Sarka Langer

Children's Phthalate Intakes and Resultant Cumulative Exposures Estimated from Urine Compared with Estimates from Dust Ingestion, Inhalation and Dermal Absorption in Their Homes and Daycare Centers

Total daily intakes of diethyl phthalate (DEP), di(n-butyl) phthalate (DnBP), di(isobutyl) phthalate (DiBP), butyl benzyl phthalate (BBzP) and di(2-ethylhexyl) phthalate (DEHP) were calculated from phthalate metabolite levels measured in the urine of 431 Danish children between 3 and 6 years of age. For each child the intake attributable to exposures in the indoor environment via dust ingestion, inhalation and dermal absorption were estimated from the phthalate levels in the dust collected from the child’s home and daycare center. Based on the urine samples, DEHP had the highest total daily intake (median: 4.42 µg/d/kg-bw) and BBzP the lowest (median: 0.49 µg/d/kg-bw). For DEP, DnBP and DiBP, exposures to air and dust in the indoor environment accounted for approximately 100%, 15% and 50% of the total intake, respectively, with dermal absorption from the gas-phase being the major exposure pathway. More than 90% of the total intake of BBzP and DEHP came from sources other than indoor air and dust. Daily intake of DnBP and DiBP from all exposure pathways, based on levels of metabolites in urine samples, exceeded the Tolerable Daily Intake (TDI) for 22 and 23 children, respectively. Indoor exposures resulted in an average daily DiBP intake that exceeded the TDI for 14 children. Using the concept of relative cumulative Tolerable Daily Intake (TDIcum), which is applicable for phthalates that have established TDIs based on the same health endpoint, we examined the cumulative total exposure to DnBP, DiBP and DEHP from all pathways; it exceeded the tolerable levels for 30% of the children. From the three indoor pathways alone, several children had a cumulative intake that exceeded TDIcum. Exposures to phthalates present in the air and dust indoors meaningfully contribute to a child’s total intake of certain phthalates. Such exposures, by themselves, may lead to intakes exceeding current limit values.

The kinetics and mechanism of SO2 oxidation by O3 on mineral dust

The oxidation of SO2 by O3 on mineral dust was studied using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Formation of sulfate was observed on the surface. A two-step mechanism that involves physisorbed SO2 followed by oxidation is presented. The formation rate was determined to be first order with respect to SO2 and zero order in O3. The reactive uptake coefficient, γ, was determined from the infrared absorbance, that was calibrated by ion chromatography, and from the geometric or the BET surface area. γSO2 was independent of the SO2 concentration and was determined to be in the order of 10−3 using the geometric surface area, or 10−7 using the BET surface area for [SO2] = 2.2 × 1012 to 2.0 × 1013 and [O3] = 5.6 × 1012 (in units of molecule cm−3). γO3 depended linearly on the O3 concentration and varied from 10−2 to 10−4 using the geometric area or 10−6 to 10−8 using the BET area for [O3] = 1.9 × 1012 to 5.5 × 1013 and [SO2] = 5.4 × 1012 (in units of molecule cm−3). In all experiments surface saturation was observed with an amount of 2 × 1019 sulfate ions g−1 on the mineral dust sample. In the presence of water vapor regeneration of active sites was observed. After several exposures to water vapor corresponding to 80% relative humidity and successive SO2 and O3 treatments the amount of formed sulfate covering the surface was increased by 47% compared to the dry experiments.

Phthalate exposure through different pathways and allergic sensitization in preschool children with asthma, allergic rhinoconjunctivitis and atopic dermatitis.

Studies in rodents indicate that phthalates can function as adjuvants, increasing the potency of allergens. Meanwhile, epidemiological studies have produced inconsistent findings regarding relationships between phthalate exposures and allergic disease in humans. The present study examined phthalate exposure and allergic sensitization in a large group of 3-5 year old children: 300 random controls and 200 cases with asthma, rhinoconjunctivitis or atopic dermatitis as reported in questionnaires. The children were clinically examined to confirm their health status. Blood samples were analyzed for IgE sensitization to 20 allergens. Adjusted logistic regressions were used to look for associations between phthalate exposure indicators (mass fractions in dust from childrens homes and daycares, metabolites in urine, and estimated daily indoor intakes from dust ingestion, inhalation and dermal absorption) and sensitization and allergic disease. No direct associations were found between phthalate exposures and asthma, rhinoconjunctivitis or atopic dermatitis. However, among children with these diseases, there were significant associations between non-dietary exposures to DnBP, BBzP and DEHP in the indoor environment (mass fractions in dust or daily indoor intakes from dust ingestion, inhalation and dermal absorption) and allergic sensitization. Some exposure pathways were more strongly associated with sensitization than others, although the results are not conclusive and require confirmation. A number of the associations depended on accounting for a childs exposure in more than one environment (i.e., daycare facility as well as home). Significant associations were not observed between phthalate metabolites in urine, which reflected exposure from diet as well as indoor pathways, and allergic sensitization.

