Bice S. Martincigh

Compound specific isotope analysis of fatty acids and polycyclic aromatic hydrocarbons in aerosols: implications for biomass burning

Fatty acids and polycyclic aromatic hydrocarbons (PAH) have been investigated as potential tracer species for the products of biomass burning. Fatty acids extracted from unburned sugar cane plants and from particulate aerosols collected during laboratory burns of sugar cane under smoldering and flaming conditions have been chemically and isotopically characterized by gas chromatographymass spectrometry (GC-MS) and gas chromatography-isotope ratio mass spectrometry (GC-IRMS), respectively. Fatty acids and PAH produced during the burning of a sugar cane field in South Africa were similarly characterized. The fatty acids identified in the aerosols collected above the fire were saturated even-chain species ranging from C12 to C22. The carbon isotopic signatures of the fatty acids ranged between -19.9°/ °° and -23.6°/ °° , and were more depleted in 13 C than the bulk sugar cane plant (-12.9°/ °° ) and the total lipid extract (-17.9°/ °° ). The isotopic signatures of the individual fatty acids were conserved during the smoldering laboratory burn. However, the fatty acids collected during the flaming burn showed a depletion of 1°/ °° to 6°/ °° relative to the fatty acids extracted from the unburned plant. This observed depletion was even greater for the fatty acids obtained from the sugar cane field burn. Low levels of various PAH were identified in aerosols from the laboratory burns. Phenanthrene, fluoranthene and pyrene obtained from the field burn aerosols were isotopically depleted relative to the bulk lipid material, with carbon isotopic signatures ranging from -22.9°/ °° to -25.4°/ °° . The alterations in the isotopic compositions of fatty acids that occur during combustion provide variables by which burn-derived compounds can be distinguished from those produced from aeolian transport of detrital vegetative matter. The combination of fatty acid isotopic data and PAH data may allow a better understanding of the relative contributions of biogenic and anthropogenic source materials to aerosols.

Ultraviolet Radiation Exposure of Children and Adolescents in Durban, South Africa¶

Abstract The solar ultraviolet radiation (UVR) exposure of 30 children and adolescents in three age groups (4–6 years, 7–9 years and 13–14 years) was measured for 1 week in late summer (February–March) in Durban, South Africa, using UVR-sensitive polysulfone film badges (PSFB) attached to the lapel region of the body. The mean and median values for all ages over the study period were 2.0 and 1.2 standard erythemal dose (SED) units, respectively, where 1 SED = 100 J·m−2. Individual PSFB doses were analyzed as a function of age, gender and behavior. No significant statistical differences were found between different age groups; however, there was a statistical difference between males and females, with males generally receiving higher PSFB doses. Subjects completed UVR exposure journals documenting their time outdoors, shade versus sun conditions, nature of their activities, clothing worn and their use of sunscreen for each day of the study. Activity patterns were noted as the most important factor influencing individual UVR dose. Ambient erythemal UVR was measured by a Yankee Environmental Systems UVB pyranometer, and a relationship between ambient UVR and individual UVR dose was derived. On average, subjects received a dose of 4.6% of the total daily erythemal UVR. Based on this factor, the potential dose of an individual over a full annual cycle was estimated. Accordingly, there were 139 days during the year when an individual with skin type I (light skin) would be likely to experience minimal erythema and 97 and 32 days for individuals with skin types II and III, respectively.

THE EXISTENCE AND STABILITY OF MIXEDLIGAND COMPLEXES IN AQUEOUS SOLUTIONS CONTAINING ZINC AND CYANIDE IONS AT ELEVATED pH VALUES

Abstract The formation and stability of binary Zn2+[sbnd]CN− and ternary Zn2+[sbnd]CN−[sbnd]OH− complexes were studied by glass electrode potentiometry in aqueous solution at 25°C and in a medium of ionic strength 0.1 mol dm−3. The solution pH was varied to cover the range 4→10. The potentiometric data were interpreted with the aid of the ESTA suite of computer programs, plots of formation functions, and a novel algorithm for model selection. It is demonstrated that the ternary complex Zn(CN)3(OH)2- is formed in significant amounts in solutions of pH > 8.5. Some evidence was also obtained for the existence of the five-coordinate species Zn(CN)3(OH)2 3- and Zn(CN)5 3- in solutions at sub-millimolar concentration levels. No polynuclear complexes were detected under these conditions. Formation constants are reported for both binary Zn2+[sbnd]CN− and ternary Zn2+[sbnd]CN−[sbnd]OH− species.

Para-aminobenzoic acid-photosensitized dimerization of thymine II. In pUC19 plasmid DNA

Abstract Para-aminobenzoic acid (PABA) photosensitizes the dimerization of contiguous thymine bases in DNA upon irradiation at wavelengths greater than 300 nm which are not absorbed by the DNA bases themselves. The kinetics and mechanism of this reaction has been studied for pUC19 plasmid DNA. The dependence of dimer yield on a variety of reaction conditions has been determined. A mechanism has been proposed to account for the major processes taking place and rate constants for the constituent reactions have been acquired from the literature, from previous studies on the simpler systems of PABA-photosensitized dimerization of free thymine base and thymidylyl-3′,5′-thymidine (TpT) and from calculation based upon a Stern—Volmer steady state analysis of the proposed mechanism and experimental data. Computer simulation of the mechanism with its associated rate constants gives dimer yields that are generally in reasonable agreement with the experimental data. Where discrepancies occur they have been explained in terms of production of other photoproducts.

