Katarina Victorin

The Benchmark Dose Method—Review of Available Models, and Recommendations for Application in Health Risk Assessment

The benchmark dose method has been proposed as an alternative to the no-observed-adverse-effect level (NOAEL) approach for assessing noncancer risks associated with hazardous compounds. The benchmark dose method is a more powerful statistical tool than the traditional NOAEL approach and represents a step in the right direction for a more accurate risk assessment. The benchmark dose method involves fitting a mathematical model to all the dose-response data within a study, and thus more biological information is incorporated in the resulting estimates of guidance values (e.g., acceptable daily intakes, ADIs). Although there is an increasing interest in the benchmark dose approach, it has not yet found its way into the regulatory toxicology in Europe, while in the United States the U.S. Environmental Protection Agency (EPA) already uses the benchmark dose in health risk assessment. Several software packages are today available for benchmark dose calculations. The availability of software to facilitate the analysis can make modeling appear simple, but often the interpretation of the results is not trivial, and it is recommended that benchmark dose modeling be performed in collaboration with a toxicologist and someone familiar with this type of statistical analysis. The procedure does not replace expert judgments of toxicologists and others addressing the hazard characterization issues in risk assessment. The aim of this article is to make risk assessors familiar with the concept, to show how the method can be used, and to describe some possibilities, limitations, and extensions of the benchmark dose approach. In this article the benchmark dose approach is presented in detail and compared to the traditional NOAEL approach. Statistical methods essential for the benchmark dose method are presented in Appendix A, and different mathematical models used in the U.S. EPAs BMD software, the Crump software, and the Kalliomaa software are described in the text and in Appendix B. For replacement of NOAEL in health risk assessment it is considered important that consensus is reached on the crucial parts of the benchmark dose method, that is, selection of risk types and the determination of a response level corresponding to the BMD, especially for continuous data. It is suggested that the BMD method is used as a first choice and that in cases where it is not possible to fit a model to the data the traditional NOAEL approach should be used instead. The possibilities to make benchmark dose calculations on continuous data need to be further investigated. In addition, it is of importance to study whether it would be appropriate to increase the number of dose levels by decreasing the number of animals in each dose group.

Review of the genotoxicity of ozone.

Ozone is a powerful oxidant, reactive to biomolecules. In aqueous solution it decomposes to give hydrogen peroxide, superoxide and hydroxy radicals which can take part in secondary reactions. Ozone is a disinfectant that inactivates both viruses and bacteria. Although other reactions are primarily responsible for the inactivation, cellular DNA is also damaged. Ozone is genotoxic to microorganisms, plants and cell cultures in vitro. The results from in vivo cytogenetic studies with laboratory animals after inhalation exposure are contradictory. Chromosome aberrations in lymphocytes, but not SCEs, have been demonstrated in Chinese hamsters but not in mice. Chromatid deletions were induced in pulmonary macrophages in rats. No cytogenetic effects have been reported for bone marrow cells or spermatocytes. The few experimental and epidemiological studies with human subjects do not allow a conclusion on the cytogenetic effects of ozone in lymphocytes in humans. No life-long cancer studies have been performed with ozone. However, after 4 and 6 months of inhalation exposure, lung adenomas were induced in strain A/J mice, but not in Swiss-Webster mice.

Review of the genotoxicity of nitrogen oxides

Nitrogen oxides (NOx) are formed in combustion processes and are major pollutants in urban air. Relatively few studies on the genotoxicity of NO2 and NO have been performed. These studies indicate that NO2 is genotoxic in vitro, but the effect of NO seems to be very slight. One in vivo study showed chromosome aberrations and mutations in lung cells after inhalation of NO2 (and NO), but tests for chromosome aberrations in lymphocytes and spermatocytes or micronuclei in bone marrow were negative after inhalation of NO2. Based on present studies, there is no clear evidence of a carcinogenic potential of NO2, although lung adenomas were induced in the susceptible strain A/J mouse. The primary metabolites of NOx are nitrite and nitrate. Nitrate seems to be devoid of genotoxic properties, but nitrite is genotoxic in vitro, and there are also positive in vivo results. Cancer studies have been mainly negative. However, carcinogenic nitrosamines have been shown to be formed in vivo after inhalation of NO2. Nitrogen oxides are key components in atmospheric smog formation, which may lead to secondary effects. Strongly mutagenic nitro-PAH compounds are easily formed, and mutagenic reaction products may be formed photochemically from alkenes.

