Computerized System for Performing Risk Assessments for Chemical

Chapter 13

Computerized System for Performing Risk Assessments for Chemical Constituents of Hazardous Waste 1

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John L. Schaum , John J. Segna , John S. Young , Carol M. Benes , and Warren R. Muir Downloaded by NATL UNIV OF SINGAPORE on May 5, 2018 | https://pubs.acs.org Publication Date: July 5, 1990 | doi: 10.1021/bk-1990-0431.ch013

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Office of Research and Development (RD-689), U.S. Environmental Protection Agency, 401 M Street, S.W., Washington, DC 20460 The Hampshire Research Institute, 1800 Diagonal Road, Alexandria, VA 22309 The U.S. Environmental Protection Agency has sponsored the development of a software system to assist environment a l personnel in conducting risk assessments at hazardous waste sites, and also i n reviewing assessments generated by contractors for correspondence with EPA and state standards. This computerized system, called Risk*Assistant, combines a series of tools, including databases, expert exposure and risk values. These tools are provided in an IBM-PC format, with a user-friendly interface that allows a user to begin using the system quickly with little or no training. 2

As the p r o c e s s o f r e g u l a t i n g and c o n t r o l l i n g t h e r e l e a s e o f p o t e n t i a l l y hazardous c h e m i c a l s i n t o t h e environment becomes a more complex t a s k , t h e U.S. E n v i r o n m e n t a l P r o t e c t i o n Agency (EPA) has moved v i g o r o u s l y t o a r i s k assessment / r i s k management / r i s k r e d u c t i o n framework f o r making r e g u l a t o r y d e c i s i o n s . C o n s e q u e n t l y , t h e EPA has u n d e r t a k e n a major e f f o r t t o g a i n an u n d e r s t a n d i n g of the r i s k assessment p r o c e s s and t o c o n s i d e r q u a l i t y and c o n s i s t e n c y i n r i s k assessments a major g o a l f o r t h e 1980s and 1990s. P a r t o f t h e p r o c e s s i n a c h i e v i n g t h i s g o a l has been t h e development o f EPA r i s k assessment guidelines. These g u i d e l i n e s i n c l u d e f o u r areas c o n c e r n i n g h e a l t h e f f e c t s , w h i l e t h e f i f t h d e a l s w i t h exposure assessment (1) Components o f R i s k Assessment The N a t i o n a l R e s e a r c h C o u n c i l (2) has d i v i d e d t h e p r o c e s s o f r i s k assessment i n t o f o u r components. These a r e : (1) Hazard I d e n t i f i c a t i o n - c o n s i s t s o f a r e v i e w o f r e l e v a n t b i o l o g i c a l and c h e m i c a l i n f o r m a t i o n b e a r i n g on whether o r n o t an agent may pose a s p e c i f i c h a z a r d . 0097-6156/90/0431-0176$06.00/0 © 1990 American Chemical Society

Hushon; Expert Systems for Environmental Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

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Performing Risk Assessmentsfor

(2) Dose-Response Assessment - i n v o l v e s d e s c r i b i n g t h e q u a n t i t a t i v e r e l a t i o n s h i p between t h e amount o f exposure t o a substance and t h e extent of t o x i c i n j u r y o r disease.

Downloaded by NATL UNIV OF SINGAPORE on May 5, 2018 | https://pubs.acs.org Publication Date: July 5, 1990 | doi: 10.1021/bk-1990-0431.ch013

(3) Human Exposure E v a l u a t i o n - i n v o l v e s d e s c r i b i n g t h e n a t u r e and s i z e o f t h e p o p u l a t i o n exposed t o a substance and t h e magnitude and d u r a t i o n o f t h e i r e x p o s u r e . The e v a l u a t i o n c o u l d c o n c e r n past, current, or future exposures. (4) R i s k C h a r a c t e r i z a t i o n - i n v o l v e s t h e i n t e g r a t i o n o f t h e d a t a and analyses from t h e f i r s t t h r e e components t o determine t h e l i k e l i h o o d t h a t humans w i l l e x p e r i e n c e any o f t h e v a r i o u s forms of t o x i c i t y a s s o c i a t e d w i t h a substance. The U.S. EPA approach t o r i s k assessments f o r t o x i c c h e m i c a l s f o l l o w s t h e format d e s c r i b e d by t h e NRC. Because Hazard I d e n t i f i c a t i o n and Dose-Response Assessment f o r an agent do n o t depend upon s p e c i f i c l o c a l s i t u a t i o n s , EPA assumes t h a t r i s k a s s e s s o r s e v a l u a t i n g s p e c i f i c s i t e s w i l l n o t conduct independent a n a l y s e s i n t h e s e a r e a s but w i l l i n s t e a d r e l y on t h e r e s u l t s o f p e e r - r e v i e w e d e v a l u a t i o n s by q u a l i f i e d a u t h o r i t i e s i n t o x i c o l o g y . EPA i s a s s e m b l i n g an agency-wide database o f such a u t h o r i t a t i v e assessments, t h e I n t e g r a t e d Risk I n f o r m a t i o n System ( I R I S ) . A l t h o u g h t h e Hazard I d e n t i f i c a t i o n and Dose-Response Assessment of an agent a r e g e n e r i c , t h e r i s k s t h a t t h e agent poses a r e s p e c i f i c t o a p a r t i c u l a r l o c a t i o n and s e t o f c i r c u m s t a n c e s i n w h i c h exposure t o t h e agent o c c u r s . I n o r d e r t o a s s e s s s i t e - s p e c i f i c r i s k s o f an agent, t h e a s s e s s o r must p e r f o r m a s p e c i f i c Exposure E v a l u a t i o n f o r the s i t e , and combine i t w i t h i n f o r m a t i o n on t h e Hazards posed by t h e agent t o y i e l d a R i s k C h a r a c t e r i z a t i o n f o r t h e s i t e . EPA r i s k assessment p r a c t i c e , (and t h e R i s k * A s s i s t a n t s o f t w a r e ) r e f l e c t s t h i s d i s t i n c t i o n between g e n e r i c and s i t e - s p e c i f i c i n f o r m a t i o n i n t h e p r e d i c t i o n o f t h e r i s k s a s s o c i a t e d w i t h an agent a t a specific site. The r e s u l t s o f a u t h o r i t a t i v e Hazard I d e n t i f i c a t i o n s and Dose-Response Assessments a r e n o t e x p e c t e d t o be r e - e v a l u a t e d by the r i s k a s s e s s o r s e v a l u a t i n g s p e c i f i c s i t e s ; t h e s e a s s e s s o r s a r e e x p e c t e d t o c o n c e n t r a t e on s i t e - s p e c i f i c Exposure E v a l u a t i o n and R i s k Characterization. Human Exposure Assessment. The assessment o f human exposure i n v o l v e s the measurement o r e s t i m a t i o n o f t h e number o f p e o p l e exposed and t h e magnitude, d u r a t i o n , and t i m i n g o f t h e i r exposure. I n some c a s e s , i t i s s t r a i g h t f o r w a r d t o measure human exposure d i r e c t l y by measuring l e v e l s o f t h e hazardous agent i n t h e ambient environment. I n most c a s e s , however, d e t a i l e d knowledge i s r e q u i r e d o f t h e f a c t o r s t h a t c o n t r o l human exposure, i n c l u d i n g those f a c t o r s w h i c h determine t h e b e h a v i o r o f t h e agent a f t e r i t s r e l e a s e i n t o t h e environment. The f o l l o w i n g t y p e s o f i n f o r m a t i o n a r e r e q u i r e d f o r an exposure a s s e s s ment: (1) Q u a n t i t i e s o f an agent t h a t timing of release.

