Potential for chlorate interference in ion chromatographic determination of total nitrogen in natural waters following alkaline persulfate digestion.

Determination of total nitrogen in aqueous samples after thermal potassium peroxydisulfate (persulfate) digestion is a commonly used alternative to the tedious Kjeldahl procedure. When ion chromatography is used to quantify the nitrate formed during digestion, there is a potential for interference from a chlorate peak if the digested sample initially contained chloride in concentrations close to or greater than the concentration of nitrogen. It was determined that this interference can be avoided either by using chromatographic conditions which cleanly resolve the nitrate and chlorate peaks (e.g., the Dionex AG9-HG column) or by using digestion reagent concentrations chosen to maintain a high pH throughout the digestion. The second alternative is not a viable option for investigators using a single digestion for both total nitrogen (TN) and total phosphorus (TP) analysis.

Susceptibilities of algae and Legionella pneumophila to cooling tower biocides.

Nine algal strains and nine Legionella pneumophila strains were tested in laboratory culture for their susceptibility to inhibition by a variety of commercially available microbiocides. The responses ranged from ineffective to effective at 1/100 the manufacturers' recommended pulse doses. Tests were also performed to determine whether the action of the microbiocide was bacteriostatic or bacteriocidal.

Bacteriostatic and bactericidal modes of action of bis(tributyltin)oxide on Legionella pneumophila.

The modes of action of bis(tributyltin)oxide (TBTO) doses between 1 X 10(4) and 6 X 10(7) molecules per cell on a single environmental isolate of Legionella pneumophila were studied by monitoring the following parameters: (i) growth, (ii) cell viability, (iii) 14C-amino acid incorporation, (iv) 14CO2 production from 14C-amino acids, (v) [3H]uridine incorporation, (vi) [3H]thymidine incorporation, (vii) oxygen consumption, (viii) cellular ATP levels, and (ix) adenylate energy charge. The amount of TBTO associated with the cells in these laboratory cultures was also compared with that remaining in the suspending medium. Most of the TBTO (68 to 88%) was found to be associated with the cells. This result explained why the cellular responses which were measured did not correlate with the TBTO concentration, but rather with the dose of TBTO to which the cells were exposed. At the lower TBTO doses tested (10(4) to 10(7) molecules per cell) a log-normal relationship was observed between the reduction in growth rate and the TBTO concentration. At intermediate TBTO doses (ca. 10(7) molecules per cell) growth stasis occurred, with nearly 100% of the cells in these cultures remaining viable for at least 5 h after treatment. The cellular function which seemed to be primarily affected at these levels of TBTO was the energy conversion mechanism, since the decline in the rates of CO2 production, oxygen consumption, and macromolecular synthesis was preceded by an immediate (within 1 min) drop in the intracellular levels of ATP and the adenylate energy charge. At the higher TBTO doses greater than 10(7) molecules per cell) an initial, precipitous, drop in the number of viable cells was observed, which was followed by a further exponential reduction of viable cells in the treated culture. This dramatic increase in bactericidal activity with a slight increase in the TBTO dose indicated that the modes of bacteriostatic and bactericidal action of TBTO were different.