Environ. Sci. Technol. 1986, 20, 249-253
Transformation of Trace Organic Compounds in Drinking Water by Enzymatic Oxidative Coupling Stephen W. Maloney, * Jacques Manem, Joel Mallevialle, and Frangois Flesslnger Laboratoire Central, Lyonnaise des Eaux, 38, rue du President Wilson, 78230 le Pecq, France
Enzymatic methods have shown promise for removing aromatic compounds from (high-strength) industrial wastewater. The removal of these compounds was studied at low levels that might be encountered in surface waters which receive some industrial discharge. The results indicate that enzymatic oxidative coupling using horseradish peroxidase and hydrogen peroxide may be useful in eliminating some aromatics that are not well-removed in biological or physical water treatment, but the nature of the byproducts must be determined to @sure that the produds are not more undesirable than the initial compounds. Introduction
A new method has been suggested for removal of aromatic compounds from water. The procedure (1,2)involves enzymatic coupling of aromatic compounds and precipitation of the less soluble, high molecular weight end products. Horseradish peroxidase (HRP) catalyzes the oxidative coupling in the presence of hydrogen peroxide. This new method has been demonstrated on a laboratory scale with synthetic mixtures at concentrations (e.g., 100 mg/L) found in industrial wastewaters. These concentrations are quite high compared to drinking water, where the levels of specific organics lie in the nanograms per liter-micrograms per liter range. However, little effect of concentration was observed for one aromatic compound that was studied at a concentration as low as 0.5 mg/L (3). Therefore, this process may be useful in drinking water treatment for the removal of trace organic compounds. Water utilities must be concerned not only with the ability of a process to eliminate a specific pollutant but also with the nature and fate of the products of the reaction. Klibanov and Morris (3)showed that a precipitate was formed during the removal of aromatic amines using HRP, so the products may be removable by sedimentation and/or filtration. However, they did not identify specific products. Schwartz and Hutchinson (4) also observed the formation of high molec4ar weight polymers, however, 3% of the substrate was converted into biphenyls. Such compounds would not be well-remoyed in conventional coagulation or filtration and may be the predominant products at low substrate concentration. The trace-level synthetic organic compounds in drinking water are usually accompanied by natural organics. These natural organics are comprised mainly of humic acids (5), which contain, among other functional groups, phenolic structures (6). Recent data suggest that humic acids may deactivate peroxidase (7). Thus, these humic acids present a potential interference in the peroxidase phenol coupling. This paper examines WRP oxidative coupling of several chlorinated phenols. These compounds were chosen because they arise from a variety of anthropogenic sources @-IO), are often toxic (11,12),and present taste and odor problems in finished drinking water (13). Feasibility at low dubstrate concentration, interferences from natural background organics, and the nature of final products were investigated. Materials and Methods
The phenolic compounds 2-chlorophenol (2-CP), 2,4dichlorophenol(2,4-DCP), and pentachlorophenol (PCP) 0013-936X/86/0920-0249$01.50/0
were taken from a phenol test kit (4-4570, Supelco, Inc., Bellefonte, PA). Radiolabeled 2,4-DCP (specific activity = 114 lCi/mg, Amersham International, Amersham, England) was used to lower the limit of detection and to follow the fate of byproducts. HRP (Type IV, Sigma Chemical Co., St. Louis, MO, EC 1.11.1.7)was assayed for activity using the manufacturer’s instructions, yielding a value of 250 units/mg. Hydrogen peroxide (30%) was purchased from Prolabo (Paris, France). The various chlorophenols were mixed in water purified by the Milli-Q system, (Millipore Corp., New Bedford, MA), filtered river water, or tap water, as noted in the text. Samples of the chlorophenols were placed in 250-mL flasks on a gyratory shaker (Model R2, New Brunswick Scientific, Edison, NJ). The chlorophenol solutions were adjusted to pH 6-7 by a 10 mM phosphate buffer. Peroxide and/or HRP were then added to the solution, and the flasks were shaken at 175 rpm for 3 h. Selected samples were then centrifuged (danetzki K24, Englesdorf, Germany) at 12 000 rpm to remove any suspended material. High-pressure liquid chromatography (HPLC) was used to identify phenols and separate the products of the reaction. The system included a Du Pont 870 pump module, 850 absorbance detector, and a 4.6 mm X 25 cm Zorbax ODS liquid chromatography column (Du Pont and Co., Wilmington, DE). Analysis of 2-CP was performed with a mobile phase of 33% methanol in water. A binary gradient (0-100% methanol in water over 25 min) was used to elute 2,4-DCP. For the radiolabeled 2,4-DCP, subsamples were collected simultaneously with absorption (254 nm) detection. These subsamples were analyzed by mixing 2 mL of subsample with 8 mL of Pic0 Fluor 30 and counting on a Tri-Carb 300C (United Technologies Packard, Zurich, Switzerland) liquid scintillation system. The products of the enzyme reaction were identified by using mass spectrometry (MS) (ZAB, VG Micromass Ltd., Chesire, England) at Centre National de Recherche Scientifique (Lyon). Samples were injected directIy onto the mass spectrometer. Results
