Deadliest Catch?
Mary hollinger, NOAA
Randall C Willis
I
Researchers and mports from China hit hard times The compounds found in the seain 2007. First, tainted wheat food were the antimicrobial agents regulators work to identify gluten provided by one Chinese malachite green, nitrofurans, gencompany prompted a widespread retian violet, and fluoroquinolone, and prevent seafood call of potentially toxic pet food. The many of which are carcinogenic. contamination. U.S. Food and Drug Administration Fluoroquinolone is linked to the (FDA) banned imports of wheat gluten development of antibiotic resistance in from that company. Later, lead paint found pathogenic bacteria. on children’s toys made in China launched another What made this announcement startling, howround of recalls. Soon after, FDA had more bad news. At a ever, was that unlike the recalls of tainted toys and toxic pet June 28 press conference, the agency announced new controls food, this ban wasn’t directed at one or two exporting compaon several species of seafood imported from China because nies but rather at the seafood industry of an entire nation. unauthorized animal drugs and food additives had been de“Despite extensive communications between FDA and aptected in those products (1). This was yet another economic propriate Chinese authorities to correct the problem,” said blow to the East Asian powerhouse, and once again the “Made Margaret Glavin, associate commissioner for regulatory affairs in China” label became suspect. with FDA, during the press conference, “we have continued © 2008 American Chemical Societ y
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All fish images from NOAA’s Historic Fisheries Collection
to find residues of certain veterinary drugs or food additives pressed in other countries around the world. that are not permitted for use in the United States in farmed Recently, Thierry Guérin and colleagues at the Agence franfish products produced in China and exported to the U.S.” çaise de sécurité sanitaire des aliments ���������������������� (AFSSA) tried to estiThe problem of unsafe seafood isn’t restricted solely to mate the amount of organotin compound (OTC) in the seafood China, however, as developed and developing nations alike diets of French consumers. The researchers examined fresh and face the challenge of maintaining a constant vigil for gaps frozen samples from around the country and correlated conin their environmental, farming, and production practices to tamination levels with seafood consumption statistics (3). keep the global seafood industry safe. America is no excep“Even though some studies have recently estimated OTC tion; according to the U.S. Environmental Protection Agency exposure from ingestion of especially fish and shellfish, the (EPA), almost 4000 fish and shellfish advisories were issued amount and percent of exposure from food in the French throughout the country in 2006 alone, up more than 10% population has not been well characterized,” says Guérin, from 2005 (Figure 1; 2). who heads Contaminants Paul Duchesne, a spokesinorganiques et minéraux de 36 NH=9 person for Health Canada, l’environnement, a unit of 19 VT=12 27 5 1072 says that the key challenges AFSSA. “The food sample 17 MA=166 11 408 4 to determining the safety of size is largely higher than RI=23 153 0 179 CT=20 seafood include the availin earlier studies and above 7 NJ=111 109 40 2 DE=42 225 126 ability of analytical methods all more representative” of 79 7 21 11 MD=59 64 52 6 9 for detecting substances of French people who consume DC=1 11 10 potential concern, includa lot of seafood. 16 3 14 22 28 ing natural toxicants and The researchers used mi66 16 39 138 0 traditional and emerging crowave digestion to extract 49 21 environmental contamithe OTC constituents from 281 nants, and the availability the fish samples. Then, they Advisories exist for 3 specific waterbodies only of the types of data needed identified OTCs by GC Statewide lakes-only advisory to conduct risk assessments coupled with microwave-inincluded in count on these substances (e.g., duced plasma atomic emisStatewide rivers and lakes advisory toxicological data as well sion spectroscopy (AES). included in count as occurrence and expoThey found that most seaStatewide coastal advisory included in count sure data). These challenges food samples were contamiStatewide advisory for marine fish included in count are particularly problemnated with a variety of OTC No advisories for chemical contaminants atic, he says, with emerging species but that butyltin contaminants. FIGURE 1. EPA fish advisories in 2006. (Adapted from Ref. 2.) compounds were most prevalent, particularly in halibut Metals as contaminants and swordfish. They also noted that contaminant concenSeafood contaminants generally fall into one of three broad trations varied widely with geographical location, seasonal categories—metals, organic pollutants, and biological organ- changes, and spawning period. Perhaps the most striking findisms—each of which presents government agencies and sea- ing was that the highest OTC levels occurred near harbor areas food producers with unique challenges. and especially during periods of intense boating activity, which With the possible exception of Hg, metal-based seafood correlated well with the prevalence of OTCs in antifouling contamination is not a