Frank Laturnus

Terrestrial natural sources of trichloromethane (chloroform, CHCl3) - An overview

The widespread use of volatile chlorinatedcompounds like chloroform, trichloroethene andtetrachloroethene in industrialized societiescauses a large annual release of thesecompounds into the environment. Due to theirrole as a source for halogen radicals involvedin various catalytic atmospheric reactioncycles, including the regulation of thestratospheric and tropospheric ozone layers,these compounds also constitute a risk fordrinking water resources as they can betransported to the groundwater fromcontaminated field sites or even fromatmospheric deposition. Therefore,identification and investigation of sources andsinks of volatile chlorinated compounds are ofparticular interest. Chloroform, a majorcontributor to natural gaseous chlorine, wasfound to be emitted by several anthropogenicand natural sources including the oceans andterrestrial areas. The origin of chloroform inthe terrestrial environment can beanthropogenic point sources, atmosphericdeposition, release by vegetation andproduction directly in the soil. The calculatedannual biogenic global chloroform emission is700 Gg, and marine and terrestrial environmentsare nearly equal contributors. The estimatedemissions from anthropogenic sources accountfor less than 10% of the estimated totalemissions from all sources. Among terrestrialsources, forests have recently been identifiedas contributing to the release of chloroform intothe environment. With the data available,annual emissions of chloroform to theatmosphere from forest sites were calculatedand compared to other natural sources. Atpresent knowledge, forests are only a minorsource in the total biogenic flux ofchloroform, contributing less than 1% to theannual global atmospheric input. However, itshould be noted that data are available forNorthern temperate forests only. The largetropical forest areas may provide a yet unknowninput of chloroform.

Formation of chloroform in spruce forest soil : results from laboratory incubation studies

The release of chloroform, 1,1,1-trichloroethane, tetrachloromethane, trichloroethene and tetrachloroethene from an organic rich spruce forest soil was studied in laboratory incubation experiments by dynamic headspace analysis, thermodesorption and gas chromatography. Performance parameters are presented for the dynamic headspace system. For spruce forest soil, the results showed a significant increase in chloroform concentration in the headspace under aerobic conditions over a period of seven days, whereas the concentration of the other compounds remained fairly constant. A biogenic formation of chloroform is suggested, whereas for the other compounds anthropogenic sources are assumed. The addition of trichloroacetic acid to the soil increased the release of chloroform from the soil. It is, therefore, suggested that trichloroacetic acid also contributed to the formation of chloroform. Under the experimental conditions, the spruce forest soil released chloroform concentrations corresponding to a rate of 12 microg m(-2) day(-1). Data on chloroform production rates are presented and compared with literature results, and possible formation mechanisms for chloroform are discussed.

Marine Macroalgae in Polar Regions as Natural Sources for Volatile Organohalogens

Marine macroalgae species from the polar regions were investigated for their importance as natural sources of volatile halogenated compounds released into the biosphere. Several different halogenated C1 to C4 hydrocarbons were identified and their release rates determined. The compounds contained mainly bromine and iodine, and form was the dominant compound released. Although an annual atmospheric input of approximately 108−1010 g bromine and 107−108 g iodine was calculated from the release rates, marine macroalgae are apparently not the major source on a global scale, as the release is up to four orders of magnitude lower than a presumed annual flow from the oceans. Despite this, macroalgae may be more important on a local scale due to their occurrence at a high biomass in the coastal regions. The present paper gives an overview about studies done on the release of volatile halocarbons by macroalgae from polar regions. Furthermore, the function of these compounds in the macroalgal metabolism is discussed.

