CURWOOD: This is Living on Earth. I'm Steve Curwood. The Bush administration is putting the brakes on regulations that would sharply reduce the amount of arsenic allowed in drinking water. EPA chief Christie Whitman says the current standard does need to be tightened, but she wants a further review of the science before taking action. Long-term exposure to low levels of arsenic has been linked to increased risk of cancer, vascular disease, and diabetes. But science couldn't say why until now. Toxicologists at Dartmouth College have discovered tiny amounts of arsenic disrupt the functioning of hormones with a mechanism never noted before. Josh Hamilton led the team. He says arsenic disrupts glucocoriticoid, a hormone that regulates a wide range of activities in our bodies.
HAMILTON: Glucocoriticoids are involved in normal blood vessel function. They regulate the immune system. They regulate glucose in our blood. They regulate cell growth. It has many, many roles, and so sorting out how this plays out in terms of the kinds of health effects that arsenic causes becomes very complicated.
CURWOOD: So, arsenic mimics the hormone we commonly call cortisone, in the cortisol family. Or, does it block it from fitting into a receptor? Or, what does it do?
HAMILTON: It actually doesn't do either of those things. Arsenic has a rather unique mechanism, which hasn't been described before. Most pesticides and other organic pollutants like that either bind to the receptor and look like the hormone or block its action. Arsenic doesn't block the binding of glucocoriticoids to the receptor, and it doesn't act like a hormone. The thing that it does is that once the receptor goes to turn on or turn off genes, it fails to function that way. So arsenic is blocking the ability of the receptor to work, but not through hormone binding.
CURWOOD: What does this hormone disrupting process have to do with skin or lung cancer? I guess those are two cancers that are closely linked to arsenic.
HAMILTON: Well, there are two animal models that have been looked at for the cancer process. And in skin, it was shown that if you give a very strong carcinogen directly onto the skin, and then you give a second chemical called a tumor promoter, which would increase the probability of cancer, applying glucocoriticoid hormone to that area would completely block the cancer process. Very similar story in the lung, where you give a carcinogen. If you give the hormone during the process, you can completely block that tumor process. So, this suggested to us that if arsenic can block the actions of this receptor, you still need probably some other driving force to get cancer, but you'll probably get many more cancers in the absence of this receptor than if it were functioning properly.
CURWOOD: In other words, it's possible that if someone is exposed to arsenic, it compromises their body's own natural ability to fight off a cancer.
CURWOOD: Talk to me about dosages and possible endocrine disruptor effects.
HAMILTON: The studies we did were on cultured cells, so it's hard to directly compare the doses that we use there with doses that a whole animal or a person would be exposed to. But the doses that we're using in cell culture that cause these endocrine-like effects are well below any levels that caused any signs of toxicity in the cells. In fact, we were down in what's called the nanomole range, or parts per trillion, and still seeing these effects. Now, if you look at what people are exposed to, it suggests to us that we could see these endocrine effects quite reasonably, probably, at the levels that people are exposed to here in the U.S.
CURWOOD: So there are some pretty broad implications here. Arsenic is everywhere, isn't it?
HAMILTON: Yes, it is. It's in the air, water, soil. We used to focus on manmade sources of arsenic, but I think we're coming to the realization that natural sources of arsenic are probably a much bigger human health problem.
CURWOOD: What kind of sources of so-called natural arsenic should people be concerned about?
HAMILTON: Well, primarily in drinking water. There are certain types of rock that are heavily arsenic-laden. If you happen to live in one of these areas and you drill a well, the groundwater will be contaminated from the arsenic that leaches out of these rocks.
CURWOOD: How can somebody protect themselves and their family from the effects of arsenic in the drinking water?
HAMILTON: I think the big issue, the underside of the iceberg, really, is people on private wells. Some of these wells exceed 500 parts per billion, which is levels that we see over in areas like Bangladesh and Taiwan. These levels are too low for people to feel sick or have other signs of poisoning. But at these levels, we expect that it's going to significantly increase the risk of cancer, diabetes, vascular disease, and other problems. People have to be told about the arsenic issues so that they can go ahead and test their water, and then they have the information to do something about it. Either to buy a remediation system for their house or switch to an alternative water source.
CURWOOD: Bottled water.
HAMILTON: Bottled water.
CURWOOD: What's your take on the need to lower the allowable level of arsenic in our drinking water?
HAMILTON: I believe that we should do that, and that there is very solid scientific and medical evidence to do so. I think the reason that it was blocked is because of financial concerns. We're the only Western country that still has a water safety level of 50 parts per billion for arsenic. The rest of Europe and Japan and other Western countries have moved to five or ten parts per billion in recognition of the fact that we think that 50 is not protective.
CURWOOD: Josh Hamilton is a professor of toxicology at Dartmouth College. Thank you so much for taking this time with us.
HAMILTON: Thank you.
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