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Comparison of PCB congener profiles in the embryos and principal prey of a breeding colony of black-crowned night-herons
Journal of Great Lakes Research 36 (2010) 548–553
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Journal of Great Lakes Research j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / j g l r
Comparison of PCB congener profiles in the embryos and principal prey of a breeding colony of black-crowned night-herons Jeffrey M. Levengood a,b,⁎, David J. Schaeffer b a b
Illinois Natural History Survey, Institute of Natural Resource Sustainability, University of Illinois, 1816 S. Oak St., Champaign, IL 61820, USA Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois, 2001 South Lincoln Ave., Urbana, IL 61802, USA
a r t i c l e
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Article history: Received 3 February 2010 Accepted 14 April 2010 Communicated by Craig Hebert Index words: PCBs Herons Prey Alewife Congeners Homologs
a b s t r a c t We compared polychlorinated biphenyl (PCB) congener profiles of embryos of black-crowned night-herons (Nycticorax nycticorax) nesting in an urban-industrialized area of Chicago, Illinois, USA, with those of regurgitated food boluses from nestlings and their primary prey. Consistent with previous studies of piscivorous birds, the PCB burden of embryos was shifted towards more heavily chlorinated congeners (those with 6, 7, and 8 chlorines), when compared to prey. The PCB congener profiles for measured and homolog concentrations in alewife (Alosa pseudoharengus) collected from Lake Michigan at the Chicago, Illinois, waterfront, closely resembled that of regurgitated food boluses collected from nestlings at the Lake Calumet colony. Also, alewife from Illinois and regurgitates were not clearly differentiated by the discriminant analyses for measured, proportional, and homolog concentrations. Congener profiles in alewife from the highly contaminated Indiana Ship Canal, which had a much higher PCB burden (geometric average = 1061.7 ng/g ww [95% CI = 648.6−1061.7 ng/g ww]) than did alewife from Illinois (158.1 [135.8−184.5]ng/g ww) and regurgitates (212.3 [177.0−254.7]ng/g ww), reflected a less-chlorinated mixture (i.e., Aroclor 1242). These results are consistent with our observations, which indicated that many of the adults of this colony were foraging along the Chicago waterfront, where alewife had lower PCB burdens. Because the congener patterns of the prey differ, the PCB congener profiles can be used to elucidate foraging patterns of colonial piscivorous birds and determine relative risks to exposed populations. © 2010 Elsevier B.V. All rights reserved.
Introduction Polychlorinated biphenyls (PCBs) are 209 synthetic chemicals (congeners) having 1 to 10 chlorines. Mixtures of PCBs were previously used as electrical insulating and hydraulic fluids, lubricants, plasticizers and flame retardants. Many PCBs are environmental toxins that are hepato-, immuno- and neurotoxic, endocrine disruptors, and possible carcinogens (Hoffman et al., 1996; Rice et al., 2003; Bursian, 2007). Although the manufacture, distribution and most uses of PCBs were banned in the United States and Canada during the 1970s, PCBs are nearly ubiquitous in the North American environment. Whereas environmental concentrations have generally declined, some heavilyindustrialized areas remain contaminated. PCBs are persistent and bioaccumulative, and have been commonly detected in herons in North America. More recently, for example, PCBs have been observed in great blue herons (GBH, Ardea herodias; Straub et al., 2007) and blackcrowned-night herons (BCNH, Nycticorax nycticorax; Levengood et al., 2007) in Illinois, USA; GBH along the St. Lawrence River in Quebec,
⁎ Corresponding author. Illinois Natural History Survey, Institute of Natural Resource Sustainability, University of Illinois, 1816 S. Oak St., Champaign, IL 61820, USA. Tel.: + 1 217/333 6767. E-mail addresses: [email protected] (J.M. Levengood), [email protected] (D.J. Schaeffer). 0380-1330/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jglr.2010.04.011
Canada (Champoux et al., 2006); BCNH and great egrets (Ardea alba) in coastal California (Henny et al., 2008), and BCNH in coastal northeastern USA (Matz and Parsons, 2004). PCB exposure in herons has been associated with: increased cytochrome P450 monooxygenase activity (Rattner et al., 1993; Levengood et al., 2007); reduced embryonic weight (Hoffman et al., 1986), reduced plasma retinol concentrations (Champoux et al., 2006), and, in combination with DDE, decreased nest attentiveness (Thomas and Anthony, 2003). PCBs also contribute, along with dioxins, to skeletal deformities (Thompson et al., 2006) and other manifestations of embryotoxity (Hoffman et al., 1993). PCB Aroclors are commercial mixtures of 60 to 90 different congeners, the latter determined by the chlorine content and position on the biphenyl backbone of the molecule. These characteristics determine the stability of the various congeners in the environment, their lipophilicity, metabolism and clearance in organisms. The resulting differences in PCB congener patterns or “profiles” in the tissues of birds have been examined in comparisons among taxa (Jaspers et al., 2008), locations (Levengood et al., 2007), between sediments and eggs (Berny et al., 2002) and among trophic levels (Guruge and Tanabe, 1997; Papp et al., 2007; Straub et al., 2007). Congener profiles can be used to “fingerprint” PCB exposure in biota, linking exposure with habitat use and/or prey utilization. For example, PCB congener profiles were associated with habitat-use patterns in migratory striped bass (Morone saxatilus) and American
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eels (Anguilla rostrata) in the Hudson and Delaware River drainages (Ashley et al., 2003). Papp et al (2007) examined PCB profiles in tree swallows (Tachycineta bicolor) and prey to elucidate prey utilization and contribution to that species' PCB exposure. Straub et al. (2007) utilized toxic equivalency factors in GBH eggs and nestlings to examine utilization of shad (Dorosoma cepedianum) from different parts of a contaminated lake. In this paper we compared PCB congener patterns, or “profiles”, in BCNH embryos, food boluses regurgitated by BCNH nestlings, and the principal prey (as observed in regurgitated boluses) from 2 locations where adult BCNH were known to forage. We hypothesized that congener profiles in embryos were reflective of those in predominant prey observed in food boluses regurgitated by nestlings, and that profiles in the boluses would be similar to that of the principal prey from areas of concentrated foraging activity.