are released

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(2) F a c t o r s c o n t r o l l i n g the f a t e of the agent i n the environment a f t e r r e l e a s e , i n c l u d i n g f a c t o r s c o n t r o l l i n g i t s movement, p e r s i s t e n c e , and d e g r a d a t i o n . (3) F a c t o r s c o n t r o l l i n g human c o n t a c t w i t h the agent, i n c l u d i n g the s i z e and d i s t r i b u t i o n o f the p o p u l a t i o n , and a c t i v i t i e s t h a t f a c i l i t a t e o r prevent c o n t a c t .


(4) P a t t e r n s of human i n t a k e s . The amount o f each type o f i n f o r m a t i o n t h a t i s a v a i l a b l e v a r i e s g r e a t l y from case t o case and may be d i f f i c u l t t o p r e d i c t a c c u r a t e l y . T h e r e f o r e , except i n f o r t u n a t e c i r c u m s t a n c e s i n w h i c h the b e h a v i o r o f an agent i n the environment i s u n u s u a l l y s i m p l e , u n c e r t a i n t i e s a r i s i n g i n exposure assessments can be s i g n i f i c a n t . The f i r s t two f a c t o r s o f the f o u r l i s t e d above are a d d r e s s e d by a wide range of e n v i r o n m e n t a l f a t e and t r a n s p o r t models t h a t v a r y i n t h e o r e t i c a l and m a t h e m a t i c a l c o m p l e x i t y and i n the e x t e n t t o w h i c h they have been v a l i d a t e d . EPA has sponsored r e s e a r c h and development of numerous such models; among the most s u c c e s s f u l implementations i s the P e r s o n a l Computer - G r a p h i c a l Exposure M o d e l i n g System or PC-GEMS (3) developed under the s p o n s o r s h i p of the O f f i c e of T o x i c Substances. Such models h e l p the r i s k a s s e s s o r t o p r e d i c t the number o f p e o p l e who may be exposed t o c h e m i c a l s l e a v i n g a s i t e , and the environmental c o n c e n t r a t i o n s t o w h i c h they might be exposed. They do n o t , however, address the c r u c i a l i s s u e s o f the p a t t e r n o f human a c t i v i t i e s t h a t r e s u l t i n c o n t a c t w i t h the agent, and the amounts o f the agent w i t h w h i c h people may come i n c o n t a c t . Such exposure i n f o r m a t i o n , r a t h e r than p r e d i c t e d or measured environmental c o n c e n t r a t i o n s , i s needed t o p r e d i c t the r i s k s ass o c i a t e d w i t h an agent. ( R i s k * A s s i s t a n t was e x p l i c i t l y designed t o provide r i s k assessors w i t h assistance i n t h i s p r e v i o u s l y neglected area.) J u s t as the models used t o p r e d i c t the t r a n s p o r t and f a t e of c h e m i c a l s i n the environment are s e n s i t i v e t o numerous s i t e - s p e c i f i c parameters such as average r a i n f a l l and s o i l t y p e s , the e q u a t i o n s used t o determine exposures f o r p a r t i c u l a r a c t i v i t y p a t t e r n s are s e n s i t i v e t o demographic parameters. These i n c l u d e g e n e r a l p o p u l a t i o n c h a r a c t e r i s t i c s (e.g. age d i s t r i b u t i o n s ) , c u l t u r a l l y - i n f l u e n c e d f a c t o r s (e.g.. r a t e s of f i s h and v e g e t a b l e c o n s u m p t i o n ) , and l o c a t i o n - s p e c i f i c f a c t o r s (e.g. w o r k p l a c e exposure p a t t e r n s are g e n e r a l l y d i f f e r e n t from those i n the home). EPA has r e c e n t l y p u b l i s h e d the r e s u l t s o f i t s e f f o r t s t o determine v a l u e s f o r numerous parameters t h a t are c h a r a c t e r i s t i c of the average p o p u l a t i o n o f the U.S. ( 4 ) , but the r i s k a s s e s s o r must a d j u s t these parameters t o f i t the s p e c i f i c p o p u l a t i o n she o r he i s e v a l u a t i n g . R i s k C h a r a c t e r i z a t i o n . The f i n a l s t e p i n r i s k assessment i n v o l v e s b r i n g i n g t o g e t h e r the i n f o r m a t i o n p r o v i d e d i n the exposure assessment w i t h i n f o r m a t i o n on the t o x i c h a z a r d s of an agent t o determine r i s k . For agents w h i c h may be c a r c i n o g e n s , the c a r c i n o g e n i c potency ( a l s o c a l l e d the s l o p e f a c t o r ) and L i f e t i m e Average D a i l y Exposure (LADE) are used t o d e r i v e an e s t i m a t e o f the p r o b a b i l i t y t h a t the s p e c i f i e d exposure w i l l i n c r e a s e c a n c e r i n c i d e n c e over background r a t e s (the



