The internal barrier of rotation (Erot) was calculated for all 209 polychlorinated biphenyls (PCBs) by using a semi-empirical method, viz. the Austin Model 1 (AMI) Hamiltonian. The difference in total energy between a forced planar state and an optimised twisted structure was defined as Erot. The Erot values were in the range of 8.33 to 483 kj/mol, and were significantly influenced by the number of chlorine atoms inortho position. An additional structural characteristic of the PCBs influencing Erot ofortho substituted congeners was substitution by chlorine atoms in vicinalmeta positions, which is assumed to prevent outward bending ofortho substituents. This so-called buttressing effect contributed with 4 to 31 kj/mol per added chlorine atom. In conclusion, the internal barrier of rotation, calculated for all 209 PCBs, provides an important structure dependent physico-chemical parameter for multivariate modelling of future quantitative structure-activity and structure-property relationships (QSARs/QSPRs).

A few case studies will be presented involving both radioactive and chemical pollution at small, medium, and large space-time scales. Reported are recent advances in the field of environmental pollution involving the use of fractals and multifractals. The mathematical tools proposed here may offer new perspectives for investigating many of the problems of nonlinear variability which commonly arise when dealing with pollutants, such as the presence of outliers and the sparseness of the sampling networks. They may also lead to a simplification of the models adopted for studying natural phenomena, thanks to a scaling approach. Finally, they may provide parameters whose values are directly related to the nonlinear dynamics involved in the pollutant distribution in the environment which, in turn, may be relevant for computer simulation and epidemiological or risk assessment purposes.

Terpenes in citrus oil must be removed to stabilize the products and to dissolve it in aqueous solution. Supercritical fluid extraction has been investigated for the terpeneless citrus oil processing as a lower temperature process. In order to achieve higher yield and higher separation selectivity, a continuous countercurrent extraction with reflux was studied at a temperature of 333 K and a pressure of 8.8 MPa. Cold-pressed orange oil from Brazil and a model mixture of 80% limonene and 20% linalool, where limonene and linalool are principal constituent of terpenes and oxygenated compounds in orange oil, were used as feed and carbon dioxide was used as solvent. Operation at total reflux was carried out to calculate the minimum number of plates required to achieve a separation between limonene and linalool. Effects of the solvent-to-feed ratio, reflux ratio, and feed inlet position on the yield and selectivity were investigated for continuous operation. The selectivity increased with the increase in the solvent-to-feed ratio. Terpeneless citrus oil was obtained on the operation at the higher solvent-to-feed ratio and longer stripping section.

“Freely-dissolved” aqueous concentrations of 9 trichlorothrough heptachlorobiphenyls are reported, alongside those in sediments and fish from the R. Severn. For most congeners, BSAFs and lipid-normalised BAFs for pike exceed those for eels. Whilst R. Severn BSAFs are comparable with those for L. Ontario trout and New Bedford Harbour flounder, R. Severn BAFs are 1–2 orders of magnitude lower. This discrepancy may be due to inter-species variability, as well as inter-laboratory differences between operational definitions of “freely-dissolved” aqueous PCB, underlining that the same operational definition must be employed if R. Severn BAFs are extrapolated elsewhere. For eels, correlation of Log Kᵒʷ with Log BAF is better (R² = 0.66) than with BSAF (R² = 0.13), whilst similar correlation coefficients (R² = 0.81 and 0.82) were observed for pike. When Log Kᵒʷ is plotted against BSAF and Log BAF for both species combined, better correlation is observed for Log BAF (R² = 0.65), than BSAF (R² = 0.36). For both species combined, the observed relationship between Log BAF and Log Kᵒʷ for trichloro-through heptachlorobiphenyls is: Log BAF = 0.96 * Log Kᵒʷ −0.24.

A two-step analytical method is developed for the isolation and characterization of polycyclic aromatic hydrocarbons (PAHs) in crude oil contaminated soil. In the first step, those crude oil components were isolated which are easily mobilized with water from the contaminated soil (determination of groundwater pollution potential). In the second step, the fraction containing the remaining crude oil compounds was extracted using toluene. After the cleanup of the fractions, both fractions were analyzed using high-performance liquid chromatography (HPLC).The HPLC of the toluene extracted fraction shows that along with the sixteen priority pollutants from the US-EPA list, many other polycyclic aromatic hydrocarbons (PAHs) are present as well. It is evident from the chromatograms that a significant amount of PAHs are present as is also the case in the fractions eluted by water.The described method allows the determination of total organic pollutants from crude oil, some of them being potential groundwater contaminants. The major part of the total pollutants could not be mobilized by water and therefore remains in the soil, which was extracted in the second step.

The combined influence of high phenol concentrations and low temperatures on aerobic and anaerobic phenol degradation kinetics was investigated in microbial enrichment cultures to evaluate temperature-inhibition relationships with respect to the ambient conditions in polluted habitats. The inhibition of microbial phenol degradation by excess substrate was found to be temperature-dependent. Substrate inhibition was intensified when temperatures were lower. This results in an elevated temperature sensitivity of phenol degradation at inhibitory substrate concentrations.The synergistic amplification of substrate inhibition at low temperatures may help to explain the limited self-purification potential of contaminated habitats such as soils, sediments and groundwater aquifers where high pollutant concentrations and low temperatures prevail.

During the last decade use of supercritical fluids in environmental applications have increased due to their unique properties. Technologies have already been developed for extraction of organic compounds from aqueous and solid environmental matrices and research on extraction of metals is in progress. In most applications, supercritical carbon dioxide is the solvent of choice because it is environmentally benign, safe, and abundant at a low cost. Recent research focus is on use of supercritical fluids as separation and reaction media. Especially as the reaction media, supercritical fluids offer properties that may significantly affect reaction rates and selectivities. The most important property is the control of solvency power through density. This aspect may be used to eliminate side reactions, exceed thermodynamic yield limitations, or control polymer chain lengths and molecular weight distributions. In the separations area, supercritical fluids can be exploited for adsorptive separations of structurally very similar compounds and for selective extraction of thermally labile compounds from natural products.