Chemical Modeling in Aqueous Systems - ACS Publications

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Chemical Modeling—Goals, Problems, Approaches, and Priorities

EVERETT A. JENNE

Downloaded by 184.158.213.107 on March 13, 2018 | https://pubs.acs.org Publication Date: March 19, 1979 | doi: 10.1021/bk-1979-0093.ch001

U.S. Geological Survey, Water Resources Division, Menlo Park, CA 94025

The b e l i e f that Science can s o l v e s o c i e t a l problems i n acceptable time frames has been discounted by the p u b l i c i n recent years (1, 2). This s i t u a t i o n , according to D. S. Saxton (3), i s a r e s u l t of the "...overreaching expectations that research....would v i s i b l y c o n t r i b u t e t o e a r l y s o l u t i o n s t o d i f f i c u l t s o c i a l problems." Since the t o t a l monetary resources a v a i l a b l e f o r studying such problems are l i m i t e d , the e f f e c t of recent p o l i c y developments and l e g i s l a t i o n has been to increase support f o r a p p l i e d s t u d i e s w i t h a r e s u l t a n t decrease i n support of fundamental research. The country as a whole has turned, and i s t u r n i n g f u r t h e r , toward the use of computational models u t i l i z i n g best guesses and r e a d i l y a v a i l a b l e parameter i n f o r m a t i o n which may have only order-ofmagnitude r e l i a b i l i t y . One r e s u l t of t h i s trend i s an enormous q u a n t i t y of r e p o r t s of a h i g h l y a p p l i e d nature coming out of i n s t i t u t e s , u n i v e r s i t i e s , and governmental agencies. Many of these r e p o r t s are of dubious value (4). The h i g h l y a p p l i e d research approach produces some short-run b e n e f i t s , but i s v i r t u a l l y c e r t a i n to produce long-term l i a b i l i t i e s . One l i a b i l i t y w i l l be that a l a r g e r part of the research community w i l l be t r a i n e d as data gatherers r a t h e r than i n f o r m a t i o n synthes i z e r s w i t h a r e s u l t a n t decrease i n the t r a n s f e r v a l u e of much of the work. I n the f i e l d of chemical modeling, the p r i n c i p a l l o n g term l i a b i l i t y w i l l be that i n s u f f i c e n t fundamental knowledge needed f o r improvement of chemical, b i o l o g i c a l , and hydrologie models w i l l not be a v a i l a b l e w i t h i n the next s e v e r a l years. Although the fundamental problems being addressed h e r e i n are l a r g e p h i l o s p h i c a l i n nature, i t i s a p p r o p r i a t e t o d e f i n e what i s meant by chemical modeling. As used h e r e i n , chemical modeling encompasses the aqueous s p e c i a t i o n of d i s s o l v e d c a t i o n i c elements among organic and i n o r g a n i c a n i o n i c l i g a n d s , of a n i o n i c elements among t h e i r complexes w i t h c a t i o n s , and both c a t i o n i c and a n i o n i c elements among t h e i r redox s t a t e s . Chemical modeling a l s o i n cludes c a l c u l a t i o n of the degree of s a t u r a t i o n of an aqueous media w i t h regard both to metastable and t o e q u i l i b r i u m s o l i d s and c a l c u l a t i o n of s o r p t i o n o r d e s o r p t i o n . A d d i t i o n a l l y , p r e 0-8412-0479-9/79/47-093-003$05.00/0 This chapter not subject to U.S. copyright Published 1979 American Chemical Society Jenne; Chemical Modeling in Aqueous Systems ACS Symposium Series; American Chemical Society: Washington, DC, 1979.


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CHEMICAL MODELING IN AQUEOUS SYSTEMS

d i c t i v e chemical modeling must i n c l u d e k i n e t i c s . Chemical modeling can be used t o d e s c r i b e the chemical c h a r a c t e r i s t i c s o f an aqueous system whether i t be a l a k e water or the f l u i d i n a human d i g e s t i v e system, given the r e q u i s i t e input data f o r the system t o be modeled as w e l l as adequate reference data (thermodynamic and k i n e t i c ) , and a p r o p e r l y constructed model. Q u a n t i t a t i v e models are v a l u a b l e because they i n c r e a s e one's a b i l i t y t o d e r i v e i n formation from data, t o p r e d i c t c e r t a i n e f f e c t s of anthropogenic i n p u t s , and t o do s e n s i t i v i t y analyses. The l a t t e r may w e l l be one of the most important and l e a s t recognized uses of such models. For example, i n recent modeling of the i n o r g a n i c s p e c i a t i o n of d i s solved s i l v e r i n San F r a n c i s c o Bay, a s e n s i t i v i t y a n a l y s i s t o t e s t the e f f e c t of metals and l i g a n d s not i n c l u d e d i n the chemical analyses i n d i c a t e d that hydrogen s u l f i d e a t the microgram-perl i t e r l e v e l would complex more s i l v e r than would c h l o r i d e i n the low s a l i n i t y p o r t i o n o f the estuary ( 5 ) . This f i n d i n g then l e d to a p r e l i m i n a r y study of d i s s o l v e d s u l f i d e i n San F r a n c i s c o Bay waters. S e n s i t i v i t y analyses can a l s o be performed to i n d i c a t e needed accuracy and p r e c i s i o n of p a r t i c u l a r analyses and parameters. Chemical models can a l s o be used i n appropriate s i t u a t i o n s to estimate b i o l o g i c a l e f f e c t s on the chemical p a r t of an ecosystem (6) . Goals The u l t i m a t e goal of a l l research i n general and chemical modeling i n p a r t i c u l a r i s a d d i t i o n a l understanding of processes and events which can, under the proper c o n d i t i o n s , f a c i l i t a t e the improvement of human l i f e p h y s i c a l l y , e m o t i o n a l l y , and a e s t h e t i c a l l y . F o r example, w i t h i n the next decade, a p p r o p r i a t e chemicaland b i o l o g i c a l - m o d e l i n g s t u d i e s of s o i l s o l u t i o n s and p l a n t n u t r i e n t uptake can a s s i s t i n i n c r e a s i n g markedly both the quantity and q u a l i t y of t e r r e s t r i a l food p r o d u c t i o n . Chemical modeling can provide i n s i g h t i n t o the b i o a v a i l a b i l i t y and the v a r i a t i o n s i n the b i o a v a i l a b i l i t y of t r a c e elements i n man s d i e t components. Processes such as s u l f i d e complexation, valence r e d u c t i o n , p r e c i p i t a t i o n and organic complexation, may s i g n i f i c a n t l y reduce the a c t i v i t y and hence the b i o a v a i l a b i l i t y of v a r i o u s t r a c e elements. Linkage to b i o l o g i c a l models w i l l c e r t a i n l y i n c r e a s e the amount of i n f o r m a t i o n which can be d e r i v e d . I n a d d i t i o n to the r e s u l t a n t p o t e n t i a l improvement i n human n u t r i t i o n , i n s i g h t i n t o the b i o a v a i l a b i l i t y of t r a c e elements from d i e t a r y components may cont r i b u t e to the c o n t r o l and a l l e v i a t i o n of some human diseases r e l a t e d to t r a c e elements. More immediate goals d i f f e r from one s c i e n t i f i c d i s c i p l i n e to another. One goal of which I am most aware i s the p r e d i c t i o n of the r o l e of aqueous s p e c i a t i o n on the b i o a v a i l a b i l i t y and t o x i c i t y of t r a c e elements t o plankton and e s t u a r i n e d e t r i t u s feeding i n v e r t e b r a t e s . I n the longer range, these s t u d i e s would be extended to i n c l u d e the v a r i o u s a q u a t i c organisms higher i n the 1

Jenne; Chemical Modeling in Aqueous Systems ACS Symposium Series; American Chemical Society: Washington, DC, 1979.


