Development of Tools to Improve Exposure Estimation for Use in Ecological Risk Assessment

Transcription

1 Development of Tools to Improve Exposure Estimtion for Use in Ecologicl Risk Assessment Regionl Risk Assessments Using ChemCAN Report to Environment Cnd CEMC Report No Prepred y: Ev Wester, Don Mcky, Jennifer Hurde Cndin Environmentl Modelling Centre Trent University Peterorough, Ontrio K9J 7B8 CANADA

2 Development of Tools to Improve Exposure Estimtion for Use in Ecologicl Risk Assessment Report to Environment Cnd Contrct No. K Report 2 Regionl Risk Assessments Using ChemCAN Septemer 30, 2003 Prepred y: Ev Wester, Don Mcky, Jennifer Hurde Cndin Environmentl Modelling Centre Trent University Peterorough, Ontrio K9J 7B8 EC Deprtmentl Representtives: Don Gutzmn Hed, Exposure Section Chemicl Evlution Division Existing Sustnces Brnch Andy Atkinson Hed, New Chemicls Evlution Section Chemicl Evlution Division New Sustnces Brnch Environment Cnd Plce Vincent Mssey, 14 th Floor Hull PQ K1A 0H3 EC Contrcting Authority: Roert Chenier Env. Protection Service Chemicl Evlution Division 351 St. Joseph Blvd 14 th Fl Hull PQ K1A 0H3

3 Tle of Contents: List of Tles nd Figures Executive Summry Introduction Bckground Study Ojectives The Role of Region-specific Environmentl Modelling Using ChemCAN Uncertinties Summry References Chemicl Selection nd Emission Rtes Regions Regionl Chemicl Fte Existing Sustnces New Sustnces Tles nd Figures: Tle 1: Selected chemicls nd their properties. Tle 2: Lndscpe prmeters with vlues common to ll regions of Cnd Tle 3: Lndscpe prmeters with vlues unique to ech region of Cnd Figure 1: Regions of Cnd s provided in the region dtse of the ChemCAN version 6.00 model. Figure 2: Reltive concentrtions in Newfoundlnd (solid r), Ontrio - mixed wood plin (htched r), nd Ssktchewn - northern (open r) for emissions scled to the re of the receiving medium. Appendix: Upgrdes to ChemCAN

4 EXECUTIVE SUMMARY In this report the regionlly-explicit, stedy-stte, ChemCAN model is used to illustrte region-toregion differences in chemicl fte leding to estimtes of regionl environmentl exposure. The differences in chemicl fte were investigted for set of four existing sustnces (enzo[]pyrene, chloroenzene, hexchloroenzene, nd chlordne) in three regions (Newfoundlnd, Ontrio - mixed wood plin, nd Ssktchewn - northern) for summer conditions. The utility of the ChemCAN model for new sustnces is discussed. Differences in environmentl concentrtions etween regions provide first estimte of regionl environmentl exposure.

5 1 INTRODUCTION 1.1 Bckground This report is the second in series of three reports prepred s prt of Contrct K Development of tools to improve exposure estimtion for use in ecologicl risk ssessment. In fulfilment of the second prt of the first milestone of the contrct, in this report the revised ChemCAN model will e used to illustrte the fte of selected new nd existing sustnces in Cnd on regionl sis. A report will e prepred to show how the ChemCAN model will e useful in the ltter stges of the screening level risk ssessment of sustnces. The revisions to the ChemCAN model re outlined in the Appendix t the end of this report. It hs een suggested tht multimedi mss lnce models such s TPL3 nd ChemCAN cn perform useful functions in the risk ssessment process (Mcky et l, 2003). Previously, upgrdes to the TPL3 model nd its potentil role in ssessing chemicl persistence in the environment were discussed (Wester et l, 2003). In this report the potentil contriution of ChemCAN to the exposure nd chemicl risk ssessment process is exmined. 1.2 Study Ojectives The ojective of this work ws stted in the contrct s follows. To illustrte how the improved cpilities of the newly upgrded ChemCAN model cn e used to ssess the chemicl fte of selected sustnces in Cnd on regionl sis. Cnd hs very diverse lndscpe nd treting ll regions s identicl cn give very misleding conclusions. A report will e developed demonstrting how useful the model will e in the ltter stges of the screening level risk ssessment of new nd existing sustnces. Cnd hs very diverse lndscpe nd treting ll regions s identicl hs the potentil to give misleding conclusions. Potentil differences in chemicl fte on regionl sis re estimted using ChemCAN in n illustrtive mode for selected sustnces. -1-

