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Keywords:

  • Arsenic speciation;
  • Fish tissue;
  • Fish advisories

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSION
  7. Acknowledgements
  8. REFERENCES

Sampling was conducted in 2002 to determine the total concentration and chemical speciation of arsenic in several marine fish and shellfish species collected from the Delaware Inland Bays and the Delaware Estuary, both of which are important estuarine waterbodies in the US Mid-Atlantic region that support recreational and commercial fishing. Edible meats from summer flounder (Paralicthys dentatus), striped bass (Marone saxatilis), Atlantic croaker (Micropogonias undulates), and hard clam (Mercenaria mercenaria) were tested. Total arsenic was highest in summer flounder, followed by hard clam, then striped bass, and finally, Atlantic croaker. Total arsenic was higher in summer flounder collected during the spring, as these fish migrated into the Inland Bays from the continental shelf, compared with levels in summer flounder collected during the fall, after these fish had spent the summer in the Inland Bays. Similarly, striped bass collected in the early spring close to the ocean had higher total arsenic levels compared with levels detected in striped bass collected later during the year in waters with lower salinity. Speciation of arsenic revealed low concentrations (0.00048–0.02 μg/g wet wt) of toxic inorganic arsenic. Dimethylarsinic acid was more than an order of magnitude greater in hard clam meats than in the other species tested, a finding that was attributed to arsenic uptake by phytoplankton and subsequent dietary uptake by the clam. Risk assessment using the inorganic arsenic concentrations was used to conclude that a fish consumption advisory is not warranted.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSION
  7. Acknowledgements
  8. REFERENCES

The Delaware Inland Bays and the nearby Delaware Estuary provide important recreational and commercial fishing opportunities for the people who reside and visit the US Mid-Atlantic region. Figure 1 shows the location of these 2 near-coastal waterways. The Delaware Estuary, which flows through the Philadelphia (PA, USA)-Camden (NJ, USA)-Wilmington (DE, USA) urban center, has several fish consumption advisories in place. In contrast, the Delaware Inland Bays, which are a series of coastal lagoons in southeastern Delaware, are far less urbanized, and no fish consumption advisories are currently in place. The Inland Bays are hydraulically connected to the Atlantic Ocean through a stabilized inlet, allowing coastal species to migrate into and out of the bays.

Baseline data regarding total arsenic in summer flounder (Paralicthys dentatus), Atlantic croaker (Micropogonias undulates), and hard clam (Mercenaria mercenaria) from the Inland Bays are presented in Table 1 along with similar data concerning total arsenic for striped bass (Marone saxatilis) from the Delaware Estuary (DNREC 2005). Figure 1 shows where these samples were collected. Baseline data regarding inorganic arsenic in fish and shellfish from the 2 waterways are not available. From Table 1, total arsenic in summer flounder has historically ranged from 0.59 to 3.27 μg/g wet weight (ww) fillet, with no indication that concentration is related to fish length. Total arsenic in the single Atlantic croaker sample was 0.91 μg/g ww fillet, whereas total arsenic in the 2 hard clam samples ranged from 0.78 to 1.66 μg/g ww edible meat. Finally, total arsenic in striped bass collected from the Delaware Estuary ranged from an estimated minimum of 0.09 μg/g ww fillet to a maximum of 1.11 μg/g ww fillet.

The first 5 striped bass samples listed in Table 1 were collected in the lower Delaware Estuary, close to the Atlantic Ocean. The second 5 striped bass samples listed in Table 1 were collected farther north, in the more urbanized/industrialized and less saline portion of the Delaware Estuary. Note that the striped bass collected in the more urban/industrial portion of the estuary had significantly lower total arsenic concentrations than the striped bass collected in the estuary near the ocean, despite being of comparable size and despite the perception that concentrations likely would be higher in more urbanized and industrialized waters. This interesting observation served as the seed for our hypothesis that marine species that migrate from the shelf waters into near-coastal waters of the Delaware Estuary and Delaware Inland Bays bring body burdens of total arsenic with them that are higher than the levels they leave with during their seaward migration. This may be true merely because the natural levels of arsenic in seawater are higher, on average, than the natural levels of arsenic in freshwater (Smedley and Kinniburgh 2002). Alternatively, or in addition, there could be a source of arsenic on the shelf waters adjacent to the Delaware Estuary and Delaware Inland Bays that has not been identified and characterized. In either event, where and how migratory coastal fish acquire their chemical body burden are important questions that provide a broader context for fish tissue monitoring and health advisory programs. An understanding of where coastal species acquire their body burden begins with an understanding of their migratory patterns.

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Figure Figure 1.. Mid-Atlantic coastal region showing the Delaware Inland Bays and the Delaware Estuary (USA) along with the locations of baseline fish and shellfish samples.