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including the yolk sac was placed in chemically clean glass jars (EP Scientific Products, Miami OK) and frozen until analysis. Alewife were collected in June of 2002 by electrofishing from Jackson Park Harbor, located on the Lake Michigan waterfront in Chicago, Illinois, IL (alewfILL), and from the Indiana Ship Canal (ISC), near East Chicago, Indiana (alewfIND) (Fig. 1). Alewife were wrapped in acetone-cleaned aluminum foil and stored frozen in plastic bags until analysis. Alewife samples from Illinois (n = 5) and ISC (n = 6) represented a total of 10 and 11 individual fish, respectively, weighing 18 to 28 g each. A map showing the locations of the Lake Calumet BCNH colony, feeding aggregations along the Chicago waterfront, and the ISC is provided in Fig. 1. Based upon our observations (see Discussion) we inferred that many of the herons feeding along the lakeshore came from the Lake Calumet colony. Chemical analysis
Methods Sample collection Nestling herons may regurgitate food when approached by potential predators. This behavior has been used to collect material for food habits (Sodhi, 1985; Hall and Kress, 2008) and contaminant exposure (Rattner et al., 2001; Straub et al., 2007) studies. Although some limited digestion of food items occurred, prey was essentially intact and in most instances readily identifiable. Thus, the chemical composition of the regurgitates was considered representative of the prey prior to consumption. A total of 34 regurgitated food boluses (hereafter regurgitates) were collected into acetone-cleaned aluminum foil during nest checks at the Lake Calumet BCNH colony (Fig. 1) in 2002 and 2003. Eggs were collected in 2002 from nests (one each from 20 nests) during late incubation and incubated to pipping in the laboratory, at which time they were euthanized. Blood and livers were harvested for biomarker analysis and the remainder of each carcass
PCB analyses were conducted by the GC–MS Group of the Illinois Sustainable Technology Center, University of Illinois. A sub-sample of each ground specimen was homogenized and extracted with acetone: hexane (1:1) following USEPA SW-846 Method 3545, Pressurized Fluid Extraction (PFE), Revision 0, December 1996. Extracts were concentrated, exchanged to dichloromethane, and evaluated for lipids. The majority of lipids were removed from extracts via gel permeation chromatography (GPC), following USEPA SW-846 Method 3640A, Gel Permeation Cleanup, Revision 1, September 1994. Extracts were then subjected to a silica gel cleanup procedure in which the analytes of interest were separated into two fractions, based on USEPA SW-846 Method 3630, Silica Gel Cleanup, Revision 3, December 1996. The appropriate fraction was analyzed for polychlorinated biphenyls (PCB) via gas chromatography-electron capture detection (GC-ECD), following USEPA SW-846 Method 8081A, Organochlorine Pesticides by Gas Chromatography, Revision 1, December 1996, and USEPA SW-846 Method 8082, Polychlorinated Biphenyls (PCBs) by Gas Chromatography,
Fig. 1. Map of southwestern Lake Michigan showing locations of the Lake Calumet black-crowned night-heron (BCNH) colony, observed BCNH feeding aggregations along the Chicago waterfront, and alewife collection locations including the Jackson Park Harbor and Indiana Ship Canal.
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Revision 0, December 1996. Results were confirmed by analyzing sample preparations via gas chromatography–mass spectrometry (GC–MS), following a modified version of USEPA SW-846 Method 8270C, Semivolatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC–MS), Revision 3, December 1996. Additionally, GC–MS was used to differentiate and quantitate some of those analytes that co-eluted on the GC-ECD. In some instances, interferences associated with the ECD for congeners 74, 138 and163, 14, 65, and 155 necessitated GC–MS confirmation. The quality assurance for the PCB congeners was generally good; a detailed summary of the qualityassurance results is provided in Supplementary data A. We examined PCB congeners 5/8, 18, 28, 31, 33, 44, 49, 52, 66, 70, 74, 77, 84/101, 95, 99, 105, 110, 118, 128, 138/163, 149, 153, 180, 183, 187, 194, and 200/201. This suite of congeners represented those likely to be encountered in fish-eating birds in this region (L Hansen, University of Illinois). Detection limits for PCB congeners ranged from 0.1 to 17 (PCB 18, 200/201) ng/g, though were typically 0.3 to 2 ng/g. Measured concentrations are presented as ng/g wet weight. Data analysis Data were checked for normality using the Shapiro–Wilk (Shapiro and Wilk, 1965) Anderson–Darling (Anderson and Darling, 1952, 1954) tests. Homogeneity of variances among groups was tested using Levene's test (Levene, 1960). The Kolmorgorov–Smirnov two sample test was used to determine if two independent samples (e.g., from different organisms) were drawn from the same population. Analyses used Systat 12.0 (Systat, Inc., Chicago, IL). Congeners were expressed as measured concentrations, the proportion of the total concentration for the sample, or homologs. Homolog concentrations in a sample were computed as the sum of the concentrations of congeners with the same number of chlorines. Proportional homolog concentrations in a sample were computed as the homolog concentration divided by the total sample concentration. A table describing the relationship between congener number and homolog group (number of chlorines) is provided in Supplementary data B. The statistical method used to identify cases with similar PCB concentrations was backward stepwise discriminant analysis (Tabachnick and Fidell, 1996). The logarithms of total PCB wetweight concentrations had normal distributions and were analyzed using analysis of variance (ANOVA). Tukey's HSD test was used to identify pairwise differences between treatments. For all analyses, P ≤ 0.05 was declared significant. Results Congener concentrations for heron embryos, regurgitates, and alewfILL, but not alewfIND, were normally distributed. Average and median total PCB concentrations were highest in embryos and were more than an order of magnitude lower in alewfILL (Table 1). The congener profiles for alewfILL and regurgitates were very similar (Fig. 2). All of the congener profiles differed significantly from each other (P b 0.001; Wilks' Lambda), except for alewfILL compared to regurg (P = 0.99; Fig. 2). AlewfIND had higher mean concentrations of less-chlorinated congeners (especially 2, 3, 4, and 5-Cl up to PCB 118) and similar concentrations of the more highly-chlorinated forms, as compared to alewfILL. With the exception of PCBs 28, 66, and 74, embryos and alewfILL contained similar concentrations of the lesschlorinated congeners. Embryos, however, had higher concentrations of many of the more highly-chlorinated congeners than the other groups. In the discriminant analysis, the first two functions account for N90% of the variance. AlewfIND and embryos were separated from each other and from alewfILL and regurgitates, while the discriminant scores and 95% confidence-bound ellipses for the latter two nearly completely overlapped (Fig. 3a).
Table 1 Summary statistics for total PCB concentrations (ng/g) in black-crowned night-heron embryos (embryo), regurgitated nestling food boluses (regurg), and alewife from Jackson Park Harbor, Illinois (alewfILL) and the Indiana Ship Canal (alewfIND).
