Respiratory tract retention of inhaled air pollutants: Report 1 : Mercury absorption by inhaling through the nose and expiring through the mouth at various concentrations

To study atmospheric mercury absorption in human respiratory passage-ways, mercury in expired air was measured in three different states of breathing: steady breathing, deep breathing and breath held after inspiration.In this study, air containing mercury was inhaled through the nose and expired through the mouth. The concentration of mercury in the exhaled air was determined by the technique of gold-amalgam trapping, heat vaporization, and flameless atomic absorption measurement.The subjects were 13 male adults, aged 25–62 years, and 38 cases were observed. Four different concentrations of mercury, 1–3, 4–6, 10–11, and 20–30 μg/m³ were used, and absorption for each was determined. When the concentration was 1–3 μg/m₃, the absorption was 74–92%, the average being 82.5%. At concentrations of 4–6, 10–11, and 20–30 μg/m₃, the absorption was 76.6–100%, 75.5–99.2%, and 79.9–95.9% respectively, and the average was 88.8%, 85.2%, and 87.7% respectively.A slightly higher rate of mercury absorption was observed in deep breathing than in steady breathing, and when expiration was suppressed for some time after inspiration, the rate increased remarkably to 97.4–99.7%. Prolonged retention of inhaled air containing mercury in the respiratory tract is believed to have caused the increased absorption.     

Metabolism of potassium bromate in rats II. In vitro studies

To learn more about the biodegradation of potassium bromate, the decomposition of bromate in various tissues of rats was studied. Bromate was degraded very slowly in human saliva and plasma of rat. However, nearly all tissue homogenates and red blood cells could degrade bromate by a mechanism which exhibited some stability to heat. Furthermore, it was suggested that the bromate degradation active component in the supernatant fraction of a liver homogenate was in part glutathione.     

Simulation of dioxin accumulation in human tissues and analysis of reproductive risk

Polychlorinated dibenzo-p-dioxin, polychlorinated dibenzofuran and dioxin-like polychlorinated biphenyl concentrations in human liver, kidney, fat, blood, muscle, richly perfused tissue (brain, lung etc.) and skin were simulated to assess the health risk for Japanese fetuses. A 40-year time course of dioxin accumulation via food ingestion was simulated using a physiologically based pharmacokinetic (PBPK) model. In richly perfused tissue, the concentration estimated by the PBPK model showed better agreement with measured concentrations than that calculated by the one-compartment model. Fetal dioxin concentration was simulated based on the assumption that the fetal concentration was almost equal to the concentration in the mother's richly perfused tissue. To assess the reproductive risk, the estimated concentration in human fetus was compared with that in rat fetus in which reproductive function showed signs of alteration by 2,3,7,8-TCDD in previous reports [Toxicol. Appl. Pharmacol. 114 (1992) 118; 146 (1997) 11; Toxicol. Sci. 53 (2000) 411; 57 (2000) 275]. The present daily intake of 2,3,7,8-TCDD is approximately 1/50 of the amount that leads to possible reproductive toxicity in the next generation. However, when 29 kinds of dioxin congeners are considered, the present level is 1/5 of the hazardous levels. For species extrapolation of dioxin risk, further study on tissue concentration versus toxicity is required.     

Determination of tissue-blood partition coefficients for a physiological model for humans, and estimation of dioxin concentration in tissues

The tissue-blood partition coefficients for a physiologically based pharmacokinetic (PBPK) model were determined, and the concentrations of 17 congeners of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in tissues in Japanese people were estimated using the model. According to the PBPK model established by Lawrence and Gobas [Chemosphere 35 (1997) 427-452], we assumed a steady-state fugacity model for Japanese people in general, and set the route of PCDD/Fs exposure only from food intake. The required partition coefficients for liver, kidney, adipose, muscle, skin, bile, gut and viscera (richly perfused tissue) were calculated using available autopsy data from eight Japanese men and women who were not accidentally exposed to PCDD/Fs. For validation of the partition coefficients, estimated PCDD/F concentrations in liver, kidney, fat, blood and muscle using the model were compared to other two sets of measured concentration data in Japanese tissues. Good agreement was obtained between estimated data and measured data, and most of the measured data were within the simulated concentration range in liver, kidney, blood and muscle. From these results, our model and calculated partition coefficients seem applicable for the estimation of congener-specific concentrations in human tissues.     

Validation of modeling approach to evaluate congener-specific concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans in air and soil near a solid waste incinerator.