Initial experiments were conducted with pentachlorophenol (PCP) using 34 mg/L or 170 mg/L peroxide, 100 units/L HRP, and 100 mg/L PCP, according to the methodology described by Klibanov and co-workers (1-3). The results did not indicate significant removal of PCP. At 34 mg/L peroxide the removal was 15-20%, and at 170 mg/L, removal was only marginally better at 20-30%. Examination of the previous work (1-3) showed that a wide range of conditions had been used, but PCP had not been studied. Thus, for the purpose of testing proven enzyme mechanism under water treatment conditions, a reportedly successful experiment (i.e., with 2-CP) was duplicated to confirm the technique. Table I shows the results for several experiments involving 2-CP. The initial experiments followed the reported procedure (2) but did not result in the 99% removal of 2-CP. However, significant removal was observed, and as can be seen in Table I, all concentrations below 1mg/L were removed or transformed at greater than 95%.
0 1986 American Chemical Society
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249
Table I. Removal and/or Transformation of 2-Chlorophenol (2-CP) by Enzymatic Oxidative Coupling 2-CP concn, mg/L 100
solvent
0.01 0.01
Milli-Q Milli-Q Milli-Q Milli-Q Milli-Q Milli-Q Mi11i-Q Mi11i-Q Milli-Q Milli-Q Mi11i-Q
0.01
tapwater
1 0.3 0.3 0.3 0.3
river river river river river
100 100 100 10 10 1 1 0.1
enzyme concn, units/L
water water water water water
1000
Envlron. Scl. Technol., Vol. 20, No. 3, 1986
centrifugation
% removal
+ + -
34 34 170 170 170 170
-
1000 1000 1000 1000 100
170 170 170 170 170
-
75 75 75-90 75-90 95 95 >95 >95 295 >95 >95
100
170
-
>95
1000 1000 1000 1000 100
170 34 170 170 170
1000 1000 1000
1000 1000
The appearance of a dark precipitate was observed at the higher concentrations as reported in the literature (3). However, no precipitate was observed for the lower concentrations. Centrifugation did not improve the removal or transformation of the 2-CP and was discontinued for most of the experiments, as shown in Table I, The effects of background organic compounds can also be seen in Table I. Filtered water was taken from a pilot plant on the river Seine upstream of Paris, France. The total organic carbon (TOC) concentration of this water was approximately 2 mg/L. 2-CP was added to a concentration of 0.3 mg/L and analyzed with several combinations of peroxide and peroxidase. The results indicated background organics, assumed to be primarily humic and fulvic acids, do not interfere in or compete with the enzymatic coupling. The limit of detection of the HPLC method for chlorophenols was approximately 0.001 mg/L. This is still quite high compared to observed phenol concentrations in water. Radiolabeled 2,4-dichlorophenol was used to lower the limit of detection and to determine where the products of the enzymatic coupling appeared on the chromatogram. After the collected samples were analyzed by UV absorption they were subsequently analyzed by scintillation counting. Table I1 shows the results of experiments conducted with the radiolabeled 2,4-DCP in tapwater and Milli-Q water. Both results are shown only when there was a difference. The differences never exceeded 5%, thus, there is further evidence that the presence of background organics in the tapwater (TOC = 2 mg/L) does not appear to interfere in the reaction. Each experiment was conducted with four combinations of chemical addition. Three of these combinations acted as controls. The first combination was the 2,4-DCP alone in the water matrix, which acted as a control on the stability of the chemical. The second combination was HRP and 2,4-DCP, to determine whether the reaction would proceed without the peroxide. The third control was the H202and 2,4-DCP in solution together, to determine if the reaction were chemical, not requiring the enzyme as a catalyst. There was no transformation of 2,4-DCP in any of the controls. Figure 1 shows typical chromatograms for HPLC analysis of 2,4-DCP. The conditions for this experiment were 120 mg/L 2,4-DCP, 170 mg/L peroxide, and 1000 units/L HRP. The chromatograms were obtained at enzymatic reaction times of 0,5, and 30 min. The times of 250
peroxide concn, mg/L
+
+
>95 >95 >95 >95 >95
Table 11. Removal and/or Transformation ( W )of 2,4-Dichlorophenol (2,4-DCP) by Enzymatic Oxidative Coupline 2,4-DCP concn, mg/L
1000
enzyme concn, units/L 100
240 120 60 24 10 3 0.6 0.06 0.008 0.0025
-
47-42
7-10
93-95 >95 >95 >95* >95 >95 >95 >90 >90
94-92 95 >95 >95 >95 >95 >90 >90
25-22 47-50
-
10 -
-
82-80 >95 >95
-
Conditions: Unless otherwise noted, all experiments were run with Milli-Q water and tapwater. Where there was a difference, Milli-Q water is shown first, e.g., 7% removal at 10 units/L peroxidase and 250 ppm 2,4-DCP. Peroxide concentration is 170 mg/L. Time of reaction is 3 h. pH range is 6.5-7. *Experiment run a t 34 mg/L and 170 mg/L peroxide.
