Sequestration of 2,3,7,8-tetrachlorodibenzo-p-dioxin by activated carbon eliminates bioavailability and the suppression of immune function in mice

Abstract

The effectiveness of activated carbon in reducing the bioavailability of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was examined from the context of using in situ sorbent amendments to remediate soils/sediments contaminated with polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs). This technology has gained rapid acceptance based on observations that activated carbon amendments predictably lower PCDD/F concentrations in water and bioaccumulation by simple aquatic organisms and earthworms; it has been assumed that bioavailability to mammals is similarly reduced, although this has been disproven for other sorbent materials. In the present study TCDD was absorbed to a microporous activated carbon (TCDD-AC) using the incipient wetness method. An aqueous suspension of TCDD-AC and an equivalent dosage of TCDD in corn oil were administered by oral gavage to B6C3F1 mice. The relative bioavailability of TCDD-AC was determined by quantifying and comparing the hepatic induction of cyp1A1 (messenger ribonucleic acid) and suppression of the immunoglobulin M antibody-forming cell immune response by the 2 forms of TCDD. A concentration-dependent response was observed for both assays when TCDD in corn oil was administered to mice. However, when equivalent masses of TCDD were administered as TCDD-AC, no induction of cyp1A1 or suppression of the immunoglobulin M antibody-forming cell response was observed. The absence of these 2 sensitive aryl hydrocarbon receptor-mediated responses in mice provides the first direct evidence that activated carbon can sequester TCDD in a form that eliminates its bioavailability to mammals. These results support the premise that activated carbon can be used to reduce the bioeffective dose of TCDD delivered to mammals and that activated carbon amendments may provide a low-cost alternative to traditional remediation technologies. Environ Toxicol Chem 2017;36:2671-2678. © 2017 SETAC.

Keywords: 2,3,7,8-Tetrachlorodibenzo-p-dioxin; Activated carbon; Bioavailability; Dioxin; Remediation; Sorbent amendment.

Figure 1

Chromatogram and mass spectrum obtained from pyrolysis GC/MS analysis of WPC activated carbon loaded with dibenzo-p-dioxin (DD) dissolved in dimethyl sulfoxide (DMSO) at 550°C. Direct observation of the loss of DD was observed for the two peaks shown in rectangular box.

Figure 2

Preliminary mice feeding experiment with three different treatments: NA - no antigenic sensitization with sRBC, Water – 200 μL of water per day for 4 consecutive days then sensitized with sRBC, and Char – activated carbon (20 mg/mL) in 200 μL of water per day for 4 consecutive days then sensitized with sRBC. * Denotes p < 0.05 compared to water control group.

Figure 3

Tetrachlorodibenzo-p-dioxin (TCDD)-induced suppression of humoral activity observed using corn oil vehicle and not observed in activated carbon. *Denotes p < 0.05 compared to respective vehicle control group. Results are representative of two separate experiments.

Figure 4

Spleen (A) and liver (B) weight to total body weight ratio. *Denotes p < 0.05 compared to the respective vehicle control.

Figure 5

Effects on cyp1a1 mRNA induction and scaled response of the fold induction in mice exposed to TCDD-AC. *Denotes p < 0.05 compared to their respective vehicle (TCDD = 0) control.