Redox potential measurements for determining the disinfecting power of chlorinated water

The kill of Escherichia coli within 3 min. was studied in chlorine-demand-free water using sodium hypochlorite, monochloramine, dichloramine, halazone, chloramine T, cyanuric acid + sodium hypochlorite and cyanuric acid + monochloramine. The redox potential and the available chlorine were measured. The redox potential was found to be better correlated with the disinfecting property of the water than was the amount of available chlorine. For individual pure chlorine compounds, the measuring of available chlorine showed in general a somewhat better correlation with reduction of the bacteria than the redox potential showed.

Emission of Mutagenic Substances From Waste Incineration Plants

Combined filter-, condensate- and XAD-extracts of flue gas samples from four different municipal solid waste (MSW) incineration plants were tested for mutagenic activity in the Ames Salmonella/microsome assay. The mutagenic activity in samples from two of the incinerators was relatively high, whereas the emission from the other two was in the same order of magnitude as from oil- or coal-fired plants of equivalent size. Generally, the material collected did not require metabolic activation for mutagenic activity. The emission of mutagenic substances was statistically correlated to the emission of carbon monoxide and polyaromatic hydrocarbons (PAH). Thus, the amount of mutagenic material can be modulated by the combustion process. Fractionation studies showed that there is not only a quantitative but also a qualitative difference in mutagenic activity between samples representing different combustion conditions.

Impact on health of chlorinated dioxins and other trace organic emissions

Abstract The potential health effects of incineration of municipal solid waste (MSW) have been studied by the Swedish National Institute of Environmental Medicine. The greatest concern for health effects relates to the emission of PCDDs and PCDFs (“dioxins”). MSW incineration is presently estimated to be a large source for the emission of these compounds into ambient air. Based upon animal experiments, and by applying safety factors in the range 200–1000, a highest tolerable daily intake (TDI) has been estimated to be 1–5 pg kg−1 of TCDD for humans. This TDI-value has been extended to cover all the congeners of PCDDs and PCDFs by the application of the concept of “TCDD-equivalents” (Eadon et al., 1983). The high concentrations found in human breast milk and fish indicate that the TDI value may be exceeded, especially among breast-milk fed babies. If the emission can be reduced to the proposed Swedish limit value of 0.1 ng m−3 n TCDD-equivalents, or less, the contribution from this source will be lowered. MSW incineration can be considered acceptable when the following aspects are taken into account: the risk estimation for TDI is conservative; there is no indication that man belongs to the most sensitive species although infants may be particularly sensitive; available studies indicate that the concept of TCDD-equivalents used overestimates the effect of mixtures of PCDDs and PCDFs; present levels in fish and human milk reflect the cumulative effect of many years of emission. Besides PCDDs and PCDFs, MSW incineration also gives rise to relatively high emissions of PAH, chlorinated PAH, phenols, benzenes and mutagenic substances under less well controlled combustion conditions. The emission of organic compounds is generally dependent on the combustion efficiency. If the combustion process is optimized and advanced flue-gas cleaning is applied so that the emission of TCDD-equivalents does not exceed 0.1 ng m−3, emission of other organics probably will not cause significant health hazards.

DNA damage in lung cells in vivo and in vitro by 1,3-butadiene and nitrogen dioxide and their photochemical reaction products

