Chronological development of heavy metal accumulation research in earthworms - A review

A chronological survey has been carried out on the development of heavy metal accumulation research in earthworms. Pioneering studies in the field of heavy metal accumulation in earthworms that set the research trend have been reviewed. Earthworms are known to increase soil fertility by converting organic components present in the soil into soil nutrients. During this process they also work on the metals, including heavy metals. A part of the metals present in the soil is processed and ejected in the cast while the remaining part is retained by the earthworm tissues. Over the past fifty years, metal accumulation research in the earthworms has moved from bioaccumulation study to identification of biomarkers for assessing metal response. Surprisingly, tropical earthworms, especially those from Indian subcontinent, have remained poorly represented in earthworm and metal accumulation research.