Soy biodiesel emissions have reduced inflammatory effects compared to diesel emissions in healthy and allergic mice

Concordance between In Vitro and In Vivo Relative Toxic Potencies of Diesel Exhaust Particles from Different Biodiesel Blends

Diesel exhaust particles (DEPs) contribute to air pollution exposure-related adverse health impacts. Here, we examined in vitro, and in vivo toxicities of DEPs from a Caterpillar C11 heavy-duty diesel engine emissions using ultra-low-sulfur diesel (ULSD) and biodiesel blends (20% v/v) of canola (B20C), soy (B20S), or tallow-waste fry oil (B20T) in ULSD. The in vitro effects of DEPs (DEPULSD, DEPB20C, DEPB20S, and DEPB20T) in exposed mouse monocyte/macrophage cells (J774A.1) were examined by analyzing the cellular cytotoxicity endpoints (CTB, LDH, and ATP) and secreted proteins. The in vivo effects were assessed in BALB/c mice (n = 6/group) exposed to DEPs (250 µg), carbon black (CB), or saline via intratracheal instillation 24 h post-exposure. Bronchoalveolar lavage fluid (BALF) cell counts, cytokines, lung/heart mRNA, and plasma markers were examined. In vitro cytotoxic potencies (e.g., ATP) and secreted TNF-α were positively correlated (p < 0.05) with in vivo inflammatory potency (BALF cytokines, lung/heart mRNA, and plasma markers). Overall, DEPULSD and DEPB20C appeared to be more potent compared to DEPB20S and DEPB20T. These findings suggested that biodiesel blend-derived DEP potencies can be influenced by biodiesel sources, and inflammatory process- was one of the potential underlying toxicity mechanisms. These observations were consistent across in vitro and in vivo exposures, and this work adds value to the health risk analysis of cleaner fuel alternatives.

Respiratory Health Effects of In Vivo Sub-Chronic Diesel and Biodiesel Exhaust Exposure

Biodiesel, which can be made from a variety of natural oils, is currently promoted as a sustainable, healthier replacement for commercial mineral diesel despite little experimental data supporting this. The aim of our research was to investigate the health impacts of exposure to exhaust generated by the combustion of diesel and two different biodiesels. Male BALB/c mice (n = 24 per group) were exposed for 2 h/day for 8 days to diluted exhaust from a diesel engine running on ultra-low sulfur diesel (ULSD) or Tallow or Canola biodiesel, with room air exposures used as control. A variety of respiratory-related end-point measurements were assessed, including lung function, responsiveness to methacholine, airway inflammation and cytokine response, and airway morphometry. Exposure to Tallow biodiesel exhaust resulted in the most significant health impacts compared to Air controls, including increased airway hyperresponsiveness and airway inflammation. In contrast, exposure to Canola biodiesel exhaust resulted in fewer negative health effects. Exposure to ULSD resulted in health impacts between those of the two biodiesels. The health effects of biodiesel exhaust exposure vary depending on the feedstock used to make the fuel.

Zebrafish irritant responses to wildland fire-related biomass smoke are influenced by fuel type, combustion phase, and byproduct chemistry

Human exposure to wildfire-derived particulate matter (PM) is linked to adverse health outcomes; however, little is known regarding the influence of biomass fuel type and burn conditions on toxicity. The aim of this study was to assess the irritant potential of extractable organic material (EOM) of biomass smoke condensates from five fuels (eucalyptus, pine, pine needle, peat, or red oak), representing various fire-prone regions of the USA, burned at two temperatures each [flaming (approximately 640°C) or (smoldering approximately 500°C)] using a locomotor assay in zebrafish (Danio rerio) larvae. It was postulated that locomotor responses, as measures of irritant effects, might be dependent upon fuel type and burn conditions and that these differences relate to combustion byproduct chemistry. To test this, locomotor activity was tracked for 60 min in 6-day-old zebrafish larvae (25-32/group) immediately after exposure to 0.4% dimethyl sulfoxide (DMSO) vehicle or EOM from the biomass smoke condensates (0.3-30 µg EOM/ml; half-log intervals). All EOM samples produced concentration-dependent irritant responses. Linear regression analysis to derive rank-order potency indicated that on a µg PM basis, flaming pine and eucalyptus were the most irritating. In contrast, on an emission-factor basis, which normalizes responses to the amount of PM produced/kg of fuel burned, smoldering smoke condensates induced greater irritant responses (>100-fold) than flaming smoke condensates, with smoldering pine being the most potent. Importantly, irritant responses significantly correlated with polycyclic aromatic hydrocarbon (PAH) content, but not with organic carbon or methoxyphenols. Data indicate that fuel type and burn condition influence the quantity and chemical composition of PM as well as toxicity.