A UV-irradiated mixture of 1,3-butadiene and nitrogen dioxide (NO2) was tested for its potency to induce DNA damage measured as single-strand breaks (SSB) in lungs of mice. Both gases were also tested separately. After 16 h exposure a UV-irradiated mixture of 40 ppm butadiene + 20 ppm NO2, but not 20 ppm butadiene + 10 ppm NO2 + UV, induced a significant increase in SSB as measured by the alkaline unwinding technique. There was no increase in the level of SSB using the alkaline elution technique during the same testing conditions. However, after 5 h exposure to 60 ppm butadiene + 30 ppm NO2 + UV both methods demonstrated a significant increase in SSB. Mice were also exposed to butadiene at 80 and 200 ppm for 16 h and at 500 ppm for 5 h. DNA damage was demonstrated in both liver and lung after 5 and 16 h (only at 200 ppm) of exposure using the unwinding technique. Using the alkaline elution assay, a significant increase in the level of SSB in lung and liver was found only after 5 h of exposure. When mice were exposed to 30 ppm NO2 for 16 h or 50 ppm for 5 h, a significant increase in SSB was found with the unwinding technique. Alveolar macrophages from mice were also exposed in vitro to the gas mixture and to butadiene and NO2 separately. In these experiments, the DNA damage was studied with the unwinding technique. A significant effect was demonstrated with 40 ppm butadiene + 20 ppm NO2 + UV. NO2 itself contributed to some extent to the increase. Reasons for the discrepancies between the unwinding and the alkaline elution techniques are discussed.

Comparison of available benchmark dose softwares and models using trichloroethylene as a model substance

By using trichloroethylene as a model substance the U.S. EPA benchmark dose software was compared to the software by Crump and the software by Kalliomaa. Dose-response and dose-effect data on the liver, kidneys, central nervous system (CNS), and tumours were selected for the evaluation. Based on the present study the U.S. EPA software is preferable to the other softwares for dichotomous data. A wider range in benchmark doses was often observed for dichotomous data when the numbers of dose levels were limited. The log-logistic model in most cases gave the best fit when ranking the dichotomous models. In addition, the log-logistic model often implied a more conservative benchmark dose. For continuous data it was more difficult to find a model describing the data. The softwares by Kalliomaa and by the U.S. EPA offered the best opportunities for benchmark dose modelling of continuous data. Flexible models, like the Hill- and the Mult model, are needed for S-shaped continuous data but these models demand more dose levels in order to describe the data. Since the number of dose levels are important for model selection study design is important and should be further evaluated.

Health effects of urban air pollutants. Guideline values and conditions in Sweden

Abstract The level of sulphur dioxide in cities has declined in many countries, and in Sweden it hardly constitutes a health problem any more. The level of nitrogen dioxide, on the contrary, has not declined. The guideline value for nitrogen dioxide is exceeded in areas with high traffic density, and may be close to the level where asthmatics could be affected. The guideline value for carbon monoxide can also be exceeded in such places and give symptoms in persons with heart and lung diseases. Levels of ozone are enhanced in the southern part of Sweden during summertime and are periodically in the range where irritation symptoms can be expected. Generally, there is an increased lung cancer incidence in cities compared to rural areas. In Sweden, it has been estimated that about 100 lung cancer cases annually may be attributed to air pollutants. Lead has been emitted in high amounts in urban areas due to the use of leaded gasoline. The blood lead levels are now declining in the population of Sweden due to reduced emissions, and are generally well below the levels where damage to the developing brain in children may occur. Environmental objectives have been set up for Sweden aiming at reductions of air pollutants by different means. If fulfilled, these plans will lead to reduced air pollutant concentrations in urban areas, which will reduce the risk for health effects in the general population.

Retinol (vitamin A) inhibits the mutagenicity of o-aminoazotoluene activated by liver microsomes from several species in the Ames test

Retinol (vitamin A) has earlier been shown to inhibit the mutagenicity of o-aminoazotoluene (OAAT) in the Salmonella/microsome assay when OAAT is activated with S9 from Sprague-Dawley rats. The results presented in this paper confirm this and also show that S9 from mice, hamsters and gerbils activates OAAT to mutagenic metabolites detected by Salmonella typhimurium TA100. However, S9 from rabbits is inactive. The S9 fraction from rabbits also shows a low aryl hydrocarbon hydroxylase (AHH) activity. The AHH activity or protein content of the microsomal fraction cannot be used to predict the activating capacity of S9 from the other species. Retinol, added in vitro, inhibits the mutagenic effect of OAAT activated by mouse, gerbil or hamster S9. The strongest inhibition is observed with hamster S9 while the inhibition of mouse and gerbil S9 is lower but still higher than in the rat.