significant problem within the U.S., paints on the hulls of boats. according to EPA statistics. It is apt to occur within confined Despite the extreme variability in OTC levels, the AFSSA regions for limited periods, often as a result of industrial dis- scientists noted that most levels were well within the European charge or release from geological sources through flooding or legislation limits. They stressed, however, that efforts must erosion. At the same time, according to EPA’s James Harvey, continue to reduce the environmental and dietary spread of concern remains about legacy chemicals residing in estuarine these compounds. As Guérin explains, the OTC dietary exor coastal sediments and the impact of these compounds in posure in children and teenagers has not yet been determined, fish tissues. and consumers are exposed to a variety of sources of OTC, “Our research group is interested in establishing estuarine such as pesticides. In addition, there is a paucity of epidemiobaseline conditions using a probabilistic sampling design that logical studies on chronic low-level oral exposure to OTC, so could help us assess water quality, sediment quality, and bio- dietary organotin levels and their associated health effects logical quality,” he says. “Many of the contaminants we found could be seriously underestimated. are long-lived in the aquatic environment. We did find that Further complicating matters is the fact that metal contamithere were regional differences in the highest level of specific nation rarely occurs in the form of a single, isolated species. contaminants, even though the same five or six contaminants Instead, one high-level contaminant often indicates an overall consistently appeared in all regions.” Similar concerns are ex- contamination problem. “There are so many environmental 2298
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william b. folsom, NMFS, NOAA
contaminants which are genpreventing the successful aperally cumulative and have plication of these techniques chronic effects [that] their adin many cases.” ditive effects on health are still not understood,” Guérin Organic pollutants says. “Cadmium, mercury, arHistorically, persistent orsenic, lead, and also tin are ganic pollutants (POPs) such the main inorganic contamias DDT, polychlorinated binants of interest for the Euphenyls (PCBs), and dioxins ropean legislation, for the have been a concern in the moment, but [nanoparticles] U.S. and much of Europe, but contamination could be a maduring the past few decades, jor problem in the very near these governments have legisfuture. Their potential threats lated tighter controls on such remain to be estimated. compounds. Now, the focus “The main problem is that is on countries such as China toxicologists have mainly evaland India, where rampant inuated only the effect of one dustrial growth has outpaced pure molecule and not a mix environmental concerns. This of some contaminants with lack of control may be probother essential elements,” he lematic for Western dinner says. “Most of the agonist or tables, because the search for antagonist effects of contamiless expensive seafood has nants are not well known, meant ever-expanding imporactually.” tation from these regions. In recognition of the poFor example, as a result of tential cumulative impact of the rapidly growing electronchronic diverse contaminant ics industry in South China, exposure, Jose Domingo and a secondary industry has excolleagues at the University panded just as quickly in the of Barcelona and Rovira i Vir- Most seafood is sold through markets, such as Seattle’s Pike Place past few years: electronics gili University (both in Spain) Market, or to companies that process and prepare packaged food. waste management and recyundertook a similar but wider cling. Unfortunately, in the analysis of human consumption of metal contaminants in sea- rush to reclaim components, recycling firms are at risk of refood sold in major centers around Catalonia (4). Using induc- leasing into the environment organic compounds such as polytively coupled plasma MS (ICPMS), the researchers monitored brominated diphenyl ethers (PBDEs), which are quickly incorthe levels of As, Pb, Cd, and Hg in fish and shellfish species. porated into an already overburdened food chain. To quantify As with the French study, the researchers found that al- the impact of these activities, the Guangzhou Institute of though metals are relatively widespread, different metals are Geochemistry’s Eddy Zeng and colleagues recently monitored present at higher levels depending on the fish and shellfish the uptake of PBDEs in seafood products throughout South species. For example, Cd peaked in clams and mussels, whereas China (5). Hg was most abundant in swordfish. Similar variability was “We conducted a comprehensive sampling program in found when the researchers correlated the seafood contami- 2005 and 2006 in 11 coastal districts of Guangdong Province, nant levels with food consumption by different age and gender collecting samples of 13 fish species and 21 nonfish seafood groups. Nevertheless, each metal was below the European leg- products,” Zeng says. “These samples have been analyzed for islation-mandated limits. persistent halogenated hydrocarbons—that is, organochlorine Although metal contamination is largely identified and pesticides, PCBs, and PBDEs. We