ENVIRONMENTAL AND ECOLOGICAL CHEMISTRY Vol. III Multimedia Fate and Transport of Organic Pollutants - Michael Matthies

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1 MULTIMEDIA FATE AND TRANSPORT OF ORGANIC POLLUTANTS Istitute of Evirometal Systems Research, Uiversity of Osabrück, Osabrück, Germay Keywords: evirometal fate, exposure, exposure assessmet, multimedia modelig, evirometal ad health risk, persistece, log rage evirometal trasport potetial, mass balace equatio, characteristic travel distace, evirometal trasport Cotets 1. Itroductio 2. Mass Balace Models 2.1. Level I: Equilibrium, No Iflow or Outflow, No Degradatio 2.2. Level II: Equilibrium, With Iflow, Outflow ad Degradatio, Steady State 2.3. Level IIdy: Equilibrium, With Iflow, Outflow ad Degradatio, Nosteady State 2.4. Level III: No Thermodyamic Equilibrium, Steady State 2.5. Level IV: No Thermodyamic Equilibrium, Nosteady State 3. Persistece ad Log-Rage Trasport Potetial 3.1. Persistece 3.2. Log-Rage Trasport Potetial 4. Assessmet of Models 5. Stregths ad Limitatios of Multimedia Models 6. Coclusios Glossary Bibliography Biographical Sketch Summary Evirometal trasport ad fate of orgaic chemical pollutats are described by a system of mass balace equatios which take ito accout the various physical, chemical ad biological exchage ad trasformatio processes i ad amog the evirometal compartmets. I multimedia models, the total eviromet is represeted as a set of spatially homogeeous boxes; oe box for each evirometal compartmet i which the chemical is assumed to be evely distributed. The umber, size, properties etc. of boxes, e.g. air, water ad soil, ca vary. Four levels of icreasig complexity are defied, depedig o the assumptios of thermodyamic equilibrium, steady ad osteady state or itermedia mass trasfer. Mass trasfer is modeled by advective trasport, e.g. depositio, ad diffusive exchage, e.g. volatilizatio. Multimedia models give isight ito the dyamics of evirometal trasport ad trasformatio of orgaic substaces idepedet of the emissio compartmet. They are used to determie the overall persistece ad log-rage trasport of orgaic pollutats ad to estimate the cocetratios/doses to which huma populatio or

2 ecosystems are or may be exposed. Multimedia models are a essetial part of risk assessmet of ew ad existig chemicals. 1. Itroductio Orgaic chemical substaces with differet physical ad chemical properties are emitted ito the eviromet due to the productio, maufacturig, use ad disposal of mamade chemical products. I order to uderstad ad quatify the fate ad distributio of orgaic pollutats i the eviromet, the mai dyamic processes of substace trasport ad trasformatio i ad betwee evirometal media eed to be described quatitatively. The eviromet is a spatially multi-structured, temporally chagig system made up of abiotic ad biotic compoets, which iteract via physical processes, such as air flow ad water flow, ad chemical processes, such as utriet cosumptio ad excretio. A commo, pragmatic procedure is to divide the system ito the evirometal compartmets air, water ad soil, which are composed of various amouts of gaseous, liquid, amorphous ad solid phases, ad which exchage substaces ad eergy. This divisio is based o the assumptio that evirometal systems ca be perceived as mixed phases. The trasport ad coversio processes such as advectio, diffusio ad degradatio, which lead to a temporal chage ad spatial distributio of substaces, take place both withi ad betwee phases. Evirometal media are frequetly uderstood as compartmets, i other words, as spatial sectios, volumes or boxes, which are homogeous withi themselves. Chemical substaces are itermixed withi them with egligible temporal delay. The assumptio upo which this approach is based, which stipulates that the itramedia itermixig occurs much more quickly tha itermedia exchage, however, has to be examied i each idividual case. The eviromet (or a sectio of it) is described as a multi-compartmet system (or multimedia system). The spatial complexity is reduced to a iterliked system of evirometal compartmets with distict geometric, physical, chemical ad biological properties, which iteract with the chemical substaces ad exchage them over the compartmet boudaries. Multimedia fate models are used for uderstadig ad quatifyig the distributio ad trasport of orgaic substaces betwee air, water, soil, ad other compartmets. They describe the relatios betwee emissios ad exposure cocetratios by solvig the mass balace equatios for these compartmets. I order to do so quatitative expressios for the mass trasfer ad degradatio process rates eed to be formulated. This chapter adopts the approach of Doald Mackay to multimedia mass balace models icludig defiitio of icreasig levels of complexity. 2. Mass Balace Models The basis for modelig the distributio of substaces i the eviromet is the priciple of mass coservatio, which states that the rate of chage of mass i a system equals the differece of iputs ad outputs. It is assumed that adverse ecotoxic effects that may occur oly egligibly affect the evirometal distributio, i other words, feedback betwee the effects, ad distributio ca be eglected. Followig the proposal of the pioeerig work of Doald Mackay, four levels I to IV of icreasig complexity are defied. These levels differ i their cosideratio of exchage ad degradatio

