Stannous chloride as a tool for mercury stripping in contaminated streams: Experimental assessment of toxicity in an invertebrate model species.

The chronic toxicity of an innovative Hg water treatment system using tin (Sn) (II) chloride (SnCl2) followed by air stripping was assessed through measurements of survival, growth, and reproduction rate in the freshwater cladoceran Ceriodaphnia dubia, a model species for toxicity testing. We first calculated the concentrations of Hg causing 25% reduction in survival and reproduction (Lethal or Inhibition Concentrations, or LC25 and IC25, for survival and reproduction, respectively) through exposure to aqueous Hg at concentrations ranging from 0 to 25,000 ng L-1. Then, we treated media (DMW and natural stream water) contaminated with Hg at LC25 and IC25 concentrations with SnCl2 at a Sn:Hg stoichiometric ratio of 8:1 and air stripping and exposed C. dubia to this Sn-amended media. Our results showed that Hg significantly affected survival, reproduction rates and impaired growth. SnCl2-treatment removed 100% of the Hg from the media at all concentrations tested with no deleterious effects on survival, growth and reproduction. Our results confirmed the efficacy of SnCl2 in removing aqueous Hg from stream water and showed that the added Sn did not impact C. dubia at the concentrations tested, supporting the suitability of SnCl2-based treatments in appropriate Hg-contaminated environments.

Evaluation of engineered sorbents for the sorption of mercury from contaminated bank soils: a column study.

As a global environmental pollutant, mercury (Hg) threatens our water resources and presents a substantial risk to human health. The rate and extent of immobilization of Hg2+ (hereafter, Hg) on engineered sorbents (Thiol-SAMMS®, pine biochar, SediMite™, Organoclay™ PM-199, and quartz sand as a control) was evaluated using flow-through column experiments. The effectiveness of the sorbents was based on (1) the percentage of Hg removed in relation to the total amount of Hg passing the sorbent column, and (2) the rate of Hg uptake compared to the nonreactive tracer bromide (Br-). All sorbents removed Hg to a certain extent, but none of the sorbents removed all the Hg introduced to the columns. Thiol-SAMMS showed the highest mean percentage of Hg removed (87% ± 2.9%), followed by Organoclay PM-199 (71% ± 0.4%), pine biochar (57% ± 22.3%), SediMite (61% ± 0.8%), and the control quartz sand (11% ± 5.6%). Thiol-SAMMS was the only sorbent to exhibit retardation of Hg in comparison to the conservative tracer Br-. For the remaining sorbents, Br- along with low concentrations of Hg were eluted within the first 3 pore volumes, indicating limited retardation of Hg. Overall, removal of Hg by sorbents was substantial, suggesting that sorbents might be suitable for deployment in contaminated environments. High concentrations of DOM leaching from the soil columns likely influenced the speciation of Hg and inhibited sorption to the sorbents. Incomplete removal of Hg by any sorbent suggests that additional optimization is needed to increase efficiency.