Background: Earthworms are an important part of food chains in soil ecosystems and their growth are adversely affected by soil contamination. In polluted soils, heavy metals are consumed by earthworms, and are carried through food chains, resulting in many adverse health impacts. Due to the sensitivity of earthworms to pollution, earthworms can be used as bio- indicators of the soil pollution.

Materials and Methods: This study was a completely random design conducted as a factorial experiment. Different levels of soil pollution to chromium were zero, 5, 10, 20, 40, 80, 160 and 320 mg kg-1 soil. Earthworms were exposed to these levels of contamination in the 4 periods (15, 30, 45 and 60 days) and the number of alive earthworms, their weights and the number of cocoons produced by earthworms were studied.

Results: Results of this study showed that an increasing concentration of chromium in soil significantly decreased the number of alive earthworms, their weights and the number of cocoons produced by them. After 15 days, it was observed that earthworm immortality and weight had decreased by13.54% and 10.76%, respectively.

Conclusion: Due to the sensitivity of earthworms to chromium in soil, they can be used as bio-indicators of soil pollution.