Denka requests weaker chloroprene classification, but EPA won't budge

LaPLACE, La.—The U.S. Environmental Protection Agency has rejected another request by Denka Performance Elastomer L.L.C. asking the EPA to revamp its 2010 assessment of chloroprene, a chemical essential for neoprene production at the southern Louisiana plant.

In its 2010 Integrated Risk Information System Toxicological Review of Chloroprene, the EPA determined that the chemical is "likely to be carcinogenic to humans" and that it has been found in levels much higher than 0.2 micrograms per cubic meter, the EPA's "inhalation unit risk" benchmark for chloroprene, for several miles around the Denka facility.

Denka filed a request for correction (RFC) with the EPA July 15, 2021—its second attempt to weaken the EPA's assessment of the chemical.

"The materials submitted by Denka present new analyses and express views on how these products should be used in the risk assessment of chloroprene, but the Denka submission does not identify errors in the 2010 IRIS assessment," Maureen Gwinn, principal deputy administrator of the U.S. EPA, stated in a March 14 rejection letter to Denka. "After careful consideration, EPA has concluded that the underlying information and conclusions presented in the 2010 IRIS (review) ... and its supporting materials are consistent with EPA's Information Quality Guidelines.

"Hence, the RFC is denied."

Denka first disputed the EPA's characterization of chloroprene in a June 2017 RFC, saying the "unrealistically conservative estimate" may overstate the cancer risk for human chloroprene exposure by up to "two orders of magnitude," or about 130 times higher than where Denka believed the cancer risk should have been categorized.

Denka's initial RFC was rejected by the EPA in 2018 on the basis that Denka "had not presented sufficient new information developed since 2010 to justify the request."

The company argued that it attempted to do just that in its second request via a 2018-20 study, funded by Denka and known as the Ramboll 2021 PBPK model.

This study was conducted by Hopewell, Va.-based Ramboll Environ and concluded in 2021.

Denka said this model for risk-based assessment uses more advanced methods for evaluating potential effects on human health.

"The model suggests the relative level of health risk from chloroprene to be as much as 130 times lower than the IRIS assessment, which would be consistent with the average to below-average levels of cancer incidences recorded near the DPE facility," Denka stated in a March 1 letter to the EPA declaring its intent to file its most recent RFC.

Denka, which reiterated it is not in violation of any EPA standards, said it will "determine its next steps" after the EPA rejected the company's second RFC.

"Denka Performance Elastomer is disappointed in the U.S. Environmental Protection Agency's decision to refuse a more accurate health model for chloroprene in its risk estimation assessment of the chemical," Jim Harris, a spokesman for Denka, told Rubber News May 4. "The updated model provided to the agency by reputable and recognized experts in the scientific community uses the best available technology and was identified by EPA as a preferable method to the agency's previous analysis. Conclusions in the updated model are consistent with other independent studies on the chemical."

Gwinn called the EPA's 2010 IRIS study "accurate, reliable, and unbiased" and claimed that it does, in fact, use the "best science available."

"While the EPA recognizes the need to update scientific research as it becomes available, the RFC process does not require that EPA evaluate the potential impact of new scientific information on an existing IRIS toxicity value," she stated in her March 14 letter.

Denka noted that it already has taken steps to reduce the chloroprene levels around the plant in St. John the Baptist Parish, which has about 42,500 residents.

The company claims it has spent upward of $35 million to reduce the pollutant levels around the facility "by as much as 85 percent" over 2014 levels.

"The safety of our employees and community is our top priority and DPE is committed to using sound science that is protective of human health," Harris said. "To honor that commitment, the company has spent over $35 million on projects designed to reduce its emissions, and years developing the best available scientific model of chloroprene metabolism.

"While EPA indicated in its March letter (that) the agency is not required to incorporate more accurate science simply because it is available, DPE will continue to strongly encourage the use of the highest quality science in any future developments.

"Denka will be reviewing EPA's decision with its science team, including any underlying documents that EPA makes available, to determine its next steps."

Neoprene production continues at the plant in spite of the EPA's rejection of Denka's request to weaken the organization's characterization of chloroprene.

The high levels of chloroprene—recorded at 24.3 micrograms per cubic meter in January 2022 (about 120 times the 0.2 micrograms per cubic meter benchmark set by the EPA in 2010)—were first tabulated in the area around Denka's plant in 2011 as part of the EPA's National Air Toxics Assessment, according to the EPA.

While the 0.2 micrograms per cubic meter mark has been established by the EPA, the benchmark has not been used by the federal organization to set any actual rules, Denka told Rubber News.

"DPE is not in violation of any EPA standards," Harris said.

Denka can submit a request for reconsideration within 90 days of the EPA's March 14 rejection of the RFC.

Denka's neoprene production facility is located in the Pontchartrain Works industrial park.