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Summer flounder are demersal fish that migrate into and out of the Inland Bays on a seasonal basis. Adults migrate into the Inland Bays during the spring from their overwintering grounds on the Continental Shelf (Wang and Kernehan 1979). They remain in the bays and along the immediate coast throughout the summer, then migrate back offshore during the fall. The adults are believed to spawn during this fall migration back to the shelf. Similarly, adult Atlantic croaker migrate into and out of the Inland Bays on a seasonal basis, entering in the spring as the water warms and leaving in the late fall as the inland water cools. Spawning occurs in the adjacent Atlantic Ocean, with peak activity between October and February (Wang and Kernehan 1979). Adult hard clam, in contrast to summer flounder and Atlantic croaker, are sedentary, year-round residents of the Delaware Inland Bays. As such, their body burden is not confounded by potential contaminant exposures received hundreds of miles away.

The migratory pattern of striped bass found in the Delaware Estuary is not fully understood, although a few major features are recognized. After spawning during the spring in low-salinity waters of the estuary, some striped bass migrate out to the Atlantic Ocean, whereas others remain in the estuary. The larger and older females are more likely to migrate back to the ocean, whereas a significant fraction of the mature males may stay within the Delaware Estuary system (ASMFC 2004).

To test our hypothesis that fish that migrate into near-coastal waters from the ocean have higher body burdens of arsenic compared with fish that migrate back offshore, it is necessary to collect fish at different times and places during their annual migration. Our strategy was to collect summer flounder, Atlantic croaker, and striped bass as these species move inland from the coast and then again later in the season, before they move back offshore. Hard clam also was tested as a resident control for the Delaware Inland Bays.

Table Table 1.. Baseline data regarding arsenic in selected marine fish and shellfish from the Delaware Inland Bays and the Delaware Estuarya
StationLatitude (N)Longitude (W)Date sampledSpeciesbSample size (n)Length (mm)Weight (g)Total arsenic (μg/g wet wt)
  1. a Fish samples were analyzed as skin-on fillets. Hard clam was analyzed as edible meats. NA = not available/applicable; J = analyte present (reported value is estimated; measured concentration was below the range for accurate quantitation); < = analyte not present at the indicated detection limit.

  2. b Hard clam, Mercenaria mercenaria; summer flounder, Paralicthys dentatus; Atlantic croaker, Micropogonias undulates; striped bass, Marone saxatilis.

138°36′03.0″−75°07′33.0″17 July 1990Hard clam21NANA0.78
238°39′08.0″−75°06′19.0″17 July 1990Hard clam11NANA1.66
138°36′03.0″−75°07′33.0″24 September 1991Summer flounder13604250.59
138°36′03.0″−75°07′33.0″24 September 1991Summer flounder13353501.06
338°36′30.9″−75°05′03.9″10 September 1992Summer flounder33353753.27
438°36′13.3″−75°04′46.2″11 August 1999Summer flounder33664502.40
538°38′07.0″−75°05′51.9″10 August 1999Atlantic croaker52742970.91
639°00′02.8″−75°10′30.3″28 February 1997Striped bass179659701.11
639°00′02.8″−75°10′30.3″28 February 1997Striped bass173044600.73
639°00′02.8″−75°10′30.3″4 March 1997Striped bass175554430.69
639°00′02.8″−75°10′30.3″4 March 1997Striped bass173045360.55
639°00′02.8″−75°10′30.3″14 April 1997Striped bass179548760.13 J
739°44′30.6″−75°29′44.7″28 May 1997Striped bass171240820.12 J
739°44′30.6″−75°29′44.7″28 May 1997Striped bass18356350<0.2
739°44′30.6″−75°29′44.7″5 June 1997Striped bass172540820.1 J
739°44′30.6″−75°29′44.7″5 June 1997Striped bass190072570.14 J
739°44′30.6″−75°29′44.7″5 June 1997Striped bass184090710.09 J

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSION
  7. Acknowledgements
  8. REFERENCES

Field collection

Ten summer flounder samples were collected by hook and line from Delaware's Inland Bays during 2002. Five individual flounder were collected in the spring of 2002 as these fish 1st entered the Inland Bays during their inland migration from offshore waters. Five individuals were then collected in the fall of 2002 during their outward migration from the Inland Bays back offshore. Attempts to secure additional flounder of the target size during the spring and fall sampling windows to make the study more powerful were unsuccessful. The flounder samples were supplemented with 5 individual Atlantic croaker samples collected by gill net from the Inland Bays during the summer of 2002. We were not able to catch croaker in the fall of 2002 during their outward migration from the Inland Bays. Finally, 2 hard clam samples were collected by hand rake from the Inland Bays during the summer of 2002. Each of the hard clam samples was composed of soft tissue (meats) from multiple clams, with the free liquid decanted before processing.

In addition to the samples collected within the Inland Bays, 10 individual striped bass samples also were collected from the nearby Delaware Estuary. Five individual striped bass were collected by gill net in late March 2002 in the lower to mid-Delaware Bay. Five additional individual striped bass were collected by electroshocking in May 2002 farther up the Delaware Estuary in the vicinity of Cherry Island Flats, an important spawning area for striped bass.

