Water-accommodated fractions of crude oil and its mixture with chemical dispersant impairs oxidase stress and energy metabolism disorders in Oryzias melastigma embryos.

In this study, marine medaka (Oryzias melastigma) embryos were exposed to different concentrations of water-accommodated fractions (WAFs) and chemically enhanced water-accommodated fractions (CEWAFs) of Oman crude oil for 14 d by semi-static exposure methods. The effects on growth and development and energy metabolism process were evaluated. Results showed that embryo survival and hatchability were decreased in a dose-dependent manner with an increase in the concentration of petroleum hydrocarbon compounds, whereas the malformation exhibited a dose-dependent increase. Compared to the control, the adenosine triphosphate (ATP) content and Na+-K+-ATPase (NKA) activities of embryos exposed to both WAFs and CEWAFs were reduced, while intracellular reactive oxygen species (ROS) levels and NADH oxidase (NOX) activities were increased. Our study demonstrated that exposure to crude oil dispersed by chemical dispersant affected the growth and development of marine medaka embryos, caused oxidative stress while produced a series of malformations in the body and dysregulation in energy metabolism. In comparison, the toxic effects of chemically dispersed crude oil might be more severe than the oil itself in the equivalent diluted concentration treatment solution. These would provide more valuable and reliable reference data for the use of chemical dispersants in oil spills.

Biomarker responsiveness in Norwegian Sea mussels, Mytilus edulis, exposed at low temperatures to aqueous fractions of crude oil alone and combined with dispersant.

Biological effects of aqueous fractions of a crude oil, alone or in combination with dispersant, were investigated in mussels, Mytilus edulis, exposed at three temperatures (5, 10 and 15 °C). Polycyclic aromatic hydrocarbons (PAHs) tissue concentrations were determined, together with genotoxicity, oxidative stress and general stress biomarkers and the Integrated Biological Response (IBR) index. The bioaccumulation of individual PAHs varied depending on the exposure temperature, with relevant bioaccumulation of phenantrene and fluoranthene at 5 °C and heavier (e.g. 5-rings) PAHs at 15 °C. The values and response profiles of each particular biomarker varied with exposure time, concentration of the oil aqueous fraction and dispersant addition, as well as with exposure temperature. Indeed, PAH bioaccumulation and biomarker responsiveness exhibited specific recognizable patterns in mussels exposed at low temperatures. Thus, genotoxicity was recorded early and transient at 5 °C and delayed but unremitting at 10-15 °C. Catalase activity presented a temperature-dependent response profile similar to the genotoxicity biomarker; however, glutathione-S-transferase responsiveness was more intricate. Lysosomal membrane stability in digestive cells decreased more markedly at 5 °C than at higher temperatures and the histological appearance of the digestive gland tissue was temperature-specific, which was interpreted as the combined effects of PAH toxicity and cold stress. It can be concluded that the profile and level of the biological effects are definitely different at low temperatures naturally occurring in the Arctic/Subarctic region (e.g. 5 °C) than at higher temperatures closer to the thermal optimum of this species (10-15 °C).

The dispersant Corexit 9500 and (dispersed) oil are lethal to coral endosymbionts.

Endosymbionts (Symbiodiniaceae) play a vital role in the health of corals. Seawater pollution can harm these endosymbionts and dispersants used during oil spill cleanup can be extremely toxic to these organisms. Here, we examined the impact of oil and a specific dispersant, Corexit-9500, on two representative endosymbionts - Symbiodinium and Cladocopium - from the Southwestern endemic coral Mussismilia braziliensis. The survival and photosynthetic potential of the endosymbionts decreased dramatically after exposure to the dispersant and oil by ~25 % after 2 h and ~50 % after 7 days. Low concentrations of dispersant (0.005 ml/l) and dispersed oil (Polycyclic Aromatic Hydrocarbons, 1132 µg/l; Total Petroleum Hydrocarbons, 595 µg/l) proved highly toxic to both Symbiodinium and Cladocopium. These levels triggered a reduction in growth rate, cell size, and cell wall thickness. After a few hours of exposure, cellular organelles were damaged or destroyed. These acute toxic effects underline the fragile nature of coral endosymbionts.

