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Keywords:

  • Polychlorinated biphenyls (PCBs);
  • Shrimp;
  • Seafood product;
  • Biomonitoring;
  • Health risk

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. SUPPLEMENTAL DATA
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

Currently, environmental studies describing levels of polychlorinated biphenyls (PCBs) in imported shrimp are limited, particularly studies of aquaculture shrimp. In the present study, we measured concentrations of the 209 PCB congeners in 84 uncooked, warm-water shrimp samples from the United States and 14 other countries in three continents. Total PCB and dioxin-like PCB (DL-PCB) levels were not significantly different between wild-caught and farm-raised shrimp, and the distribution of total PCB levels did not vary considerably by country of origin although significant differences were observed in some cases. Regional trends in both total PCB and DL-PCB concentrations were observed, with the highest concentrations measured in shrimp from North America followed by Asia and then South America. The lower chlorinated homologues (i.e., mono-, di-, and tri-PCBs) generally comprised a greater fraction of the total levels measured in farm-raised shrimp and shrimp from Asia and South America whereas higher chlorinated homologues (i.e., hepta-, octa-, nona-, and deca-PCBs) contributed more to levels in wild-caught shrimp and shrimp from North America. Estimated daily intake of PCBs associated with shrimp consumption ranged from 2 pg/kg/d (shrimp from South America) to 15 pg/kg/d (shrimp from North America). Results from the present study were comparable to other studies conducted recently and demonstrate that exposure to PCBs from consumption of farm-raised and wild-caught shrimp imported from different regions are not likely to pose any health risks. Environ. Toxicol. Chem. 2012; 31: 1063–1071. © 2012 SETAC


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. SUPPLEMENTAL DATA
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

Beginning in the 1920s, polychlorinated biphenyls (PCBs) were synthesized as technical mixtures for a wide range of applications, most commonly for manufacturing electronic appliances 1. Producing and using PCBs has been banned for decades in most regions, including in the United States and Europe. However, these chemicals degrade slowly in the environment and are therefore ubiquitous in soil, sediments, and biota worldwide 2. Because they are highly lipophilic, PCBs readily bioaccumulate in the food chain with consumption of meat, fish, and dairy products, which are the predominant exposure sources for humans 3–9.

Common aquatic foods such as catfish, char, salmon, tilapia, trout, mussels, oysters, squid, clams, and crab have been studied widely, and in some cases have been documented to contain measurable levels of PCBs 10–19. Shrimp are of particular interest due to high consumption rates worldwide. In the United States, shrimp has surpassed canned tuna as the number one consumed seafood product, reaching four pounds per capita in 2007, nearly double the 1990 consumption rate 20. Wild shrimp are omnivorous foragers of plankton and other small plants and decaying sea life. In some cases, PCB levels in wild shrimp have been found to be related to regional, point-source contamination 21–23. Farm-raised shrimp are typically raised in coastal ponds where they are fed a diverse array of fish-, plant-, and even soy-based feed throughout their life cycle 24–28. Presumably, the presence of PCBs in farm-raised shrimp would indicate the presence of PCBs in the feed.

The Gulf of Mexico is the source of approximately 80% of domestic shrimp and is home to several fishery regulations that enforce closed, marine-protected areas and restrict shrimping and fishing to promote sustainability 20, 29. Concerns regarding the short- and long-term sustainability of the Gulf of Mexico as a principal shrimping region for the U.S. were escalated after the explosion of the Deepwater Horizon drilling rig in April 2010, which resulted in the largest accidental marine oil spill in the history of the petroleum industry at that time. The U.S. Federal Government's subsequent fishing bans covered up to one-third of the Gulf waters; consequently, this increased the overall demand in the United States for imported shrimp. According to the U.S. Department of Agriculture, shrimp imports to the United States from Thailand and Ecuador between January and August 2010 increased 17% compared to the same period in 2009. In 2008, the U.S. Food and Drug Administration (FDA), which is tasked with inspecting shrimp imports for safety, inspected less than 2% of the total U.S. shrimp imports (more than 1.1 billion pounds and 29% of total edible imports) 20, 30.