At the point of collection, all fish samples were individually wrapped in aluminum foil, labeled, placed into a plastic zip-lock bag, and then stored in a cooler on wet ice for transport back to the laboratory. On arrival at the laboratory, the samples were logged, weighed, and measured. All finfish were prepared for analysis as skin-on fillets using precleaned cutting tools and cutting surfaces. Individual fillets were passed through a precleaned meat grinder to produce a consistent tissue homogenate. The homogenate was stored in precleaned glassware and frozen at −20°C until being shipped on dry ice to Battelle Marine Sciences Laboratory for arsenic analysis.

Laboratory

The ground fish tissue samples were received frozen at the Battelle Marine Sciences Laboratory. The samples were logged and inspected to determine if any breakage or thawing had occurred during shipping. The samples were reported to be in good condition on arrival. When ready for analysis, the wet tissue samples were thawed, and 0.5 g of wet tissue was digested in 10 mL of 2 M hot sodium hydroxide at 80 °C for 8 h or overnight. The digestates were stored at 4°C before being analyzed for total arsenic by inductively coupled plasma-mass spectrometry using US Environmental Protection Agency (USEPA) Method 200.8 (USEPA 1994) and by hydride atomic absorption using USEPA Method 1632A (USEPA 2001) for arsenic speciation. These same methods were used in the analysis of marine fish reported by the USEPA (USEPA 2003) and by researchers who investigated total and inorganic arsenic in a market basket survey (Schoof et al. 1999). A 1-mL aliquot of the digestate was analyzed for inorganic arsenic [sum of arsenic(III) and arsenic(V)], monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) at pH 1 by arsine generation with the reducing-agent sodium borohydride. The arsine and methyl arsines were collected on a cryogenic column before quantification by atomic absorption using a quartz tube with an air-hydrogen flame positioned in the light path.

Table Table 2.. Quality-assurance results for 2002 samplesa
 Total arsenic (μg/g wet wt)bInorganic arsenic (μg/g wet wt)MMA (μg/g wet wt)DMA (μg/g wet wt)
  1. a MMA = monomethylarsonic acid; DMA = dimethylarsinic acid; NA = not available/applicable; NC = not certified; NS = not spiked; J = detected above blank and less than the method detection limit; U = not detected.

  2. b Results for total arsenic are listed on a wet weight basis except for the standard reference material, which are expressed on a dry weight basis.

Procedural blanks
Procedural blank 10.04U0.03 0.01 0.04U
Procedural blank 20.04U0.03 0.01 0.04U
Matrix spike results
Amount spiked13.9 4.64 4.64 4.64 
0203029–0012.19 0.03U0.01U0.00757J
0203029–001 MS13.6 5.80 5.81 4.64 
Amount recovered11.4 5.80 5.81 4.64 
% Recovery82% 125% 125% 100% 
Amount spiked14.6 4.87 4.87 4.87 
0205053–0040.362 0.03U0.01U0.04U
0205053–004 MS12.3 5.98 6.11 4.39 
Amount recovered11.9 5.98 6.11 4.39 
% Recovery82% 123% 125% 90% 
Standard reference material
DORM-217.1 NA NA NA 
Certified value18.0 NC NC NC 
Range±1.1       
% Difference5% NA NA NA 
Replicate analysis results
0209047–006A1.32 0.03U0.01U0.04U
0209047–006A1.27 0.03U0.01U0.04U
Relative % difference4% NA NA NA 

Quality-control testing included procedural blanks, matrix spikes, replicate analyses, and analysis of a certified reference material (DORM-2, dogfish muscle tissue) obtained from the National Research Council of Canada (Ottawa, ON). Table 2 summarizes the quality-assurance results. The results for the procedural blanks were below the method detection limits of 0.04 μg/g ww for total arsenic, 0.03 μg/g ww for inorganic arsenic, 0.01 μg/g ww for MMA, and 0.04 μg/g ww for DMA. The mean procedural blank for inorganic arsenic was 0.006 μg/g ww. The field samples were corrected for this mean procedural blank by subtracting 0.006 μg/g ww from the inorganic arsenic concentrations in the field samples. No detectable signal was found for MMA or DMA in the procedural blanks. The arsenic speciation results that were detected above the blank and less than the method detection limit were reported with a “J” flag. If no signal was detected after blank correction, then the concentrations were reported at the detection limit and with a “U” flag. The results for matrix spikes and laboratory replicates were within the method performance criteria. The result for total arsenic in DORM-2 was within 5% of the certified value of 18.0 μg/g dry weight. DORM-2 is not certified for the arsenic species. The concentration of DMA in DORM-2 was 0.36 μg/g dry weight, which compares well with a concentration of 0.28 μg/g dry weight reported by Goessler et al. (1997). Based on the quality-assurance results, the data were judged to be suitable for subsequent use and analysis.

