The Food and Drug Administration found recently that samples of a feed by-product from dozens of corn-ethanol plants were contaminated with antibiotics. With that news, producing vehicle fuel from grain is looking not only like a wasteful and inefficient process, but also like a danger to human health.

Growing corn is a leading cause of soil erosion as well as water depletion and pollution. Corn ethanol plants further stress our water supplies by consuming four gallons of water for every gallon of fuel produced.

Now to the list of ethanol’s environmental insults we can add pharmaceutical pollution.

There’s nothing inherently wrong with getting help from biological processes to meet industrial needs. But when colossal volumes of product and enormous profits are at stake, as they are in the alternative-fuel industry, biological methods can backfire disastrously.

To survive economically, ethanol plants depend on sales of distillers grains, solid material left over from corn fermentation. Distillers grains are a nutritious, high-protein livestock feed. But they can be laced with multiple antibiotics, the FDA and University of Minnesota scientists have found.

Addition of antibiotics is one of several methods ethanol manufacturers use to control bacterial contamination. Bacteria interfere with the work of yeast cultures that convert sugars to ethanol. Antibiotics can increase ethanol output by 1 to 5 percent, according to Ethanol Producer magazine.

That sounds small, but that extra efficiency could boost profits by many millions of dollars as national production is scaled up from its current 9 billion gallons per year.

The discovery of antibiotics in distillers grains has raised concern that ethanol plants could breed and disperse drug-resistant bacteria, and that those bugs could share their genes with bacterial species that cause human diseases. Sampling by university and industry researchers has turned up antibiotic-resistant bacteria in the processing streams of ethanol plants.

This case of pharmaceutical contamination comes on top of a half-century of over-prescribing antibiotics for medical and veterinary use, along with routine feeding of the drugs to healthy livestock to promote growth. Nature’s predictable response: bacterial populations that can no longer be killed by drugs that were once used to treat them. Now, of 90,000 Americans who die of bacterial infections each year, more than 60,000 are killed by such drug-resistant types, according to the Centers for Disease Control.

The ethanol industry says that one widely used drug, virginiamycin, doesn’t show up in meat produced with distillers grains, so we need not worry about the food supply. But such assurances take the narrowest possible view of the threat.

Johns Hopkins University researchers argued in 2008 that public health officials have also taken a narrow approach to antibiotic resistance, thinking clinically “rather than ecologically in terms of reservoirs of resistance genes that may flow across the microbial ecosystem.” Use of the drugs in agriculture is more widespread than in medicine, and, they contend, creates excellent conditions for the spread of resistant organisms.

In fact, it’s already happening, with germs borne via manure, air, groundwater, soil, flies and irrigation water.

The Johns Hopkins review concluded that overuse of antibiotics in agriculture “has compromised the efficacy of most antimicrobials used in the United States and throughout the world.”

Distillers grains are set to move beyond the feedlot, having been tested as fertilizer on farms, lawns and gardens, and as feed in fish and shrimp farming. The pet food industry also is starting to use distillers grains, and we don’t know what evolutionary mischief might start going on in the feces of dogs, which harbor an especially rich range of bacterial species.

Meanwhile, methods being developed to manufacture new biofuels also depend on biological processes. If and when fuels from algae or cellulose are taken to the billions-of-gallons scale, vast new quantities of antibiotics could be deployed.

Ethanol can be manufactured without using antibiotics — just ask the liquor distillers — so all such drugs should be banned from biofuel production.

In fact, ethanol’s drug problem is just the latest of many reasons to impose a moratorium on production of fuels from grains. If industry cannot supply sufficient quantities of alternative fuels without risking an even deeper medical crisis, it might just be another sign that our thirst for vehicle fuel has outgrown all ecological limits.