Organoiodine formation during humification in peatlands

Abstract

Although two billion people in the world are suffering from iodine deficiency there is little information on the chemical fate of iodine in the terrestrial environment. Here we show that peatlands play a major role in terrestrial iodine cycling. Chemical data from two peat profiles from Patagonia, Chile imply that transformation of iodine from its inorganic form to organoiodine compounds during early humification in peatlands is a key process in storage of iodine in the terrestrial environment. Once bound in peat, iodine remains stable for thousands of years. In the earth's peatlands, net accumulation of iodine since the last glacial period is estimated to be 12-36 teragrams (1 Tg=10 12 g). These data suggest that peatlands are a major reservoir of iodine in terrestrial ecosystems. Our novel model of iodine distribution in the terrestrial environment demonstrates the key role of peatlands in burial and reemission of organically bound iodine.

Carbon isotopes and iodine concentrations in a Mississippi River delta core recording land use, sediment transport, and dam building in the river’s drainage basin

“…No I/C data is available from Mississippi River wetlands. However, both ratios appear somewhat higher than reported I/C ratios in peat bogs from Southern Chile (e.g., 1x10 -5 ; Keppler et al, 2004).…”

“…This has exposed peat deposits with radiocarbon ages of 2000-4000 years, and δ 13 C values of -24.6 to -25 ‰. Keppler et al (2004) found that peatlands sequester large amounts of iodine with average concentrations of 5-36 mg/kg, therefore, one could recognize such layers in a sedimentary record by their unusually high iodine concentrations.…”

Halogens in pore water of peat bogs – the role of peat decomposition and dissolved organic matter

“…Today halogens are known to be involved in a large number of biogeochemical mechanisms related to the transformation of organic matter and some of these processes are basic for the understanding of the biogeochemical cycling of halogens. Natural formation of organohalogens in nearly all aquatic and terrestrial environments is widely accepted to be a key mechanism for the retention and enrichment of halogens in soils (Öberg, 2002) and peatlands (Keppler and Biester, 2003;Biester et al, 2004). Enzymatic processes such as haloperoxidases and halogenases are thought to be the major source of natural halogenated organic compounds in the environment (e.g.…”

“…Being solely built up by organic matter, they are ideal natural laboratories to study the role of organic matter transformation processes in the biogeochemical cycling of halogens. Data on halogens in peat are still limited to a small number of studies (Chagué-Goff and Fyfe, 1996;Maw and Kempton, 1982;Shotyk, 1997;Silk et al, 1997;Keppler and Biester, 2003;Biester et al, 2004).…”

“…The major mechanism of halogen retention by peat is the formation of organohalogens (Silk et al, 1997;Biester, 2003, Biester et al, 2004). For example, Keppler et al (2004) demonstrated that peat has a large capacity to retain atmospheric iodine through formation of organoiodine and that mires and bogs are major terrestrial sinks for iodine.…”