WATER QUALITY--Preservation of Nutrient Samples for Nutrient Analysis; An Update on Two Issues In Reply Refer To: January 23, 1985 WGS-Mail Stop 412 QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM 85.07 Subject: WATER QUALITY--Preservation of Nutrient Samples for Nutrient Analysis; An Update on Two Issues Since Quality of Water Branch Technical Memorandum 80,26 was issued directing the use of HgCl2/NaCl tablets plus chilling at 4 degrees C for preservation of water samples for nutrient determination, there has been periodic debate over the effectiveness of this treatment relative to others. Recently also, evidence has surfaced that the preservative tablets may be randomly contaminated with ammonia (NH3-N), either as a trace impurity in the original reagents or by sorption of gaseous NH3 from the laboratory or field-office atmosphere. The purposes of this memorandum are to discuss results of studies recently completed with regard to these matters, advise the field and project offices on steps to take at once to reduce the chance of NH3 contamination, and describe additional studies planned or underway. The attached memorandum from Marvin Fishman and LeRoy Schroder dated October 18, 1984, describes the results of tests conducted in the Denver Central Laboratory for effectiveness of five popular preservation treatments over a l6-day period. The findings and implications are clear; the combination of the HgCL2/NaCl tablet with chilling at 4 degrees C is the best of the treatments tested. We intend to retain this treatment as the standard practice within Water Resources Division (WRD) until a better one is demonstrated. The second memorandum from Marvin Fishman, also attached, describes studies conducted in both Central Laboratories to determine the levels of NH3-N contamination in preservative tablets in storage at those facilities. Analyses were performed by automated wet-chemical techniques in both labs. Atlanta finds no significant contamination down to the detection limit (0.002 mg/L) whereas Denver finds contamination around a level of 0.01 mg/L. There is also an indication in the Denver lab that NH3-N might be sorbed from the atmosphere into samples standing open awaiting analysis (witness the slight but steady increase in results of replicate determinations). These results will be checked shortly by exchanging tablets between laboratories for reanalysis. We will alert you of the results when these studies are complete. A major unanswered question is the degree to which the preservative tablets have become contaminated during storage in field and project offices. We will get a fast assessment of this question by a random sampling of preservative tablets in at least four District Offices. Marvin Fishman has been asked to send bottles of ammonia-free water to Districts selected at random. The Districts will add a tablet selected at random to all but one bottle, leaving that one as a travel blank, and return the samples for analysis at no charge to the District. Appropriate action will be taken based on an evaluation of the data. Despite the uncertainties regarding degree of NH3-N contamination in the tablets, it seems prudent to take some steps at once to reduce the chances of contamination and to prevent erroneous analyses of water samples. Field and project offices are advised to take the following steps immediately: 1. Assess the possibility that NH3 gases are or have been present in the area where the tablets are stored--is the area cleaned periodically with ammonia-containing solutions, has concentrated ammonia been left open to the atmosphere outside a hood, do personnel smoke in the area, is the area affected by automotive exhaust? If exposure is suspected, discard all remaining tablets and reorder from the Central Laboratory. 2. Isolate all remaining tablets from the ambient atmosphere. Protection from all ammonia sources is essential! Tablets must be kept in a sealed container. The ammunition can recommended for storing metallic mercury is satisfactory. 3. Until further notice, the preservative tablets should be used only for samples in which NH3-N determination is not requested or where expected concentrations are above 0.02 mg/L and the regular analysis is requested (LC 0301: detection limit 0.01 mg/L). If pristine-area, precipitation, or otherwise low ionic-strength samples are being analyzed and LC 0830 (low-level colorimetric) is requested, special arrangements should be made with the receiving laboratory to obtain priority handling (at no additional charge), and samples should be shipped chilled without preservatives by an overnight express carrier. Please be discrete; none of us want the labs to be overloaded with priority requests. As a reminder, the preservative tablets cannot be used when LC 0520 (Ion chromotographic anion determination) is requested. 4. Each District is encouraged to conduct its own tests for NH3-N contamination at cost to the District. Ammonia-free water may be prepared by adjusting deionized or distilled water to pH 8 with NaOH or KOH and boiling for about 15 minutes. Submit at least one blank and three samples with tablets (selected at random) added. Alert the laboratory that the bottles are for test purposes and indicate which are blanks and which are tests because the laboratory standards need to be changed if HgCl2 is absent. Please send a copy of the data to the Quality of Water Branch. Stocks of tablets at the laboratories are sufficient to carry us through fiscal year 1985. The process of reordering will be accelerated and a different packaging arrangement will be sought. David A. Rickert Acting Chief, Quality of Water Branch 2 Attachments A, B, FO, PO This memorandum temporarily modifies instructions given in Quality of Water Branch Technical Memorandum 80.26. Key words: Water quality, sampling, preservation