Archive for the ‘toxics’ Category
|Herbicide exposure causes male frogs to turn into female frogs
Monday, March 1st, 2010
How do you turn a male frog into a female frog that breeds with other male frogs? Expose them to herbicides that are routinely sprayed on agricultural fields worldwide.
Last year, Tyrone Hayes from UC Berkeley gave a talk at Bowdoin about his career’s work studying the impacts of endocrine-disrupting chemicals on amphibian development.
This week’s Early Edition of the Proceedings of the National Academy of Sciences features some of this research.1
Excerpts:
Atrazine is one of the most widely used pesticides in the world. Approximately 80 million pounds are applied annually in the United States alone, and atrazine is the most common pesticide contaminant of ground and surface water. Atrazine can be transported more than 1,000 km from the point of application via rainfall and, as a result, contaminates otherwise pristine habitats, even in remote areas where it is not used. In fact, more than a half million pounds of atrazine are precipitated in rainfall each year in the United States.
In addition to its persistence, mobility, and widespread contamination of water, atrazine is also a concern because several studies have shown that atrazine is a potent endocrine disruptor active in the ppb (parts per billion) range in fish, amphibians, reptiles, and human cell lines, and at higher doses (ppm) in reptiles, birds, and laboratory rodents. Atrazine seems to be most potent in amphibians, where it is active at levels as low as 0.1 ppb. Although a few studies suggest that atrazine has no effect on amphibians under certain laboratory conditions, in other studies, atrazine reduces testicular volume; reduces germ cell and Sertoli cell numbers; induces hermaphroditism; reduces testosterone; and induces testicular oogenesis. Furthermore, atrazine contamination is associated with demasculinization and feminization of amphibians in agricultural areas where atrazine is used and directly correlated with atrazine contamination in the wild.
Using an experiment where his team exposed frogs to a 2.5 parts per billion atrizine solution, here’s what they found:
Atrazine-exposed males were both demasculinized (chemically castrated) and completely feminized as adults. Ten percent of the exposed genetic males developed into functional females that copulated with unexposed males and produced viable eggs. Atrazine exposed males suffered from depressed testosterone, decreased breeding gland size, demasculinized/feminized laryngeal development, suppressed mating behavior, reduced spermatogenesis, and decreased fertility. These data are consistent with effects of atrazine observed in other vertebrate classes. The present findings exemplify the role that atrazine and other endocrine-disrupting pesticides likely play in global amphibian declines.
The main implication of this chemically induced sex switching is that it has the potential to disrupt breeding and contribute to the amphibian declines observed worldwide:
Although many studies have focused on death from disease and its role in global amphibian declines and sudden enigmatic disappearances of populations, virtually no attention has been paid to the slow gradual loss of amphibian populations due to failed recruitment. The present study suggests several ways that exposure to endocrine disruptors such as atrazine may lead to population level effects in the wild and contribute to amphibian declines. Certainly, the inability to compete for females and the significant decline in fertility in exposed males, as reported in the present study, will have a direct impact on exposed populations.
1Hayes, T. et al (2010) Atrazine induces complete feminization and chemical castration in male African clawed frogs (Xenopus laevis). Proceedings of the National Academy of Sciences. doi:10.1073/pnas.0909519107
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Photo credit: http://www.flickr.com/photos/arte/ / CC BY-NC 2.0
Tags: pesticides
Posted in biodiversity science, pollutants, toxics | No Comments »
Are nanoparticles in consumer products increasing your cancer risk?
Tuesday, November 17th, 2009
The field of nanotechnology is exploding, and many materials, such as titanium (Ti), are being shrunk and used in consumer products like sun tan lotions, cosmetics, and toothpaste.
It has been traditionally thought that inert materials like Ti won’t cause health issues because they don’t react with molecules in our cells. New research from UCLA’s Jonsson Comprehensive Cancer Center published in Cancer Research suggests that this conventional wisdom may be flawed.
Ti appears to migrate throughout the body, causing DNA/chromosome breakage and inflammation (both of which are linked to cancer) and oxidative stress causing cell death. Rather than chemically reacting with molecules in cells, the high surface area of the tiny particles appears to cause cell molecules to change.
The manufacture of TiO2 nanoparticles is a huge industry, Schiestl said, with production at about two million tons per year. In addition to paint, cosmetics, sunscreen and vitamins, the nanoparticles can be found in toothpaste, food colorants, nutritional supplements and hundreds of other personal care products.