A concise modeling approach using long-term averaged meteorological data was developed to estimate site-specific concentrations of congeners of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) near a solid waste incinerator. This approach consists of calculation of atmospheric dispersion, dry and wet deposition of gaseous and particle-bound congeners, and non-steady-state concentrations in soil. The predictability of this approach was evaluated by comparison of calculated concentrations of congeners in soil with those measured at eight locations near a municipal solid waste incinerator (MSWI). The variation of these concentrations due to variability of meteorological parameters is small. A considerable number of mean values show good agreement with measured concentrations within a factor of three. The reasonable agreement between calculated and measured concentrations indicates that algorithms for the calculation of vapor-phase deposition and non-steady-state concentrations in soil must be included in the modeling approach for an accurate estimation of the concentrations of congeners of PCDD/Fs emitted from MSWIs to the atmosphere. For a detailed estimation of site-specific concentrations, it is important to specify the bulk density of soil in the evaluated area, together with meteorological parameters.     

A GIS-based evaluation of the effect of decontamination on effective doses due to long-term external exposures in Fukushima

Despite the enormous cost of radiation decontamination, there has been almost no quantitative discussion on how much it would reduce the long-term external radiation exposure in the Evacuation Zone and Planned Evacuation Zone (restricted zone) in Fukushima. The aim of this study is to assess the effectiveness of decontamination and return options and to identify important parameters for estimating the long-term cumulated effective dose (CED) during 15, 30 and 70 year period using data on land-use, population and decontamination in the restricted zone (about 1100 km²) in Fukushima.     

Determination of nonylphenol ethoxylates and octylphenol ethoxylates in environmental samples using 13C-labeled surrogate compounds

Alkylphenol polyethoxylates (APEOs) have been widely used as nonionic surfactants in a variety of industrial and commercial products. Typical compounds are nonylphenol polyethoxylates (NPEOs) and octylphenol polyethoxylates (OPEOs), which serve as precursors to nonylphenol (NP) and octylphenol (OP), respectively. NP and 4-t-OP are known to have endocrine disrupting effects on fish (medaka, Oryzias latipes), so it is important to know the concentrations of APEOs in the environment. Because the analytical characteristics of these compounds depend on the length of the ethoxy chain, it is necessary to use appropriate compounds as internal standards or surrogates. We synthesized two 13C-labeled surrogate compounds and used these compounds as internal standards to determine NPEOs and OPEOs by high-performance liquid chromatography (LC)-mass spectrometry. Method detection limits were 0.015 microg/L for NP (2)EO to 0.037 microg/L for NP(12)EO, and 0.011 microg/L for OP(3,6)EO to 0.024 microg/L for OP (4)EO. NPEO concentrations in water from a sewage treatment plant were less than 0.05-0.52 microg/L for final effluent and 1.2-15 microg/L for influent. OPEO concentrations were less than 0.05-0.15 microg/L for the final effluent and less than 0.05-1.1 microg/L for influent.     

Behavior of potassium in bread by ion chromatography

Public attention was aroused when mutagenicity was found in potassium bromate (KBrO₃) which has been used as an oxidizing agent in baking bread. Ion chromatography was found to be very useful for analyzing bromide and bromate ions in food. The residual condition of potassium bromate added to bread in the baking process was clarified.It was found that the residual rate of bromate ions in bread was approximately 30% at the added level of 100 μg/g, but it decreased markedly when the added levels went down. At 40 μg/g no residue was detected.     

Assessment of groundwater contamination by nitrate leaching from intensive vegetable cultivation using geographical information system

This study employed the Geographical Information System (GIS) technology to investigate nitrate contamination of groundwater by agrochemical fertilizers in the Kakamigahara Heights, Gifu Prefecture, central Japan. Thematic information and chemical data of groundwater from the Heights were analyzed in a GIS environment to study the extent and variation of nitrate contamination and to establish spatial relationships with responsible land use types. The high and correlated concentrations of Ca(2+), Mg(2+), SO(4)(2-), and NO(3)(-) reflected the polluted nature of the unconfined highly permeable Kakamigahara aquifer. Ninety percent of the water samples showed nitrate concentrations above the human affected value (3 mg/l NO(3)(-)), while more than 30% have exceeded the maximum acceptable level (44 mg/l NO(3)(-)) according to Japan regulations. The spatial analyses indicated that groundwater contamination by nitrate is closely associated with one specific land use class, the "vegetable fields". The nitrate concentration of groundwater under vegetable fields was significantly higher than that under urban land or paddy fields. Most of the unacceptable nitrate levels were encountered in boreholes assigned to "vegetable fields" but a few were also found in boreholes allotted to "urban" class. Therefore, the vegetable fields were considered the principal source of nitrate contamination of groundwater in the Kakamigahara. However, contamination from urban sources is also possible.     

Metabolism of potassium bromate in rats I. In vivo studies

Potassium Bromate was administered orally to rats and its fate in the body was studied. The bromate was rapidly absorbed from the digestive tract and was partly excreted in the urine within two hours of administration. No bromate was detected in body organs or in the blood 24 hours after dosing. Excretion of bromate into the urine was proportional to the dose, except that at 2.5mg/kg or less no excretion was observed. The administration of bromate increased the bromide concentration in various organs and in urine.