• Energy Research

PLoS one 11(9), e0163862 (2016). doi:10.1371/journal.pone.0163862 Published by PLoS, Lawrence, Kan.

Coals contain native polycyclic aromatic compounds (PACs), which include polycyclic aromatic hydrocarbons (PAHs), and heterocyclic aromatic compounds (NSO-PACs) in considerably varying amounts up to 2500 mg/kg. Whereas PAC bioavailability and toxicity from coals are generally considered to be low, few studies have considered potential variations arising from the composition of different coal types including native PAC content. In the present study, fine particles of different coal types exhibiting variable properties were systematically investigated regarding their PAC bioavailability. PAH content reached up to 79 mg/kg EPA-PAH and 865 mg/kg total PAH. Determination of the toxic potential of extracted PACs in bioassays showed inhibition of Caenorhabditis elegans reproduction (up to 94%) and increased mortality of Danio rerio embryos (up to 100%) after exposure to extracts from lignite, sub-bituminous, and bituminous coals. Anthracite extracts showed no effects. Contact assays using whole coal samples revealed no toxicity to D. rerio embryos in any of the coal samples, suggesting low bioavailability of PACs. In contrast, C. elegans reproduction was inhibited by direct coal contact; however, the observed toxicity probably resulted from other coal effects. The results suggest that despite the high toxic potential of PACs present, their bioavailability from different coal types is very limited and independent of coal properties and native PAH content.

Investigations of the bioavailability and toxicity of polycyclic aromatic compounds (PAC) have rarely considered the heterogeneity of coals and the impact of more polar PAC besides polycyclic aromatic hydrocarbons (PAH). Earlier, we investigated the toxicity of eight heterogeneous coals and their extracts. In the present study, the hazard potential with respect to mechanism-specific toxicity of polar fractions of dichloromethane extracts from coals was studied. Polar extract fractions of all coal types except for anthracite induced EROD activity (determined in RTL-W1 cells), independent of coal type (Bio-TEQs between 23 ± 16 and 52 ± 22 ng/g). The polar fractions of all bituminous coal extracts revealed mutagenic activity (determined using the Ames Fluctuation test). No significant mutation induction was detected for the polar extract fractions from the lignite, sub-bituminous coal and anthracite samples, which indicates a higher dependency on coal type for polar PAC here. Additionally, information on bioavailability was derived from a bioaccumulation test using the deposit-feeding oligochaete Lumbriculus variegatus which was exposed for 28 days to ground coal samples. Despite the high toxic potential of most coal extracts and a reduced biomass of Lumbriculus in bituminous coal samples, bioaccumulation of PAH and mortality after 28 days were found to be low. Limited bioaccumulation of PAH (up to 3.6 ± 3.8 mg/kg EPA-PAH) and polar PAC were observed for all coal samples. A significant reduction of Lumbriculus biomass was observed in the treatments containing bituminous coals (from 0.019 ± 0.004 g to 0.046 ± 0.011 g compared to 0.080 ± 0.025 g per replicate in control treatments). We conclude that bioavailability of native PAC from coals including polar PAC is low for all investigated coal types. In comparison to lignite, sub-bituminous coals and anthracite, the bioavailability of PAC from bituminous coals is slightly increased.

In the past few years, the development and use of biofuels for the transport sector have attracted growing attention worldwide due to their promising benefits including a reduced dependence on fossil fuels and a potential to slow down the effect of global climate change. Nevertheless, concerns have also started to emerge regarding their potentially adverse environmental impacts and possible effects on human health. In this context, literature research was carried out to obtain an overview of the current research activities on the (eco)toxicological relevance of biofuels. The literature review revealed an increase in research activities on biofuels, in general, especially within the last four years. In contrast, comparatively few research activities were focused on the (eco)toxicological effectiveness of biofuels or their emissions even though this topic will be of great relevance as soon as a biofuel becomes commercially marketed in the future. Furthermore, the results of the available studies vary widely. Several findings on acute and mechanism-specific toxicity indicate less or comparable effects induced by biofuels in comparison to fossil diesel fuels. However, indications for negative impacts that are inducible both by the biofuels themselves and their emissions were found. Based on the data available, an (eco)toxicological relevance or human health risks associated with spills or the use of biofuels currently cannot be ruled out. Therefore, additional experimental studies are necessary to provide a more comprehensive dataset for the identification of future alternative fuels with low environmental impact.