6 2 THE ROLE OF REGION-SPECIFIC ENVIRONMENTAL MODELLING For sustnces of environmentl concern, it is useful to improve on the generl pproximtions produced y using the EQC or EUSES stndrd environments. These stndrd environments provide common pltform for compring nd rnking of sustnces for persistence, or potentil for longrnge trnsport. As sustnces ecome the focus of greter efforts, models using lndscpe prmeters specific to n ctul loction provide etter estimtes of the concentrtions to e expected in tht region prior to estimting exposure to wildlife or humns residing in the region. The purpose of regionl modelling is to produce resonle estimtes of the concentrtions to which wildlife nd humns in region my e exposed using ctul or expected emission rtes. Oviously, ctul monitoring dt for sustnce re preferred where they exist nd estimtion methods should e used only where such dt do not exist. The role of regionl models is s n economicl id in directing monitoring progrms for existing sustnces nd to provide estimtes for new sustnces prior to commercil production nd relese. Regionl ssessments, which focus on estimting concentrtions in loction, require more input dt thn evlutive ssessments, which focus on rnking or compring sustnces. Specificlly, in regionl ssessment, ctul emissions re required while for evlutive ssessments, where persistence, or potentil for long-rnge trnsport re the key model outputs, stndrd emission rtes re sufficient. For this reson, chemicl prtitioning tendencies should e sought first through chemicl properties lone, nd then in n evlutive environment. Regionl environments should e seen s providing refinement of ny prtitioning estimte. Concentrtions in the individul environmentl medi re the key outcome of region-specific environmentl modelling efforts. The ChemCAN model contins dtse of regions of Cnd thus fcilitting this higher level of regionl discrimintion in the fte of sustnces cross the country. This model ws initilly descried in Mcky et l (1991) with upgrdes to version 6.00 descried in the Appendix to this -2-

7 report nd in Wester et l (2003). Wester et l (2003c) focussed on the wide rnge of lndscpe prmeter vlues required to descrie the regions of Cnd. They used the overll residence time of the chemicl in the region to show how lndscpe prmeters, individully nd collectively, impct regionl fte. 3 USING CHEMCAN 3.1 Chemicl Selection nd Emission Rtes Four chemicls of differing prtitioning properties for which dt re redily ville, nmely enzo[]pyrene (B[]p), chloroenzene (CB), hexchloroenzene (HCB) nd trns-chlordne, were selected for this study. Their properties re given in Tle 1. No temperture correction is pplied to the degrdtion hlf-lives y the ChemCAN model s there is lck of chemicl-specific dt. Where dt exist, degrdtion hlf-lives specific to the environment temperture should e used. An ppeling feture of models such s ChemCAN is their linerity with respect to emission. Provided the emission pttern, i.e., the proportion of sustnce emitted to ech environmentl medium, is known, the results cn e scled to simulte ctul emission rtes, or the emissions to ech medium cn e considered seprtely nd the results re dditive. For this study, to focus ttention on the region-to-region differences in chemicl fte, the emission pttern ws ssumed to e the sme in ech region. Emission rtes to ir were scled to the totl re of ech region to remove the ovious effect of region size. Emission rtes to wter nd soil were scled to the re of the wter nd soil respectively. Emission ptterns typicl for the sustnces were used. 3.2 Regions ChemCAN contins division of Cnd into 24 regions sed on the ecozones identified y Environment Cnd nd with considertion of the distriution of popultion nd industril ctivity, politicl oundries, dringe sins, nd climte. In defining regions it is necessry tht ech re -3-