Surface active dicationic ionic liquids as green oil spill dispersants.

The utilization of chemical dispersants as a way of mitigating of oil spills in marine eco-system has been extensively documented worldwide. Hence, in this research we have successfully synthesized two amphiphilic asymmetric Dicaionic Ionic Liquids (DILs). The efficacy of these synthesized DILs as dispersants was assessed using the baffled flask test (BFT). The results indicated a dispersant effectiveness ranging from 47.98 % to 79.76 % for the dispersion of heavy crude oil across various temperature ranges (10-30 °C). These dispersant-to-oil ratios (DOR) were maintained at 3: 100 (V%), showcasing promising dispersant capabilities for mitigating heavy crude oil spills. Additionally, acute toxicity tests conducted on Nile tilapia and Oreochromis niloticus have demonstrated the relatively low toxicity of the IL-dispersants, with Lethal Concentration 50 (LC50) values exceeding 100 ppm after 96 h. This suggests a practically slight toxic effect on the tested fish. In summary, the newly developed IL-dispersants are considered to be conducive to environmentally benign oil spill remediation.

Biocompatible and Biodegradable Surfactants from Orange Peel for Oil Spill Remediation.

Oil spill remediation plays a vital role in mitigating the environmental impacts caused by oil spills. The chemical method is one of the widely recognized approaches in chemical surfactants. However, the most commonly used chemical surfactants are toxic and non-biodegradable. Herein, two biocompatible and biodegradable surfactants were synthesized from orange peel using the ionic liquid 1-butyl-3-methylimidazolium chloride (BMIMCl) and organic solvent dimethylacetamide (CH3CN(CH3)2) as reaction media. The acronyms SOPIL and SOPOS refer to the surfactants prepared with BMIMCl and dimethylacetamide, respectively. The surface tension, dispersant effectiveness, optical microscopy, and emulsion stability test were conducted to examine the comparative performance of the synthesized surfactants. The Baffled flask test (BFT) was carried out to determine the dispersion effectiveness. The toxicity test was performed against zebrafish (Danio rerio), whereas the closed bottle test (CBT) evaluated biodegradability. The results revealed that the critical micelle concentration (CMC) value of SOPIL was lower (8.57 mg/L) than that of SOPOS (9.42 mg/L). The dispersion effectiveness values for SOPIL and SOPOS were 69.78% and 40.30%, respectively. The acute toxicity test demonstrated that SOPIL was 'practically non-toxic' with a median lethal concentration of more than 1000 mg/L after 96 h. The biodegradation rate was recorded as higher than 60% for both surfactants within 28 days, demonstrating their readily biodegradable nature. Considering these attributes, biocompatible and biodegradable surfactants derived from orange peel emerge as a promising and sustainable alternative for oil spill remediation.

Reliable assessment of carbon black nanomaterial of a variety of cell culture media for in vitro toxicity assays by asymmetrical flow field-flow fractionation.

Carbon black nanomaterial (CB-NM), as an industrial product with a large number of applications, poses a high risk of exposure, and its impact on health needs to be assessed. The most common testing platform for engineered (E)NMs is in vitro toxicity assessment, which requires prior ENM dispersion, stabilization, and characterization in cell culture media. Here, asymmetric flow field-flow fractionation (AF4) coupled to UV-Vis and dynamic light scattering (DLS) detectors in series was used for the study of CB dispersions in cell culture media, optimizing instrumental variables and working conditions. It was possible to disperse CB in a non-ionic surfactant aqueous solution due to the steric effect provided by surfactant molecules attached on the CB surface which prevented agglomeration. The protection provided by the surfactant or by culture media alone was insufficient to ensure good dispersion stability needed for carrying out in vitro toxicity studies. On the other hand, cell culture media in combination with the surfactant improved dispersion stability considerably, enabling the generation of shorter particles and a more favourable zeta potential magnitude, leading to greater stability due to electrostatic repulsion. It was demonstrated that the presence of amino acids in the culture media improved the monodisperse nature and stability of the CB dispersions, and resulted in a turn towards more negative zeta potential values when the pH was above the amino acid isoelectric point (IEP). Culture media used in real cell culture scenarios were also tested, and in vitro toxicity assays were developed optimizing the compatible amount of surfactant.

