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Anal. Chem. 1981, 53, 214-219
Determination of Organochlorine Pesticides and Polychlorinated Biphenyls in Water by Gas Chromatography John D. Miliar," Richard E. Thomas, and Herbert J. Schattenberg, 111 Department of Environmental Sciences, Southwest Research Instltute, f.0. Drawer 285 10, San Antonio, Texas 78284
A study has been made of procedural steps involved -In assaylng organochlorine pesticides and polychiorlnated biphenyls in water. Generally, excellent recoveries were obtained for 25 prlorlty pollutants extracted wlth dlchioromethane and 15% dichioromethane in hexane at pHs 2, 7, and 10. The effects of pH, temperature, and residual chiorlne (2 ppm) on the preservation of these substances for a period of 7 days were determined, and the best conditions for storage are given. Elution of the substances from Florisli and alumina cleanup columns gave excellent recoveries. Appllcation of the method to five wastewaters was attempted. Three of the wastewaters could be satisfactorily analyzed, spiked, and reanalyzed at zero time and after storage for 7 days under selected physical conditions. Two of the wastewaters could not be analyzed completely because of Irreduclble amounts of electron capture-sensitive interferences.
The priority pollutants list published by the US.Environmental Protection Agency contains 18 organochlorine pesticides (OCP) and 7 polychlorinated biphenyls (PCBs) considered to be environmental hazards if they are discharged indiscriminately in industrial effluents. Therefore, a method adequate for monitoring the levels of these materials in effluents and waters affected by such effluents is required. The development of the electron-capture detector provided the potential for analyzing for organochlorine compounds with great sensitivity, and a basic method has evolved that is comprised of these steps: solvent extraction, concentration of the extract, cleanup of the extract, and gas chromatography with electron-capture detection (1-3). Only relatively minor procedural changes have been reported in the last 10 years. Substitution of a more selective detector, such as the Hall electrolytic conductivity detector (4), often results in a loss of sensitivity, imposing a position that is counter to the demands of the times. This paper reports a systematic effort to determine recoveries of all of the OCP and PCBs on the priority pollutants list by extraction with two solvents at three pHs and after cleanup with two adsorbents. The effects of pH, temperature, and residual chlorine on the preservation of spiked samples were determined, and results from the application of the method to wastewater samples are given also.
EXPERIMENTAL SECTION Apparatus. The gas chromatograph used was a HewlettPackard, Model 5710A, equipped with a Model 18713A linear EC detector, interfaced to a Hewlett-Packard 3354 data system. The analytical column was 1.8 m X 6.35 mm glass tubing packed with 1.5% SP-2250plus 1.95% SP-2401on 100/120 mesh Supelcoport (Supelco 1-1947). Operating parameters were usually as follows: oven temperature, 200 "C; detector temperature, 300 "C; injection port temperature, 225 "C; carrier gas (5% methane in argon) flow rate, 60 mL m i d . Occasionally, oven temperatures of 180 or 160 "C were used when chromatographing early eluting PCBs to facilitate manual peak height measurements. 0003-2700/81/0353-0214$01,00/0
The separatory funnels used were 2OOO-mL capacity with Teflon stopcocks, the Kuderna-Danish apparatus was Kontes K-570000, 500-mL size, and the chromatographic columns were Kontes K-420540-234. Reagents. All solvents used were Burdick and Jackson distilled-in-glass solvents, suitable for pesticide residue analysis. The ethyl ether contained 2% ethyl alcohol as preservative. Sodium sulfate, Baker's 5-381, ACS, anhydrous, granular was used in the extraction and preservation studies. This product must be purified by either of two ways: heating in thin layers at 450-500 "C overnight or, preferably, extracting in a Soxhlet apparatus with dichloromethane (DCM) for 16 h, before use (5). In the part of the program in which wastewater extractions were performed, Baker's 5-3375, sodium sulfate, anhydrous, 12-60 mesh was used. This product has been prepared especially for residue analysis and a solvent rinsing (100 mL of hexane poured through 50 g in a chromatography tube) cleaned it sufficiently. Florisil, PR grade (60/100 