The tropospheric degradation of volatile organic compounds: a protocol for mechanism development

There are many possible micronucleus assays involving different test organisms and tissues. Because micronuclei arise from chromosomal fragments or chromosomes that are not incorporated into daughter nuclei at the time of cell division, the assay detects both clastogens and agents that affect the spindle apparatus. We know of no case in which micronuclei and chromosomal breakage (or loss) have been shown to occur independently of one another in any dividing cell population. This relationship is so close that false-positives and false-negatives (insofar as the detection of tissue-specific chromosome damage is concerned) should be determined primarily by the statistics of sampling. The production of micronuclei in various experimental organisms has been reviewed. Although there are several promising experimental approaches such as the use of meiotic plant cells or human cells in culture, only one form of the assay, the in vivo mammalian bone-marrow polychromatic erythrocyte (PCE) assay, has been sufficiently developed to be considered a standard assay. More than 150 chemicals have been tested in this assay, with varying degrees of rigor. The data from the literature have been summarized and evaluated in light of the work Group's recommendations for an adequate test. The standards for an adequate test are an important part of the recommendations. These standards, although based on the most recent information available to us, are subject to change because this assay is still evolving. The most important recommendations in this report are: (1) at least 500 PCE should be examined from each of 8 animals to detect an increase of about 4‰ (per thousand) PCE when the background is less than 4 per 1000, (2) sampling should be extended to at least 72 h after the initial treatment, with sampling intervals no greater than 24 h, and (3) the highest possible doses should be used. The success rate of the assay to detect chemicals designated by the Environmental Protection Agency (EPA) as carcinogens is difficult to estimate for several reasons. First, few chemicals designated as noncarcinogens were studied, although in routine testing noncarcinogens are expected to be much more common than carcinogens. Hence, the rate of false-positives (insofar as the detection of cancer is concerned), which ought to be one of the strongest features of the assays, could not be estimated. Second, few chemicals have been tested as rigorously as this report recommends. Hence, the rate of false-negatives is almost certainly overestimated. (It is, nevertheless, obvious that false-negatives are to be expected for any tissue-specific in vivo assay like the micronucleus assay. For example diethylnitrosamine, which produces chromosomal aberrations, micronuclei, and cancer in the liver, is not detected in the bone-marrow micronucleus assay.) Third, many carcinogens are species-specific and this fact has not been taken into account. Considering these caveats, the uncorrected detection rate of the chemicals designated as carcinogens by EPA is about 50%. We believe that this would have been significantly higher had all tests been performed according to the test criteria. Further improvements in the assay are to be expected and these may lead to improvements in its success rate. Recent developments are discussed.

The induction of micronuclei as a measure of genotoxicity: A report of the U.S. environmental protection agency Gene-Tox program☆

Organic peroxy radicals: Kinetics, spectroscopy and tropospheric chemistry

Atmospheric oxidation of monoterpenes contributes to formation of tropospheric ozone and secondary organic aerosol, but their products are poorly characterized. In this work, we report a series of outdoor smog chamber experiments to investigate both gaseous and particulate products in the ozone oxidation of four monoterpenes: α-pinene, β-pinene, Δ^3-carene, and sabinene. More than ten oxygenated products are detected and identified in each monoterpene/O_3 reaction by coupling derivatization techniques and GC/MS detection. A denuder/filter pack sampling system is used to separate and simultaneously collect gas and aerosol samples. The identified products, consisting of compounds containing carbonyl, hydroxyl, and carboxyl functional groups, are estimated to account for about 34–50%, 57%, 29–67%, and 24% of the reacted carbon mass for β-pinene, sabinene, α-pinene, and Δ^3-carene, respectively. The identified individual products account for >83%, ∼100%, >90%, and 61% of the aerosol mass produced in the ozone reaction of β-pinene, sabinene, α-pinene, and Δ^3-carene. The uncertainty in the yield data is estimated to be ∼ ±50%. Many of the products partition between gas and aerosol phases, and their gas-aerosol partitioning coefficients are determined and reported here. Reaction schemes are suggested to account for the products observed.

Gas-phase ozone oxidation of monoterpenes: Gaseous and particulate products

Unattenuated solar photo rate coefficients and excess energies for dissociation, ionization, and dissociative ionization are presented for atomic and molecular species that have been identified or are suspected to exist in the atmospheres of planets, satellites (moons), comets, or as pollutants in the Earth atmosphere. The branching ratios and cross sections with resonances have been tabulated to the greatest detail possible and the rate coefficients and excess energies have been calculated from them on a grid of small wavelength bins for the quiet and the active Sun at 1 AU heliocentric distance.

James F. Meagher

Papers

Photo-oxidation of CH3CHO vapor at 3130 Å

The oxidation of acetyl radicals

The photooxidation of CD3N2CD3

Reaction of hydroxyl radical with ethylene

Mutagenic testing of diethylhydroxylamine, nitroethane, and diethylamine hydrogen sulfite