Implications of Granite Counter Top Construction and Uses

D. Bernhardt1 CHP; A Gerhart2; L. Kincaid3 CIH Granite is a term for natural stones such as pegmatites, migmatites, gneisses, and schists used for residential countertops, and other indoor trim. Some granites are anatectic alaskites similar to the Rossing uranium deposits. Uranium and thorium concentrations range from those similar to normal soil (roughly 0.04 Bq/g, 1 pCi/g) to over 15 Bq/g of uranium; with lower concentrations of thorium. Regulations in the European Community and Canada exclude elevated stone from these markets. In the U.S. radiation screening limits by some companies (0.2 to 0.3 μGy/hr) and the supply have resulted in limiting the installations of elevated stone to a fraction of the total market being installed in homes, but elevated slabs are still installed. The primary health risk to workers is due to airborne dust, from sawing and milling granite slabs which contain free silica, heavy metals, and uranium and thorium. Depending on work-place controls, the primary risk may be silicosis, but there are also potential risks from other toxin materials (e.g., beryllium) and radiation exposure. Potential health risks to consumers using granite are primarily due to the increased concentration of indoor radon and external gamma dose from the uranium and thorium in the granite. The presentation will provide assessments for workers and estimates of the elevated indoor radon and gamma dose for consumers. Assessments using controlled chambers, modeling, and indoor measurements indicate that some granite slabs similar to the screening levels can increase the indoor 222Rn concentration by about 40 Bq/m3 (1 pCi/l), with higher concentrations for more elevated slabs. Granite counter tops with elevated gamma exposure rates of about 1 μGy/hr result in potential gamma doses that are a significant fraction of 1mSv/yr, a basic criterion for the general population. 1 Consultant Radiation Protection, PO Box 571768, Salt Lake City, 84157, daveb077@msn.com; 2 Web Master, Oklahoma City, OK, webmaster@solidsurface alliance.org; 3 Industrial Hygiene Services, 20255 Glasgow Dr., Saratoga, CA, 95070, nanosafety@gmail.com Presented Works in Progress Health Physics Society, July 13, 2009

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Executive Summary• Granite is a common term for rock slabs used

for kitchen countertops & other features in homes.

• The objective is to evaluate radiation doses to workers in fabrication shops and consumers in homes with granite.

• About 5 % of granite sold in the U.S. has elevated concentrations (several times natural background) of NORM, containing uranium and thorium.

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• Due to limited worker protection in fabrication shops, workers fabricating granite with elevated NORM are exposed to significant radiation doses:– Inhalation: Potential doses of several Sv/yr,

doses much greater than the radiation worker dose limits of 10 CFR 20. These are not radiation workers.

– Inadvertent ingestion doses and external gamma doses of tenths of a mSv/yr.

• Potential radiation doses to home owners where granite with elevated NORM is installed include:– External gamma; 0.6 mSv/year– Radon: 34 Bq/m³; EDE dose 1.3 mSv/yr

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Objective• Briefly describe the composition of material

which is commonly called granite.• Identify radiation exposure pathways

associated with fabrication and use of granite.

• Identify some of work performed to assess potential radiation exposures.

• Assess potential radiation exposure to workers in fabrication shops.

• Assess potential exposures to consumers.

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Description of Granite– Granite is used as a term for natural stones

such as pegmatites, migmatites, gneisses, and schists

– Some granites are anatectic alaskites similar to the Rossing uranium deposits

– U-238 and Th-232 concentrations range from those similar to normal soil (0.04 Bq/g, 1 pCi/g) to over 15 Bq/g (400 pCi/g) of uranium; with lower concentrations of thorium. Nominal low level concentrations of U and Th in granite are similar to soil (NCRP 2009).

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Focus of Presentation• Presentation focuses on elevated granite:

– Workers in fabrication shops.– Home owners with granite counter tops and

other granite uses.• Most mining/quarrying takes place outside

of U.S. and this is outside the focus of this presentation.

• Environmental contamination around fabrication shops and disposal of waste is outside the focus of this presentation.

Characteristics of Selected ElevatedGranite Stones

- Table 1 gives information to characterizeselected granite stones containing concentrationsof NORM significantly above natural soils.

