Abstract
Abstract - The use of earthworms to bioremediate soil results in decreasing the pollutant concentration through a bioaccumulation mechanism of the contaminants in the earthworm's body. The present work is an empirical study that was carried out on soils contaminated with chromium and cadmium. Organic matter in the amount of 5% and 9% of soil weight was added. Chromium and cadmium concentrations in soil and in the body of worms were measured at two time periods of 21 and 42 days. According to the results, increasing from 5% to 9% the organic material of the soil contaminated with chromium at the initial concentration of 0.06 mg/g, the removal efficiency decreased by 5%. In 0.1 mg/g concentration the bioremediation efficiency decreased by 20%, showing that the earthworms probably have more tendency to consume the organic material and low tendency for consuming the soil contaminated by metal. Results showed that, considering the increased mortality of worms in the soil at a concentration of 0.08 mg/g of chromium, using this method is not recommended. For cadmium we require more study, though we can say that the organic material had no influence on the bioremediation of the soil.
Highlights
The advances of humanity towards industrialization caused the production and entrance of hazardous pollutants such as carcinogenic compounds, toxins and heavy metals into the environment
The mortality rate at the initial concentration of 0.04 mg/g for these sampling days were 0 and 11.1%, respectively, and, at a concentration of 0.08 mg/g cadmium, 0% and 33.3%, respectively, which shows a clear increase in the mortality level of worms with the increase of chromium concentration in soil, while little change was observed in the mortality of worms upon increasing the concentration of cadmium in soil
This study showed that the toxicity of chromium during the time is more severe than the toxicity of cadmium on the viability of earthworms, meaning that, with passing time, chromium causes more deaths than cadmium in the population of earthworms
Summary
The advances of humanity towards industrialization caused the production and entrance of hazardous pollutants such as carcinogenic compounds, toxins and heavy metals into the environment. The use of earthworms for soil bioremediation is a biological method, so that the pollutant concentrations in the soil are reduced through bioaccumulation mechanisms in the body of the earthworms (Matscheko et al, 2002, Slizovskiy and Kelsey, 2010). These organisms can accumulate high concentrations of heavy metals in their body (Li et al, 2010). During their study, Avila et al (2009) identified that increasing the organic material can reduce the toxicity of heavy metals in the body of earthworms. During their study, Avila et al (2009) identified that increasing the organic material can reduce the toxicity of heavy metals in the body of earthworms. Irizar et al (2015) concluded during their study that, if the organic material in the soil is low, earthworms are not able to digest the soil and, as a result, the toxicity of cadmium increases in them, and the mortality and disorder in reproduction rise. Haghparast et al (2013) showed that organic material is a source of energy for Eisnia Fetida earthworms and increases the percentage of their survival
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