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Goals, Problems, Approaches, and Priorities

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food c h a i n . The o v e r a l l goal of t h i s symposium i s to promote the science of chemical modeling i n three ways: 1) by promoting the immediate exchange of i n f o r m a t i o n v i a o r a l p r e s e n t a t i o n s by as many workers i n the f i e l d as p r a c t i c a b l e ; 2) by f o s t e r i n g the maximum amount of d i s c u s s i o n of research g o a l s , problems, approaches, and p r i o r i t i e s ; and 3) by preparing a s t a t e - o f - t h e - a r t record i n the form of symposium proceedings. Further goals are to improve the q u a l i t y as w e l l as the a p p l i c a b i l i t y of chemical models i n ensuing years and to help minimize d u p l i c a t i o n of computerized chemical models by i n c r e a s i n g the v i s i b i l i t y of those already a v a i l a b l e . Although new approaches and mathematical frameworks are o b v i o u s l y to be encouraged, i t would appear more p r o f i t a b l e to the s c i e n t i f i c community to upgrade and expand the a v a i l a b l e models r a t h e r than to generate a d d i t i o n a l ones of s i m i l a r type and s t r u c t u r e . This view comes out of our experience that the computer codes, and indeed the models themselves, can be rendered l a r g e l y e r r o r f r e e only by extended use over time by knowledgeable i n v e s t i g a t o r s . I t i s hoped that the formal (7) and i n f o r m a l d i s c u s s i o n s of a t t r i b u t e s of chemical models w i l l i n c r e a s e the r e l i a b i l i t y and usefulness of the next generation of chemical models. Problems Important r e s t r a i n t s to the usefulness of a v a i l a b l e chemical models are inadequacies i n the 1) c a p a b i l i t y to c h a r a c t e r i z e the organic l i g a n d s of n a t u r a l waters; 2) knowledge of redox s t a t u s of waters to permit r e a l i s t i c computation of r e d o x - c o n t r o l l e d s p e c i a t i o n ; 3) a v a i l a b l e thermodynamic data; 4) knowledge of the time dependency of the v a r i o u s processes (such as v a r i a t i o n i n apparent t r a c e element c o n c e n t r a t i o n during a t i d a l c y c l e ) i n general and of k i n e t i c data f o r chemical and b i o l o g i c a l processes i n p a r t i c u l a r ; and 5) e r r o r estimates f o r the preceding r e s t r a i n t s . The f i e l d of chemical modeling i s a l s o c o n s t r a i n e d by the: 6) need f o r comprehensive analyses of the systems to be modeled; 7) l i m i t a t i o n s of the q u a l i t y and scope of published data; 8) s c a r c i t y of adequate l i t e r a t u r e reviews; 9) d i f f i c u l t i e s i n o r g a n i z i n g and conducting i n t e g r a t e d i n t e r d i s c i p l i n a r y s t u d i e s ; and to a l e s s e r e x t e n t , 10) l i m i t a t i o n i n q u a l i t y of graduate training. Organic Ligands. I n v e s t i g a t i o n s of organic compounds d i s solved i n surface waters have l a r g e l y d e a l t w i t h i d e n t i f i c a t i o n of s p e c i f i c compounds or groups (e.g., phenols, polyaromatic hydrocarbons, e t c . ) , determination of complexation c a p a c i t y , o r s e p a r a t i o n — w i t h v a r i a b l e types of c h a r a c t e r i z a t i o n — i n t o f u l v i c and humic-acid f r a c t i o n s . The i n f o r m a t i o n developed i n these s t u d i e s has not been shown to be p a r t i c u l a r l y u s e f u l to q u a n t i t a t i v e chemical modeling. The analyses of s p e c i f i c compounds or



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groups of compounds have come about because of t a s t e and odor problems i n d r i n k i n g water and subsequently because of t h e p o s s i b l e t o x i c i t y of these compounds t o food c h a i n components and the t o x i c i t y and c a r c i n o g e n i c p o t e n t i a l o f these compounds to man. Complexat i o n - c a p a c i t y values have served to i d e n t i f y and dramatize the p o t e n t i a l l y important r o l e of d i s s o l v e d organic compounds as l i g a n d s capable of promoting the s o l u b i l i z a t i o n and h y d r o l o g i e t r a n s p o r t of t r a c e elements. However, there seems l i t t l e p o i n t i n c o n t i n u i n g these determinations s i n c e t h e i r magnitude i s now known and i t i s not apparent how they can be used i n q u a n t i t a t i v e chemical modeling. The s p e c i a t i o n of c a t i o n s among organic as w e l l as i n o r g a n i c l i g a n d s r e q u i r e s estimates of t h e i r molar q u a n t i t i e s and of t h e i r s t a b i l i t y constants. Two p o s s i b i l i t i e s e x i s t . One i s that there are only a few important n a t u r a l organic l i g a n d s f o r each metal. The other i s that organic complexation i s the r e s u l t of a host of s p e c i f i c organic l i g a n d s , each of which i s present i n too small an amount to be i n d i v i d u a l l y important. I f the former p o s s i b i l i t y proves t o be t r u e , the i n d i v i d u a l l i g a n d s can be i d e n t i f i e d by techniques such as l i q u i d and t h i n - l a y e r chromatography. I f the l a t t e r p o s s i b i l i t y proves t r u e , then an approach such as that of Leenheer and Huffman (8) which f r a c t i o n a t e s s o l u b l e organic compounds i n t o s o l u b i l i t y and f u n c t i o n a l group c l a s s e s w i l l be required. Redox-Dependent S p e c i a t i o n . Valence s t a t e determines the t o x i c i t y of an element. I t g r e a t l y a f f e c t s the complexation s t r e n g t h between metals and v a r i o u s l i g a n d s , hence the degree of s a t u r a t i o n of water w i t h r e s p e c t t o s o l i d phases. There i s almost complete l a c k of agreement w i t h i n the s o i l science and geochemical communities as to the s i g n i f i c a n c e and u s e f u l n e s s of platinume l e c t r o d e e s t i m a t i o n s of redox s t a t u s . The techniques of e s t i mating the c o n c e n t r a t i o n of the valence s t a t e s of i n d i v i d u a l couples a t t h e i r environmental l e v e l s are only now becoming a v a i l a b l e . These techniques o f f e r c o n s i d e r a b l e promise f o r future studies. A v a i l a b l e Thermodynamic Data. There a r e s e v e r a l problems regarding a v a i l a b l e thermodynamic data. The a p p r o p r i a t e thermodynamic data do not e x i s t f o r many s o l i d s of environmental i n t e r e s t . This i s p a r t i c u l a r l y t r u e f o r the s o l i d s which a r e e x t e n s i v e l y s u b s t i t u t e d , such as the c r y p t o c r y s t a l l i n e manganese oxides or the m e t a l l i c hydroxy s u l f a t e s and phosphates. G r e a t l y divergent thermodynamic data e x i s t f o r numerous aqueous complexes and s o l i d s ; some of these values d i f f e r by orders of magnitude. Thus, there i s a great need f o r thorough e v a l u a t i o n and s e l e c t i v e r e d e t e r m i n a t i o n . The e v a l u a t i o n of thermodynamic data i s v e r y time-consuming, r e q u i r i n g e x t e n s i v e l i t e r a t u r e searches and c o n s i d e r a b l e knowledge of a n a l y t i c a l techniques. The e x p e r t i s e and e f f o r t r e q u i r e d to o b t a i n the r e q u i r e d q u a l i t y of r e s u l t s