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a c t u a l e q u a t i o n i s [1 - exp (-LADE χ S l o p e ) ] , w h i c h p r e c l u d e s r i s k s g r e a t e r than 1.0). F o r non-cancer t o x i c e f f e c t s , s t a n d a r d p r a c t i c e i s t o compute a Hazard Index, w h i c h i s t h e r a t i o o f t h e Average D a i l y Exposure (ADE) t o t h e R e f e r e n c e Dose (RfD). Hazard I n d i c e s l e s s than 1.0 a r e assumed n o t t o be a s s o c i a t e d w i t h a s i g n i f i c a n t r i s k o f t o x i c effects. W h i l e t h e r i s k c h a r a c t e r i z a t i o n c a l c u l a t i o n s themselves a r e s t r a i g h t f o r w a r d t h e way i n w h i c h t h e i n f o r m a t i o n i s p r e s e n t e d i s important. F o r example, t h i s step can be f a r more complex than i n d i c a t e d h e r e , e s p e c i a l l y i f problems a s s o c i a t e d w i t h d u r a t i o n and/or t i m i n g o f exposure a r e c o n s i d e r e d . F u r t h e r , a t many s i t e s i t i s n e c e s s a r y f o r t h e a s s e s s o r t o c o n s i d e r p o s s i b l e i n t e r a c t i o n s among s e v e r a l agents. The n o n - c a r c i n o g e n i c and t h e c a r c i n o g e n i c r i s k values, together w i t h t h e i r associated estimates o f u n c e r t a i n t y , are the f i n a l measures o f t h e p o s s i b i l i t y o f human i n j u r y o r d i s e a s e from a g i v e n exposure o r range o f e x p o s u r e s . S t a n d a r d i z i n g R i s k Assessment The EPA r e l i e s on a r i s k assessment approach t o make b e t t e r r e g u l a t o r y d e c i s i o n s . However, r i s k assessment i s a m u l t i - d i s c i p l i n a r y p r o c e s s p o t e n t i a l l y i n v o l v i n g t h e e f f o r t s o f a n a l y t i c a l and e n v i r o n m e n t a l chemists, biologists, environmental engineers, statisticians, t o x i c o l o g i s t s , and o t h e r s as a p p r o p r i a t e ( 5 ) . I t i s r a r e l y p o s s i b l e to o b t a i n e x t e n s i v e i n v o l v e m e n t from p r o f e s s i o n a l s i n a l l o f t h e r e l e v a n t d i s c i p l i n e s f o r any s i t e - s p e c i f i c r i s k assessment. S t a f f i n g l i m i t a t i o n s mean t h a t t h e r i s k a s s e s s o r i n t h e f i e l d must o f t e n make do w i t h l i m i t e d h e l p from p r o f e s s i o n a l s i n some r e l e v a n t d i s c i p l i n e s . EPA i s n a t u r a l l y i n t e r e s t e d i n p r o d u c i n g r i s k assessments o f t h e highest possible q u a l i t y . T h i s r e q u i r e s t h a t each assessment i s s e n s i t i v e t o s i t e - s p e c i f i c c o n d i t i o n s , w h i l e using procedures t h a t are c o n s i s t e n t w i t h those o f o t h e r agency-sponsored assessments. Both i n c o n s i s t e n c y i n approach and l a c k o f t e c h n i c a l q u a l i t y (such as i n s e n s i t i v i t y t o l o c a l c o n d i t i o n s ) r e p r e s e n t problems i n t h e r i s k assessment p r o c e s s . EPA i s a c t i v e l y engaged i n s e v e r a l e f f o r t s t o m a i n t a i n q u a l i t y and c o n s i s t e n c y i n r i s k assessment, i n t h e f a c e o f d i s t i n c t l y l i m i t e d p r o f e s s i o n a l resources. The t r a i n i n g o f p r o f e s s i o n a l p e r s o n n e l i n t h e r i s k assessment p r o c e s s i s an ongoing a c t i v i t y a t EPA. However, c l a s s r o o m t r a i n i n g i s o n l y a p a r t i a l answer t o EPA* s r i s k assessment dilemma. It l e s s e n s , b u t has n o t e l i m i n a t e d , t h e p r e s s u r e o f EPA t o r e v i e w t e c h n i c a l reports w i t h l e s s experienced p r o f e s s i o n a l personnel. The development o f a computer s o f t w a r e system, R i s k * A s s i s t a n t , t o a s s i s t e n v i r o n m e n t a l p e r s o n n e l i n c o n d u c t i n g r i s k assessments and r e v i e w i n g assessments g e n e r a t e d by c o n t r a c t o r s , r e p r e s e n t s a complementary approach t o i n c r e a s i n g t h e t e c h n i c a l q u a l i t y and c o n s i s t e n c y o f r i s k assessments. Risk*Assistant Capabilities Software f o r r i s k assessment must address a v a r i e t y o f i n f o r m a t i o n manipulations, i n c l u d i n g data r e t r i e v a l , c a t e g o r i c a l or rule-based d e c i s i o n s , and m a t h e m a t i c a l c a l c u l a t i o n s . Such a range o f m a n i p u l a t i o n s a r e n o t f u l l y a d d r e s s e d by any s i n g l e programming approach. F o r