To our knowledge, little published data exists regarding PCB levels in wild or farm-raised shrimp imported into the United States. Given the recent and considerable increase in consumption of imported shrimp, the present evaluation of differences in PCB loadings for imported and domestic shrimp and assessment of daily PCB intake is timely. In the present study, we present PCB levels measured in uncooked shrimp from U.S. coastal waters as well as shrimp imported from 14 different countries in North America, South America, and Asia. All 209 PCB congeners were quantified, and where possible, the results compared to those from other studies. Total PCB concentrations and congener patterns in farm-raised and wild shrimp were compared to assess the degree to which specific contamination sources could be identified. The data were also used to estimate daily dietary PCB intake for U.S. shrimp consumers, which was compared to regulatory criteria currently considered to be protective of the general population.

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. SUPPLEMENTAL DATA
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

Sample collection

Between February and April 2009, 84 warm-water uncooked shrimp samples were purchased from commercial fish markets, supermarkets, and grocery stores in the San Francisco and Sacramento areas in northern California, United States. All shrimp samples were headless, tail-on, and either frozen or previously frozen at time of purchase. The majority of samples were purchased in bags from commercial distributors of seafood products, while the remaining samples were purchased by the pound at market or store “seafood counters.” All shrimp originated from 14 countries in three continents: North America, South America, and Asia. The countries of origin included Argentina (n = 1), Bangladesh (n = 10), Belize (n = 2), Canada (n = 1), China (n = 1), Ecuador (n = 7), India (n = 3), Indonesia (n = 10), Malaysia (n = 2), Mexico (n = 11), Panama (n = 3), Thailand (n = 14), United States (n = 10), and Vietnam (n = 8).

Purchased quantities of shrimp ranged from approximately 0.2 kg to 1.8 kg with a median size of 0.3 kg. Shrimp counts, when available, ranged from 13 to 15 per pound to 91 to 110 per pound, with the majority of samples having counts between 13 to 15 per pound and 41 to 50 per pound. All sampling information, including information regarding origin and sample type (wild-caught or farm-raised), was verified through package labels or from store employees. After purchase, all samples were wrapped individually, labeled, frozen on ice in coolers, and shipped overnight to the analytical laboratory.

PCB analysis

Approximately 25 grams of shrimp from each purchase sample were composited for analysis. Composites were analyzed by Vista Analytical Laboratory (El Dorado Hills, CA, USA) for all 209 PCB congeners according to U.S. Environmental Protection Agency (U.S. EPA) Method 1668A using high-resolution gas chromatography-mass spectrometry. We used U.S. EPA Method 8290 to determine the lipid content of all samples. In total, 168 PCB congeners/congener groups were reported and summed to estimate total PCB loadings for each sample. Total dioxin-like PCB (DL-PCB) concentrations were determined by summing the 12 nonortho and mono-ortho congeners with dioxin-like activity (PCBs 77, 81, 126, 169, 105, 114, 106/118, 123, 156, 157, 167, and 189), and DL-PCB toxic equivalency concentrations were calculated by summing the product of the concentration for each dioxin-like congener and the associated 2005 World Health Organization toxic equivalency factor 31. The dioxin-like PCBs are of particular interest due to the toxicological properties they share with 2,3,7,8-tetrachlordibenzo-p-dioxin 31. Because of the co-elution of PCB 106 with PCB 118, a dioxin-like congener, PCB 106 is included in estimates of DL-PCBs. Further details on co-eluting congeners are provided in the Supplemental Data (Table S1).

Statistical analysis

Samples with nondetected concentrations were assumed to have a value equal to the sample-specific limit of detection divided by the square root of two. The limits of detection are described further in the Supplemental Data in addition to nondetected congeners and the effect of limits of detection on PCB concentrations (Fig. S1–S4).

Differences between/among groups were examined using the Wilcoxon rank sum test (Kruskal-Wallis when more than two categories were compared). The Holm-Bonferroni correction was used to adjust the critical alpha value when making multiple comparisons. For sample type, differences in the average percent of PCB homologue fractions and the average percent contributions of individual congeners to DL-PCB concentrations were examined using Student's t test. For the various countries and continents of origin, the same differences were examined using analysis of variance. All data management and analyses were completed using SAS software Version 9.3 and an alpha level of 0.05.

Outlier analysis

PCB concentrations were evaluated further to identify samples with unusually high levels relative to the other samples. A probable outlier was defined as a sample with total PCB concentrations more than three times the interquartile range, and a possible outlier was defined as a sample with total PCB concentrations between 1.5 and 3.0 times the interquartile range.