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g e n e r a l l y preclude a comprehensive e v a l u a t i o n of numerous comp l e x e s , s o l i d s , or elements i n the course of a s i n g l e research p r o j e c t or c o n t r a c t . However, s c i e n t i s t s f r e q u e n t l y are comp e l l e d by the nature of t h e i r s t u d i e s to undertake c o m p i l a t i o n and s e l e c t i o n w i t h or without use of e v a l u a t i o n techniques, s i n c e adequately evaluated compilations are not a v a i l a b l e . Hence, the compilations made by s i n g l e i n v e s t i g a t o r s are o f t e n not as thorough and comprehensive as i s d e s i r a b l e . The U.S. N a t i o n a l Bureau of Standards (NBS) i s the governmental agency w i t h primary r e s p o n s i b i l i t y f o r t h i s area although the U.S. G e o l o g i c a l Survey shares r e s p o n s i b l i t y w i t h the NBS i n regard to minerals and the U.S. Department of Energy shares r e s p o n s i b i l i t y w i t h regard to the t r a n s u r a n i c elements. The e v a l u a t i o n and s e l e c t i o n of "best" values i s a job of such magnitude that most of the NBS p u b l i c a t i o n s of the l a s t decade (9, 10, 11, 12, 13) present only s e l e c t e d v a l u e s . The s u b s t a n t i a t i n g references and d i s c u s s i o n f o r these compilations are to f o l l o w i n subsequent NBS p u b l i c a t i o n s . One recent p u b l i c a t i o n (14) on thorium gives the c r i t i c a l e v a l u a t i o n and r e f e r e n c e s . C r i t i c a l e v a l u a t i o n and documentation e f f o r t s need to be g r e a t l y a c c e l e r a ted. As one step i n t h i s d i r e c t i o n , the NBS i s funding two s t u d i e s devoted to the e v a l u a t i o n and s e l e c t i o n of "best s o l u b i l i t y s t u d i e s from the l i t e r a t u r e f o r the carbonate, h a l i d e , phosphate, and s u l f i d e s a l t s of the a l k a l i and a l k a l i n e earths plus V, Cr, Mo, and U (by A l l e n C l i f f o r d of V i r g i n i a P o l y t e c h n i c a l I n s t i t u t e ) and of Cu, Zn, Cd, Sb, Hg, Pb, and As (by Lawrence Clever of Emory U n i v e r s i t y ) . These two reviews are part of Commission V. 6.1 of the I n t e r n a t i o n a l Union of Pure and A p p l i e d Chemistry (IUPAC) program of c o m p i l a t i o n and c r i t i c a l e v a l u a t i o n of the a v a i l a b l e l i t e r a t u r e on s o l u b i l i t y . The thermodynamic data f o r environmentally and geochemically important complexes and s o l i d s ( c h i e f l y , n o n s i l i c a t e ) of 29 elements (Ag, As, Au, Ba, B i , Ca, Cd, Co, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, N i , Pb, Sb, Se, Sn, Sr, Te, Th, T i , U, V, W, and Zn) are being s e m i - c r i t i c a l l y reviewed by Donald Langmuir and Hugh Barnes of Pennsylvannia State U n i v e r s i t y w i t h NBS funding. P o l y s u l f i d e complexes are to be included i n t h e i r review. The s t a t u s of the thermodynamic data on s u l f i d e - and p o l y s u l f i d e - m e t a l complexes w i l l a l s o be discussed i n a r e v i s e d e d i t i o n of "Hydrothermal Ore D e p o s i t s " e d i t e d by Hugh Barnes (15). C r i t i c a l reviews of thermodynamic data published i n the l a s t few years i n c l u d e the four-volume s e r i e s of M a r t e l l and Smith (16, 17, 18, 19), three on organic and one on i n o r g a n i c l i g a n d s ; and the s i n g l e volumes of Christensen et ad. (20) f o r metall i g a n d heats, e t c . , of Baes and Mesmer (21) f o r c a t i o n h y d r o l y s i s , of Langmuir (22) f o r uranium, and of Robie et_ a l . (23) f o r numerous m i n e r a l s . R e l i a b l e a c t i v i t y c o e f f i c i e n t s f o r marine waters or f o r waters of even higher s a l i n i t y continue to be a problem i n c a l c u l a t i o n of aqueous s p e c i a t i o n and computation of m i n e r a l 11


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e q u i l i b r i a . In p a r t i c u l a r , the a p p r o p r i a t e technique to use f o r uncharged i o n p a i r s remains i n d i s p u t e (24). However, the chemical-modeling e r r o r s a t t r i b u t a b l e to u n c e r t a i n t i e s i n a c t i v i t y c o e f f i c i e n t s are g e n e r a l l y l e s s than the u n c e r t a i n t i e s due to other causes such as m i s s i n g or u n r e l i a b l e thermodynamic v a l u e s , m i s s i n g a n a l y t i c a l data, and incomplete model components (5). A d d i t i o n a l l y , a major assessment of a c t i v i t y - c o e f f i c e n t e s t i m a t i o n i s now underway (25). Another p o t e n t i a l problem i n q u a n t i t a t i v e i=iqueou| s p e c i a t i o n i s polymerization. Various elements (Be , Se , Ce , Zn , , V C r * , Mo ]], U F e * , Co , N i * , Ru**, C u \ Z n \ Al , Ga , I n , L n , Pb +, S b , and B i ) are s a i d to e x h i b i t t h i s behavior (26, 21, 27). To the extent that p o l y m e r i z a t i o n occurs and i s not accounted f o r i n the aqueous-speciation submodel, the a c t i v i t y of the v a r i o u s s o l u t e species and s a t u r a t i o n s t a t e of s o l i d forms w i l l be overestimated. For example, the apparent o v e r s a t u r a t i o n of San F r a n c i s c o Bay waters w i t h s i l v e r s u l f i d e was decreased by about 10 percent when the p o l y s u l f i d e complexes of Ag and Cu were included i n the aqueous s p e c i a t i o n submodel (E.A. Jenne and J.W. B a l l , unpublished data, 1978). There i s l i t t l e agreement among the r e l e v a n t s c i e n t i f i c communities as to the p r i o r i t i e s f o r o b t a i n i n g m i s s i n g thermodynamic data. Top p r i o r i t i e s on my own l i s t are f o r data on n a t u r a l organic l i g a n d s , p o l y s u l f i d e complexes (data f o r Ag and Cu e x i s t , 28), low-temperature s o l i d s o l u t i o n of t r a c e elements i n i r o n and i n manganese s u l f i d e ^ and i n c r y p t o c r y s t a l l i n e s u b s t i t u t e d (Ba, L i , Sr) manganese o x i d e s ; and the s o l i d s o l u t i o n s of Sr, Ba, Mn, and Mg i n CaC03, and v a r i o u s t r a n s i t i o n metals p l u s Sr and Ba i n MnC0 . I t should be noted that because of k i n e t i c i n h i b i t i o n s i n the p r e c i p i t a t i o n of v a r i o u s s o l i d s , i t i s h i g h l y d e s i r a b l e i n s o l u b i l i t y and d i s s o l u t i o n s t u d i e s that p h y s i c a l i d e n t i f i c a t i o n of p r e c i p i t a t e s and r e s i d u e s be made by o p t i c a l , X-ray d i f f r a c t i o n , and e l e c t r o n microscopy and d i f f r a c t i o n techniques. 2