Diesel exhaust impairs TREM2 to dysregulate neuroinflammation

Background

Air pollution has been linked to neurodegenerative diseases, including Alzheimer’s disease (AD), and the underlying neuroimmune mechanisms remain poorly understood. TREM2 is a myeloid cell membrane receptor that is a key regulator of disease-associated microglia (DAM) cells, where loss-of-function TREM2 mutations are associated with an increased risk of AD. At present, the basic function of TREM2 in neuroinflammation is a point of controversy. Further, the impact of air pollution on TREM2 and the DAM phenotype is largely unknown. Using diesel exhaust (DE) as a model of urban air pollution exposure, we sought to address its impact on TREM2 expression, the DAM phenotype, the association of microglia with the neurovasculature, and the role of TREM2 in DE-induced neuroinflammation.

Methods

WYK rats were exposed for 4 weeks to DE (0, 50, 150, 500 μg/m³) by inhalation. DE particles (DEP) were administered intratracheally once (600 μg/mouse) or 8 times (100 μg/mouse) across 28 days to male mice (Trem2^+/+, Trem2^−/−, PHOX^+/+, and PHOX^−/−).

Results

Rats exposed to DE exhibited inverted-U patterns of Trem2 mRNA expression in the hippocampus and frontal cortex, while TREM2 protein was globally diminished, indicating impaired TREM2 expression. Analysis of DAM markers Cx3Cr1, Lyz2, and Lpl in the frontal cortex and hippocampus showed inverted-U patterns of expression as well, supporting dysregulation of the DAM phenotype. Further, microglial-vessel association decreased with DE inhalation in a dose-dependent manner. Mechanistically, intratracheal administration of DEP increased Tnf (TNFα), Ncf1 (p47^PHOX), and Ncf2 (p67^PHOX) mRNA expression in only Trem2^+/+ mice, where Il1b (IL-1β) expression was elevated in only Trem2^−/− mice, emphasizing an important role for TREM2 in DEP-induced neuroinflammation.

Conclusions

Collectively, these findings reveal a novel role for TREM2 in how air pollution regulates neuroinflammation and provides much needed insight into the potential mechanisms linking urban air pollution to AD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-020-02017-7.

Inflammation, oxidative stress and genotoxicity responses to biodiesel emissions in cultured mammalian cells and animals

Biodiesel fuels are alternatives to petrodiesel, especially in the transport sector where they have lower carbon footprint. Notwithstanding the environmental benefit, biodiesel fuels may have other toxicological properties than petrodiesel. Particulate matter (PM) from petrodiesel causes cancer in the lung as a consequence of delivery of genotoxic polycyclic aromatic hydrocarbons, oxidative stress and inflammation. We have reviewed articles from 2002 to 2019 (50% of the articles since 2015) that have described toxicological effects in terms of genotoxicity, oxidative stress and inflammation of biodiesel exhaust exposure in humans, animals and cell cultures. The studies have assessed first generation biodiesel from different feedstock (e.g. rapeseed and soy), certain second generation fuels (e.g. waste oil), and hydrogenated vegetable oil. It is not possible to rank the potency of toxicological effects of specific biodiesel fuels. However, exposure to biodiesel exhaust causes oxidative stress, inflammation and genotoxicity in cell cultures. Three studies in animals have not indicated genotoxicity in lung tissue. The database on oxidative stress and inflammation in animal studies is larger (13 studies); ten studies have reported increased levels of oxidative stress biomarkers or inflammation, although the effects have been modest in most studies. The cell culture and animal studies have not consistently shown a different potency in effect between biodiesel and petrodiesel exhausts. Both increased and decreased potency have been reported, which might be due to differences in feedstock or combustion conditions. In conclusion, combustion products from biodiesel and petrodiesel fuel may evoke similar toxicological effects on genotoxicity, oxidative stress and inflammation.