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example, many e x p e r t system s h e l l s are n o t o p t i m a l environments f o r p e r f o r m i n g e x t e n s i v e c a l c u l a t i o n s , a l t h o u g h they a r e f a r more c o n v e n i e n t than programming languages as a means o f e n c o d i n g c a t e g o r i cal decisions. In v i e w o f the l i m i t a t i o n s o f each o f the common approaches t o programming f o r a d d r e s s i n g the range o f problem t y p e s encountered i n r i s k assessment, R i s k * A s s i s t a n t was d e s i g n e d as a modular s o f t w a r e system. I n o t h e r words, i t i s a s e r i e s o f s e p a r a t e programs, each o f which addresses a p a r t i c u l a r component o f r i s k assessment. A l l the programs are l i n k e d by a common "system s h e l l , " t h a t ensures each program i s p r o v i d e d w i t h the i n f o r m a t i o n i t needs from o t h e r programs and a l l o w s u s e r s t o use as many o f the programs as a r e needed w i t h a minimum o f e f f o r t . Because o f i t s modular d e s i g n , R i s k * A s s i s t a n t can r e a d i l y be "customized" t o address the s p e c i f i c a n a l y t i c a l needs o f any d e s i g n a t e d group o f u s e r s . The c u r r e n t v e r s i o n has f o c u s e d on the needs o f EPA and s t a t e p e r s o n n e l who generate o r r e v i e w r i s k a s s e s s ments o f hazardous waste t r e a t m e n t , s t o r a g e , and d i s p o s a l f a c i l i t i e s . Components o f R i s k A s s i s t a n t . There are t h r e e main components o f the R i s k * A s s i s t a n t s o f t w a r e system, each o f w h i c h r e f l e c t s a d i f f e r e n t approach t o u s i n g the i n f o r m a t i o n c o n t a i n e d i n the system. Each segment makes use o f the same f a m i l y o f program modules, but s e l e c t s d i f f e r e n t s u b s e t s o f these modules t o address p a r t i c u l a r q u e s t i o n s . Main A n a l y s e s . The main a n a l y s e s s e c t i o n o f the s o f t w a r e system i n c l u d e s those program modules t h a t d i r e c t l y a s s i s t the u s e r i n e i t h e r g e n e r a t i n g o r r e v i e w i n g exposure and r i s k assessments f o r hazardous waste s i t e s . They i n c l u d e modules f o r Case D e s c r i p t i o n , Exposure Assessment, and R i s k C h a r a c t e r i z a t i o n , as w e l l as a s e r i e s o f Superfund C h e c k l i s t Modules. Case D e s c r i p t i o n . O b v i o u s l y , any s i t e - s p e c i f i c r i s k assessment r e q u i r e s i n f o r m a t i o n on the r e l e v a n t c h a r a c t e r i s t i c s o f the s i t e . The Case D e s c r i p t i o n module a l l o w s the u s e r o f R i s k * A s s i s t a n t t o e n t e r o r modify b o t h the d e s c r i p t i v e i n f o r m a t i o n r e g a r d i n g a s i t e o f p o t e n t i a l c h e m i c a l r e l e a s e and the s a m p l i n g and a n a l y t i c a l d a t a ( i n c l u d i n g quantitation l i m i t s ) associated with that s i t e . I t a l s o a l l o w s the u s e r t o s e l e c t s u b s e t s o f d a t a a s s o c i a t e d w i t h a s i t e f o r use i n any of the o t h e r R i s k * A s s i s t a n t a n a l y s e s . Exposure Assessment. As n o t e d above, the R i s k * A s s i s t a n t s o f t w a r e i s i n t e n d e d t o b u i l d on EPA*s e x i s t i n g i n f o r m a t i o n base on e n v i r o n m e n t a l f a t e and t r a n s p o r t m o d e l l i n g , e x t e n d i n g i t t o r i s k - r e l e v a n t exposure calculations. A c c o r d i n g l y , i t does not i n c o r p o r a t e m a t h e m a t i c a l models o f the e n v i r o n m e n t a l t r a n s p o r t and f a t e o f c h e m i c a l s , but t a k e s as i t s s t a r t i n g p o i n t u s e r - s p e c i f i e d d a t a on e n v i r o n m e n t a l c o n c e n t r a t i o n s o f c h e m i c a l s t o w h i c h p e o p l e might be exposed. The A d d i t i o n a l A n a l y s e s d i s c u s s e d below, however, do i n c l u d e t o o l s t o a s s i s t the r i s k a s s e s s o r i n s e l e c t i n g a p p r o p r i a t e t r a n s p o r t models. As n o t e d above, the exposures a c t u a l l y e x p e r i e n c e d by people i n an environment contaminated by c h e m i c a l s depend n o t o n l y the conc e n t r a t i o n s o f the c h e m i c a l s i n e n v i r o n m e n t a l media but a l s o on the s p e c i f i c d e t a i l s o f the a c t i v i t i e s i n w h i c h they engage. F a c t o r s such as i n h a l a t i o n r a t e s , time spent i n the home and o u t d o o r s , and the



13.