c II
Dhrnol
0 IO 0 10 Flgure 1. HPLC chromatograms showlng 2,4-DCP removal and byproduct formation by HRP-H202: effects of reaction time.
reaction me shown in the boxes and should not be confused with the time of HPLC analysis, shown on the chromatogram base line. Several byproduct peaks are shown in the latter chromatograms as the 2,4-DCP disappears.
9 t OH
I6 i
loo
Unaccounted
cl@
73
60
3
CI
sV
304
I
m i
CI2
Cl2
320
236
40 %
J 20 CI
0
06
3
24
60
0 120 240
CI
252
C‘2
360
2,4-DCP (rng/L)
Flgure 2. Distribution of radiolabeled fractions after treatment with various concentrations of 2,4-DCP using 100 units/L HRP and 170 mg/L H,O,.
ci
Cl
254
376
I
,100
00 60
B a
Cl
3
CI
322
2
0
40 %
J 20
‘0 40 2,4-DCP (mg/L)
Figure 3. Distribution of radiolabeled fractions after treatment with various concentrations of 2,CDCP using 10 units/L HRP and 170 mg/L H202.
(Note: Byproduct formation was not observed by HPLC/UV analysis for 2-CP.) Figures 2 and 3 show mass balances on the radiolabeled 2,4-DCP. Figure 2 represents the data obtained with 100 units/L HRP, and Figure 3 represents 10 units/L HRP. Both figures have the same general shape. However, at the higher HRP concentration, the features of the curves are pushed to the right (to the higher substrate concentrations). A relatively stable distribution of the products is achieved at higher 2,4-DCP concentrations for the 100 units/L HRP than for the 10 units/L experiments. The figures show the percentage of added carbon-14 as the difference between two lines. Thus, the two lines representing 2,4-DCP rapidly converge as the concentration of initial 2,4-DCP decreases. The use of the label indicates that at least two major classes of byproducts are formed. The first class, an apparently polar fraction, is eluted early in the analysis and does not appear to be accompanied by a response on the absorbance detector. Significant amounts of the label are also found associated with the 2,4-DCP peak (when present) and the second major class, a nonpolar fraction, which does exhibit response on the detector in the region of the byproducts shown on Figure 1. There was also a large amount of “unaccounted” radiolabel in some cases. The data in these figures also show that there are levels at which the concentration of peroxidase becomes limiting. In Figure 2, the 95% transformation level is achieved somewhere between 24 and 3 mg/L 2,4-DCP when the peroxidase concentration is 100 units/L. Figure 3 shows that 95% transformation is not achieved until about 0.6 mg/L when the enzyme concentration is 10 units/L. A short series of experiments were conducted to investigate the “unaccounted” carbon-14 in the mass balance
Figure 4. Byproduct identification for HRP-peroxide oxidative coupling of 2,4-DCP (100 mg/L 2,4-DCP, 1000 units/L HRP, 170 mg/L H,02).
