How safe are kelp supplements?

Recently, I have noticed that kelp supplements are available just about everywhere. But how safe are they?

An article in the Journal of Dermatology related this horror story:

A 54-year-old woman was referred to the University of California, Davis, Occupational Medicine Clinic with a 2-year history of worsening alopecia and memory loss. She also reported having a rash, increasing fatigue, nausea, and vomiting, disabling her to the point where she could no longer work full-time. A thorough exposure history revealed that she took daily kelp supplements. A urine sample showed an arsenic level of 83.6 microg/g creatinine.

So the researchers conducted a study:

To evaluate the extent of arsenic contamination in commercially available kelp, we analyzed nine samples randomly obtained from local health food stores. Eight of the nine samples showed detectable levels of arsenic higher than the Food and Drug Administration tolerance level of 0.5 to 2 ppm for certain food products. None of the supplements contained information regarding the possibility of contamination with arsenic or other heavy metals.

The researchers warn that under-regulation of supplements may be putting the public in danger:

The 1994 Dietary Supplement Health and Education Act (DSHEA) has changed the way dietary herbal therapies are marketed and regulated in the United States. Less regulation of dietary herbal therapies will make inadvertent toxicities a more frequent occurrence.

My own reaction: it depends how you define "regulation." Contaminated products and products sourced from contaminated environments should be banned entirely. As for uncontaminated products, it's far preferable that the government mandate warning labels than ban products entirely. Why? First, people will turn to unsafe sources if they think the product is helpful -- as happens with street drugs, defeating the purpose of a ban. Second, it's not the role of governments to make choices for people. Improved testing and labeling offers an important and in many respects, urgently required advance on current practice.

The authors further advise:

Clinicians should be aware of the potential for heavy metal toxicity due to chronic use of dietary herbal supplements. Inquiring about use of dietary supplements is an important element of the medical history.

And patients should make themselves familiar with the up-to-date scientific literature on any drug or supplement they consume. This has never been so easy to do.

If you are not familiar with the science, what would be the point of taking any supplement? You could just as easily be putting yourself at further risk!

Finally, I can see two other potential problem with kelp. First, concerns the extremely high iodine content of some species. This may put some people at risk of toxicity. Second, some places where seaweed is gathered may be contaminated by industrial waste or pollutants. And some seaweeds may contain toxic heavy metals such as iron or aluminum. I have read that lead contamination is an issue with various kinds of supplements sourced from China.