Chloroform in a pristine aquifer system: Toward an evidence of biogenic origin

Ambient air, soil air, and groundwater were monitored for volatile halogenated organic compounds in a pristine spruce forest at Klosterhede, Denmark. Although this location is remote from industrial areas and free of any point sources of either soil or groundwater contamination, several volatile chlorinated hydrocarbons were detected. The concentration profiles of chloroform indicated a formation of this compound in the soil. Low concentrations were found in ambient air (0.02 ng L−1), higher concentrations in the upper soil layers (9.6 ng L−1 at 0.75 m below the surface), and a decrease with increasing depth (down to 1.5 ng L−1 just above the groundwater table at 7.5 m below the surface). For the other identified chlorinated compounds the concentration profiles were different from those of chloroform and exhibited less systematic variation between ambient air and soil air and with increasing depth. In the phreatic groundwater, high concentrations (up to 1.6 μg L−1) of chloroform and low concentrations (<0.01 μg L−1) of the other chlorinated compounds identified in air were found. Of the seven volatile brominated and iodinated compounds analyzed in ambient air, soil air, and groundwater, only bromoform was found and only in the upper soil layer. For chloroform a formation in the spruce forest soil is suggested, leading to concentrations in the groundwater in the micrograms per liter range.

Biodegradation of chlorinated solvents in a water unsaturated topsoil

In order to investigate topsoils as potential sinks for chlorinated solvents from the atmosphere, the degradation of trichloromethane (CHCl(3)), 1,1,1-trichloroethane (CH(3)CCl(3)), tetrachloromethane (CCl(4)), trichloroethene (C(2)HCl(3)) and tetrachloroethene (C(2)Cl(4)) was studied in anoxic laboratory experiments designed to simulate denitrifying conditions in water unsaturated topsoil. Active denitrification was demonstrated by measuring the release of 15N in N(2) to the headspace from added 15N labeled nitrate. The degradation of chlorinated aliphatic compounds was followed by measuring their concentrations in the headspace above the soil. The headspace concentrations of all the chlorinated solvents except CH(3)CCl(3) were significantly (P<or=0.05) lower after 41 days in biologically active batches as compared to sterile batches. For the compounds with significantly decreasing headspace concentrations, the decline was the least for CHCl(3) within the 41 days of incubation. The headspace concentrations of trichloro- and tetrachloroethene decreased more than 50% during the first 20 days with no considerable indication of abiotic transformation. While slow abiotic removal was observed, tetrachloromethane was completely biotransformed after 16 days. Based on the results in this study, we conclude that anaerobic topsoils are potential sinks for these contaminants, and that a natural attenuation potential exists, even in water unsaturated topsoils.

Formation of Chloroform in Soil. A Year-round Study at a Danish Spruce Forest Site

Soil air from top soil of a Danish spruce forest was investigatedmonthly from December 1997 to December 1998 for the occurrence ofchloroform, 1,1,1-trichloroethane, tetrachloromethane, trichloroethene and tetrachloroethene. Within the monitoring period, three different patterns of soil air concentrations wereidentified. For chloroform, concentrations peaked in spring and autumn while 1,1,1-trichloroethane and tetrachloromethane peakedduring mid winter. Trichloroethene and tetrachloroethene, concentrations remained constant throughout the year. The relative ratios of soil air concentrations to ambient air concentrations indicated a natural production of chloroform, while the other chlorinated compounds investigated probably originated from non-point source pollution. The seasonal variation of the chloroform concentration suggested a productionby microorganisms, as high chloroform concentrations were found in the soil in warm and humid periods of the year (spring and autumn) with high microbial activity.

Mixed function oxidase dependent biotransformation of polychlorinated biphenyls by different species of fish from the North Sea

Mixed function oxidase (MFO) dependent biotransformation of polychlorinated biphenyls (PCBs) was measured in three different fish species from the North Sea. Liver microsomes of plaice (Pleuronectes platessa), dab (Limanda limanda) and cod (Gadus morhua) were isolated and incubated with different PCB congeners. Metabolites of PCBs were identified as monohydroxylated PCBs. Hydroxylation took place in meta- or para-position of the PCB molecules, preferential in para-position. Metabolization and metabolic rates depended on the substitution pattern of PCBs and the degree of chlorination. Biotransformations were also species dependent. The flatfish dab and plaice exhibited higher metabolic rates than cod.