wash off all the root hairs --- with the attached mycorrhizal hyphae (which you cannot see) ---- before eating a root crop.  


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