also collected riverine runoff quantified through ICPMS or some form of AES, these meth- samples from the eight major runoff outlets of the Pearl River ods can accomplish only so much on their own and are being Delta between March 2005 and February 2006.” taxed by new challenges, according to Guérin. “Despite adUsing gel permeation chromatography and GC/MS, the vances in instrumentation, methods, standardization, and even researchers found BDE congeners in 98.5% of the seafood legislation, there are still many problems that remain unsolved, samples, with oysters showing the highest total BDE concenand many questions are still not answered,” he says. “For ex- tration. However, they found great variation among species in ample, molecular detection techniques greatly improved the the prevalence of different BDE congeners. The researchers reliability of species identification; however, matrix effects, speculated that these variations may represent differences in low concentrations, or the instability of element species are feeding habits and metabolism. A p r i l 1 , 2 0 0 8 / A n a ly t i c a l C h e m i s t r y
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Despite the widespread contamination, the researchers determined that overall PBDE levels in the region were lower than in many regions around the world, including The Netherlands, Singapore, and Hong Kong. However, they warn that the study was largely qualitative and that a more quantitative analysis would require a better understanding of the local BDE mixtures as well as more solid knowledge about the mechanisms governing environmental transformation of PBDEs. “One of the challenges is to ensure the quality of sample extraction and purification,” Zeng says. “Seafood generally (a)
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FIGURE 2. GC/MS profiles of TrBDD (3U1) and three TeBDDs (4U1, 4U2, 4U3) in (a) perch, (b) mussels, and (c) algae from waters off the Swedish coast versus (d) a standard. (Adapted from Ref. 6.) 2300
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contains high levels of lipid contents, which may interfere with the identification and quantitation of target analytes. “Another challenge is to prevent or minimize degradation of BDE-209, which can degrade under sunlight or at high temperatures. To do so, we had to use amber vials to store extracts and a 15 m column to analyze BDE-209 separately from other congeners.” Perhaps surprisingly, industry is not necessarily the main contamination source, as noted in the recent study by Umeå University’s Peter Haglund and colleagues in Sweden and Japan (6). The researchers monitored the development of a new environmental stressor—polybrominated dibenzo-p-dioxins (PBDDs)—in the Bothnian Sea and the Baltic Proper off the coast of Sweden. They then compared the spatial distribution and bioaccumulation of these compounds with those of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/ Fs), which are largely the result of industrial effluent. The researchers examined several species of marine and freshwater fish, shellfish, and mussels by using GC/high-resolution MS to identify the different chemical constituents (Figure 2). They noted that unlike PCDD/Fs, which are almost exclusively linked to freshwater sources, the PBDDs were found only in marine seafood. Furthermore, PBDD levels were consistent along the entire coast, suggesting that the source is diffuse and therefore likely to be natural. On the basis of earlier research, the scientists speculate that the PBDDs are produced by algae or cyanobacteria and then passed up the food chain through filter feeders, such as mussels, that are consumed by fish and eventually humans. According to the researchers, the introduction of new POPs to the seafood market is particularly problematic, because the present levels of PCDD/Fs in many catches of fatty Baltic fish already exceed European Commission limits. Given that EU legislation only recently recognized brominated organics as a potential problem, the scientists say, the health risks associated with Scandinavian seafood consumption may be underestimated. According to Health Canada’s Duchesne, trend analyses have shown that the levels of older POPs, such as PCBs and dioxins, in seafood and other foods have been in a steady decline during the past few years and thus so has human exposure. Continued vigilance is needed to ensure that newer chemicals—particularly those of a lipophilic nature—do not accumulate in the environment and the food chain. With particular reference to natural toxicants, Duchesne adds, continued monitoring and surveillance are needed to ensure that regulatory agencies remain aware of potential changes in the occurrence or levels of various toxicants in different regions. “This may become more important in the future due to external influences, such as climate change,” he says.
Biological organisms
Of the three major forms of seafood contamination, microbial contamination—bacteria, viruses, parasites—may be the most challenging. This contamination can occur at almost any point in the process chain from wild or cultivated growth to food
Vibrio Salmonella STEC O157 Campylobacter Listeria
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FIGURE 3. Relative rates (compared with 1996–1998) of foodborne infections in the U.S. (Adapted from Ref. 7.)