To meet the increasing demand for energy, development of alternative and renewable energy sources, such as bioenergy, has accelerated during the last decade. In this context, biofuels are one potential replacement for fossil fuels, although their impact on the environment has not been widely studied. Only a few studies are available on toxicity of biofuels and biofuel combustion. Furthermore, for a complete understanding of the environmental impact, the entire life cycle of a biofuel has to be analyzed. This study is an exemplary ecotoxicological investigation of a biomass-to-biofuel production process with respect to the generation of environmentally relevant contaminants either by means of biomass pretreatment or microbial activity. Our aim is the demonstration of the suitability of ecotoxicological biotests as part of a comprehensive hazard assessment of biofuels and related samples or processes. Five ecotoxicological endpoints were assayed to determine the impact of four different biomass pretreatments on process substrates and effluent toxicities. Four different test organisms (bacterium, yeast, fish cell line, and fish embryo) from different trophic levels as well as a combination of acute and mechanism-specific biotests were applied to strengthen the ecotoxicological relevance of this investigation. Biotest results revealed cytotoxic, acute embryotoxic and mutagenic effectiveness, and weak estrogenic activity, with biomass toxicity depending on the mechanism of substrate pretreatment. Open microbial communities (reactor microbiomes) involved in the production process decreased the toxicity considerably to levels of the product n-butyric acid due to degradation of inhibiting by-products, verifying their simultaneous biomass conversion and detoxification potential. Our results demonstrate that ecotoxicological biotests are useful tools for the biofuel industries to gain environmental friendliness as a selling point.

In a former study, a German lignite extract exhibited toxicity to Danio rerio and Caenorhabditis elegans and was shown to have mutagenic and dioxin-like activity. Besides the comparatively low content of known toxic polycyclic aromatic hydrocarbons (PAH), highly intensive peaks of m/z 274 and m/z 324 were observed during the chromatographic analysis. These compounds are assumed to be alkylated chrysenes and picenes (3,3,7-trimethyl-1,2,3,4-tetrahydrochrysene, 1,2-(1'-isopropylpropano)-7-methylchrysene and an isomer of the latter, 1,2,9-trimethyl-1,2,3,4-tetrahydropicene and 2,2,9-trimethyl-1,2,3,4-tetrahydropicene). These compounds are intermediates in the diagenetic formation of chrysene and picene from triterpenoids. Due to their general high abundance in lignites and the toxicity observed for the lignite extract, the mechanism-specific toxicity and bioavailability of these compounds were investigated in the present study using the approach of effect-directed analysis. After the separation of the compounds from other PAH, their mutagenic activity (Ames Fluctuation test) and dioxin-like activity (EROD activity) were studied. Both, mutation induction factor (up to 2.9±2.7) and dioxin-like activity (Bio-TEQ of 224±75 pg/g; represents the amount (pg) 2,3,7,8-tetrachlorodibenzo-p-dioxin per g coal that would provoke the same toxic effect) were rather low. Bioavailability estimated by the bioaccumulation test with Lumbriculus variegatus was also very limited. Based on the obtained results, the environmental risk of the highly abundant alkylated chrysenes and picenes in lignites is concluded to be low.

Cyanobacterial blooms are of global concern due to the multiple harmful risks they pose towards aquatic ecosystem and human health. However, information on the fate of organic pollutants mediated by cyanobacterial blooms in eutrophic water remains elusive. In the present study, endocrine disruptive potentials of phytoplankton samples were evaluated throughout a year-long surveillance in a large and eutrophic freshwater lake. Severe cyanobacterial blooms persisted during our sampling campaigns. Estrogenic agonistic, anti-estrogenic, anti-androgenic, and anti-glucocorticogenic effects were observed in the phytoplankton samples using in vitro reporter gene bioassays. 27 endocrine disrupting chemicals (EDCs) of different modes of action were detected in the samples via UPLC-MS/MS system. Results from mass balance analysis indicated that the measured estrogenic activities were greater than the predicted estrogenic potencies from chemical analysis, demonstrating that chemical analysis of targeted EDCs is unable to fully explain the compounds responsible for the observed estrogenicities. Results from Spearman's correlation analysis concluded that the concentrations of ten EDCs in phytoplankton samples were negatively correlated with cyanobacterial biomass, suggesting the potential occurrence of biomass bio-dilution effects of EDCs due to the huge biomass of cyanobacteria during bloom seasons. The present study provided complementary information about the potential endocrine disruptive risks of cyanobacterial blooms, which is important for understanding and regulating EDCs in eutrophic lakes.