S C H A U M ET AL.


amounts o f v a r i o u s types o f foods consumed w i l l have s i g n i f i c a n t impact on exposures a t any g i v e n e n v i r o n m e n t a l c o n c e n t r a t i o n o f a chemical. EPA has r e c e n t l y r e l e a s e d the f i r s t volume c o n t a i n i n g the r e s u l t s of an e f f o r t t o o b t a i n the most r e l i a b l e p o s s i b l e v a l u e s f o r a v a r i e t y o f exposure parameters. T h i s document, The Exposure F a c t o r s Handbook (A), covers 12 commonly c o n s i d e r e d exposure s c e n a r i o s . The exposure assessment module of R i s k * A s s i s t a n t i n c o r p o r a t e s the a l g o r i t h m s f o r c a l c u l a t i n g exposures under each o f these s c e n a r i o s , f o r a l l e n v i r o n m e n t a l media f o r w h i c h the s c e n a r i o i s a p p l i c a b l e . The u s e r can s e l e c t any o r a l l of the exposure s c e n a r i o s t h a t are r e l e v a n t t o the e n v i r o n m e n t a l media t h a t are c o n t a m i n a t e d a t a s i t e . Where more t h a n one c o n t a m i n a t e d medium c o u l d i n f l u e n c e a s c e n a r i o , the u s e r has the o p t i o n of s e l e c t i n g the most a p p r o p r i a t e medium. As a f u r t h e r a i d t o the r i s k a s s e s s o r , R i s k * A s s i s t a n t i n c o r p o r a t e s a database of the "average" and "reasonable w o r s t - c a s e " v a l u e s f o r the parameters a p p l i c a b l e t o each o f the exposure s c e n a r i o s . The "average" v a l u e i s a u t o m a t i c a l l y p r o v i d e d as a d e f a u l t . However, such "average" v a l u e s may not be a p p r o p r i a t e f o r p a r t i c u l a r l o c a t i o n s o r p o p u l a t i o n s , and the u s e r has the a b i l i t y t o s u b s t i t u t e the "reasona b l e w o r s t case" parameter v a l u e , o r any o t h e r a p p r o p r i a t e v a l u e f o r the s p e c i f i c p o p u l a t i o n under c o n s i d e r a t i o n , f o r each parameter i n each s c e n a r i o . Such an approach p r o v i d e s f o r r i s k assessments t h a t are r e s p o n s i v e t o the c o n t e x t o f s p e c i f i c s i t e s , y e t r e t a i n a fundamental c o n s i s t e n c y o f approach. Sets o f s c e n a r i o s and parameters t h a t a p p l y t o p a r t i c u l a r p o p u l a t i o n s of i n t e r e s t t o a u s e r may be s t o r e d f o r f u t u r e use. Exposure v a l u e s are r e p o r t e d f o r each r o u t e of exposure ( o r a l and i n h a l a t i o n r o u t e s are c o v e r e d i n the c u r r e n t v e r s i o n and the dermal r o u t e w i l l be developed i n the f u t u r e ) f o r each d i f f e r e n t s c e n a r i o and f o r each r o u t e of exposure per each c o n t a m i n a t e d medium. A key a d d i t i o n a l f e a t u r e p r o v i d e d by the exposure assessment module i s the a b i l i t y t o a u t o m a t i c a l l y c a l c u l a t e s e v e r a l i n d i c e s o f the u n c e r t a i n t y a s s o c i a t e d w i t h the assessment. W i t h a few keys t r o k e s , the u s e r can c a l c u l a t e the exposures a s s o c i a t e d w i t h b o t h "average" and "reasonable w o r s t case" parameter v a l u e s , as w e l l as o t h e r c o m b i n a t i o n s of parameter v a l u e s . I n a d d i t i o n , f u t u r e v e r s i o n s w i l l a l l o w the u s e r t o examine the r e l a t i v e c o n t r i b u t i o n t o exposure o f each of the s c e n a r i o s s e l e c t e d f o r e v a l u a t i o n . R i s k C h a r a c t e r i z a t i o n . Once a q u a n t i t a t i v e exposure assessment has been made, R i s k * A s s i s t a n t a l l o w s the u s e r t o a u t o m a t i c a l l y c a l c u l a t e l i f e t i m e excess cancer r i s k and/or a h a z a r d i n d e x f o r t o x i c nonc a r c i n o g e n i c e f f e c t s of c h r o n i c exposure f o r any agent i n c l u d e d i n the t o x i c i t y databases w h i c h c u r r e n t l y i n c l u d e about 300 compounds. The a p p r o p r i a t e h a z a r d v a l u e s ( s l o p e - p o t e n c y f a c t o r s and r e f e r e n c e doses) f o r the r e l e v a n t r o u t e s of exposure are a u t o m a t i c a l l y r e t r i e v e d from the d a t a b a s e s . The u n c e r t a i n t y c a l c u l a t i o n s i n the exposure a s s e s s ment can a l s o be r e t r i e v e d t o a s s e s s the range of r i s k s a s s o c i a t e d w i t h a g i v e n exposure s i t u a t i o n . R i s k * A s s i s t a n t y i e l d s a s e p a r a t e r i s k e s t i m a t e f o r each c h e m i c a l under c o n s i d e r a t i o n , and f o r each r o u t e o f exposure t o the c h e m i c a l ( o r a l , i n h a l a t i o n , or d e r m a l ) . The u s e r can r e a d i l y combine these e s t i m a t e s t o o b t a i n an o v e r a l l e s t i m a t e of the r i s k s a s s o c i a t e d w i t h


