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

Earthworms are an important part of food chain in soil ecosystem. In polluted soils, heavy metals are consumed by earthworms and transferred to other organisms through food chain, resulting in many adverse health impacts. Due to the benefits of earthworms for soil fertility, it is important to assess the effects of soil pollution on population, biomass and functions of earthworms. To determine the effects of organic matter on earthworms´ growth, in a soil with different levels of chromium, a factorial experiment with completely randomized design and three replications was performed. The levels of soil chromium were 0, 5, 10, 20, 40, 80, 160 and 320 mg kg-1 and the rates of organic matter (cow manure) added 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 living earthworms, their weights, the number of produced cocoons and the chromium concentrations of earthworm tissues were determined. The results of analysis of variance of data showed that the number of living earthworms, their weights and the number of produced cocoons decreased as the exposure time and the level of soil pollution by chromium increased. The chromium concentrations of earthworm tissues increased as the exposure time and the levels of soil chromium increased. The number of living earthworms, their weights and the number of produced cocoons increased as the level of soil organic matter increased.