Are asthmatics more sensitive to irritants?

Asthma is a heterogeneous inflammatory disease characterized by increased airway hyper-responsiveness to external stimuli such as irritants. One may speculate that asthmatics are more sensitive to irritants in the air than healthy subjects, i.e. react at lower concentrations. We reviewed the scientific support for this speculation and investigated to what extent asthma is considered when setting exposure limits and guidance values. We found that the experimental studies comparing healthy and asthmatic subjects are often inconclusive. Still, the available studies are underused, by expert committees and industry alike. Data for a few irritants suggest that asthmatics are up to three-fold more sensitive than the healthy. The most abundant data were found for sulfur dioxide. Here, a benchmark concentration analysis suggests a nine-fold difference in sensitivity. Based on these data a default assessment factor of 10 is suggested when setting exposure limits and guidance values for irritants.

Biodiesel fuels: A greener diesel? A review from a health perspective

Biodiesels have been promoted as a greener alternative to diesel with decreased emissions and health effects. To investigate the scientific basis of the suggested environmental and health benefits offered by biodiesel, this review examines the current state of knowledge and key uncertainties of pollutant profiles of biodiesel engine exhaust and the associated the respiratory and cardiovascular outcomes. The ease and low cost of biodiesel production has facilitated greater distribution and commercial use. The pollutant profile of biodiesel engine exhaust is distinct from diesel, characterised by increased NOx and aldehyde emissions but decreased CO and CO₂. Lower engine-out particulate matter mass concentrations have also been observed over a range of feedstocks. However, these reduced emissions have been attributable to a shift towards smaller sized particulate emissions. The toxicity of biodiesel engine exhaust has been investigated in vitro using various lung cell, in vivo evaluating responses induced in animals and through several human exposure studies. Discrepancies exist across results reported by in vitro and in vivo studies, which may be attributable to differences in biodiesel feedstocks, engine characteristics, operating conditions or use of aftertreatment systems across test scenarios. The limited human testing further suggests short-term exposure to biodiesel engine exhaust is associated with cardiopulmonary outcomes that are comparable to diesel. Additional information about the health effects of biodiesel engine exhaust exposure is required for effective public health policy.

Inflammatory and functional responses after (bio)diesel exhaust exposure in allergic sensitized mice. A comparison between diesel and biodiesel

Many cities fail to meet air quality standards, which results in increased risk for pulmonary disorders, including asthma. Human and experimental studies have shown that diesel exhaust (DE) particles are associated with worsening of allergic asthma. Biodiesel (BD), a cleaner fuel from renewable sources, was introduced in the eighties. Because of the reduction in particulate matter (PM) emissions, BD was expected to cause fewer adverse pulmonary effects. However, only limited data on the effect of BD emissions in asthma are available.

OBJECTIVE

Determine whether BD exhaust exposure in allergic sensitized mice leads to different effects on inflammatory and functional responses compared to DE exposure.

METHODS

Balb/C mice were orotracheally sensitized with House Dust Mite (HDM) or a saline solution with 3 weekly instillations. From day 9 until day 17 after sensitization, they were exposed daily to filtered air (FA), DE and BD exhaust (concentration: 600 μg/m³ PM_2.5). Lung function, bronchoalveolar lavage fluid (BALF) cell counts, cytokine levels (IL-2, IL-4, IL-5, IL-17, TNF-α, TSLP) in the BALF, peribronchiolar eosinophils and parenchymal macrophages were measured.

