Air samples were taken onboard the RRS Bransfield on an Atlantic cruise from the United Kingdom to Halley, Antarctica, from October to December 1998, with the aim of establishing PCB oceanic background air concentrations and assessing their latitudinal distribution. Great care was taken to minimize pre- and post-collection contamination of the samples, which was validated through stringent QA/QC procedures. However, there is evidence that onboard contamination of the air samples occurred,following insidious, diffusive emissions on the ship. Other data (for PCBs and other persistent organic pollutants (POPs)) and examples of shipboard contamination are presented. The implications of these findings for past and future studies of global POPs distribution are discussed. Recommendations are made to help critically appraise and minimize the problems of insidious/diffusive shipboard contamination.

We investigated the seasonality of the air-water gas transfer of hexachlorocyclohexanes (HCH) in Lake Ontario. These organochlorine pesticides were measured in air and water samples collected on weekly cruises on Lake Ontario from May to October 1993. Air concentrations ranged from 51 to 200 pg m -3 for R-HCH and from 8 to 133 pg m -3 for γ-HCH. Surface water concentrations of R-HCH showed a small seasonal variation: mean values decreased from 922 ( 73 pg L -1 in May to 679 ( 47 pg L -1 in August and gradually increased to 897 ( 76 pg L -1 by October. Levels of γ-HCH did not show seasonal differences and averaged 357 ( 25 in surface waters. Air-water fugacity gradients of R-and γ-HCH were used to predict the direction of air-water gas exchange of these isomers. Reversals in exchange direction were observed for both compounds on time scales of days, weeks, and months. On average, air-water gas transfer of HCH was depositional in May and early June, reversed to volatilizational by August, and returned to depositional for both HCH isomers in October. Net fluxes of R-HCH calculated using a two-film gas exchange model ranged from -50 (deposition) to 25 ng m -2 day -1 (volatilization). Net fluxes of γ-HCH ranged from -63 to 7 ng m -2 day -1 . We estimate that 15 kg of R-HCH was removed and 37 kg of γ-HCH was added to Lake Ontario by air-water gas transfer from May to October 1993.

Porphyrins are the molecules which are at the heart of most biochemical reactions involved in bioremediation. This review paper discusses the chemical structures, the biosynthetic pathways and the occurrence of porphyrins in the environment. The parallel between the mammalian and bacterial cytochrome P-450 enzyme systems and the similarity of the reactions at the molecular level is brought to the attention of the reader. Experiments where porphyrins and corrinoids are used as catalysts in the absence of the enzymes or the bacterial cells are opening the field of biochemical remediation, somewhere midway between biological and abiotic reactions. La présence et le rôle des porphyrines dans l'environnement: implications possibles pour la biorestaurationRésumé Les porphyrines sont les molécules qui se retrouvent au coeur de la plupart des réactions biochimiques impliquées dans la biorestauration. Cet article passe en revue les structures chimiques, les chaînes de biosynthèse et la présence des porphyrines dans l'environnement. On dresse un parallèle entre les systèmes enzymatiques cytochromes P-450 d'origine bactérienne et mammifère et la similitude de leurs réactions au niveau moléculaire est soulignée. Des essais où les porphyrines et les corrinoïdes sont utilisées comme catalyseurs en l'absence d'enzymes ou de cellules bactériennes ouvrent la voie à la restauration biochimique, quelque part entre les réactions biologiques et abiotiques.