N Median Arithmetic mean Standard deviation Variance* Min–Max Shapiro–Wilk P-value** Anderson–Darling P-value**
Embryo
Regurg
alewfILL
alewfIND
20 1998.2 2229.6 1155.4 1,335,031.1 586.4–4678.9 0.30 N0.15
32 244.9 232.8 80.3 6,447.0 36.1–356.4 0.072 0.065
5 156.5 159.2 19.6 384.8 133.8–186.5 0.99 N0.15
6 733.5 1301.4 958.6 918,918.3 637.9–3255.0 0.003 b0.01
*Variances were heterogeneous by Bartlett's test and Levene's test (P b 0.05). **Tests of normal distribution.
The proportional concentrations for congeners 31, 44, 70, 84/101, 110, 128, 138/163, 153, 183, and 194 failed to meet the a priori stepwise inclusion criterion of P ≤ 0.15. The first and second discriminant functions together accounted for 97.1% of the total variance. Figure. 3b shows that embryos and alewfIND were well-separated by the two functions but there was much overlap between alewfILL and regurgitates. One alewfILL was wrongly classified as a regurgitate; similarly, one of the regurgitates was misclassified as an alewfILL. Homologs with 2, 5, 6, and 8 chlorines were not statistically significant (P N 0.15) and the stepwise algorithm dropped them from the final two discriminant functions, which together accounted for 100% of the total variance. Homologs with 3, 4, and 7 chlorines differentiated embryos and alewfIND from each other, although a portion of their 95% confidence-bound ellipses overlapped with that of regurgitates (Fig. 3c). The ellipse calculated for embryos also coincided with that of alewfILL to some degree. There was substantial overlap in the 95% ellipses of alewfILL and regurgitates. All alewfIND and embryo samples were correctly classified whereas all alewfILL were misclassified as regurgitates, and one regurgitate was misidentified as alewfILL. AlewfIND contained a higher proportion of PCBs with 3 and 4 chlorines, and a lower proportion of congeners with 5, 6, and 7 chlorines, compared to the other groups (Fig. 4; P b 0.001 for all comparisons of AlewfIND using 1-way ANOVA and Tukey's HSD test, on the proportions, arc-transformed proportions, and ranks). Embryos contained greater proportions of hexa- and hepta-forms and lower percentages of tetrachlorobiphenyls, than regurgitates, alewfIND and alewfILL. The penta- and hexachlorbiphenyls made similar contributions to the PCB burden in alewfILL, heron embryos, and regurgitates, but these homologs made a significantly smaller contribution to the burden in alewfIND (P b 0.001, on proportions and arcsin-proportion) (Fig. 4). In embryos, the congeners with 6 chlorines made the greatest contribution to total composition of PCBs, whereas tetrachlobiphenyls did so in alewfIND. Discussion The PCB congener profiles for measured, proportional, and homolog concentrations in alewife collected from Illinois waters of Lake Michigan closely resembled that of regurgitated food boluses collected from nestlings at the Lake Calumet colony. Also, these groups were not clearly differentiated by the discriminant analyses, particularly when homolog proportional concentrations were examined. These results are consistent with our hypothesis that large numbers of adult herons from this colony foraged along the Chicago, Illinois, waterfront during the inshore spawning run of the alewife, but there could be other explanations. The only scenario that can be ruled out is that the birds were foraging extensively in the ISC. In our studies of this colony (Levengood et al., 2005) we noted that alewife, a pelagic species that spends much of the year offshore, predominated in food boluses regurgitated by nestlings. On numerous occasions we
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Fig. 2. Mean PCB congener concentrations in alewife from Jackson Park Harbor, Illinois (alewfILL) and the Indiana Ship Canal (alewfIND), black-crowned night-heron embryos (embryo), and regurgitated nestling food boluses (regurg).
observed large numbers of adult BCNH flying in a generally northerly direction (towards the Chicago lakefront) when leaving the colony to feed. Concurrently, BCNH were observed to approach the lakefront near downtown Chicago, Illinois, from the south and form large feeding aggregations (Fig. 1). The conclusion that a large portion of the colony was feeding fish from Lake Michigan to their young has ramifications for contaminant exposure for this colony as a whole, as only small numbers (≤10 BCNH/location) were observed to be feeding in highly contaminated environments such as the ISC. In a similar comparison, Straub et al. (2007) examined PCB concentrations, biomagnification factors, and toxic equivalency factors in GBH eggs, chicks, diet, and prey from a lake having an area of contaminated sediments. In that study the diet of chicks raised in proximity to the contaminated portion of the lake contained a small proportion of shad from the contaminated area.
The pattern of PCB congeners in alewife from the ISC was reflective of a mixture with a “light” profile, or a greater proportion of lower chlorinated congeners (i.e., Aroclors 1242, ΣPCBs 6-74). Indeed, Aroclors 1242 and 1248 predominate in tributaries (Marti and Armstrong, 1990) and nearshore sediments (Swackhamer and Armstrong, 1987) of Lake Michigan and 1221 and 1242 account for about 85% of the Aroclors in the sediments of Waukegan Harbor (Risatti et al., 1990). In a recent paper presenting the results of “… the first intensive survey of polychlorinated biphenyls (PCBs) in the surficial sediment of the Indiana Harbor and Ship Canal (IHSC) in East Chicago, Indiana,… The PCB congener signal strongly resembles the original technical mixture Aroclor 1248 that has experienced a small amount of weathering — less than 2.5% by mass for the statistically different congeners — consistent with desorption, volatilization, and microbial dechlorination” (Martinez et al., 2009, in press). Indeed, the
Fig. 3. Plot of discriminant function scores for: a) measured, b) measured proportional, and c) homolog proportional PCB concentrations in alewife from Jackson Park Harbor, Illinois (alewfILL) and the Indiana Ship Canal (alewfIND), black-crowned night-heron embryos (embryo), and regurgitated nestling food boluses (regurg). Ellipses represent 95% confidence intervals.
