The effects of exposure time, different levels of arsenic and organic matter on earthworms´ growth

In polluted soils, heavy metals are consumed by earthworms and transferred to other organisms through food chains. Due to the sensitivity of earthworms to pollution, they can be used as bio-indicators for soil pollution evaluation. To determine the effects of organic matter on sensitivity of earthworms to different levels of soil arsenic, a factorial experiment with completely randomized design and three replications was performed. The levels of soil arsenic were 0, 5, 10, 20, 40, 80, 160 and 320 mg kg-1 and the rates of added organic matter were 0, 5 and 10 % w/w. The earthworms were exposed to soil pollution for different time periods (0, 15, 30, 45 and 60 days) and after that the number of alive earthworms, their weights, the number of produced cocoons and the concentrations of arsenic in tissues of earthworms were determined. Anova results showed that the number of alive earthworms, their weights, the number of produced cocoons decreased as the exposure time and level of soil pollution by arsenic increased. The concentrations of arsenic in tissues of earthworms increased as the exposure time and levels of arsenic in polluted soils increased. The number of alive earthworms, their weights and the number of produced cocoons increased as the level of soil organic matter increased. But the concentrations of arsenic in earthworm tissues decreased as the level of soil organic matter increased. As the concentrations of arsenic in earthworm tissues increased, the weights of earthworms and the number produced cocoons by them decreased.