The surfactant co-formulant POEA in the glyphosate-based herbicide RangerPro but not glyphosate alone causes necrosis in Caco-2 and HepG2 human cell lines and ER stress in the ToxTracker assay.

The toxicity of co-formulants present in glyphosate-based herbicides (GBHs) has been widely discussed leading to the European Union banning the polyoxyethylene tallow amine (POEA). We identified the most commonly used POEA, known as POE-15 tallow amine (POE-15), in the widely used US GBH RangerPro. Cytotoxicity assays using human intestinal epithelial Caco-2 and hepatocyte HepG2 cell lines showed that RangerPro and POE-15 are far more cytotoxic than glyphosate alone. RangerPro and POE-15 but not glyphosate caused cell necrosis in both cell lines, and that glyphosate and RangerPro but not POE-15 caused oxidative stress in HepG2 cells. We further tested these pesticide ingredients in the ToxTracker assay, a system used to evaluate a compound's carcinogenic potential, to assess their capability for inducing DNA damage, oxidative stress and an unfolded protein response (endoplasmic reticulum, ER stress). RangerPro and POE-15 but not glyphosate gave rise to ER stress. We conclude that the toxicity resulting from RangerPro exposure is thus multifactorial involving ER stress caused by POE-15 along with oxidative stress caused by glyphosate. Our observations reinforce the need to test both co-formulants and active ingredients of commercial pesticides to inform the enactment of more appropriate regulation and thus better public and environmental protection.

Integrative description of changes occurring on zebrafish embryos exposed to water-soluble crude oil components and its mixture with a chemical surfactant.

The effects of crude oil spills are an ongoing problem for wildlife and human health in both marine and freshwater aquatic environments. Bioassays of model organisms are a convenient way to assess the potential risks of the substances involved in oil spills. Zebrafish embryos (ZFE) are a useful to reach a fast and detailed description of the toxicity of the pollutants, including both the components of the crude oil itself and substances that are commonly used for crude oil spill mitigation (e.g. surfactants). Here, we evaluated the survival rate, as well as histological, morphological, and proteomic changes in ZFE exposed to Water Accumulated Fraction (WAF) of light crude oil and in mixture with Dioctyl Sulfosuccinate Sodium (DOSS, e.g. CEWAF: Chemically Enhanced WAF), a surfactant that is frequently used in chemical dispersant formulations. Furthermore, we compared the hydrocarbon concentration of WAF and CEWAF of the sublethal dilution. In histological, morphological, and gene expression variables, the ZFE exposed to WAF showed less changes than those exposed to CEWAF. Proteomic changes were more dramatic in ZFE exposed to WAF, with important alterations in spliceosomal and ribosomal proteins, as well as proteins related to eye and retinal photoreceptor development and heart function. We also found that the concentration of high molecular weight hydrocarbons in water was slighly higher in presence of DOSS, but the low molecular weight hydrocarbons concentration was higher in WAF. These results provide an important starting point for identifying useful crude-oil exposure biomarkers in fish species.

Melatonin-Activated Receptor Signaling Pathways Mediate Protective Effects on Surfactant-Induced Increase in Jejunal Mucosal Permeability in Rats.

A well-functional intestinal mucosal barrier can be compromised as a result of various diseases, chemotherapy, radiation, and chemical exposures including surfactants. Currently, there are no approved drugs targeting a dysfunctional intestinal barrier, which emphasizes a significant medical need. One candidate drug reported to regulate intestinal mucosal permeability is melatonin. However, it is still unclear if its effect is primarily receptor mediated or antioxidative, and if it is associated with enteric neural pathways. The aim of this rat intestinal perfusion study was to investigate the mechanisms of melatonin and nicotinic acetylcholine receptors on the increase in intestinal mucosal clearance of 51Cr-labeled ethylenediaminetetraacetate induced by 15 min luminal exposure to the anionic surfactant, sodium dodecyl sulfate. Our results show that melatonin abolished the surfactant-induced increase in intestinal permeability and that this effect was inhibited by luzindole, a melatonin receptor antagonist. In addition, mecamylamine, an antagonist of nicotinic acetylcholine receptors, reduced the surfactant-induced increase in mucosal permeability, using a signaling pathway not influenced by melatonin receptor activation. In conclusion, our results support melatonin as a potentially potent candidate for the oral treatment of a compromised intestinal mucosal barrier, and that its protective effect is primarily receptor-mediated.

