Bioaccumulation of total mercury in the earthworm Eisenia andrei

Shirley Le Roux; Priscilla Baker; Andrew Crouch

doi:10.1186/s40064-016-2282-6

Bioaccumulation of total mercury in the earthworm Eisenia andrei

Springerplus. 2016 May 20;5(1):681. doi: 10.1186/s40064-016-2282-6. eCollection 2016.

Authors

Shirley Le Roux¹, Priscilla Baker¹, Andrew Crouch²

Affiliations

¹ SensorLab, Chemistry Department, University of the Western Cape, PB X17, Bellville, 7535 South Africa.
² Faculty of Science, University of the Witwatersrand, Private Bag 3, Johannesburg, 2050 South Africa.

Abstract

Earthworms are a major part of the total biomass of soil fauna and play a vital role in soil maintenance. They process large amounts of plant and soil material and can accumulate many pollutants that may be present in the soil. Earthworms have been explored as bioaccumulators for many heavy metal species such as Pb, Cu and Zn but limited information is available for mercury uptake and bioaccumulation in earthworms and very few report on the factors that influence the kinetics of Hg uptake by earthworms. It is known however that the uptake of Hg is strongly influenced by the presence of organic matter, hence the influence of ligands are a major factor contributing to the kinetics of mercury uptake in biosystems. In this work we have focused on the uptake of mercury by earthworms (Eisenia andrei) in the presence of humic acid (HA) under varying physical conditions of pH and temperature, done to assess the role of humic acid in the bioaccumulation of mercury by earthworms from soils. The study was conducted over a 5-day uptake period and all earthworm samples were analysed by direct mercury analysis. Mercury distribution profiles as a function of time, bioaccumulation factors (BAFs), first order rate constants and body burden constants for mercury uptake under selected conditions of temperature, pH as well as via the dermal and gut route were evaluated in one comprehensive approach. The results showed that the uptake of Hg was influenced by pH, temperature and the presence of HA. Uptake of Hg(2+) was improved at low pH and temperature when the earthworms in soil were in contact with a saturating aqueous phase. The total amount of Hg(2+) uptake decreased from 75 to 48 % as a function of pH. For earthworms in dry soil, the uptake was strongly influenced by the presence of the ligand. Calculated BAF values ranged from 0.1 to 0.8. Mercury uptake typically followed first order kinetics with rate constants determined as 0.2 to 1 h(-1).

Keywords: Bioaccumulation; Bioaccumulation factor; Bioavailability; Earthworms; Humic acid; Mercury; Soil.