To address the strain identity issue, researchers are increasingly relying on genomic technologies, such as microarrays and PCR. For example, Jessica Nordstrom and colleagues at FDA’s Gulf Coast Seafood Laboratory and the Alaska Department of Environmental Conservation developed a multiplex, real-time PCR assay that allowed them not only to detect the presence of Vibrio spp. bacteria in oysters but also to identify and quantify pathogenic V. parahaemolyticus strains in a background of excess nonpathogenic species (8). (V. parahaemolyticus is related to the microbe that causes cholera and can trigger gastrointestinal problems such as watery diarrhea, abdominal cramping, nausea, and vomiting.) The researchers used three gene sequences as markers of species identity and pathogenicity to develop oligonucleotide primers for their PCR assay, and they tested the system on oyster samples from several coastal areas around Alaska. They found that by adjusting the relative concentrations of the oligonucleotides, they could identify as few as 10 colony-forming units (CFUs) of pathogenic bacteria per reaction in the presence of high concentrations (103-fold greater) of nonpathogenic strains. Furthermore, they detected single microbe species down to 1 CFU/reaction. Even with the genetic methods, however, assay preparation time continues to be a problem. Most assays require several rounds of culture incubation in general and selective growth media, both to subdivide the microbial mixture and to generate enough sample to be detectable. Furthermore, microbes evolve rapidly, and researchers must be vigilant that a negative result is due to a lack of pathogen and not a mutation within that strain.
processing to meal preparation. Furthermore, unlike heavymetal or POP contamination, which can take years of chronic consumption before becoming dangerous to public health, microbial contamination can become a health threat rapidly: some bacterial or viral infections become deadly within days. Depending on the introduction and importation of foreign food stocks and dietary practices into the country, the incidence of different foodborne microbes has varied significantly in the U.S. over the years (Figure 3; 7). Historically, food-processing companies and regulators have relied on the same basic culturing techniques used by medical specialists to isolate and identify potential microbial contamination. Unfortunately, these methods can be both labor- and An action plan time-intensive, and the results may come too late for some With the globalization of the seafood industry and the changpeople. During the past decade or so, however, molecular ing seafood consumption habits of people worldwide, state, methods have accelerated the identification timelines, and these methods are reaching the point where on-site testing is often feasible. Because of their binding specificity, antibodies have frequently been used for contaminant testing, whether through ELISAs, dipstick technology, or beadbased tests. The advantage of immunologic methods is that they are often portable and easy to use, and ELISAs are amenable to high-throughput screening. The challenge, however, is that the antibodies generally bind to a relatively common cell-surface target that is capable of highlighting the presence of a microbe without necessarily offering any information about the particular strain(s) involved. Thus, a food shipment can be flagged for possible contamination, but further analysis is necessary to say specifically what the contaminant is. Fish are kept on the checker, a sorting table, before they are measured and weighed. A p r i l 1 , 2 0 0 8 / A n a ly t i c a l C h e m i s t r y
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ALLEN M. SHIMADA, NMFS, NOAA
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In a small number of cases, the adulterant that regulators find in seafood is not a contaminating chemical or microbe but an entirely different species of seafood. According to a recent report by the Food and Agriculture Organization of the United Nations, to produce a wider array of seafood-based products cheaply in the face of dwindling supplies of traditional food stocks, many seafood producers are turning to more abundant or more easily farmed species to supplement their supplies (11). And given that so much of the food is processed—so that most distinguishing morphological features such as fins, shells, and scales have been removed— there is little concern about being caught by inspectors. Thus, the question becomes: how much of that Maryland crab cake is actually Maryland blue crab? Recent legislation in Europe requires that foodstuffs carry a complete record of their species, geographical, and cultivation history. But because no validated analysis protocols are available to fully authenticate fish or shellfish, importers have had to rely largely on the honesty of the exporter. This reality is changing, however, as agencies are looking at a variety of methods to identify seafood. Genomics and proteomics methods have provided some assistance, by enabling researchers to identify the key genetic or protein signatures of different species within a mélange of sample. Unfortunately, processing and cooking can have a deleterious effect on DNA and proteins. In this case, immunohistochemistry approaches (e.g., ELISAs) or NMR-based methods may be necessary to identify the seafood sources. The one challenge with most of these methods, however, is that samples have to be analyzed off-line, often following several time- and labor-intensive steps that can be very damaging to time-sensitive foodstuffs. Recently, Scott Hale and Javier Gayo of North Carolina State University used visible and NIR spectroscopy to identify the contents of tinned crabmeat obtained from a local supermarket (12). The researchers combined samples of two known crab species—Atlantic blue and blue swimmer—in 10% increments to see how well they could distinguish the relative contributions in the vis–NIR spectra (Figure 4). They found that by scanning samples of known crab species at 2 nm intervals across 400–1700 nm, they could generate absorption spectra that would allow them to clearly distinguish homogenous crabmeat samples from adulterated samples. Furthermore, unlike the other authentication methods, vis–NIR offers the opportunity of performing analyses quickly on-line.
