Industrial food production has enlisted many innovative, albeit controversial, tools in recent years -- broad-spectrum pesticides and genetically modified organisms, for example. But, as concerned experts point out, large-scale crop and livestock producers haven't tossed out all of their old tools just yet.

"Arsenic still enjoys extensive use in U.S. agricultural activities," said Konstantinos Makris, an environmental health expert at the Cyprus International Institute for Environmental and Public Health in association with Harvard School of Public Health.

As The Huffington Post reported earlier this month, recent studies suggest that potentially harmful levels of the known carcinogen -- also a suspected hormone disruptor -- have infiltrated fruit juices and rice products, in addition to its known presence in some sources of drinking water.

The contamination likely results from a combination of trace amounts of naturally-occurring arsenic in soil and water, as well as historic and current human uses of the chemical element.

American farmers relied heavily on pesticides containing arsenic in the late 19th and early 20th centuries. While most of these arsenic-based pesticides have since been banned in the U.S., residues still haunt the soil today. And one arsenical compound, MSMA, continues to be legally applied to crops.

MSMA use may be on the rise thanks in part to the industry's new friends. Proliferating resistance of pigweed to Roundup brand weedkiller, which has been used widely on crops genetically engineered to resist the broad-spectrum herbicide, has forced some farmers to revert to arsenic to rid their fields of the weed.

"We keep going back to the future," said Sandra Steingraber, a biologist and author with expertise in toxic chemicals. "Now we're going all the way back to beginning of the 20th century to dig up some of these things we had buried long ago."

Also remaining legal in the U.S. is the more recent practice of spurring growth and fending off disease in chickens and turkeys with arsenic-laced feed. While drugmaker Pfizer suspended sale last year of the most popular arsenic-based drug in the U.S., 3-nitro, better known as roxarsone, the pharmaceutical giant continues to manufacture and export the feed to countries that might then export meat back to the U.S., said Michael Hansen, senior scientist with Consumers Union. But more worrisome than the potential trace amounts in meat, according to many experts, is what results from the popular use of dried poultry waste as a fertilizer.

"The process of drying and pelletizing poultry manure concentrates the arsenic, so the end product has far higher concentrations than the starting manure levels have -- which are already very high," said Joshua Hamilton, senior scientist at the Marine Biological Laboratory in Woods Hole, Mass.

Last month, shortly after Consumer Reports published findings of measurable levels of arsenic in rice, a group of Arkansas rice farmers filed a lawsuit against Tyson and other poultry producers, arguing that contaminated fertilizer has threatened their livelihood.

"The elevated arsenic found in the rice supply has led to a drop in the market price," Scott Powell, a lawyer representing the farmers, told The Huffington Post.

Today, U.S. rice is widely grown in the same south-central soil that once produced cotton -- a crop historically doused with arsenical pesticides. On top of the lingering arsenic residue, rice growers often add fertilizer made from poultry litter.

"We're still reviewing the lawsuit, but will say it appears to be an example of creative lawyers trying to use frivolous litigation to extract money from companies that have done nothing wrong," Tyson spokesman Gary Mickelson said in a statement. "We will vigorously defend ourselves. None of our chickens are given feed additives containing arsenic."

Pfizer told The Huffington Post that U.S. sales of roxarsone remain suspended "pending the on-going evaluation of relevant scientific data regarding the use of this product in animals."

A second arsenic-containing poultry drug continues to be legally marketed in the U.S. by Pfizer. Histostat, better known as nitarsone, is the only product approved by the FDA for the prevention of a potentially deadly condition in turkeys and chicken called blackhead, according to Pfizer, the world's largest drugmaker.

When asked about use of arsenic in turkeys, Mike Martin, spokesperson for Cargill, told HuffPost that the company's feed formulations are proprietary information and its components would not be disclosed.

Carla Daniels, a spokeswoman for the FDA, said that any action on arsenic-based drugs "will be taken into consideration" once the agency completes its study of arsenic in rice samples.

As for the remaining approved uses of MSMA, including on cotton fields and golf courses, Julia Valentine, an EPA spokeswoman, said that the agency "will launch a comprehensive evaluation to address new data to determine if any additional actions need to be taken."

The European Union banned roxarsone more than a decade ago, and never granted approval of organic arsenical herbicides such as MSMA.

Whether low levels of exposure to arsenic, such as the amounts most commonly found in food and water, are really hazardous to human health is not clear. Prior governmental risk assessments -- such as that done before the EPA set its current standard for drinking water -- have been based on cancer risks alone. The EPA is now developing a new risk assessment that includes both cancer and non-cancer, according to Valentine.

Recent experiments have “raised concerns” that the EPA drinking water standard of 10 parts of arsenic per billion parts of water “may not be sufficiently low to prevent adverse health effects in humans,” said Antonio Planchart, a biologist at North Carolina State University, whose research has linked exposures at this standard level in zebrafish to immune problems.

Other recent studies suggest an array of non-carcinogenic effects of arsenic exposure, such as the development of type 2 diabetes, heart disease and reproductive disorders. Many of these same health concerns have been increasingly tied to toxic chemicals, past and present, that can disrupt human hormones at very low doses.

"Legacy pollutants reflect stupid decisions made in the past," said Patty Lovera, assistant director of the non-profit Food and Water Watch, adding her hope that acknowledging the danger prior applications of arsenic poses today will help stop additional use in the future. "This is a teachable moment."