Table Table 3.. Arsenic speciation of marine fish and shellfish from the Mid-Atlantic region, USAa
SampleWaterbodyLatitude (N)Longitude (W)Date sampledSpeciesbSample size (n)Length (mm)Weight (g)Total arsenic (μg/g wet wt)Inorganic arsenic (μg/g wet wt)MMA (μg/g wet wt)DMA (μg/g wet wt)
  1. a Inorganic arsenic data are blank corrected. Fish samples were analyzed as skin-on fillets. Hard clam was analyzed as edible meats. DE = Delaware; MMA = monomethylarsonic acid; DMA = dimethylarsinic acid; J = detected above blank and less than the method detection limit; U = not detected.

  2. b Summer flounder, Paralicthys dentatus; Atlantic croaker, Micropogonias undulates; hard clam, Mercenaria mercenaria; striped bass, Marone saxatilis.

0205072–001DE Inland Bays38°36′13.3″−75°04′46.2″29 May 2002Summer flounder152015003.330.03U0.00342J0.0119J
0205072–002DE Inland Bays38°36′13.3″−75°04′46.2″29 May 2002Summer flounder14458402.580.03U0.00115J0.00503J
0205072–003DE Inland Bays38°36′13.3″−75°04′46.2″29 May 2002Summer flounder14107203.080.03U0.01U0.0117J
0205072–004DE Inland Bays38°36′13.3″−75°04′46.2″4 June 2002Summer flounder150012002.250.03U0.01U0.00559J
0205072–005DE Inland Bays38°36′13.3″−75°04′46.2″11 June 2002Summer flounder147510501.800.03U0.00198J0.00790J
0209047–002DE Inland Bays38°36′13.3″−75°04′46.2″17 September 2002Summer flounder13905851.490.00048J0.01U0.00839J
0209047–003DE Inland Bays38°36′13.3″−75°04′46.2″18 September 2002Summer flounder14257402.130.03U0.01U0.00729J
0209047–004DE Inland Bays38°36′13.3″−75°04′46.2″23 September 2002Summer flounder14459502.080.03U0.00183J0.00562J
0209047–005DE Inland Bays38°36′13.3″−75°04′46.2″30 September 2002Summer flounder145211000.950.03U0.00268J0.00603J
0209047–006DE Inland Bays38°36′13.3″−75°04′46.2″30 September 2002Summer flounder149013751.320.03U0.00247J0.00662J
0207096–001DE Inland Bays38°40′09.6″−75°07′26.3″30 July 2002Atlantic croaker13335350.800.03U0.00344J0.0570J
0207096–002DE Inland Bays38°40′09.6″−75°07′26.3″30 July 2002Atlantic croaker13464500.480.00057J0.01U0.0286J
0207096–003DE Inland Bays38°40′09.6″−75°07′26.3″30 July 2002Atlantic croaker13376000.790.03U0.00289J0.0412 
0207096–004DE Inland Bays38°40′09.6″−75°07′26.3″30 July 2002Atlantic croaker13156400.800.03U0.01U0.0643 
0207096–005DE Inland Bays38°40′09.6″−75°07′26.3″30 July 2002Atlantic croaker1328550 0.03U0.01U0.0573 
0207064–001DE Inland Bays38°38′10.3″−75°06′03.5″15 July 2002Hard clam3569280.930.00898 0.01U0.268 
0207092–001DE Inland Bays38°36′03.0″−75°07′33.0″29 July 2002Hard clam2065181.530.02009 0.00294J0.528 
0203029–001DE Estuary38°59′57.4″−75°18′57.6″21 March 2002Striped bass166528502.190.03U0.01U0.00757J
0203029–002DE Estuary38°59′57.4″−75°18′57.6″21 March 2002Striped bass168430001.230.03U0.00323J0.0182J
0203029–003DE Estuary38°59′57.4″−75°18′57.6″21 March 2002Striped bass166229001.070.03U0.00276J0.0111J
0203029–004DE Estuary38°59′57.4″−75°18′57.6″21 March 2002Striped bass167127501.170.03U0.00342J0.0243J
0203029–005DE Estuary38°59′57.4″−75°18′57.6″21 March 2002Striped bass162625501.100.03U0.00352J0.0249J
0205026–001DE Estuary39°44′30.6″−75°29′44.7″8 May 2002Striped bass166633900.880.03U0.00432J0.0243J
0205053–001DE Estuary39°44′30.6″−75°29′44.7″22 May 2002Striped bass166627220.920.00168J0.01U0.0146J
0205053–002DE Estuary39°44′30.6″−75°29′44.7″22 May 2002Striped bass161522681.580.03U0.00228J0.0310J
0205053–003DE Estuary39°44′30.6″−75°29′44.7″22 May 2002Striped bass160523130.660.03U0.00255J0.04U
0205053–004DE Estuary39°44′30.6″−75°29′44.7″22 May 2002Striped bass165726310.360.03U0.00245J0.0129J
Detection limit        0.040.03 0.01 0.04 

