Article pubs.acs.org/est
Metabolic Concentration of Lipid Soluble Organochlorine Burdens in the Blubber of Southern Hemisphere Humpback Whales Through Migration and Fasting Susan M. Bengtson Nash,*,† Courtney A. Waugh,‡,∥ and Martin Schlabach§ †
Griffith University, School of Environment, Southern Ocean Persistent Organic Pollutants Program (SOPOPP), QLD 4111, Australia ‡ The University of Queensland, The National Research Centre for Environmental Toxicology, QLD 4108, Australia § The Norwegian Institute for Air Research (NILU), 2007 Kjeller, Norway ABSTRACT: Southern hemisphere humpback whales undertake the longest migrations and associated periods of fasting of any mammal. Fluctuations in lipid energy stores are known to profoundly affect the toxicokinetics of lipophilic organochlorine compound (OC) burdens. Results from blubber biopsy sampling of adult, male humpback whales at two time points of the annual migration journey revealed dramatic concentration effects for the majority of OC compounds. The observed concentration effect was, however, not linear with measured average blubber lipid loss indicating significant redistribution of OCs and hence the importance of alternate lipid depots for meeting the energetic demands of the migration journey. Applying lipophilic OC burdens as novel tracers of whole-body lipid dynamics, the observed average concentration index suggests an average individual weight loss of 13% over 4 months of the migration journey. This value is based upon lipid derived energy and is in good agreement with previous weight prediction formulas. Notably, however, these estimates may greatly underestimate individual weight loss if significant protein catabolism occurs. Biomagnification factors between migrating southern hemisphere humpback whales and their principal prey item, Antarctic krill, closely resembled those of baleen whales feeding on herbivorous zooplankton in the Arctic. This study emphasizes the importance of considering prolonged periods of food deprivation when assessing chemical risks posed to wildlife. This is of particular importance for Polar biota adapted to extremes in ecosystem productivity.
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INTRODUCTION Organochlorine (OC) persistent organic pollutants (POPs) are toxic, global contaminants that reach Polar latitudes through temperature-driven fractionation processes.1 OC structures are readily incorporated into the lipid-dependent diets of Polar food webs.2 Marine mammals accumulate the greatest levels of OCs due to their longevity, high lipid proportion of body mass, and their position at the top of marine food chains.3 Polar biota have adapted to the productivity extremes of high latitude environments. Often life history behaviors incorporate extended periods of fasting, migration, or hibernation. In recent years, fluctuation in body energy stores has emerged as an important confounding factor for consideration when assessing OC exposure and risk in humans and wildlife alike, e.g., refs 4−9. Lipolysis releases stored energy which is used to fuel metabolic processes, growth, and maintenance during times of energy deficit. The concomitant release of lipophilic OCs into circulation is not, however, accompanied by parallel elimination, resulting in redistribution of these toxins to, and concentration within, remaining lipid stores. It is while in circulation that the OC burdens have the greatest potential for © XXXX American Chemical Society
reaching sensitive tissues and target sites of toxicity. In such a manner, periods of lipid mobilization must be viewed as times of “re-exposure” and in clinical settings have been linked to disruption of endocrine function.6,8 Baleen (filter-feeding) whales such as humpback whales (Megaptera novaeangliae) are attributed a lower chemical risk category compared to odontocete (toothed) whales due to their lower trophic position and therefore relatively lower associated daily OC intake.10 Frequently, however, baleen whales are capital breeders, relying on accumulated energy stores for reproduction and associated periods of fasting. As such, they experience extreme fluctuations in lipid dynamics, and breeding periods may represent a time of elevated risk to both individuals and dependent young.9 Southern hemisphere humpback whales spend the Austral summer in their Antarctic feeding grounds before undertaking Received: April 10, 2013 Revised: July 12, 2013 Accepted: July 16, 2013
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dx.doi.org/10.1021/es401441n | Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Environmental Science & Technology
Article
γ-HCH); chlordanes (CHL; trans-chlordane, cis-chlordane, oxychlordane, chlordene, heptachlor, trans-nonachlor, cis-nonachlor); and toxaphenes (Tox-26 or B8-1413, Tox-32 or B7515, Tox-40 + Tox-41 or B8-1414 + B8-1945, Tox-42a or B8806, Tox-44 or B8-2229, Tox-50 or B9-1679, Tox-62 or B91025). Twenty-three, of the total 58 blubber samples, were also analyzed for the additional cyclodines: dieldrin, aldrin, isodrin, endrin, heptachlor-exo epoxide, heptachlor-endo epoxide, endosulfan I, endosulfan II, and endosulfane-sulfate as well as trifluralin. Contaminant values are reported on a lipid weight basis (l.w.) in nanograms per gram (ng/g). Extraction and Cleanup. Analytical methods are described elsewhere.17 In brief, approximately 0.3 g blubber was thoroughly homogenized in a miniature, laboratory, stainless steel blender (Waring) with anhydrous Na2SO4. The dried sample was extracted on a cold column with ethyl acetate/ cyclohexane (1:1). The sample extract underwent a series of cleanup steps. Either one of the following two methods were utilized for cleanup of samples: (Method 1) The extract was concentrated and cleaned by gel permeation chromatography (GPC) followed by an aluminum oxide column and finally a silica column cleanup step. (Method 2) The extract was combined with concentrated sulphuric acid (H2SO4), mixed and left to partition overnight. The unwanted acid matrix was removed and the step repeated until the H2SO4 fraction remained clear. The sample fraction was further cleaned on a silica column. All sample extracts were