Vanadium is a trace metal found in many earth materials, including petroleum and coal. It is emitted as particulate matter when these materials are burned, and can also be released as accidental, or “fugitive,” emissions during mining, extraction and processing. Natural sources of vanadium emissions include volcanic eruptions and the weathering of rocks.

The researchers synthesized published data and provided a quantitative summary of the global biogeochemical cycle of vanadium (V), including both human-derived and natural fluxes.

Through mining of V ores (130 × 10⁹ g V/y) and extraction and combustion of fossil fuels (600 × 10⁹ g V/y), humans are the predominant force in the geochemical cycle of V at Earth’s surface. Human emissions of V to the atmosphere are now likely to exceed background emissions by as much as a factor of 1.7, and, presumably, we have altered the deposition of V from the atmosphere by a similar amount. Excessive V in air and water has potential, but poorly documented, consequences for human health.

Much of the atmospheric flux probably derives from emissions from the combustion of fossil fuels, but the magnitude of this flux depends on the type of fuel, with relatively low emissions from coal and higher contributions from heavy crude oils, tar sands bitumen, and petroleum coke. Increasing interest in petroleum derived from unconventional deposits is likely to lead to greater emissions of V to the atmosphere in the near future.

Our analysis further suggests that the flux of V in rivers has been incremented by about 15% from human activities. Overall, the budget of dissolved V in the oceans is remarkably well balanced—with about 40 × 10⁹ g V/y to 50 × 10⁹ g V/y inputs and outputs, and a mean residence time for dissolved V in seawater of about 130,000 y with respect to inputs from rivers.

—Schlesinger et al.

The health risks of exposure to airborne vanadium particles are not as well documented as those for other metallic airborne contaminants such as mercury or lead, but growing evidence suggests breathing vanadium-rich aerosols can impair respiratory functions and exacerbate conditions such as asthma and chronic obstructive pulmonary disease (COPD).

Oil and coke refineries are generally built in areas where residents don’t have the political or economic clout to fight back, Schlesinger noted. For example, one of North America’s largest coke refineries is on the southeast side of Chicago.

We’re still in the early phase of understanding the risks people living in these areas face, but I suspect we’ll see a growing focus on the issue as the use of heavy oils and petroleum coke continues to rise in coming years.

—lead author William H. Schlesinger, James B. Duke Professor Emeritus of Biogeochemistry at Duke’s Nicholas School of the Environment

Emily M. Klein, professor of earth sciences at Duke’s Nicholas School, and Avner Vengosh, professor of geochemistry and water quality at Duke’s Nicholas School, conducted the new study with Schlesinger.

Their paper is the first to quantify the amount of inputs to the global vanadium cycle coming from all sources, natural and human.

About 10 years ago, another team of researchers tried to do this but with much less data. “Our analysis builds on theirs by providing the first quantifiable numbers for the release of vanadium from unconventional heavy-petroleum fuels, and updating numbers for all other sources to put these human impacts into context. Seeing all these numbers together for the first time, the unescapable takeaway is that human impact on the vanadium cycle is greater than our well-publicized impacts on the movement of lead through the atmosphere or the release of mercury from coal.

—William Schlesinger

Resources

• William H. Schlesinger, Emily M. Klein, and Avner Vengosh (2017) “Global biogeochemical cycle of vanadium” PNAS doi: 10.1073/pnas.1715500114