8 e sufficiently homogeneous in ecologicl conditions such tht ssessments of chemicl fte cn e meningful. Figure 1 shows the regionl divisions of Cnd. Regions 1, 7 nd 14; Newfoundlnd, Ontrio - Mixed Wood Plin, nd Ssktchewn - Northern re used here to demonstrte the regionl nture of chemicl fte. The properties of these regions re given in Tles 2 nd 3. A detiled discussion of the methods used to identify the regionl properties is given in Wester et l (2003c). 3.3 Regionl Chemicl Fte Existing Sustnces A set of four existing sustnces re used to illustrte the regionl vrition in concentrtions s estimted y ChemCAN. Figure 2 shows the results for emissions scled to the reltive size of the receiving medium in ech region. The verge temperture of ech region during summer is used for these simultions to void the less relile su-zero pproximtions. Only the most likely receiving medi re simulted for ech sustnce. An emission of enzo[]pyrene to ir ws simulted for ech of the three regions in summer. Environmentl concentrtions, upon which exposure depends, vry etween the regions s shown in Figure 2. For exposure through inhltion, clerly twice s much B[]p cn e emitted into the ir in the Ssktchewn region s compred to the Ontrio region for the environment to experience the sme exposure. By mss, B[]p prtitions primrily to soil in ll three regions under the stedy-stte conditions in the ChemCAN model. The higher concentrtions in sediment re the result of smller volume. A similrity ws seen etween the frction of the region covered y lnd nd the mss frction of B[]p in the soil: Newfoundlnd 98.3% lnd, 98.4% in soil; Ontrio - mixed wood plin 68.0% lnd, 77.7% in soil; Ssktchewn - northern 89.3% lnd, 92.1% in soil. This suggested tht while the chemicl ws relesed to ir, ecuse it prtitions strongly to the soil, the frction of soil in the region is key fctor in determining the fte of B[]p. The trnsport into soil is enhnced in Ontrio - mixed wood plin nd Ssktchewn - northern, possily y the longer ir residence times -4-

9 in those regions. Exposure is estimted to e highest for sediment-dwelling orgnisms in northern Ssktchewn. When emitted to ir hexchloroenzene prtitions primrily to soil with smll frction in ir. The frction of HCB in soil is proportionl to the frction of lndmss present in ech region. The frction of HCB present in ir cn not e explined y the frction of lndmss lone. Other regionlly-specific lndscpe prmeters hve n influence on this result. The regionl temperture my e the lndscpe prmeter controlling the frction of HCB in ir. Trns-chlordne, pesticide, when relesed to soil, hs very strong tendency to remin there, i.e., less thn 2% prtition to the other primry medi in the ChemCAN model environments. With the emissions scled to the lndmss of ech region, the concentrtion of chlordne in the soils of the three regions in very similr. With similr mounts present in the sediment of ech region, the smller volume of sediment in Newfoundlnd gives much higher concentrtion. Most chloroenzene in southern Ontrio is emitted to ir, however, smll frction is lso emitted to wter nd soil (McLeod et l 1999). Therefore, ll three possiilities were exmined. When emitted to ir, on constnt per unit re sis, ChemCAN suggests tht northern Ssktchewn would e roughly three times more contminted thn Newfoundlnd. This, in turn, suggests much higher risk of exposure in northern Ssktchewn ssuming the sme reltive emissions - which re unlikely since Ontrio-mixed wood plin is more populted. When relesed to ir, CB follows the sme trend s B[]p relesed to ir with the frction of wter cover eing the controlling fctor for the sme resons. In generl, CB tends to remin in the receiving medium. Thus, the similr concentrtions in the wter nd sediment of the three regions for emissions to wter scled to the frction of wter cover present. The lower concentrtion in the soil in Ontrio - mixed wood plin when emissions re to soil scled to the frction of lndmss present is not explined y the lower lndmss frction. It my e due to the competing influence of the rin rte nd the ir residence time elevting the mounts nd thus concentrtions in oth Newfoundlnd nd Ssktchewn - northern. -5-

10 While n ttempt hs een mde to explin the differences seen in concentrtions etween the regions, these re not definitive. A more exhustive study would e required to verify tht the key lndscpe prmeters identified here for ech chemicl re correct. The purpose of the preceding discussion hs een to show tht the different regions cn e expected to hve different concentrtions of the sustnces. There is ovious merit in using region-specific lndscpe prmeter for regionl evlutions of sustnces New Sustnces In mnner similr to tht used ove for four existing sustnces, the ChemCAN model could e used to simulte the fte of new sustnce in region of Cnd, or other defined region. Using the new chemicl s properties nd n estimte of oth the emission pttern nd emission levels, concentrtions in the vrious environmentl medi could e clculted y the ChemCAN model. These concentrtions provide n estimte of levels to which wildlife nd humns in the regions my e exposed if the sustnce ws to e used in such wy s to e relesed into the environment s estimted. 4 UNCERTAINTIES The ChemCAN model clcultions were used y McLeod et l (2002) in the development of simpler lterntive to Monte Crlo determintions of model outcome uncertinty. Their study included detiled nlysis for the cse of enzo[]pyrene emitted to ir in single region, Ontriomixed wood plin. They were le to identify the chemicl, nd lndscpe prmeters which contriuted most to the overll uncertinty in the totl mss of enzo[]pyrene present in the region, ssuming stedy-stte is chieved. This provides templte of the procedure to e followed in ny regionlly-explicit evlution of chemicl fte. However, it is premture to generlize these results nd ny model outcome is expected to depend on ll input prmeters. The key contriuting input uncertinties re lso expected to e different in ech cse. We pln to exmine this in more detil in n upcoming puliction. -6-

