Increased toxicity of benzo(a)pyrene-7,8-dihydrodiol in the presence of polychlorobiphenylols

Benzo(a)pyrene (BaP) and polychlorinated biphenyls (PCBs) often co-exist in contaminated environments. Polychlorobiphenylols (OH-PCBs), formed by CYP-dependent monooxygenation of PCBs, are potent inhibitors of the glucuronidation of hydroxylated BaP metabolites. We hypothesized that OH-PCBs could drive the biotransformation of (−)BaP-7,8-dihydrodiol (BaP-7, 8-D) away from detoxication and towards formation of the reactive metabolite. A mixture of five OH-PCBs with 4–6 Cl atoms was infused into isolated, perfused, biliary intact livers (n=3 fish) removed from 3-methylcholanthrene-induced channel catfish. Controls (n=3) were infused with vehicle. Subsequently, [³H]-BaP-7, 8-D was infused into each liver and bile was collected for 1 h. The livers were taken for analysis of metabolites and DNA adducts. Induction status was confirmed by EROD assay. Bile was analyzed for metabolites. It was found that preinfusion of the mixture of OH-PCBs reduced the extent of glucuronidation of BaP-7, 8-D and increased the formation of DNA adducts 5-fold over controls. GSH conjugates, tetrols and triols were increased in the OH-PCB-infused fish, providing further support for our hypothesis that if the glucuronidation were inhibited, CYP-dependent activation would increase. These studies suggest a mechanism for synergy of toxicity of PAH and PCBs.     

THE SEARCH FOR HUMBOLDT

HUMBOLDT'S COSMOS: Alexander von Humboldt and the Latin American Journey That Changed the Way We See the World. By Gerard Helferich. THE HUMBOLDT CURRENT: Nineteenth‐Century Exploration and the Roots of American Environmentalism. By Aaron Sachs.     

Formation of monazite via prograde metamorphic reactions among common silicates: implications for age determinations

Three lines of evidence from schists of the Great Smoky Mountains, NC, indicate that isogradic monazite growth occurred at the staurolite-in isograd at ∼600°C: (1) Monazite is virtually absent below the staurolite-in isograd, but is ubiquitous (several hundred grains per thin section) in staurolite- and kyanite-grade rocks. (2) Many monazite grains are spatially associated with biotite coronas around garnets, formed via the reaction Garnet + Chlorite + Muscovite = Biotite + Plagioclase + Staurolite + H₂O. (3) Garnets contain high-Y annuli that result from prograde dissolution of garnet via the staurolite-in reaction, followed by regrowth, and rare monazite inclusions occur immediately outside the annulus and in the matrix, but not in the garnet core. Larger monazite grains also exhibit quasi-continuous Th zoning with high Th cores and low Th rims, consistent with monazite growth via a single reaction and fractional crystallization during prograde growth. Common silicates may host sufficient P and LREEs that reactions among them can produce observable LREE phosphate. Specifically phosphorus contents of garnet and plagioclase are hundreds of parts per million, and dissolution of garnet and recrystallization of plagioclase could form thousands of phosphate grains several micrometers in diameter per thin section. LREEs may be more limiting, but sheet silicates and plagioclase can contain tens to ∼100 (?) ppm LREE, so recrystallization of these silicates to lower LREE contents could produce hundreds of grains of monazite per thin section. Monazite ages, determined via electron and ion microprobes, are ∼400 Ma, directly linking prograde Barrovian metamorphism of the Western Blue Ridge with the “Acadian” orogeny, in contrast to previous interpretations that metamorphism was “Taconian” (∼450 Ma). Interpretation of ages from metamorphic monazite grains will require prior chemical characterization and identification of relevant monazite-forming reactions, including reactions previously viewed as involving solely common silicates.     

Paleogene paleoclimate reconstruction using oxygen isotopes from land and freshwater organisms: the use of multiple paleoproxies

Understanding past climate change is critical to the interpretation of earth history. Even though relative temperature change has been readily assessed in the marine record, it has been more difficult in the terrestrial record due to restricted taxonomic distribution and isotopic fractionation. This problem could be overcome by the use of multiple paleoproxies. Therefore, the δ¹⁸O isotopic composition of five paleoproxies (rodent tooth enamel, δ¹⁸O_Phosphate = +17.7 ± 2.0‰ n = 74 (VSMOW); fish scale ganoine δ¹⁸O_Phosphate = +19.7 ± 0.7‰ n = 20 (VSMOW); gastropod shell δ¹⁸O_Calcite = −1.7 ± 1.3‰ n = 50 (VPDB); charophyte gyrogonite δ¹⁸O_Calcite = −2.4 ± 0.5‰ n = 20 (VPDB); fish otolith δ¹⁸O_Aragonite = δ¹⁸O = −3.6 ± 0.6‰ n = 20 (VPDB)) from the Late Eocene (Priabonian) Osborne Member (Headon Hill Formation, Solent Group, Hampshire Basin, UK) were determined. Because diagenetic alteration was shown to be minimal the phosphate oxygen component of rodent tooth enamel (as opposed to enamel carbonate oxygen) was used to calculate an initial δ¹⁸O_{Local water} value of 0.0 ± 3.4‰. However, a skewed distribution, most likely as a result of the ingestion of evaporating water, necessitated the calculation of a corrected δ¹⁸O_{Local water} value of −1.3 ± 1.7‰ (n = 62). This δ¹⁸O_{Local water} value corresponds to an approximate mean annual temperature of 18 ± 1°C. Four other mean paleotemperatures can also be calculated by combining the δ¹⁸O_{Local water} value with four independent freshwater paleoproxies. The calculated paleotemperature using the fish scale thermometry equations most likely represents the mean temperature (21 ± 2°C) of the entire length of the growing season. This should be concordant with the paleotemperature calculated using the Lymnaea shell thermometry equation (23 ± 2°C). The lack of concordance is interpreted to be the result of diagenetic alteration of the originally aragonitic Lymnaea shell to calcite. The mean paleotemperature calculated using the charophyte gyrogonite thermometry equation (21 ± 2°C), on the other hand, most likely represents the mean temperature of a single month toward the end of the growing season. The fish otolith mean paleotemperature (28 ± 2°C) most likely represents the mean temperature of the warmest months of the growing season. An approximate mean annual temperature of 18 ± 1°C, in addition to a mean growing season paleotemperature of 21 ± 2°C (using fish scale only) with a warmest month temperature of 28 ± 2°C, and high associated standard deviations suggest that a subtropical to warm temperate seasonal climate existed during the deposition of the Late Eocene Osborne Member.     