- Granite slabs elevated in U and Th representonly about 5 % of the U.S. market;

But, U and Th concentrations in some ofthese slabs are 10 to more than 100 timesnormal natural background concentrations.

- Concentrations can vary extensively throughout

some granite slabs; hence results for the samestone by investigators may vary.

- Exposure rates were measured with surveyinstruments (generally NaI or CsI detectors) ofdifferent makes and no effort has been made tonormalize them.

- There are numerous papers in the literatureproviding information on various granite stones:- However, only limited information was

incorporated in this summary table becausenames were not provided for the stones,

papers focused on radon flux emissions (didnot give concentrations of U or Th) or thepaper focused on stones with concentrationssimilar to natural soil (e.g., U-238 37 Bq/g(1 pCi/g).

- Al-Saleh (2007) provides information on 19granite stones Saudi, India, et al., with thehighest concentration of uranium being 314Bq/kg for Azoles Bahea from Brazil.

- Salas (2006) provides information on manygranite stones from Brazil, but identifiesthem by a classification and does notidentify them by the trade name. Thehighest U or Th concentrations Salas identifies are for stones ranging from about370-600 Bq/kg (10-15 pCi/g).

- EHE 2008 provides extensive data ongranite stones; however:- Numeric values are difficult to interpret- It is difficult to correlate the different

sets of data in this report.

- The data set in Table 1 focuses on data availablefor and used in the assessments for thispresentation.

Table 1. Characteristics of Selected Granite Stones (Rn flux from one side, total take times two)

Stone Name

Reference Country Origin Concentration (Bq/kg) U-238 Th-232

Exp Rate uR/hr

Rn Flux Bq/m2-sec

Juparana Bordeaux EHE 2008 Brazil 1200 0.012

Juparana Bordeaux Kitto 2009 Brazil 910-3550 70-850

Juparana Bordeaux This paper Brazil 20-300+

Juparana Bordeaux ARS Lab 2008 Brazil 2590-16700 810-4800

Juparana Bordeaux Steck 2009 5700 520 65 0.049

Carioca Gold This paper About less than 40

Nile Gold EHE 2008 1500 0.022

Four Seasons Kitto 2009 Brazil 2100 380 14-28

Four Seasons This paper Brazil Ave 37; max over 600

Four Seasons Brodhead2009

Brazil 0.03 &0.06

Niagara Gold This paper <200-600

Baltic Brown This paper Ave 45

Natural Bkgd Ave NCRP 2009 37 (1 pCi/g) 37 5-10 0.02

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Experimental Assessments • Inhalable air sampling, by CIH, in shop

cutting and milling elevated granite; analyzed for uranium by ICP-MS.

• Radon and External Gamma Surveys in homes.

• Laboratory analysis of granite samples.• “Radon Chamber” assessment of release

of radon from slabs:– Measured air exchange rate of chamber– Continuously measured radon in chamber

Dose to WorkersFabrication Shop

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Workers in Fabrication Shops• Shops often have poor dust control — fans

blowing dust out the door• They may provide respirators (dust mask

or half-face), but workers often don’t use them and there are seldom fitness tests.

• Essentially no personal hygiene safety programs; i.e., preventing smoking, chewing, or drinking in the shop.

• There are often no lunch rooms, and minimal hand washing.

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Airborne Dust in Granite Shop

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Granite Shop, Worker with Respirator; OSHA Was Present

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Assessment Program re Exposure of Fabrication Shop Workers

- CIH performed sampling for inhalable airborne particulates during shop fabrication of slabs of elevated granite.

- Assessed inadvertent ingestion dose re dirty hand scenarios.

- Assessed external gamma dose using MicroShield Computer program.

- Based on elevated granite with NORM concentrations orders of magnitude above natural background for soil (37 Bq/kg or 1 pCi/g).

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Granite Used for Worker Doses

Granite Material

Gamma Exp μR/hr

U Conc. Granite BqBq/kg/kg

Airborne U Conc. mg/m³

Giallo Antico ~50 0.0075

Four Seasons & J. Bordeaux

20-280 Up to 16,700

0.19-0.32

Airborne Dust; Mass Conc.

