[5] He began his professional career in the Kansas City regional office of the U.S. Environmental Protection Agency in 1976 and has worked in numerous other scientific venues since then.

His reasoning was that current farming practice's dependence on fossil fuels needed to grow (including fertilizer and pesticides), harvest and ferment the corn is highly inefficient thermodynamically.

More recently, he has argued that a systematic approach and life cycle view be taken for climate-related actions, especially the need for scientifically credible risk assessments to inform the rapid expansion in the production of electric vehicles (EVs).

As such, extraction and processing of rare earth elements and metals, especially copper, cobalt, and lithium will be met with large environmental risks that must be factored into large-scale decisions during the transition away from fossil fuels.

in addition, Vallero argues that there are major challenges ahead on the disposal and recycling of EV batteries, which calls for a sound application of Design for the Environment (DfE) methods, especially disassembly, decontamination, and reuse.

In the book, "DUST: The inside Story of its Role in the September 11th Aftermath," [8] the late American scientist Paul Lioy credited Vallero with leading the way to sampling of hazardous air pollutants in and around Ground Zero following the 9/11 attacks on the World Trade Center.

In her book, "Hormone Deception",[11] Lindsey Berkson credits Vallero as among the first to apply exposure science to endocrine disruptors.