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Fig. 4. Mean PCB homolog concentrations expressed as a proportion of total measured concentrations in alewife from Jackson Park Harbor, Illinois (alewfILL) and the Indiana Ship Canal (alewfIND), black-crowned night-heron embryos (embryo), and regurgitated nestling food boluses (regurg).
congener pattern we observed in alewfIND was very similar to that of the sediments in the ISC (see Supplementary data C). It has been demonstrated that PCB patterns in migratory fish may reflect recent habitat use (Elskus et al., 1994; Ashley et al., 2000, 2003). The alewife is a pelagic species that spends much of the year offshore in the deeper, cooler waters of Lake Michigan. The warmer nearshore waters in spring (approximately mid-April in southern lake Michigan) induce the alewife to migrate inshore to spawn, where they stay for several months until ever-increasing water temperatures drive them offshore again (John Dettmers, Great Lakes Fishery Commission, personal communication). It seems that alewife using the contaminated ISC exhibit a PCB profile that differs from that of alewife using the Chicago, Illinois lakefront. The penta- and hexa-congeners together represented 66 and 29%, respectively, of the total measured PCB load in alewife from Illinois and the ISC. In contrast tri- and tetrachloro-PCBs comprised 67% in alewife from the IN Ship Canal, but only 22% of total PCBs in alewfILL. Alewife from Grand Traverse Bay in northern Lake Michigan (Stapleton et al., 2002) and Lake Ontario (Braune and Norstrom, 1989) had congener profiles similar to that of alewife from waters of the Chicago, Illinois, lakefront in our study, i.e., a predominance of congeners having 5, 6, and 7 chlorines (Stapleton et al., 2002). The congener pattern in alewife from the highly contaminated ISC was reflective of Aroclor 1242, i.e., composed primarily of similar proportions of congeners having 3 and 4 chlorines. The greater contribution of the less-chlorinated forms is similar to that of striped bass and American eels (Anguilla rostrada) using the upper Hudson River (an area contaminated with Aroclor 1242) and having had apparent recent exposure to unweathered PCBs (Ashley et al., 2003). Concentrations of “light” congeners, those having 2, 3 and 4 chlorines, were much higher in alewife from the ISC (P b 0.001, t test on logarithms). The notable exception was PCB 77 (P N 0.6), although the mean and median concentrations of PCB 77 were still 2.6- and 7.0fold higher in the ISC alewife (Fig. 2). Typically, less-chlorinated PCBs (≤5 Cl) have a more rapid uptake (Oberg et al., 2002) and are more rapidly metabolized and eliminated (Matthews and Anderson, 1975; Oberg et al., 2002) than higher-molecular-weight congeners. Upon exposure, however, these compounds may be initially high in perfused tissue (Kania-Korwell et al., 2005) so that alewife from the ISC had a PCB profile indicative of parent PCB, e.g., Aroclor 1242. Homolog patterns in embryos were shifted toward more heavily chlorinated or “Major Steady State” congeners (sensu Hansen, 2001:48). This is commonly observed in higher trophic levels, and is
ascribed to greater metabolism of the less-chlorinated forms (Guruge and Tanabe, 1997). Penta-, hexa- and heptachlorobiphenyls together accounted for 91% in herring gull eggs (Braune and Norstrom, 1989), similar to the 87% observed in BCNH embryos in our study. Congener profiles of the eggs of little egrets (Egretta garzetta) in France were shifted towards more highly-chlorinated forms (Berny et al., 2002). Verreault et al (2006) reported that more heavily chlorinated PCBs tended to be retained in maternal tissues of the glaucous gull (Larus hyperboreus). Similarly, maternal transfer of PCBs from chicken hens to eggs is related to the degree of chlorination (Bargar et al., 2001). Degree of chlorination, however, does not fully account for the congener patterns we observed. Chlorine substitution patterns appear to dictate the rate of PCB metabolism in fish-eating birds (Borlakoglu et al., 1988; Tanabe et al., 1988; Braune and Norstrom, 1989; Hebert et al., 2000). Congeners 28, 66 and 74, which have chlorines in the para positions on each phenyl ring, displayed higher concentrations in embryos than expected based on the degree of chlorination of the molecules. These congeners are less-readily metabolized than those lacking chlorine substitutions at para positions (Borlakoglu et al., 1988; Tanabe et al., 1988; Boon et al., 1994). Also, the heron embryos had lower concentrations of congeners 95, 110, and 149 than expected based on chlorination of those molecules. These congeners have adjacent unchlorinated meta-para positions, making them more susceptible to metabolism (Borlakoglu et al., 1988; Tanabe et al., 1988; Boon et al., 1994). In preparation for egg formation, some bird species feed extensively after migration to replace nutrients lost during migration in preparation for egg formation. Therefore, toxicants in eggs of migratory species may reflect local sources (Furness and Greenwood, 1993). BCNH begin to arrive at the Lake Calumet colony in late March and clutch initiation starts during the third week of April and continues into late May and early June (Levengood et al., 2005). This would seem to allow ample time to replace lipids lost during migration with locally-derived sources (Kelly et al., 1993; Matz and Parsons, 2004), which may contain elevated concentrations of environmental contaminants. In our study, profiles of measured, proportional, and homolog concentrations in alewife from the Chicago, IL, lakefront closely resembled those of regurgitated food boluses from BCNH nestlings. Consistent with other studies, homolog patterns in embryos were shifted towards more heavily chlorinated PCBs. Profiles in alewife from a highly contaminated environment reflected a less-heavily chlorinated mixture, consistent with historic PCB sources, e.g., Aroclor 1242. These findings have ramifications for the PCB exposure of this colony as a whole. Although large numbers of nestling herons were fed alewife containing a higher proportion of less-readily metabolized congeners, total PCB concentrations were nearly 5-fold greater in alewife from the ISC (Levengood et al., 2007). Thus, a lower PCB load was transferred to embryos than if adults had foraged extensively in the Indiana Ship Canal.
Acknowledgements L Weidenmann and C Teausant, Illinois Sustainable Technology Center (ISTC), UIUC, performed chemical analyses and calculations. L Hansen, Department of Veterinary Biosciences (VB), University of Illinois at Urbana-Champaign (UIUC) and M Piwoni,(ISTC) provided valuable insights. A Klement, W Marcisz, C Williamson, K Wysocki and L Munoz conducted heron foraging surveys. Three Rivers Environmental Assessments conducted fish collections. S Schantz, VB UIUC, kindly reviewed an earlier draft of the manuscript. Funding was provided by the ISTC, Chicago Department of Environment, and the Illinois Department of Natural Resources through a grant from the Illinois Wildlife Preservation Fund. The Associate Editor (Hebert) and two anonymous reviewers provided helpful suggestions on the
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manuscript. Jonathan Keating, JGLR Editor's Assistant, kindly prepared the final versions of the figures.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jglr.2010.04.011.
