'I
Water chemicals codex
' 3 -
The National Academy of Sciences has recommended specifications for the purity of chemicals used to treat drinking water; the first compilation covers direct additives
performance, packaging, storage, or handling. Analytical procedures were selected from compendia on methodology and protocol, adopted from manufacturers, or derived from methods set forth in the scientific literature. Data on toxi-
Robert Rehwoldt National Research Council Washington, D.C. 20418
The availability and production of potable water are matters of great national and worldwide concern. In the U.S.alone, an estimated 1-2 billion TABLE 1 gal of drinking water must be provided C h e m i c a l s used for water each day. To comply with health and other applicable standards for treating treatment in 1981 (tons) that amount of potable water, supCoagulation and tkcculatla, pliers used more than 1.2 million tons 127 of chemicals in 198 I , according to an 1 .A l i m. American Water Works Association 15 583 (AWWA) report (Table I). 6 I86 Large segments of the U.S. popu4 260 lation come in contact with chemical odium aluminate 2 esa additives used for water disinfection, m s sulfate 1 coagulation, softening, corrosion coniadium silicate 1 trol, fluoridation, and other water I DiatomaoeOusearih treatment functions. Thus, in 1979, a memorandum of understanding was I clay (bentonite) ection and OxIdation signed by the Food and Drug Administration and the Environmental Pro440 &lorite tection Agency, by which responsibilhlorine ity for monitoring and controlling ;odium chlwite 6 369 these additives, whether direct or in- i Ammonia gfslliquid 2 direct, was vested in the EPA. Not long thereafter, in response to a request from EPA, the National Research Council, an arm of the National Academy of Sciences, undertook to recommend minimum acceptable purity specifications for such substances. Accordingly, the Committee on Water Treatment Chemicals was formed and entrusted with the taskof developing such specifications, first for ' Activatedcarbonn direct additives, and later, as feasible, Ii phasphates for indirect additives. After two years of deliberations, the committee pro- : Sodiumchoride duced a Water Treatment Chemicals Codex. The codex is meant to supplement existing compendia on water treatment chemicals and is confined to information on purity as it is related to , Denver. wo..Jumt 1981 health. It does not address product
I
,
.
W0A
Environ. Sci. Technol.. VoI. 16, No. 11, 198P
I
cologic aspects were obtained from the scientific literature, from chemical manufacturers, and from the Code of Federal Regulations. Purity requirements The committee recognizes that the assignment of purity requirements depends upon the toxicity of the contaminant and the use patterns of the additive. Although the interpretation of toxicological data concerning these contaminants is at times controversial and depends upon an evolving science, the toxicological data base for water treatment chemical impurities is improving steadily. To arrive at its recommended contaminant limits, the committee met with EPA with the aim of compiling a list of priority chemicals (Table 2). This list was then categorized according to use pattern, that is, those chemicals used in coagulation and flocculation; softening, precipitation and pH control; disinfection and oxidation; and miscellaneous treatment applications. In drafting the monographs in each category, a subgroup of the committee reviewed current data on known impurities in the chemicals, grades of manufactured products, use patterns, and other variables. The committee also developed a list of impurities to be considered. Initially, the list was identical to that of the regulated inorganic impurities specified by the National Interim Drinking Water Regulations developed in response to the Safe Drinking Water Act of 1974. This list was subsequently modified to include those substances for which there is evidence of occurrence as contaminants in water treatment chemicals. The toxicology subgroup of the committee supplied toxicological data on these substances, including information on possible genotoxic or epigenetic (nongenetic cellular damage) effects.
0013-936X/82/0916-0616A$01.25/0
0 1982 American Chemical Society
Recommended maximum impurities In general, the committee felt that it would he appropriate to utilize the maximum contaminant level (MCL) for calculating the allowable contaminant level contributed by an impurity in a water treatment chemical, unless there was no current MCL for that impurity, or where there was new information concerning either the toxicity of the contaminant or the current status of the MCL.
An MCL was thus converted to a Recommended Maximum Impurity Content (RMIC) for the additive by the following equation: RMIC
--
MCL Maximum dosage X safety factor - MCL (mg/L) X lo6 mg/kg MD (mg/L) X SF
where maximum dosage (MD) for the water treatment chemical was based
The basic form of the codex is a series of individual monographs, each dealing with a specific compound. Each monograph contains the following information:
MCL = 0.002 mg/L Water treatment additive:
chemical formula physicalpropelt function werange purity requiremen
Maximum dosage (MI)) = 500 mg/L Safety factor = 0.1 RMIC
analytical procedures a) Sample preparation-special pr 1ate. In cases where the chemical added is not soluble in water, the analytical procedures apply to a leachate of that material as obtained under the conditions described. 6) Sample analysis-techniques are given either as citations ofexisting recwnked orocedures or as lxocedures d e v e l o d smificaiiv for the
.
