In a study analyzing 239 tissue samples from women diagnosed with breast cancer, scientists found 59 per cent had been exposed to the bovine leukemia virus (BLV) compared to 29 per cent of tissue samples from women without.

While stressing that the results do not prove that BLV infection causes breast cancer, lead researcher Gertrude Buehring, a professor of virology in the Division of Infectious Diseases and Vaccinology at UC Berkeley’s School of Public Health, said the presence of BLV in humans could be a significant indicator of risk.

“As many as 37 per cent of breast cancer cases may be attributable to BLV exposure,” the paper published in the online journal PLOS ONE said.

“This odds ratio is higher than any of the frequently publicized risk factors for breast cancer, such as obesity, alcohol consumption and use of post-menopausal hormones,” said Buehring.

Bovine leukemia virus infects dairy and beef cattle’s blood cells and mammary tissue. The retrovirus is easily transmitted among cattle primarily through infected blood and milk, but causes disease in fewer than five per cent of infected animals.

A 2007 U.S. Department of Agriculture survey of bulk milk tanks found that 100 per cent of dairy operations with large herds of 500 or more cows tested positive for BLV antibodies. Even dairy operations with small herds of fewer than 100 cows tested positive for BLV 83 per cent of the time.

The PLOS ONE paper noted that pasteurization renders the virus non-infectious, as does thorough cooking of beef. However, it said the virus, which is readily transmitted from cow to calf, may have become established in the human population before pasteurization became common in the 1920s and may still be entering the population through consumption of raw milk and undercooked beef.

It was believed until recently, based on studies done in the 1970s, that the BLV could not be transmitted to humans, but research published by Buehring last year overturned those results.

“The tests we have now are more sensitive, but it was still hard to overturn the established dogma that BLV was not transmissible to humans. As a result, there has been little incentive for the cattle industry to set up procedures to contain the spread of the virus,” she said.

There is precedence for viral origins of cancer. Hepatitis B virus is known to cause liver cancer, and the human papillomavirus can lead to cervical and anal cancers. Notably, vaccines have been developed for both those viruses and are routinely used to prevent the cancers associated with them.

Buehring emphasized that this study does not identify how the virus infected the breast tissue samples in their study. The virus could have come through the consumption of unpasteurized milk or undercooked meat, or it could have been transmitted by other humans.

As well, she said researchers must still confirm that infection with the virus happened before, not after, the breast cancer developed.

If BLV were substantiated as a risk factor for breast cancer, its detection in breast fluid cells or tissues might serve as a biomarker to identify women at higher risk for developing breast cancer.

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If this trajectory does not change, soil erosion, combined with the effects of climate change, will present a huge risk to global food security over the next century, warns a review paper authored by some of the top soil scientists in the country.

The paper singles out farming, which accelerates erosion and nutrient removal, as the primary game changer in soil health.

“Ever since humans developed agriculture, we’ve been transforming the planet and throwing the soil’s nutrient cycle out of balance,” said the paper’s lead author, Ronald Amundson, a professor of environmental science, policy and management at the University of California, Berkeley. “Because the changes happen slowly, often taking two to three generations to be noticed, people are not cognizant of the geological transformation taking place.”

In the paper published Thursday, May 7, in the journal Science, the authors say that soil erosion has accelerated since the industrial revolution, and we’re now entering a period when the ability of soil, “the living epidermis of the planet,” to support the growth of our food supply is plateauing.

A future ‘phosphorus cartel’

The authors identify the supply of fertilizer as one of the key threats to future soil security. Farmers use three essential nutrients to fertilize their crops: nitrogen, potassium and phosphorus. The paper credits the discovery of synthetic nitrogen production in the early 1900s to significantly increased crop yields that supported dramatic global population growth. Because the process of synthesizing nitrogen is energy intensive, its supply is dependent on fossil fuels.

Unlike nitrogen, potassium and phosphorus come from rocks and minerals, and the authors point out that those resources are not equitably distributed throughout the world. The United States has only one to two per cent of the world’s potassium reserves, and its reserves of phosphorus are expected to run out in about three decades.

“This could create political challenges and uncertainties,” said Amundson. “Morocco will soon be the largest source of phosphorus in the world, followed by China. These two countries will have a great deal of say in the distribution of those resources. Some people suggest we will see the emergence of a phosphorus cartel.”

Contributing to climate change

Another threat to soil security relates to its role as a mass reservoir for carbon. Left unperturbed, soil can hold on to its stores of carbon for hundreds to thousands of years. The most recent estimates suggest that up to 2,300 gigatons of carbon are stored in the top three metres of the Earth’s soil — more carbon than in all the world’s plants and atmosphere combined. One gigaton is equal to a billion tons.

But agriculture’s physical disruption of soil releases stored carbon into the atmosphere. Based on the area of land used for farming worldwide, 50 to 70 gigatons of carbon have been released into the atmosphere throughout human history, according to the paper. Proponents of sequestration, the long-term storage of carbon in soil, have argued that regaining this carbon will be a means to mitigate continuing fossil fuel emissions of the greenhouse gas.

“Carbon sequestration plans won’t make a dent in the amount of soil released by climate change,” countered Amundson. “The amount of carbon stored through sequestration would be tiny compared to the potential amount lost through global warming.”

Of particular concern is the large carbon stores in the soils in the planet’s polar regions. Researchers have found that temperatures are increasing at greater rates in the northern latitudes.

“Warming those areas is like filling your freezer with food, then pulling the plug and going on vacation,” said Amundson. “There will be a massive feast of bacteria feeding on the food as the plug gets pulled on the stored carbon in the frozen soil. Microbes are already starting the process of converting the carbon to CO2 and methane.”

Recycling soil nutrients

The authors recognize the human reliance on farming and note that most of the Earth’s most productive soils are already in agricultural production. However, they argue for better management of the soils we rely upon.

One proposal is to stop discarding nutrients captured in waste treatment facilities. Currently, phosphorus and potassium are concentrated into solid waste rather than cycled back into the soil. Additionally, more efficient management is needed to curtail losses from soil.

Excess nitrogen, for example, is considered a pollutant, with the run-off sapping oxygen from the nation’s waterways, suffocating aquatic life and creating dead zones in coastal margins.

Amundson noted that it did not take too long to get people to start separating paper, glass and aluminum cans from their trash for recycling.

“We should be able to do this with soil,” said Amundson. “The nutrients lost can be captured, recycled and put back into the ground. We have the skill set to recycle a lot of nutrients, but the ultimate deciders are the people who create policy. It’s not a scientific problem. It’s a societal problem.”

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