RESULTS

HDM-sensitized animals presented increased lung elastance (p = 0.046), IgG1 serum levels (p = 0.029), peribronchiolar eosinophils (p = 0.028), BALF levels of total cells (p = 0.020), eosinophils (p = 0.028), IL-5 levels (p = 0.002) and TSLP levels (p = 0.046) in BALF. DE exposure alone increased lung elastance (p = 0.000) and BALF IL-4 levels (p = 0.045), whereas BD exposure alone increased BALF TSLP levels (p = 0.004). BD exposure did not influence any parameters after HDM challenge, while DE exposed animals presented increased BALF levels of total cells (p = 0.019), lymphocytes (p = 0.000), neutrophils (p = 0.040), macrophages (p = 0.034), BALF IL-4 levels (p = 0.028), and macrophagic inflammation in the lung tissue (p = 0.037), as well as decreased IgG1 (p = 0.046) and IgG2 (p = 0.043) levels when compared to the HDM group.

CONCLUSION

The results indicate more adverse pulmonary effects of DE compared to BD exposure in allergic sensitized animals.

Mutagenicity emission factors of canola oil and waste vegetable oil biodiesel: Comparison to soy biodiesel

Canola (or rapeseed) oil and waste vegetable oil (WVO) are used commonly to make biodiesel fuels composed completely from these oils (B100) or as blends with petroleum diesel (B0). However, no studies have reported the mutagenic potencies of the particulate matter with diameter ≤2.5 μm (PM_2.5) or the mutagenicity emission factors, such as revertants/MJ_thermal (rev/MJ_th) for these biodiesel emissions. Using strains TA98 and TA100 with the Salmonella (Ames) mutagenicity assay, we determined these metrics for organic extracts of PM_2.5 of emissions from biodiesel containing 5% soy oil (soy B5); 5, 20, 50, and 100% canola (canola B5, B20, B50, B100), and 100% waste vegetable oil (WVO B100). The mutagenic potencies (rev/mg PM_2.5) of the canola B100 and WVO B100 emissions were generally greater than those of B0, whereas the mutagenicity emission factors (rev/MJ_th, rev/kg fuel, and rev/m³) were less, reflecting the lower PM emissions of the biodiesels relative to B0. Nearly all the rev/mg PM_2.5 and rev/MJ_th values were greater in TA98 with S9 than without S9, indicating a relatively greater role for polycyclic aromatic hydrocarbons, which require S9, than nitroarenes, which do not. In TA100 -S9, the rev/mg PM_2.5 and rev/MJ_th for the biodiesels were generally ≥ to those of B0, indicating that most of these biodiesels produced more direct-acting, base-substitution mutagenic activity than did B0. For B100 biodiesels and petroleum diesel, the rev/MJ_th in TA98 + S9 ranked: petroleum diesel > canola > WVO > soy. The diesel emissions generally had rev/MJ_th values orders of magnitude higher than those of large utility-scale combustors (natural gas, coal, oil, or wood) but orders of magnitude lower than those of inefficient open burning (e.g., residential wood fireplaces). These comparative data of the potential health effects of a variety of biodiesel fuels will help inform the life-cycle assessment and use of biodiesel fuels.

Lung effects of 7- and 28-day inhalation exposure of rats to emissions from 1st and 2nd generation biodiesel fuels with and without particle filter - The FuelHealth project

