Written by Dr. Joe Costa
Please email corrections and suggestions. Please note that the information in the table may be outdated. Click on the various links to see the latest advisories.
Toxic Contaminants and Seafood Safety
Contaminants in seafood such as petroleum hydrocarbons, combustion products, and pesticides pose a potential threat to human health. The amount of these contaminants in seafood can vary considerably depending upon the animal’s proximity to sources of these contaminants. These contaminants may accumulate in fish at levels that can cause illness. However, rarely are illnesses associated with these contaminants caused by consuming a single meal. Rather, concern for these contaminants primarily focuses on diseases (such as cancer), or human development (e.g. birth defects) associated with long term or life-long consumption of contaminated seafood.
The US FDA has set these “action limits” on contaminants:
|Deleterious Substance||Level||Food Commodity||Reference|
|Aldrin/Dieldrin||0.3 ppm||All fish||Compliance Policy Guide sec. 575.100|
|Benzene hexachloride||0.3 ppm||Frog legs||Compliance Policy Guide sec. 575.100|
|Chlordane||0.3 ppm||All fish||Compliance Policy Guide sec. 575.100|
|Chlordecone||0.3 ppm||All fish Crabmeat||Compliance Policy Guide sec. 575.100|
|DDT, TDE, DDE||5.0 ppm||All fish||Compliance Policy Guide sec. 575.100|
|Diquat||0.1 ppm||All fish||40 CFR 180.226|
|Fluridone||0.5 ppm||Fin fish and crayfish||40 CFR 180.420|
|Glyphosate||0.25 ppm||Fin fish||40 CFR 180.364|
|| Arsenic||76 ppm||Crustacea||FDA Guidance Document|
|86 ppm||Molluscan bivalves||FDA Guidance Document|
|| Cadmium||3 ppm||Crustacea||FDA Guidance Document|
|4 ppm||Molluscan bivalves||FDA Guidance Document|
|| Chromium||12 ppm||Crustacea||FDA Guidance Document|
|13 ppm||Molluscan bivalves||FDA Guidance Document|
|| Lead||1.5 ppm||Crustacea||FDA Guidance Document|
|1.7 ppm||Molluscan bivalves||FDA Guidance Document|
|| Nickel||70 ppm||Crustacea||FDA Guidance Document|
|80 ppm||Molluscan bivalves||FDA Guidance Document|
|| Methyl Mercury||1 ppm||All fish||Compliance Policy Guide sec. 540.600|
|Heptachlor / Heptachlor Epoxide||0.3 ppm||All fish||Compliance Policy Guide sec. 575.100|
|Mirex||0.1 ppm||All fish||Compliance Policy Guide sec. 575.100|
|Polychlorinated Biphenyls (PCB’s)||2.0 ppm||All fish||21 CFR 109.30|
|Simazine||12 ppm||Fin fish||40 CFR 180.213a|
|2,4-D||1.0 ppm||All fish||40 CFR 180.142|
|Note: the term “all fish” refers to fresh or saltwater fin fish, crustaceans, and other forms of aquatic animal life, but excludes all mollusks (snails and bivalve clams).|
Generally these limits are used by state fisheries and public health agencies for consumption advisories, rather than the outright prohibition of fishing. However, in grossly contaminated areas likely New Bedford Harbor, there is an out-right ban on fishing and lobstering for sale or consumption because of very high PCB levels in those species. For shellfish, state shellfishing agencies may use the degree of chemical contamination as part of their classification for determining whether an area is closed to shellfishing. Interestingly, in New Bedford Harbor, the taking of shellfish is prohibited because of bacterial concentrations in the water, not toxic compound contamination. Shellfish tend not to accumulate PCBs to critical levels.
Hydrocarbons and Seafood Safety
The delay in opening shellfish beds in Buzzards Bay after the Bouchard No. 120 spill has called attention to the fact that no national standards have been established by the US Food and Drug Administration for lifetime cancer risks for hydrocarbons in seafood. The reason for this is complicated, and the crux of the issue actually goes back decades. In fact, when we wrote the Buzzards Bay management plan (CCMP) in 1991, the state was drafting PAH policies, which we thought would apply to seafood. The policies were not finalized, and the delay revolves around what threat hydrocarbons in shellfish pose to human health, how to characterize complex mixtures of hydrocarbons in seafood, and how to establish acceptable risk levels needed to protect human health. The issue is exacerbated by the fact that there are few national regulatory standards for low level hydrocarbon contamination of seafood, and each state may adopt its own standards (particularly if interstate commerce is not involved).