from the HPLC analysis. Filters prior to the HPLC were suspected of trapping some of the reaction products. A solution of HRP (lo00 units/L), peroxide (170 mg/L), and 2,4-DCP was prepared and shaken for 3 h. The resulting solution was then filtered. The precolumn frit (20 pm) was tested directly and shown not to remove any radioactivity from the treated water sample. The HPLC column has a 2-pm frit, but it could not be tested directly. Membranes of that size were not readily available in the laboratory, so a 0.45-pm silver membrane was used. For the 0.45-pm membrane, approximately 50% of the radioactivity was removed. This is somewhat higher than the amount not accounted for in the mass balance, but this is likely due to the smaller fiiter size used. Based on these observations, the unaccounted material is tentatively attributed to filtration of polymerized aromatic compounds. Conversely, approximately 50% or more of the products remain water soluble. The second major consideration in a treatment study for potable water (after evaluating efficacy) is the nature and fate of the products of the process. Figure 4 shows selected results from the MS analysis of the products of the reaction when 2,4-DCP was the micropollutant. Among the byproducts, compounds that are similar to dioxins and dibenzofurans are identified. Fragments with up to four ring units were identified, and it is likely that longer polymers were also present. This contrasts with results obtained with a laccase (14) in which diphenol formation was observed.
Discussion The application of enzyme technology to water treatment has been evaluated here for one system of enzymes. Several chlorinated phenols were chosen for evaluation of HRP in this study. A protocol was designed to use laboratory-scale experiments to answer the following questions with respect to the feasibility of enzymes in drinking water treatment: (1)effectivenessat low organic concentrations; Environ. Scl. Technol., Vol. 20, No. 3, 1986 251
(2) absence of interference from background organic; (3) nature of the products of the reaction; (4) fate of the products of the reaction; (5) nature of byproducts from standard water treatment unit operations, e.g., chlorination, ozonation, adsorption; and (6) interference between standard unit operations and the enzyme reaction. A key feature of this study was the use of radiolabeled substrates to determine the distribution of products and to work at low substrate concentrations. Trace organics commonly found in drinking water are at concentrations requiring extraction from a large volume of water and subsequent concentration steps. The use of radiolabels allows a laboratory-scale study to proceed near raw water organic concentrations with relatively small amounts of water and allows the distribution of byproducts to be generally determined without identifying all the individual components. The results of this study follow the process through step 3. Due to the possible formation of undesirable products of the reaction (dioxins),the study of HRP was terminated a t this step. However, there were also several positive observations with regard to enzymatic processes in drinking water treatment. Effect of Hydrogen Peroxide and Enzyme Concentrations. Using several enzyme and substrate combinations demonstrated two important aspects of the process. The first observation is that the capacity of the enzyme reaction is limited, and at high concentrations of substrate compared to enzyme, the substrate is not well-removed and/or altered. This can be seen by comparison of Figures 2 and 3. For example, at 100 units/L peroxidase and 24 mg/L 2,4-DCP, only 6% of the original 2,4-DCP remained unchanged, whereas 53% remained unreacted when 10 units/L was used. Although this may seem to be an obvious expected result, recall that it is the peroxide and substrate that are being consumed in the reaction and the enzyme is there as a catalyst. The reactions were all conducted at 170 mg/L hydrogen peroxide. Thus, the reactants at each substrate (2,4-DCP) concentration in Figures 2 and 3 are similar; only the catalyst concentration is different. Increasing the time did not improve removal for the lower enzyme concentration. Two explanations are proposed for this phenomenon. (1)When the ratio of Hz02 to enzyme was high, Hz02acted as an inhibitor. Thus, increasing the enzyme concentration would lower the ratio and remove the inhibition, thus increasing the removal. (2) The H20zwas being consumed in an unrelated reaction for which it had less affinity than the HRP reaction. Thus, increasing the enzyme concentration increased removal by using the Hz02in the oxidative coupling reaction before it was consumed in the competing side reaction. The data from this study are not sufficient to determine whether one of these explanations, or another reason, was responsible for the observed results with the lower enzymes concentrations. A second important observation is that at the levels of trace organics normally encountered in drinking water, very little enzyme may be required to effect greater than 95% removal. Although 10 units/L peroxidase was insufficient for good removal in the milligram per liter substrate range, it appeared to work quite well at lower concentrations, which were closer to levels observed in raw waters. Reaction Byproducts and Their Formation Mechanisms. The reaction products (polymers containing dioxin and furan type linkages) for HRP were disappointing. Previous research with HRP and phenol (16) 252