Increased use of 1st and 2nd generation biofuels raises concerns about health effects of new emissions. We analyzed cellular and molecular lung effects in Fisher 344 rats exposed to diesel engine exhaust emissions (DEE) from a Euro 5-classified diesel engine running on B7: petrodiesel fuel containing 7% fatty acid methyl esters (FAME), or SHB20 (synthetic hydrocarbon biofuel): petrodiesel fuel containing 7% FAME and 13% hydrogenated vegetable oil. The Fisher 344 rats were exposed for 7 consecutive days (6 h/day) or 28 days (6 h/day, 5 days/week), both with and without diesel particle filter (DPF) treatment of the exhaust in whole body exposure chambers (n = 7/treatment). Histological analysis and analysis of cytokines and immune cell numbers in bronchoalveolar lavage fluid (BALF) did not reveal adverse pulmonary effects after exposure to DEE from B7 or SHB20 fuel. Significantly different gene expression levels for B7 compared to SHB20 indicate disturbed redox signaling (Cat, Hmox1), beta-adrenergic signaling (Adrb2) and xenobiotic metabolism (Cyp1a1). Exhaust filtration induced higher expression of redox genes (Cat, Gpx2) and the chemokine gene Cxcl7 compared to non-filtered exhaust. Exposure time (7 versus 28 days) also resulted in different patterns of lung gene expression. No genotoxic effects in the lungs were observed. Overall, exposure to B7 or SHB20 emissions suggests only minor effects in the lungs.

Inflammatory marker and aryl hydrocarbon receptor-dependent responses in human macrophages exposed to emissions from biodiesel fuels

Biodiesel or renewable diesel fuels are alternative fuels produced from vegetable oil and animal tallow that are being considered to help reduce the use of petroleum-based fuels and emissions of air pollutants including greenhouse gases. Here, we analyzed the gene expression of inflammatory marker responses and the cytochrome P450 1A1 (CYP1A1) enzyme after exposure to diesel and biodiesel emission samples generated from an in-use heavy-duty diesel vehicle. Particulate emission samples from petroleum-based California Air Resource Board (CARB)-certified ultralow sulfur diesel (CARB ULSD), biodiesel, and renewable hydro-treated diesel all induced inflammatory markers such as cyclooxygenase-2 (COX)-2 and interleukin (IL)-8 in human U937-derived macrophages and the expression of the xenobiotic metabolizing enzyme CYP1A1. Furthermore, the results indicate that the particle emissions from CARB ULSD and the alternative diesel fuel blends activate the aryl hydrocarbon receptor (AhR) and induce CYP1A1 in a dose- and AhR-dependent manner which was supported by the AhR luciferase reporter assay and gel shift analysis. Based on a per mile emissions with the model year 2000 heavy duty vehicle tested, the effects of the alternative diesel fuel blends emissions on the expression on inflammatory markers like IL-8 and COX-2 tend to be lower than emission samples derived from CARB ULSD fuel. The results will help to assess the potential benefits and toxicity from biofuel use as alternative fuels in modern technology diesel engines.

High-Throughput Video Processing of Heart Rate Responses in Multiple Wild-type Embryonic Zebrafish per Imaging Field

Heart rate assays in wild-type zebrafish embryos have been limited to analysis of one embryo per video/imaging field. Here we present for the first time a platform for high-throughput derivation of heart rate from multiple zebrafish (Danio rerio) embryos per imaging field, which is capable of quickly processing thousands of videos and ideal for multi-well platforms with multiple fish/well. This approach relies on use of 2-day post fertilization wild-type embryos, and uses only bright-field imaging, circumventing requirement for anesthesia or restraint, costly software/hardware, or fluorescently-labeled animals. Our original scripts (1) locate the heart and record pixel intensity fluctuations generated by each cardiac cycle using a robust image processing routine, and (2) process intensity data to derive heart rate. To demonstrate assay utility, we exposed embryos to the drugs epinephrine and clonidine, which increased or decreased heart rate, respectively. Exposure to organic extracts of air pollution-derived particulate matter, including diesel or biodiesel exhausts, or wood smoke, all complex environmental mixtures, decreased heart rate to varying degrees. Comparison against an established lower-throughput method indicated robust assay fidelity. As all code and executable files are publicly available, this approach may expedite cardiotoxicity screening of compounds as diverse as small molecule drugs and complex chemical mixtures.

The potential of omics approaches to elucidate mechanisms of biodiesel-induced pulmonary toxicity

BACKGROUND

Combustion of biodiesels in place of fossil diesel (FD) has been proposed as a method of reducing transport-related toxic emissions in Europe. While biodiesel exhaust (BDE) contains fewer hydrocarbons, total particulates and carbon monoxide than FD exhaust (FDE), its high nitrogen oxide and ultrafine particle content may still promote pulmonary pathophysiologies.