solvent exchanged to isooctane prior to quantification. Quantification. The isomer identification and quantification was carried out by high-resolution gas chromatography/highresolution mass spectrometry (HRGC/HRMS) using a Hewlett-Packard 5890II (1990−2003) or 6890N (2003− 2006) gas chromatograph coupled to an AutoSpec mass spectrometer (Micromass Waters, Manchester UK). Resolution of mass spectrometer was >10000. For most compounds, the electron ionization mass spectrometry in selected ion monitoring mode (GC/EI-HRMS-SIM) was applied. To get the best sensitivity for chlordanes and toxaphenes, however, electron capture negative ionization mode (GC/ECNI-HRMSSIM) was used. Two SIM values were monitored for each isomer group.13C-labeled isomers were used as the internal standard for each group. Additionally, the recovery rates of the added internal standard compounds were determined. Quality Control. A 13C-labeled PCB/chlorinated pesticide internal standard was added to the top of the cold column prior to extraction. Prior to HRGC/HRMS analysis, an unlabeled 1,2,3,4-tetrachloronaphthalene (TCN) recovery standard was added to the sample vial. Prior to each new series of samples, the blank of the complete clean-up and quantification procedures was determined. Reported sample concentrations were lab blank adjusted by subtracting the average series blank values or level of detection (LOD) from the sample concentration. The retention time of the native was within 3 s of the corresponding 13C-labeled isomer. The isotope ratio of the two monitored masses was within +20% of the theoretical value. The signal noise was >3/1 for quantification. At least once a year, the laboratory participates in an international laboratory intercalibration exercise. Statistical Analysis. Concentration values that fell below the method level of quantification (LOQ) were assigned a zero value for calculation of summary statistics. Data sets were subjected to a Kolomogorov−Smirnov test and were found to have non-normal distributions. Log-transformation of data did
the longest migrations known in any mammal (as long as 10 000 km) 11 to equatorial regions for winter breeding and calving. These migrations are associated with up to 9 months of fasting and come at an enormous energetic cost to individuals, estimated to lose between 25 and 50% of their summer body mass.12 Southern hemisphere humpback whales therefore represent model populations for further investigating redistribution and metabolic concentration of lipophilic OCs in wildlife.13 The objectives of this study were not only to provide the first published data concerning OC burdens in southern hemisphere humpback whales but also to investigate the changes in blubber lipid content and lipid normalized OC burdens that occur between two time points of the annual migration. These findings are further used to investigate lipid dynamics and foodchain biomagnification and discuss chemical risks posed to wildlife during times of energy deficit.
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EXPERIMENTAL SECTION Sample Collection. Skin and blubber biopsies were collected from free swimming individuals in Moreton Bay Marine Park, North Stradbroke Island, southeast Queensland, Australia (approximately 27° 26 S, 153° 34 E). Individuals moving along this migration path are representative of the International Whaling Commission categorized breeding stock, E1. Fifty-eight skin and blubber biopsies were collected from free-swimming males as described in detail elsewhere.14 Adult males were targeted in this study to avoid the confounding factors associated with pregnancy and lactation in females. Sampling was performed at two time points during the annual migration (2008−2011), and as such, samples were categorized into two cohorts: (1) “early migration”, defined as individuals sampled on the northward leg of the journey, traveling to breeding grounds (sampled in June/July), and presumed to be in overall good nutritional condition and (2) “late migration”, defined as individuals on the southward leg of the journey, returning to Antarctic feeding grounds (sampled September/ October), and presumed to be in overall poorer nutritional condition. Upon collection, blubber was separated from the skin and stored at −20 °C in furnaced, amber glass vials until time of analysis. Animal work was conducted under the University of Queensland and Griffith University Animal Research Ethics Committee (Approval Numbers NRCET/ 309/08/SBN, NRCET/273/07/SBN, ENTOX/207/09/SBN, ENV/17/10/AEC). Lipid Determination. Approximately 30 mg of each blubber sample was used for lipid extraction. Individual samples were extracted using a modified Bligh and Dyer methanol− chloroform−water extraction method15 as described in detail elsewhere.14 Lipid class profiles were determined by an Iatroscan Mark V TH10 thin layer chromatograph coupled with a flame ionization detector.16 The total blubber percent lipid was calculated by summing the individual lipid class percentages. Chemical Analysis. Analytes. All samples were analyzed for 58 analytes including 32 polychlorinated biphenyls (PCBs) (IUPAC numbers: 18, 28, 31, 33, 37, 47, 52, 66, 74, 99, 101, 105, 114, 118, 122, 123, 128, 138, 141, 149, 153, 156, 157, 167, 169, 170, 180, 183, 187, 189, 194, 206, and 209) and the organochlorine pesticides, mirex, hexachlorobenzene (HCB), pentachlorobenze (PeCB); the dichlorodiphenyltrichloroethane (DDT) group (o,p′-DDE, p,p′-DDE, o,p′-DDD, p,p′DDD, o,p′-DDT, p,p′-DDT); hexachlorocyclohexanes (α-, β-, B
dx.doi.org/10.1021/es401441n | Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Environmental Science & Technology
Article
Table 1. Summary Statistics for Lipid Percent and Concentrations (ng/g Lipid) of Detectable OCs in Superficial Blubber of Southern Hemisphere Humpback Whales (Megaptera novaeangliae) at Two Migration Time Pointsa
mean blubber lipid (%) compound PCBs tri-CBs 18
early migration
late migration
mean ± SD (n)
mean ± SD (n)
concentration index (CI)
median/range
median/range
[late mean]:[early mean]
39.0 ± 18.2 (45) 38.0/0.12−0.72 concentration
0.78
50.0 ± 13.0 (22) 44.0/0.22−0.63 concentration % detection
0.63 ± 1.4 (22) 0.06/
