Soil Micro-organism Test

Microorganisms are important for the breakdown and transformation of soil organic matter, with many species contributing to different aspects of soil fertility. It is not possible to assess the impacts of soil contaminants on individual microorganisms in soils and extrapolate these effects to the whole community.

For indigenous soil microorganisms, our ecotoxicity test assessed the functional integrity of microbial nitrogen cycling by measuring nitrogen mineralisation from standardised plant material. Our test was derived from the draft OECD guideline (OECD 1996) for testing the effect of chemicals on microbial processes as based on the recommendations of the European and Mediterranean Plant Protection Organization (EPPO 1994).

As recommended by the soil microbial tests workgroup at the workshop on standardised test methods for soils (Fairbrother et al. 1999), toxicity in natural soils containing indigenous microbial communities was examined. We selected three control subsoils representative of metal contaminated sites in New Zealand. However, we were unable to obtain satisfactory and reproducible dose-response relationships between nitrogen mineralisation and exposure to metals using this microbial test method, in all except for one test. We are therefore unable to report the ecotoxicity values for micro-organisms in New Zealand soils.