Experimental and natural early diagenetic mobility of Sr and Mg in biogenic carbonates

Ammonium acetate dissolution experiments were performed on shell material of the modern bivalves, Crassostrea virginica (calcite) and Mercenaria mercenaria (aragonite). Their purpose was to determine the order of preferential dissolution of Sr, Mg and Ca; these results subsequently were compared with Sr, Mg and Ca data from other Recent as well as ancient mollusks.Results from these experiments suggest the following relative order of abundance of readily exchangeable Mg and Sr in biogenic carbonates: Mg(arag) > Mg(calc) > Sr(calc) > Sr(arag). It is apparent that incongruent dissolution of minerals with different solubilities cannot entirely explain the observed dissolution patterns for Sr, Mg and Ca in these biogenic carbonates. Secular changes in whole shell Mg and Sr concentrations for Recent and unrecrystallized fossil mollusks suggest an order of “ionic mobility” in diagenesis identical to the order of abundance for readily exchangeable ions found in the NH₄Ac dissolution experiments. It is concluded that this “ionic mobility” is due to a post mortem, early diagenetic (pre-recrystallization) approach to equilibrium with the surrounding chemical environment.     

Hidden philosophies: How geographic thought has been limited by its theoretical models

Dominant theoretical models in geography have been drawn by analogy from theories in economics and biology. The philosophical assumptions which underlie this transfer are normally unexamined. The economic model itself rests on a mechanical analogy and on a philosophy of science which emphasizes empiricism, determination and reductionism. The ecological model, while realist at base, is limited by the ontological priority it grants to Nature. Though some recent approaches in Marxism echo these old antinomies, a Marxist model based on the philosophy of internal relations offers an opportunity to transcend these barriers.     

Li,Sr, Mg,and Na in foraminiferal calcite shells from laboratory culture,sediment traps,and sediment cores

Constant-temperature laboratory culture experiments of the planktonic foraminiferal species Globigerinoides sacculifer (Brady) suggest that the ratios of Li and Sr to Ca in the shells are a function of these ratios in the culture solutions. $\text{Mg}\text{Ca}$ and $\text{Na}\text{Ca}$ in the shells did not vary with changes of these ratios in the culture solution. These are the first direct determinations of the relationship between foraminiferal shell chemistry and solution composition.The possibility of temperature dependence for the minor elemental composition of foraminiferal shells was also investigated in the laboratory and by analysis of several planktonic and one benthic foraminiferal species from sediment trap and sediment core samples. The $\text{Sr}\text{Ca}$, $\text{Mg}\text{Ca}$, and $\text{Na}\text{Ca}$ ratios in the natural samples roughly correlate with calcification temperature, whereas differences in the Li/Ca ratios are small and not systematically related to temperature. However, laboratory culture experiments at 20°C and 30°C showed no variation in the $\text{Li}\text{Ca}$, $\text{Sr}\text{Ca}$, $\text{Mg}\text{Ca}$, and $\text{Na}\text{Ca}$ ratios with calcification temperature for the planktonic foraminifera G. sacculifer and Orbulina universa. Therefore, observed differences in the $\text{Sr}\text{Ca}$, $\text{Mg}\text{Ca}$, and $\text{Na}\text{Ca}$ ratios for the sediment trap and core foraminiferal samples cannot be ascribed to direct effects of calcification temperature, but may be due to some other environmental factor which is correlated with temperature.     

A catalog of station coordinates for GEOS-C orbit determination

Center-of-mass coordinates for 57 tracking sites participating in the GEOS-C mission are given in a unified system having a common origin and scale. The positions were obtained either directly from analyses of satellite observations or from survey ties to colocated sites with coordinates previously determined by various investigators from optical, laser of doppler data. The uncertainty of the positions in nearly all cases is 5 m in each coordinate. Data reductions show that station coordinates of this quality introduce a rapidly changing error into the altitude of a satellite unless global tracking constrains the orbit.