Ppb In Air Research Articles

Estimating the risk of liver cancer associated with human exposures to chloroform using physiologically based pharmacokinetic modeling

A physiologically based pharmacokinetic (PB-PK) model for CHCl 3 has been used to prepare estimates of the probability that human populations exposed to low levels of CHCl 3 will develop liver tumors similar to those seen in rodent bioassays. The PB-PK model for CHCl 3 was based on a model reported earlier by Corley et al. (1990), but this model differed from that of Corley et al. in that it was also capable of describing a pharmacodynamic endpoint: induction of cytotoxicity in the liver of CHCl 3-exposed animals produced by reactive metabolites of CHCl 3. Pharmacodynamic descriptions in this model were derived from experimental measurements of cell replication ([ 3H]thymidine incorporation) as well as from quantitative histopathology in the liver of rats and mice. Two different approaches were used for hazard evaluation: (1) a “Safety Factor” approach based on no observed effect levels for liver tumors, and (2) calculation of lower confidence limits on risk-specific doses with the GLOBAL83 computer program. In each case, cytotoxicity produced by reactive CHCl 3 metabolites was used as the measure of “dose” to the liver. The Safety Factor approach suggested that continuous exposure of human populations to concentrations of CHCl 3 less than 2840 ppb in air or 13,900 ppb in water would not be likely to significantly increase the risk of developing liver tumors. The second approach suggested a “plausible upper 95% confidence limit” of 1 × 10 −5 for lifetime excess cancer risk for human populations continuously exposed to 2200 or 13,100 ppb CHCl 3 in air or water, respectively.

Negative ion mobility spectrometry for selected inorganic pollutant gases and gas mixtures in air

Spectra for inorganic gases common to combustion emissions were obtained in air by using negative ion mobility spectrometry (NIMS). Gases were characterized individually from 10 to over 4000 ppb in air and in two binary mixtures of SO/sub 2//NO/sub 2/ and HCl/SO/sub 2/. Spectra for HCl and SO/sup 2/ were distinguished by single intense peaks at reduced mobilities (K/sub 0/) of 2.98 cm/sup 2//(V s) and 2.30 cm/sup 2//(V s), respectively. The product ion for NO/sub 2/ had a K/sub 0/ of 2.80 cm/sup 2//(V s) as determined using binary mixture studies and was unresolved otherwise from reactant ions. In contrast, NIMS spectra for H/sub 2/S showed three peaks that were concentration dependent and had mobility values of 2.38, 2.28, and 1.70 cm/sup 2//(V s). Peak currents for H/sup 2/S ranged from 10 to 50 pA and the estimated limit of detection (LOD) was 10 ppb. Peak currents for SO/sub 2/ ranged from 15 to 65 pA and the estimated LOD was 2 ppb. The range of peak currents for HCl was comparatively large at 140-215 pA and estimated LOD was NO/sub 2/ > SO/sub 2/. 39 references, 5 figures, 1 table.« less

Importance of the amorphous fraction of polypropylene in the resistance to radiation-induced oxidative degradation

Radiation-induced oxidative degradation of two types of polypropylene (PP-A and PP-B) and of their blends in sheet form was studied in air with irradiation doses up to 10 Mrad. The elongation at break (γB) scarcely changed with irradiation dose below a critical value (Dc), but decreased drastically on irradiation a little in excess of Dc. The critical dose (Dc) increased rapidly with increasing amorphous fraction (fa) of the polypropylene, the relationship being expressed by an empirical equation, 33·5. The G values (3·1) for main-chain scission obtained for the irradiation of PP-A and PP-B in air were almost equal. The oxidation yield (Yox), defined as the amount of ketones produced per gram of polymer, depends on both the total dose of irradiation (D) and the amorphous fraction (fa) according to the relationship, 11·4 fa3·0D1·3. On the basis of these results, the important rôle of the amorphous fraction (fa) of polypropylene resin in its resistance to radiation-induced oxidative degradation is discussed.