A cross-comparison of biosurfactants as marine oil spill dispersants: Governing factors, synergetic effects and fates.

Biosurfactant-based dispersants (BBDs) may be more effective, cost-efficient and environmentally friendly than dispersants currently used for oil spill response. An improved understanding of BBD performance is needed to advance their development and commercial use. In this study, the ability of four BBDs, i.e. sufactins, trehalose lipids, rhamnolipids and exmulsins, alone and as various combinations to disperse Arabian light crude oil and weathered Alaska North Slope crude oil was compared to a widely used commercial oil dispersant (Corexit 9500A). Surfactin and trehalose lipids, which have balanced surface activity/emulsification ability, showed dispersion efficacy comparable to Corexit 9500A. Rhamnolipids (primarily a surface-active agent) and exmulsins (primarily an emulsifier) when used alone had significantly lower efficacy. However, blends of these surfactants had excellent dispersion performance because of synergistic effects. Balanced surface activity and emulsification ability may be key to formulate effective BBDs. Of the BBDs evaluated, surfactins with an effective dispersant-to-oil ratio as low as 1:62.3 and trehalose lipids with high oil affinity, biodegradation rate, and low toxicity characteristics show the most promise for commercial development.

A new antibacterial nano-system based on hematoporphyrin-carboxymethyl chitosan conjugate for enhanced photostability and photodynamic activity.

To promote bactericidal activity, improve photostability and safety, novel antibacterial nanoparticle system based on photodynamic action (PDA) was prepared here through conjugation of photosensitizer hematoporphyrin (HP) onto carboxymethyl chitosan (CMCS) via amide linkage and followed by ultrasonic treatment. The system was stable in PBS (pH 7.4) and could effectively inhibit the photodegradation of conjugated HP because of aggregation-caused quenching effect. ROS produced by the conjugated HP under light exposure could change the structure of nanoparticles by oxidizing the CMCS skeleton and thereby significantly promote the photodynamic activity of HP and its photodynamic activity after 6 h was higher than that of HP·2HCl under the same conditions. Antibacterial experiments showed that CMCS-HP nanoparticles had excellent photodynamic antibacterial activity, and the bacterial inhibition rates after 60 min of light exposure were greater than 97%. Safety evaluation exhibited that the nanoparticles were safe to mammalian cells, showing great potential for antibacterial therapy.

Ionic liquid-biosurfactant blends as effective dispersants for oil spills: Effect of carbon chain length and degree of saturation.

The well-known toxicity of conventional chemical oil spill dispersants demands the development of alternative and environmentally friendly dispersant formulations. Therefore, in the present study we have developed a pair of less toxic and green dispersants by combining lactonic sophorolipid (LS) biosurfactant individually with choline myristate and choline oleate ionic liquid surfactants. The aggregation behavior of resulted surfactant blends and their dispersion effectiveness was investigated using the baffled flask test. The introduction of long hydrophobic alkyl chain with unsaturation (attached to choline cation) provided synergistic interactions between the binary surfactant mixtures. The maximum dispersion effectiveness was found to be 78.23% for 80:20 (w/w) lactonic sophorolipid-choline myristate blends, and 81.15% for 70:30 (w/w) lactonic sophorolipid-choline oleate blends at the dispersant-to-oil ratio of 1:25 (v/v). The high dispersion effectiveness of lactonic sophorolipid-choline oleate between two developed blends is attributed to the stronger synergistic interactions between surfactants and slower desorption rate of blend from oil-water interface. The distribution of dispersed oil droplets at several DOR were evaluated and it was observed that oil droplets become smaller with increasing DOR. In addition, the acute toxicity analysis of developed formulations against zebra fish (Danio rerio) confirmed their non-toxic behavior with LC50 values higher than 400 ppm after 96 h. Overall, the proposed new blends/formulations could effectively substitute the toxic and unsafe chemical dispersants.