Environ. Sci. Technol., Vol. 20, No. 3, 1986
indicated that o,o’-biphenol was the product (Note: MS identification was not used). Furthermore, coupling of 2,4-DCP by a fungal laccase also resulted in a biphenol (14). In the latter study, MS identification was used. Preliminary MS studies with another phenol (0-cresol) in this laboratory (15) have not shown the dioxin-type linkage between units in the polymerized product. Rather, the carbon-carbon link as reported for HRP and phenol (16) was observed. Thus, the polymerization mechanism on HRP may be different depending on the aromatic substrate and possibly on substituted chlorine molecules. The occurrence of dioxin and furan types linkages in the oxidative coupling of phenols has been observed using other enzymes and other substrates. The tyrosinase-catalyzed oxidation of catechol has a dioxin-type linkage as one of the possible products (17-19). The furan-type linkage has been observed for oxidation of p-cresol by hydrogen peroxide in the presence of HRP (19,20). This furan-type linkage was found to be 13.4% of the yield, with the predominant products being the carbon-carbon link as observed in this laboratory (15)for o-cresol. Scott (21) observed that the C-C linkage was more common than C-0, except when steric hindrance became a major factor. This gives further evidence that the presence of the chlorine on the phenol (which could cause steric hindrance) is responsible for yielding the undesirable products. Unfortunately, it is the chlorinated phenols that are the greater problem (rather than phenol) because they are more toxic and present a taste and odor in drinking water. The capability of chlorine substitutions to modify the HRP/peroxide/aromatic reaction may also explain why the system was ineffective for pentachlorophenol removal at 100 units/L HRP. The results obtained for PCP at 100 units/L, 170 mg/L peroxide, and approximately 100 mg/L substrate show that removal was on the order of 30%. Previouis investigators (1, 2) have shown that 3chlorophenol is not well-removed (95% of 100 mg/L), and other poorly removed compounds were better removed when treated as a mixture with well-removed compounds (2). Thus, chlorine substituted at critical positions on the phenol may modify the polymerized product and/or substantially inhibit the reaction. Water Treatment Application. When HRP was used to transform a concentrated solution of 2-4-DCP, dioxins and furan derivatives were detected among the byproducts. If such potentially toxic byproducts were produced in water treatment, the use of HRP to remove aromatic compounds may be undesirable. However, in realistic water treatment applications chlorinated phenols are present in trace concentrations. Moreover, naturally occurring organics may enter into the reaction in a manner that significantly alters the byproducts. Consequently, studies should be done to characterize the fate of aromatic compounds in natural waters when HRP is used in potable water treatment. Conclusions Enzymatic coupling of aromatic compounds is feasible under conditions similar to water treatment. Background organics do not appear to interfere in the process. However, 50 % or more of the product compounds remain water soluble (i.e,, pass through a 0.45-pm filter). Thus the specific organic is changed but not completely removed from the water. The removal of some chlorophenols at the levels (nanogram per liter-microgram per liter) ordinarily encountered in natural water requires small amounts of the en-
Environ. Sci. Technol. 1986. 20, 253-256
McCarty, P. L. J. Environ. Eng. Diu. Am. SOC.Civ. Eng. 1980, 106-114. Schnitzer, M.; U. Khan, S. U. “Humic Substances in the Environment”; Marcel Dekker: New York, 1972. Pflug, Z. Z. Pflanzenernach. Bodenkd. 1980,432-440. Wolkoff, A. W.; Larose, R. H. J . Chromatog. 1974, 99, 731-743. Rudling, L. Water Res. 1970, 4, 533-537. Baker, R. A. J . Am. Water Works Assoc. 1966,58,751-760. Stanlake, G. J.; Finn, R. K. Appl. Environ. Microbiol. 1982, 44, 1421-1427. Stecher, P. G. et al. “The Merck Index”, 8th ed.; Merck and Company, Inc.: Rahway, NJ, 1968. Smith, J. G.; Lee, S.; Netzer, A. Water Res. 1976, 10, 985-990. Bollag, J. M.; Liu, S. Y.; Minard, R. D. Appl. Environ. Microbiol. 1979, 38, 1, 90-92. Manem, J.; Bruchet, A; Fraisse, B.; Maloney, S. W. Presented at the International Symposium on Analytical Methods and Problems in Biotechnology (ANABIOTEC), Noordwijkerhout, The Netherlands, April 1984. Danner, D. J.; Brignaz, P. J.; Arceneaux, D., Jr.; Patel, V. Arch. Biochem. Biophys. 1973,156, 759-763. Forsyth, W. G. C.; Quensel, V. C.; Roberts, J. B. Biochim. Biophys. Acta 1960, 37, 322-326. Forsyth, W. G. C.; Quensel, V. C. Biochim. Biophys. Acta 1957,25, 155-160. Brown, B. R. “Oxidative Coupling of Phenols”; Taylor, W. I., Battersby, A.R., Eds.; Edward Dekker: New York, 1967; p p 167-201. Westerfield, W. W.; Lowe, C. J. Biol. Chem. 1942, 145, 463-470. Scott, A. I. “Oxidative Coupling of Phenols”; Taylor, W. I., Battersby, A. R., Eds.; Edward Dekker: New York, 1967; pp 95-117.
