Biomagnification of Toxic PCB Congeners in the ... - ACS Publications

Chapter 20

Biomagnification of Toxic PCB Congeners in the Lake Michigan Foodweb

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on April 1, 2018 | https://pubs.acs.org Publication Date: January 15, 2000 | doi: 10.1021/bk-2001-0772.ch020

A . G . Trowbidge and D . L. Swackhamer

1

Environmental and Occupational Health, School of Public Health, University of Minnesota, Minneapolis, M N 55455 Corresponding Author 1

This study examined whether AHH-inducing PCBs preferentially biomagnify relative to total PCBs in aquatic foodwebs. Organisms from the Lake Michigan lower trophic level foodweb were collected at two locations over the course of two years. This study determined that not only do AHH-inducing PCBs biomagnify, but they biomagnify to a greater extent than do total PCBs. TEQs were calculated and were also found to preferentially biomagnify.

INTRODUCTION Polychlorinated biphenyls (PCBs) have been investigated by researchers since 1966 when they werefirstidentified in fish and eagle tissue and human hair samples (1). Today, these chemical compounds still pose a serious environmental threat even though their production in the United States was formally banned in 1979. They have been identified in a multitude of biotic and abiotic samples, including samples from remote pristine locations (2-9) Concerns attributed to PCBs stem from their environmental persistence, ability to bioaccumulate and their potential toxicity. These stable compounds are of particular concern in aquatic systems where their concentrations are usually low due to their hydrophobic nature, but reach much higher concentrations in top predator fish because of their ability to bioaccumulate and biomagnify in the aquatic foodweb. This poses a serious health threat to humans since the primary source of PCBs in the human diet is due to the consumption offishfromcontaminated water (10-12).

266

© 2001 American Chemical Society Lipnick et al.; Persistent, Bioaccumulative, and Toxic Chemicals I ACS Symposium Series; American Chemical Society: Washington, DC, 2000.


267 Not all PCBs invoke the same toxic responses in all species. The PCB family of 209 congeners exhibit different magnitudes of toxicity and manifest their toxicity under different modes of action (13-16). One small subset of individual PCB congeners has been the focus of much toxicological research. These congeners include PCBs with no ortho, two para and two or more meta chlorines, their monoortho analogs and some di-ortho congeners (14). They are structurally similar to highly toxic 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and exhibit similar toxic responses (13, 15, 17). These toxic compounds promote induction of the aryl hydrocarbon hydroxylase (AHH) enzyme system which elicits such symptoms as body weight loss, dermal toxicity, immunotoxicity, and adverse effects on reproduction and development (15). While these PCB compounds are less toxic than TCDD, they often contribute more to total TCDD-type toxicity due to their higher concentrations in environmental matrices (17-19). Smith et al. found that more than 90% of the TCDD-type toxicity in chinook salmon was attributed to 3 of the AHHinducing PCBs (20). Even with this toxicity potential, there are only a handful of reports concerning their distribution or dynamics in aquatic or terrestrial ecosystems (20-25). Because of the lack of exposure data for AHH-inducing PCBs, risk assessments are most often performed using total PCB measurements. An assumption inherent in this approach is that the exposure to AHH-inducing congeners is proportional to the total PCBs throughout the risk assessment model. This study examines congener specific concentrations for 16 individual AHH-inducing PCBs found in lower trophic level organisms in the Lake Michigan foodweb. It compares the proportion of AHHinducing PCB congeners relative to total PCBs, biomagnification factors for AHHinducing PCBs and total PCBs and toxic equivalency (TEQs) values among the foodweb trophic levels.

LAKE MICHIGAN SAMPLING Lake Michigan is one of the Great Lakes that has been severely affected by the discovery of PCBs in top predator fish. Lake trout and coho salmon exceed the U.S. Food and Drug Administration concentration guidelines for commercial sale. This discovery created devastating effects on a multibillion-dollar fishing and tourism industry (26). As a result, PCBs in Lake Michigan's top predator fish have been researched quite extensively, but little is known about PCB concentrations in the components that make up their food source. The primary components of the pelagic foodchain include phytoplankton at the base of the foodweb, herbivorous zooplankton, Mysis, forage fish such as alewife and rainbow smelt and top predators such as lake trout and coho salmon. Components of the benthic foodchain include detritus, Diporeia sp forage fish such as bloater chub and sculpin, and the top predator lake trout and coho salmon (27). Both foodweb branches obtain PCBs from water, and the benthic branch includes sediments as a PCB source. 9

Lipnick et al.; Persistent, Bioaccumulative, and Toxic Chemicals I ACS Symposium Series; American Chemical Society: Washington, DC, 2000.