11 5 SUMMARY Three sustnces hve een exmined here s n illustrtion of the process y which regionl differences cn e exmined. In risk ssessment it would e necessry to know the ctul emissions of existing sustnces or predicted emissions of new sustnces for ech region nd full sensitivity nd uncertinty nlysis should e undertken for ech region of interest. Gthering complete nd relile emission dt hs often proven prolemtic. However, s this report demonstrtes the environmentl concentrtions cn e expected to e different cross Cnd nd thus it is expected tht the exposure to humns nd wildlife will lso chnge with loction sed on the lndscpe prmeters of the region. Wheres generic evlutive environments provide useful preliminry chemicl ssessments, it should e pprecited tht region-to-region differences cn introduce sustntil chnges in fte, concentrtion, nd exposure. As result, if evlutive ssessments yield concentrtions within n order of mgnitude of levels of concern there is incentive to conduct region-specific ssessments. To complete such n ssessment requires detiled determintion of the uncertinty of ech model outcome nd its primry sources. Clerly, regionl models provide n inexpensive tool for directing monitoring progrms for existing sustnces nd to provide estimtes for new sustnces prior to commercil production nd relese. -7-

12 REFERENCES Agriculture nd Agri-Food Cnd, Soil Lndscpes of Cnd, Version 2.1. Ntionl Soil DtBse, Agriculture nd Agri-Food Cnd. Brnthouse, L, Fv, J., Humphreys, K., Hunt, R., Lison, L., Noesen, S., Norris, G., Owens, J., Todd, J., Vigon, B., Weitz, K., Young, J., Life-Cycle Impct Assessment: the Stte-of-the-Art. Report of the SETAC Life-Cycle Assessment (LCA) Impct Assessment Workgroup. Society of Environmentl Toxicology nd Chemistry (SETAC). Beyer, A., Wni, F., Gouin, T., Mcky, D., Mtthies, M Selecting Internlly Consistent Physicl-Chemicl Properties of Orgnic Compounds. Environ. Toxicol. Chem. 21: Byers, A.R.; Bshour, W. (Eds.), Reder s Digest Atls of Cnd. Reder s Digest Assocition (Cnd), Toronto, Ontrio. Cole, J.G., Mcky, D., Correltion of Environmentl Prtitioning Properties of Orgnic Compounds: The Three Soluilities Approch. Environ. Toxicol. Chem. 19, Cousins, I. T., Mcky, D Strtegies for including vegettion comprtments in multimedi models. Chemosphere. 44: Environment Cnd, Cndin Climte Normls Fisheries nd Environment Cnd, Hydrologicl Atls of Cnd. Cndin Ntionl Committee for the Interntionl Hydrologicl Decde. Finizio, A., Mcky, D., Bidlemn, T., Hrner T., Octnol-Air Prtition Coefficient s Predictor of Prtitioning of Semi-Voltile Orgnic Chemicls to Aerosols. Atmos. Environ. 31, Hmmond Atls of Cnd nd the World, Mplewood, N.J. Mcky, D Multimedi Environmentl Models: The Fugcity Approch - Second Edition, Lewis Pulishers, Boc Rton, pp Mcky, D., Pterson, S., Tm, D.D., Assessments of Chemicl Fte in Cnd: Continued Development of Fugcity Model. A report prepred for Helth nd Welfre Cnd. Mcky, D., Pterson, S. nd Shiu, W.Y., Generic Models for Evluting the Regionl Fte of Chemicls. Chemosphere. 24,

