A brief review and evaluation of earthworm biomarkers in soil pollution assessment

Earthworm biomarker response to pollutants has been widely investigated in the assessment of soil pollution. However, whether and how the earthworm biomarker-approach can be actually applied to soil pollution assessment is still a controversial issue. This review is concerned about the following points: 1. Despite much debate, biomarker is valuable to ecotoxicology and biomarker approach has been properly used in different fields. Earthworm biomarker might be used in different scenarios such as large-scale soil pollution survey and soil pollution risk assessment. Compared with physicochemical analysis, they can provide more comprehensive and straightforward information about soil pollution at low cost. 2. Although many earthworm species from different ecological categories have been tested, Eisenia fetida/andrei is commonly used. Many earthworm biomarkers have been screened from the molecular to the individual level, while only a few biomarkers, such as avoidance behavior and lysosomal membrane stability, have been focused on. Other aspects of the experimental design were critically reviewed. 3. More studies should focus on determining the reliability of various earthworm biomarkers in soil pollution assessment in future research. Besides, establishing a database of a basal level of each biomarker, exploring biomarker response in different region/section/part of earthworm, and other issues are also proposed. 4. A set of research guideline for earthworm biomarker studies was recommended, and the suitability of several earthworm biomarkers was briefly evaluated with respect to their application in soil pollution assessment. This review will help to promote further studies and practical application of earthworm biomarker in soil pollution assessment.