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An analysis of variance test for normality (complex samples). Biometrika 52, 591–611. Sodhi, N.S., 1985. Food of black-crowned night heron nestlings. Pavo 23, 47–52. Stapleton, H.M., Skubinna, J., Baker, J.E., 2002. Seasonal dynamics of PCB and toxaphene bioaccumulation within a Lake Michigan food web. J. Great Lakes Res. 28, 52–64. Straub, C.L., Maul, J.D., Halbrook, R.S., Spears, B., Lydy, M.J., 2007. Trophic transfer of polychlorinated biphenyls in great blue heron (Ardea herodias) at Crab Orchard National Wildlife Refuge, Illinois, United States. Arch. Environ. Contam. Toxicol. 52, 572–579. Swackhamer, D.L., Armstrong, D.E., 1987. Distribution and characterization of PCBs in Lake Michigan water. J. Great Lakes Res. 13, 24–36. Tabachnick, G.B., Fidell, L.S., 1996. Using Multivariate Statistics. HarperCollins College Publishing, New York, NY. Tanabe, S., Watanabe, S., Kan, H., Tatsukawa, R., 1988. Capacity and mode of PCB metabolism in small cetaceans. Mar. Mamm. Sci. 4, 103–124. 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Journal of Great Lakes Research j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / j g l r
Comparison of PCB congener profiles in the embryos and principal prey of a breeding colony of black-crowned night-herons Jeffrey M. Levengood a,b,⁎, David J. Schaeffer b a b
Illinois Natural History Survey, Institute of Natural Resource Sustainability, University of Illinois, 1816 S. Oak St., Champaign, IL 61820, USA Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois, 2001 South Lincoln Ave., Urbana, IL 61802, USA
a r t i c l e
i n f o
Article history: Received 3 February 2010 Accepted 14 April 2010 Communicated by Craig Hebert Index words: PCBs Herons Prey Alewife Congeners Homologs
a b s t r a c t We compared polychlorinated biphenyl (PCB) congener profiles of embryos of black-crowned night-herons (Nycticorax nycticorax) nesting in an urban-industrialized area of Chicago, Illinois, USA, with those of regurgitated food boluses from nestlings and their primary prey. Consistent with previous studies of piscivorous birds, the PCB burden of embryos was shifted towards more heavily chlorinated congeners (those with 6, 7, and 8 chlorines), when compared to prey. The PCB congener profiles for measured and homolog concentrations in alewife (Alosa pseudoharengus) collected from Lake Michigan at the Chicago, Illinois, waterfront, closely resembled that of regurgitated food boluses collected from nestlings at the Lake Calumet colony. Also, alewife from Illinois and regurgitates were not clearly differentiated by the discriminant analyses for measured, proportional, and homolog concentrations. Congener profiles in alewife from the highly contaminated Indiana Ship Canal, which had a much higher PCB burden (geometric average = 1061.7 ng/g ww [95% CI = 648.6−1061.7 ng/g ww]) than did alewife from Illinois (158.1 [135.8−184.5]ng/g ww) and regurgitates (212.3 [177.0−254.7]ng/g ww), reflected a less-chlorinated mixture (i.e., Aroclor 1242). These results are consistent with our observations, which indicated that many of the adults of this colony were foraging along the Chicago waterfront, where alewife had lower PCB burdens. Because the congener patterns of the prey differ, the PCB congener profiles can be used to elucidate foraging patterns of colonial piscivorous birds and determine relative risks to exposed populations. © 2010 Elsevier B.V. All rights reserved.
Introduction Polychlorinated biphenyls (PCBs) are 209 synthetic chemicals (congeners) having 1 to 10 chlorines. Mixtures of PCBs were previously used as electrical insulating and hydraulic fluids, lubricants, plasticizers and flame retardants. Many PCBs are environmental toxins that are hepato-, immuno- and neurotoxic, endocrine disruptors, and possible carcinogens (Hoffman et al., 1996; Rice et al., 2003; Bursian, 2007). Although the manufacture, distribution and most uses of PCBs were banned in the United States and Canada during the 1970s, PCBs are nearly ubiquitous in the North American environment. Whereas environmental concentrations have generally declined, some heavilyindustrialized areas remain contaminated. PCBs are persistent and bioaccumulative, and have been commonly detected in herons in North America. More recently, for example, PCBs have been observed in great blue herons (GBH, Ardea herodias; Straub et al., 2007) and blackcrowned-night herons (BCNH, Nycticorax nycticorax; Levengood et al., 2007) in Illinois, USA; GBH along the St. Lawrence River in Quebec,
⁎ Corresponding author. Illinois Natural History Survey, Institute of Natural Resource Sustainability, University of Illinois, 1816 S. Oak St., Champaign, IL 61820, USA. Tel.: + 1 217/333 6767. E-mail addresses: [email protected] (J.M. Levengood), [email protected] (D.J. Schaeffer). 0380-1330/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jglr.2010.04.011
Canada (Champoux et al., 2006); BCNH and great egrets (Ardea alba) in coastal California (Henny et al., 2008), and BCNH in coastal northeastern USA (Matz and Parsons, 2004). PCB exposure in herons has been associated with: increased cytochrome P450 monooxygenase activity (Rattner et al., 1993; Levengood et al., 2007); reduced embryonic weight (Hoffman et al., 1986), reduced plasma retinol concentrations (Champoux et al., 2006), and, in combination with DDE, decreased nest attentiveness (Thomas and Anthony, 2003). PCBs also contribute, along with dioxins, to skeletal deformities (Thompson et al., 2006) and other manifestations of embryotoxity (Hoffman et al., 1993). PCB Aroclors are commercial mixtures of 60 to 90 different congeners, the latter determined by the chlorine content and position on the biphenyl backbone of the molecule. These characteristics determine the stability of the various congeners in the environment, their lipophilicity, metabolism and clearance in organisms. The resulting differences in PCB congener patterns or “profiles” in the tissues of birds have been examined in comparisons among taxa (Jaspers et al., 2008), locations (Levengood et al., 2007), between sediments and eggs (Berny et al., 2002) and among trophic levels (Guruge and Tanabe, 1997; Papp et al., 2007; Straub et al., 2007). Congener profiles can be used to “fingerprint” PCB exposure in biota, linking exposure with habitat use and/or prey utilization. For example, PCB congener profiles were associated with habitat-use patterns in migratory striped bass (Morone saxatilus) and American
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eels (Anguilla rostrata) in the Hudson and Delaware River drainages (Ashley et al., 2003). Papp et al (2007) examined PCB profiles in tree swallows (Tachycineta bicolor) and prey to elucidate prey utilization and contribution to that species' PCB exposure. Straub et al. (2007) utilized toxic equivalency factors in GBH eggs and nestlings to examine utilization of shad (Dorosoma cepedianum) from different parts of a contaminated lake. In this paper we compared PCB congener patterns, or “profiles”, in BCNH embryos, food boluses regurgitated by BCNH nestlings, and the principal prey (as observed in regurgitated boluses) from 2 locations where adult BCNH were known to forage. We hypothesized that congener profiles in embryos were reflective of those in predominant prey observed in food boluses regurgitated by nestlings, and that profiles in the boluses would be similar to that of the principal prey from areas of concentrated foraging activity.