Aluminum sulfate Ammonia Ammonium hyaoxide Ammonium sulfate Calcium hydroxide Catclum hypochlwne Calcium ox*
csrbon,acthrated. w
w and powder
on maximum patterns known by the committee to be representative of water treatment practice. The safety factor (SF) used in the calculation of the RMIC was 10, reflecting the view of the committee that no more than 10% of a given MCL value should be contributed by a given impurity in a water treatment chemical. Some may argue for a higher safety factor, but 10% was deemed reasonable by the committee in view of other uncertainties and approximations relating to the fate of impurities introduced during treatment. A sample calculation of an RMIC is performed as follows. Contaminant mercury (Hg):
.
Gerbil dioxide ChlaiW
Ferric chloride Ferric sulfate Ferrous sulfate Sadivn mbtabisulfite Fluosilicic acM Sodium silicolluoride potassium permanganate %dimpolyphosphate elassv Sodium aluminate Sadium m m a i
- .. .. ..
.
- 0.002 mg Hg/L
X 106 mg/kg 500 mg additive/L X 0.1 RMIC = 0.4 mg Hg/kg additive
The codex contains RMIC values for impurities of concern at selected additive dose levels, which are reported to one significant figure. RMIC values defining the purity of each water treatment chemical are also contained in individual monographs and may be used as guidelines for the water works industry. At present, the codex contains 26 monographs; an additional 15 are expected to be completed by the end of this year. The user should note that if actual dosages applied exceed those upon which the monograph is based, appropriate RMIC values should be extrapolated from the table. In addition, although no documented cases were found, if a contaminant is suspected of creating additional health Envirm. SCI. Techol.. VoI. 16, No. 11. 1982
017A
concerns because of radioactivity, RMIC values must be calculated in accordance with radiation limits set fortb in the Code of Federal Regulations. The RMIC levels are based upon information available to the committee. It is impossible to recommend maximum content levels for unusual or unexpected impurities, the presence of which would depend upon the method of manufacture and the quality of raw materials used. If unusual raw materials or unusual methods of manufacture go into the preparation of a treatment chemical, the user should require appropriate certification of purity from the vendor or manufacturer, to prove that the chemical is suitable for application to the making of potable water. Analytical methods Preferred sampling, sample preparation, and analytical methods for the determination of impurities are cited. Methods that arecited or appear in the codex should be considered as the preferred analytical procedures; alternative methods may be used if they can be shown to be equivalent. It is recognized that a contaminant
in a water treatment chemical may require special sample preparation or analysis methods, because of the nature of the chemical matrix. For such chemicals, the recommended special procedures are included in the codex. Some areas of concern Although for the most part, the committee relied on published MCLs for recommending impurity limits, there were some areas of concern. For example, the RMIC values for lead are based upon an MCL of 0.05 mg L-I. There is considerable evidence that lead is more widespread than has been previously thuught and that lead poisoning is still a serious problem in the U S . Therefore, even though the committee finally accepted the current MCL as a basis for calculating an RMIC for lead, supporting material submitted to EPA contained a recommendation that the agency critically evaluate the existing lead standard. Another troublesome case is that of carbon tetrachloride, which is a common contaminant in the manufacture of chlorine. The committee felt that if it made no recommendation for maximum content, it would be shirking its
duty. However, any attempt todefine health risks quantitatively in terms of exposure to a carcinogen-which carbon tetrachloride is suspected of being-is extremely complex; in many cases, appropriate data do not exist. EPA has published a notice of proposed rulemaking for volatile organics; and until that process is completed, the committee has recommended an RMIC for carbon tetrachloride in chlorine of 100 mg kg-I. The genotoxic or epigenetic potential of water treatment chemical impurities, which can present yet another problem, was evaluated on a caseby-case basis. Appropriate data bases were investigated, and published risk assessments or other exposure models were considered. Review and revision It is expected that the codex will be reviewed continuously and that annual supplements will be issued. The supplements may contain lists of additional chemicals and revisions of the mongraphs contained in the present codex, as well as revisions of analytical procedures. Distribution of the codex is planned for the end of this year. Information about ordering it can be obtained from the National Academy of Sciences, Washington, D.C. 20418. It is hoped that the Water Treatment Chemicals Codex will be used in conjunction with other existing voluntary standards, such as those developed by the American Water Works Association. It is recommended that more extensive data bases on the purity of drinking water additives be developed and that this information be used continuously to revise and update the codex.
Robed Rehwoldt is currently a senior staff of icer of the national Research Counci , National Academy of Sciences, in Washingion, D.C. Prior to assuming his position at NRC he taught and conducted research on the toxicity of metal ions to aquatic communities. He has published a number of papers in that field and has acted as a consultant in enuironmenfal problems. He receiued his B.S. from Queens College in New York and a Ph.D. in analytical chemistry from Lehigh Uniuersity.
If
618A
Environ. Scl. Technol.. Vol. 16. No. 11. 1982
