Caution: Please do your own “Due Dilligence” - I am NOT a health, nutrition, fishing, nor toxicology expert - caveat emptor applies.
Bioaccumulative Pollutants in Fish:
Although the United States has “advisories” for at least 39 chemical contaminants in fish, there are 5 prime offenders: Mercury, PCBs, DDT, Chlordane, and Dioxins. Concentrations (in fish) of these contaminants increases at each level of the food
chain, with the predictable result that larger individuals, and top predator species will have the highest concentrations (up to a million times higher than the water’s concentration).
Other contaminents of concern include: Heavy Metals (arsenic, cadmium, chromium, copper, lead, selenium, & zinc), Organochlorine Pesticides, and a myriad of other compounds.
Shark, Swordfish, King Mackerel, Tilefish, Turtles, Many Shellfish (near industrialized regions), and Albacore Tuna
(mercury levels in tuna vary. Store-bought tuna steaks and canned albacore tuna generally contain higher levels of mercury than canned light tuna)
The fish that are lowest in contaminants generally are small(er) in size, low in fat, and species that don’t live or feed on the bottom of waterways,
Some authorities recommend species such as: Anchovies, Arctic Char, Crawfish, Pacific Flounder, Herring, King Crab, Sanddabs, Scallops, Pacific sole; wild Alaska
and Pacific Salmon.
Limit fish consumption
by category, not individual species. For example, both cod and mahimahi are moderate-mercury fish, and only one from this category should be eaten per month -- not one meal of cod and one of mahimahi.
* These lists are NOT to be considered complete nor authoratative.
Methylmercury is different than DDTs and PCBs because it is in all parts
of fish, including the muscle tissue/fillet. Eating less fish suspected to have high levels of mercury is the only way to reduce your exposure, since there are no cooking
methods that will reduce mercury levels in seafood.
and 3. DDT
(and it’s degradation products: DDE & DDD)
DDTs and PCBs build up in the fatty parts
of fish. Eat less fatty individuals, and species of fish. Remove the skin & available fat prior to cooking
. Utilize cooking & preparation methods that reduce fat (ie: Allow fat to drain while broiling, grilling, or baking it on a rack). Do not use the drippings for sauces or gravies.
is a chemical that was used as a pesticide in the United States from 1948 to 1988. Chlordane does not dissolve in water
, however, it is sufficiently long lived that it may travel long distances and be deposited on land or in water
far from its source. Chlordane or the chemicals that chlordane changes into accumulate in some form in the fat of in fish, shellfish, birds, and mammals. The good news is that a number of advisories for chlordane have been rescinded in recent years as the chemical slowly decreases in the environment
, according to EPA's National Listing of Fish and Wildlife Advisories.
(Dioxin1) are an ubiquitous environmental contaminant, inadvertently created during industrial processes such as incineration and pulp bleaching, hence are more likely to be found in polluted waters near industrialized regions. Dioxins and furans are some of the most toxic chemicals known to science. Since dioxin is fat-soluble, it bioaccumulates up the food chain, so that dioxin levels in fish can be 100,000 times that of the surrounding environment
Preparation & Cooking
You can reduce the level of PCBs, Dioxins and Chlordane (but not mercury) by properly cleaning
, skinning and trimming the species and by following the five basic preparation & cooking recommendations below:
1. Cook fish and shellfish thoroughly. Handle raw fish as you would handle other raw meat products. Take care not to cross-contaminate cooked food or vegetables with the utensils used to cook raw fish, and wash utensils and hands thoroughly in between handling. Cook, freeze or refrigerate fish soon (immediately) after capture. Bruised or brown spots indicate decomposition, and possibly bacteria.
2. Before cooking, remove and do not eat the organs, head, skin and the dark fatty tissue
along the lateral line, backbone and belly of fish, nor the tomalley of lobster (green gland) and the mustard of crabs, where toxins are likely to accumulate.
3. Avoid batter or breading, because they hold in the liquid that may contain contaminants.
4. Bake or broil the fish on an elevated rack that allows fats to drain to the pan below; do not fry in a pan. Serve less fried fish; frying seals
in chemical pollutants that might be in the fish's fat. On the other hand, grilling or broiling allows fat to drain away.
5. After cooking, discard all liquids. Do not reuse for soup or sauces.
The longer a fish lives, the more toxins it can accumulate. Eat younger, smaller individuals. In the case of PCB, dioxin and chlordane contamination, fish with lower fat content contain fewer of these contaminants, while fish with higher fat content, such as bluefish, contain higher levels. These contaminants accumulate in the fatty parts of the fish over time. Large bluefish (over six pounds), for example, have been found to exceed federal standards for PCBs and, therefore, should not be consumed by expectant mothers. It is generally safe, however, to eat most other low-fat commercial
fish, such as flounder, Pollock, cod, shrimp, clams, scallops, oysters, mussels and farm-raised fish, such as catfish and salmon, since they have been found to be low in PCBs. A recent regional study of the American lobster has shown elevated levels of PCBs, cadmium and dioxin in the green gland (tomalley hepatopancreas). This finding is consistent with other lobster studies conducted in waters of the northeastern coastal states. Therefore, consumers are advised to remove and not consume the green gland of all American lobsters caught off the coast from Maine
to New Jersey
, as well as avoid products made from the lobster green gland. This advisory does not apply to other edible portions of the lobster.
Generally, larger and older fish have had more time to bioaccumulate mercury from their food and the water than smaller and younger fish. In addition, large predatory fish (like sharks and swordfish) near the top of marine
food chains are more likely to have high levels of mercury than fish lower in marine
food chains due to the process of biomagnification. Fish can also absorb organic chemicals (such as PCBs, dioxins and DDT) from the water, suspended sediments, and their food. In contaminated areas, bottom-dwelling fish are especially likely to have high levels of such toxins because these substances run off the land and settle to the bottom.
It's been suggested that the levels of most contaminants may not be as high in less-developed (or more remote) regions - such South & Central America
Besides industrial pollutants and other human-made contaminants, some seafood may also contain natural toxins if fish eat harmful algae or bacteria. In warm tropical waters, a toxin called ciguatera can work
its way up the food chain and be present in toxic levels in large, predatory fish. Cooking does not destroy the toxin, and consumption
of ciguatoxic fish can cause intense flu-like symptoms. (See my posting on "Ciguatera")
In addition, fish like tuna, mackerel, bluefish and mahimahi begin decomposing soon after capture. If not stored properly, they may develop a histamine called scombrotoxin. Eating fish (even cooked fish) with high concentrations of scombrotoxin can cause an allergylike reaction, which is treatable with an antihistamine.
Uncooked fish may contain disease-causing bacteria, viruses or parasites. Raw oysters, clams and other shellfish pose a particular risk since they are filter feeders - straining tiny particles from the seawater for food. If the seawater contains disease-causing microorganisms, these accumulate in the shellfish. The Norwalk virus, which causes intestinal illness in humans, is often associated with eating raw oysters and clams. For this reason, it is important to get raw shellfish from a reliable source, or ensure that your shellfish is cooked thoroughly.
Some Further Reading:
U.S. EPA - Fish Advisories
U.S. FDA - Mercury Levels in Commercial
Fish and Shellfish
A Guide to Healthy Eating of the Fish You Catch
and Cooking Instructions to Reduce Dioxin, PCBs, and DDT in Fish
Fish Advisories (specific species)
HTH, and “Caveat Emptor”