The role of earthworms (Eisenia fetida) in influencing bioavailability of heavy metals in soils

Abstract

The effects of earthworm (Eisenia fetida) activity on soil pH, dissolved organic carbon (DOC), microbial populations, fraction distribution and bioavailability of heavy metals (Zn, Cu, Cr, Cd, Co, Ni, and Pb) in five Chinese soils were investigated using pot experiments. A three-step extraction procedure recommended by the European Community Bureau of Reference (BCR; now Standards, Measurements and Testing Programme of the European Community) was used to fractionate the metals in soils into water soluble, exchangeable and carbonate bound (B1), Fe-oxides and Mn-oxides bound (B2) and organic matter and sulfide bound (B3). After the soils were treated with earthworms, the soil pH, watersoluble metal fraction and DOC increased. A significant correlation was obtained between the increased DOC and the increased metals in the water-soluble fraction. The heavy metals in fraction B1 increased after earthworm treatments, while those in fraction B3 decreased. No significant differences were observed for heavy metals in fraction B2. The microbial populations in soil were enumerated with the dilution plate method using several media in the presence of earthworms. The microbial populations increased due to earthworm activity. The biomass of wheat shoots and roots, and the heavy metal concentrations in wheat roots and shoots, were also increased due to the earthworm activity. The present results demonstrated that earthworm activity increases the mobility and bioavailability of heavy metals in soils.

Earthworms Eisenia fetida affect the uptake of heavy metals by plants Vicia faba and Zea mays in metal-contaminated soils

“…The significant difference was observed for the C 2 concentration, which represents the highest CaCl 2 extractable Cd soil concentration. These findings are inconsistent with previous studies, which suggested an increase in the availability of metal fractions as a result of earthworm activities (Wen et al, 2004;Coeurdassier et al, 2007;Udovic and Lesta, 2007). Lukkari et al (2006) however reported an increase of Zn fractions in the presence of earthworms, concluding that earthworms tended to decrease the mobility of Zn in the soil.…”

“…The presence of earthworm increased Cd concentration in Z. mays, except for the control, probably because the amount of available Cd was too low. An increase in metal concentration for plants in the presence of earthworms was also observed by Wen et al (2004). Yu et al (2005) found that earthworm activities increased Cd uptake and plant growth, thereby improving the phytoextraction efficiency of metal hyperaccumulators in low to medium level metal-contaminated soils.…”

“…Lukkari et al (2006) however reported an increase of Zn fractions in the presence of earthworms, concluding that earthworms tended to decrease the mobility of Zn in the soil. In some studies, the addition of earthworms has been shown to decrease or not affect the fraction of metals bound to either organic matter or carbonates (Wen et al, 2004;Ruiz et al, 2011). The lack of observed differences in the availability of other metals (Cu, Pb, and Zn) between the control and the earthworm-inhabited Fig.…”

Acute Toxicity of Bismuth to the Earthworm <i>Eisenia andrei</i>

“…Furthermore, a novel test, namely, simulated earthworm gut, recently developed based on the enzymatic composition of the gastrointestinal fluid of E. andrei appeared to be most promising for predicting availability of metals in soil than chemical extraction methods [44]. The concentration of bioaccessible Bi recorded in the present study due to E. andrei activity was greater than those reported by Wen, et al [45] for Cr, Co, Ni, Zn, Cu, Cd, and Pb using E. fetida. This was possibly caused by a stronger affinity of Bi to form chelating complexes with metallophores and other biomolecule produced by earthworm.…”

Response of soil enzyme activities to synergistic effects of biosolids and plants in iron ore mine soils

“…To prevent the substrate from escaping through the holes at the bottom and the possibility of roots growing out of the pots (Hu et al 2013a, b), pieces of frost cloth were placed at the bottom before placing the substrate. Since the 100 % water-holding capacity (WHC) of tailings was determined prior to trial set-up, each pot containing the mixed substrate was adjust to 60 % WHC using tap water and left to stabilize for 2 days (Ruiz et al 2009;Wen et al 2004;Wang et al 2007). Thereafter, 25 seeds (Grant et al 2002) of Cynodon dactylon were sown 2 cm deep (Du et al 2014) in each pot.…”