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including the yolk sac was placed in chemically clean glass jars (EP Scientific Products, Miami OK) and frozen until analysis. Alewife were collected in June of 2002 by electrofishing from Jackson Park Harbor, located on the Lake Michigan waterfront in Chicago, Illinois, IL (alewfILL), and from the Indiana Ship Canal (ISC), near East Chicago, Indiana (alewfIND) (Fig. 1). Alewife were wrapped in acetone-cleaned aluminum foil and stored frozen in plastic bags until analysis. Alewife samples from Illinois (n = 5) and ISC (n = 6) represented a total of 10 and 11 individual fish, respectively, weighing 18 to 28 g each. A map showing the locations of the Lake Calumet BCNH colony, feeding aggregations along the Chicago waterfront, and the ISC is provided in Fig. 1. Based upon our observations (see Discussion) we inferred that many of the herons feeding along the lakeshore came from the Lake Calumet colony. Chemical analysis
Methods Sample collection Nestling herons may regurgitate food when approached by potential predators. This behavior has been used to collect material for food habits (Sodhi, 1985; Hall and Kress, 2008) and contaminant exposure (Rattner et al., 2001; Straub et al., 2007) studies. Although some limited digestion of food items occurred, prey was essentially intact and in most instances readily identifiable. Thus, the chemical composition of the regurgitates was considered representative of the prey prior to consumption. A total of 34 regurgitated food boluses (hereafter regurgitates) were collected into acetone-cleaned aluminum foil during nest checks at the Lake Calumet BCNH colony (Fig. 1) in 2002 and 2003. Eggs were collected in 2002 from nests (one each from 20 nests) during late incubation and incubated to pipping in the laboratory, at which time they were euthanized. Blood and livers were harvested for biomarker analysis and the remainder of each carcass
PCB analyses were conducted by the GC–MS Group of the Illinois Sustainable Technology Center, University of Illinois. A sub-sample of each ground specimen was homogenized and extracted with acetone: hexane (1:1) following USEPA SW-846 Method 3545, Pressurized Fluid Extraction (PFE), Revision 0, December 1996. Extracts were concentrated, exchanged to dichloromethane, and evaluated for lipids. The majority of lipids were removed from extracts via gel permeation chromatography (GPC), following USEPA SW-846 Method 3640A, Gel Permeation Cleanup, Revision 1, September 1994. Extracts were then subjected to a silica gel cleanup procedure in which the analytes of interest were separated into two fractions, based on USEPA SW-846 Method 3630, Silica Gel Cleanup, Revision 3, December 1996. The appropriate fraction was analyzed for polychlorinated biphenyls (PCB) via gas chromatography-electron capture detection (GC-ECD), following USEPA SW-846 Method 8081A, Organochlorine Pesticides by Gas Chromatography, Revision 1, December 1996, and USEPA SW-846 Method 8082, Polychlorinated Biphenyls (PCBs) by Gas Chromatography,
Fig. 1. Map of southwestern Lake Michigan showing locations of the Lake Calumet black-crowned night-heron (BCNH) colony, observed BCNH feeding aggregations along the Chicago waterfront, and alewife collection locations including the Jackson Park Harbor and Indiana Ship Canal.
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Revision 0, December 1996. Results were confirmed by analyzing sample preparations via gas chromatography–mass spectrometry (GC–MS), following a modified version of USEPA SW-846 Method 8270C, Semivolatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC–MS), Revision 3, December 1996. Additionally, GC–MS was used to differentiate and quantitate some of those analytes that co-eluted on the GC-ECD. In some instances, interferences associated with the ECD for congeners 74, 138 and163, 14, 65, and 155 necessitated GC–MS confirmation. The quality assurance for the PCB congeners was generally good; a detailed summary of the qualityassurance results is provided in Supplementary data A. We examined PCB congeners 5/8, 18, 28, 31, 33, 44, 49, 52, 66, 70, 74, 77, 84/101, 95, 99, 105, 110, 118, 128, 138/163, 149, 153, 180, 183, 187, 194, and 200/201. This suite of congeners represented those likely to be encountered in fish-eating birds in this region (L Hansen, University of Illinois). Detection limits for PCB congeners ranged from 0.1 to 17 (PCB 18, 200/201) ng/g, though were typically 0.3 to 2 ng/g. Measured concentrations are presented as ng/g wet weight. Data analysis Data were checked for normality using the Shapiro–Wilk (Shapiro and Wilk, 1965) Anderson–Darling (Anderson and Darling, 1952, 1954) tests. Homogeneity of variances among groups was tested using Levene's test (Levene, 1960). The Kolmorgorov–Smirnov two sample test was used to determine if two independent samples (e.g., from different organisms) were drawn from the same population. Analyses used Systat 12.0 (Systat, Inc., Chicago, IL). Congeners were expressed as measured concentrations, the proportion of the total concentration for the sample, or homologs. Homolog concentrations in a sample were computed as the sum of the concentrations of congeners with the same number of chlorines. Proportional homolog concentrations in a sample were computed as the homolog concentration divided by the total sample concentration. A table describing the relationship between congener number and homolog group (number of chlorines) is provided in Supplementary data B. The statistical method used to identify cases with similar PCB concentrations was backward stepwise discriminant analysis (Tabachnick and Fidell, 1996). The logarithms of total PCB wetweight concentrations had normal distributions and were analyzed using analysis of variance (ANOVA). Tukey's HSD test was used to identify pairwise differences between treatments. For all analyses, P ≤ 0.05 was declared significant. Results Congener concentrations for heron embryos, regurgitates, and alewfILL, but not alewfIND, were normally distributed. Average and median total PCB concentrations were highest in embryos and were more than an order of magnitude lower in alewfILL (Table 1). The congener profiles for alewfILL and regurgitates were very similar (Fig. 2). All of the congener profiles differed significantly from each other (P b 0.001; Wilks' Lambda), except for alewfILL compared to regurg (P = 0.99; Fig. 2). AlewfIND had higher mean concentrations of less-chlorinated congeners (especially 2, 3, 4, and 5-Cl up to PCB 118) and similar concentrations of the more highly-chlorinated forms, as compared to alewfILL. With the exception of PCBs 28, 66, and 74, embryos and alewfILL contained similar concentrations of the lesschlorinated congeners. Embryos, however, had higher concentrations of many of the more highly-chlorinated congeners than the other groups. In the discriminant analysis, the first two functions account for N90% of the variance. AlewfIND and embryos were separated from each other and from alewfILL and regurgitates, while the discriminant scores and 95% confidence-bound ellipses for the latter two nearly completely overlapped (Fig. 3a).