3,000 Bq/kg (80 pCi/g)

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Parameters Used for Shop Worker Dose Assessment

Parameter Value UnitsU Concentration Gamma Dose 3700 Bq/kg

U Concentration Ingestion Dose 1750 Bq/kg

Inhalation Rate; 2000-hr/yr 1.2 m³/hr

Inadvertent Ingestion; 250 day-yr 200 mg/day

Th-232 Concentration 38 % of U

U-235 Concentration Natural U Ratio

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Airborne Sampling for U

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Fabrication Shop Worker Dose Calculation Procedures

• Inhalation and Ingestion Doses: – US EPA Federal Guidance Report 11 for

dosimetry re NRC 10 CFR 20– ICRP Publication 68 for updated dosimetry– Performed dual dose calculations for both

long-term (S&Y) and intermediate (M/W) retention

• External Gamma Dose from Granite Slabs; MicroShield Version 5

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Summary Shop Workers Potential Radiation Exposure

Exposure Mode mSv/yr Exposure Duration

Inhalation Airborne Dust; 10 CFR 20 (Y), 0.24 mg/m³

2,400 2000-hr Yr

Inhalation Airborne Dust; 10 CFR 20, 0.24 mg/m³

120 5% 100-hr

Inadvertent Ingestion of Dust, Based on 10 CFR Dosimetry

0.30 2000-hr Yr

External Gamma Dose 0.53 1500-hr Yr

Inhalation EDE Dose for Granite Shop Workers; Re U Air Sampling

DosimetryFor Calculations

0.32 mg U/m³Sv/Yr

0.24 mg U/m³ Sv/Yr

0.0075 mg U/m³Sv/Yr

0.24 mg/m³, 5% of YrSv/Yr

ICRP 68 Updated Dosimetry

Longterm Retention (S) 0.43 0.32 0.010 0.016

Intermediate Retention (M) 0.65 0.49 0.015 0.025

NRC 10 CFR 20 using FG #11

Longterm Retention (Y) 3.1 2.3 0.073 0.12

Intermediate Retention (W) 3.2 2.4 0.074 0.12

NRC 10 CFR 20 Regulations Radiation Workers 0.05 Sv/yr; General Pop 0.001 Sv/yr

Doses based on Inhalable area sampling by CIH; samples processed for uranium. Doses based on Th-232 being 38% of U andall decay products being in secular equilibrium.

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Inhalation Dose Shop Workers; Contributions from U-238, U-235, and Th-232 Decay Chains; 0.24 mg/m³ Sample

U-238 U-235 Th-232Dosimetry Calculations Sv/yr Sv/yr Sv/yrICRP Publication 68Long-term Retention (S) 0.18 0.023 0.12Intermediate Retent (M) 0.27 0.08 0.14

10 CFR 20 re Fed G #11Long-term Retention (Y) 1.1 0.20 1.1Intermediate Retent (W) 0.71 0.27 1.4

Limitations of Assessment• Preliminary Assessment of Potential Dose from

Airborne Radioactivity• “Area” Air Sampling• Sampled Inhalable Particulates—no explicit

particle size information• Short-term, 30-min sample period; limited due to

resources• Dosimetry:

– Fed G #11, 10 CFR 20; used 1 µm EAD– ICRP Pub 68, 5 µm EADProbably conservative due to sampling procedure

Potential Exposure Home Owners

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Home Owners Radiation Exp• Radon exposure due to Rn exhalation

from granite– Hard to distinguish from other sources– Other sources; soil, building materials, water,

natural gas, ambient air• External Gamma from U & Th and decay

products (K-40 generally limited significance) in granite

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Parameters Home Owner Exp

• Home 2000 ft², 186 m²• Granite area; 90ft², 8.4 m²• Air change rate of new energy efficient

home; 0.1 air changes per hour• Gamma exposure; 3700 Bq/kg U-238,

U-235 natural abundance, Th-232 38% of U-238

• Rn flux; measured 0.045 Bq/m²-sec; calculated from Rn Room 0.051 Bq/m²-sec

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Kitchen Countertop Layout

The following slide shows the hypothetical kitchen countertop layout for the gamma dose calculation. The countertop is composed of:- 3 Sections 2 by 5 ft, 1.25 inch thick- 2 Backsplashes 1.5 by 5 ft

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Home Dose Calc. Procedures• External Gamma:

– MicroShield Version 5; 3 2x5 ft slabs with 2 backsplash slabs

– 4 hours/day, 350 days per year exposure• Indoor Radon:

– Concentration based on equilibrium with air change rate (Cember 2009)

– 40% equilibrium, 70% occupancy, 10 mSv/WLM (NCRP 2009)

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Potential Doses to Home Owners

Doses Based on Four Seasons Granite, relatively elevated—42 uR/hr material

• Rn Supplemental to Background Concentration:– Rn Concentration: 34 Bq/m³, 0.9 pCi/l; @ 0.1 ACH– EDE Dose 1.3 mSv/year; at 70% occupancy.

• External Gamma Dose– Occupancy 4 hr/day 0.63 mSv/yr

• Total EDE Dose 1.9 mSv/yr; compared to criterion of 1 mSv/yr for general population.

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Rn & Gamma Doses In Homes

The doses can be scaled linearly for different parameters.

- Rn concentration & dose scale linearly with amount of granite, home size, and home ACH. However, the denoted amount of granite is reasonable for this size home.

- Gamma dose scales linearly with source concentration and exposure time; 4 hr/dy

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Summary and ConclusionsAssessments were performed for granite material with

elevated concentrations of NORM.• Potential doses for fabrication shop workers exceed the

regulations for radiation workers by more than a factor of 10. These are not designated radiation workers.– The high potential doses for workers are due to the combination

of elevated granite slabs and the indication of undesirable worker health and safety practices.

• Potential doses for home owners, due to radon and external gamma exceed the general population criterion of 1 mSv/yr.

• Need more extensive investigations to improve estimates of doses

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Reduction of ExposuresPotential radiation exposures in shops and

homes can be reduced by excluding highly elevated granite materials; e.g., limit slabs to less than about 20 µR/hr (net above background). Consider European Stds.h

- Implement improved health and safety in fabrication shops:- Respiratory protection (silica & rad)- Improve personal hygiene H&S

Supporting Information

References Al-Saleh (2007), Al-Saleh, F.S., Al-Berzan, B., Measurements of Natural Radioactivity in Some Kinds of marble and Granite Used in Riyadh Region, J. Nuclear and Radiation Physics, 2/1:25-36, 2007. ARS (2008), ARS International Lab, Port Allen, Louisiana, report of results for granite samples, 5/22/08. Brodhead (2009), William Brodhead, WPB Enterprises, wpb-radon.com, personal communication to Al Gerhart, 3/2009. Cember (2009), H. Cember, T.E. Johnson, Health Physics, Mc Graw Hill, Fourth Edition, 2009. EC (1999), European Commission, Directorate General Environmental Nuclear Safety and Civil Protection, Radiological Protection Principles Concerning the Natural Radioactivity of Building Materials, Radiation Protection 112, 1999. EHE (2008), Environmental Health & Engineering, Inc., Assessing Exposure to Radon and Radiation from Granite Countertops, Needham, MA, 11/21/2008. EPA(1988), Environmental Protection Agency Federal Guidance Report 11, EPA 520/1-88, 1988. ICRP (1994) Dose Coefficients for Intakes of Radionuclides by Workers. ICRP Publication 68. Annals of the ICRP 24(4). Elsevier Science Ltd., Oxford. Kitto (2009) Kitto, M.E. New York, Department of Health, Personal communication of data to D.E. Bernhardt, email 6/09/09. Kitto (2009a) Kitto, M.E., Haines, D.K., and Arauso, H.D., Emanation of Radon from Household Granite, Health Physics, 96/4: 477-482 (2009). NCRP (2009) National Council on Radiation Protection and Measurements. Ionizing Radiation Exposure of the Population of the United States, NCRP Report No. 160, 2009. Salas (2006) Salas, H.T., Nalini, H.A., Jr, and Mendes, J.C., Radioactivity Dosage Evaluation of Brazilian Ornamental Granitic Rocks Based on Chemical Data, with Mineralogical and Lithological Characterization, Environ Geol 49: 520-526, 10/2007. Steck (2008) Steck, Daniel, St. Johns University, Collegeville, MN, personal communication to D.E. Bernhardt, L. Kincaid, and A. Gerhart, 5/18/09.