mesh), as received from the Johns-Mansville distributor, was placed in a solvent-rinsed stainless steel pan, covered with solvent-rinsed aluminum foil having numerous small holes in it made by an ice pick, and kept in an oven at 130-140 "C for at least 16 h before use. The alumina used was Woelm, neutral, Super 1,04583. Hexane-washed Hengar granules were used to prevent bumping of extracts during concentration. Standard solutions of endosulfan sulfate and endrin aldehyde were obtained from Nanogens, Inc. All other OCPs and PCBs were obtained from the Quality Assurance Section, Environmental Protection Agency, Health Effects Research Laboratory, Environmental Toxicology Division, Analytical Chemistry Branch (MD 69), Research Triangle Park, NC. Procedure. The single-compound pesticides were divided into two analytical groups of eight each, based on their GC separability, to minimize the number of individual operations that had to be performed. The two groups were as follows: group 1,a-BHC, p-BHC, &BHC, heptachlor epoxide, 4,4'-DDE, 4,4'-DDD, 4,4'DDT, endosulfan sulfate; group 2, yBHC, heptachlor, aldrin, endosulfan I, dieldrin, endrin, endosulfan 11, endrin aldehyde. The multicompound substances, chlordane, toxaphene, and Aroclors (ARs) 1016,1221,1232,1242,1248,1254, and 1260, were handled individually, making a total of 11analytical groups that were taken through the program operations. Glassware was subjected to ordinary laboratory washing, solvent rinsed, and then placed in an oven at 275 "C or higher, overnight. Before use the glassware was solvent rinsed again. Extraction Study. Unchlorinated well water from the Edwards Underground Aquifer was used as the spiking medium because it was lower in interferences than water from a widely used supercartridge deionization system. The pH of the water was adjusted to 2,7, or 10 with H2S04or NaOH, and then 1-L portions were spiked with 100-rL volumes of acetone solutions containing the amounts of the OCPs or PCBs shown in Tables I and I1 and extracted with DCM or 15% DCM in hexane following the procedure given in 1973 in the Federal Register (1) for obtaining OCP from industrial effluents. Extracts were dried with Na2S04and concentrated to 10 mL in a Kuderna-Danish apparatus. Preservation Study. This study was conducted with the same water used in the extraction study to determine the effects of a 7-day storage period, under various physical conditions, on the recovery of the 25 substances from spiked clean water samples. Eight samples of each analytical group were spiked at the same concentrations and at the same pHs as in the extraction study. Four of the samples were also spiked with 2 ppm NaOC1. Two 0 1981 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 53, NO. 2, FEBRUARY 1981
Table I. Extraction with DCM av % recovery pH2 p H 7 pH 10 aldrin (30)a a-BHC (20) 8-BHC (40) T-BHC (20) 6 -BHC (40) 4,4‘-DDD(120) 4,4’-DDE (60) 4,4’-DDT(1 60) dieldrin (60) endosulfan I ( 5 0 ) endosulfan I1 (100) endosulfan sulfate (310) endrin (90) endrin aldehyde (230) heptachlor (20) heptachlor epoxide (40) chlordane (380) toxaphene (3800) Aroclor 1016 (1290) Aroclor 1221 (3000) Aroclor 1232 (3000) Aroclor 1242 (1500) Aroclor 1248 (2250) Aroclor 1254 (750) Aroclor 1260 (1500)
64 97 94 109 104 97 94 102 96 98 98 98 106 100 59 100 103 93 89
77 92 99 96 91 101
46c 95 95 92 92 97 92 104 100 102 99 92 108 92 60 100 99 104 87 96 84 101 92 101 100
68 92 91 101 97 93 81 92 101 101 94 89 108 99 72 89 102 111 88 80 83 104 91 96 100
a Amount in ng added to 1 L of water. Average of three replicates, Average of four replicates.
Table 11. Extraction with 15% DCM in Hexane av % recovery pH2 pH7 pH10 aldrin (30)a a-BHC (20) 8-BHC (40) T-BHC (20) 6 -BHC (40) 4,4’-DDD(120) 4,4’-DDE(60) 4,4’-DDT(160) dieldrin (60) endosulfan I ( 5 0 ) endosulfan I1 (100) endosulfan sulfate (310) endrin (90) endrin aldehyde (230) heptachlor (20) heptachlor epoxide (40) chlordane (380) toxaphene (3800) Aroclor 101 6 ( 1 290) Aroclor 1221 (3000) Aroclor 1232 (3000) Aroclor 1242 (1500) Aroclor 1248 (2250) Aroclor 1254 (750) Aroclor 1260 (1500)
60 95 101 106 95 98 93 104 99 102 100 94 104 102 70 93 103 100 85 75 82 102 96 104 101
54c 98 104 106 93 103 96 105 100 104 103 92 104 91 63 99 101 100 93 87 93 100 97 101 99
73b 98 104 86 103 103 85 105 102 104 99 96 103 105 77 99 103 102 82 65 89 96 94 103 99
a Amount in ng added to 1 L of water, Average of three replicates. Average of four reolicates.
