Fate Of Organic Material Research Articles

Radiolysis of Macromolecular Organic Material in Mars‐Relevant Mineral Matrices

AbstractThe fate of organic material on Mars after deposition is crucial to interpreting the source of these molecules. Previous work has addressed how various organic compounds at millimeter depths in sediments respond to ultraviolet radiation. In contrast, this study addressed how high‐energy particle radiation (200‐MeV protons, simulating the effect of galactic cosmic rays and solar wind at depths of <4–5 cm) influences organic macromolecules in sediments. Specifically, we report the generation of organic‐acid radiolysis products after exposure to radiation doses equivalent to geological time scales (1–7 Myr). We found that formate and oxalate were produced from a variety of organic starting materials and mineral matrices. Unlike ultraviolet‐driven reactions that can invoke Fenton chemistry to produce organic acids, our work suggests that irradiation of semiconductor surfaces, such as TiO2 or possible clay minerals found on Mars, forms oxygen and hydroxyl radical species, which can break down macromolecules into organic acids. We also investigated the metastability of benzoate in multiple mineral matrices. Benzoate was added to samples prior to irradiation and persisted up to 500 kGys of exposure. Our findings suggest that organic acids are likely a major component of organic material buried at depth on Mars.

Shielding biomolecules from effects of radiation by Mars analogue minerals and soils

AbstractOrganic compounds have been delivered over time to Mars via meteorites, comets and interplanetary dust particles. The fate of organic material on the surface of Mars must be affected by the Martian environment, in particular by ultraviolet (UV) and other ionizing radiation. Penetration depth of UV radiation into soils is in the sub-millimetre to millimetre range and depends on the properties of the soil. The aim of this research is to study the possible protective role of Martian analogue minerals and soils for survivability of biomolecules against UV radiation and to compare their decomposition rates within a 1 mm-thick portion of the surface. Results demonstrated that minerals offer significant protection to biomolecules purine, pyrimidine and uracil against UV photolysis. In the absence of these minerals, organic compounds are completely degraded when subjected directly to UV photolysis equivalent to only 5 Martian day's exposure. However, similar UV exposure of organics dried from solution onto powdered calcium carbonate (calcite; CaCO3), calcium sulphate (anhydrite; CaSO4), clay-bearing Atacama dessert soil and 7 Å clay mineral kaolinite [Al2Si2O5(OH)4] results in only 1–2% loss of organics. Mixtures of purine and uracil with calcium carbonate exposed to gamma radiation of 3 Gy (3 Gray), which corresponds to approximately 15 000 days on Mars, results in up to 10% loss of organics. By contrast, these organic compounds completely decomposed upon mixing with iron oxide (Fe2O3) before UV irradiation. As the search for extinct or extant life on Mars has been identified as a goal of top priority in NASA's Mars Exploration Program and continues with several missions planned to the red planet by both NASA and the European Space Agency (ESA) in the next few decades, our findings may play a useful role in identifying optimal target sites on the Martian surface for future missions.

Organics in environmental ices: sources, chemistry, and impacts

Abstract. The physical, chemical, and biological processes involving organics in ice in the environment impact a number of atmospheric and biogeochemical cycles. Organic material in snow or ice may be biological in origin, deposited from aerosols or atmospheric gases, or formed chemically in situ. In this manuscript, we review the current state of knowledge regarding the sources, properties, and chemistry of organic materials in environmental ices. Several outstanding questions remain to be resolved and fundamental data gathered before an accurate model of transformations and transport of organic species in the cryosphere will be possible. For example, more information is needed regarding the quantitative impacts of chemical and biological processes, ice morphology, and snow formation on the fate of organic material in cold regions. Interdisciplinary work at the interfaces of chemistry, physics and biology is needed in order to fully characterize the nature and evolution of organics in the cryosphere and predict the effects of climate change on the Earth's carbon cycle.