Once in the system, the TiO2 nanoparticles accumulate in different organs because the body has no way to eliminate them. And because they are so small, they can go everywhere in the body, even through cells, and may interfere with sub-cellular mechanisms.
Photo credit: http://www.flickr.com/photos/29487767@N02/ / CC BY-NC-SA 2.0
Posted in pollutants, risk analysis, technology, toxics | No Comments »
How do women respond to household chemical exposure?
Sunday, November 15th, 2009
Every day, we are exposed to a cocktail of synthetic chemicals from consumer products. How harmful are these? In an earlier post, I described how risk analysis is an important scientific process for determining exposure, effects, and overall risk of these chemicals.
One thing missing from these analyses is how people respond to information about their chemical exposure. In a recent issue1 of the Journal of Health and Social Behavior, Rebecca Altman and colleagues addressed this by analyzing what they call the “exposure experience” of women in Cape Cod, MA—an area with elevated breast cancer rates.
What did they find?
Posted in gender, pollutants, risk analysis, toxics | No Comments »
Do our daily routines put our health at risk?
Wednesday, October 14th, 2009
Every day, we are exposed to synthetic chemicals and radiation from consumer products. If you asked me how risky these products are, my responses might range from “I don’t know” to “I don’t want to know” to “If they’re on the market, let’s hope they’re safe!” Unfortunately, it’s difficult to know if many of the things we use every day really are safe.
Risk analysis is a four-step process by which scientists determine whether chemicals or other agents are unhealthy:
- Step 1: Hazard screening–Does a chemical look or act like other chemicals already known to be harmful or safe?
- Step 2: Exposure characterization–How much are we exposed to and how much accumulates in our bodies?
- Step 3: Effects characterization–How do different doses of an agent lead to different health effects, or what we commonly refer to as “dose-response curves”? This is usually achieved using short-term lab animal tests or epidemiological data that show things like health effects of people working at industry sites or living in contaminated neighborhoods.
- Step 4: Risk characterization–Given that we identify a chemical as being potentially dangerous (Step 1), and can measure our exposure (Step 2) and the effects that this specific exposure has on health (Step 3), what is the likelihood or risk that we will experience ill health as a result of the exposure?
As the EPA will tell you, there is often poor understanding of the long term risks of synthetic chemicals and radiation. Much of this comes from the fact that
- We have not screened many of the chemicals on the market for potential safety. Here’s a quote from the EPA’s website in 1996, which was subsequently removed:
For the majority of the approximately 3,000 high production volume industrial chemicals produced in the United States in 1996, we have little or no publicly available hazard screening data. These chemicals, non-polymers produced in quantities of more than one million pounds per year, are found in the workplace and in thousands of consumer products. Even fewer data are available for the remainder of the some 70,000 chemicals on the EPA’s inventory.
- Rigorous effects characterizations are hard to do. Lab animal tests (rats, mice, etc.) are useful, but they are not a perfect substitute for understanding human health impacts. Moreover, the kinds of long-term data we need rarely exist because that’s the nature of short grant funding cycles. We know very little about the synergistic effects of multiple chemicals interacting in our bodies. Finally, health problems analyzed in epidemiological studies can often be confounded with other lifestyle issues, such as weight, diet, exercise, and smoking.
Thus, we know we are exposed to these things, and we can even measure them in our bodies and in infants, but we don’t know very well how this translates to long term health risk.
To some, this uncertainty might be license to ignore the issue. To others, it necessitates better education about what’s in or emanating from our products so that we can decide for ourselves whether or not to limit exposure.
The Environmental Working Group has compiled several interesting lists of consumer products including specific ingredients that have the potential to be harmful:
- Shopper’s guide to pesticides in food
- Shopper’s guide to cosmetics and health care products
- Shopper’s guide to sunscreens
- Shopper’s guide to cell phone radiation
So go ahead and check out your favorite vegetable, shampoo, cell phone, or toothpaste, and see what comes up.
photo credit: http://www.flickr.com/photos/w610guy/ / CC BY-NC-ND 2.0
Tags: chemical, cosmetics, pollutant, radiation
Posted in environmental science, pollutants, risk analysis, shopping guides, toxics | 2 Comments »
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