Application of Biologically Based Lumping To Investigate the Toxicokinetic Interactions of a Complex Gasoline Mixture

Effect of Gasoline Exposure on Hematological Parameters of Gas Station Workers in Mekelle City, Tigray Region, Northern Ethiopia

Background

The adverse health effects of chronic gasoline exposure may be related to impairment of the hematopoietic system with bone marrow suppression, an increased risk of blood cell morphology abnormality and developing cancer.

Objective

To assess the effect of gasoline exposure on hematological parameters among gas station workers in Mekelle City, Tigray Region, Northern Ethiopia.

Methods

This cross-sectional study was carried out on 43 subjects (exposed group) and 77 subjects (unexposed group) with matched age and sex. Socio-demographic characteristics and duration of exposure data were collected using a structured questionnaire and an observation checklist. Sysmex XP-300 was used for hematological analysis and stained peripheral blood smear was examined for any abnormality. Data were entered and analyzed using SPSS version 23.

Results

Of exposed individuals, 28/43 (65.1%) and 49/77 (63.6%) of controls were males. The average exposure time was 5.19±4.38 years, with an average working hour of 11.74±1.89 hours/day. The mean RBC count (10¹²/L), HCT (%), HGB (g/dl) and platelets count (10⁹/L) of the exposed group were significantly lower (4.88±0.573, 43.29±3.71, 15.04±1.33 and 248.95±58.19) compared with controls (5.35±0.533, 44.95±3.10, 15.59±1.26 and 292.45±62.17) at p<0.05, respectively. The MCH (pg) (30.48±2.06 vs 29.52±1.66) and MCHC (g/dl) (34.83±0.988 vs 34.32±0.927) were significantly higher in the exposed group compared with controls (p<0.05). HCT, RBC, HGB and platelet counts were significantly decreased with increased years of exposure (p<0.05). The peripheral blood film examination revealed basophilic stippling and macrocytosis in 9.3% of the exposed group.

Conclusion

Long-term exposure to gasoline at gas stations affected RBC parameters and platelet count. A significant negative correlation was noted between duration of exposure and HGB, HCT and platelet count, warranting implementation of protective measures at gas stations.

Fire Suppression Agents Combined with Gasoline in Aquatic Ecosystems: A Mixture Approach

Fire suppression agents are recommended for extinguishing fires by flammable liquids and frequently end in water bodies, combined with the fuels. There is a lack of toxicity information on these commercial formulations and the effects of mixtures of fire suppression agents and fuels. The aim of the present study was to evaluate the toxic effects of different fire suppression agents, the gasoline water-soluble fraction (GWSF), and mixtures of each fire suppression agent and GWSF. Individual tests were performed with Daphnia similis and Artemia sp.; the most toxic fire suppression agents to D. similis and Artemia sp. were F-500®, Cold Fire®, Agefoam®, and Kidde Sintex® 1%; the GWSF was the least toxic. The concentration addition model was used to predict the mixture effects and evaluate synergism/antagonism, dose ratio dependence, and dose level dependence. Cold Fire with GWSF showed dose level deviation to D. similis, marked mainly by synergism; for Artemia sp., the dose ratio pattern was predicted, with a synergistic response mainly by Cold Fire. Agefoam and GWSF behaved additively for D. similis and dose ratio for Artemia sp., with synergism being caused by Agefoam. Kidde Sintex 1% with GWSF were dose ratio for both organisms, with Kidde Sintex 1% being responsible for synergism. Our results show that some mixtures of fire suppression agents and GWSF may cause toxicity to aquatic organisms, posing risk in a real environmental scenario, such as a major fire combat. Environ Toxicol Chem 2021;40:767-779. © 2020 SETAC.

Role of Physiologically Based Kinetic modelling in addressing environmental chemical mixtures - A review

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The availability and applicability of Physiologically Based Kinetic (PBK) models for mixtures is reviewed.

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PBK models can support risk assessment of mixtures by incorporating the toxicokinetic processes.

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Quantitative structure-activity relationship (QSAR) models can be used to fill data gaps in PBK modelling.

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PBK models for mixtures can be improved by including various types of interactions.