Sensitivity to oil dispersants: Effects on the valve movements of the blue mussel Mytilus edulis and the giant scallop Placopecten magellanicus, in sub-arctic conditions.

In response to accidental oil spills at sea, chemical oil dispersants are utilized to limit negative impacts on nearby littoral zones. However, current evidence suggests that such dispersants may be toxic to aquatic organisms. Blue mussels (Mytilus edulis) and giant scallops (Placopecten magellanicus) were exposed to different environmentally relevant concentrations of oil dispersant and their behavioural responses were closely monitored using high frequency (10Hz) valvometry. Behavioural valve responses included rapid closures when oil dispersant was added to the experimental tanks. At higher concentrations, the mussels remained closed throughout the exposure period. The giant scallop displayed escape behaviours (clapping) prior to mortality, suggesting toxicity of the oil dispersant. Relationships between different behavioural indicators and oil dispersant concentrations were observed for both species, but with different trends. While scallops demonstrated positive correlations between gaping behaviours and dispersant concentration, mussels exhibited a concentration threshold beyond which the gaping behaviour was characteristic of longer closure periods. This study highlights behavioural response differences consistent with bivalve-specific biological traits: the continuous valve closure of an intertidal species, M. edulis, firmly attached to the substrate, and the escapement behaviours of a semi-mobile subtidal species, P. magellanicus. From these observations, it appears that valvometry could be used as a tool for environmental assessments.

Hepatotoxicity of the anionic surfactant linear alkylbenzene sulphonate (LAS) in bullfrog tadpoles.

The liver of anurans play an important role in metabolism, including detoxification, the biotransformation of molecules, and the storage of metabolites. Surfactants are part of domestic and industrial effluents. The effects of linear alkylbenzene sulfonate (LAS) on anuran liver remain unknown, however, some studies have evaluated the effects of LAS on the skin, gills, heart, testes, and liver of fishes. Here, we tested the hypothesis that LAS is hepatotoxic, promoting morphometric alterations in hepatocytes along with inflammation in the tissue, altering hepatic catabolism. We evaluated the effects of a LAS concentration that is considered environmentally safe in Brazilian inland waters on the liver of Lithobates catesbeianus tadpoles, including studies on morphology, morphometry, immunology, and metabolism. LAS exposure promoted enlargement of liver sinusoids and vacuolization of hepatocytes. Exposure to LAS also increased the area of mast cells and melanomacrophages (MMs). Additionally, LAS exposure increased hemosiderin inside MMs, suggesting alterations in the catabolism and storage of iron. Hepatocyte size increased after exposure to LAS, suggesting cytotoxic effects. Integrative analyses (i.e., morphometric, metabolic, and immunological) demonstrated hepatotoxic effects of LAS. These types of studies are key to understanding the negative effects of these substances on tadpole health, as these liver alterations impair anuran homeostasis.

Ecotoxicity of oil sludges and residuals from their washing with surfactants: soil dehydrogenase and ryegrass germination tests.

Oil sludge washing (OSW) with surfactants and co-solvents is used to recover the oil, and this process leaves some residuals (sediments and surfactant solution). Currently, there are no data on the ecotoxicological effects of these OSW residuals from different sludges. This study evaluated the toxicity of OSW residuals from washing four types of oil sludges with five surfactants (Triton X-100 and X-114, Tween 80, sodium dodecyl sulphate (SDS) and rhamnolipid) and a co-solvent (cyclohexane). The toxicity of the residuals was evaluated with the impact on the soil microbial dehydrogenase activity (DHA) and ryegrass (Lolium perenne) seed germination. There was a high DHA detected directly in the sludges and all OSW residual combinations, but this activity could not be attributed to the DHA itself but to some chemical interferences. The DHA was then tested in the soils amended with the OSW residuals to simulate a bioremediation scenario. There were no chemical interferences in this case. In general, the INTF concentrations were significantly higher at low concentrations, 1 and 5% (p < 0.01). There were no significant differences in the DHA at high concentrations of OSW residuals (10, 25 and 50%) which implied that the concentration of the contaminants is not directly proportional to the levels of ecotoxicity. Unexpectedly, the INTF values of the 10, 25 and 50% rhamnolipid-OSW residuals were significantly lower than the Triton X-100 residuals. The ryegrass germination rates were higher than 70% with no apparent phytotoxicity symptoms in the seedlings. Particularly, there was a highly significant negative effect of the residuals on the germination rates at high concentrations (p < 0.01). Given that the extractable petroleum hydrocarbon (EPH) concentrations in the OSW residual-amended soils in both DHA and germination tests were very low (13-21 ppm), other co-contaminants could be contributing to the toxicity. These findings implied that biotreatment techniques can be applied to treat the OSW residuals if necessary.

