Toxicity of biodiesel, diesel and biodiesel/diesel blends: comparative sub-lethal effects of water-soluble fractions to microalgae species

Effects of the water-soluble fraction of the mixture fuel oil/diesel on the microalgae Dunaliella tertiolecta through growth

There is evidence that water-soluble fraction (WSF) from fuel oil/diesel mixture affects marine microbiota. In order to establish a sequence of WSF effects during microalgal growth, this work aimed to monitor Dunaliella tertiolecta exposed to WSF during 15 days. Three different pigments (chlorophyll a, lutein, and β-carotene) and four metabolites (protein, lipids, fatty acids, and phenols) were studied, and FTIR spectroscopy was used to determine the biomolecular transitions of lipids and their accumulation. The results show that D. tertiolecta triggered a physiological and biochemical response with changes in growth rate, pigments, phenols, lipids, and proteins of the microalga, although fatty acid profile was unaltered. For all the biochemical parameters altered, there were significant differences with the controls. At the end of the assay, exposed D. tertiolecta showed similar values with the control on all the compounds analyzed, except lipids. FTIR absorbance showed an increase in unsaturated acyl chains within the exposed microalgae, giving support for a possible uptake of hydrocarbons from WSF. Variation in pigments and phenol contents is presented as an integrated antioxidant response to the stress imposed by WSF. Overall, this research provides information about the effects of WSF on D. tertiolecta, and the ability of this microalga to recover after long-term exposure to the water-soluble fraction of fuel oil/diesel.

Microalgae Water Bioremediation: Trends and Hot Topics

The need to reduce costs associated with the production of microalgae biomass has encouraged the coupling of process with wastewater treatment. Emerging pollutants in municipal, industrial, and agricultural wastewaters, ranging from pharmaceuticals to metals, endanger public health and natural resources. The use of microalgae has, in fact, been shown to be an efficient method in water-treatment processes and presents several advantages, such as carbon sequestration, and an opportunity to develop innovative bioproducts with applications to several industries. Using a bibliometric analysis software, SciMAT, a mapping of the research field was performed, analyzing the articles produced between 1981 and 2018, aiming to identifying the hot topics and trends studied until now. The application of microalgae on water bioremediation is an evolving research field that currently focuses on developing efficient and cost-effective treatments methods that also enable the production of add-value products, leading to a blue and circular economy.

Analyzing the toxicity of bisphenol-A to microalgae for ecotoxicological applications

Bisphenol-A (BPA) is a chemical used in the production of polycarbonate plastic and epoxy resins that may be related to the occurrence of human endocrine disorders. The present study aims to indicate a microalgae for use in ecotoxicological tests concerning BPA contamination of aquatic environments by analyzing its toxicity for the freshwater species Pseudokirchneriella subcapitata, and the two marine species Tetraselmis chuii and Skeletonema costatum. The standardization of the test involved determination of suitable nominal concentrations of BPA and the most appropriate species for use as biomarkers. S. costatum and P. subcapitata demonstrated resistance to BPA, features that are not of interest for toxicity markers. T. chuii presented an adequate sensitivity to BPA, compatible with parameters used in human toxicology for this substance, and is indicated as a potential biomarker for the presence of BPA in marine environments. The IC₅₀ of T. chuii was 2.5 μM with R² = 0.9, indicating reliability to demonstrate that low concentrations of BPA has significant toxicity to this species.

Comparative study of phytotoxicity and genotoxicity of soil contaminated with biodiesel, diesel fuel and petroleum

The worldwide spillage of fossil fuels causes an ever-increasing environmental concern due to their resistance to biodegradation and toxicity. The diesel fuel is one of the derivative forms of petroleum that is widely used in the world. Its composition has many aromatic compounds and long hydrocarbons chains, both persistent and hazardous, thus requiring complex microbial dynamics to achieve full biodegradation. At this point, biodiesel has advantages because it is produced from renewable sources. It also has a relatively fast biodegradation. Biodiesel formulation chemically varies according to the raw material used for its production. While vegetable oils tend to have homogeneous proportions of linoleic and oleic fatty acids, animal fats have an heterogeneous distribution of stearic, palmitic and oleic fatty acids. As some studies have already detected the toxic potential of biodiesel from vegetable oil, this study sought information on the phytotoxic and genotoxic potential of animal fat-based biodiesel and compare it with fossil fuel as diesel fuel and crude petroleum. The impacts on the microbial activity of soils contaminated with biodiesel, diesel fuel and crude petroleum were performed by the dehydrogenase activity. Phytotoxicity tests were performed with Eruca sativa seeds and genotoxicity bioassays with Allium cepa seeds. The results showed a rapid assimilation of biodiesel by the autochthonous soil microorganisms. Soil contaminated with either diesel or crude petroleum inhibited the root and hypocotyl elongation of E. sativa. Overall, petroleum contaminated soils showed higher genotoxic potential. Biodiesel from animal fat was rapidly assimilated by soil microorganisms and did not present significant phytotoxic or genotoxic potential, but significantly reduced the mitotic index of A. cepa roots. Our results showed that biodiesel from animal fat have rapid biodegradability. Biodiesel also led to less impacts during seed development and lower genotoxic potential when compared to crude petroleum and diesel fuel. In addition, biodiesel from animal fat does not present the same toxicity demonstrated by biodiesel from soybean-based biodiesel described in current literature.