MAIN BODY

Using a complement of in vitro and in vivo studies, this review documents progress in our understanding of pulmonary responses to BDE exposure. Focusing initially on hypothesis-driven, targeted analyses, the merits and limitations of comparing BDE-induced responses to those caused by FDE exposure are discussed within the contexts of policy making and exploration of toxicity mechanisms. The introduction and progression of omics-led workflows are also discussed, summarising the novel insights into mechanisms of BDE-induced toxicity that they have uncovered. Finally, options for the expansion of BDE-related omics screens are explored, focusing on the mechanistic relevance of metabolomic profiling and offering rationale for expansion beyond classical models of pulmonary exposure.

CONCLUSION

Together, these discussions suggest that molecular profiling methods have identified mechanistically informative, novel and fuel-specific signatures of pulmonary responses to biodiesel exhaust exposure that would have been difficult to detect using traditional, hypothesis driven approaches alone.

Effects of Simulated Smog Atmospheres in Rodent Models of Metabolic and Immunologic Dysfunction

Air pollution is a diverse and dynamic mixture of gaseous and particulate matter, limiting our understanding of associated adverse health outcomes. The biological effects of two simulated smog atmospheres (SA) with different compositions but similar air quality health indexes were compared in a nonobese diabetic rat model (Goto-Kakizaki, GK) and three mouse immune models (house dust mite (HDM) allergy, antibody response to heat-killed pneumococcus, and resistance to influenza A infection). In GK rats, both SA-PM (high particulate matter) and SA-O3 (high ozone) decreased cholesterol levels immediately after a 4-h exposure, whereas only SA-O3 increased airflow limitation. Airway responsiveness to methacholine was increased in HDM-allergic mice compared with nonallergic mice, but exposure to SA-PM or SA-O3 did not significantly alter responsiveness. Exposure to SA-PM did not affect the IgM response to pneumococcus, and SA-O3 did not affect virus titers, although inflammatory cytokine levels were decreased in mice infected at the end of a 7-day exposure. Collectively, acute SA exposures produced limited health effects in animal models of metabolic and immune diseases. Effects of SA-O3 tended to be greater than those of SA-PM, suggesting that gas-phase components in photochemically derived multipollutant mixtures may be of greater concern than secondary organic aerosol PM.

Differential exposure and acute health impacts of inhaled solid-fuel emissions from rudimentary and advanced cookstoves in female CD-1 mice

BACKGROUND

There is an urgent need to provide access to cleaner end user energy technologies for the nearly 40% of the world's population who currently depend on rudimentary cooking and heating systems. Advanced cookstoves (CS) are designed to cut emissions and solid-fuel consumption, thus reducing adverse human health and environmental impacts.

STUDY PREMISE

We hypothesized that, compared to a traditional (Tier 0) three-stone (3-S) fire, acute inhalation of solid-fuel emissions from advanced natural-draft (ND; Tier 2) or forced-draft (FD; Tier 3) stoves would reduce exposure biomarkers and lessen pulmonary and innate immune system health effects in exposed mice.

RESULTS

Across two simulated cooking cycles (duration ~ 3h), emitted particulate mass concentrations were reduced 80% and 62% by FD and ND stoves, respectively, compared to the 3-S fire; with corresponding decreases in particles visible within murine alveolar macrophages. Emitted carbon monoxide was reduced ~ 90% and ~ 60%, respectively. Only 3-S-fire-exposed mice had increased carboxyhemoglobin levels. Emitted volatile organic compounds were FD ≪ 3-S-fire ≤ ND stove; increased expression of genes involved in xenobiotic metabolism (COX-2, NQO1, CYP1a1) was detected only in ND- and 3-S-fire-exposed mice. Diminished macrophage phagocytosis was observed in the ND group. Lung glutathione was significantly depleted across all CS groups, however the FD group had the most severe, ongoing oxidative stress.