Integration of untargeted and targeted mass spectrometry-based metabolomics provides novel insights into the potential toxicity associated to surfynol.

The intake of toxic compounds through the diet as a result of migration processes from food packaging is of increasing concern. It has been shown that the surfactant commercially known as surfynol, which is commonly used in food-contact materials, is capable of migrating from multilayer containers into the food, reaching potentially harmful concentration levels. In the present study, the integration of an untargeted and a targeted metabolomics approach has been carried out using NTERA-2 germinal cells as in-vitro model, to make further progress in elucidating the molecular mechanisms associated with the toxicity of surfynol. This study has allowed the identification of different altered metabolites mainly related with energy-acquiring, cell development and cellular defense mechanisms. While glutamine, L-threonine, propanoate, octadecanoate and carbamate were found at higher concentrations in cells exposed tu surfynol, L-valine, oxalate, phosphate, phenylalanine and myoinositol were found inhibited. Additionally, concentrations of ATP, ADP and NAD+ were found significantly inhibited, supporting the idea that surfynol induces glycolysis inactivation. The results obtained strengthen the evidence of the toxicity associated to surfynol; therefore, reinforcing the need for a more comprehensive study on the viability of its use in food packaging.

Modulation of cytotoxicity by consecutive adsorption of tannic acid and pesticides on surfactant functionalized zeolites.

This study investigated the environmental application of FAU type zeolites modified with cationic surfactants (cetylpyridinium chloride, tetrapropylammonium chloride and benzalkonium chloride). Adsorbent characterization was conducted using Fourier-transform infrared and Raman spectroscopy, thermogravimetry and differential thermal analysis, atomic force microscopy and X-ray powder diffraction. The efficiency for tannic acid adsorption from aqueous solution on the surface of prepared composites is studied and the adsorption process was modelled with different isotherm equations. Surfactant modifications of zeolites led to improved adsorption properties compared to FAU zeolites alone. The proposed mechanism controlling the adsorption of tannic acid onto surfactant modified zeolites mainly relies on π-π and hydrophobic interactions. The investigated materials are promising adsorbents for tannic acid and similar phenolics and may be important for environmental and dietary aspects of polyphenol persistence and usage. Further on, functionalized zeolites were studied for insecticide acetamiprid removal, prior to and after tannic acid retention. Promising findings of insecticide co-adsorption with tannic acid led to cytotoxicity evaluation. The cytotoxicity modulation effect of zeolites and tannic acid on acetamiprid points to the essential role of both components in insecticide toxicity reduction.

In Vitro to In Vivo Concordance of Toxicity Using the Human Proximal Tubule Cell Line HK-2.

The renal proximal tubule cell line, human kidney 2 (HK-2), recapitulates many of the functional cellular and molecular characteristics of differentiated primary proximal tubule cells. These features include anchorage dependence, gluconeogenesis capability, and sodium-dependent sugar transport. In order to ascertain how well HK-2 cells can reliably reveal the toxicological profile of compounds having a potential to cause proximal tubule injury in vivo, we sought to evaluate the effects of known proximal tubule toxicants using the HK-2 cell line. We selected 20 pure nephrotoxic compounds that included chemotherapeutic drugs, antibiotics, and heavy metal-containing compounds and evaluated their ability to induce HK-2 cell injury relative to 10 innocuous pure compounds or cell culture media alone. We performed a comprehensive set of in vitro cellular toxicological assays to evaluate cell viability, oxidative stress, mitochondrial integrity, and a specific biomarker of renal injury, Kidney Injury Molecule 1. For each of our selected compounds, we were able to establish a reproducible profile of toxicological outcomes. We compared our results to those described in peer-reviewed publications to understand how well the HK-2 cellular model agrees with overall in vivo rat or human toxicological outcomes. This study begins to address the question of how well in vitro data generated with HK-2 cells can mirror in vivo animal and human outcomes.