Squalene and Cholesterol in Dust from Danish Homes and Daycare Centers

Given the rate at which humans shed their skin (desquamation), skin flakes that contain squalene and cholesterol are anticipated to be major constituents of indoor dust. These compounds have been detected in more than 97% of the dust samples collected from 500 bedrooms and 151 daycare centers of young children living in Odense, Denmark. The mass fractions of squalene in dust were approximately log-normally distributed (homes: GM = 32 μg/g, GSD = 4.3; daycare centers: GM = 11.5 μg/g, GSD = 4.3); those of cholesterol displayed a poorer fit to such a distribution (homes: GM = 625 μg/g, GSD = 3.4; daycare centers: GM = 220 μg/g, GSD = 4.0). Correlations between squalene and cholesterol were weak (r = 0.22). Furthermore, the median squalene-to-cholesterol ratio in dust (~0.05) was more than an order of magnitude smaller than that in skin oil. This implies sources in addition to desquamation (e.g., cholesterol from cooking) coupled, perhaps, with a shorter indoor lifetime for squalene. Estimated values of squalenes vapor pressure, while uncertain, suggest meaningful redistribution from dust to other indoor compartments. We estimate that dust containing squalene at 60 μg/g would contribute about 4% to overall ozone removal by indoor surfaces. This is roughly comparable to the fraction of ozone removal that can be ascribed to reactions with indoor terpenes. Squalene containing dust is anticipated to contribute to the scavenging of ozone in all settings occupied by humans.

Rates of reaction between the nitrate radical and some unsaturated alcohols

Rate coefficients for nitrate radical gas-phase reactions with prop-2-en-l-ol (allyl alcohol), but-1-en-3-ol, and 2-methylbut-3-en-2-ol have been determined. Both absolute (fast flow discharge with diode laser detection of NO3) and relative (batch reactor and FTIR spectroscopy) rate techniques were used to measure the rate coefficients. The rate coefficients at 294 K are: (1.3 ± 0.2) × 10−14, (1.2 ± 0.3) × 10 −14, and (2.1 ± 0.3) × 10−14 cm3 molecule−1 s−1 for prop-2-en-1-ol, but-1-en-3-ol, and 2-methylbut-3-en-2-ol, respectively. The activation energy for reaction of NO3 with prop-2-en-1-ol was determined to 2.8 ± 2.5 kJ mol−1 in the temperature range between 273 and 363 K. The atmospheric importance of unsaturated alcohols and structure-reactivity considerations are also discussed.

Flux of organic compounds from grass measured by relaxed eddy accumulation technique

Fluxes of some Volatile Organic Compounds (VOC) from grass were measured at a golf course in western Sweden, using the Relaxed Eddy Accumulation (REA) technique. The sampling was done by collecting VOC onto adsorbent tubes and the analysis was performed by thermal desorption followed by GC/MS. High emissions were observed after cutting. Transient fluxes of (Z)-3-hexenyl acetate (0.51 microg m(-2) s(-1)), (Z)-3-hexen-1-ol (0.14 microg m(-2) s(-1)) and (Z)-3-hexenal (0.40 microg m(-2) s(-1)) were measured, even at low temperatures. The REA technique requires a relatively large fetch area that is sometimes not available. Therefore, a procedure for correcting measured fluxes from a limited fetch is suggested.

Products from the gas-phase reaction of some unsaturated alcohols with nitrate radicals

Five structurally similar unsaturated alcohols, 2-propene-1-ol (allyl alcohol), 3-butene-2-ol, 2-methyl-3-butene-2-ol (MBO232), 2-butene-1-ol (crotyl alcohol) and 3-methyl-2-butene-1-ol (MBO321), were examined to clarify their atmospheric degradation pathways via oxidation initiated by NO3 radicals. The reactions were investigated using a 0.153 m3 static glass reactor equipped with long-path FTIR spectroscopy. The experiments were performed at a pressure of 1020±5 mbar and at a temperature of 297±2 K in air or nitrogen as the bath gas. The identified and quantified gas phase products were small carbonyl compounds such as acetone, formaldehyde, acetaldehyde, glycolaldehyde and 2-nitrooxy acetaldehyde. The specific products and their yields varied for the five studied alcohols as follows: formaldehyde 37(±1)% and 2-nitrooxy acetaldehyde 41(±7)% from allyl alcohol; acetaldehyde 28(±6)%, formaldehyde 2(±1)% and 2-nitrooxy acetaldehyde 33(±4)% from 3-butene-2-ol; acetone 63(±6)% and 2-nitrooxy acetaldehyde 67(±8)% from MBO232; acetaldehyde 12(±2)%, formaldehyde 10(±3)% and glycolaldehyde 7(±2)% from 2-butene-1-ol; acetone 21(±6)%, formaldehyde 11(±3)% and glycolaldehyde 29(±10)% from MBO321. In addition, yields were estimated for total organic nitrates using an average integrated absorption cross section of unspecified organic nitrates. Tentative reaction schemes were proposed from the yielded products. The distribution between bond breakage and other processes such as abstraction of a hydrogen atom from the alkoxy radical, formed in the degradation process, was estimated. The small carbonyl compounds were produced by the bond breakage mechanisms. Large multi-functional organic compounds e.g. 1-hydroxy-3-nitrooxy-3-methyl-2-butanone from MBO321 were proposed to be formed by hydrogen abstraction. From the product distribution, the contribution of the number of methyl group substituents at the α and γ carbon atoms, influencing the bond breakage pattern, is discussed. The observed bond cleavage trends are correlated to a substitution pattern where electron donating methyl substituents increase the stability of the leaving radical groups.