Dietary intake of PCBs

Daily PCB intake associated with consuming shrimp was estimated using median wet weight, total PCB concentrations measured in this study, and the average and 95th percentile daily ingestion rates of freshwater/estuarine shellfish for the U.S. population (2.7 g/d and 12.8 g/d, respectively), as reported in the U.S. EPA Exposure Factors Handbook 32. An exposure frequency of 365 d per year, average time of 70 years, standard body weight of 70 kg, and exposure duration of 30 years were assumed for all estimates.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. SUPPLEMENTAL DATA
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

General sample characteristics

The mean percent lipid content of all 84 samples was 0.44% (95% CI: 0.39–0.48). Average percent lipid content for farm-raised shrimp (mean = 0.42%, 95% CI: 0.36–0.47) was slightly lower than that for wild-caught samples (mean = 0.48%, 95% CI: 0.41–0.55), but no significant difference in lipid levels was observed. Of the 84 samples, 27% (n = 23) were wild-caught, 69% (n = 58) were farm-raised, and 4% (n = 3) were not labeled as either wild-caught or farm-raised.

Of the shrimp samples from Asia, almost all (n = 43, 89%) were farm-raised, whereas 6% (n = 3) were wild-caught and 4% (n = 2) were not identified as either wild-caught or farm-raised. Similarly, most of the shrimp from South America (n = 7, 87%) were farm-raised; only one sample was wild-caught. In contrast, most of the shrimp from North America (n = 19, 70%) were wild-caught, whereas 26% (n = 7) were farm-raised and 4% (n = 1) were not identified as either wild-caught or farm-raised. The country of origin could not be definitively established for one farmed shrimp sample.

Total and dioxin-like PCB concentrations

Lipid-adjusted total PCB and DL-PCB concentrations are presented in Table 1 for all samples and by sample type. DL-PCB toxic equivalency concentrations are described in the Supplemental Data (Table S2). Wet weight levels for all samples ranged from 0.11 to 2.40 ng/g for total PCBs (median = 0.18 ng/g) and from 0.002 to 0.19 ng/g for DL-PCBs (median = 0.01 ng/g). Median concentrations measured in wild-caught and farm-raised shrimp did not vary significantly for either total PCB or DL-PCB loadings (all p > 0.05). Furthermore, no significant differences were identified between wild-caught and farm-raised median PCB concentrations within each of the three continents (all p > 0.05). Although not statistically significant, a clear pattern did emerge with stratification of the data by continent. Specifically, the maximum, mean, and median levels of total PCBs and DL-PCBs were uniformly greater in North America with Asia and South America following sequentially (Fig. 1); only maximum and mean total PCB concentrations measured in farmed shrimp from South America were greater than levels measured in Asia. Correspondingly, North American samples had the greatest variability; measured levels in samples from Asia and South America were much less variable. For example, total PCBs in samples from North America ranged from 21 to 696 ng/g lipid weight (lw) (standard deviation [SD] = 166 ng/g lw), whereas Asian and South American samples ranged from 19 to 212 ng/g lw (SD = 34 ng/g) and 18 to 221 ng/g (SD = 69 ng/g), respectively.

Table 1. Distribution of total and dioxin-like polychlorinated biphenyls (PCBs; ng/g lipid weight) for all shrimp samples and by sample type
 All samplesWild-caughtFarm-raised
(n = 84)(n = 23)(n = 58)
Total PCBs
 Minimum1.79E + 011.90E + 011.80E + 01
 Median4.57E + 014.10E + 014.90E + 01
 95th percentile2.29E + 029.10E + 017.50E + 01
 Maximum6.96E + 026.96E + 025.02E + 02
DL-PCBs
 Minimum3.60E – 014.00E – 013.00E – 02
 Median3.23E + 002.00E + 003.00E + 00
 95th percentile1.94E + 017.00E + 005.50E + 00
 Maximum4.03E + 012.90E + 014.03E + 01
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Figure 1. Distribution of total and dioxin-like polychlorinated biphenyl concentrations in uncooked, warm-water shrimp by continent and sample type. PCB = polychlorinated biphenyl; DL-PCB = dioxin-like polychlorinated biphenyl.

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The distribution of total and dioxin-like PCB concentrations is shown by country of origin in Figures 2 and 3, respectively. The Kruskal-Wallis test, in which only countries with a minimum of four samples were included, indicated that the distribution of total PCB concentrations did not vary by country of origin (p > 0.05). Except for Belize (median = 431 ng/g lw), median values were fairly similar, ranging from 27 ng/g lw (Ecuador) to 82 ng/g lw (India). Because only two samples could be collected for Belize, it was not possible to compare statistically the distribution of these samples to those from other countries. In contrast to total PCB levels, DL-PCB concentrations varied significantly among countries with four or more samples (p < 0.01). Further evaluation indicated these findings might be due to significant differences in concentrations of samples from Bangladesh and Indonesia (median = 1.25 and 6.48 ng/g lw, respectively; p = 0.03).