Enhanced marine monitoring and toxicity study of oil spill dispersants including Corexit EC9500A in the presence of diluted bitumen.

Observations made for the analysis of the oil spill dispersant tracer dioctyl sulfosuccinate (DOSS) during LC50 toxicity testing, highlighted a stability issue for this tracer compound in seawater. A liquid chromatography high-resolution quadrupole time-of-flight mass spectrometry (LC/QToF) was used to confirm monooctyl sulfosuccinate (MOSS) as the only significant DOSS breakdown product, and not the related isomer, 4-(2-ethylhexyl) 2-sulfobutanedioate. Combined analysis of DOSS and MOSS was shown to be applicable to monitoring of spill dispersants Corexit® EC9500A, Finasol OSR52, Slickgone NS, and Slickgone EW. The unassisted conversion of DOSS to MOSS occurred in all four oil spill dispersants solubilized in seawater, although differences were noted in the rate of MOSS formation. A marine microcosm study of Corexit EC9500A, the formulation most rapid to form MOSS, provided further evidence of the stoichiometric conversion of DOSS to MOSS under conditions relevant to real world dilbit spill. Results supported combined DOSS and MOSS analysis for the monitoring of spill dispersant in a marine environment, with a significant extension of sample collection time by 10 days or longer in cooler conditions. Implications of the unassisted formation of MOSS and combined DOSS:MOSS analysis are discussed in relation to improving dispersant LC50 toxicity studies.

Effects of Conventional Surfactants on the Activity of Designed Antimicrobial Peptide.

In this article, the interaction between a designed antimicrobial peptide (AMP) G(IIKK)3I-NH2 (G3) and four typical conventional surfactants (sodium dodecyl sulfonate (SDS), hexadecyl trimethyl ammonium bromide (C16TAB), polyoxyethylene (23) lauryl ether (C12EO23), and tetradecyldimethylamine oxide (C14DMAO)) has been studied through surface tension measurement and circular dichroism (CD) spectroscopy. The antimicrobial activities of AMP/surfactant mixtures have also been studied with Gram-negative Escherichia coli, Gram-positive Staphylococcus aureus, and the fungus Candida albicans. The cytotoxicity of the AMP/surfactant mixtures has also been assessed with NIH 3T3 and human skin fibroblast (HSF) cells. The surface tension data showed that the AMP/SDS mixture was much more surface-active than SDS alone. CD results showed that G3 conformation changed from random coil, to ß-sheet, and then to α-helix with increasing SDS concentration, showing a range of structural transformation driven by the different interactions with SDS. The antimicrobial activity of G3 to Gram-negative and Gram-positive bacteria decreased in the presence of SDS due to the strong interaction of electrostatic attraction between the peptide and the surfactant. The interactions between G3 and C16TAB, C12EO23, and C14DMAO were much weaker than SDS. As a result, the surface tension of surfactants with G3 did not change much, neither did the secondary structures of G3. The antimicrobial activities of G3 were little affected in the presence of C12EO23, slightly improved by C14DMAO, and clearly enhanced by cationic surfactant C16TAB due to its strong cationic and antimicrobial nature, consistent with their surface physical activities as binary mixtures. Although AMP G3 did not show activity to fungus, the mixtures of AMP/C16TAB and AMP/C14DMAO could kill C. albicans at high surfactant concentrations. The mixtures had rather high cytotoxicity to NIH 3T3 and HSF cells although G3 is nontoxic to cells. Cationic AMPs can be formulated with nonionic, cationic, and zwitterionic surfactants during product development, but care must be taken when AMPs are formulated with anionic surfactants, as the strong electrostatic interaction may undermine their antimicrobial activity.