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3 +

3

Time Dependency. The time dependency of geochemical and environmental-chemistry processes i s a l a r g e l y unrecognized but o f t e n important v a r i a b l e . For example, i t i s not unusual f o r 50 percent or more of the t o t a l annual sediment t r a n s p o r t of a r i v e r to occur i n the course of a s i n g l e storm event (29, p. 487). Marked time v a r i a t i o n s a l s o occur w i t h d i s s o l v e d c o n s t i t u e n t s . G i r v i n et. a l . (30) r e p o r t the c o n c e n t r a t i o n of d i s s o l v e d N i and Zn at a South San Francisco Bay s t a t i o n to vary by f a c t o r s of 1.42 and 1.56, r e s p e c t i v e l y , through a t i d a l c y c l e . S i m i l a r l y , concentrations of d i s s o l v e d t r a c e element v a r i e d i n a complex manner between main-channel and near-shore ( t i d a l f l a t ) s t a t i o n s . D i u r n a l v a r i a t i o n s i n the apparent degree of s a t u r a t i o n of surface waters w i t h respect to c e r t a i n s o l i d s may r e s u l t from b i o l o g i c a l a c t i v i t y and temperature changes. Recent s t u d i e s (V.C. Kennedy, U.S. Geol. Survey, unpublished data, 1978) have shown


1. J E N N E


9


pronounced d i u r n a l v a r i a t i o n i n phosphate concentrations i n a short reach of a stream c o n t a i n i n g considerable attached algae. The apparent s a t u r a t i o n of ZnSiU3 i n a s m a l l stream has been found to vary d i u r n a l l y (V.C. Kennedy and E.A. Jenne, unpublished data, 1978). These observations and others i n d i c a t e that r e a l i s t i c a p p l i c a t i o n of chemical models must take cognizance of the time s c a l e s of b i o l o g i c , h y d r o l o g i e , and chemical processes. E r r o r Estimates. L i t t l e a t t e n t i o n has been paid to e r r o r s a s s o c i a t e d w i t h e i t h e r the thermodynamic or the a n a l y t i c a l data u t i l i z e d i n chemical models. M.L. Good (31) considers t h i s to be one of the four p r i n c i p a l problems of the day w i t h regard to use and misuse of s c i e n t i f i c data. I t i s e s s e n t i a l that chemical models compute propagated standard d e v i a t i o n s f o r t h e i r a n a l y t i c a l , thermodynamic, and k i n e t i c data. This p r o v i s i o n e x i s t s i n the model of B a l l et a l . ( 3 2 ) . System C h a r a c t e r i z a t i o n . A f u r t h e r l i m i t a t i o n to the adequate t e s t i n g of chemical models and to t h e i r a p p l i c a t i o n t o environmental problems i s the extensive system c h a r a c t e r i z a t i o n ( e s p e c i a l l y chemical analyses) o f t e n r e q u i r e d . Adequate charact e r i z a t i o n o f t e n n e c e s s i t a t e s many d i f f i c u l t and time-consuming analyses, some of which must be done on s i t e , and the c o l l e c t i o n — w i t h adequate p r e s e r v a t i o n — o f numerous subsamples. The appropriate i n t e r f a c i n g of chemical w i t h b i o l o g i c and hydrologie models i s a r a t h e r d i f f i c u l t problem. For example, the p r e d i c t i o n of trace-element bioaccumulation by phytoplankton may r e q u i r e i n some instances that the uptake r a t e s and the compartmentalized l o s s r a t e s f o r v a r i o u s s o l u t e species of the e l e ment present i n the system be known. The e f f e c t , i f any, on compartmentalized l o s s r a t e s of the p a r t i c u l a r s o l u t e species taken up (e.g. HgCH + vs H g ) a l s o needs to be known. The i n t e r a c t i o n e f f e c t of the c o n c e n t r a t i o n of one element upon the uptake and l o s s r a t e s of another element, such as Hg on Se (33, 34, 3 5 ) , a l s o need to be known. I n many i n s t a n c e s , hydrodynamic models may have to be l i n k e d with,or otherwise i n c o r p o r a t e d , i n t o the b i o l o g i c and chemical models to permit p r e d i c t i o n s o f , f o r example, increased trace-element l e v e l s i n o y s t e r s r e s u l t i n g from increased anthropogenic inputs to an estuary. 2+

3

L i m i t a t i o n s of Published Data. The development, t e s t i n g , and s u c c e s s f u l a p p l i c a t i o n of comprehensive chemical models r e q u i r e s at l e a s t moderate amounts of wisdom, experience, and time. I n the f i r s t h a l f of t h i s decade, u n i v e r s i t i e s , i n s t i t u t e s , and government agencies rushed headlong i n t o environmental chemistry. The r e s u l t has been a marked i n c r e a s e i n the number of r e p o r t s of the occurrence and d i s t r i b u t i o n of t r a c e elements, but t h i s great e f f o r t has produced s u r p r i s i n g l y few s t u d i e s of fundamental processes and r e a c t i o n s that would provide an understanding of observed t r a c e element r e d i s t r i b u t i o n . Most of the analyses



10


reported i n such s t u d i e s have been on p o o r l y c h a r a c t e r i z e d , or even u n c h a r a c t e r i z e d , samples. G e n e r a l l y , trace-element data have been reported f o r sediment, or f o r b i o t a , or f o r water, but only i n f r e q u e n t l y f o r a l l t h r e e . Even more r a r e i s the i n c l u s i o n of u s e f u l hydrodynamic data and atmospheric i n p u t s . A t r i v i a l but i l l u s t r a t i v e example of the r e s u l t of l a c k of experience p l u s l a c k of an adequate l i t e r a t u r e review i s the f e d e r a l l y funded c o n t r a c t study of a few t r a c e elements i n a surface water wherein the c a r e f u l handling of s t e r i l e b o t t l e s — w i t h p l a s t i c gloves ( t o avoid contamination o f the b o t t l e s w i t h t r a c e elements from the f i n g e r s ) — i s noted w i t h obvious p r i d e but no mention i s made of any f i l t r a t i o n o r p r e s e r v a t i o n of the samples or even of the p o s s i b l e need f o r these steps! The l a r g e number of chemical analyses of s o - c a l l e d "whole-water" samples ( i . e . , water samples from which the suspended sediment has not been removed by f i l t r a t i o n or other means) i s an example of the generation of a l a r g e amount of data from which l i t t l e i n f o r m a t i o n can be der i v e d . Proper sampling and sample p r e s e r v a t i o n a r e e s s e n t i a l t o h i g h - q u a l i t y analyses. I t should be noted that "composite" time, d i s c h a r g e , or load a r e g e n e r a l l y not u s e f u l f o r chemical-modeling studies. Adequate L i t e r a t u r e Reviews. I conclude t h a t f a c t o r s other than t o t a l monies a v a i l a b l e f o r research a r e r e s p o n s i b l e f o r l i m i t i n g the s c i e n t i f i c progress i n the f i e l d s of environmental chemistry i n general and of chemical modeling i n p a r t i c u l a r . This c o n c l u s i o n r e s u l t s from the f o l l o w i n g observations. The i n c r e a s e i n the amount of e a r t h - s c i e n c e data published has been tremendous and the r a t e a t which i t i s being published continues to i n c r e a s e . This lament i s of course not new. Barnaby R i c h i s quoted as w r i t i n g i n 1613 that "one of the diseases of t h i s age i s the m u l t i p l i c i t y of books: they doth so overcharge the world that i t i s not able to d i g e s t the abundance of i d l e matter t h a t i s every day hatched and brought f o r t h i n t o the w o r l d " ( 3 6 ) . In the 10 years f o l l o w i n g 1965, the number of papers, patents, and other published r e p o r t s c i t e d by Chemical A b s t r a c t s was a l most as l a r g e as i n the 58 preceding years (37) . The i n c r e a s e i n the absolute amount of published products i s c o r r e l a t e d w i t h the r e l a t i v e l a c k of p r o d u c t i v i t y of an i n c r e a s i n g p r o p o r t i o n of a v a i l a b l e research monies and manpower. Present i n v e s t i g a t o r s are i n c r e a s i n g l y unaware of p r e v i o u s l y published data, p a r t i c u l a r l y the data which have r e c e n t l y become a v a i l a b l e or which have been published i n j o u r n a l s o u t s i d e of the i n v e s t i g a t o r ' s subd i s c i p l i n e . The l a r g e q u a n t i t y of published data and i t s d i s p e r s i o n i n almost innumerable j o u r n a l s and other p u b l i c a t i o n s e r i e s i s , in p a r t , m i t i g a t e d by the p r e p a r a t i o n of review a r t i c l e s . However, the problem s t i l l remains because time, i n the order of years, passes before s y n t h e s i z e r s (reviewers) garner the l a r g e q u a n t i t i e s of s c a t t e r e d new data and d i s t i l l i n f o r m a t i o n from them. A f u r ther problem i s that many of the reviews a r e a c o m p i l a t i o n of


