Subject(s)
Career Choice , Mental Health , Occupational Medicine , History, 20th Century , Humans , Physicians/psychologyABSTRACT
The production of N2 gas via anammox was investigated in sediment slurries at in situ NO2- concentrations in the presence and absence of NO3-. With single enrichment above 10 microM 14NO2- or 14NO3- and 15NH4+, anammox activity was always linear (P < 0.05), in agreement with previous findings. In contrast, anammox exhibited a range of activity below 10 microM NO2- or NO3-, including an elevated response at lower concentrations. With 100 microM NO3-, no significant transient accumulation of NO2- could be measured, and the starting concentration of NO2- could therefore be regulated. With dual enrichment (1 to 20 microM NO2- plus 100 microM NO3-), there was a pronounced nonlinear response in anammox activity. Maximal activity occurred between 2 and 5 microM NO2-, but the amplitude of this peak varied across the study (November 2003 to June 2004). Anammox accounted for as much as 82% of the NO2- added at 1 microM in November 2003 but only for 15% in May 2004 and for 26 and 5% of the NO2- added at 5 microM for these two months, respectively. Decreasing the concentration of NO3- but holding NO2- at 5 microM decreased the significance of anammox as a sink for NO2-. The behavior of anammox was explored by use of a simple anammox-denitrification model, and the concept of a biphasic system for anammox in estuarine sediments is proposed. Overall, anammox is likely to be regulated by the availability of NO3- and NO2- and the relative size or activity of the anammox population.
Subject(s)
Bacteria, Anaerobic/metabolism , Gene Expression Regulation, Bacterial , Geologic Sediments/microbiology , Nitrates/metabolism , Nitrites/metabolism , Quaternary Ammonium Compounds/metabolism , Rivers/microbiology , Anaerobiosis , Bacteria, Anaerobic/enzymology , Bacteria, Anaerobic/growth & development , Geologic Sediments/chemistry , Models, Biological , Nitrate Reductases/metabolism , Nitrite Reductases/metabolism , Oxidation-Reduction , Rivers/chemistryABSTRACT
A chemical product tanker, The Ievoli Sun, was abandoned and later sank approximately 11 miles NW of Alderney in the English Channel in October 2000. The vessel carried a mixed cargo comprising 4000 tonnes of styrene, and 1000 tonnes each of methyl ethyl ketone and isopropyl alcohol. These chemicals are of low to moderate toxicity to aquatic life, are not persistent and have a low potential for bio-accumulation. Both of the solvents are miscible in water, whilst styrene is practically insoluble and, following release, it will rise to the sea surface and rapidly evaporate. More than 1000 tonnes of styrene are believed to have been lost to sea during the incident, resulting in an aerial plume of vapour which crossed Alderney and episodic contamination of air and water in the immediate vicinity of the wreck site. Analysis of edible tissues using coupled gas chromatography/mass spectrometry demonstrated low-level styrene contamination of crabs recovered from pots laid very close to the wreck site prior to the incident. These concentrations posed no risks to human consumers, and no fishery controls were implemented. The remainder of the styrene and the ship's main bunker fuel were recovered from the wreck on the seabed, whilst the two chemical solvents were released to the water column in a slow, controlled manner.