Comparative assessment of acute and chronic ecotoxicity of water soluble fractions of diesel and biodiesel on Daphnia magna and Aliivibrio fischeri

The widespread use of diesel as a transportation fuel and the introduction of biodiesel into the world energy matrix increase the likelihood of aquatic contamination with these fuels. In this case, it is important to know the environmental impacts caused by water-soluble fraction (WSF) of these fuels, since it is the portion that can result in long-term impacts and affect regions far away from the location of a spill. Therefore, we evaluated and compared the aquatic ecotoxicity of the WSF of biodiesel and diesel through acute ecotoxicity tests with the aquatic microcrustacean Daphnia magna and the marine bacteria Aliivibrio fischeri, as well as chronic ecotoxicity tests with D. magna. The WSF of diesel was 2.5-4 folds more toxic than the WSF of biodiesel in acute ecotoxicity tests. Similarly, a comparison of the chronic ecotoxicity demonstrated that the WSF of diesel was more toxic than the WSF of biodiesel. WSF of diesel causes chronic effects on reproduction, longevity and growth of D. magna (NOEC was 12.5, 12.5, 6.25%, respectively), while WSF of biodiesel did not present significantly different results compared to the control for any of the parameters evaluated in any of the dilutions tested (NOEC> 25%). To the best of our knowledge, this is the first study that compares the chronic ecotoxicity of WSF of diesel and biodiesel on D. magna.

Toxicity bioassay of waste cooking oil-based biodiesel on marine microalgae

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The individual components of the biodiesel had a lower toxicity threshold than in the complex mixture.

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The B20 sample proved to be the most toxic for the red algae P. purpureum.

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The B100 sample showed the highest level of toxicity for the microalgae A. ussuriensis, C. muelleri and H. akashiwo.

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The sample of petroleum diesel B0 showed less toxicity compared to B20 and B100.

The world biodiesel production is increasing at a rapid rate. Despite its perceived safety for the environment, more detailed toxicity studies are mandatory, especially in the field of aquatic toxicology. While considerable attention has been paid to biodiesel combustion emissions, the toxicity of biodiesel in the aquatic environment has been poorly understood. In our study, we used an algae culture growth-inhibition test (OECD 201) for the comparison of the toxicity of B100 (pure biodiesel), produced by methanol transesterification of waste cooking oil (yellow grease), B0 (petroleum diesel fuel) and B20 (diesel-biodiesel blended of 20% biodiesel and 80% petroleum diesel fuel by volume). Two marine diatoms Attheya ussuriensis and Chaetoceros muelleri, the red algae Porphyridium purpureum and Raphidophyte Heterosigma akashiwo were employed as the aquatic test organisms. A sample of biodiesel from waste cooking oil without dilution with petroleum diesel (B100) showed the highest level of toxicity for the microalgae A. ussuriensis, C. muelleri and H. akashiwo, compared to hexane, methanol, petroleum diesel (B0) and diluted sample (B20). The acute EC₅₀ in the growth-inhibition test (96 h exposure) of B100 for the four species was in the range of 3.75–23.95 g/L whereas the chronic toxicity EC₅₀ (7d exposure) was in the range of 0.42–16.09 g/L.

Comparing the Toxicity of Water-Soluble Fractions of Biodiesel, Diesel and 5% Biodiesel/Diesel Blend on Oreochromis niloticus Using Histological Biomarkers

This study estimated end compared the potential toxic effects of the water-soluble fractions (WSF) of biodiesel (B100), diesel and the commercial biodiesel (B5) on Oreochromis niloticus. After a 24 h-exposition to WSF-0% (control) and WSF-serial concentrations of 4.6%, 10%, 22%, 46% and 100%, samples of gill and liver of the exposed fishes were fixed in Bouin's solution, processed, stained using hematoxylin/eosin and analyzed by light-microscopy. WSF-hydrocarbons and methanol contents, analyzed by gas chromatography, were checked against the occurrence of abnormal histopathological alterations. These were not found in the control and WSF-4.6% exposed fishes, while exposures to or above 10%-WSF resulted in histopathological alterations whose severity increased in a dose-dependent manner, being higher in fishes exposed to WSF-diesel, or WSF-B5 when compared to biodiesel. These results, which were corroborated by the chemical analyses, highlighted the histological technique as an appropriate diagnostic tool that can be used for the preservation of water bodies' quality.

Estimation of biodiesel cytotoxicity by using acid phosphatase as a biomarker of lysosomal integrity

Biodiesel is promoted as environmentally less harmful than diesel fuel. Nevertheless its water-soluble-fraction (WSF) may contain methanol, which appears by a reversion of the transesterification reaction, when biodiesel contacts water. This paper evaluated the loss of the lysosomal membrane integrity in liver homogenate of juvenils Tilapia exposed to biodiesels-WSF, through the increase of the acid phosphatase activity, as an evidence of citotoxicity. Differences in the enzyme activity levels (3.4, 2.3 and 0.8 mU mg(-1) total protein over the control value, which was 1.6 mU mg(-1) total protein), found for castor oil, waste cooking-oil and palm oil-biodiesels, respectively, were indicative of their toxicity according to this decreasing trend. WSF-chromatograms suggest the cytotoxicity as related to methanol.