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Negative-Ion Chemical Ionization Mass Spectrometry and Ames Mutagenicity Tests of Granular Activated Carbon Treated Waste Water R. B. Baird, J. P. Gute, C. A. Jacks, L. B. Neisess, M. H . Nellor, J. R. Smyth, and A. S. Walker County Sanitation Districts of Los Angeles County, San Jose Creek Water Quality Laboratory, Whittier, CA 90601 Granular activated carbon (GAC) removed >70% of the TA98 mutagenicity from secondary effluent during a normal 6-week cycle. Negative-ion chemical ionization (NICI) gas chromatography-mass spectrometry (GC-MS) and silver nitrate derivatization showed that removal of labile organohalides paralleled the mutagen removal, consistent with a causal relationship. Chlorina tion did not consistently increase or decrease mutagenicity, al though NICI showed that some silver-reactive organohalides were reduced and others were formed during chlorination. Silver reaction formation of additional compounds was also demon strated by NICI; the number was less after either GAC or chlori nation. Consistent with the results, it was hypothesized that there is a reservoir of halogenated high molecular weight material that can yield smaller electrophilics and that GAC is effective in re moving much of this residue.
Τ
* ·- HE CHARACTERIZATION OF ORGANC I COMPOUNDS
in mutagenic residues f r o m water and waste water is the subject of many literature reports and ongoing studies. O n l y a very f e w have successfully iden tified discrete compounds that appear to b e responsible f o r the mutagenicity (1-4). Instead, most studies have identified up to several hundred individual organics, f e w of which were known mutagens contributing to sample mutagenicity. In a ground water replenishment 0065-2393/87/0214/0641$06.00/0 © 1987 American Chemical Society
Suffet and Malaiyandi; Organic Pollutants in Water Advances in Chemistry; American Chemical Society: Washington, DC, 1986.
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study, w e reported that the k n o w n mutagens and major unknowns characterized b y gas chromatography/electron impact mass spectrometry ( G C / E I - M S ) contributed little, if any, to the mutagenicity in resin concentrates of organic residues f r o m ground water, storm water, river water, a n d reclaimed waste water (5). H o w e v e r , the use of 4nitrothiophenol ( N T P ) as a selective nucleophile for electrophiles such as organohalides and epoxides (6, 7) and silver nitrate for labile organic halogens showed that chemical derivatization was an effective complement to GC-negative-ion chemical ionization M S ( G C / N I C I - M S ) and Ames mutagen assay for tentatively classifying the chemical nature of some of the mutagens (5, 8) and other reactive electrophiles. Although neither the structure nor sources of the compounds were identified, analyses of mutagenic residues b y G C / N I C I - M S and Ames assay before and after derivatization were consistent with the contributions of organohalides and epoxides to sample mutagenicity. Several of these compounds were detected i n more than one sample type (5). Because granular activated carbon ( G A C ) effectively removes mutagenic activity f r o m drinking water (9) and because these mutagens have yet to be identified, it was desirable to evaluate G A C for removing suspected mutagens f r o m reclaimed water before its use i n ground water replenishment. It was also desirable to examine chlorine disinfection as a possible source of these materials because chlorination has been implicated as a cause of toxic organics. This chapter presents data on the removal of mutagens b y G A C i n a full-scale municipal waste water treatment facility, the effects of chlorination on mutagen formation, and the characterization b y chemical derivatization and G C / N I C I - M S of reactive electrophiles i n these samples.
Experimental Treatment Plant Operations. The Pomona Water Reclamation Plant is a conventional activated sludge faculty treating 10 million gal per day of combined domestic and industrial waste water. Four GAC filters are operated on a staggered 6-week cycle: three units are operated while one is regenerated in a Nichols multiple-hearth furnace. Secondary effluent is split between the three operating filters and gravity fed at a rate providing an empty-bed contact time of 10 min. Each filter is 32 ft long X 16 ft wide X 22 ft high and filled with 80,000 lb of carbon to a depth of 6 feet. During normal operation, the units are periodically backwashed with chlorinated GAC effluent (tertiary effluent) to reduce clogging. For this study, the filters were backwashed with unchlorinated effluent to avoid chlorine contact with organics adsorbed on the carbon. GAC-filtered effluent containing 10-12 mg/L of N H 3 N is routinely disinfected with an average dose of 7 mg/L of chlorine to achieve a typical residual of 3-4 mg/L of chloramine following a 2-h contact time. Effluent turbidity is routinely 5% of the internal standard (decachlorobiphenyl) response.
Results and Discussion Mutagenicity Patterns. Mutagenicity data for the G A C filtration and chlorination unit processes are summarized in Tables I and II, respectively. Removal of mutagenicity by G A C ranged from 71% to 92%> for TA98 (avg = 83$) and from 62* to 94% for TA100 (avg = 798) over the 6-week operational cycle. No temporal trend in mutagen removal
Table I. Summary of GAC Mutagenicity Removal GAC Influent (rev/L)
GAC Effluent ( rev/L)
Percent Removal
Sample
TA98
TA100
TA98
TA100
TA98
TA100
09/27 09/29 10/01 10/05 10/07 10/12 10/18 10/20 10/22 10/26 10/28 11/01 11/03 11/05
7970 9560 9750 12000 17900 7270 11700 7350 8700 Τ 6610 10300 7250 6120
12100 13900 9540 16000 23200 13800 11400 10500 5030 Τ 6010 13300 7700 6340
1890 980 920 1770 1410 1380 1590 2150 740 100 1020 1570 2020 1170
3020 860 1320 3350 4050 2860 2840 2330 1130 Τ 1160 2460 2970 1780
76 90 91 85 92 81 86 71 92
75 94 86 79 83 79 75 78 78
85 85 72 81
81 82 62 72
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N O T E : Τ denotes toxic.
Suffet and Malaiyandi; Organic Pollutants in Water Advances in Chemistry; American Chemical Society: Washington, DC, 1986.
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Table II. Summary of Mutagenicity Results from Chlorination of GAC Effluents
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GAC Influent (rev/L)
CI Effluent (rev/L)
Percent Change
Sample
TA98
TA100
TA98
TA100
TA98
TA100
11/19 11/29 12/01 12/08 12/13 12/15 12/21 12/27 01/03 01/05
1400 2830 1390 2180 2740 420 1900 1490 670