of the chlorinated and two of the unchlorinated samples were each stored in darkness at 4 “C, and the other two identical sets of pairs were stored in darkness at 24 OC. Storage containers were glass bottles (946 mL) sealed with aluminum-foil-lined caps, applied immediately after sample preparation. Care was taken not to slosh the contents onto the aluminum lining of the cap after the bottles were sealed. Aluminum-lined caps were chosen over Teflon-lined caps because Bellar and Lichtenberg (6)reported possible losses of PCBs with the latter caps during storage of samples. Samples were extracted as in the extraction study, at the pH at which they
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were stored, using 15%DCM in hexane as the extracting solvent. Liquid-Solid Column Chromatography. The percent recoveries and the elution patterns of the 25 substances from Florisil and alumina were determined by preparing for each analytical group five columns of each adsorptive solid that were identically spiked and eluted, followed by analysis of the recovered fractions. The Florisil column procedure incorporated features of methods published earlier ( 2 , 3 ,7). The column was prepared by gently packing to a height of 10 cm Florisil PR taken directly from storage at 130-140 “C for a minimum of 24 h. A layer of Na2S041-2 cm in height was added. The column was immediately wetted with 60 mL of hexane and drained to the top of the Na2S04,and then a 5-mL volume of hexane containing the spike of one of the groups was put on the column which was drained again to the top of the Na2S04. Elution was then performed with 200-mL volumes of 6, 15, and 50% ethyl ether in hexane, collecting each 200-mL fraction in a Kuderna-Danish flask for concentration to a 10-mL final volume. The alumina column procedure was based on the method of Telling, Sissons, and Brinkman (8). Ninety grams of alumina and 10 mL of water were mixed in a capped jar until smooth flowing. The deactivated alumina was allowed to stand for 24 h before use. The column was prepared with a slurry of 22 g of the deactivated alumina in hexane, topped with 1-2 cm of Na2S04, and washed with 20 mL of hexane. The spikes were applied in 5-mL volumes followed by elution in succession with 40 mL of hexane, 110 mL of hexane, and 100 mL of 50% ethyl ether in hexane. Each fraction was collected and concentrated in a Kuderna-Danish apparatus to a final volume of 10 mL. Wastewater Application. The techniques described above were tested on five wastewaters. Two of the wastewaters were from plants manufacturing OCP or other chlorinated products, one was from an “organics or plastics” manufacturer (products of manufacture were not revealed), and the other two were from a municipal sewage treatment system in a highly industrialized area, one being the plant influent and the other being the chlorinated final effluent. Analyses of the wastewater for the 25 pollutants were conducted, followed by spiking and recovery testa. Six glass containers of wastewater (946 mL) were spiked in amounts equal to that used in the liquid-solid column chromatography studies earlier in the program. Three of the samples were analyzed immediately and three were sealed and then stored for 7 days in darkness at 4 O C before being analyzed. The percent recovered at zero time was considered to be the “method recovery” value (i.e., percent of amount spiked) and the percent recovered after storage for 7 days was considered to be the “preservation recovery” (Le,,percent of zero time assays),calculated as follows: let k = background (amount found in the unspiked wastewater), let y = quantity added to wastewater, let x o = quantity found in spiked wastewater at zero time for replicates 1,2, or 3, let xoav = average quantity found in spiked wastewater at zero time, and let x l = quantity found in spiked wastewater after 7 days for replicates 1,2, or 3. Then “method recovery” = (xo - k)100/y% (calculated for each replicate) and “preservation recovery” = (x7)(100)/xoav% (calculatedfor each replicate). The preservation recovery is intended to reflect degradation of the substance during storage. As such, the amount found at time zero represents the total amount (background plus spike) in the water. No correction is made for background under the assumption that both background and spike are affected by storage conditions in the same manner. The precision of the analyses was estimated by using the range of the triplicate determinations. The range is defined as the arithmetic difference between the highest and lowest observed values among the replicates. Method of Quantitation. The solutions of the analytical groups used for spiking samples were also used to prepare the standard solutions used in determining percent recoveries. At the time spiking was done, the same volume of spiking solution used for the spike was placed into hexane in a 10-mL volumetric flask and then the solution level was brought to the mark. Since the final volume of an extract at the end of the last concentration step before analysis was always 10 mL, the two solutions were directly comparable. A solvent-flush technique was used to inject 5-pL volumes of both solutions into the GC. The quantities of substances in the analytical groups were ratioed to each other on