3 processes, as well as dyamics (see Table 1.). The most sigificat aspect is the differetiatio betwee steady state ad (thermodyamic) equilibrium. Steady state meas that everythig i the system remais costat. The substace masses of all d mi evirometal compartmets do ot chage with time, i.e. = 0 where i is the dt umber of mixed compartmets. (Thermodyamic) equilibrium is a special case whe the cocetratio ratios betwee all media (compartmets) are at their equilibrium partitio ratio. Level Thermodyamic I- ad Degradatio Itermedia Steady Output equilibrium Outflow mass trasfer state I Yes No No No Not applicable Equilibrium mass distributio II Yes Yes Yes No Yes Steady state iput/output balace IIdy Yes Yes Yes No No As II, but dyamic mass ad cocetratio course III No Yes Yes Yes Yes Steady state iput/output balace with itermedia exchage IV No Yes Yes Yes No As III, but dyamic mass ad cocetratio course Table 1: Mass balace models of icreasig complexity I Level I, a isolated system that exchages either mass or chemical potetial with its eviromet is described. The substace mass withi the system is merely distributed to the compartmets. This equilibrium state occurs immediately ad without delay, sice it is assumed that the system is i thermodyamic equilibrium at all times.

4 I Level II, the assumptio of thermodyamic equilibrium is retaied, but cotiual iflows ad outflows, as well as losses through degradatio, are additioally take ito accout. The origial Level II, which assumes steady state, was later exteded to the dyamic, osteady-state case of Level IIdy, which simulates the fate of cocetratios over the whole time scale. I Levels III ad IV, additioal iteral advective ad diffuse exchage processes, such as depositio, volatilizatio ad sedimetatio, are take ito accout. These processes lead to a temporal delay ad to a deviatio of ay state from the thermodyamic equilibrium, due to resistaces at the phase boudaries. Level III models look oly at steady state, while Level IV models deal with the geeral osteady-state solutio over the whole time-scale. I order to be able to compare the four levels with oe aother, Doald Mackay itroduced the Uit World cocept. The eviromet is divided ito the mai compartmets air, soil, surface water, ad sedimet. Volumes, boudary areas ad other evirometal properties are parameterized for either a global or regioal eviromet. EUSES (Europea System for the Evaluatio of Substaces) assumes area of 200 by 200 kilometers, which is divided ito 97 percet soil ad 3 percet fresh water. The height of atmospheric mixig layer is 1000 meters; depth of the water is 3 meters, that of soil is 10 cetimeters, ad that of sedimet 3 cetimeters. These lead to the volumes give i Figure 1. For simplificatio purposes, the three soils, cosidered i EUSES, were combied ito oe. Figure 1: Regioal multimedia distributio model with four compartmets; modified from EUSES the Europea Uio System for the Evaluatio of Substaces, Europea Chemicals Bureau, Ispra (1996) Mass balace models ca equivaletly be formulated by usig fugacity ad fugacity capacities. Fugacity correspods to the partial pressure i a compartmet ad ca be viewed as the escapig tedecy of a substace. The followig basic equatio applies C = f Z (1) where C is the cocetratio of a substace (here: mol m -3 ), f is the fugacity (Pa) ad Z is the fugacity capacity (mol m -3 Pa -1 )). I thermodyamic equilibrium the fugacities f ad f of two adjacet phases i ad j are equal. This leads to: i j ( ) ( ) C C = f Z f Z = Z Z = K (2) i j i i j j i j ij