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Figure 2. Distribution of total polychlorinated biphenyl (PCB) concentrations in uncooked, warm-water shrimp by country.

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Figure 3. Distribution of dioxin-like polychlorinated biphenyl (DL-PCB) concentrations in uncooked, warm-water shrimp by country.

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Homologue and congener patterns

The homologue and congener patterns for total PCB and DL-PCB concentrations by sample type and continent of origin are illustrated in Figures 4 and 5 and in the Supplemental Data (Fig. S5–S8). As illustrated in Figure 4, the percent contribution of numerous homologue groups (mono-, tri-, hexa-, hepta-, octa-, nona-, and deca-PCBs) to total PCB concentrations differed among the three continents of origin (all p < 0.05), with the highest chlorinated congeners contributing more to PCB loadings of North American shrimp than samples from Asia or South America. These results are consistent with the differences noted in wild-caught and farm-raised homologue patterns for total PCBs (Figure S5), as samples from Asia and South America were primarily comprised of farmed shrimp, whereas samples from North America were predominantly wild-caught.

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Figure 4. Average contribution of each homologue fraction to total polychlorinated biphenyl concentrations (95% confidence interval) measured in shrimp from Asia, North America, and South America.

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Figure 5. Average percent contribution of each individual congener to dioxin-like polychlorinated biphenyl concentrations (95% confidence interval) measured in shrimp from Asia, North America, and South America.

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Congener patterns for DL-PCB levels were similar when evaluated by continent of origin as well. Only the average percent contribution of congeners 77 and 167 varied significantly (p = 0.03 and p = 0.02, respectively) (Fig. 5). Of the nonortho congeners, PCB 77 contributed the most, followed by PCBs 126 and 169 for all regions, with summed nonortho congeners contributing approximately 10% to total DL-PCB levels. Congener patterns for DL-PCB concentrations by sample type and total PCB concentrations by continent and sample type are presented in the Supplemental Data (Fig. S6–S8).

Outlier analysis

Table 2 summarizes lipid-adjusted total and DL-PCB concentrations for the nine and eight samples identified as outliers, respectively. The average number of congeners detected in these samples (89) was nearly double the average number of congeners detected for all other samples (46). Of the nine samples identified as outliers based on total PCB levels, 56% were farm-raised, and 67% originated from a North American country. More specifically, the three samples with the highest concentrations were from the United States and Belize. The homologue fractions for these nine samples are described in detail in the Supplemental Data (Table S3).

Table 2. Concentrations of total and dioxin-like polychlorinated biphenyls (PCBs; ng/g lw) and descriptive data for samples identified as outliers based on total PCB concentrations and dioxin-like PCB concentrations
OutlierSample typeCountryTotal PCBs
1WildUSA6.96E + 02
2WildUSA2.29E + 02
3WildUSA3.40E + 02
4WildMexico1.92E + 02
5FarmBelize3.61E + 02
6FarmBelize5.02E + 02
7FarmIndonesia2.12E + 02
8FarmEcuador2.21E + 02
9FarmIndia1.42E + 02
OutlierSample typeCountryDL-PCBs
1WildUSA1.71E + 01
2WildUSA1.94E + 01
3WildUSA2.90E + 01
4WildMexico1.56E + 01
5FarmBelize3.09E + 01
6FarmBelize4.03E + 01
7FarmIndonesia1.98E + 01
10FarmIndonesia1.22E + 01

For the samples characterized as outliers based on DL-PCB concentrations, half were farmed and half wild. Seventy-five percent were from a country in North America. Similar to total PCB outliers, the highest DL-PCB levels were measured in a sample from the United States and two farm-raised samples from Belize. Interestingly, these two samples were obtained from separate, independent markets on different dates.

Dietary PCB intake estimates

Dietary intake estimates of total PCBs associated with shrimp consumption are presented in Table 3. Total PCB intake from consuming farm-raised and wild-caught shrimp ranged between 2.5 and 13.9 pg/kg/d, whereas intake rates among the various regions of origin ranged from 2.2 to 15.4 pg/kg/d. As expected, intake based on total PCB levels of the nine samples ascertained as outliers was considerably higher.