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the basis of their specific detector responses so that all peaks generated were always on scale at one electrometer attenuation setting. The peaks generated were related to the quantities of substances injected by both manual peak height measurements and electronic integration of areas. Area measurements were usually dependable for all the single-compound pesticides. However, for the multipeak pesticides and the PCBs, disagreement often occurred between the data from area measurements and those from peak-height measurements. In these instances, the peak-height measurements were found to be the more reliable of the two. Recoveries for the multipeak substances were based on the average of the values for recovery given by each peak measured during analysis. In the extraction study, only three peaks were measured for chlordane; for the remainder of the program, six peaks were measured. For all other multipeak substances, 6-11 peaks were measured for each substance throughout the entire program. RESULTS AND DISCUSSIONS Extraction Study. The average recoveries from clean water are given in Tables I and 11. All substances were extracted with better than 80% efficiency regardless of solvent or pH, except for aldrin and heptachlor. The reasons for the notably lower recoveries of these two compounds are unknown. The extraction data were subjected to statistical analysis by a two-way analysis of variance (ANOVA) procedure, with the 5% significance level used in all tests. In some instances, the precision of the individual analyses allowed differences to be termed significant that were too small to be of any practical importance. Although the overall best extraction of the pesticides and PCBs in the study was with 15% DCM in hexane at pH 10, the differences between these results and those obtained a t other pHs with the same solvent or with 100% DCM are not of such magnitude as to exclude these other conditions from use. Satisfactory extraction is obtained with either solvent at any of the three pHs. However, if the substance being assayed is definitely designated beforehand, a slight advantage may be available in some cases by considering the combined pH-solvent effects on the extraction of that particular substance (9). One advantage in using DCM is that it can be drained from the separatory funnel first and the sample remains in the funnel ready for the next extraction; whereas, with the DCM-hexane solvent, the sample must always be drained before the extract can be removed. Then the sample must be poured back into the funnel for the next extraction. Preservation S t u d y in Clean Water. The results were submitted to statistical analysis, by an ANOVA procedure, to determine the optimum storage conditions for each group and to estimate the recoveries that could be expected for each substance. Mean recoveries at 4 "C for all pHs are shown in Table 111, and Table IV gives the mean recoveries a t 24 "C for all pHs. The beneficial effects of storage at 4 "C were obvious, but the question of which pH was best was not answered with equal clarity. Recoveries at pH 7 were similar to those a t pH 2, and p H 10 was actually beneficial in some cases, although endosulfan I and I1 completely disappeared. The only effect that was attributed exclusively to chlorine was on aldrin at pHs 2 and 7 . Other instances where a chlorine effect is indicated in the tables, the effect was in combination with one or both of the other two test parameters. As was the case with the extraction study conditions, the analyst may be able to select a particular set of conditions that is best for preserving a particular substance. In addition to the effects already mentioned, several others were significantly large. a-BHC, 7-BHC, and 6-BHC showed losses of 66% or larger at 24 OC and pH 10. Greater than 80% of heptachlor disappeared when stored at 24 O C in the absence of chlorine. At 24 OC and pH 2 , about 75% of the endrin disappeared. Only 5-10% of the endosulfan sulfate remained after storage at all conditions. Endrin aldehyde disappeared
Table 111. Mean Recoveries from Preservation Test in Clean Water at 4 "Ca % recovery PH 2 PH 7 pH 10 aldrin a-BHC 8-BHC 7-BHC 6 -BHC 4,4'-DDD 4,4'-DDE 4,4'-DDT
8gb (15)' 64 86 100 80 98 94 94 105 96 102
