Study Asserts Granite Safety
The executive summary to Assessing Exposure to Radon and Radiation from Granite Countertops, released on Nov. 17 by Needham,-based Environmental Health & Engineering Inc.(EH&E), revealed that tests of different types of granite found that none exceeded thresholds set by government regulators.
“Natural stone is a minor contributor to concentrations of radon gas within homes,” noted the summary from the independent environmental-testing group, adding that “absorbed dose associated with radiation emissions for all of the slabs tested are well below health-protective guidelines.”
In the EH&E study, commissioned by the Marble Institute of America, scientists conducted more than 400 tests of 115 different varieties of granite countertops. The tested stones comprise approximately 80 percent of the annual U.S. market share for granite countertops, based on the most recent market data available, as well as several exotic stones.
EH&E tested 39 different slabs of 27 unique varieties of stone for full-slab tests. It also tested one to nine smaller samples of 24 of the stones from the full-slab selection, plus 88 other types of stone.
The study found that, in measuring annual radiation doses – assuming a close proximity to the stone – all the tested granite slabs failed to reach the 0.3 millisievert-per-year level set by the European Commission (EC); building materials under that limit are exempted from restrictions. (The United States doesn’t have a standard on this.)
The study also noted that the radiation-dose measurements assume that a person is 6” away and parallel to a full slab for four hours a day. Given that countertops are mounted horizontally and people are standing or sitting vertically at varying distances, the study also notes that actual radiation doses would be lower.
In radon testing, none of the slabs studied reached the 4 picocuries per liter (pCi L) predicted indoor radon-concentration level set by the federal Environmental Protection Agency (EPA) for mitigation. None of the 15 most-popular granites – including New Venetian Gold, Tropical Brown, Baltic Brown and Galaxy Black – even reached 0.02 pCi L in estimated radon concentration, which is half of the average outdoor level for the entire United States.
The testing of 213 smaller samples from 112 different types of stone paralleled the full-slab radon testing, with only a few rising above 0.02 pCi L in estimated radon concentration.
Several varieties did score above the norm for granites in radiation and radon testing by EH&E. Two of three Nile Gold and one of three Kashmir Gold slabs, along with a slab of Juperana Bordeaux, showed annual doses above 0.1 millisievert-per-year, but well under the EC’s 0.3 exemption level.
With radon, one Nile Gold slab showed a predicted indoor radon concentration above 0.2 pCi L, and the Juperana Bordeaux slab went above 0.1 pCi L. Of the 213 smaller samples, only two granites – Crema Bordeaux and Niagara Gold – had notable pCi L predicted concentrations, and both were well below the 0.1 level. All of these were still well below the 0.4 pCi L of average U.S. exposure outdoors and far away from the 4 pCi L mark where the EPA recommends mitigation.
The EH&E study noted that “a portion of stones used as countertops may contain limited areas that are enriched in radioactive materials relative to the remainder of the slab,” which it noted “in the order of less than 10 percent of the surface area.
“Detailed measurements of these enriched areas showed that they make a negligible contribution to potential doses of ionizing radiation.”
The study also noted that “the stones at the lower end of radon emissions were found to account for the vast majority of sales, and also exhibited little variability among slabs.
“The varieties of granite countertop that exhibited the greatest variability of radon flux among slabs represent a small fraction of the U.S. market.”
The new study is being submitted for peer review and publication in a scientific journal, a process that can take several months.