zyme. The application of 10 units/L HRP was sufficient to remove 95% of the 2,4-DCP at the concentration of 600 pg/L. This result cannot be generalized to all aromatic compounds. There appear to be several products of HRP reactions, depending on the substrate. These include polyphenols with carbon-carbon bonds on an aromatic ring, chlorinated furans, and dioxins. The products, rate, and extent of the reaction may be related to chlorine (or other functional group) substitution on the ring. Chlorine substitution appears to inhibit the reaction and favor the formation of dioxins and chlorinated furans, This illustrates the need to identify the products of an enzyme reaction when it is being applied to water treatment. The products of the enzymatic coupling are dependent on the substrate substituent groups. In drinking water treatment, operators have only limited control over raw water quality. Since chlorinated phenols may be partially transformed into dioxins and chlorinated furans, further research is required to evaluate the risk, if any, that this process presents in its application to potable water treatment. Registry No. 2-CP, 95-57-8; 2,4-DCP, 120-83-2;PCP, 87-86-5; HRP, 9003-99-0; hydrogen peroxide, 7722-84-1.
Literature Cited (1) Klibanov, A. M.; Alberti, E.; Morris, D.; Felshin, L. M. J. Appl. Biochem. 1980,2,414-421. (2) Alberti, B. N.; Klibanov, A. M. Proc. Biotechnol. Bioeng. Symp. 1981,11, 373-379. (3) Klibanov, A. M.; Morris, E. D. Enzyme Microbiol. Technol. 1981,3, 119-122. (4) Schwartz, R. D. Hutchinson, D. B. Enzyme Microbiol. Technol. 1981,3, 361-367.
Received for review September 21, 1984. Revised manuscript received September 9, 1985. Accepted October 21, 1985.
PCBs Have Declined More Than DDT-Group Residues in Arctic Ringed Seals (Phoca hispida) between 1972 and 1981 Richard F. Addison* and Maurice E. Zinck Department of Fisheries and Oceans, Marine Ecology Laboratory, Bedford Institute of Oceanography, Dartmouth, N.S., Canada B2Y 4A2
Thomas G. Smith Arctic Biological Station, Ste. Anne de Bellevue, P.Q., Canada H9X 3R4
Mean DDT-group concentrations in the blubber of western Arctic ringed seals (Phoca hispida) sampled in 1981were less than 1pg-g-l wet weight blubber, and mean PCB concentrations were less than 2 pg-g-’ wet weight. Male seals had higher concentrations than did females. PCB concentrations were about half of those in a sample of the same population taken in 1972, when allowance was made for the variation of residue concentrations with age, sex, and condition. This decline probably results from the ban on PCB manufacture and use imposed in the early 1970s. Concentrations of DDT-group residues did not show any clear decline over the same interval, and the relative proportions of p,p’-DDT and p , p ’-DDE suggested that there is a continuing supply of DDT to the western Arctic. The most probable source of this is by atmospheric or water transport from the Far East, where DDT was used until at least the late 1970s.
Introduction Concentrations of organochlorine residues in seal blubber vary with the animal’s age, sex, and condition. In 0013-936X/86/0920-0253$01.50/0
males, residue concentrations in blubber tend to increase with age (1-4)) and a similar trend is seen in other marine mammals ( 5 , 6 ) . This probably occurs because the males have no route other than slow metabolic degradation by which to excrete these compounds. In female seals, residue concentrations appear not to increase with age ( 2 , 3 )or at least not as sharply as in males ( 4 ) . We have attributed this difference (7) to the females’ ability to “excrete” large amounts of lipid (e.g., 8) and its associated residue burden during lactation; some residues may also be transferred to the fetus during its development (9). In both males and females, residue concentrations are inversely related to blubber thickness (2,4);presumably, this reflects preferential deposition or catabolism of lipid relative to that of organochlorines. To detect trends in residue concentrations in seals that may indicate changes in environmental contamination by organochlorines,we must eliminate these natural variables. We can do this most simply by analyzing reproducing females, in which residue concentrations are virtually independent of age. Also, since lactating females secrete a
Published 1986 by the American Chemical Society
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