RESULTS AND DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSION
  7. Acknowledgements
  8. REFERENCES

Table 3 provides a description of the 2002 field samples along with the total and speciated arsenic results. Total arsenic was measured above a detection limit of 0.04 μg/g in all 27 field samples. Overall, the concentrations of total arsenic found in the present study were similar to the baseline data appearing in Table 1. The nominal ordering of total arsenic concentrations among the species tested in the present study was as follows: Summer flounder (incoming), summer flounder (outgoing), hard clam, striped bass (bay), striped bass (flats), and Atlantic croaker. This ordering, along with the center and spread in the total arsenic data, is shown in Figure 2. To our knowledge, the arsenic speciation results shown in Table 3 are the 1st such data to appear in the literature for marine fish and shellfish collected from Mid-Atlantic coastal waters.

Table 4 presents the detection frequencies for the various forms of arsenic in the field samples, and Table 5 presents summary statistics for total arsenic and DMA in the field samples. Table 5 also presents summary statistics for inorganic arsenic in hard clam and MMA in striped bass. Summary statistics are not presented for inorganic arsenic in species other than hard clam or for MMA in species other than striped bass because of the low frequency of detection for such cases. For the purposes of Table 5, in the few cases when nondetections were involved, true values were assumed to be present at one-half the detection limit.

Total arsenic in summer flounder

Total arsenic in the incoming flounder spanned from a minimum of 1.8 μg/g ww to a maximum of 3.33 μg/g ww. In the outgoing flounder, total arsenic ranged from a minimum of 0.95 μg/g ww to a maximum of 2.13 μg/g ww. The median total arsenic concentration in the incoming flounder, 2.58 μg/g ww, is statistically greater than the median concentration in the outgoing flounder, 1.49 μg/g ww (Mann-Whitney, p = 0.0367). This difference was not related to differences in length between the incoming and outgoing fish. Although the incoming flounder as a group were slightly longer than the outgoing flounder (median total length: incoming flounder, 475 mm; outgoing flounder, 445 mm), this difference was not statistically significant (Mann-Whitney, p = 0.3457). Furthermore, no underlying statistically significant relationship was found between individual lengths of flounder and individual total arsenic concentrations (ANOVA, p = 0.6315). We therefore conclude that the arsenic concentration in the incoming flounder is, indeed, greater than that in the outgoing flounder and that this difference is not explained by differences in length.

To provide broader regional context for the summer flounder data collected in the present study, we compared our results to summer flounder data collected approximately 200 km to the north in the New York Bight Apex. Scientists from the National Oceanic and Atmospheric Administration reported an average total arsenic concentration of 1.72 μg/g ww in 14 summer flounder fillet samples collected in September 1993 (Deshpande et al. 2000). The raw data of those authors indicate a minimum, maximum, and median of 1.22, 2.34, and 1.61 μg/g ww, respectively, for total arsenic. These values are similar to the results of the summer flounder samples collected from the Delaware Inland Bays in the fall of 2002 (outbound fish). However, the concentrations in the 1993 New York Bight samples are nominally lower than those in the summer flounder samples collected from the Delaware Inland Bays in the spring of 2002 (inbound fish).

Total arsenic in striped bass, Atlantic croaker, and hard clam

For striped bass, the total arsenic concentration in the fish collected from the Delaware Bay ranged from 1.07 to 2.19 μg/g ww, with a median of 1.17 μg/g ww. In comparison, the total arsenic concentration in the striped bass collected upstream at the Cherry Island Flats ranged from 0.36 to 1.58 μg/g ww, with a median of 0.88 μg/g ww. The median concentration in the Delaware Bay fish was greater than the median concentration in the fish from the Cherry Island Flats when viewed at the 90% confidence level but not when viewed at the 95% confidence level (Mann-Whitney, p = 0.0947). Median lengths between the 2 striped bass groups were not different (Mann-Whitney, p = 0.2948), and no underlying statistically significant relationship was found between total arsenic and length among individual striped bass (ANOVA, p = 0.7623).

Total arsenic in the 5 Atlantic croaker samples ranged from 0.48 to 0.8 μg/g ww, with a median of 0.79 μg/g ww. No statistically significant relationship was found between length and total arsenic for croaker (ANOVA, p = 0.3554). The range of total arsenic in the 5 croaker samples from the Inland Bays was within the range of 0 to 2.1 μg/g ww reported by the USEPA for Atlantic croaker samples collected from the Louisianian Province (Summers et al. 1992). Finally, total arsenic in the 2 hard clam samples collected from the Inland Bays was 0.93 and 1.53 μg/g ww, with a median of 1.23 μg/g ww.