While seafood inspectors reject conspicuously “tainted” seafood that may cause immediate illness (the human nose can detect fairly low concentrations of certain hydrocarbons), most states have not adopted low level hydrocarbon contamination standards that address risks of cancer associated with lifelong consumption of seafood. In the US FDA’s recently implemented Seafood Hazard Analysis and Critical Control Point program (HACCP), contamination of seafood by hydrocarbon mixtures is not even addressed (the program addresses certain metals, pesticides, and classes of chlorinated hydrocarbons, like PCBs). In Massachusetts, in the absence of established federal and state standards and policies for low level hydrocarbon contamination, state officials find themselves simultaneously grappling with seafood safety issues revolving around the Bouchard No. 120 spill, together with the broader issue of hydrocarbon contamination found in many harbors and estuaries derived from boat engines, street runoff, atmospheric deposition of soot, and old creosote pilings to name a few sources.
Establishing contaminant limits
Federal and State governments have generally adopted a chemical-specific approach to regulating toxic compounds in the environment and in food sources. Under this approach, the concentration of a particular contaminant is applied to a specific numeric criteria or standard for that contaminant. For example, everyone agrees that lead in drinking water is not good for child health and development, and the US EPA has set a Maximum Contaminant Level (MCL) of 15 parts per billion (ppb or ng/L) of lead in drinking water supplies. Similar drinking water standards apply to pesticides and hydrocarbons. For example, the limit for the pesticide Chlordane in drinking water is 5 parts per billion (ppb), and single hydrocarbon contaminants like benzene, a constituent in gasoline, has a limit of 2 ppb.
These standards are based on current knowledge of human health and scientific studies and adopted acceptable risk levels (ARLs. These recommended standards sometimes change over time as new health studies are published (nearly always lowering). For example, the drinking water limit for arsenic is currently 50 ppb, but the EPA has proposed changing the limit to 10 ppb by 2006. This proposed rule change has caused considerable debate because of the expected expense to municipal governments associated with removing low-level arsenic from water supplies in some parts of the country. This has lead to questions over the validity of the arsenic studies, and whether certain naturally occurring arsenic compounds pose the same risk as arsenic compounds used in laboratory studies.
Like drinking water, the EPA and the FDA have proposed certain contaminant levels in seafood. These “action limits” are generally higher than allowed in drinking water because the amount of seafood ingested is much smaller than compared to drinking water. For example, while the EPA limits Chlordane in drinking water to 5 parts per billion (Massachusetts limits are now 2 ppb), the FDA recommended a maximum Chlordane level in seafood of 300 parts per billion.
When it comes to oil spills, a standard for lifelong consumption exposure is considerably harder to adopt, because petroleum products are composed of hundreds or even thousands of individual compounds, and common oil mixtures like “No. 6″fuel oil are highly variable among refineries. Some of the individual compounds in these oil mixtures are not well studied. Because of this complexity and variability of petroleum mixtures, regulatory agencies do not use single “indicator” compounds (e.g. benzene) to assess risk. Rather, some measure of total hydrocarbon content and risk is evaluated instead.
Sometimes Total Petroleum Hydrocarbons are evaluated in seafood, but in evaluating human risks, it has long been recognized that not all hydrocarbons should be considered equally. For example, hydrocarbons associated with the combustion of oil and fuels (from autos, furnaces, etc., called “pyrogenic” hydrocarbons) are considered more carcinogenic than hydrocarbons from natural seeps, crude oil, or even refined oil products like fuel oil (called “petrogenic” hydrocarbons). Hydrocarbons composed of multiple fused six-carbon rings (called Polycyclic Aromatic Hydrocarbons, or PAHs, or sometimes called Polynuclear Aromatics) are also viewed as a greater threat to human health. One of these PAH compounds, called Benzo[alpha]Pyrene (BaP), is particularly carcinogenic, and has been well studied. One recent trend has been to characterize complex hydrocarbon mixtures found in seafood by assigning a BaP-equivalency to characterize carcinogenic risks associated with all the PAHs in the mixture. However, for practical reasons, BaP equivalency analyses are really based on only quantifying 14 specific PAH compounds that may be found in seafood.
