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Earthworms and heavy metals

Dr Greg Willis gwillbro at intermet.net.au
Mon Jun 28 04:15:47 EST 1999

In the recent publication  "Earthworms in Australia", by the Australian
author, David Murphy, he states that "...earthworms can decontaminate soils
polluted with heavy metals...". In checking the citations to which he
refers in support of this contention he cites the work of Ireland, 1975,
OIKOS, 26, 74-79 (et al). However, the process by which Murphy concludes
that heavy metal contaminated soil is actually "decontaminated" is not
clearly stated or implied. It might be that since they (the worms) are
capable of taking up zinc, lead and cadmium into their bodies at levels
which are several magnitudes higher than the contaminated soils, it is
suggested that they carry off the heavy metals and then deposit them in
uncontaminated soils. But this process of dilution is not really a process
of "decontamination", per se.  

Are there any other processes by which worms, or other invertebrates, 
are capable of decontaminating soils polluted with heavy metals, or is it 
that they are simply tolerant of extremely high concentrations. I would 
suggest that since such contaminants are elemental, it would be difficult 
to "detoxify" such soil. Or perhaps changing the form of heavy metals by 
chemically altering the salts attached to them may render them less toxic. 
(for example, some forms of arsenic are toxic while others are 
medicinal". Is such a process known to occur and would it occur in 
earthworms? Or are there other such processes?  

Thank you for any information
Dr. Gregory L. Willis 
<gwillbro at intermet.net.au>

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