268 Based on this understanding of the Lake Michigan foodweb, major components occupying the lower trophic levels of the pelagic foodweb were chosen for sample collection along with a major benthic component. Sample collection was executed as part of the Lake Michigan Mass Balance Study (LMMBS) funded by the U.S. EPA Great Lakes National Program Office. Samples for the LMMBS were collected from eleven sites over seven cruises and analyzed on a congener specific basis for 110 PCB congeners. A subset of the LMMBS samples were re-analyzed for concentrations of AHH-inducing PCBs which often co-elute with other PCB congeners. Figure 1 illustrates site locations, dates of collection and sample media which were used for this study. Briefly, two site locations were chosen for reanalysis, sites 180 and 380. Samples were collected during 1994 and 1995. Sample media collected included water (dissolved phase), phytoplankton (10-100 μιη), bulk net zooplankton (>100 μηι), Mysis relicta, and Diporeia sp. Water samples were collected at the same depth as phytoplankton samples. Dissolved phase PCBs were collected on XAD-2 resin. Approximately 300L of water was processed for each dissolved phase sample. Phytoplankton samples were collected via "phytovibes", a cone-shaped frame with a l m opening which held a stationary 10 μηι Nitex net with a detachable collection cup at the bottom. A motor vibrated the structure to facilitate water removal. Samples werefilteredonto GF/F fiber filters and ranged from 0.14 to 3.93 g dry weight. Microscopic analysis indicated a pure phytoplankton sample for this size fraction (10 - 100 μηι). 2

Organisms collected under the heading of zooplankton included bulk zooplankton (>100 μηι), Mysis relicta and Diporeia sp. Bulk zooplankton was collected via vertical net tows using 100 μιη nets that produced a sample dominated by zooplankton, but occasionally containing some colonial diatoms. Mysis relicta were collected either by vertical net tows using 500 μπι nets or by benthic sled tows. Diporeia were collected by benthic sled tows. Organisms were hand picked to get a suitable and pure sample. Subsamples of bulk phytoplankton, zooplankton, Mysis and Diporeia were collected for particulate organic carbon (POC) analysis.

ANALYTICAL PROCEDURES All samples (whole organisms) used in this project were extracted in a Soxhlet apparatus. Extracts were subsequently batch extracted to remove additional water, lipids were removed using 6% deactivated alumina column, and compound separation was performed using a combined column of 0% deactivated silica and 1% deactivated alumina. Prior to extraction, PCB congeners #14 (3,5-dichlorobiphenyl), #65 (2,3,5,6-tetrachlorobiphenyl) and #166 (2,3,4,4',5,6-hexachlorobiphenyl) were added as surrogates. Media-appropriate volumes of two internal standards,



> 100 μπόι bulk Hand picked Hand picked XAD

10 -100 μιη

Michigan.

Samples analyzed for AHH-inducing PCBs were collected as part of the EPA Lake Michigan Mass Balance Study. (Sites 180 & 380)

16 AHH inducing PCBs

Analytes:

June, August, October, 1994 Jan., March, Aug., Sept 1995

Seven cruises:

Biota Samples Phytoplankton Zooplankton Mysis Diporeia Dissolved

FIGURE I. Sampling sites, collection dates and media collected from Lake

Field Sampling


270


congeners #30 (2,4,6-trichlorobiphenyl) and #204 octachlorobiphenyl) were added prior to instrumental analysis.

(2,2',3,4,4\5,6,6'-

Extracts were re-analyzed for specific AHH-inducing PCBs (Table I) using gas chromatographic (Hewlett Packard 5890A) mass spectrometry (Hewlett-Packard 5988A) with selected ion monitoring (SIM) and the mass spectrometer operated in the negative ion mode (GC/MS-NI). A method developed by Schmidt and Hesselberg (28) was adapted for use in this project. This method utilizes the fact that GC/MS in the negative ion mode is very selective and sensitive to highly chlorinated compounds. AHH-inducing PCB congeners often co-elute with other congeners having a different number of chlorine atoms which allows them to be differentiated by negative ion mass spectrometry. To ensure high quality data a strict set of QA criteria were invoked for this research project. A full Quality Assurance Project Plan was prepared and approved by EPA (29). This plan included criteria for accuracy, precision, blank values, and detection limits.