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EXPERT SYSTEMS FOR ENVIRONMENTAL APPLICATIONS


a s i t e , b u t t h e s o f t w a r e does n o t a u t o m a t i c a l l y p r o v i d e such combined e s t i m a t e s , because t o do so r e q u i r e s c o n s i d e r a b l e judgement. The t o x i c i t y o f any g i v e n c h e m i c a l can v a r y q u a l i t a t i v e l y , as w e l l as q u a n t i t a t i v e l y , w i t h t h e r o u t e o f exposure; i f s o , i t would be i n a p p r o p r i a t e t o combine r i s k e s t i m a t e s from d i f f e r e n t exposure r o u t e s . The judgement o f w h i c h c h e m i c a l s w i l l produce a d d i t i v e , l e s s than-additive, or more-than-additive t o x i c e f f e c t s s i m i l a r l y requires more d e t a i l e d knowledge o f t h e i r t o x i c modes o f a c t i o n t h a n i s contained w i t h i n t h i s software. Superfund C h e c k l i s t s . Under t h e Comprehensive E n v i r o n m e n t a l Response, Compensation, and L i a b i l i t y A c t (CERCLA o r S u p e r f u n d ) , much o f EPA's r e s p o n s i b i l i t y c o n s i s t s o f r e v i e w i n g r i s k assessments g e n e r a t e d by other p a r t i e s . R e c e n t l y , t h e guidance document t h a t i n d i c a t e s a p p r o p r i a t e procedures f o r p e r f o r m i n g r i s k assessments under Superfund (6) has been c o m p l e t e l y r e p l a c e d ( 7 ) . A s e r i e s o f automated checkl i s t s are being incorporated i n t o R i s k * A s s i s t a n t that w i l l a s s i s t p e r s o n n e l i n e v a l u a t i n g r i s k assessments g e n e r a t e d by o t h e r p a r t i e s f o r c o n s i s t e n c y w i t h t h i s new g u i d a n c e . The i n i t i a l modules i n c l u d e procedures f o r r e v i e w i n g t h e c o l l e c t i o n and a n a l y s i s o f samples o f e n v i r o n m e n t a l media t h a t may be c o n t a m i n a t e d , and f o r r e v i e w i n g t h e assessment o f human exposures. L i k e t h e Exposure Assessment Module d e s c r i b e d above, t h e Exposure C h e c k l i s t w i l l a u t o m a t i c a l l y c a l c u l a t e the e f f e c t s o f a l t e r n a t i v e exposure s c e n a r i o parameters on t h e r e s u l t i n g exposures. A d d i t i o n a l A n a l y s e s . A l t h o u g h t h e Main A n a l y s e s p r o v i d e d i n R i s k * A s s i s t a n t c o v e r t h e e s s e n t i a l c o r e o f s i t e - s p e c i f i c r i s k assessment, i t i s a n t i c i p a t e d t h a t r i s k a s s e s s o r s w i l l a l s o need a s s i s t a n c e i n o t h e r areas. The s o f t w a r e system c u r r e n t l y addresses t h r e e c o n c e r n s : t h e need f o r s e t t i n g p r i o r i t i e s f o r s i t e r e v i e w based on m i n i m a l d a t a , t h e f r e q u e n t need t o use models t o p r e d i c t t h e t r a n s p o r t o f c h e m i c a l s from the s i t e t o p o p u l a t e d a r e a s , and t h e need t o d i s t i n g u i s h between p r o b a b l e and l e s s l i k e l y c o n d i t i o n s o f exposure. Q u i c k * R i s k . QUICK*RISK i s a program d e s i g n e d f o r r a p i d , "back o f t h e envelope" r i s k c a l c u l a t i o n s , p r i m a r i l y f o r t h e purposes o f s c r e e n i n g or d i r e c t i n g f u r t h e r r e s e a r c h . The u s e r need o n l y p r o v i d e a l i s t o f c h e m i c a l s and c o n c e n t r a t i o n s ( o r e s t i m a t e s o f t h e c h e m i c a l c o n c e n t r a t i o n s ) f o r a i r , water, f i s h , o r s o i l . The system t h e n uses a s e t o f p r e - s p e c i f i e d assumptions t o r e p o r t on t h e r i s k s o f t h e c h e m i c a l s a t the s p e c i f i e d c o n c e n t r a t i o n s from d r i n k i n g w a t e r , i n h a l a t i o n , f i s h consumption, o r s o i l i n g e s t i o n . Both l i f e t i m e excess c a n c e r r i s k s and c h r o n i c n o n - c a r c i n o g e n i c ( t o x i c ) r i s k s a r e e v a l u a t e d , u s i n g "reasona b l e w o r s t case" assumptions f o r t h e s e l e c t e d exposure s c e n a r i o s . The system a l s o e s t i m a t e s c o n c e n t r a t i o n s i n each s e l e c t e d e n v i r o n m e n t a l medium t h a t c o r r e s p o n d t o a o n e - i n - a - m i l l i o n c a r c i n o g e n i c r i s k . Model S e l e c t i o n A s s i s t a n t s . As n o t e d e a r l i e r , a wide v a r i e t y o f models have been developed t o p r e d i c t t h e t r a n s p o r t o f contaminants i n v a r i o u s e n v i r o n m e n t a l media. These models d i f f e r i n t h e amount and type o f d a t a they r e q u i r e , i n t h e n a t u r e and c o m p l e x i t y o f t h e u n d e r l y i n g p r o c e s s e s they r e f l e c t , and i n t h e s p e c i f i c contaminants and s e t s o f e n v i r o n m e n t a l c i r c u m s t a n c e s they were d e s i g n e d t o


13.

SCHAUMETAL.