MMA and DMA

Monomethylarsonic acid was detected in 17 of the 27 samples, for an overall detection frequency of 63%. All 17 detections were “J” qualified. The minimum detected MMA concentration was 0.00115 μg/g ww, and the maximum was 0.00432 μg/g ww. The trimmed mean MMA concentration in the incoming flounder was 0.00229 μg/g ww, whereas that for the outgoing flounder was nearly equal at 0.00233 μg/g ww. The trimmed means for the striped bass samples were 0.00323 μg/g ww for the samples collected from the Delaware Bay and 0.0029 μg/g ww for the striped bass collected farther up estuary near the Cherry Island Flats. No significant relationship was found between MMA and fish length.

Dimethylarsinic acid was detected in 26 of the 27 samples, for an overall detection frequency of 96%. All 10 detections in summer flounder and all 9 detections in striped bass were “J” qualified. In contrast, only 1 of the 5 croaker detections was “J” qualified, and neither of the detections in clam were “J” qualified. The peak DMA concentration, 0.528 μg/g ww, was found in 1 of the hard clam samples. The median for the 2 clam samples, 0.398 μg/g ww, was much greater than any of the other species tested. Croaker had the 2nd highest median DMA concentration at 0.057 μg/g ww. The median DMA concentration in the incoming flounder, 0.0079 μg/g ww, was not statistically different than the median in the outgoing flounder at 0.0066 μg/g ww (Mann-Whitney, p — 0.83). Similarly, the median DMA concentration in the striped bass collected from Delaware Bay, 0.018 μg/g ww, was not significantly different from the median in the striped bass collected near the Cherry Island Flats at 20 μg/kg (Mann-Whitney, p = 0.60). Dimethylarsinic acid was not related to length for flounder or striped bass; however, DMA did show a strong inverse relationship to length for croaker (ANOVA, p = 0.0294, R2 = 83.7%).

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Figure Figure 2.. Variation in total arsenic concentration in selected marine fish and shellfish species from the Mid-Atlantic region, USA.

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With regard to the DMA levels in the hard clam and croaker samples, it is important to note that samples for both species were collected within 2 weeks of each other in the middle of the summer (15 July 2002 to 30 July 2002). It is postulated that the appearance of DMA in these species is related to arsenic transformations that occur in phytoplankton during this time period, coupled with attendant food-chain exposure. It is recognized that phytoplankton take up arsenate from aqueous solution, reduce the arsenate to arsenite, and methylate the arsenite to produce MMA and DMA, which are then excreted (Phillips 1990; Neff 1997). Recently, Hellweger and Lall (2004) successfully modeled the time course of this transformation by showing the gradual appearance of DMA during the summer period, when algal growth rates slow under phosphorus-limiting conditions. Considering that hard clams feed directly on phytoplankton by filtering large quantities of water, the clams likely were exposed to DMA primarily through their algal diet and, to a lesser extent, through the water that they pump. Croaker forage for a variety of organisms on and in the surface sediments, including small mollusks (e.g., clams and snails) (Diaz and Onuf 1985). Being bottom-feeders, they also inadvertently ingest detritus, which may include algae in various stages of decay. Croaker therefore are exposed to DMA through their diet. We speculate that DMA concentrations are lower in the croaker than in the clam because the croaker is migratory whereas the clam is not, resulting in shorter durations of exposure for the croaker. Finally, the inverse relationship between DMA and croaker length may reflect a higher proportion of phytoplankton in the diet of smaller croaker. This also may explain why DMA was detected only in the smallest flounder.

Inorganic arsenic

Inorganic arsenic was detected in only 5 of the 27 samples, for an overall detection frequency of 19%. A single detection occurred in each of the finfish species and in both clam samples. All detections were “J” qualified. The single detection in summer flounder, 0.00048 μg/g ww, occurred in the smallest flounder caught in the present study. It also was the 1st flounder caught in the fall. The detected concentration in croaker was 0.00057 μg/g ww, whereas the detected concentration in striped bass was 0.00168 μg/g ww. The peak inorganic arsenic concentration was found in 1 of the hard clam samples at 0.02 μg/g ww; this was the same sample that had the peak DMA detection. The median inorganic arsenic concentration for the 2 clam samples was 0.0145 μg/g ww. These inorganic arsenic concentrations are exceedingly low but, nevertheless, are consistent with levels reported by the EPA and by Schoof for several marine fish species (Schoof et al. 1999; USEPA 2003).

Figure 3 shows the percentage inorganic arsenic in the samples assuming that the nondetected inorganic arsenic results actually were present at one-half the detection limit of 0.03 μg/g ww. Using this assumption, mean percentage inorganic arsenic values ranged from a high of 1.7% for croaker to a low of 0.7% for summer flounder. For the 2 hard clam samples, in which no assumptions were necessary regarding detection levels, the percentage of arsenic in the inorganic form was 0.96% and 1.3%, yielding an average of 1.1%. The overall mean for all 27 samples was 1.2%, again assuming that nondetected values were present at one-half the detection limit. The percentages found in the present study are within the range reported in the literature for a variety of marine fish and shellfish species (Nriagu and Simmons 1990; Chew 1996; Donahue and Abernathy 1999; Johnson and Roose 2002; Kirby and Maher 2002; De Gieter et al. 2002; USEPA 2003).