Table 3. Estimated daily intake of total polychlorinated biphenyls from shrimp consumption (PCBs; pg/kg/d)
 Mean ingestion rate95th Percentile ingestion rate
All samples2.913.8
Sample type
 Wild-caught2.913.9
 Farm-raised2.511.7
Location of origin
 North America3.215.4
 South America2.210.4
 Asia2.913.9
Outliers (Total PCBs)24.3115.4

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. SUPPLEMENTAL DATA
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

Interstudy comparisons of PCB levels in aquatic biota can be confounded by many uncertainties. First, analytical methods and reported results commonly differ as to the number of analyzed PCB congeners, methods of calculating/estimating total PCB concentrations, analytical limits of detection and methods for assessing nondetected concentrations. In addition, individual study results are often reported as wet weight, dry weight, or lipid weight. Second, the issue of temporality (e.g., comparing more recent results to older studies) can be difficult to address. Lastly, variability in shrimp species life span, feeding habits, and metabolism may play a crucial role in PCB loadings. For example, Storelli et al. 33 reported medians of 13, 25, and 115 ng/g lw for wild-caught red shrimp (Aristeus antennatus), pink shrimp (Parapenaeus longirostris), and golden shrimp (Plesioniea martia), respectively, from the same region in the southern Adriatic Sea. These findings may also reflect differences in habitation depth, because in general, PCB loadings of marine organisms have been shown to increase with greater depth 34–36. In the present study, the species of shrimp for each sample could not be identified, presenting a potential source of bias.

Additional uncertainty arises as a result of the small numbers of samples from some countries. Although China is one of the largest producers and exporters of seafood products, at the time of sampling, shrimp imported from China were not readily available for purchase at the markets/grocers from which samples were collected. Accordingly, only one sample from this country was obtained, with a total PCB concentration of 59.2 ng/g lw. This is less than levels measured by Jiang et al. 17 (103.6 ng/g lw, n = 4) and Liang et al. 37 in farmed shrimp (range = 147–212 ng/g lw, n = 91 and 55, respectively). Only Nakata et al. 38 reported lower levels (17 ng/g lw). Although samples were grouped and compared by continent to address this shortcoming and provide a more meaningful assessment, the small number of shrimp samples collected does not necessarily allow generalization of these findings, and further study is likely needed.

Despite these limitations, our findings in general are consistent with other recently reported results. Table 4 summarizes published total PCB concentrations measured in uncooked shrimp since 1999. Similar to the findings presented here, most of the lipid-adjusted levels ranged from 10 to 800 ng/g, although some samples collected in Belgium 39 and Thailand 16 contained total PCB levels greater than 1,000 ng/g lw. Regardless, the results of the present study were generally far lower than values published 20 to 30 years ago. For example, in 1977 Sims et al. 40 reported wet weight total PCB levels of 14 to 1,000 ng/g in Canadian wild shrimp, whereas in the present study wet weight total PCB levels in wild shrimp ranged from 0.11 to 2.40 ng/g. Similarly, Roose et al. 41 reported a mean lipid-adjusted value of 402 ng/g in wild shrimp collected between 1984 and 1993 in the Belgian continental shelf, almost 10 times the median value measured in wild shrimp in the present study (45.7 ng/g lw). Explanations for such dramatic differences include (1) quantitative improvements in analytical methods—in 1999, the U.S. EPA released Revision A of Method 1668, which expanded the analytical scope to include all 209 PCB congeners; (2) continuously decreasing levels in the environment due to production cessation in most countries; (3) degradation of existing levels; and (4) implementation of environmental control measures and regulations over the last several decades.

Table 4. Published concentrations of polychlorinated biphenyls measured in wild-caught and farm-raised shrimp between 1999 and 2009
LocationnWet weight (ng/g)Lipid weight (ng/g lw)Sample typeCollection yearReference
  • a

    Pooled samples.

  • b

    Multiple species.

Hong Kong914.57 ± 0.551147 ± 14.1Farmb1997Liang et al. 37
556.44 ± 2.28212 ± 90.4
Argentina45a9.7323.3Wild1997Gonzalez Sagrario et al. 46
China37a0.217Not reported2000Nakata et al. 38
Adriatic Sea30a0.714102Wildb2001Storelli et al. 33
30a0.628419
30a0.346493
Belgium2312.251875.39Wild2001Voorspoels et al. 39
Spain70-196a1.829Not reportedNot reported2002Bordajandi et al. 47
Canada40.10–1.15Not reportedWild2002Rawn et al. 14
130.0423–1.980Not reportedFarm
China4Not reported103.55Not reported2003-2004Jiang et al. 17
SpainNot reported0.46Not reportedNot reported2005Bocio et al. 15
Thailand211.9 (0.05–2.70)774.61 (19.95–1100.57)Wild2006-2007Jaikanlaya et al. 16
Baltic Sea17334.69 (2.64–11.61)Not reportedWildNot reportedMarcotrigiano and Storelli 48

