Temporal Changes in Purity and Specific Activity of Tritium-Labeled 2,3,7,8-Tetrachlorodibenzo-p-dioxin:  Radiopurity Model for Toxicology

Abstract

The specific activity ( S ) and radiopurity ( R ) of tritium labeled 2,3,7,8-tetrachlorodibenzo-p-dioxin, [3H]TCDD, were measured by gas chromatography/mass spectrometry (GC/MS) while attempting to accurately characterize TCDD doses received by invertebrates, fish, and fish embryos during several toxicology studies conducted over a 3 year period. The [3H]TCDD sample was found to consist of six TCDD analogues involving hydrogen, deuterium, and tritium substitution at the 1,6-dibenzo-p-dioxin carbon positions and a complex mixture of impurities (with and without tritium labels). Planar aromatic impurities were identified as tolyl-TCDD adducts and appeared to result from the decay of 3H radiolabels to produce TCDD carbocations which reacted with the solvent, toluene. Formation of TriCDD and tolyl-TriCDDs, from both TCDD and tolyl-TCDDs, probably resulted from radiolysis-induced loss of a chlorine to form TriCDD free radicals which reacted with toluene. The measurement of S for [3H]TCDD by GC/MS was accurate and precise (±3%) because relative, rather than absolute, amounts of the analogues were determined. Changes in S over time were accurately modeled as a function of the conversion of each [3H]TCDD analogue to a solvent-TCDD analogue at a rate determined by 3H loss due to decay. Storage, purification, and use of tritiated chemicals for toxicology studies requires consideration of the 3H decay-related phenomena. For example, hydroxylated TCDD is an expected decay reaction product of [3H]TCDD in tissues and may be misidentified as a metabolite.

Long‐term fate and bioavailability of sediment‐associated 2,3,7,8‐tetrachlorodibenzofuran in littoral enclosures

“…A single impurity (approximately 4.5%) was identified by gas chromatography‐mass spectrometry (GC‐MS) as 2,3,7‐trichlorodibenzofuran. Fernandez et al [24] found dechlorination to be the major degradation route for tritiated TCDD; presumably this is also the reason that trichlorodibenzofuran was found in our parent compound. The TCDF was added to four of the enclosures as a sediment slurry (10 g wet weight surface sediment/L water/enclosure).…”

“…Tritiated 2,3,7,8‐tetrachloro[4,6‐ 3 H]dibenzofuran (hereafter referred to as TCDF) had a specific activity of 140 dpm/pg and 95.5% radiochemical purity. The TCDF was purified by reverse‐phase high‐performance liquid chromatography (HPLC) before use, which is the most effective method for removing impurities formed by the radiolysis of 3 H‐labeled TCDD [24]. Purity was confirmed by assay of HPLC fractions using liquid scintillation counting (LSC) and by gas chromatography with electron‐capture or mass spectrometry detection.…”

Review: Self‐radiolysis of compounds containing tritium and carbon‐14

“…Fernandez et al demonstrated tritiated 2,3,7,8‐tetrachlorobenzo‐p‐dioxin (TCDD) decomposes via tritium loss and the resulting carbocation reacts with toluene affording nonradioactive ortho, para, and meta tolulyl‐TCDDs (Figure 1). 85,86 …”

27 Radiochemistry

“…The b radiation of tritium will induce all manner of ion^molecule and radical reactions to the detriment of the labelled moiety and will lead to the formation of a wide range of contaminants each with a very high speci¢c activity. This aspect of labelling has been studied 59 in detail for 2,3,7,8-tetrachlorobenzo-p-dioxin and the subtle nature of the labelled impurities identi¢ed. The dangers of the presence of such impurities leading to false conclusions is emphasised.…”