The role of Physiologically Based Kinetic (PBK) modelling in assessing mixture toxicology has been growing for the last three decades. It has been widely used to investigate and address interactions in mixtures. This review describes the current state-of-the-art of PBK models for chemical mixtures and to evaluate the applications of PBK modelling for mixtures with emphasis on their role in chemical risk assessment. A total of 35 mixture PBK models were included after searching web resources (Scopus, PubMed, Web of Science, and Google Scholar), screening for duplicates, and excluding articles based on eligibility criteria. Binary mixtures and volatile organic compounds accounted for two-thirds of the chemical mixtures identified. The most common exposure route and modelled system were found to be inhalation and rats respectively. Twenty two (22) models were for binary mixtures, 5 for ternary mixtures, 3 for quaternary mixtures, and 5 for complex mixtures. Both bottom-up and top-down PBK modelling approaches are described. Whereas bottom-up approaches are based on a series of binary interactions, top-down approaches are based on the lumping of mixture components. Competitive inhibition is the most common type of interaction among the various types of mixtures, and usually becomes a concern at concentrations higher than environmental exposure levels. It leads to reduced biotransformation that either means a decrease in the amount of toxic metabolite formation or an increase in toxic parent chemical accumulation. The consequence is either lower or higher toxicity compared to that estimated for the mixture based on the additivity principle. Therefore, PBK modelling can play a central role in predicting interactions in chemical mixture risk assessment.

Advancing internal exposure and physiologically-based toxicokinetic modeling for 21st-century risk assessments

Scientifically sound, risk-informed evaluation of chemicals is essential to protecting public health. Systematically leveraging information from exposure, toxicology, and epidemiology studies can provide a holistic understanding of how real-world exposure to chemicals may impact the health of populations, including sensitive and vulnerable individuals and life-stages. Increasingly, public health policy makers are employing toxicokinetic (TK) modeling tools to integrate these data streams and predict potential human health impact. Development of a suite of tools for predicting internal exposure, including physiologically-based toxicokinetic (PBTK) models, is being driven by needs to address large numbers of data-poor chemicals efficiently, translate bioactivity, and mechanistic information from new in vitro test systems, and integrate multiple lines of evidence to enable scientifically sound, risk-informed decisions. New modeling approaches are being designed "fit for purpose" to inform specific decision contexts, with applications ranging from rapid screening of hundreds of chemicals, to improved prediction of risks during sensitive stages of development. New data are being generated experimentally and computationally to support these models. Progress to meet the demand for internal exposure and PBTK modeling tools will require transparent publication of models and data to build credibility in results, as well as opportunities to partner with decision makers to evaluate and build confidence in use of these for improved decisions that promote safe use of chemicals.

A re-evaluation of PETROTOX for predicting acute and chronic toxicity of petroleum substances

The PETROTOX model was developed to perform aquatic hazard assessment of petroleum substances based on substance composition. The model relies on the hydrocarbon block method, which is widely used for conducting petroleum substance risk assessments providing further justification for evaluating model performance. Previous work described this model and provided a preliminary calibration and validation using acute toxicity data for limited petroleum substance. The objective of the present study was to re-evaluate PETROTOX using expanded data covering both acute and chronic toxicity endpoints on invertebrates, algae, and fish for a wider range of petroleum substances. The results indicated that recalibration of 2 model parameters was required, namely, the algal critical target lipid body burden and the log octanol-water partition coefficient (K_OW ) limit, used to account for reduced bioavailability of hydrophobic constituents. Acute predictions from the updated model were compared with observed toxicity data and found to generally be within a factor of 3 for algae and invertebrates but overestimated fish toxicity. Chronic predictions were generally within a factor of 5 of empirical data. Furthermore, PETROTOX predicted acute and chronic hazard classifications that were consistent or conservative in 93 and 84% of comparisons, respectively. The PETROTOX model is considered suitable for the purpose of characterizing petroleum substance hazard in substance classification and risk assessments. Environ Toxicol Chem 2017;36:2245-2252. © 2017 SETAC.

Risk assessment of environmental mixture effects

Determining interactions of multi-component environmental mixtures towards accurate risk assessment.