ARCHIVED - Fish and Seafood Survey

2002

Background

Fish and seafood are rich in many essential nutrients and can contribute to a healthy diet for Canadians. However, these and other foods sometimes contain environmental contaminants, usually at very low levels.

As a result, Health Canada undertakes regular surveillance activities to monitor the level of contaminants in foods. These surveillance reports provide current estimates of the exposure of Canadians to these contaminants and are a valuable tool to improve risk assessments and to develop the appropriate strategies to manage risks that may be associated with these contaminants.

In addition to the yearly Canadian Total Diet Study, which targets background levels of contaminants in food, Health Canada recently undertook a specific survey on fish and seafood. Farmed and wild caught fish and seafood products sold at the retail level were sampled in Vancouver, Toronto and Halifax during March, 2002. Samples of farmed and wild caught char, oysters, salmon, shrimp and tilapia were analysed for dioxins, furans, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and veterinary drugs. Shark, marlin, swordfish and tuna (canned and fresh/frozen) samples were analysed for total mercury and methylmercury. The resulting data are being used in Health Canada's health risk assessment updates for persistent organic pollutants and other chemical contaminants in the Canadian food supply. It should be noted that at the time of sampling, there was only limited availability of wild caught oysters, salmon, shrimp and tilapia in retail outlets and that edible portions only (skin and bone removed) were analysed for the various targeted contaminants. This report presents data on PCBs and PBDEs in these samples along with a preliminary health risk assessment based on exposure to these contaminants through fish consumption. Information on other contaminants will be provided as the data and health risk assessments become available.

PCBs (Polychlorinated biphenyls)

PCBs are found in small quantities in all food commodities of animal origin, including fish, and in humans. PCB levels in the sampled fish and seafood products (Table 1) were quite low, with average values not exceeding 18 ppb (1 ppb or "part per billion" is equal to 0.000000001 grams total PCBs per gram).

This is consistent with findings from other monitoring activities by Health Canada which have shown steady declines during the past 20 years in both intake and human tissue levels of PCBs. There is no general trend of PCB levels between the farmed and wild caught fish species: levels present in farmed and wild caught char are very similar; wild caught tilapia contained approximately 3 times more than the farmed tilapia; and farmed salmon contained approximately 2.5 times more PCBs than wild caught salmon.

While diet remains the predominant route of exposure for the majority of the Canadian population, based on the highest average concentration of PCBs in fish found in this survey, Health Canada has determined that Canadians are not exposed to PCBs in foods at levels that pose a health risk and that there is no need for specific advice regarding fish consumption and PCB exposure.

Table 1: Contaminants in Retail Fish and Seafood Products: Summary Statistics for Total PCB Levels (results expressed in ppb*).
Species Source N Mean Standard Error of the Mean Standard Deviation Minimum Maximum
Char Farmed 6 6.5 1.5 3.7 3.5 13.5
Wild 5 5.4 1.1 2.5 3.1 9.7
Oysters Farmed 12 1.6 0.6 1.9 0.2 6.7
Wild 4 0.4 0.03 0.06 0.4 0.5
Salmon Farmed 19 17.5 2.4 10.6 4.4 45.1
Wild 3 6.6 3.4 5.9 2.8 13.5
Shrimp Farmed 13 0.3 0.1 0.5 0.04 2.0
Wild 4 0.4 0.2 0.5 0.1 1.1
Tilapia Farmed 15 1.8 1.1 4.2 0.06 16.6
Wild 3 5.3 4.3 7.5 0.3 14.0

* ppb is parts per billion, and represents 0.000000001 grams of total PCBs per gram of sample (edible portion)

N = number of samples tested

Differences in total PCB levels between farmed and wild species were not statistically significant (p > 0.05). Total PCB levels between species were significantly different (p < 0.0001) with farmed salmon containing the highest average level ( 17.5 ppb) followed by farmed char (6.5 ppb).

PBDEs (Polybrominated diphenyl ethers)

PBDEs are commercially produced substances that are used as flame retardants in a wide variety of consumer products, which have similar chemical properties to PCBs, and are also regarded as being environmentally persistent and bioaccumulative, meaning that they accumulate in body tissues. Measurements in animals (fish, marine mammals) and humans (milk) have indicated that levels have been increasing during the past 10-15 years. Human milk levels are reported to be higher for North-America than Europe. Recent dietary surveys from European countries (Netherlands, Spain, Sweden, UK) and Canada have identified food as one possible route of exposure to PBDEs.

However, dietary intake estimates of PBDEs for Canada (Canadian Total Diet Study) are similar to that found in several European countries. It is therefore suggested that other sources than food contribute significantly to human exposure. These sources include some consumer products (when used as additive flame retardants), air, water and dust particles.

PBDE levels in the sampled fish and seafood products (Table 2) did not exceed 5.5 ppb. While there is some limited evidence suggesting that the concentrations of PBDEs are higher in farmed fish and seafood products, Health Canada's opinion is that the current levels found in any retail food are not considered to be a health concern. Health Canada will continue to update the health risk assessment for PBDEs as more data becomes available.

Table 2. Contaminants in Retail Fish and Seafood Products: Summary Statistics for Total PBDE Levels (results expressed in ppb).
Species Source N Mean Standard Error of the Mean Standard Deviation Minimum Maximum
Char Farmed 5 1.0 0.4 1.0 0.4 2.7
Wild 5 0.6 0.1 0.3 0.3 1.1
Oysters Farmed 11 0.7 0.1 0.5 0.006 1.4
Wild 4 0.4 0.08 0.2 0.3 0.6
Salmon Farmed 19 2.2 0.3 1.4 0.4 5.5
Wild 3 0.6 0.2 0.3 0.1 1.3
Shrimp Farmed 13 0.2 0.06 0.2 <0.001 0.7
Wild 4 0.1 0.05 0.09 0.009 0.2
Tilapia Farmed 12 0.6 0.4 1.4 0.04 5.0
Wild 3 0.1 0.09 0.2 0.01 0.3

* ppb is parts per billion, and represents 0.000000001 grams of total PBDEs per gram of sample (edible portion)

N = number of samples tested

Differences in total PBDE levels between farmed and wild species were not statistically significant (p > 0.05). Total PBDE levels between species were significantly different (p < 0.0001) with farmed salmon containing an average level of 2.2 ppb followed by farmed char (1.0 ppb).

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