Heinz Friedrich Schöler

Halocarbons produced by natural oxidation processes during degradation of organic matter

Volatile halogenated organic compounds (VHOC) play an important role in atmospheric chemical processes—contributing, for example, to stratospheric ozone depletion. For anthropogenic VHOC whose sources are well known, the global atmospheric input can be estimated from industrial production data. Halogenated compounds of natural origin can also contribute significantly to the levels of VHOC in the atmosphere. The oceans have been implicated as one of the main natural sources, where organisms such as macroalgae and microalgae can release large quantities of VHOC to the atmosphere. Some terrestrial sources have also been identified, such as wood-rotting fungi, biomass burning and volcanic emissions. Here we report the identification of a different terrestrial source of naturally occurring VHOC. We find that, in soils and sediments, halide ions can be alkylated during the oxidation of organic matter by an electron acceptor such as Fe( III): sunlight or microbial mediation are not required for these reactions. When the available halide ion is chloride, the reaction products are CH 3Cl, C2H5Cl, C3H7Cl and C4H9Cl. (The corresponding alkyl bromides or alkyl iodides are produced when bromide or iodide are present.) Such abiotic processes could make a significant contribution to the budget of the important atmospheric compounds CH3Cl, CH3Br and CH3I.

Binding and mobility of mercury in soils contaminated by emissions from chlor-alkali plants

Chlor-alkali plants are known to be an important source of Hg emissions to the atmosphere and related contamination of soils in their vicinity. In the present study, the results of Hg speciation and mobility of Hg in soils affected by Hg emissions from three chlor-alkali plants are compared. Solid phase mercury speciation analyses was carried out using a mercury-thermo-desorption technique with the aim of distinguishing elemental Hg [Hg(0)] from Hg(II)-binding forms. Mercury species in soil leachates were distinguished using an operationally defined method, which is based on the reactivity of soluble Hg compounds. Results show that the Hg(0) emitted from the plants could not be detected in any of the investigated soils. This indicates quantitative re-emission or oxidation of this Hg species in the atmosphere or soils. In most soils Hg was predominately bound to organic matter. Only in sandy soils deficient in organic matter was Hg, to a larger extent, sorbed onto mineral soil components. Leachable Hg in most soils occurred as non-reactive, soluble organic Hg complexes such as fulvic acid-bound Hg, and reach their highest values (90 microg kg(-1)) in soils rich in organic matter. Concentrations of reactive, soluble Hg compounds were highest in sandy soils where the content of organic matter was low. Leachability of Hg was found to be inhibited in soils with a high content of clayey soil components. The distribution of Hg in soil profiles suggests that migration of Hg to deeper soil layers (approx. 20 cm) is most effective if Hg is bound to soluble organic complexes, whereas reactive Hg or weak Hg complexes are effectively retained in the uppermost soil layer (5 cm) through sorption on mineral surfaces.

Estimating distribution and retention of mercury in three different soils contaminated by emissions from chlor-alkali plants: part I

Mercury emissions from chlor-alkali plants have been past and present sources of soil contamination with Hg. Here we calculate net mercury (Hg) deposition to soils in the vicinity (100-1000-m downwind) of three-chlor alkali plants. Calculations were based on spatial distribution patterns of Hg concentrations in soils, which were extrapolated by kriging. Moreover, we investigated to what extent Hg deposition depends on the elevation of receptors and canopy throughfall. Mercury concentrations in soil exceed background values up to a factor of 56 and show enrichment factors between 2 and 5.8 calculated from the median Hg concentration. Net deposition rates range between 2356 and 8952 microg m(-2) year(-1), which is up to 224-fold the background values. Net deposition of Hg to soils at the three sites varies between 1.2 and 2.4% of total emitted Hg. Highest deposition rates were found at sites with extended elevated or forested areas. Here, Hg concentrations in soils increased by a factor of up to 7.3 in elevated (+180 m) forest areas compared to non-elevated grassland soils.

Elevated mercury accumulation in a peat bog of the Magellanic Moorlands, Chile (53‡S) ^ an anthropogenic signal from the Southern Hemisphere

Increasing mercury deposition rates in the Northern Hemisphere recorded in natural archives such as peat bogs or lake sediments have been documented in numerous studies. However, data on atmospheric Hg deposition in the Southern Hemisphere dating back to pre-industrial times are rare. Here, we provide a continuous record of atmospheric Hg deposition in the Southern Hemisphere recorded by an ombrotrophic peat bog of the Magellanic Moorlands, Chile (53‡S), extending back 3000 yr. Pre-industrial mercury accumulation rates range between 2.5 and 3.9 Wg/m 2 /yr. In the past 100 yr, Hg accumulation rates increased 18-fold from about 3 Wg/m 2 /yr to a maximum of 62.5 Wg/m 2 /yr. If Hg accumulation rates were normalized to peat accumulation rates, maximum rates were 7.9 Wg/m 2 / yr, which is only 2.5 times the pre-industrial rates. Thus, Hg accumulation rates normalized to peat accumulation rates are more comparable to the three-fold net increase in atmospheric Hg concentrations estimated for the same period. We suggest that the increase in Hg accumulation rates in the Magellanic Moorlands within the past 100 yr is at least partly attributed to global dispersion of Hg derived from anthropogenic sources in the Northern Hemisphere. The finding that no increase of atmospheric deposition of Pb could be observed in the bog indicates the extraordinary long-range transport and ubiquitous dispersion of anthropogenic derived gaseous Hg compared to other metals. < 2002 Elsevier Science B.V. All rights reserved.