1.

JENNE


11


"who

found what" i n s t e a d of a c r i t i c a l e v a l u a t i o n and s y n t h e s i s . The r a p i d r a t e of data generation and the s o p h i s t i c a t i o n of techniques and methods o f t e n r e q u i r e d f o r s i g n i f i c a n t research progress can make the products of many s m a l l , one-to-two year grant or c o n t r a c t s t u d i e s of minimal v a l u e . These short-term grants o f t e n do not permit the buildup of e x p e r t i s e necessary to make s i g n i f i c a n t research c o n t r i b u t i o n s . The short-term grants are not conducive to generating i n f o r m a t i o n about mechanisms and processes because observations must be terminated on a r e l a t i v e l y i n f l e x i b l e time schedule during which completion of a f i n a l r e p o r t i s i m p e r a t i v e . The time at which i t i s necessary to terminate observations and measurements o f t e n c o i n c i d e s w i t h the time at which f u r t h e r observations have the g r e a t e s t p o t e n t i a l to i n c r e a s e the i n v e s t i g a t o r s ' c h a r a c t e r i z a t i o n and knowledge of the system. (Obviously, the s m a l l discontinuous grant or cont r a c t may r e s u l t i n a s i g n i f i c a n t c o n t r i b u t i o n where i t complements or adds to an ongoing program.) The funding of long-term i n v e s t i g a t i v e programs at the n a t i o n a l l a b o r a t o r i e s and w i t h i n i n v e s t i g a t i v e governmental agencies has become i n c r e a s i n g l y d i f f i c u l t . I t must a l s o be noted that there has been a s h i f t i n grant and c o n t r a c t funding away from b a s i c research toward applied research. I n t e r d i s c i p l i n a r y Approach. The i n t e g r a t e d i n t e r d i s c i p l i n a r y approach to research i s d i f f i c u l t . That i t should be p o s s i b l e i s shown by, f o r example, the GEOSEX, Manganese Nodule, Deep Sea D r i l l i n g , and RANN (Research A p p l i e d to N a t i o n a l Needs; 38) p r o j e c t s (Pb at the U n i v e r s i t y of I l l i n o i s and M i s s o u r i , Mo at the U n i v e r s i t y of Colorado), funded by the N a t i o n a l Science Found a t i o n . I t would be h i g h l y d e s i r a b l e , and i t should be p o s s i b l e , f o r funding agencies to promote the common use of s e l e c t e d s i t e s and samples by i n v e s t i g a t o r s from the v a r i o u s d i s c i p l i n e s . In many cases, a good deal more i n f o r m a t i o n would be generated by the use of s p l i t s of samples, being c o l l e c t e d i n other s t u d i e s , the use of a r c h i v e d samples, and the use of i n t e r c a l i b r a t i o n and intercomparison samples than by the use of some l o c a l or d i s t a n t set of s p e c i a l samples. Obviously, c o n s i d e r a b l e care must be taken i n the s e l e c t i o n of such samples where unstable c o n s t i t u e n t s or absolute numbers of t r a c e c o n s t i t u e n t s are to be r e p o r t e d . More g e n e r a l l y , use of a l i m i t e d number of samples c o l l e c t e d i n previous or other on-going s t u d i e s would serve to t i e the v a r i o u s s t u d i e s together and to f a c i l i t a t e i n t e r p o l a t i o n and e x t r a p o l a t i o n . That i s , the time has come to concentrate on the generation of i n f o r m a t i o n as opposed to the accumulation of data. The v a r i o u s i n t e r d i s c i p l i n a r y groups d i f f e r s i g n i f i c a n t l y i n at l e a s t two ways. In some, there i s l i t t l e i n t e g r a t i o n of the substudies wherein each i n v e s t i g a t o r c a r r i e s out h i s own i n v e s t i g a t i o n more-or-less independently of the other substudies. In o t h e r s , the emphasis i s on i n t e r r e l a t i o n s h i p and p r i o r i t i e s are set by consensus. Integrated i n t e r d i s c i p l i n a r y groups a l s o d i f f e r i n the way they form. They may come about v i a management