Several states have used BaP-equivalency to evaluate seafood, or contamination after an oil spill, some have used Total PAH. What values of BaP-equivalency or Total PAH are considered “safe?”In different states, and in different oil spills, different values have been selected. Sometimes different standards are used in different species. Why is this the case? In the last decade, a very specific equation has been used to calculate the acceptable contaminant concentration in seafood. However, the calculated acceptable concentration limit depends on several assumptions used with this equation. The three key assumptions that health officials make that most affect the calculation of the action limit concentrations are as follows:
1) What is the Acceptable Risk Level (ARL)? For drinking water, the ARL often adopted is one cancer in one million over a 70-year lifetime for the average weight adult. However, for foods, states often adopt a lifetime risk of one cancer in one hundred thousand over 70 years.
2) How much seafood is consumed each month? Sometimes unlimited consumption is considered one 8 ounce serving every day. Sometimes 16 days of consumption per month are used. Few people consume this much shellfish, so lower average consumption rates may be used, which in turn will raise the acceptable concentration.
3) What is the BaP Cancer Slope Factor? This is a technical term derived from cancer and epidemiological studies, but health officials have a little flexibility in defining how conservative a measure this will be, which in turn affects the seafood action limit concentration.
Bottom Line Numbers
The methods discussed above relate to fish consumption advisories (how often an adult should consume a particular species). This discussion does not address the regulatory opening and closing of shellfish beds, which historically has only been prompted when there is an overt immediate health risk (e.g. avoiding sickness and death from pathogens or “red tide”toxins). In the case of finfish, to address life-long exposure issues, the trend among regulators during the past decade has been to issue health advisories as to how many meals of a particular fish species should be consumed each month. This helps many states avoid closing freshwater ponds to fishing because of high mercury or pesticides levels that exist in some areas. However, in the case of shellfish, which may be harvested in various “open” areas, and sold to the public, there has been a strong desire by health officials to simply define areas open and closed to shellfishing, and avoid issuing health advisories on shellfish consumption. Because shellfish beds in enclosed embayments and harbors typically are closed first to bacteria before they show elevated hydrocarbon levels, and because shellfish do not have high lipid (fat) content which would bioaccumulate certain contaminants, the reliance on bacterial classifications to protect human health has been a reasonable policy.
One recent EPA seafood advisory recommended that health officials adopt a 6-ppm (parts per million) limit of PAHs for seafood. If this limit were adopted as the basis of shellfish bed open status, many harbors along the East Coast of the US would be closed to shellfishing, because, unlike fish, shellfish to not metabolize (break down) PAHs, and the compounds may bioaccumulate in their tissues. After the Exxon Valdez oil spill, BaP-Equivalency advisory levels for subsistence consumers (using only a ten-year exposure period) were 3 ppb BaPE for salmon, 5 ppb BaPE for finfish,11 ppb BaPE for crustaceans, and 120 ppb BaPE for bivalve mollusks. Following the Kure oil spill, the California Department of Health Services adopted advisory action levels of 34 ppb BaPE for the average shellfish consumer and 5 ppb BaPE for frequent shellfish consumption. These levels were not used to establish the opening or closing of shellfish beds.
What will the Massachusetts Department of Public Health and the Division of Marine establish as the standard to open and close shellfish beds due to the Bouchard No. 120 spill? Will that action limit have implications for unoiled bays in the Commonwealth affected by non-point sources of PAH? Will there be a lower threshold PAH consumption advisory level? These questions remain unresolved.
Whatever decisions are made, the public could find the decisions contentious or confusing. As noted in one NOAA publication: “The public wants to know whether the seafood is safe to eat; yet the answers given are typically posed in terms of ‘acceptable risk’ or ‘not a significant risk.'”The same document pointed out that Alaskan village residents became upset when it was pointed out that samples of smoked fish contained carcinogenic hydrocarbon levels hundreds of times higher than any shellfish samples collected from oiled beaches, and nearly 10,000 times higher than found in wild salmon. The report noted, “residents considered eating smoked salmon to be an acceptable, voluntary risk, and eating oil-contaminated seafood to be an involuntary, unacceptable risk.” Even the meaning of the analytical results can seem questionable when it was pointed out that the leafy vegetable Kale shows a PAH concentration (from naturally occurring plant compounds) three to fifty times higher than smoked fish. With this kind of information, the report concluded, “risk comparisons should be made carefully.”
