The UK retailer this week withdrew two batches of its own-brand Super Strength Fish Oil Capsules, because they were found to contain dioxin levels in excess of EU limits.
This withdrawal and the accompanying 'for information' food alert from the Food Standards Agency (FSA) comes just four weeks after similar action from Seven Seas.
Dioxins and dioxin-like PCBs (polychlorinated biphenyls) are chemicals that occur almost everywhere in our environment. Bi-products of combustion, they can be created either naturally through events such as forest fires or through man-made processes.
Their ubiquity means they are found in all foods, but highest levels are found in edible fish and other products with a high animal fat content.
Dioxins can build up in the human body if too-high levels are consumed. High levels have been linked to a number of health problems, such as cancer, immune and nervous system disorders, liver damage and sterility.
The tolerable daily intake of dioxins - that is, the amount that may be consumed every day over a lifetime without causing harm - is 2pg (picograms) per kilogram of bodyweight.
The EU limits for dioxins in fish oil intended for human consumption were set in July 2002 at 2pg/g. Since then, however, more information has become available on dioxin-like PCBs, leading to the introduction of a combined limit of 10pg/g as of November 4 2006.
A spokesperson for the Food Standards Agency (FSA) told NutraIngredients.com that the Boots supplements would not pose a direct and immediate threat to the health of anyone who took them, which was why they have only been withdrawn from sale, rather than a full product recall having been issued.
But it seems Boots is not taking any chances with its customer base; it is today sending letters to all of its Advantage Cardholders who may have bought the affected products.
The FSA was unable to comment on why there have been two incidents of supplement companies withdrawing fish oil products from market within weeks of each other.
Boots had not responded to NutraIngredients.com's inquiry about the matter prior to publication.
Seven Seas has said that it is conducting investigations with the third-party supplier of the ingredient that failed to meet the specifications.
"With immediate effect, increased quality measures and controls have been implemented by the supplier to ensure that the technical variance will not occur again in the future with Seven Seas products," it said.
The dioxin levels in the withdrawn Seven Seas products were said to be only "slightly" in excess of permitted levels; 2.7pg of doixins were found in a 1g capsule of Seven Seas Extra High Strength Cod Liver Oil.
In fact, the permitted levels for fish oils are much lower than for other foodstuffs.
Of the 2.7pg in the 1g capsule, Professor Andre McLean, professor of toxicology at Universite College London said, "one could get more from a teaspoon of butter".
A half an ounce of butter would contribute 3.6pg of dioxins.
Seven Seas said that if consumers found they had purchased an affected batch, the supplements could still be safely consumed.
In recent years a raft of studies have provided support for health benefits of including fish in the diet - with the most convincing date for cardiovascular health, cognistive function and infant and maternal health. In particular, omega-3, of which oily fish is amongst the best sources, has become a household term.
It is widely agreed that consumers would be doing themselves a disservice if they avoided fish and fish oils out of fear of contaminents which, according to current advice, pose no risk if consumed only at small levels.
Some suppliers have moved to lower the dioxing and PCB levels in their fish oil, in a bid to prevent consumer confidence being dented.
For instnace, EPAX pledged last month that its omega-3 concentrates - both triglyceride and ethyl ester - will from now on contain no more than 5 pg/g of dioxins, furans and dioxin-like PCBs combines. Its previous specification limit was 7.5 mg/g.