CONCLUSIONS

These results are consistent with reports associating exposure to solid fuel stove emissions with modulation of the innate immune system and increased susceptibility to infection. Lower respiratory infections continue to be a leading cause of death in low-income economies. Notably, 3-S-fire-exposed mice were the only group to develop acute lung injury, possibly because they inhaled the highest concentrations of hazardous air toxicants (e.g., 1,3-butadiene, toluene, benzene, acrolein) in association with the greatest number of particles, and particles with the highest % organic carbon. However, no Tier 0-3 ranked CS group was without some untoward health effect indicating that access to still cleaner, ideally renewable, energy technologies for cooking and heating is warranted.

A paler shade of green? The toxicology of biodiesel emissions: Recent findings from studies with this alternative fuel

BACKGROUND

Biodiesel produced primarily from plants and algal feedstocks is believed to have advantages for production and use compared to petroleum and to some other fuel sources. There is some speculation that exposure to biodiesel combustion emissions may not induce biological responses or health effects or at a minimum reduce the effects relative to other fuels. In evaluating the overall environmental and health effects of biodiesel production to end use scenario, empirical data or modeling data based on such data are needed.

SCOPE OF REVIEW

This manuscript examines the available toxicology reports examining combustion derived biodiesel emissions since approximately 2007, when our last review of the topic occurred. Toxicity derived from other end uses of biodiesel - e.g., spills, dermal absorption, etc. - are not examined. Findings from biodiesel emissions are roughly divided into three areas: whole non-human animal model exposures; in vitro exposures of mammalian and bacterial cells (used for mutation studies primarily); and human exposures in controlled or other exposure fashions.

MAJOR CONCLUSIONS

Overall, these more current studies clearly demonstrate that biodiesel combustion emission exposure- to either 100% biodiesel or a blend in petroleum diesel- can induce biological effects. There are reports that show biodiesel exposure generally induces more effects or a greater magnitude of effect than petroleum diesel, however there are also a similar number of reports showing the opposite trend. It is unclear whether effects induced by exposure to a blend are greater than exposure to 100% biodiesel. Taken together, the evidence suggest biodiesel emissions can have some similar effects as diesel emissions on inflammatory, vascular, mutagenic, and other responses.

GENERAL SIGNIFICANCE

While acute biodiesel exposures can show toxicity with a variety of endpoints, the potential effects on human health need further validation. Additionally there are few or no findings to date on whether biodiesel emissions can induce effects or even a weaker response that petroleum diesel with repeated exposure scenarios such as in an occupational setting. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu.

Comparative toxicity and mutagenicity of soy-biodiesel and petroleum-diesel emissions: overview of studies from the U.S. EPA, Research Triangle Park, NC

Biodiesel use as a fuel is increasing globally as an alternate to petroleum sources. To comprehensively assess the effects of the use of biodiesel as an energy source, end stage uses of biodiesel such as the effects of inhalation of combusted products on human health must be incorporated. To date, few reports concerning the toxicological effects of the emissions of combusted biodiesel or blends of biodiesel on surrogates of health effects have been published. The relative toxicity of the combusted biodiesel emissions compared to petroleum diesel emissions with short term exposures is also not well known. To address the paucity of findings on the toxicity of combusted biodiesel emissions, studies were undertaken at the U.S. Environmental Protection Agency laboratories in Research Triangle Park, North Carolina. The studies used a variety of approaches with nonhuman animal models to examine biological responses of the lung and cardiovascular systems induced by acute and repeated exposures to pure biodiesel and biodiesel blended with petroleum diesel. Effects of the emissions on induction of mutations in bacterial test strains and mammalian DNA adducts were also characterized and normalized to engine work load. The emissions were characterized as to the physicochemical composition in order to determine the magnitude of the differences among the emissions utilized in the studies. This article summarizes the major finding of these studies which are contained within this special issue of Inhalation Toxicology. The findings provided in these articles provide information about the toxicity of biodiesel emissions relative to petroleum diesel emissions and which can be utilized in a life cycle analyses of the effects of increased biodiesel usage.