More than 20 Missouri hog farms have reported an increase in emergency manure releases since US pork producer Smithfield Foods took them over in 2006, an environmental advocacy group says, citing equipment failures and improper maintenance that raise concerns about the impact on air and water quality.

The group, Socially Responsible Agriculture Project (SRAP), reviewed 30 years of Missouri Department of Natural Resources (DNR) records on 21 hog farms now owned by Smithfield, the nation's top pork company, which bought them in 2006 from Premium Standard Farms (PSF), reported Reuters.

Citing the state data, the group found that more than 4.6 million gallons of manure had been released into emergency containment structures or spilled into waterways in the past 15 years - an increase of 70% from the previous 15 years during PSF's ownership.

State regulators verified SRAP's data, but said the vast majority of the releases from the Smithfield operations were contained on site and never reached nearby waterways.

The causes of the manure releases include clogged pipes, equipment failure and lack of proper maintenance, according to the records contained in the report, which DNR verified are accurate.

Smithfield said it had yet to review the report and was proud of its environmental record. It questioned the group's analysis and said the figures for the volume of manure releases "seems inaccurately high."

The company said that its number of violations had fallen because of improvements to its manure management.

“We are proud of our environmental compliance record in the state in recent years,” said Jim Monroe, the company’s vice president of corporate affairs.

The number of site visits by DNR inspectors fell 49% over the same period, and the number of violations from the state fell 94%, according to the data. Missouri is the seventh-largest hog state, according to US Department of Agriculture (USDA) data.

Scott Dye, research and reports specialist at SRAP and author of the report, said the DNR has not done enough to address the releases. “We’re seeing the same type of spills, caused by the same things,” he said.

Brian Quinn, DNR’s information officer, said the state routinely inspects emergency containment structures and investigates all complaints and incidents, though not all result in site visits.

"Releases to secondary containment are not violations, because there is no discharge of wastewater to a location where it is reasonably certain to enter waters of the state,” he said.

Communities near large-scale livestock farms have long complained of poor air and water quality. The American Public Health Association in 2019 called for a moratorium on new construction of such facilities because of their threat to public health.

Regulation of animal confinements has prompted debate in Missouri between environmental groups, lawmakers and industry. In 2019, state lawmakers passed a law nullifying county health ordinances that imposed stricter regulations.