5 The partitio coefficiet K ca therefore be expressed by equilibrium cocetratio ij ratio or the quotiet of the fugacity capacities. Differet fugacities i adjacet phases show that the system is ot i equilibrium. The fugacity cocept eables the differeces of the varyig model types Level I to IV to be show clearly (see Figures 2, 4 ad 5) Level I: Equilibrium, No Iflow or Outflow, No Degradatio With this level it is assumed that the whole substace amout i the system is ifiitely rapid distributed to all compartmets i accordace with the partitio coefficiets. The substace mass i the system remais costat, sice there are either iflows, outflows or degradatio. The result is the equilibrium distributio of a substace i a evaluative eviromet, as it would ted to adapt itself if exchage were uihibited. The compartmet of etry is uimportat, because redistributio is assumed to be istataeous. If the whole substace mass i the system m (kg) cosistig of compartmets with t the volumes V 1,.., V (m 3 ) is kow, the masses m,..., 1 m ad cocetratios C,..., 1 C eed to be determied. The followig serves as a mass balace equatio mt = C1 V1+ C2 V2 + + C V. (3) I (thermodyamic) equilibrium the followig applies: Ci / C1 = Ki 1, where i is from 1 to ad K 11 is 1. This leads to: m = C V + C K V + + C K V (4) t ( ) C m V K V K V (5) 1 = t From this the partitio coefficiets K ca be used to calculate all other cocetratios ij C i, ad the masses ca also be determied with the use of m = V C. (6) i i i The priciple is portrayed i Figure 2. Compartmets 1,2,..., are assumed to be commuicatig pipes or boxes. Uihibited exchage is possible betwee the boxes. All boxes are filled to the same height ( h ). The system is i equilibrium. Aalogously, a system of commuicatig pipes filled with water ca be imagied. The substace masses m i are represeted by the volumes i the pipes. The height h is the fugacity f ad, as the measure of the equilibrium state, is the same height i all pipes. The fugacity capacity Zi is represeted by width b. Accordig to Eq. (1), the areas from height h (= fugacity f ) multiplied by width b (= fugacity capacity Z i ) lead to cocetratios C. i The depths l i correspod to the compartmet volumes V. i

6 The oly substace properties, which are required for calculatio by Level I model, are the partitio coefficiets K ij betwee adjacet compartmets. Partitio coefficiet betwee air ad water, K AW, ca be computed from Hery's law costat H by dividig it by a factor R T, where R is the gas costat ad T is the absolute temperature. For orgaic substaces, H is give by the ratio of vapor pressure p ad water solubility S of the pure compoud. Partitio coefficiet betwee soil ad water, W K, ca be estimated from -octaol/water partitio coefficiet SW K, which is based OW o the assumptio that sorptio to soil particles is govered by lipophilic soil orgaic carbo cotet OC. May regressios revealed a close relatio betwee K ad OW K, OC which is the partitio coefficiet betwee OC ad water. Fially, K is estimated by SW multiplyig K with the fractio of OC ad the ratio of the bulk soil desity ad soil OC water cotet. Similar approach is applied to the estimatio of the partitio coefficiet betwee sedimet ad water. Partitio coefficiet betwee air ad soil is immediately give as the ratio of K ad AW K (see Ecological Chemistry). SW For the three substaces 2,3,7,8-tetrachlorodibezo-p-dioxi (TCDD), liear alkylbezee sulfoate (LAS) ad bezee, the mass distributio to the media of air, water, soil ad sedimet are calculated for the simplified regioal sceario from Figure 1. Substace data are give i Figure 3 together with the results of the Level I model. The predomiat percetage of 2,3,7,8-TCDD accumulates i the soil ad sedimet, while LAS maily resides i water, ad bezee accumulates i the air. This leads to the coclusio that bezee is maily dispersed by wid, LAS is carried with water flow, while 2,3,7,8-TCDD is rather immobile. Figure 2: Multimedia mass balace model Level I