13 Mcky, D., Shiu, W.Y., M, K.C Physicl-Chemicl Properties nd Environmentl Fte nd Degrdtion Hndook. CRCnetBASE 2000, Chpmn & Hll CRCnetBASE, CRC Press LLC., Boc Rton, FL. (CD-ROM.) Mcky, D., Hurde, J., Wester, E The role of QSARs nd fte models in chemicl hzrd nd risk ssessment. Proceedings of the QSAR 2002 Conference, Ottw My Qunt. Struct.-Act. Relt. - Com. Sci. 22: McLeod, M., Mcky, D., An ssessment of the environmentl fte nd exposure of enzene nd the chloroenzenes in Cnd. Chemosphere 38: McLeod, M., Frser, A., Mcky, D Evluting nd Expressing the Propgtion of Uncertinty in Chemicl Fte nd Bioccumultion Models. Environ. Toxicol. Chem. 21: Todd, J.A., Currn, M.A., Stremlined Life-Cycle Assessment: A Finl Report from the SETAC North Americ Stremlined LCA Workgroup. Society of Environmentl Toxicology nd Chemistry (SETAC). Wni, F., Mcky, D., Hoff, J.T., The importnce of snow scvenging of PCB nd PAH vpors. Environ. Sci. Technol. 33: Wester, E., Hurde, J., Mcky, D., Swnston, L., Hodge, A Development of Tools to Improve Exposure Estimtion for Use in Ecologicl Risk Assessment: Report 1 - The TPL3 Upgrde. Report to Environment Cnd Wester, E., Hurde, J., Mcky, D Upgrding the ChemCAN Model: Version 4.95 to CEMC Report No. 2003xx. Trent University, Peterorough, Ontrio. (In press.) Wester, E., Mcky, D., DiGurdo, A., Kne, D., Woodfine, D. 2003c. Regionl Differences in Chemicl Fte Model Outcome. Chemosphere. (Accepted for puliction, August 2003.) -9-

14 Tle 1: Properties of selected chemicls. B[]p CB HCB trns-chlordne Molr mss, g/mol Dt Temperture, C Prtitioning properties Wter Soluility, g/m 3 Vpor Pressure, P Log K OW x x Rection hlf-lives, hours Air Wter Soil Sediment Enthlpies of Phse Chnge (used to modify prtition coefficients) kj/mol K OW K AW K OA c c Prtitioning to Aerosols: K P (:g/m 3 ) = 1.5 x K OA Mcky et l (2000) Beyer et l (2002) c Estimted where no vlues were ville.

15 Tle 2: Lndscpe prmeters with vlues common to ll regions of Cnd s given in the ChemCAN 6.00 dtse. Height Air 2 km Density, kg/m 3 Depth Freshwter 20 m Aerosols 2400 Soil 10 cm Prticles in wter 2400 Sediment 1 cm Fish 1000 Costl Wter 100 m Soil solids 2400 Sediment solids 2400 Costl wter width 1 km Plnts 900 Volume Frction Prticles in Air Prticles in Wter Biot in Wter 2 x x Trnsport Velocities, m/h U1 ir side ir-wter MTC 3 U2 wter side ir-wter MTC 0.03 Fish Lipid Frction U4 erosol dry deposition velocity 10.8 Vegettion Lipid Frction 0.01 d U5 soil ir phse diffusion MTC 0.04 Soil Air Frction 0.2 U6 soil wter phse diffusion MTC 10-5 Wter Frction 0.3 U7 soil ir oundry lyer MTC 1 Solids Frction 0.5 U8 sediment wter diffusion MTC 10-4 Sediment Wter Frction 0.7 U9 sediment deposition velocity 4.6 x 10-8 Solids Frction 0.3 U10 sediment resuspension velocity 1.1 x 10-8 Orgnic Cron Frction, g/g Wter Prticulte 0.2 U 13 sediment uril 3.5 x 10-8 Soil Solids 0.02 U14 ir trnsfer to higher ltitudes 0.01 Sediment Solids 0.04 Rin Scvenging Rtio (erosols) 2 x 10 5 Fitted solids-wter prtition coefficient for groundwter sorption ttenution 500 Snow Scvenging Rtio (erosols) Costl Residence Time 4.17 dys Notes: Costl wter depth is zero for inlnd regions. Sediment uril (U13) is clculted s U9 - U10. Dt Sources: Mcky et l 1992 Mcky 2001 (p. 178) c selected from Wni et l 1999 d Cousins nd Mcky c

16 Tle 3: Lndscpe prmeters with vlues unique to ech region of Cnd s given in the ChemCAN 6.00 dtse. Newfoundlnd Ontrio - Mixed Wood Plin Totl Are (km 2 ) Wter Are (%) Cost Length (km) Ssktchewn - Northern Rin Rte, U3 (m/h) Averge Temperture (/C) Winter Summer Residence Time (dys) Air Wter Ref., e c c c c d Costl Wter 4.17 N/A N/A Notes: U11, 12, nd 15 the soil wter runoff, soil solids runoff, nd leching to groundwter re lso regionlly dependent prmeters ut re clculted from the rin rte s given in equtions elow. U11 = U3 x 0.4; U12 = U3 x ; U15 = U3 x 0.1 Dt Sources: Agriculture nd Agri-Food Cnd 1995 Hmmond Atls 1986 c Environment Cnd 1991 d Fisheries nd Environment Cnd 1978 e Byers et l 1995

17 km 7 Figure 1: Regions of Cnd s provided in the region dtse of the ChemCAN version 6.00 model.

