Technical Note: Reactivity of C1 and C2 organohalogens formation – from plant litter to bacteria

J J Wang,T W Ng,Q Zhang,X B Yang,P K Wong,A T Chow,R A Dahlgren

doi:10.5194/bg-9-3721-2012

Abstract

Abstract. C1/C2 organohalogens (organohalogens with one or two carbon atoms) can have significant environmental toxicity and ecological impact, such as carcinogenesis, ozone depletion and global warming. Natural halogenation processes have been identified for a wide range of natural organic matter, including soils, plant and animal debris, algae, and fungi. Yet, few have considered these organohalogens generated from the ubiquitous bacteria, one of the largest biomass pools on earth. Here, we report and confirm the formation of chloroform (CHCl3) dichloro-acetonitrile (CHCl2CN), chloral hydrate (CCl3CH(OH)2) and their brominated analogues by direct halogenation of seven strains of common bacteria and nine cellular monomers. Comparing different major C stocks during litter decomposition stages in terrestrial ecosystems, from plant litter, decomposed litter, to bacteria, we found increasing reactivity for nitrogenous organohalogen yield with decreasing C/N ratio. Our results raise the possibility that natural halogenation of bacteria represents a significant and overlooked contribution to global organohalogen burdens. As bacteria are decomposers that alter the C quality by transforming organic matter pools from high to low C/N ratio and constitute a large organic N pool, the bacterial activity is expected to affect the C, N, and halogen cycling through natural halogenation reactions.

Highlights

Several C1/C2 organohalogens have been documented to be carcinogenic and toxic (USEPA, 1999), whereas some volatile species pose threats to ozone depletion (Anderson et al, 1991; Read et al, 2008) or serve as greenhouse gases (Lashof and Ahuja, 1990; Montzka et al, 2011)
Many efforts have identified a wide range of natural organic matters (NOMs) from soils, plant and animal debris, algae, and fungi as precursors of organohalogens (Nightingale et al, 1995; Hoekstra et al, 1998; Keppler et al, 2000; Myneni, 2002; Fahimi et al, 2003; Hamilton et al, 2003; Huber et al, 2009), there is great uncertainty associated with source inventories and fluxes for C1/C2 organohalogens, with few taking bacteria precursors into account
Bacteria may constitute one of the largest precursors for organohalogens that has been overlooked, assuming that bacterial materials can be halogenated like other natural organic matter

Summary

Introduction

Several C1/C2 organohalogens have been documented to be carcinogenic and toxic (USEPA, 1999), whereas some volatile species pose threats to ozone depletion (Anderson et al, 1991; Read et al, 2008) or serve as greenhouse gases (Lashof and Ahuja, 1990; Montzka et al, 2011). Bacteria may constitute one of the largest precursors for organohalogens that has been overlooked, assuming that bacterial materials can be halogenated like other natural organic matter.

Results

Conclusion