Table Table 4.. Frequency of detection of arsenic in Mid-Atlantic (USA) marine fish and shellfisha
SpeciesbSample size (n)Total arsenic (μg/g wet wt)Inorganic arsenic (μg/g wet wt)MMA (μg/g wet wt)DMA (μg/g wet wt)
  1. a Fish samples were analyzed as skin-on fillets. Hard clam was analyzed as edible meats. MMA = monomethylarsonic acid; DMA = dimethylarsinic acid.

  2. b Summer flounder, Paralicthys dentatus; Atlantic croaker, Micropogonias undulates; hard clam, Mercenaria mercenaria; striped bass, Marone saxatilis.

Summer flounder (inbound)55035
Summer flounder (outbound)55135
Atlantic croaker55125
Hard clam22212
Striped bass (bay)55045
Striped bass (flats)55144
Total count272751726
% 10018.56396.3
Table Table 5.. Summary statistics for arsenic in Mid-Atlantic (USA) fish and shellfisha
 Total arsenic (μg/g wet wt fillet)
 Summer flounder (inbound)Summer flounder (outbound)Atlantic croakerHard clamStriped bass (bay)Striped bass (flats)
Count555255
Average2.611.590.691.231.350.88
Median2.581.490.791.231.170.88
Standard error0.280.230.070.300.210.20
Minimum1.800.950.480.931.070.36
Maximum3.332.130.801.532.191.58
 DMA (μg/g wet wt fillet)
 Summer flounder (inbound)Summer flounder (outbound)Atlantic croakerHard clamStriped bass (bay)Striped bass (flats)
Count555255
Average0.008420.006790.049680.398000.017210.02056
Median0.007900.006620.057000.398000.018200.02000
Standard error0.001460.000490.006490.130000.003470.00330
Minimum0.005030.005620.028600.268000.007570.01290
Maximum0.011900.008390.064300.528000.024900.03100
 Other (μg/g wet wt fillet)
 Hard clam inorganic arsenicStriped bass (bay) MMAStriped bass (flats) MMA   
  1. a DMA = dimethylarsinic acid; MMA = monomethylarsonic acid. Summer flounder, Paralicthys dentatus; Atlantic croaker, Micropogonias undulates; hard clam, Mercenaria mercenaria; striped bass, Marone saxatilis.

Count255   
Average0.014540.003590.00332   
Median0.014540.003420.00255   
Standard error0.005560.000380.00056   
Minimum0.008980.002760.00228   
Maximum0.020100.005000.00500   

Risk assessment and fish advisory

Human health risk associated with the consumption of chemical contaminants in seafood depends on the concentration of the contaminant in the seafood (Cf), the consumption rate of seafood (CR), the exposure frequency (EF) and duration (ED), the body weight of the consumer (BW), the averaging time (AT), and the dose-response metric for the chemical (e.g., q1* for the cancer endpoint and RfD [reference dose] for noncancer effects). For the cancer endpoint, lifetime risk can be calculated as (Cf)(CR)(EF)(ED)(q*1)/((BW)(AT)). For noncancer effects, risk is calculated as (Cf)(CR)(EF)(ED)/((RfD)(BW)(AT)).

In seafood, arsenic can exist in many forms, including the inorganic species arsenite (III) and arsenate (V), as well as the organic species arsenobetaine, arsenocholine, MMA, DMA, arsenosugars, and arsenolipids (Cullen and Reimer 1989; Chew 1996). The question then arises as to which concentration should be specified for Cf in the above risk equations. Current guidance indicates that the sum of the inorganic species arsenite and arsenate should be used (USEPA 2000a). The various organic arsenic compounds in fish and shellfish are considered to be relatively nontoxic (ATSDR 2000). For purposes of the current risk assessment, Cf in the above equations was set equal to the single inorganic arsenic concentration detected in each of the fish species. For hard clam, Cf was taken as the average inorganic arsenic concentration detected in the 2 clam samples.

The EF value was set to 350 d/y, whereas the ED value was set to 30 y. This latter assumption is consistent with the standard assumption used in Delaware's fish contaminant monitoring program (DNREC and DHSS 2005). For the cancer endpoint, AT was set to 365 d/y multiplied by 70 y, or 25,550 d. For the noncancer endpoint, AT was set to 365 d/y multiplied by 30 y, or 10,950 d. Assumptions for EF, ED, and AT are consistent with Federal Superfund guidance (USEPA 1989; USEPA 1991). Body weight was taken as 70 kg, also to maintain consistency with standard risk assessment practice (USEPA 1991). A cancer slope factor (q*1) of 1.5 mg/kg/d was used for the cancer assessment, whereas an RfD value of 0.0003 mg/kg/d was used for the noncancer assessment (http://www.epa.gov/iris). Both the slope factor and the reference dose apply to inorganic arsenic.