12


d e c i s i o n s or they may form v o l u n t a r i l y . The l a t t e r type are termed " a s s o c i a t i v e i n t e r d i s c i p l i n a r y groups." Integrated i n t e r d i s c i p l i n a r y groups appear to form only where at l e a s t p a r t of the funding i s i n common. The q u a l i t y of the s c i e n t i f i c products from i n t e g r a t e d i n t e r d i s c i p l i n a r y s t u d i e s i s n e a r l y always above average because of the m u l t i d i s c i p l i n a r y view p o i n t s and wide range of experience of the i n v e s t i g a t o r s t h e i r broad coverage of j o u r n a l s , and t h e i r p r o f e s s i o n a l c o n t a c t s . Such groups c o n s i s t i n g of a h a l f dozen or more p r o f e s s i o n a l members o f t e n have much l e s s elapsed time between a v a i l a b i l i t y of funds and s i g n i f i c a n t progress because a base, i n terms of experi e n c e , and a v a i l a b l e techniques, s u p p l i e s and equipment, i s normally much broader than that of smaller p r o j e c t groups. These l a r g e r groups r e q u i r e l e s s investment i n s m a l l equipment items than i s r e q u i r e d f o r the same number of p r o f e s s i o n a l s organized i n smaller p r o j e c t s and can f r e q u e n t l y a f f o r d more expensive equipment. A s s o c i a t i v e i n t e r d i s c i p l i n a r y groups can be formed by i n v e s t i g a t o r s (without common funds) w i t h overlapping i n t e r e s t s f o r the purpose of sharing r e s e a r c h - l i t e r a t u r e r e s u l t s , l i t e r a t u r e searching i n f o r m a t i o n , experience, equipment, space, support personnel, c o n t i n u i n g peer review, and encouragement. This i s the common academic approach to i n t e r d i s c i p l i n a r y s t u d i e s . D.R. Carson (3) b e l i e v e s that the s h i f t i n g of research emphasis towards the a p p l i e d end of the spectrum w i l l be accompanied by more l a r g e - s c a l e i n t e r d i s c i p l i n a r y research i n u n i v e r s i t i e s . However, i t should be noted that the language and conceptual b a r r i e r s encountered by those undertaking i n t e r d i s c i p l i n a r y research sometimes take months to years to overcome (39). S u c c e s s f u l i n t e r d i s c i p l i n a r y groups r e q u i r e c e r t a i n common attributes: 1. Both i n t e g r a t e d and a s s o c i a t i v e i n t e r d i s c i p l i n a r y groups r e q u i r e at l e a s t one of the f o l l o w i n g — a p r o j e c t d i r e c t o r , lead i n v e s t i g a t o r , c o o r d i n a t o r , or one or more strong i n d i v i duals to e s t a b l i s h and maintain coherence. A s s o c i a t i v e m u l t i d i s c i p l i n a r y groups may f u n c t i o n w i t h a committee (which may be informal) of s e n i o r i n v e s t i g a t o r s when there i s a shared research or i n t e l l e c t u a l commitment. 2. Senior i n v e s t i g a t o r s must get along w e l l or the group w i l l break down and cease to f u n c t i o n . 3. There must be frequent exchange of i n f o r m a t i o n (as opposed to data) v i a a common c o f f e e group and(or) p e r i o d i c seminars on problems, p r e l i m i n a r y f i n d i n g s , and p l a n s . This provides continuous "peer" review and c r i t i q u i n g of approaches and r e s u l t s . Exchanges of recent l i t e r a t u r e searches, d i s c o v e r i e s , and summaries of " i n progress" and unpublished s t u d i e s then occurs n a t u r a l l y . 4. The group, or i n d i v i d u a l p r o j e c t s contained t h e r e i n , should be of a m u l t i y e a r or c o n t i n u i n g nature. In p a r t i c u l a r , key l e a d e r s h i p and a n a l y t i c a l personnel should have a high


1.

JENNE


degree of c o n t i n u i t y . One or more of the s e n i o r i n v e s t i g a t o r s must spend a great d e a l of time r e a d i n g , e x t r a c t i n g and s y n t h e s i z i n g i n f o r m a t i o n from l i t e r a t u r e and experimental data. This task can be shared among s e v e r a l of the p a r t i c i p a n t s , as i s g e n e r a l l y the case w i t h graduate students i n a s s o c i a t i v e m u l t i d i s c i p l i n a r y academic groups. 6. E s t a b l i s h i n g time goals f o r s u c c e s s i v e phases of study, and reviewing them p e r i o d i c a l l y , i s e s s e n t i a l to m a i n t a i n i n g the necessary sense of purpose and achievement. However, such time goals should be set c o n s e r v a t i v e l y and should be recognized as being g o a l s , not as a b s o l u t e s . The nature of s c i e n t i f i c i n q u i r y w i l l o f t e n preclude the attainment of such goals w i t h i n the i n i t i a l time frame. T h e i r c h i e f v a l u e i s as a y a r d s t i c k to measure the r e l a t i v e m e r i t of v a r i o u s promising and i n t e r e s t i n g substudies. 7. Formal and i n f o r m a l p o s t - d o c t o r a l and v i s i t i n g - s c i e n t i s t appointments provide new areas of needed e x p e r t i s e and provide accomodation f o r the normal year-to-year a c c o r d i o n - l i k e p a t t e r n of funding l e v e l s of both c o n t r a c t research and f e d e r a l agency programs, 8. The a d m i n i s t r a t i v e c h a i n needs to recognize the e x i s t e n c e of these groups, and to encourage, and, to some e x t e n t , to deal w i t h them as u n i t s . There are c e r t a i n problems p e c u l i a r t o , or at l e a s t more prominent w i t h , these i n t e r d i s c i p l i n a r y groups than w i t h the more conventional i n d i v i d u a l - s c i e n t i s t research s t u d i e s . These i n c l u d e the p r e p u b l i c a t i o n sharing of data as w e l l as s i g n i f i c a n t ideas and concepts, which obscures r i g h t s to authorship of papers and determination of s e n i o r authorship and of s e n i o r versus j u n i o r authorship. These are important matters because they impinge so h e a v i l y on p r o f e s s i o n a l standing and advancement, and on access to research funding. P r o f e s s i o n a l and i n s t i t u t i o n a l r e c o g n i t i o n of the e f f o r t s of the one or more i n v e s t i g a t o r s who c o n t r i b u t e a s i g n i f i c a n t or even a major p o r t i o n of t h e i r time to c o o r d i n a t i o n i s perhaps the most d i f f i c u l t problem, p a r t i c u l a r l y w i t h a s s o c i a t i v e groups, as V.C. Kennedy p o i n t s out (U.S. Geol. Survey, w r i t ten communication, 1978): "Most s c i e n t i s t s do q u a l i t y research f o r one or both of two reasons; f i r s t , they wish to s a t i s f y t h e i r i n t e n s e i n t e r e s t or c u r i o s i t y i n a c e r t a i n f i e l d , or second, they see a f i n a n c i a l or p r o f e s s i o n a l advancement from the s u c c e s s f u l completion of the work. Success i n the second case almost guarantees success i n the f i r s t . In s c i e n c e , success i n the second case commonly i s t i e d to r e c o g n i t i o n of the s c i e n t i s t as a generator of new ideas or techniques as i n d i c a t e d by f i r s t authorship on published t a l k s or papers. The use of "Doe, et a l . " to cover s e v e r a l authors of a paper i s an example of the downgrading of other c o n t r i b u t o r s to a paper. There i s no widely 5.


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recognized means of d i s t i n g u i s h i n g coauthors from j u n i o r authors. The r e s u l t i s that o f t e n each member of a cooperating group gets to p u b l i s h a short paper w i t h himself as s e n i o r author and others as j u n i o r authors. Because numbers of papers a r e important a l s o , we get a r e p e t i t i o n , or near r e p e t i t i o n , of the same ideas spread w i d e l y . S i n g l e , comprehensive r e p o r t s by m u l t i p l e authors of approximately equal s c i e n t i f i c s t a t u s are r a r e except where one i n d i v i d u a l c a r r i e s much of the load or the r e p o r t i s broken down to i d e n t i f y separate p a r t s by authorship. One thought i s to use some other i d e n t i f i c a t i o n of authorship i n s t e a d of one person's name. Perhaps the use of an acronym f o r the authors and an acknowledgements s e c t i o n d e s c r i b i n g each person's c o n t r i b u t i o n would work i n some i n s t a n c e s . " An example of the use of an acronym i s that of FOAM (Friends of Anoxic Mud, 4 0 ) . A s i g n i f i c a n t p a r t of the research e f f o r t of i n t e r d i s c i p l i nary s t u d i e s i s , and w i l l be, done by graduate students and postd o c t o r a l f e l l o w s , A major problem i n the u t i l i z a t i o n of graduate students and p o s t - d o c t o r a l f e l l o w s i s the matter of p r e p a r a t i o n of j o u r n a l a r t i c l e s from the research work. A completed t h e s i s i s i n and of i t s e l f o f t e n a s u f f i c i e n t l y traumatic experience that immediately proceeding to the p r e p a r a t i o n of j o u r n a l a r t i c l e s i s a d i f f i c u l t task f o r most advanced degree r e c i p i e n t s to f a c e . I n deed, t h e s i s completion i n v a r i a b l y continues beyond the a n t i c i p a ted date so that there i s r a r e l y time to work on follow-up j o u r n a l a r t i c l e s . I t i s g e n e r a l l y d i f f i c u l t to get p o s t - d o c t o r a l f e l l o w s to summarize t h e i r research a t r e g u l a r i n t e r v a l s . There are i n e v i t a b l y one o r two more very important things which they f e e l must be i n v e s t i g a t e d before t e r m i n a t i o n of the appointment. I n t h i s way, the b l o c k of time reserved f o r p r e p a r a t i o n of j o u r n a l a r t i c l e s can e a s i l y evaporate. However, t h i s d i f f i c u l t y may be minimized by a " c o n t r a c t " to the e f f e c t that the t h e s i s or postgraduate study i s incomplete u n t i l i t has been reduced to acceptable d r a f t s of j o u r n a l a r t i c l e s . Research s c i e n t i s t s i n v o l v e d i n i n t e r d i s i c p l i n a r y research i n the m i s s i o n - o r i e n t e d F e d e r a l Agencies must face an a d d i t i o n a l c o n f l i c t between the "need" to w r i t e papers and the "need" a t the agency to achieve c e r t a i n o b j e c t i v e s w i t h i n a f i x e d time p e r i o d . Often a complex choice must be made between these two demands on the s c i e n t i s t . On the one hand, i t can be argued that the i n i t i a l phases of a study were a t the taxpayer's expense so they must be reported i n the a r c h i v a l l i t e r a t u r e . On the other hand, p r e s s i n g on to the fundamental g o a l of an adequate understanding of some process o r to the development of some model may i n some instances be considered of s u f f i c i e n t importance t o o v e r r i d e the need f o r and v a l u e of any i n t e r i m s c i e n t i f i c paper(s)*. I t seems c l e a r


