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Science & the Public

Beefy hormones: New routes of exposure

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NEW ORLEANS On any given day, some 750,000 U.S feedlots are beefing up between 11 million and 14 million head of cattle. The vast majority of these animals will receive muscle-building steroids — hormones they will eventually excrete into the environment. But traditional notions about where those biologically active pollutants end up may need substantial revising, several new studies find.

They were reported at the annual meeting of the Society of Environmental Toxicology and Chemistry, which ended Monday.

A typical feedlot cow will shed 50 pounds of urine and feces per day. These wastes may be collected in lagoons or composted for later use in fertilizing fields.

Throughout the past decade, scientists have become concerned about environmental risks that these wastes might pose if they wash, untreated, into waterways. Evidence has certainly linked waters receiving runoff from feedlots with sex alterations in fish — females that exhibit some masculinization and males that look somewhat feminized.

But indicting specific livestock hormones to such changes is proving tricky. And one reason, argues Alan Kolok of the University of Nebraska, in Omaha, is that scientists have made a number of what now appear to be questionable assumptions. Such as that the excreted hormones affecting fish will always be in the water, that downstream concentrations of these steroids will be greater than upstream values and that hormone levels in tiny streams will be more concentrated than in substantially bigger waterways.

“They’re all perfectly good a priori assumptions,” Kolok says. But in each case, he reports, “What we’re finding in the field is that they’re just not holding up.”

Transgender effects
In one set of tests, his group exposed fathead minnows for a week to a slurry of manure from cattle that had received steroid implants containing androgens (testosterone surrogates such as trenbolone acetate) and estrogens. Compared to males in untreated aquarium water, exposed males developed a combination of feminizing and demasculinizing changes. These included a reduction in male secondary-sex characteristics (the animals’ typically enlarged heads bearing prominent bumps). These guys also showed an activation of certain genes responsive to estrogen.

The effects most likely trace to the presence of estrogens from the implants, notes Marlo Sellin, a member of the Nebraska team (at the College of Public Health). Female minnows showed no impact from the implanted-cows’ manure.

So manure is dumping estrogens into the water, which is feminizing fish in the wild. Right? Ah, no.

“In the field [i.e. rivers] we see anti-estrogenic effects,” Sellin observes, “which maybe suggests that cow manure is not the cause.” Then again, she notes that excreted hormones can morph into chemicals that act differently than their parent compounds, particularly if the starting chemicals have been transformed by aquatic microbes. (Bacteria can alter hormones by attaching or detaching chemical groups.)

In another set of experiments, Sellin and Kolok’s team placed minnows in tanks of either clean water or water collected from the Elkhorn River, downstream of confined animal feeding operations, or CAFOs. Nebraska’s Elkhorn watershed is home to 2,200 CAFOs (a small share of the state’s 15,000 — each holding a minimum of 500 head of cattle). The environmental scientists added sediment from the Elkhorn River to an aquarium hosting river water and to another tank containing clean water.

The surprise, and this was a big one: Females given a one-week vacation in Elkhorn River water exhibited no hormonal changes unless the river sediment was also present. Where it was, those she minnows developed defeminizing changes — even in they had been swimming in otherwise clean water.

Kolok and Sellin still don’t know what it is about the sediment that makes a difference. It’s possible that some microbes in it have transformed otherwise inactive hormone metabolites into some biologically active compounds. Or perhaps biologically active metabolites in the water tend to glom onto sediment particles and remain there — until fish eat those sediment particles (which they do) or until something releases a share of the metabolites back into the water. A paper describing the unexpected sediment data will appear soon in Aquatic Toxicology.

Kolok plans to follow up this work by screening for a broader spectrum of potential hormonally active steroid metabolites in the water and sediment. His group will also investigate how fish are affected: through hormones encountered in their diet, as water flows over their gills, or both.

But the big take home message, Kolok emphasized at the meeting, is that a lot could be missed by assuming any or all CAFO-shed hormones or hormone-blocking pollutants will necessarily hang out in downstream waters.

Blowing in the wind
In some areas of the country, like west Texas, water may play next to no role in exposures to hormone-laced feedlot wastes, according to Philip Smith of Texas Tech University in Lubbock. In the arid and oft-windy West, his team finds, dust can ferry substantial quantities of livestock hormones through the air —  probably together with traces of the wastes that had carried these veterinary pharmaceuticals out of the cow.

For whatever reason, winds in his region often kick up around 5 to 6 p.m. At the meeting, Smith showed photos taken about a half-hour apart of the same feedlot building. In one, the structure was clearly visible and you could read signs on its side. In another, dust temporarily obscured visibility to where it looked like dense fog had rolled in.

Thirty mile per hour winds can scour the parched earth. But sometimes local winds hit 60 or 80 mph — “and I’m not exaggerating,” notes colleague George Cobb. This part of the country can also be quite dry, he adds. “You can go months without rain.”

One only has to encounter these regular dust blizzards in the vicinity of a CAFO to wonder what those airborne particles might be made from, Smith says. But rather than just speculate, he and Cobb set up high-volume dust samplers during dinner-hour periods in the spring and fall of this year to find out.

Their pilot-scale sampling turned up steroid-laced dust blowing off of 12 CAFOs (five measured around April and all dozen measured in the month leading up to Nov. 12). Values tended to be higher in spring, where peak concentrations of trenbolone metabolites, depending on the compound, ranged from 30 to 83 nanograms per gram of dust. In the fall, they tended to peak at between 5 and 29 ng/g.

To date, when people study excreted livestock hormones, “all of the emphasis has been on water and runoff,” Smith says. “And I understand that perspective, because I’ve lived in areas where rain, fog and dew are prevalent. But that’s not the case here.”

The obvious question is: What do these concentrations mean? Are they unhealthy — that is, unhealthier than breathing in dust generally? “We have no idea,” he says, “but we will be trying to understand if this is something we should be worried about. Like is it bioavailable? How quickly do these [pollutants] degrade? And how far do they travel?”

Adds Cobb, it’s also important to learn whether these drugs preferentially attach to certain size dust particles — like maybe the especially tiny motes that can be inhaled deeply into lungs. Indeed, work at Texas Tech and elsewhere has shown small dust particles can travel long distances, crossing continents and even oceans.

Citations

Sellin, M.K., . . . and A.S. Kolok. 2009. The Endocrine Activity of Beef Cattle Wastes: Do Growth-Promoting Steroids Make a Difference? Aquatic Toxicology (in press). DOI: 10.1016/j.aquatox.2009.10.004

Sellin, M.K., D.D. Snow, and A.S. Kolok. 2009. Reductions in Hepatic Vitellogenin and Estrogen Receptor Alpha Expression by Sediments from an Agriculturally Impacted Waterway.Aquatic Toxicology 92(May):221. DOI: 10.1016/j.aquatox.2009.02.004
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