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Metabolomic Study of the Earthworm Provides Insight into Soil Contamination

“1HNMR-based metabolomics along with metal accumulation and histological detection provide a reliable approach for interpreting time-dependent metabolic mechanisms in earthworms.”

Earthworms are considered to represent a reliable and straightforward means of assessing soil toxicity. They account for 60% of soil biomass, are continually surrounded by soil and are essential for the breakdown of organic matter.

Earthworms obtain nutrients by ingesting soil, and so any soil contaminants will enter the body of an earthworm. The prevalence of earthworms makes them easy to locate and collect allowing the presence of contaminants to be readily assessed, giving an indication of soil toxicity1.

The effect of pollutants on the numbers of earthworms, cocoon production and growth in earthworms have been used for many years to monitor soil quality3. However, although these are the recommended endpoints, they do not give information regarding specific responses to pollutants or the mechanisms by which toxicity is caused.

To obtain such knowledge, it is necessary to study biological responses, such as oxidative stress and altered gene expression. In addition, parameters relating to survival, growth, development and reproduction are generally longer-term effects and may not become apparent in shorter-term studies or if the levels of contaminants are low.

A more sensitive analysis methodology—metabolomics— is now being widely used to investigate the extent of the toxic effects of contaminants and the timescale over which the toxicity arises. Metabolomics is the study of chemical processes involving metabolites and how they are affected by changes to their surrounding4. It has been widely used in a range of toxicology investigations and is now being used increasingly in assessment of environmental stress.

Metabolomics studies using high-frequency nuclear magnetic resonance (1H NMR) metabolomics simultaneously measure hundreds of endogenous metabolites. It is therefore possible to determine effects on upstream processes, e.g., altered protein expression, in addition to the direct effects of external environmental stimuli.

This also provides information regarding the timing of the onset of toxicity from a given contaminant, whereby providing an insight in the mechanism of action. The value of environmental metabolomics has been clearly demonstrated in investigations into the toxicity of pesticides6.

A recent study used 1H NMR-based metabolomics to profile the time-dependent metabolic responses of earthworms (Eisenia fetida) exposed to soil contaminated with low levels of lead for 28 days7. Worm extracts were analyzed at regular intervals using a Bruker AVANCE 500 MHz spectrometer at 298 K.

Levels of lead in the worms were found to increase with increasing exposure to the contaminated soil6. The most severe toxicity was observed 14 days after exposure began. This indicates that earthworms should be exposed for at least 14 days to allow the toxic effects of contaminants to become apparent. Myo-inositol, 2-hexyl-5-ethyl-3-furansulfonate (HEFS), scyllo-inositol, succinate, alanine and maltose were identified as potential biomarkers for the early detection of exposure to lead.

1H NMR-based metabolomics is thus a suitable methodology for studying time-dependent metabolic mechanisms in earthworms, providing data that can be directly related to practical real-life scenarios.

To learn more about the Bruker Biospin AVANCE III 500 spectrometer, visit the Bruker website.

References

  1. Guidelines for the Testing of Chemicals NO.207 Earthworm, Acute Toxicity Tests. 1984, Adopted 04 April, 2004.
  2. Nahmani J, et al. A review of studies performed to assess metal uptake by earthworms. Environmental pollution. 2007;145:402–424.
  3. Ma W-cW. Critical body residues (CBRs) for ecotoxicological soil quality assessment: copper in earthworms. Soil Biology and Biochemistry. 2005;37:561–568.
  4. Nicholson JK and Lindon JC. Systems biology: metabonomics. Nature, 2008;455:1054–1056.
  5. Simpson MJ and McKelvie JR. Environmental metabolomics: New insights into earthworm ecotoxicity and contaminant bioavailability in soil. Anal. Bioanal. Chem. 2009;394:137–149.
  6. Lankadurai BP, et al. 1H NMR-based metabolomic analysis of polar and non-polar earthworm metabolites after sub-lethal exposure to phenanthrene. Metabolomics 2013;9:44–56.
  7. Tang R, et al, Time-dependent responses of earthworms to soil contaminated with low levels of lead as detected using 1H NMR metabolomics. RSC Adv. 2017;7:34170.