Mercury Accumulation in Eisenia Hortensis from FGDG and Mercury Chloride Amended Soils.

Flue gas desulfurization gypsum (FGDG) is a useful byproduct in agricultural systems. The primary heavy metal within FGDG that draws public interest is Hg. The objective of this study was to determine the bioaccumulation of Hg by the European earthworm, Eisenia hortensis, from a Lawther silty clay and a Flaming sandy loam amended with equivalent Hg rates of FGDG and HgCl₂.  In a 4-week growth chamber study using 3 kg of soil per pot, the five treatments were: 1) control, 2) 4.08 µg Hg/pot applied as 4.48 Mg FGDG/ha, 40.8 µg Hg/pot applied as 44.8 Mg FGDG/ha, 4.08 µg Hg/pot as HgCl₂, and 40.8 µg Hg/pot as HgCl₂. In each pot 100 live worms were added. Once the worms were added to the pots, deionized water was added and adjusted each week to maintain 25% gravimetric water content.  Each week, 10 worms were extracted from each pot, depurated for 24 h, washed, frozen, freeze-dried, ground using a stainless steel ball mill, and total Hg determined using combustion (DMA-80, Milestone Inc., Shelton, CT). Results indicate that bioaccumulation of Hg across treatments ranged from about 0.08 to 0.15 mg Hg/kg of worm tissue with no discernable accumulation with time. Bioaccumulation factors (BF) for the Lawther soil were similar between the control and high Hg rates and were generally lower than the BF from the lower organic matter Flaming soil (4.9 vs 2.5% OM, respectively). Bioaccumulation factors for the Flaming soil were again similar between treatments and time except for the high rate of HgCl₂ which was nearly double (7.0) at day 28 vs day 7.