Inhibition of microbial H2S production in an oil reservoir model column by nitrate injection.

The effect of nitrate addition on microbial H2S production in a seawater-flooded oil reservoir model column with crude oil as carbon and energy source was investigated. Injection of 0.5 mM nitrate for 2.5-3.5 months led to complete elimination of H2S (initially 0.45-0.67 mM). The major decline in H2S level coincided with the first complete nitrate consumption and production of nitrite. When nitrate was excluded, H2S production resumed after approximately 2.5 months and reached previous levels after approximately 5 months. Using a fluorescent antibody technique, three populations each of sulfate-reducing bacteria (SRB) and nitrate-reducing bacteria (NRB) were monitored. SRB dominated the anoxic zone prior to nitrate addition, comprising 64-93% of the total bacterial population. The monitored NRB constituted less than 6% and no increase was observed during nitrate addition (indicating that other, unidentified, NRB populations were present). After 1-3 months without significant H2S production (3.5-5.5 months with nitrate), the SRB population collapsed, the fraction being reduced to 9-25%. The dominant SRB strain in the column, which constituted on average 94% of the monitored SRB population, was partly/completely inhibited by 50/75 microM nitrite in batch culture tests. Similar nitrite concentrations (50-150 microM) were detected in the column when the H2S level declined, indicating that nitrite inhibition was the main cause of H2S elimination. The results from this study indicate that nitrate/nitrite can be used to prevent detrimental SRB activity in oil reservoirs.

Xenobiotic biodegradation test using attached bacteria in synthetic seawater.

The aerobic biodegradability of aniline, used as reference chemical, has been performed in synthetic seawater with attached biomass in a continuously fed reactor (biofilm chemostat reactor, BCR). Marine bacteria inocula came from local marine fish aquarium filters to limit the geographic and seasonal variations in quality. A pretreatment of these inocula combining 5-microns filtration and centrifugation was used to concentrate bacteria and remove organic carbon contamination of the test. The performances of the BCR were tested in comparison with simple shake flask tests. Among the different variables tested, the ratio S0/X0 (initial concentration of xenobiotic to initial density of the inoculum), the presence of dissolved oxygen, and the hydraulic residence time appear to be the key parameters controlling the length of the biodegradation process. On the other hand, the addition of a cosubstrate (easily biodegradable compound) does not provide advantages. Thus, marine biofilm chemostat reactors with a high density of attached bacteria (around 10(7) cells cm-2) and fed with synthetic seawater plus nitrogen provide good tools for screening biodegradability of chemicals in the marine environment.

Ready biodegradability test in seawater: a new methodological approach.

To estimate the persistence of xenobiotic in the environment, a new ultimate mineralization approach for assessing ready biodegradability in seawater has been developed, based on the OECD 301 B guideline for freshwater. a few changes in the currently accepted procedure have been made to adapt the test to seawater. The assays, realized with seawater as test medium and inoculum, give high variability results of biodegradability. To lower this variability a synthetic marine medium joined to a highly concentrated inoculum from a marine aquarium filter have been used. The results reveal (i) a decrease of variability, together with an increase in degradation rate of the tested chemicals due to a better control of inoculum and test medium, and (ii) no difference in easy biodegradable compound (sodium benzoate) biodegradation rate when two marine aquarium inocula are tested. This study demonstrates that the ready biodegradability test developed on synthetic marine medium and inoculum from marine aquarium filter minimizes the effect of the sample location on the biodegradation results of compounds and allows classifying chemicals as a function of their biodegradability.

Difficult parents. From adversaries to partners.

The pediatrician's job becomes frustrating when it is necessary to deal with difficult parents. Some physicians may not have the training or inclination to engage such parents in a therapeutic partnership. This paper discusses tools available to physicians which will help them develop an effective partnership that includes uncovering the hidden meaning behind a child's illness; understanding the reciprocal nature of partnerships; and the importance of determining each party's goals, roles, and expectations. Negotiating these steps enables physicians to develop a productive relationship with difficult parents of sick children. This strategy can facilitate the child's medical care and improve the parents' and physician's satisfaction with the services rendered. This paper also discusses steps to take when these attempts are not sufficient to handle the situation.

Survey of admission policies for child and adolescent inpatient services: a national sample.

In a national sampling of child inpatient directors, survey responses suggested variability in the use of many admission criteria. Yet, severity of symptoms, potential effectiveness of outpatient treatment, and extent of medical complications appeared to be commonly used admission criteria. DSM-III diagnoses were inconsistently used admission criteria, and many diagnoses were considered suitable for admission in extenuating circumstances only.