Photoproducts formed by near-UV irradiation of thymine in the presence of p-aminobenzoic acid

Abstract In addition to the four isomers of cyclobutane thymine dimer, two non-dimer photoproducts of thymine (5,6-dihydrothymine and 5-hydroxymethyluracil) were detected when free thymine base was irradiated at 324 nm in the presence of p-aminobenzoic acid (PABA) at pH 7.0. The yields were found to be enhanced in the presence of phosphate buffer. Irradiation of thymidine at 324 nm in the presence of PABA lead to the formation of 5,6-dihydrothymidine.

PARA-AMINOBENZOIC ACID-PHOTOSENSITIZED DIMERIZATION OF THYMINE. I: IN DNA-RELATED MODEL SYSTEMS

Abstract Para-aminobenzoic acid (PABA) is able to photosensitize the dimerization of two adjacent thymines in aqueous solutions of free thymine base or thymidylyl-3′,5′-thymidine at wavelengths greater than 300 nm where thymine does not absorb. The dependence of dimer yield on a variety of reaction conditions when these two DNA- related systems were irradiated in the presence of PABA has been investigated. Reaction mechanisms have been proposed to account for the major processes taking place. The rate constants for the various constituent reactions have been assigned on the basis of experiment, values cited in the literature and calculations based upon these values as well as calculation based upon Stern—Volmer steady state analysis of the proposed mechanisms. Computer simulation of these mechanisms gave dimer yields which were in reasonable agreement with the experimental data.

The potential carcinogenic effect of Uvinul DS49―a common UV absorber used in cosmetics

Abstract The photosensitized production of thymine dimer at 324 nm was investigated using disodium-2,2′-dihydroxy-4,4′-dimethoxybenzophenone sulphonic acid (tradename, Uvinul DS49) as sensitizer. Yields of the dimer for various irradiation times, initial thymine concentrations and initial sensitizer concentrations were determined for the free thymine base in aqueous medium. A reaction mechanism is proposed for total thymine dimer formation together with the corresponding rate constants. The mechanism and rate constants were computer simulated to support their validity.

A sensitive immunoassay technique for thymine dimer quantitation in UV-irradiated DNA

Abstract This paper describes an immunological technique for thymine dimer quantitation which is more sensitive than the high performance liquid chromatography (HPLC) method used previously in our laboratory. Calf thymus DNA was irradiated in the presence of the photosensitizer acetophenone to induce the formation of cis-syn thymine dimers exclusively. These DNA solutions were then denatured and injected into New Zealand white rabbits to raise antibodies against the thymine dimer. Blood was drawn from the rabbits at regular intervals and the crude serum was used in an immunoblotting protocol which immobilized the antigen-antibody complex on a membrane system. Subsequent detection and quantitation of the thymine dimer antigen was performed by enhanced chemiluminescence (ECL). Dilutions of the antibody used in the above protocol could be quantitatively related to the UV-irradiated DNA antigen, i.e. the thymine dimer. It is shown that this technique is 4000–8000 times more sensitive than the HPLC technique used previously. The above immunoblotting/ECL protocol was then used to test the validity of a proposed mechanism for acetophenone-photosensitized dimerization of thymine in DNA at concentrations more relevant to cellular systems, but previously undetectable by HPLC.

Thymine Dimer Formation Mediated by the Photosensitizing Properties of Pharmaceutical Constituents

Thymine dimer formation is a major photochemical lesion of UV-irradiated DNA and has been implicated as a precursor in skin cancer. Certain pharmaceutical constituents, such as the sunscreen absorbers para-aminobenzoic acid, Uvinul DS49, Eusolex 232 and the tranquillizer chlorpromazine, have the potential to photosensitise thymine dimerisation in thymine-containing systems. The yields of thymine dimer, obtained from the UV-irradiation of thymine substrates in the presence of the photosensitisers, were determined by reverse phase HPLC. Computer simulations of the experimental results were used to establish the kinetics and mechanisms of photosensitised thymine dimerisation in the various systems investigated. Initial studies involved the photosensitisation of free thymine base in aqueous medium. In this system, sunscreen agents were found to be effective photosensitisers of thymine dimerisation. The PABA photosensitisation of thymine dimer formation in the more biologically relevant system, pUC19 plasmid DNA, was investigated. The kinetic mechanism for the photosensitised dimerisation of contiguous thymines in pUC19 plasmid DNA at pH 7 is reported.

A critical review of the occurrence of perfluoroalkyl acids in aqueous environments and their removal by adsorption onto carbon nanotubes

The presence of perfluoroalkyl acids (PFAAs) in aquatic environments is a cause of concern, due to their toxicity, possible ecological impact and adverse effects in man. The release of these pollutants into receiving water bodies occurs primarily through the discharge of untreated wastewater and industrial effluents. Consequently, there is a need to remediate wastewater containing these compounds before its discharge. In this review, the occurrence of PFAAs in water streams is reviewed, with the aim of providing in-depth information on the harmful effects arising through exposure to these pollutants by both man and the environment. One viable strategy for the removal of PFAAs from wastewaters is adsorption. This technique is discussed in relation to a number of conventional adsorbents and they are compared with the behaviour of a more effective adsorbent, namely, carbon nanotubes (CNTs). In particular, various functionalization strategies can increase the efficiency of CNTs for the removal of PFAAs. Sorption of PFAAs onto CNTs demonstrates good removal efficiencies and equilibrium is attained faster than with conventional adsorbents. This is attributed to the inherent properties of CNTs, such as large surface area/porosity, and the ease with which new functional groups are introduced onto the walls of the tubes. The adsorption mechanism of PFAAs is primarily enhanced through electrostatic interactions; however, other intermolecular forces, such as hydrogen bonding, hydrophobic interactions and ion-exchange, also play a role. This review aims at providing information on the occurrence and fate of PFAAs and the interactions involved in their removal from aqueous solutions by CNTs.