Bamfield, British Columbia

 Health and Nutrition

Edible Kelp

Health Issues of Heavy Metals and Radioactive Substances:

Heavy metals are elements detrimental to human health. Kelp do not distinguish between beneficial micronutrients and dangerous heavy metals and radioactive substances. Often heavy metals are associated with industrial and domestic activities and may be discharged into the sea near inhabited areas. Levels of heavy metals in edible kelp products are high relative to vegetables.

The range of some heavy metals in nine species of edible kelp from Asia and North America and their estimated daily consumption by Japanese*

Element	Concentration range (micrograms per gram dry weight)	Daily Japanese intake (micrograms per day)
Arsenic	20.00 - 79.00	640
Mercury	**nd - 0.40	8
Lead	nd - 0.64	5
Cadmium	0.02 - 2.80	29
Chromium	nd - 1.30	84

*Source: C. van Netten et al. (2000) The Science of the Total Environment, Volume 255, Pages 169-175.

**nd, element not detected.

However, these values do not address the question of bioavailability. For example, some forms of arsenic may be accumulated in human tissue more efficiently than others. Also, heavy metals may be bound to the seaweed in different forms, some of which are indigestible by humans. The Japanese, who, on the average eat 7.3 dry grams seaweed a day, take in relatively high loads of heavy metals. H owever, there is no evidence this is a health issue.

Jane Teas and colleagues (University of South Carolina) have expressed concerned over the potential of iodine toxicity for non-Asian populations: those who are not subjected to iodine-rich foods from birth. There may be iodine-sensitive individuals and care should be taken not to ingest too much kelp. They cited Parascelsus's (1493-1541, the father of toxicology) philosophy: "All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy."

A special case is the distribution of iodine-131, a radioactive product of nuclear plant melt-downs. Our bodies cannot distinguish between this hot form of iodine and the cold form that is essential to our good health. Protection against iodine-131 is to saturate our thyroid glands with cold iodine so "there is no room at the inn."

Melt-downs have global impact. Following the Chernobyl accident levels of iodine-131 were noted in rockweed in Sweden at 31,700 Bq per kg dry weigh and on the west coast of North America of 4900 Bq per kg dry weight (1 Bq = 1 radioactive decay per second) (Druehl et al. 1988. Marine biology 98:125-129).

Dr. K. Starosta (Simon Fraser University) and K. Nielsen (The Royal Military College of Canada), studying the impact of the Japanese nuclear plant troubles, have noted levels of 118-250 Bq/kg dry rockweed on the west coast. At present levels one would have to eat about 8 kg of rockweed (about one large garbage can full) to get the same radiation exposure as from flying from Montreal to Vancouver.