18 B[]p Emitted to Air CB Emitted to Air Air Wter Soil Sediment Air Wter Soil Sediment HCB Emitted to Air CB Emitted to Wter Air Wter Soil Sediment Air Wter Soil Sediment Chlordne Emitted to Soil CB Emitted to Soil Air Wter Soil Sediment Air Wter Soil Sediment Figure 2: Reltive concentrtions in Newfoundlnd (solid r), Ontrio - mixed wood plin (htched r), nd Ssktchewn - northern (open r) for emissions scled to the re of the receiving medium.

19 APPENDIX: UPGRADES TO CHEMCAN The ChemCAN model ws developed for Helth Cnd in 1991 nd the first version to e mde puliclly ville ws version 4.95, relesed in My of Since then severl improvements hve een mde, oth in the equtions used nd in the softwre. Incresed trnsprency hs een chieved to enle the user to inspect the code nd identify key ssumptions. Dt inputs hve een chnged to llow for K OA, the octnol-ir prtition coefficient, to e used directly. Equtions nd outcomes relting to prtitioning to erosols nd deposition processes from the tmosphere hve een improved. Su-freezing conditions re now ddressed. Some improvements hve een mde in regionl lndscpe prmeters such s frction of wter cover, rin rte, nd verge tempertures. Temperture corrections re included for prtitioning ut not for degrdtion rte constnts for which there is little ville dt. As noted y Brnthouse et l (1998) nd Todd nd Currn (1999) it is importnt to mke models trnsprent to the user. Thus, to improve the understnding of how this stedy-stte model works to mimic the physicl relity, ChemCAN is now fully trnsprent, i.e., ll the equtions cn e viewed y the user. This is of criticl importnce s users ecome more knowledgele out the processes involved in the environmentl fte of sustnces nd more models ecome ville. With trnsprent model, ny nd every discrepncy etween the outcomes of one model nd nother or etween monitoring dt nd model outcome, cn e trced to its origin. The cuse of difference my e either model input or the eqution used to descrie process. When equtions nd vlues re not visile to the user, it is not possile to identify nd thus understnd the origin of difference. Chemicl properties re the first set of model inputs required. Type 1 chemicls re orgnic sustnces with pprecile vpour pressures nd wter soluilities. For these sustnces, greter flexiility hs een introduced for defining their prtitioning properties. As suggested y Cole nd Mcky (2000), ny two of the three prtition coefficients, octnol-wter (K OW ), octnol-ir (K OA ), nd ir-wter (K AW ) my e used with the third eing clculted from the other two. Prtitioning to erosols is now treted using either of two simple correltions with K OA s descried y Finizio et l. (1997). In previous versions of ChemCAN, wet nd dry erosol deposition were descried y

20 single prmeter for convenience nd simplicity. This vlue ws not intuitive nd did not llow for differentition etween rin nd snow. Now, wet erosol deposition with either rin or snow is hndled seprtely from dry deposition. At su-freezing tempertures there is reduced evportion nd wter runoff to mimic ice formtion. Snow cover is not treted y the model. The second set of input prmeters required y ChemCAN is the regionl lndscpe prmeters. All lndscpe prmeters re now ccessile to the user. The complete dtse of 24 regions of Cnd hs een retined. Other regions cn e dded. If Cndin region is modified, the originl set of prmeters remins nd the modified region is considered to e new region. This llows greter flexiility without the risk of mis-understndings etween users who my hve modified region either y intention or y ccident. The finl set of input prmeters required is the emissions nd inflow concentrtions. For these lyout more consistent with other CEMC models is now used. Since the relese of version 4.95 in 1996, our collective experience with model development hs resulted in chnges in interfce lyout nd terminology. The terminology used nd the lyout of informtion re criticl to effective communiction of model requirements, cpilities, nd results. This version of ChemCAN hs updted lyout nd terminology to e more consistent with other CEMC models. Improved input error checking mkes the softwre more stle. These re detiled in Wester et l (2003). Model results etween the two versions of the model re consistent. For Type 2 nd 3 chemicls, results re identicl.