Red Tides, Saxitoxin, and other PSP Toxins
Until the Spring of 2005, when May nor’easters, heavy rains, and cooler temperatures appeared to have created and blown in a remarkably intense bloom of the red tide dinoflagellate Alexandrium, red tides had never resulted in a closure of shellfishing in Buzzards Bay. Because of this event, we have added the information and links below.
In the 2001 Fish and Fisheries Products Hazards and Controls Guidance (Ch. 6), the USDA provides this information:
Contamination of fish with natural toxins from the harvest area can cause consumer illness. Most of these toxins are produced by species of naturally occurring marine algae (phytoplankton). They accumulate in fish when they feed on the algae or on other fish that have fed on the algae. There are also a few natural toxins which are naturally occurring in certain species of fish.
There are five recognized fish poisoning syndromes in the United States: paralytic shellfish poisoning (PSP), neurotoxic shellfish poisoning (NSP), diarrhetic shellfish poisoning (DSP), amnesic shellfish poisoning (ASP), and ciguatera fish poisoning (CFP)…..
Paralytic shellfish poisoning in the U.S. is generally associated with the consumption of molluscan shellfish from the northeast and northwest coastal regions of the U.S. PSP in other parts of the world has been associated with molluscan shellfish from environments ranging from tropical to temperate waters. In addition, in the U.S., PSP toxin has recently been reported from the viscera of mackerel, lobster, Dungeness crabs, tanner crabs, and red rock crabs. While the viscera of mackerel are not normally eaten, the viscera of lobster and crabs are. However, the levels of PSP toxin that are found in lobster tomalley are not likely to pose a health hazard unless large quantities are eaten from a heavily contaminated area.
Diarrhetic shellfish poisoning is generally associated with the consumption of molluscan shellfish. There has been no documented occurrence to date in the U.S. However, instances have been documented in Japan, southeast Asia, Scandinavia, western Europe, Chile, New Zealand, and eastern Canada. Amnesic shellfish poisoning is generally associated with the consumption of molluscan shellfish from the northeast and northwest coasts of North America. It has not yet been a problem in the Gulf of Mexico, although the algae that produces the toxin has been found there. ASP toxin has recently been identified as a problem in the viscera of Dungeness crab, tanner crab, red rock crab, and anchovies along the west coast of the United States. The viscera of anchovies are also eaten. Marine toxins are not ordinarily a problem in scallops if only the adductor muscle is consumed. However, products such as roe-on scallops and whole scallops do present a potential hazard for natural toxins.
The FDA has established action levels for all of the natural toxins except CFP.
PSP- 0.8 ppm (80ug/100g) saxitoxin equivalent;
NSP- 0.8 ppm (20 mouse units/100g) brevetoxin-2 equivalent;
DSP- 0.2 ppm okadaic acid plus 35-methyl okadaic acid (DXT 1);
ASP- 20 ppm domoic acid, except in the viscera of Dungeness crab, where 30 ppm is permitted.
There are no validated, rapid methods that are suitable for shipboard, dockside, or commercial testing of lots of fish for any of these toxins.
Note: A new version of the guidance was released in 2011, click to read the 2011 FDA guidance.
Symptoms of PSP poisoning include numbness or tingling of the lips, gums, tongue, face, headache, dizziness, loss of coordination, numbness in limbs, general weakness; nausea and vomiting, and in extreme cases respiratory distress and paralysis that may lead to death within 2-24h.
A good slideshow presentation on PSP poisoning and harmful alagal blooms (HAB) by JoAnn Burkholder is at Harmful Algae and Seafood Safety Harmful Algae and Seafood Safetypresentation.
Additional Reading on toxics and Seafood Safety
NOAA Document: Managing Seafood Safety after an Oil Spill A key document being used by health officials (1 MB pdf file).
U.S. Food and Drug Administration Seafood Hazard Analysis and Critical Control Point site.
EPA mid-Atlantic study page showing EPA recommended tissue concentration limits used in issuing fish advisories.