Importance of Considering the Framework …

1 Importance of Considering theFramework principles in RiskAssessment for Metals1 CHARLES A. MENZIE*Exponent, Alexandria, VirginiaLINDA M. ZICCARDIYVETTE W. LOWNEYE xponent, Boulder, ColoradoANNE FAIRBROTHERSCOTT S. SHOCKJOYCE S. TSUJIE xponent, Bellevue, WashingtonDIEM HAMAIDEBORAH PROCTORE xponent, Irvine, CaliforniaELIZABETH HENRYSTEAVE H. SUExponent, New York, New YorkMICHAEL W. KIERSKIMARGARET E. MCARDLEE xponent, Maynard, MassachusettsLISA J. YOSTE xponent, St. Paul, MinnesotaThe recent EPA Framework for Metals Risk Assessmentprovides the opportunity for contextual risk assessment forsites impacted by metals (such as the depicted Dauntless Minein Colorado).In 2007, three documents were published that emphasizedimportant considerations when evaluating exposure to andpotential health and environmental effects of metals in theenvironment.

2 The Metals Environmental Risk AssessmentGuidance(MERAG)projectwaslaunc hedbytheInternationalCouncil of Mining and Metals and Eurometraux, withregulatory endorsement provided by the UK Department forEnvironmentalFoodandRuralAffairs(DEFR A).Theguidanceand associated fact sheets were developed to providescientific and regulatory guidance on the most advancedscientific concepts for metals (1). The guidance documenthighlighted the Importance of Considering background,essentiality, speciation, mobility, and bioavailability whenconsidering the potential adverse health effects of metals. Italso addressed issues related to bioaccumulation and bio-magnification. A related document focused on how theseissues should be considered specifically for human healthrisk characterization (2).Also in 2007, the Environmental Protection Agency(EPA) published theFramework for Metals Risk assessment (3).

3 The Framework is based on a set of principles that areconsistent with the scientific considerations set forth in theMERAG guidance and are special attributes of metals. Thefive Framework principles are1. Metals are naturally occurring constituents in theenvironment and vary in concentrations across geo-graphic All environmental media have naturally occurringmixtures of metals, and metals often are introducedinto the environment as Somemetalsareessentialformaintainingprop erhealthof humans, animals, plants, and The environmental chemistry of metals strongly influ-ences their fate and effects on human and The toxicokinetics and toxicodynamics of metals de-pend on the metal, the form of the metal or metalcompound, and the organism s ability to regulate and/or store the principles have been increasingly recognized asimportant for addressing exposure to and risk from metalsin the environment.

4 The publications cited above provide abroad technical and regulatory foundation for incorporatingthe principles into metals risk assessments. Our experiencewith metals risk assessments indicates that some principlesare especially important for some metals and less importantfor others, and thus, case-specific information is paper provides our view of the relative Importance ofthe Framework principles for exposure and risk assessmentof particular metals and metalloids. The ratings of relevant1 Editor s Note: To our delight atES&T, we have started to receiveFeatures and Viewpoints by independent author(s) coincidentallyoverlapping both in topic and review schedule. Within days of thispaper s acceptance another specifically concerning selenium in theenvironment was accepted. The choice was thus made to presentboth manuscripts in the same issue (November 15, 2009;43[22]).

5 Readers of this piece by Menzie et al. are therefore encouraged toread that by Luoma and Presser (DOI ).LINDA ZICCARDIE nviron. Sci. ,43,8478 848284789 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 43, NO. 22, 2009 American Chemical SocietyPublished on Web 08/31/2009importance presented in Table 1 reflect the authors experi-encewithbothhumanhealthandecologi calriskassessmentsfor metals associated with mining and manufacturingoperations, products, and hazardous waste sites, particularlyin North America, but also in other countries. We havedeveloped a thorough understanding of the many factorsthatinfluencemetalspecies( ,valencestates),metalforms( , inorganic and organic), and metal states (phases) ( ,in solution, or bound to dissolved organic matter orparticulates), and the resulting bioavailability of such chemi-cal species.