Abiotic Fe(III) induced mineralization of phenolic substances

The redox process between iron(III) (in dissolved form and as the mineral phase ferrihydrite) and phenolic substances has been examined. We investigated the relationship between the structure and reactivity for the dihydrobenzene reductants catechol, hydroquinone and resorcine, and for the 2-methoxyphenol guaiacol with iron(III), by determining the rate of the Fe(III) reduction as well as the production of CO2. This work demonstrates that catechol and guaiacol will be effectively oxidized to CO2 by reducing iron(III). Hydroquinone shows a reduction of iron(III), but no accompanying mineralization could be determined. In contrast, resorcine showed no reaction with Fe(II). The deciding factor on whether or not mineralization occurs were controlled by the position of the hydroxy groups. It is shown that phenolic substances with two hydroxy groups in the orthoposition or at least one hydroxy group and a methoxy group can be oxidized to CO2 while iron(III) is reduced.

Formation of chloroacetic acids from soil, humic acid and phenolic moieties

The mechanism of formation of chloroacetates, which are important toxic environmental substances, has been controversial. Whereas the anthropogenic production has been well established, a natural formation has also been suggested. In this study the natural formation of chloroacetic acids from soil, as well as from humic material which is present in soil and from phenolic model substances has been investigated. It is shown that chloroacetates are formed from humic material with a linear relationship between the amount of humic acid used and chloroacetates found. More dichloroacetate (DCA) than trichloroacetate (TCA) is produced. The addition of Fe(2+), Fe(3+) and H(2)O(2) leads to an increased yield. NaCl was added as a source of chloride. We further examined the relationship between the structure and reactivity of phenolic substances, which can be considered as monomeric units of humic acids. Ethoxyphenol with built-in ethyl groups forms large amounts of DCA and TCA. The experiments with phenoxyacetic acid yielded large amounts of monochloroacetate (MCA). With other phenolic substances a ring cleavage was observed. Our investigations indicate that chloroacetates are formed abiotically from humic material and soils in addition to their known biotic mode of formation.

The occurence of trichloroacetic acid (tcaa) - indications of a natural production?

Abstract TCAA was identified in the nanogram range in several environmental compartments including bog water, glacier ice, snow, rain, spring water and in soil lysimeters. Some of these results indicate a naturally induced formation of TCAA. In addition different short chained aliphatic acids (acetic acid, malic acic, lactic acid, fumaric acid, malonic acid, citric acid, acetonedicarboxylic acid), which are involved in soil processes were incubated with the chlorinating enzyme chloroperoxidase (CPO) from the fungus Caldariomyces fumago and converted in the presence of sodium chloride and hydrogenperoxide. Trichloroacetic acid (TCAA) was formed in all reactions in concentrations ranging from some promille to 8% in regard of the applied enzyme.

Determination of mercury species in natural waters at picogram level with on-line RP C18 preconcentration and HPLC-UV-PCO-CVAAS

A new technique has been developed for the determination of methyl-, ethyl-, methoxyethyl-, ethoxyethyl-, phenyl- and inorganic mercury in natural water samples. The mercury compounds have been complexed for the preconcentration on RP C18 columns by sodium pyrrolidinedithiocarbamate (SPDC), sodium diethyldithiocarbamate (SDDC) and hexamethyleneammonium (HMA) — hexamethylenedithiocarbamate (HMDC), separated by HPLC and determined by UV-PCO-CVAAS (ultra violet, post column oxidation, cold vapour atomic absorption spectrometry). The standard deviations are in the range of 6.9 to 11.8%. The recoveries amount to 86%, 78%, 88%, 83%, 79% and 84% for methyl-, ethyl-, methoxyethyl-, ethoxyethyl-, phenyl- and inorganic mercury for the enrichment from 300 ml water samples. The detection limit for methyl mercury is 0.5 ppt. This new on-line preconcentration procedure has been tested with rain, drinking, surface and process water samples.

Interfacing high-performance liquid chromatography and cold-vapour atomic absorption spectrometry with on-line UV irradiation for the determination of organic mercury compounds

A liquid chromatographic method with on-line UV irradiation was developed for the determination of organic mercury compounds by cold-vapour atomic absorption spectrometry (AAS). Methyl-, ethyl-, phenyl- and inorganic mercury were separated on R.P C18 columns. An UV-irradiation lamp was used for the on-line destruction of the organomercury compounds. Sample and NABH4 solution were continuously fed to the reaction vessel where mercury was reduced. The volatilized mercury was swept into the absorption cell of a cold-vapour AAS system by nitrogen. The detection limit for methylmercury is 80 pg absolute (S/N = 3).

Preservation of hypericin and related polycyclic quinone pigments in fossil crinoids

The fringelite pigments, a group of phenanthroperylene quinones discovered in purple coloured specimens of the Upper Jurassic crinoid Liliocrinus, demonstrate exceptional preservation of organic compounds in macrofossils. Here we report the finding of hypericin and related phenanthroperylene quinones in Liliocrinus munsterianus from the original ‘Fringeli’ locality and in the Middle Triassic crinoid Carnallicrinus carnalli. Our results show that fringelites in fact consist of hypericin and closely related derivatives and that the stratigraphic range of phenanthroperylene quinones is much wider than previously known. The fossil occurrence of hypericin indicates a polyketide biosynthesis of hypericin-type pigments in Mesozoic crinoids analogous to similar polyketides, which occur in living crinoids. The common presence of a characteristic distribution pattern of the fossil pigments and related polycyclic aromatic hydrocarbons further suggests that this assemblage is the result of a stepwise degradation of hypericin via a general diagenetic pathway.