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that i f the p r e l i m i n a r y or i n i t i a l f i n d i n g s are such that they can reasonable be expected to a f f e c t ongoing or i n - t h e - p l a n n i n g stage research elsewhere s i g n i f i c a n t l y then the f i n d i n g should be published w i t h the d i s p a t c h . I f the primary v a l u e w i l l be an a d d i t i o n to some author's b i b l i o g r a p h y and l i s t of p r o j e c t r e p o r t s , then the p u b l i c i n t e r e s t may be e q u a l l y w e l l served by moving as e x p e d i t i o u s l y as p o s s i b l e to the f i n a l o b j e c t i v e . This approach i s hazardous i n the case of a s i n g l e i n v e s t i g a t o r i n that a change of j o b or an untimely death may cause the l o s s of the monies which supported man-years of research. Graduate T r a i n i n g . Another avenue to increased s c i e n t i f i c progress i n c l u d e s the improved academic p r e p a r a t i o n of research s c i e n t i s t s . We should, of course, heed the admonition of Hubbert (41) " — t h a t t h i n k i n g i s p e c u l i a r l y an i n d i v i d u a l e n t e r p r i s e , and that the g r e a t e s t of a l l s c i e n t i f i c achievements — those of the great s y n t h e s i z e r s from G a l i l e o to E i n s t e i n — have, almost without e x c e p t i o n , been the work of individuals." T r a i n i n g i n s c i e n t i f i c research i s presumed to be of a h i g h q u a l i t y i n t h i s country, but i s i n f a c t not i n v a r i a b l y so. Such t r a i n i n g f o r the Ph. D. degree should i n c l u d e : 1) a summer i n f i e l d work (outside of the t h e s i s t o p i c i f necessary) and a summer i n l a b o r a t o r y work; 2) experience i n the p r e p a r a t i o n of c r i t i c a l l i t e r a t u r e reviews; 3) a t l e a s t one t e c h n i c a l paper submitted f o r p u b l i c a t i o n before t h e s i s w r i t i n g i s s t a r t e d ; 4) arrangements f o r adequate t e c h n i c a l s u p e r v i s i o n of t h e s i s research; 5) adequate knowledge p l u s experience i n the b e h a v i o r a l sciences (pyschology, s o c i o l o g y , e t c . ) ; and 6) experience i n one a s s o c i a t i v e i n t e g r a t e d research study. C o n s i d e r a t i o n should be given to dropping nont h e s i s advanced degrees from both the p h y s i c a l and b i o l o g i c a l sciences. Some d i s c u s s i o n of the f i r s t of the above t r a i n i n g items may be i n order. I n t h i s day of s p e c i a l i z a t i o n , i t may seem strange to r e q u i r e a t h e o r e t i c a l chemist to spend a summer i n a f i e l d ecosystem study. This aspect of graduate education i s intended to f a c i l i t a t e i n t e r d i s c i p l i n a r y research and to provide the experience t o a s s i s t i n b r i d g i n g the gap between f i e l d and l a b o r a t o r y research. S i m i l a r l y , the research achievements of many b r i g h t young graduates are l i m i t e d more by t h e i r i n a b i l i t y to work w e l l w i t h others than by l i m i t a t i o n of i n t e l l i g e n c e or w i l l i n g n e s s to work hard. Some focused t r a i n i n g i n b e h a v i o r a l sciences might w e l l increase the i n t r i n s i c value of graduates t r a i n e d i n t h i s way. Approaches and P r i o r i t i e s How, then, can the progress of Science i n general and of chemical modeling i n p a r t i c u l a r be promoted i n the f o l l o w i n g



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decade? Several avenues e x i s t . I t seems c l e a r that one avenue i s f o r research r e l a t i n g to chemical modeling to be c a r r i e d out w i t h i n the context of i n t e g r a t e d i n t e r d i s c i p l i n a r y , m u l t i s c i e n t i s t s t u d i e s . As R u s s e l l Peterson (42) has r e c e n t l y pointed out, " . . . s p e c i a l i z a t i o n has been necessary f o r s c i e n t i f i c and t e c h n o l o g i c a l advance; and we have learned much more and learned i t q u i c k l y by breaking down phenomena i n t o v a r i o u s compartments and studying them from the standpoints of b i o l o g y , p h y s i c s , chemistry, and so f o r t h . But we must remember that our world does not e x i s t i n compartments; i t comes i n s i n g l e , i n t e r r e l a t e d communities, each part of which a f f e c t s other parts.... i t would do w e l l f o r s c i e n t i s t s to e s t a b l i s h the h a b i t of stepping back o c c a s i o n a l l y from the immediate task to r e f l e c t on what k i n d of world he or she wants f o r h i s or her c h i l d r e n and g r a n d c h i l d r e n and cons i d e r whether the work he or she i s doing i s l e a d i n g i n the r i g h t d i r e c t i o n . I f not, the s c i e n t i s t should have the courage to a l t e r h i s course, even i f i t means some near-term personal s a c r i f i c e . I t r e q u i r e s courage to speak and a c t e f f e c t i v e l y a g a i n s t the s t a t u s quo. But we can b r i n g about the e s s e n t i a l changes. To do so w i l l r e q u i r e that we look at things comprehensively and work toward worldwide goals that provide f o r improving the q u a l i t y of l i f e everywhere." And as E. Odum (43) has s t a t e d so s u c c i n t l y , " I t i s s e l f - e v i d e n t that science should not only be r e d u c t i o n i s t i n the sense of seeking to understand phenomena by d e t a i l e d study of s m a l l e r and smaller components, but a l s o s y n t h e t i c and h o l i s t i c i n the sense of seeking to understand l a r g e components as f u n c t i o n a l wholes,-—Science and technology during the past h a l f century have been so preoccupied w i t h reductionism that s u p r a i n d i v i d u a l systems have s u f f e r e d benign n e g l e c t . We are abysmally ignorant of the ecosystems of which we are dependent p a r t s . — t h e time has come to g i v e equal time, and equal research and development funding, to the higher l e v e l s of b i o l o g i c a l o r g a n i z a t i o n i n the h i e r a r c h i a l sequences. I t i s i n the p r o p e r t i e s of the l a r g e - s c a l e , i n t e g r a t e d systems that h o l d s o l u t i o n s to most of the long-range problems of society." C l e a r l y , i n t e g r a t e d , i n t e r d i s c i p l i n a r y , m u l t i s c i e n t i s t e f f o r t s are r e q u i r e d to achieve the goal of p r e d i c t i v e chemical modeling of aquatic ecosystems and to make progress toward the goal of understanding the b i o a v a i l a b i l i t y of t r a c e elements to the v a r i o u s food chain components w i t h i n the next decade. Funding agencies could w e l l develop ways of p e r m i t t i n g and even of encouraging i n d i v i d u a l i n v e s t i g a t o r s to continue along given broad t o p i c a l or technique pathways to enhance the production