Table 1 Summary statistics for total PCB concentrations (ng/g) in black-crowned night-heron embryos (embryo), regurgitated nestling food boluses (regurg), and alewife from Jackson Park Harbor, Illinois (alewfILL) and the Indiana Ship Canal (alewfIND).
N Median Arithmetic mean Standard deviation Variance* Min–Max Shapiro–Wilk P-value** Anderson–Darling P-value**
Embryo
Regurg
alewfILL
alewfIND
20 1998.2 2229.6 1155.4 1,335,031.1 586.4–4678.9 0.30 N0.15
32 244.9 232.8 80.3 6,447.0 36.1–356.4 0.072 0.065
5 156.5 159.2 19.6 384.8 133.8–186.5 0.99 N0.15
6 733.5 1301.4 958.6 918,918.3 637.9–3255.0 0.003 b0.01
*Variances were heterogeneous by Bartlett's test and Levene's test (P b 0.05). **Tests of normal distribution.
The proportional concentrations for congeners 31, 44, 70, 84/101, 110, 128, 138/163, 153, 183, and 194 failed to meet the a priori stepwise inclusion criterion of P ≤ 0.15. The first and second discriminant functions together accounted for 97.1% of the total variance. Figure. 3b shows that embryos and alewfIND were well-separated by the two functions but there was much overlap between alewfILL and regurgitates. One alewfILL was wrongly classified as a regurgitate; similarly, one of the regurgitates was misclassified as an alewfILL. Homologs with 2, 5, 6, and 8 chlorines were not statistically significant (P N 0.15) and the stepwise algorithm dropped them from the final two discriminant functions, which together accounted for 100% of the total variance. Homologs with 3, 4, and 7 chlorines differentiated embryos and alewfIND from each other, although a portion of their 95% confidence-bound ellipses overlapped with that of regurgitates (Fig. 3c). The ellipse calculated for embryos also coincided with that of alewfILL to some degree. There was substantial overlap in the 95% ellipses of alewfILL and regurgitates. All alewfIND and embryo samples were correctly classified whereas all alewfILL were misclassified as regurgitates, and one regurgitate was misidentified as alewfILL. AlewfIND contained a higher proportion of PCBs with 3 and 4 chlorines, and a lower proportion of congeners with 5, 6, and 7 chlorines, compared to the other groups (Fig. 4; P b 0.001 for all comparisons of AlewfIND using 1-way ANOVA and Tukey's HSD test, on the proportions, arc-transformed proportions, and ranks). Embryos contained greater proportions of hexa- and hepta-forms and lower percentages of tetrachlorobiphenyls, than regurgitates, alewfIND and alewfILL. The penta- and hexachlorbiphenyls made similar contributions to the PCB burden in alewfILL, heron embryos, and regurgitates, but these homologs made a significantly smaller contribution to the burden in alewfIND (P b 0.001, on proportions and arcsin-proportion) (Fig. 4). In embryos, the congeners with 6 chlorines made the greatest contribution to total composition of PCBs, whereas tetrachlobiphenyls did so in alewfIND. Discussion The PCB congener profiles for measured, proportional, and homolog concentrations in alewife collected from Illinois waters of Lake Michigan closely resembled that of regurgitated food boluses collected from nestlings at the Lake Calumet colony. Also, these groups were not clearly differentiated by the discriminant analyses, particularly when homolog proportional concentrations were examined. These results are consistent with our hypothesis that large numbers of adult herons from this colony foraged along the Chicago, Illinois, waterfront during the inshore spawning run of the alewife, but there could be other explanations. The only scenario that can be ruled out is that the birds were foraging extensively in the ISC. In our studies of this colony (Levengood et al., 2005) we noted that alewife, a pelagic species that spends much of the year offshore, predominated in food boluses regurgitated by nestlings. On numerous occasions we
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Fig. 2. Mean PCB congener concentrations in alewife from Jackson Park Harbor, Illinois (alewfILL) and the Indiana Ship Canal (alewfIND), black-crowned night-heron embryos (embryo), and regurgitated nestling food boluses (regurg).
observed large numbers of adult BCNH flying in a generally northerly direction (towards the Chicago lakefront) when leaving the colony to feed. Concurrently, BCNH were observed to approach the lakefront near downtown Chicago, Illinois, from the south and form large feeding aggregations (Fig. 1). The conclusion that a large portion of the colony was feeding fish from Lake Michigan to their young has ramifications for contaminant exposure for this colony as a whole, as only small numbers (≤10 BCNH/location) were observed to be feeding in highly contaminated environments such as the ISC. In a similar comparison, Straub et al. (2007) examined PCB concentrations, biomagnification factors, and toxic equivalency factors in GBH eggs, chicks, diet, and prey from a lake having an area of contaminated sediments. In that study the diet of chicks raised in proximity to the contaminated portion of the lake contained a small proportion of shad from the contaminated area.
The pattern of PCB congeners in alewife from the ISC was reflective of a mixture with a “light” profile, or a greater proportion of lower chlorinated congeners (i.e., Aroclors 1242, ΣPCBs 6-74). Indeed, Aroclors 1242 and 1248 predominate in tributaries (Marti and Armstrong, 1990) and nearshore sediments (Swackhamer and Armstrong, 1987) of Lake Michigan and 1221 and 1242 account for about 85% of the Aroclors in the sediments of Waukegan Harbor (Risatti et al., 1990). In a recent paper presenting the results of “… the first intensive survey of polychlorinated biphenyls (PCBs) in the surficial sediment of the Indiana Harbor and Ship Canal (IHSC) in East Chicago, Indiana,… The PCB congener signal strongly resembles the original technical mixture Aroclor 1248 that has experienced a small amount of weathering — less than 2.5% by mass for the statistically different congeners — consistent with desorption, volatilization, and microbial dechlorination” (Martinez et al., 2009, in press). Indeed, the
Fig. 3. Plot of discriminant function scores for: a) measured, b) measured proportional, and c) homolog proportional PCB concentrations in alewife from Jackson Park Harbor, Illinois (alewfILL) and the Indiana Ship Canal (alewfIND), black-crowned night-heron embryos (embryo), and regurgitated nestling food boluses (regurg). Ellipses represent 95% confidence intervals.