The findings in the present study demonstrated the distribution of PCB levels (total or DL-PCB) in wild-caught and farm-raised shrimp did not vary significantly regardless of whether the data were aggregated or stratified by continent. This is consistent with the findings of Rawn et al. 14 who reported similar total PCB levels (wet wt) in farm-raised and wild caught shrimp from Canada, indicating that shrimp farming practices, wherein shrimp are raised primarily on man-made fish- and plant-based feed, result in total PCB loadings similar to those found in shrimp that forage omnivorously in the wild. Few significant differences in PCB levels (total or DL-only) were observed between the various continents and countries of origin; the only exception was higher levels of DL-PCBs in Indonesia compared to Bangladesh. Nevertheless, a discernable pattern was observed when the data were evaluated by continent, with total PCB and DL-PCB levels higher in shrimp from North America followed by Asia and South America. In the present study, higher PCB concentrations in North American shrimp were primarily a result of elevated levels in U.S. samples.

Homologue and congener-specific profiles suggested that PCB intake from consuming shrimp from North America would result, generally, in being exposed to the more heavily chlorinated congeners; more specifically, to many of the DL-PCB congeners. In particular, wild shrimp contained a larger fraction of the higher chlorinated congeners (hexa- through deca-PCBs) relative to farm-raised shrimp, and most of the DL-PCB congeners were also present at higher concentrations in wild shrimp. Storelli et al. 33 and Voorspoels et al. 39 also reported that the more heavily chlorinated congeners predominated in wild shrimp from southern and northern Europe, and Jaikanlaya et al. 16 reported that tri- and tetra-PCBs were dominant in wild shrimp from Thailand 16, 33, 39. Varying homologue patterns among wild shrimp from different areas most likely reflect different specific or regional environmental PCB sources.

As in previous studies, contamination of environmental media from Aroclor and other PCB mixtures could be a potential source for higher shrimp PCB loadings, particularly in the United States, given the persistent use of these compounds until the late 1970s. Of the approximately 1,400 million pounds of PCBs manufactured in the United States and 150 million pounds exported by the United States between 1930 and 1975, nearly all was in the form of various Aroclors 10. Aroclor mixtures are a common source of PCBs found in aquatic systems, and PCB 118 is the predominant congener of most Aroclors. For example, Aroclors 1242, 1254, and 1260 are composed of approximately 8, 48, and 12% PCB 118, respectively 42. PCB 118 is relatively resistant to degradation and metabolism and is therefore often the most dominant congener in sediments and tissues of aquatic biota 43. In the present study, PCB 118 accounted for a considerable proportion of levels measured in shrimp samples, such that Aroclor mixtures may be a potential source of PCB loadings found in the shrimp. This is particularly likely given that Aroclors containing high levels of congener 118 continued to account for a significant portion of the Aroclor market even as production of some Aroclor mixtures decreased or ceased entirely in the early 1970s 10. Nevertheless, further examination using statistical methods such as principal component analysis may help determine if Aroclors are indeed a source of contamination.

Overall, levels measured in the current study were far below the U.S. FDA's tolerance level of 2 µg/g for PCBs in fish 44. Similarly, conservative estimates of dietary PCB intake were all less than the U.S. EPA's estimate of the maximum daily dose for Aroclors 1,016 (70,000 pg/kg/d) and 1,254 (20,000 pg/kg/d), below which noncancer adverse health effects (i.e., immunological, neurological) are not expected to occur over a lifetime 45. These results indicate that significant consumption of domestic or imported shrimp is unlikely to pose PCB-related health hazards and further suggest that any changes in shrimp consumption that may have occurred following the Deepwater Horizon incident did not significantly affect dietary PCB intake.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. SUPPLEMENTAL DATA
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

The authors are thankful to L. Nguyen for her assistance with this project and contribution to the data analysis for this manuscript. Funding for the sample collection, laboratory analysis, and subsequent data analysis described in the present study was provided by ChemRisk and Vista Analytical Laboratory.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. SUPPLEMENTAL DATA
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information
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Supporting Information

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. SUPPLEMENTAL DATA
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

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