Aquatic Toxicity Calculation of Mixtures: A Chemical Activity Approach Incorporating a Bioavailability Reduction Concept

A calculation estimating the effect concentration (EL/LL50) of a water-accommodated fraction (WAF) for mixture toxicity is proposed. The method is based on chemical activity where the activity of a molecule is its effective concentration taking into account intermolecular interactions. First, the thermodynamic influence of each constituent on the solubility of the others within the mixture (i.e. the concentration of each constituent in the "loading rate") is determined. Then, the non-bioavailable fraction is determined and removed to calculate the true concentration of each constituent exerting toxicity. Finally, the loading rate is adjusted until the sum of activities of the bioavailable fractions is equal to the fraction-weighted average of toxic activity of each constituent. This process is a mechanistic interpretation of experimental WAF tests. The methodology has been validated comparing toxic loading rates of 13 reliable experimental WAF studies on fish, daphnids, and algae. The predictions were all within a factor of 2 of the study outcomes and can be considered as accurate as the laboratory studies. This is in contrast to the standard additivity method which consistently overestimates the toxicity of these mixtures by at least a factor of 2 up to over an order of magnitude or even more.

Petroleum Hydrocarbon Contamination in Terrestrial Ecosystems-Fate and Microbial Responses

Petroleum hydrocarbons represent the most frequent environmental contaminant. The introduction of petroleum hydrocarbons into a pristine environment immediately changes the nature of that environment, resulting in reduced ecosystem functionality. Natural attenuation represents the single, most important biological process which removes petroleum hydrocarbons from the environment. It is a process where microorganisms present at the site degrade the organic contaminants without the input of external bioremediation enhancers (i.e., electron donors, electron acceptors, other microorganisms or nutrients). So successful is this natural attenuation process that in environmental biotechnology, bioremediation has developed steadily over the past 50 years based on this natural biodegradation process. Bioremediation is recognized as the most environmentally friendly remediation approach for the removal of petroleum hydrocarbons from an environment as it does not require intensive chemical, mechanical, and costly interventions. However, it is under-utilized as a commercial remediation strategy due to incomplete hydrocarbon catabolism and lengthy remediation times when compared with rival technologies. This review aims to describe the fate of petroleum hydrocarbons in the environment and discuss their interactions with abiotic and biotic components of the environment under both aerobic and anaerobic conditions. Furthermore, the mechanisms for dealing with petroleum hydrocarbon contamination in the environment will be examined. When petroleum hydrocarbons contaminate land, they start to interact with its surrounding, including physical (dispersion), physiochemical (evaporation, dissolution, sorption), chemical (photo-oxidation, auto-oxidation), and biological (plant and microbial catabolism of hydrocarbons) interactions. As microorganism (including bacteria and fungi) play an important role in the degradation of petroleum hydrocarbons, investigations into the microbial communities within contaminated soils is essential for any bioremediation project. This review highlights the fate of petroleum hydrocarbons in tertial environments, as well as the contributions of different microbial consortia for optimum petroleum hydrocarbon bioremediation potential. The impact of high-throughput metagenomic sequencing in determining the underlying degradation mechanisms is also discussed. This knowledge will aid the development of more efficient, cost-effective commercial bioremediation technologies.

Synthesis of inorganic polymers under ionizing and super high frequency irradiation: role of reaction media

This article provides a general overview of the results of research on the influence of the reaction media and various types of electromagnetic radiation on the polymerization of inorganic monomers, carried out during the last decade at UNESCO Chair in Green Chemistry for Sustainable Development of Dmitry Mendeleev University of Chemical Technology of Russia.

Atmospheric aerosol water-soluble organic carbon measurement: a theoretical analysis

The measurement of Water-Soluble Organic Carbon (WSOC) in atmospheric aerosol is usually carried out by sample collection on filters, extraction in ultrapure water, filtration, and measurement of the total organic carbon. This paper investigates the role of different conditions of sampling and extraction as well as the range of solubilities of the organic compounds that contribute to the WSOC. The sampling and extraction of WSOC can be described by a single parameter, P, expressing the ratio of water used per volume of air sampled on the analyzed filter. Two cases are examined in order to bound the range of interactions of the various organic aerosol components with each other. In the first we assume that the organic species form an ideal solution in the particle and in the second that the extraction of a single compound is independent of the presence of the other organics. The ideal organic solution model predicts that species with water solubility as low as 10(-4) g L(-1) contribute to the measured WSOC. In the other end, the independent compounds model predicts that low-solubility (as low as 10(-7) g L(-1)) compounds are part of the WSOC. Studies of the WSOC composition are consistent with the predictions of the ideal organic solution model. A value of P = 0.1 cm(3) m(-3) is proposed for the extraction of WSOC for typical organic aerosol concentrations (1-10 μg m(-3)). WSOC measurements under high concentration conditions often used during source sampling will tend to give low WSOC values unless higher P values are used.

Composition of the water accommodated fractions as a function of exposure times and temperatures

The water accommodated fractions (WAFs) of nine oils in seawater have been studied. The oils range from light condensate to heavy crude, and include one highly biodegraded oil and one very wax rich oil. This study has identified large variations in the chemical composition of WAFs, depending on oil type, temperature, and mixing time. Experiments at different temperatures (2-13 degrees C) showed that it takes longer time to reach equilibrium at the lowest temperatures, and that this varies for the different oil types. Oils with higher pour point (wax rich oils) need a longer time to establish WAF in equilibrium than oils with lower pour points (naphthenic oils). At 13 degrees C a mixing time of 48h, as recommended in standard procedures, seems to be sufficient for asphalthenic and paraffinic oils. The results demonstrated that for WAF prepared from an unknown oil, or at lower temperatures, different mixing times should be tested. Since the WAF often is used in toxicity testing, the toxicity might be underestimated if the mixing time is too short.