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Figure Figure 3.. Inorganic arsenic as a percentage of total arsenic in selected marine fish and shellfish from the Mid-Atlantic region, USA. Bars are means, and error bars are standard errors. Nondetected values are assumed to be present at half the detection limit.

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With regard to seafood consumption rate, site-specific quantitative information for the Delaware Inland Bays is not available. Detailed information is available, however, for the nearby Delaware Estuary, where a study-wide average consumption rate of 17.5 g fish/d was determined for recreational anglers and their households (KCA 1994). Coincidentally, this is the same consumption rate used by the USEPA in deriving fish tissue chemical-contaminant screening values for recreational anglers (USEPA 2000b). This consumption rate was used for purposes of the current risk assessment.

Using the values and equations above, the calculated cancer and noncancer risks are shown in Table 6. From these results, consuming these species increases the lifetime cancer risk from as little as 7.4 × 10−8 (i.e., 1 additional possible cancer in a population of 13.5 million people) for flounder up to 2.2 × 10−6 (1 additional possible cancer in a population of ∼450,000 people) for hard clam. Given the uncertainties inherent in current cancer risk assessment, the actual risks may be lower and could actually be zero. The true cancer risk, which is unknown, is unlikely to be greater than that shown in the table. With regard to noncancer risks, we see that noncancer health risks are all well below a hazard index of 1 and, therefore, are of little concern. In sum, the cancer and noncancer health risks shown in the table are considered de minimus by the health and natural resources agencies that are responsible for issuing fish consumption advisories in Delaware. As such, no advisory was believed to be warranted based on the measured levels of inorganic arsenic in these species.

Table Table 6.. Summary of human health cancer and noncancer risks associated with ingestion of inorganic arsenic in Mid-Atlantic (USA) marine fish and shellfisha
SpeciesLifetime cancer riskNoncancer health risk
  1. a Summer flounder, Paralicthys dentatus; Atlantic croaker, Micropogonias undulates; striped bass, Marone saxatilis; hard clam, Mercenaria mercenaria.

Summer flounder7.4E-083.8E-04
Atlantic croaker8.8E-084.6E-04
Striped bass2.6E-071.3E-03
Hard clam2.2E-061.2E-02

It is interesting to consider the risks and potential risk management actions that may have ensued if the concentration of inorganic arsenic had been estimated by multiplying total arsenic by 10%, which is a default assumption recommended by the US Food and Drug Administration when only total arsenic data are available (USFDA 1993). For example, the median concentration of total arsenic in the incoming flounder was 2.58 μg/g ww. Ten percent of that value yields an estimated inorganic arsenic concentration of 0.258 μg/g ww. Substituting this value into the cancer risk equation, we see that lifetime cancer risk becomes 4 × 10−5 (1 additional possible cancer in a population of 25,000). Under current risk management policies, an advisory may have been issued in this case, especially if considered in conjunction with other contaminants present in the fish.

CONCLUSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSION
  7. Acknowledgements
  8. REFERENCES

We confirmed our hypothesis that marine species that migrate from offshore shelf waters into the Delaware Inland Bays and the Delaware Estuary bring body burdens of total arsenic with them higher than the levels they leave with during their seaward migration. This was true for summer flounder entering the Inland Bays and for striped bass moving upstream in the Delaware Estuary. The higher total arsenic concentration in the inbound fish was not attributable to greater fish length. Additional study will be needed to determine the underlying reasons for the higher total arsenic concentrations in the inbound fish.

Whereas total arsenic was detected in all fish and shellfish samples analyzed in the present study, inorganic arsenic was detected in only 5 of the 27 samples. The detected concentrations of inorganic arsenic were quite low, ranging from 0.00048 to 0.02 μg/g ww. From the total and inorganic arsenic concentrations, the maximum possible percentage of inorganic arsenic among the 4 species tested ranged from 0.7% to 1.7%. Using the concentrations of inorganic arsenic detected in the fish and shellfish along with standard exposure assumptions, upper-bound lifetime cancer risks associated with consuming these species range from 7.4E-8 (1 in 13.5 million) to 2.2E-6 (1 in 450,000). We concluded that a fish consumption advisory is not warranted.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSION
  7. Acknowledgements
  8. REFERENCES

The State of Delaware provided funding for this work. Personnel from the State of Delaware's Division of Water Resources and the Division of Fish and Wildlife secured and processed the field samples. David Wolanski provided mapping support. Finally, we wish to acknowledge the thoughtful comments and suggestions of the anonymous reviewers on the draft manuscript.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSION
  7. Acknowledgements
  8. REFERENCES
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