Aspen paper making has long been a problem for many farmers, particularly in parts of the West.
The industry has been battling with a new class of fungicides that the U.S. Food and Drug Administration has said are more effective and less toxic than previously used.
Now, a new study says the two new fungicides, aspen paper and a class of other common fungicides called pyridoxine, are also potentially more dangerous.
Both chemicals have been linked to tumors, liver damage, miscarriages and birth defects in rats, mice and other mammals.
“The new pyrids are potentially very dangerous and need to be carefully monitored,” said Robert Hahn, an associate professor of toxicology at the University of Pennsylvania who was not involved in the research.
“We need to monitor the use of the other fungicides.”
Aspen and pyridine are not the only common fungicide used in papermaking.
The World Health Organization has said there is a “possible link” between the use and developmental problems in humans.
Aspen is a common insecticide and has been found to cause reproductive problems in some animals.
In the 1980s, a large study in Germany showed that it was linked to birth defects.
But the study was stopped by the European Food Safety Authority.
Some experts say that in the 21st century, as the new papermakers come under increasing scrutiny from regulators, they should be treated more closely.
“If you use them in the right circumstances, they’re probably safe,” said Paul Hays, a professor of environmental toxicology and pesticide sciences at the California Institute of Technology.
“But I think we need to make sure that there’s a proper level of monitoring and control.”
Hays has published a series of studies in peer-reviewed journals on the health effects of papermaking chemicals.
Hays said he and his colleagues found no association between aspen and reproductive problems.
Hahn said it’s also unclear whether the effects of the new fungicide on rats were similar to the effects on humans.
“They were all different,” he said.
“I think we still have a lot to learn about the human side.”
The new papermaker chemicals, which are also used in a class called boron nitrate, are designed to kill certain types of bacteria that cause toxic blooms in fruits and vegetables.
The chemicals have a half-life of about six months, so they can be used safely in paper making for decades.
But they are not approved by the FDA, and it’s unclear how long they will remain in use.
“This is not a pesticide that is used to control pests,” Hays told The Associated Press in an interview.
“It’s just a way to kill bacteria.”
The study was published online in the journal Science Advances.
The FDA has not commented on the new findings.
The company that markets the papermakers used in the study, Papercraft Products, said it is working with regulators to review the safety of the chemicals.
“Papercraft Products has made significant improvements in paper-making efficiency and yields over the last decade,” the company said in a statement.
“These improvements have resulted in a substantial decline in paper loss from use.”
The company said the company was conducting a voluntary safety assessment of the papermaking materials.
It said the chemicals have also been shown to be less toxic to the environment than previous versions.