6 Table 1 incorporates our knowledge that certainformsofmetalsaremoretoxicthanothe rs,andthatregulatorytoxicity values are developed for forms of metals that mayor may not represent the forms present in the Framework relative Importance ofthe individual principles for metals most commonly en-countered in site-specific risk assessments is summarized metalloids such as Sb and As that share properties ofboth metals and nonmetals, we also consider application ofthe principles to organometallics such as methyl mercury,organoarsenic, and organoselenium where relevant, becausethese chemicals can be important in a risk assessmentcontext. The information summarized for the metals andmetalloids(hereaftercollectivelyrefer redtoas metals )listedin Table 1 reflects the cumulative knowledge and riskassessment experience of the authors.

7 We considered the 23 metals and metalloids of interest as identified in theFramework, and then selected the chemical species includedin Table 1 based on our collective expertise and metals thatare known risk drivers . In what follows, our intent as metalsassessmentpractitionerswasnottopro videacomprehensivereview on how each principle influences each metal, butrather, to focus on metals of greatest interest to the riskassessment community and for which our experience hasshown that one or more principles are especially is well established ( ,4-6) that con-centrations of metals in native rocks and soils vary consider-ably across geographic areas. Table 1 indicates that naturaloccurrencebecomesanincreasinglyim portantconsiderationwhen risk-based limits approach or fall below the naturalbackground. This can occur because exposure assumptionsused to derive the risk-based values, and the actual factorsthatdetermineexposure,areinconsis tent( ,seediscussionof bioavailability under Principle 4), or because the risk-based concentrations are based on estimates oftheoreticalriskextrapolated from toxicity observed at high doses, ,itisimportantto consider regional variations and that plant and animalpopulations are shaped, at least in part, by local conditions,including soil and sediment mineralogy (7).

8 We identified the consideration of natural occurrence ashighly important for human health and/or ecological riskassessments for Al, As, Ba, Be, Cr(III), Fe, Pb, and Se. Al andAs are discussed further, as s soil screening guidance (8) recognized that Al, thethird-most abundant element in the Earth s crust, is oftenidentified as a chemical of concern in ecological riskassessments because of the conservative nature of thescreening benchmarks and toxicity reference values (TRVs)that are based on toxicity tests using Al in solution. Relyingon TRVs derived from toxicity studies using soluble formscanresultinhazardquotients(HQs)from food-webmodelingthat indicate risks ( , HQs>1) for Al concentrations thatTABLE Importance of Metals principles in Human Health and Ecological Risk AssessmentaaNotes: L, low, never or rarely a consideration; M, moderate, sometimes a consideration; H, high, often a consideration;RfD, reference dose; hh, human health; eco, 43, NO.

9 22, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY98479are below natural background. While Al toxicity is associatedwith soluble Al, soil and sediment analytical chemistrymethodsmeasuretotalAl,including naturalAl,mostofwhichis bound in insoluble mineral complexes such as alumino-silicates which are not bioavailable (8). Based on theseconsiderations,EPA(8)nowrecommendst hatAlbeidentifiedas a chemical of concern only for sites with soil pH< ,because as pH decreases below this level, Al becomesincreasingly soluble, bioavailable, and example of a health-based screening level that fallsbelow natural background is provided by As. EPA screeninglevels for As in soil, based on cancer risk, are and (note that all soil concentrations are in dry weight)for residential and industrial exposure, respectively. Naturalbackground As concentrations in soils range from 1 to>20 mg/kg, and even higher in naturally mineralized areas(4).

10 Setting health-based criteria below the natural back-ground is a dilemma for As and has resulted in target risksat the upper end of the risk management range, and in theuse of state, regional, or local background concentrations inlieu of more stringent health-based criteria. Exposures viaenvironmental media may also be small relative to normalbackground exposures, because of the ubiquitous presenceof inorganic As in the diet and in drinking water. As a result,exposure to inorganic As from incidental soil ingestion isgenerally lower than intake from background dietary sourcesuntilsoilconcentrationsexceed100m g/kg(9).Thus,althoughcancer risk assessments may predict elevated excess risksassociated with As in soil, comparison to background dietaryexposures helps place such risks in perspective with risks associated with mixtures of metalsin the environment depend on the degree to which one metalinfluences either exposure to or the effects of another.