UV absorption spectrum of CH3OCH2 radicals and kinetics of the reaction of CH3OCH2O2 radicals with NO and NO2 in the gas phase

Abstract Alkyl and alkylperoxy radicals originating from dimethyl ether have been studied in the gas phase at 296 K. A pulse radiolysis-UV absorption technique was used. Absorption cross-sections were quantified over the wavelength range 220–350 nm. At 230 nm, σCH3OCH2 = (4.2 ± 0.5) × 10−18 cm2 molecule−1 has been obtained. Rate constants for the reaction of the alkylperoxy radical with NO and NO2 were determined to be (9.1 ± 1.0) × 10−12 cm3 molecule−1 s−1 and (7.9 ± 0.4) × 10−12 cm3 molecule−1 s−1, respectively.

Rates of reaction between the nitrate radical and some aliphatic alcohols

Rate coefficients for the gas-phase reaction of NO3 with methanol, ethanol and propan-2-ol have been determined. Absolute rates were measured at temperatures between 258 and 367 K using the fast flow–discharge technique. The measured rate coefficients (in units of 10–15 cm3 molecule–1 s–1) at 295 K are: 0.132 ± 0.024, 1.37 ± 0.10 and 3.13 ± 0.64 for methanol, ethanol and propan-2-ol, respectively. The temperature dependence of the rate coefficients can be expressed as Arrhenius equations: kmethanol=(1.06 ± 0.51)× 10–12 exp[–(2093 ± 803)/T], kethanol=(6.99 ± 1.21)× 10–13 exp[–(1815 ± 419)/T] and kpropan-2-ol=(1.54 ± 0.75)× 10–12 exp[–(1743 ± 1009)/T](in units cm3 molecule–1 s–1). An attempted product study, using N2O5, as the NO3 source, failed since the alcohols react with N2O5, producing alkyl nitrates. The estimated upper limit for rate coefficients for reaction of N2O5 with methanol, ethanol and propan-2-ol at 296 K in the gas phase were (2.0 ± 1.0)× 10–19, (3.9 ± 2.0)× 10–19, and (4.8 ± 2.5)× 10–19 cm3 molecule–1 s–1, respectively. The error limits correspond to the 95%-confidence interval.

Reactions of acrolein, crotonaldehyde and pivalaldehyde with Cl atoms: structure–activity relationship and comparison with OH and NO3 reactions

Rate coefficients for the reaction of acrolein (prop-2-en-1-al), crotonaldehyde (but-2-en-1-al) and pivalaldehyde (2,2-dimethylpropanal) with chlorine atoms were determined. The resulting rate coefficients were (1.8 ± 0.3) × 10−10, (2.2 ± 0.4) × 10−10 and (1.2 ± 0.2) × 10−10 (cm3 molecule−1 s−1) for acrolein, crotonaldehyde and pivalaldehyde, respectively. Rate coefficients for chlorine atom reaction with propanal, butanal, 2-methylpropanal and trans-but-2-ene were determined to be (1.2 ± 0.2) × 10−10, (1.5 ± 0.3) × 10−10, (1.5 ± 0.3) × 10−10 and (3.0 ± 0.6) × 10−10 (cm3 molecule−1 s−1), respectively. The relative rate technique was used with propene as the reference compound. The experiments were carried out at 297 ± 2 K and 1020 ± 2 mbar using a 0.153 m3 borosilicate glass reactor with long-path FTIR spectroscopy as the analytical tool. Synthetic air and nitrogen were used as bath gases. Literature values of the corresponding hydroxyl and nitrate radical rate coefficients were confirmed. The chemical characteristics of the organic substances have a limited influence on the reactivity with Cl, a larger effect in the OH-case but are decisive for the NO3 reactions. Introduction of an aldehydic carbonyl group into an unsaturated compound reduces the reactivity of a neighboring double bond for reaction with all three radicals. The unsaturated aldehydes reacting with NO3 show a rate coefficient that is lower than both the corresponding simple alkene and aliphatic aldehyde, indicating that also the reactivity of the aldehydic hydrogen atom is affected. The results show that during the morning hours, Cl atoms may be the most significant oxidising agent for organic substances in urban coastal air.