Transformation of organic matter in agricultural soils: radiocarbon concentration versus soil depth

Radiocarbon measured by accelerator mass spectrometry (AMS) was used as a tracer to study the origin and fate of organic materials in soils. Fractionation methods used to separate the heterogeneous organic material into functionally defined pools of different stability included acid–alkali–acid extraction and density fractionation. 14C values of the humin fraction, isolated from samples of different field trials at the agricultural station Rotthalmünster (Germany), yielded 14C decreases of about 30% to 54% from the surface soil to ca. 65 cm depth. These results indicate a progressive enrichment of stable organic compounds with increasing soil depth. In contrast, a minor decline in 14C concentrations of the humic acid fraction, which mostly showed higher 14C values than the humin, reflect the translocation of modern organic carbon towards greater depth. Low radiocarbon levels of the light occluded particulate organic matter (<1.6 g/cm 3), obtained by density separation, suggest stabilization of organic carbon in soil aggregates. A comparison of 14C results for density fractions from field trials located in a rural and an industrialized region reflect their susceptibility to contamination by fossil fuel-derived carbon and their heterogeneous composition. As a consequence individual short-chain phospholipid fatty acids (PLFA), as indicators for viable soil microbial biomass, were isolated by preparative capillary gas-chromatography. Compound-specific radiocarbon analysis of the isolated PLFAs revealed the assimilation of different substrates for their synthesis. 14C concentrations of the monounsaturated PLFAs ( n-C16:1, n-C17:1, and n-C18:1), which were close to the modern atmospheric 14C level, suggest a high specificity to young carbon sources. The saturated PLFAs, isolated from the plough-horizon, were synthesized from sub-recent soil organic carbon (SOC) as shown by a higher contribution of bomb- 14C. A considerable 14C decrease from the surface to 30–45 cm soil depth of the saturated PLFAs indicates the incorporation of more stabilized SOC particularly in subsoil i/ a-C15:0, n-C16:0, and n-C17:0 PLFAs.

Exobiology missions proposed in Japan to utilize International Space Station

The Japanese portion of International Space Station offers opportunities to conduct exobiology experiments and observations at its exposed facility. Preparatory studies have been conducted to define proposals for its possible utilization. Research subjects have been proposed from quite diverse fields of exobiology. It ranges from a basic scientific mission, such as a survey on formation and fate of organic materials under space environment, to a part of an engineering project related to quarantine technology for planetary probes dedicated to exobiology exploration. Besides technical feasibility of implementation of those payloads on the space system, scientific assessment is strongly required to elucidate key issues of exobiology conducted in near Earth orbit. Even research facilities in low Earth orbit, although literally in space, give quite a different environment from that of interstellar space in many aspects. Scientific significance of conducting exobiology there should be based on uniqueness of employing microgravity and its synergetic effects with other factors for exobiology. Because of the quite limited chance of executing space experiments, as well as high cost of its execution, proposed subjects should be proved to possess great competitiveness against studies on the ground where space environment could also be well simulated with less cost. An international forum for exobiology might play an important role to formulate prioritized plan and strategy of the discipline. Such a body could orchestrate exobiology in Earth orbit under complementary relationships among scientific endeavors carried on by scientists who participate in collaborative efforts.

Ageing Effects of Highmolecular Weight Organic Acids Which can be Isolated from Landfill Leachates

The huge number of landfills and the resulting seepage water leads to a negative influence on the ground water quality. Organic acids were isolated over a period of three years from anaerobic and aerobic leachate water and from model aquifers which were fed by the leachates. The amount of isolated DOC increased from the anaerobic samples to the aerobic ones. The characterization of the isolated acids clearly reflects an increase of the molecular weight and of the functional group content with increasing age of the landfill, and in the process of aerobic digestion. The results are not only of interest for a detailed understanding of the fate of organic material from landfill leachates and of the transport of pollutants in the groundwater, but represent a man-made influence on the genesis of humic substances.

BIOMARKERS Occurence, Utility, and Detection

The study of natural products in plants, animals, bacteria, fungi, and other living systems has long been of interest to chemists, biochemists, and analytical chemists. Generally, however, these scientists are concerned only with the isolation and identification of compounds present in living systems. A relatively small but rapidly growing scientific discipline has emerged over the past two decades involving scientists primarily interested in the fate of organic material and associated natural products after their demise and deposition in the sedimentary record and conversion into fossil fuels or chemical fossils. Organic compounds present in the original source material whose carbon skeleton is preserved throughout the geological record are referred to as biomarkers. In this Report the authors will introduce some of the basic concepts of petroleum geochemistry and the key role that analytical chemistry has played in the development of this discipline. They will also discuss areas in which geochemical research is most likely to develop in the next few years, and they will examine the major analytical challenges the organic geochemist will meet in conducting geochemical research during the next decade.