e v a l u a t e . EPA has r e c e n t l y p u b l i s h e d two guidance documents t o h e l p the exposure and r i s k a s s e s s o r s e l e c t m a t h e m a t i c a l models f o r use i n exposure assessments (8-9) . These two documents c o v e r s u r f a c e w a t e r and groundwater models and a s s i s t i n m a t c h i n g models t o the a n a l y t i c a l needs, a v a i l a b l e d a t a , r e s o u r c e s , and model e x p e r i e n c e o f the u s e r . E x p e r t systems p l a n n e d f o r R i s k * A s s i s t a n t w i l l i n c o r p o r a t e the l o g i c a l s t r u c t u r e and i n f o r m a t i o n from each o f these two documents, and use a s e r i e s o f q u e s t i o n s r e g a r d i n g the s i t e and the g o a l s o f the m o d e l i n g e x e r c i s e t o guide the u s e r i n s e l e c t i n g an a p p r o p r i a t e t r a n s p o r t model. A n t i c i p a t e d f u t u r e developments o f these systems w i l l p r o v i d e more e x t e n s i v e i n f o r m a t i o n t o the u s e r on the r e a s o n i n g employed t o match models t o a u s e r ' s a n a l y t i c a l needs and r e s o u r c e s . Exposure Pathways. An exposure pathway f o r a t o x i c c h e m i c a l c o n s i s t s of a means by w h i c h the c h e m i c a l i s r e l e a s e d t o the environment, i t s t r a n s p o r t over a s h o r t or l o n g d i s t a n c e t o an a r e a i n w h i c h p e o p l e may come i n c o n t a c t w i t h i t , w h i c h may o r may not i n v o l v e i t s movement from one e n v i r o n m e n t a l medium t o a n o t h e r , and i t s coming i n t o c o n t a c t w i t h the s k i n , d i g e s t i v e t r a c t , o r r e s p i r a t o r y system o f a p e r s o n . An e x p e r t system p l a n n e d f o r R i s k * A s s i s t a n t a d d r e s s e s the p r o b a b i l i t y t h a t v a r i o u s exposure pathways w i l l be of c o n c e r n a t a hazardous waste s i t e . T h i s module guides u s e r s i n c o n s i d e r i n g f a c t o r s t h a t may i n c r e a s e or decrease the l i k e l i h o o d t h a t a c h e m i c a l w i l l be r e l e a s e d from a u n i t such as a l a n d f i l l o r s u r f a c e impoundment t o any environmental media. I f r e l e a s e cannot be r u l e d o u t , f a c t o r s a f f e c t i n g t r a n s p o r t t o an a r e a of p o t e n t i a l exposure are c o n s i d e r e d . I f the presence of c o n t a m i n a t i o n i n an a r e a of p o t e n t i a l exposure cannot be d i s c o u n t e d , p o t e n t i a l exposure s c e n a r i o s are reviewed. The end r e s u l t i s a l i s t i n g of p o t e n t i a l exposure pathways t h a t the u s e r may have t o c o n s i d e r f o r the s i t e . Databases. The Database component o f R i s k * A s s i s t a n t a l l o w s the u s e r to l o o k up i n f o r m a t i o n d i r e c t l y i n any o f the d a t a b a s e s , w i t h o u t u s i n g the a n a l y t i c a l programs. These databases are a u t o m a t i c a l l y c a l l e d up as n e c e s s a r y d u r i n g R i s k * A s s i s t a n t a n a l y s e s , but a u s e r may simply want t o r e p o r t s p e c i f i c i n f o r m a t i o n about a c h e m i c a l o r c h e m i c a l s . The databases c o n t a i n e d i n the system are d e s c r i b e d below. T o x i c Hazards. E i t h e r i n f o r m a t i o n on the c a r c i n o g e n i c potency o f a chemical (Slope Factor, Weight-of-Evidence Class designation), estimates of n o n - c a r c i n o g e n i c t o x i c p o t e n t i a l (Reference Dose, U n c e r t a i n t y and M o d i f y i n g F a c t o r s , and Statement o f C o n f i d e n c e ) , o r b o t h , can be r e p o r t e d f o r s e v e r a l hundred c h e m i c a l s . V a l u e s f o r b o t h i n h a l a t i o n and o r a l exposure are a v a i l a b l e . I f the d e s i r e d t o x i c i t y v a l u e f o r a c h e m i c a l has not y e t been i n c l u d e d i n I R I S , an a l t e r n a t i v e database e x t r a c t e d from the H e a l t h E f f e c t s Assessment Summary Tables (HEAST) i s a u t o m a t i c a l l y searched. Chemical P r o p e r t i e s . The p h y s i c a l - c h e m i c a l p r o p e r t i e s of an agent i n f l u e n c e not o n l y i t s f a t e and t r a n s p o r t i n the g e n e r a l environment but a l s o i t s b e h a v i o r i n m i c r o - e n v i r o n m e n t s i n w h i c h exposure may occur. Thus, the v o l a t i l i t y and w a t e r s o l u b i l i t y of a c h e m i c a l w i l l i n f l u e n c e i t s tendency t o v o l a t i l i z e from domestic w a t e r i n t o


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E X P E R T SYSTEMS FOR E N V I R O N M E N T A L APPLICATIONS

184


h o u s e h o l d a i r . Among t h e more i m p o r t a n t p h y s i c a l - c h e m i c a l p r o p e r t i e s i n c l u d e d i n t h e databases a r e : (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)

M o l e c u l a r Weight Vapor P r e s s u r e Water S o l u b i l i t y Henry's Law Constant Octanol-Water P a r t i t i o n C o e f f i c i e n t O r g a n i c Carbon P a r t i t i o n C o e f f i c i e n t Bioconcentration Factor D i f f u s i v i t y i n Water Diffusivity i nAir Melting Point B o i l i n g Point

R e g u l a t o r y and A d v i s o r y S t a n d a r d s . I n some c a s e s , r a t h e r than p e r f o r m i n g a d e t a i l e d r i s k assessment f o r a s p e c i f i c s i t u a t i o n , a u s e r may w i s h t o r e l y upon t h e r i s k assessments t h a t u n d e r l i e v a r i o u s p u b l i s h e d r e g u l a t o r y and a d v i s o r y s t a n d a r d s . I n o t h e r cases (such as a t Superfund s i t e s ) , t h e u s e r would want t o know t h e r e l a t i o n s h i p between o b s e r v e d c o n c e n t r a t i o n s and r e g u l a t o r y / a d v i s o r y standards even i f she o r he i n t e n d e d t o p e r f o r m an independent r i s k assessment. R i s k * A s s i s t a n t c o n t a i n s databases o f standards and a d v i s o r y v a l u e s developed by t h e F e d e r a l government, S t a t e governments, and o t h e r b o d i e s , such a s : Federal

Standards:

(1) Maximum Contaminant L e v e l s and Maximum Contaminant L e v e l s p e c i f i e d under t h e Safe D r i n k i n g Water A c t

Goals

(2) R e p o r t a b l e Q u a n t i t i e s f o r e n v i r o n m e n t a l d i s c h a r g e s p e c i f i e d under the C l e a n Water A c t and Comprehensive E n v i r o n m e n t a l Response, Compensation, and L i a b i l i t y (Superfund) A c t (3) N a t i o n a l Ambient A i r Q u a l i t y Standards s p e c i f i e d under t h e C l e a n A i r Act (4) P e r m i s s i b l e Exposure L i m i t s f o r workroom a i r s p e c i f i e d under t h e O c c u p a t i o n a l S a f e t y and H e a l t h A c t State

Standards:

(1) S t a t e Water Q u a l i t y Standards (2) New J e r s e y Maximum Contaminant L e v e l s f o r D r i n k i n g Water Advisory

values:

(1) D r i n k i n g Water H e a l t h A d v i s o r i e s s p e c i f i e d under t h e Safe D r i n k i n g Water A c t (2) Ambient Water Q u a l i t y C r i t e r i a s p e c i f i e d under t h e C l e a n Water A c t


13.

