Cabbages, etc.

Last week at the annual National Meeting of my professional society (SETAC – the Society of Environmental Toxicology and Chemistry) my professional and private lives coalesced in a very interesting exchange. One of the poster sessions focused on Emerging Issues in Environmental Toxicology; this year's hot topics are Endocrine Disruptors (chemicals in the environment that act like hormones and mess up an organism's normal endocrine balance), amphibian abnormalities (people are finding a lot of deformed frogs and salamanders in the wild and it has been speculated that everything from acid rain to UV radiation to endocrine disruptors are the cause), and perchlorates (chemicals found in aviation fuel and fertilizer -- i.e., made in very large quantities -- which have been found in groundwater and about which, in 1998, government and scientists alike sudden-ly discovered they knew NOT A THING with respect to its environmental hazard). In this session I stopped to read a poster about a frog experiment that somehow managed to roll all three issues together. And right there, in the middle of the first paragraph, was the word, THYROXINE. You know, thyroid hormone. {ED. See Page 9 about thyroid testing}

Thyroxine, as we know, controls many metabolic functions. In frogs, this includes metamorphosis -- the miraculoustransformation from gill-breathing polliwog (tadpole) to lung-breathing long-jumper. In the experimental exposure of tadpoles to perchlorate, none of the deformities seen in the environment occurred. Instead, the tadpoles did not go through metamorphosis on the same time schedule as the unexposed (control) tadpoles did - they were much slower and, at higher concentrations, they did not metamorphose at all and just became very big tadpoles.

Thus, perchlorates are suspected to inhibit thyroxine activity. The reason this is important to frogs is that a delay in metamorphosis may result in population decreases as the tadpole food supply changes seasonally; tadpoles are more susceptible to predation and to the toxic effects of chemicals which may enter the water than are adult frog; and their reproductive cycle can be totally thrown off. Tadpole exposure to perchlorates in the environment may be significant due to the presence of perchlorates in fertilizer, which can run off treated fields and yards in especially high concentration in the spring when tadpoles are growing.

Calliope with Frog

The author of the poster, a nice gentleman from the US Geological Survey, asked if I was interested in perchlorates. I am, I said, if they affect thyroxine. I explained about the dogs, whereupon we had a nice conversation about hypothyroidism and diet. He said 15% of American women over the age of 40 are hypothyroid, and it has become more severe in the past two decades as we assiduously avoid salt -- thus cutting down our consumption of iodine (which is needed for the endogenous activation of thyroxine). We should all be using a reasonable quantity of iodized salt, he said. As for perchlorates in the diet, the foods rich in them are the Crucifers (mustards) -- including turnips, cabbage, kale, broccoli, Brussels sprouts, cauliflower, etc -- but only if they are long-boiled. [For some reason this conjured up generations of plump, hairy middle-aged Eastern European women; could many more of them have been hypothyroid because of their diet?] When I mentioned taking a kelp supplement, he directed me (practically led me by the hand) to another USGS poster regarding perchlorates. In this study, some of his colleagues had investigated the source and levels of perchlorates in common fertilizers. Lo and behold, of a dozen or so fertilizer ingredients, only three had significant quantities of perchlorates -including kelp, at 866 mg/kg (dry weight -- the detection limit for perchlorate was about 5 mg/kg).

Mind you, this was unprocessed kelp, so I don't know how those perchlorate levels relate to those which may be present in dietary kelp supplements. Nor can I guess, from the levels he exposed his frogs to, what levels of dietary or environmental perchlorate might inhibit thyroxine activity in humans or dogs. Still, I doubt kelp confers a huge health benefit beyond providing some iodine (which may be canceled out by the perchlorate). So, this weekend I bought a container of sea salt, which contains iodine, and I will sprinkle it on the meatloaf I make for the dogs and on my own lightly steamed broccoli. I don't share crucifers with the dogs for esthetic reasons -- they cause the worst GAS!