7 Figure 3: Mass percetages for three sample compouds calculated with Level I ad the model preseted i Figure 1; 2,3,7,8-TCDD (2,3,7,8-tetrachloro-dibezo-p-dioxi), LAS (liear alkyl bezee sulfoate) Bibliography TO ACCESS ALL THE 20 PAGES OF THIS CHAPTER, Visit: Boethlig R.S. ad Mackay D. (2000). Hadbook of Property Estimatio Methods for Chemicals. Evirometal ad Health Scieces. Lewis Publ.: Boca Rato. [Compilatio of estimatio methods of substace properties eeded for evirometal modelig.] Brades L.J., de Hollader H., va de Meet D. (1996). Simple Box 2.0: a ested multimedia fate model for evaluatig the evirometal fate of chemicals. Natioal Istitute of Public Health ad the Eviromet: Bilthove (Niederlade). Report o [This report describes i detail a spatially ested approach of multimedia models.] Cowa C., Mackay D., Feijtel T., va de Meet D., di Guardo A., Davies J. ad Mackay N. (1995). The Multi-Media Fate Model: A vital tool for predictig the fate of chemicals. SETAC Press: Pesacola. [Compariso of various multimedia models ad their applicatio for regulatory purposes.] Europea Commissio (1996). Techical Guidace Documet i Support of the Commissio Directive 93/67/EEC o Risk Assessmet for New Notified Substaces ad the Commissio Regulatio (EC) 1488/94 o Risk Assessmet for Existig Substaces, Parts I-IV. Office for Official Publicatios of the Europea Commuities: Luxembourg. [Describes methods ad models for exposure ad risk assessmet; icludes a regioal multimedia distributio model.] Mackay D. ad Paterso S. (1979). Fidig fugacity feasible. Eviro. Sci. Techol. 13, [The first scietific paper o multimedia modelig.] Mackay D. (2001). Multimedia Evirometal Models. The Fugacity Approach. 2 d ed. Lewis Publ.: Boca Rato. [A basic textbook for multimedia fate modelig. Recommeded for further readig.] Mackay D., Shiu W. Y. S., Ma K. C. (1992). Illustrated Hadbook of Physical-Chemical Properties ad Evirometal Fate for Orgaic Chemicals. Lewis Publ.: Boca Rato. [Collectio of substace data for several persistet substace classes; cotais measured ad estimated literature data with refereces.] Scheriger M. (2002): Persistece ad Spatial Rage of Evirometal Chemicals. Wiley-VCH: Weiheim. [This book describes coupled multimedia models to calculate global trasport ad persistece. It is recommeded as a itroductio to hazard ad risk assessmet of persistet orgaic pollutats (POPs).] Trapp S., Matthies M. (1998). Chemodyamics ad Evirometal Modelig. A Itroductio. Spriger: Berli. [Textbook for graduate studets ad self study.] Biographical Sketch Professor studied physics at the Uiversities i Müster ad Müche, Germay. I 1971 he fiished his udergraduate studies with B.Sc. thesis i Medical Physics. I 1975 he received his

8 Ph.D. i Physical Chemistry from the Uiversity of Müche, Faculty of Chemistry. His Ph.D. thesis was o hydroge bods i eergy rich biochemical compouds. From he worked as a research associate i at Istitute of Biophyics, Uiversity of Giesse. Two years later he became a research associate at the Natioal Cetre of Eviromet ad Health i Müche-Neuherberg. He worked o radiatio risk aalysis, radioecology ad chemical exposure ad risk assessmet. I 1987 he became the head of the Project Group o Hazard Assessmet of Chemicals. I 1992 he was appoited as a full professor of Applied Systems at the Uiversity of Osabrück. He fouded the Istitute for Evirometal Systems Research i 1994 ad is its director sice the. His major iterests are evirometal systems sciece, systems ecology ad biogeochemical cycles, trasport modelig of pollutats i air, soil ad water, exposure ad risk assessmet, itegrated modelig ad assessmet. Professor Matthies participated i several atioal ad iteratioal projects o exposure modelig, comparative risk assessmet, lograge trasport modelig of persistet orgaic pollutats ad geo-refereced exposure assessmet. The results of his research are documeted i over 150 articles i scietific jourals, proceedigs ad hadbooks ad 40 scietific reports ad books. He served as a cosultat for iteratioal orgaizatios (OECD, EU) ad various atioal agecies such as the Germa Federal Evirometal Protectio Agecy ad Federal Miistry of Research ad Techology.