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federal, and international agencies are making great efforts to develop programs that address the import–export aspects of seafood safety and the root causes of the problems. FDA’s seafood hazard analysis and critical control point (HACCP) system, which is just over a decade old, was designed to help companies identify problem points within their food-handling businesses and to offer advice on how to rectify potential threats before they become health issues (9). In the case of the seafood industry, HACCP covers everything from getting the fish into the processing plant to transporting the products to consumers, highlighting opportunities to improve processes along the way. Unlike the European programs, however, which apply to the complete production chain, U.S. seafood HACCP regulations apply only to processors (10). 2.0 1.5 Log (1/R)
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FIGURE 4. Vis–NIR absorbance spectra of mixtures of meat from Atlantic blue (Callinectes sapidus) and blue swimmer (Portunus pelagicus) crabs in 10% increments. (Adapted from Ref. 12.)
From the seafood importation perspective, the challenge is in convincing international trading partners to implement similar programs in their jurisdictions to reduce the domestic inspection workload. “[Our] inspection effort is directed at foreign processors that have demonstrated a history of poor compliance with Canadian standards,” says Mary Ann Green, director of the Fish, Seafood, and Production Division of the Canadian Food Inspection Agency (CFIA). “On the other hand, inspection effort is reduced through the establishment of Memoranda of Understanding or Mutual Recognition Agreements with other countries having reliable inspection systems.” Ultimately, however, international agreements don’t eliminate the risks of something slipping through, and inspection agencies can’t examine every shipment. So, they play a numbers game. “CFIA uses a risk-based approach to determine the frequency at which to inspect imported product,” Green says. “The frequency varies based on food safety risk, the history of compliance of a particular product, the history of compliance of the processor, and the country of origin of the product.” From Zeng’s perspective, the challenge to ensure safer seafood from China will be for the government to find ways to balance economic growth and environmental protection. “There have been accidents in which seafood products im-
ported to Europe [from China] contained substantially higher levels of toxic substances than allowable thresholds, due to the lack of attention to quality control,” Zeng says. “As a result, seafood products exported by China to Western countries will inevitably be subject to rigorous inspection by Western agencies until better protective measures are in place.” Nevertheless, China is making headway, adds Zeng. The evidence is a trend of diminishing contamination of seafood with organic compounds such as DDT and PCBs. This follows the government’s enactment of stricter environmental policies on these compounds in the 1980s and 1990s. “We believe that some of the environmental issues facing China will have to be resolved with stringent law enforcement and international collaboration,” he says. With the continuing assistance of organizations like FDA and the development of new technologies to identify contaminants before they become problems, this dream will, hopefully, become reality. Randall C Willis is a freelance writer based in Toronto.
References (1)
U.S. FDA. Transcripts of FDA Press Conference on Seafood Imported from China; July 2007; www.fda.gov/bbs/transcripts/transcript062807.pdf.
(2)
U.S. EPA. 2005/2006 National Listing of Fish Advisories; July 2007; www. epa.gov/waterscience/fish/advisories/2006/tech.html. (3) Guérin, T.; Sirot, V.; Volatier, J. L.; Leblanc, J. C. Sci. Total Environ. 2007, 388, 66–77. (4) Falcó, G.; Llobet, J. M.; Bocio, A.; Domingo, J. J. Agric. Food Chem. 2006, 54, 6106–6112. (5) Guo, J. Y.; et al. J. Agric. Food Chem. 2007, 55, 9152–9158. (6) Haglund, P.; et al. Environ. Sci. Technol. 2007, 41, 3069–3074. (7) Centers for Disease Control and Prevention Foodborne Diseases Active Surveillance Network. Preliminary FoodNet Data on the Incidence of Infection with Pathogens Transmitted Commonly Through Food—10 States, 2006. MMWR 2007, 56, 336–339; www.cdc.gov/ mmwr/preview/mmwrhtml/mm5614a4.htm?s_cid=mm5614a4_e. (8) Nordstrom, J. L.; et al. Appl. Environ. Microbiol. 2007, 73, 5840–5847. (9) U.S. FDA. Seafood HACCP; www.cfsan.fda.gov/~comm/haccpsea. html. (10) Buzby, J. C., Ed. International Trade and Food Safety: Economic Theory and Case Studies; Economic Research Service, U.S. Department of Agriculture, 2003; www.ers.usda.gov/Publications/aer828. (11) Martinez, I.; James, D.; Loréal, H. Application of Modern Analytical Techniques To Ensure Seafood Safety and Authenticity ; United Nations Food and Agriculture Organization Fisheries Technical Paper 455, 2005; www.fao.org/docrep/008/y5970e/y5970e00.htm. (12) Gayo, J.; Hale, S. A. J. Agric. Food Chem. 2007, 55, 585–592.
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