RESULTS AND DISCUSSION Of the 16 AHH-inducing PCB congeners analyzed, only two were not used in quantitation of total toxic PCB congeners. PCB 126 was removed from the data set due to interference from surrogate standard PCB 166. An attempt was made to account for this interference, however the resulting PCB 126 concentrations were not reliable. PCB 170 was removed from the data set since it could not be separated from congener 190 and has the same molecular weight The first step in analyzing the data was to determine if concentration normalization to either lipid or organic carbon was appropriate. Normalizing data is only appropriate when contaminant concentration varies in direct proportion to the normalizing factor (30). If these criteria are not met and data normalization is performed, incorrect conclusions can result Although lipid content varied among trophic levels (see Table II), the relationship between both lipid and organic carbon to contaminant concentration was weak or insignificant for each sample type analyzed. It was not deemed appropriate to normalize congener concentrations to either lipid or organic carbon. Therefore these values remain on a dry weight basis. Concentration data was evaluated for spatial and temporal differences using ANOVA (SPSS Inc.). No significant differences were discovered and the data were averaged for further analysis.


271


Table IL Average total AHH-inducing PCB concentration and Σ T E Q for each sample media collected. Ν

Diss. Phyto Zoopl Mysis Dip.

% Lipid ±sid

MEAN (ng/g)

STD DEV

XTEQ

ZFEQ

XTEQ

(pg/g) (Safe)

—

1.0E-05 5.1 30.7 95.2 134.1

9.37E-06 2.2 23.0 41.4 33.6

2.7E-06 2.1 5.5 14.3 30.9

(pg/g) (WHO human) 1.1E-06 0.8 1.9 6.7 9.1

(pg/g) (WHO fish) 3.4E-08 0.02 0.10 0.32 0.48

10 12 12 11 10

5+2 20+9 15+8 16+11

Table L Analyzed A H H - Inducing PCB congeners CONGENER NUMBER

81 77 123 118 114 105 138 158 126 128 167 156 157 169 170 189

CO-ELUTING PCB CONGENERS

110 149 131 163 166

SUBSTITUTION PATTERN

3A4\5 3,3\4,4' 2\3,4,4\5 2,3\4,4\5 2,3,4,4',5 2.3,3\4,4' 2,2\3AA\S* 2,3,3\4,4\6 3,3\4,4',5 2,2\3,3',4,4' 2,3,3 \4,4\5 2,3,3 ,4,4 ,5' 3,3 ,4,4 ,5,5' 2,2\3,3',4,4',5 2.3,3·,4,4·,5,5· ,

,

190

,

ΐ

ORTHO SUBmTUTION

non non mono mono mono mono di di non di mono mono mono non di mono


272 Concentrations


Average concentrations of total AHH-inducing PCBs (sum of 14 congeners) and the sum of the toxic equivalent concentration (ZTEQ) for each environmental media are listed in Table II. For summation purposes values less than the method detection limit were set to zero. Total AHH-inducing PCB concentrations for the dissolved phase ranged from 2 to 30 pg/L, which corresponds to 2e-06 to 3e-05 ng/g in equivalent units to the foodweb. Phytoplankton concentrations ranged from 2 to 9 ng/g, and bulk zooplankton concentrations rangedfrom3 to 71 ng/g. The concentrations for Mysis and Diporeia rangedfrom34 to 167 ng/g and 79 to 196 ng/g. Patterns of individual AHH-inducing PCB congeners in each media are shown in Figure 2. A similar pattern is apparent for each media with congeners 118 and 138 dominating in all cases. There is an overall trend for AHH-inducing PCBs to increase with each step of the foodchain.

Preferential Biomagnification Before examining the dynamics of AHH-inducing congeners relative to total PCB, we first determined if the AHH-inducing congeners biomagnified between trophic levels. The top graph of Figure 3 represents average trophic level contaminant concentrations that were determined by summing the 14 AHH-inducing PCBs analyzed in this study. Bioaccumulation of AHH-inducing PCBs is clearly indicated. Significant increases are observed between dissolved phase and Mysis and Diporeia (p

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