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Fig. 4. Mean PCB homolog concentrations expressed as a proportion of total measured concentrations in alewife from Jackson Park Harbor, Illinois (alewfILL) and the Indiana Ship Canal (alewfIND), black-crowned night-heron embryos (embryo), and regurgitated nestling food boluses (regurg).
congener pattern we observed in alewfIND was very similar to that of the sediments in the ISC (see Supplementary data C). It has been demonstrated that PCB patterns in migratory fish may reflect recent habitat use (Elskus et al., 1994; Ashley et al., 2000, 2003). The alewife is a pelagic species that spends much of the year offshore in the deeper, cooler waters of Lake Michigan. The warmer nearshore waters in spring (approximately mid-April in southern lake Michigan) induce the alewife to migrate inshore to spawn, where they stay for several months until ever-increasing water temperatures drive them offshore again (John Dettmers, Great Lakes Fishery Commission, personal communication). It seems that alewife using the contaminated ISC exhibit a PCB profile that differs from that of alewife using the Chicago, Illinois lakefront. The penta- and hexa-congeners together represented 66 and 29%, respectively, of the total measured PCB load in alewife from Illinois and the ISC. In contrast tri- and tetrachloro-PCBs comprised 67% in alewife from the IN Ship Canal, but only 22% of total PCBs in alewfILL. Alewife from Grand Traverse Bay in northern Lake Michigan (Stapleton et al., 2002) and Lake Ontario (Braune and Norstrom, 1989) had congener profiles similar to that of alewife from waters of the Chicago, Illinois, lakefront in our study, i.e., a predominance of congeners having 5, 6, and 7 chlorines (Stapleton et al., 2002). The congener pattern in alewife from the highly contaminated ISC was reflective of Aroclor 1242, i.e., composed primarily of similar proportions of congeners having 3 and 4 chlorines. The greater contribution of the less-chlorinated forms is similar to that of striped bass and American eels (Anguilla rostrada) using the upper Hudson River (an area contaminated with Aroclor 1242) and having had apparent recent exposure to unweathered PCBs (Ashley et al., 2003). Concentrations of “light” congeners, those having 2, 3 and 4 chlorines, were much higher in alewife from the ISC (P b 0.001, t test on logarithms). The notable exception was PCB 77 (P N 0.6), although the mean and median concentrations of PCB 77 were still 2.6- and 7.0fold higher in the ISC alewife (Fig. 2). Typically, less-chlorinated PCBs (≤5 Cl) have a more rapid uptake (Oberg et al., 2002) and are more rapidly metabolized and eliminated (Matthews and Anderson, 1975; Oberg et al., 2002) than higher-molecular-weight congeners. Upon exposure, however, these compounds may be initially high in perfused tissue (Kania-Korwell et al., 2005) so that alewife from the ISC had a PCB profile indicative of parent PCB, e.g., Aroclor 1242. Homolog patterns in embryos were shifted toward more heavily chlorinated or “Major Steady State” congeners (sensu Hansen, 2001:48). This is commonly observed in higher trophic levels, and is
ascribed to greater metabolism of the less-chlorinated forms (Guruge and Tanabe, 1997). Penta-, hexa- and heptachlorobiphenyls together accounted for 91% in herring gull eggs (Braune and Norstrom, 1989), similar to the 87% observed in BCNH embryos in our study. Congener profiles of the eggs of little egrets (Egretta garzetta) in France were shifted towards more highly-chlorinated forms (Berny et al., 2002). Verreault et al (2006) reported that more heavily chlorinated PCBs tended to be retained in maternal tissues of the glaucous gull (Larus hyperboreus). Similarly, maternal transfer of PCBs from chicken hens to eggs is related to the degree of chlorination (Bargar et al., 2001). Degree of chlorination, however, does not fully account for the congener patterns we observed. Chlorine substitution patterns appear to dictate the rate of PCB metabolism in fish-eating birds (Borlakoglu et al., 1988; Tanabe et al., 1988; Braune and Norstrom, 1989; Hebert et al., 2000). Congeners 28, 66 and 74, which have chlorines in the para positions on each phenyl ring, displayed higher concentrations in embryos than expected based on the degree of chlorination of the molecules. These congeners are less-readily metabolized than those lacking chlorine substitutions at para positions (Borlakoglu et al., 1988; Tanabe et al., 1988; Boon et al., 1994). Also, the heron embryos had lower concentrations of congeners 95, 110, and 149 than expected based on chlorination of those molecules. These congeners have adjacent unchlorinated meta-para positions, making them more susceptible to metabolism (Borlakoglu et al., 1988; Tanabe et al., 1988; Boon et al., 1994). In preparation for egg formation, some bird species feed extensively after migration to replace nutrients lost during migration in preparation for egg formation. Therefore, toxicants in eggs of migratory species may reflect local sources (Furness and Greenwood, 1993). BCNH begin to arrive at the Lake Calumet colony in late March and clutch initiation starts during the third week of April and continues into late May and early June (Levengood et al., 2005). This would seem to allow ample time to replace lipids lost during migration with locally-derived sources (Kelly et al., 1993; Matz and Parsons, 2004), which may contain elevated concentrations of environmental contaminants. In our study, profiles of measured, proportional, and homolog concentrations in alewife from the Chicago, IL, lakefront closely resembled those of regurgitated food boluses from BCNH nestlings. Consistent with other studies, homolog patterns in embryos were shifted towards more heavily chlorinated PCBs. Profiles in alewife from a highly contaminated environment reflected a less-heavily chlorinated mixture, consistent with historic PCB sources, e.g., Aroclor 1242. These findings have ramifications for the PCB exposure of this colony as a whole. Although large numbers of nestling herons were fed alewife containing a higher proportion of less-readily metabolized congeners, total PCB concentrations were nearly 5-fold greater in alewife from the ISC (Levengood et al., 2007). Thus, a lower PCB load was transferred to embryos than if adults had foraged extensively in the Indiana Ship Canal.
Acknowledgements L Weidenmann and C Teausant, Illinois Sustainable Technology Center (ISTC), UIUC, performed chemical analyses and calculations. L Hansen, Department of Veterinary Biosciences (VB), University of Illinois at Urbana-Champaign (UIUC) and M Piwoni,(ISTC) provided valuable insights. A Klement, W Marcisz, C Williamson, K Wysocki and L Munoz conducted heron foraging surveys. Three Rivers Environmental Assessments conducted fish collections. S Schantz, VB UIUC, kindly reviewed an earlier draft of the manuscript. Funding was provided by the ISTC, Chicago Department of Environment, and the Illinois Department of Natural Resources through a grant from the Illinois Wildlife Preservation Fund. The Associate Editor (Hebert) and two anonymous reviewers provided helpful suggestions on the
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manuscript. Jonathan Keating, JGLR Editor's Assistant, kindly prepared the final versions of the figures.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jglr.2010.04.011.
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