The plant was built and operated by DuPont in the 1960s. Since then, a portion of the facility has produced neoprene by synthesizing and polymerizing chloroprene.

Neoprene, invented by DuPont in 1931, is a synthetic rubber used to make medical and military equipment, clothing and consumer products like cell phone cases. It also is used as a base resin in adhesives, electrical insulation and coatings.

Chloroprene is a colorless liquid with an ether-like odor, and is on the Hazardous Substance List because it is regulated by OSHA and cited as such by numerous federal agencies, including the EPA.

Denka Performance Elastomer, a joint venture between Tokyo-based Denka Co. Ltd. (70 percent) and Mitsui Co. Ltd. (30 percent, also out of Tokyo) acquired the neoprene production facility Nov. 1, 2015, from DuPont and established headquarters in LaPlace.

Denka employs about 230 people at the facility, representing the second-largest private employer in St. John the Baptist Parish.

According to Denka, Ramboll's conclusions support the revamping of the inhalation unit risk (IUR) threshold and an updated risk model for chloroprene—the same risk model Denka has been trying to get the EPA to budge on since its original IRIS in 2010.

"The information supports the conclusion that chloroprene is less carcinogenic to humans than to the female B6C3F1 mouse," Denka said in its July 15, 2021, RFC. "Based on discussions with EPA's Office of Research and Development, this RFC does not address all risk factors required for the determination of the IUR; however, considering the PBPK model results alone, it appears that the 2010 IUR may overstate human risk by more than two orders of magnitude."

As well, Denka asserts the Louisiana Tumor Registry reports that "incidents of cancer are at or below statewide averages for cancers of potential concern."

This information is disputed by the EPA and the residents of St. John the Baptist Parish, who filed a civil rights complaint against the Louisiana Department of Environmental Quality on April 6, alleging that the LDEQ "discriminates on the basis of race in violation of Title VI of the Civil Rights Act of 1964."

About 60 percent of St. John residents are Black.

"Despite DPE's belief that the facility's chloroprene emissions do not pose a risk to the community, DPE reduced its chloroprene emissions ... under a voluntary agreement with Louisiana Department of Environmental Quality and because of DPE's commitment to excellence in environmental stewardship," Denka stated.

"Even so, we recognize that there continue to be concerns about the cancer risk posed by chloroprene, and DPE is committed to addressing those concerns based on the best available scientific information."

Denka added that it expected the EPA to use information on IURs more in line with similar chemicals, such as vinyl chloride, 1,3-butadiene and benzene.

The EPA and Denka also had differing opinions as to the aforementioned use of mice as test subjects in the 2010 IRIS study.

"EPA ... established the inhalation unit risk for chloroprene based on the default assumption that human beings are as sensitive to chloroprene exposure as the most sensitive species in the laboratory, namely the female mouse," Denka said.

The EPA acknowledged in its March 14 rejection of Denka's second RFC that the difference between mouse and human metabolism would have provided additional metrics.

However, the EPA countered that the Ramboll analysis does not take into account cancers outside the lung, such as liver, gastrointestinal or other immune system cancers—malignant tumors that also occurred in mice bioassays.

"Ramboll's analyses assert that the risk of human lung cancer is minimal compared to mice, making the current IRIS IUR an overestimate of risk," the EPA writes. "EPA has not undertaken the technical analysis to reach a conclusion on concurrence with this assertion.

"But, if accepted at face value, the lung only accounts for about 40 percent of the total cancer incidence in mice. Since the existing Ramboll model cannot be used to address risk in other tissues, the same standard inter-species scaling as used in the 2010 IRIS Toxicological Review would need to be applied to estimate cancer risk for those other tissues."

Overall, the EPA concluded that even if the Ramboll PBPK model was "applied to the extent possible," the total estimated cancer risk would be reduced by no more than 50 percent.

"This factor of two difference is well within the generally accepted uncertainty for cancer risk estimation," according to the EPA. "Hence, EPA concludes that the 2010 Toxicological Review did not overestimate the human cancer risk by multiple orders of magnitude, as contended by Denka and Ramboll."

Denka said in 2017 that the only ambient standard for IURs applicable to chloroprene is a Louisiana eight-hour benchmark of 857 micrograms per cubic meter.

Denka itself wrote that achieving the EPA threshold of 0.2 micrograms per cubic meter is not possible.

"DPE's state-of-the-art emission reduction projects technologically cannot achieve this extraordinarily low ambient target," the company said. "Moreover, as a result of the erroneous IUR, (Denka) has suffered severe reputational damages. Public statements by EPA have led the public to expect the attainment of this extraordinarily low value.

"Citizen activists picket the facility and local schools wearing red T-shirts emblazoned with 'Only 0.2 will do.'

"For DPE, this matter is at a crisis point," the company wrote in its initial RFC in 2017.

Five years later, and especially for the residents of St. John the Baptist Parish, that may be the one characterization on which both sides agree.