Atmospheric carbon tetrachloride: another man-made pollutant

Theoretical insights into the reductive metabolism of CCl4 by cytochrome P450 enzymes and the CCl4-dependent suicidal inactivation of P450

The one-electron reduction product, ˙CCl₃, irreversibly inactivates P450 via covalently binding to the meso-carbon, whereas the two successive one-electron reductions product, :CCl₂, reversibly inhibits P450 by coordinating to iron.

Pattern and sources of naturally produced organohalogens in the marine environment: biogenic formation of organohalogens

The pattern of organohalogens found in the marine environment is complex and includes compounds, only assignable to natural (chloromethane) or anthropogenic (hexachlorobenzene, PCBs) sources as well as compounds of a mixed origin (trichloromethane, halogenated methyl phenyl ether).The chemistry of the formation of natural organohalogens is summarized. The focus is put on volatile compounds carrying the halogens Cl, Br, and I, respectively. Though marine natural organohalogens are quite numerous as defined components, they are mostly not produced as major compounds. The most relevant in terms of global annual production is chloromethane (methyl chloride). The global atmospheric mixing ratio requires an annual production of 3.5-5 million tons per year. The chemistry of the group of haloperoxidases is discussed. Incubation experiments reveal that a wide spectrum of unknown compounds is formed in side reactions by haloperoxidases in pathways not yet understood.

Arctic Ocean Ventilation Studied with a Suite of Anthropogenic Halocarbon Tracers

The chlorofluoromethanes (CFMs: CCl(2)F(2) and CCl(3)F), methyl chloroform (CH(3)CCl(3)), and carbon tetrachloride (CCl(4)) have been measured in deep waters of the Arctic Ocean. Oceanic and atmospheric inventories of these compounds result from known anthropogenic releases; because the CFMs and CCl(4) are also chemically nonreactive, they can be used as transient tracers of ocean circulation. The input history of CCl(4) is longer than that of any other transient tracer identified to date( approximately 70 years). This long input history, together with an e-folding time scale of increase(tau) of approximately 28 years, makes CCl(4) potentially the most useful tracer for calibrating models of the oceanic uptake of the fossil-fuel CO(2) transient(tau approximately 25 years). The bottom water of the Nansen Basin, Arctic Ocean, has detectable CCl(4) but undetectable CFM(s) and CH(3)CCl(3), which suggests either that the bottom water is approximately 50 years old, or that there is a small, nonanthropogenic component of atmospheric CCl(4)(<6 parts per trillion by volume).

Atmospheric Halocarbons, Hydrocarbons, and Sulfur Hexafluoride: Global Distributions, Sources, and Sinks

The global distribution of fluorocarbon-12 and fluorocarbon-11 is used to establish a relatively fast interhemispheric exchange rate of 1 to 1.2 years. Atmospheric residence times of 65 to 70 years for fluorocarbon-12 and 40 to 45 years for fluorocarbon-l1 best fit the observational data. These residence times rule out the possibility of any significant missing sinks that may prevent these fluorocarbons from entering the stratosphere. Atmospheric measurements of methyl chloroform support an 8-to 10-year residence time and suggest global average hydroxyl radical (HO) concentrations of 3 x 10(5) to 4 x 10(5) molecules per cubic centimeter. These are a factor of 5 lower than predicted by models. Additionally, methyl chloroform global distribution supports Southern Hemispheric HO levels that are a factor of 1.5 or more larger than the Northern Hemispheric values. The long residence time and the rapid growth of methyl chloroform cause it to be a potentially significant depleter of stratospheric ozone. The oceanic sink for atmospheric carbon tetrachloride is about half as important as the stratospheric sink. A major source of methyl chloride (3 x 10(12)grams per year), sufficient to account for nearly all the atmospheric methyl chloride, has been identified in the ocean.