Mechanisms in sensitized photochemistry of environmental chemicals

This review consists of three main parts. After a short discussion of the theory of photochemistry, the three major mechanisms (radiative, short range and long range) for the transfer of electronic excitation energy from sensitizers (donors) to substrates (acceptors) are described. Criteria for the selection of. sensitizers are a high efficiency of intersystem crossing (in the case of triplet sensitization) and energy transfer, and strong absorption at wavelengths longer than those at which the acceptor absorbs. Two mechanisms of sensitized photo‐oxygenation, viz. the radical and singlet oxygen type, are discussed.

The second part of this review deals with photosensitizers, with a strong emphasis on compounds of importance in environmental photochemistry on the one hand and those interesting from a mechanistic point of view on the other.

The third part describes photo‐inducers and their role in photoreactions.

Additional literature references (to January 1978) are presented at the end of this review.     

Retention of PCDDS and PCDFS in the liver of the rat and hamster after oral administration of a municipal incinerator fly ash extract

A single dose of an extract from 16 and 5 grams fly ash was administered orally to male rats and hamsters. In the rat 1,2,3,7,8‐PnCDD had the highest retention (41%) in the liver. The congener with the highest retention in the liver of the hamster was 2,3,4,7,8‐PnCDF (70.9%). In two oral multiple dose experiments with rats, highest liver retentions were found for 1,2,3,7,8‐PnCDD (51.7%) and 1,2,3,6,7,8‐HxCDD (59.8%). With the exception of 2,3,4,6,7‐PnCDF, all PCDDs and PCDFs retained in the liver of rat and hamster had a 2,3,7,8 chlorine substitution pattern. In both types of experiments with rats the retention of 2,3,7,8‐TCDF in the liver was very low, 1.1–2.8% of the total dose. In the liver of the hamster retention of 2,3,7,8‐TCDF was almost equal to that of 2,3,7,8‐TCDD, indicating that the hamster is probably metabolizing 2,3,7,8‐TCDF Jess efficiently than the rat. In all experiments 1,2,3,7,8‐PnCDD and 2,3,4,7,8‐PnCDF were retained in the liver more efficiently than 2,3,7,8‐TCDD. Based on first order pharmacokinetic calculations, it was found that the earlier published k_e value of 0.55 for 2,3,7,8‐TCDF in the liver of the rat was also applicable. Using the same calculations for 2,3,7,8‐TCDD (k_e = 0.029) a 30% difference was found between calculated and actual measurements, but calculated results were still within the 95% confidence limits of the actual measurements.     

Supercritical fluid extraction of polycyclic aromatic hydrocarbons from marine sediments and soil samples

Supercritical fluid extraction (SFE) was used to extract polycyclic aromatic hydrocarbons (PAH) from a certified sample of marine sediment. This sample contains a great number of organic pollutants that are present in low concentrations. The extractions were carried out at 50 and 80 degrees C, at a pressure varying from 230 to 600 bar and using CO2 in the supercritical phase and the effect of three organic modifiers (methanol, n-hexane and toluene), added at 5%/vol, at the same temperature and pressure conditions, were then considered. PAHs were characterized by GC-MS and the recover yield was estimated for 6 PAHs that were representative of those present in the sample, according to their molecular weight and to the number of condensed rings. The analytical conditions giving the best recovery efficiency were used on an unpolluted soil sample spiked with 11 PAHs of environmental importance at a concentration similar to that certified for the sediment sample. An increase in the yield of recovered PAHs, using methanol as co-solvent, was observed while higher temperatures caused a negative effect on the quantity of recovered pollutants. The recovery yield for PAHs from the spiked soil sample was measured and found to be greater than 90%. Better recoveries were obtained for those compounds with higher molecular weight.