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of s i g n i f i c a n t i n f o r m a t i o n — a s opposed to gathering more data. This c o n t i n u i t y of i n v e s t i g a t i v e area or i n v e s t i g a t i v e techniques appears to be e s s e n t i a l to i n c r e a s e the i n t r i n s i c value of r e search products. The a c c e l e r a t i o n i n r a t e of data generation by the s c i e n t i f i c community and the s o p h i s t i c a t i o n of techniques and methods o f t e n r e q u i r e d f o r s i g n i f i c a n t research progress r e q u i r e the b u i l d u p of e x p e r t i s e and equipment. The r a p i d changes i n s o c i e t a l concerns and governmental programs o f t e n r e s u l t i n p r i n c i p a l i n v e s t i g a t o r s ' t a k i n g on s t u d i e s i n t a n g e n t i a l or even t o t a l l y new areas t h i s d i v e r s i o n of e f f o r t f r e q u e n t l y d e t r a c t s from o r i g i n a l goals and from b u i l d i n g up of e x p e r t i s e i n a given area. The net e f f e c t of these c o n d i t i o n s i s that too many i n v e s t i gators are: 1) i n s u f f i c i e n t l y knowledgeable of published i n f o r mation; 2) unacquainted w i t h the conventional wisdom of the f i e l d ; and 3) unable to secure adequate funding of s u f f i c i e n t d u r a t i o n to maximize the s c i e n t i f i c value of t h e i r t e c h n i c a l products. The l a c k of p e r t i n e n t r e l i a b l e thermodynamic data needed f o r chemical modeling i s a problem which could be r e s o l v e d i n the near f u t u r e f o r waters to which i o n - a s s o c i a t i o n models a r e a p p l i c a b l e . This progress would be f a c i l i t a t e d by a coordinated e f f o r t among the funding agencies, the c o m p i l a t i o n - e v a l u a t i o n agencies, and p r o f e s s i o n a l s o c i e t y groups. S a t i s f a c t o r y modeling of b r i n e s and other concentrated waters w i l l r e q u i r e a major focused e f f o r t . The p r i o r i t y of v a r i o u s n a t i o n a l problems to whose s o l u t i o n chemic a l modeling could c o n t r i b u t e needs to be e s t a b l i s h e d . A s i m i l a r e v a l u a t i o n and p r i o r i t i z a t i o n i s needed f o r k i n e t i c data. Summary Trust i n , and support f o r , s c i e n t i f i c i n v e s t i g a t i o n of fundamental processes has weakened i n the l a s t decade. I n c r e a s i n g emphasis has been given to the "black-box" type of modeling s o l u t i o n s to environmental problems. The u l t i m a t e goal of r e search i n g e n e r a l , and of chemical modeling i n p a r t i c u l a r , i s human betterment. I hope t h i s symposium w i l l c o n t r i b u t e toward t h i s primary o b j e c t i v e . The immediate goals of t h i s symposium are the promoting of the t i m e l y exchange of p e r t i n e n t i n f o r m a t i o n ; the f o s t e r i n g of extensive d i s c u s s i o n of g o a l s , problems, approaches, as w e l l as research p r i o r i t i e s ; and the p r e p a r a t i o n of a symposium proceedings. The p r i n c i p a l r e s t r i c t i o n s on u s e f u l a p p l i c a t i o n of chemical models, to problems ranging from aqueous s p e c i a t i o n to b i o a v a i l a b i l i t y i n the human d i g e s t i v e system, i n c l u d e inadequate knowledge of n a t u r a l organic l i g a n d s ; of redox processes; of thermodynamic, time-dependent and k i n e t i c i n f o r mation and anthropogenic i n p u t s ; and inadequate c h a r a c t e r i z a t i o n of the n a t u r a l systems being modeled. What many observers cons i d e r a low r a t e of progress being made i n s o l v i n g these problems i s due, i n p a r t , to the short term of funding a v a i l a b l e t o many i n v e s t i g a t o r s , to inadequate cognizance and s y n t h e s i s of the a v a i l a b l e t e c h n i c a l l i t e r a t u r e s on the p a r t of some i n v e s t i g a t o r s


18


and t o the l a c k of i n t e g r a t e d , i n t e r d i s c i p l i n a r y , s t u d i e s i n many of the systems being modeled.

multiscientist

Acknowledgments P l e a s u r a b l e d i s c u s s i o n s w i t h Ronald James, Jack F e t h , A l a n Jackman, Ralph Cheng, Ray Wildung, and Harvey Drucker, but most e s p e c i a l l y w i t h Vance Kennedy, are acknowledged. Donald Langmuir, Harry L e l a n d , Frank T r a i n e r , and p a r t i c u l a r l y David R i c k e r t provided v e r y h e l p f u l reviews.


Abstract The ultimate goal of research in support of chemical modeling, as in most scientific research, is the improvement of human life physically, emotionally, and aesthetically through the understanding and prediction of processes and events. More immediate objectives include reliable aqueous speciation of trace elements between their valence states and among organic and inorganic ligands, and prediction of sorption equilibria and kinetic parameters as well as solubility controls on trace element solute levels. The objective is to predict toxicity and bioaccumulation in aquatic organisms and ultimately in man. The complex and interactive nature of aqueous speciation (redox states, organic and inorganic complexation) and of sorption-desorption by sediment and biota, and the precipitation-dissolution of solid phases,requires comprehensive models and extensive analyses of an adequate number of appropriately collected and preserved samples. The prediction of chronic toxicity and bioaccumulation of trace elements w i l l require the linking of chemical models to biologic and hydrologic models. This mandates a multiscience, interdisciplinary approach to the development, testing, and application of comprehensive models to assist in solving and preventing environmental problems. Important restraints on the evolution of superior chemical models are the inadequacies in the: 1) capability to characterize the organic ligands of natural waters; 2) knowledge of redox status of waters, which does not permit r e a l i s t i c computation of redox-controlled speciation; 3) available thermodynamic data; 4) knowledge of the time dependency of the various processes in general (such as variation in apparent trace-element concentration during a t i d a l cycle) and kinetic data for chemical and biological processes in particular; and 5) error estimates for the preceding restraints. The f i e l d of chemical modeling is also constrained by the: 6) need for comprehensive analyses of the systems to be modeled; 7) limitations of published data; 8) scarcity of adequate literature reviews; 9) d i f f i c u l t i e s in organizing and conducting integrated interdisciplinary studies; and to a lesser extent, 10) limitation in quality of graduate training.


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