SCHAUMETAL.

Performing Risk Assessments for H

(3) T h r e s h o l d L i m i t V a l u e s f o r workroom a i r promulgated by American Conference o f Governmental I n d u s t r i a l H y g i e n i s t s

185 the


S t a t e w a t e r q u a l i t y s t a n d a r d s w i l l f r e q u e n t l y be " a p p l i c a b l e " o r " r e l e v a n t and a p p r o p r i a t e " r e q u i r e m e n t s f o r a Superfund s i t e . F o r most s t a t e s and c h e m i c a l s , the p a r t i c u l a r s t a n d a r d s t h a t a p p l y t o a w a t e r body depend upon the d e s i g n a t i o n o f the w a t e r body as a member of a p a r t i c u l a r c l a s s , w i t h the s e t o f c l a s s e s v a r y i n g among s t a t e s . R i s k * A s s i s t a n t c o n t a i n s an automated procedure t o h e l p the u s e r i n s e l e c t i n g the most a p p r o p r i a t e w a t e r body c l a s s i f i c a t i o n s f o r h e r o r his p a r t i c u l a r s i t e . User I n t e r f a c e . The o b j e c t o f s o f t w a r e systems f o r r i s k assessment i s t o make the p r o c e s s o f g e n e r a t i n g o r r e v i e w i n g r i s k assessments e a s i e r f o r system u s e r s . Software t h a t i s not easy t o l e a r n o r use, o r t h a t r e q u i r e s c o n s t a n t r e f e r e n c e t o manuals o r o t h e r support documents, w i l l do l i t t l e t o h e l p r i s k a s s e s s o r s f a c e d w i t h a demanding w o r k l o a d . A c c o r d i n g l y , a key emphasis i n the development of R i s k * A s s i s t a n t i s t h a t the s o f t w a r e be u s a b l e by persons w i t h l i t t l e o r no computer e x p e r i e n c e , w i t h o u t the need f o r t r a i n i n g , and t h a t the m a j o r i t y o f a u s e r ' s q u e s t i o n s can be answered i n t h e s o f t w a r e , w i t h o u t the need t o r e f e r t o manuals. The development o f t e c h n i c a l manuals i s an i m p o r t a n t p a r t of the R i s k * A s s i s t a n t e f f o r t , but the u s e r s h o u l d not need t o r e f e r t o these manuals f r e q u e n t l y . To a v o i d the need f o r u s e r s t o r e l y on manuals, s e v e r a l f e a t u r e s have been added t o the u s e r i n t e r f a c e f o r R i s k * A s s i s t a n t ( i . e . , the menus by w h i c h the u s e r e n t e r s and r e t r i e v e s i n f o r m a t i o n ) . These are d e s c r i b e d b r i e f l y below. I n a d d i t i o n , an e f f o r t has been made reduce the amount o f t y p i n g r e q u i r e d o f the u s e r t o a bare minimum and t o make the k e y s t r o k e s t h a t a c t i v a t e the system as obvious as p o s s i b l e . Help Screens. Each menu i n R i s k * A s s i s t a n t has one o r more a s s o c i a t e d HELP s c r e e n s , a c c e s s i b l e by p r e s s i n g a f u n c t i o n key. The HELP s c r e e n e x p l a i n s how t o s e l e c t an i t e m from a menu, change a d e f a u l t v a l u e , or enter data. E x p l a n a t i o n Screens. I n a d d i t i o n t o HELP screens t h a t i n s t r u c t the u s e r how t o do something, EXPLANATION screens t e l l the u s e r why she o r he i s b e i n g asked t o make a c h o i c e o r e n t e r d a t a . A brief e x p l a n a t i o n o f the r e l e v a n c e o f a p a r t i c u l a r c h o i c e t o the o v e r a l l r i s k assessment p r o c e s s i s p r o v i d e d ; i f a p p r o p r i a t e , a l t e r n a t i v e v a l u e s f o r d a t a e n t r i e s are g i v e n . Reference Screens. Whenever R i s k * A s s i s t a n t p r o v i d e s a d e f a u l t v a l u e , a REFERENCE s c r e e n can be c a l l e d up t o p r o v i d e a c i t a t i o n f o r the l i t e r a t u r e source from w h i c h the v a l u e was t a k e n . Notepad. Each menu i n R i s k * A s s i s t a n t has an a s s o c i a t e d Notepad s c r e e n . By p r e s s i n g a f u n c t i o n key, the u s e r can c a l l up the notepad f o r the menu, and use i t t o e x p l a i n i m p o r t a n t f e a t u r e s o f h i s o r h e r assessment, o r the reasons u n d e r l y i n g the s e l e c t i o n o f p a r t i c u l a r values.


186



Novice User Pathway, The u s e r o f R i s k * A s s i s t a n t has the o p t i o n , a t any p o i n t , o f u s i n g the system i n e i t h e r an " e x p e r i e n c e d u s e r " , o r a "novice u s e r " mode. A f u n c t i o n key t o g g l e s between the two modes. In the "novice u s e r " mode, each key menu i s preceded by one o r more screens e x p l a i n i n g i t s p l a c e i n the r i s k assessment p r o c e s s and i n d i c a t i n g how t o make an a p p r o p r i a t e response.


Design C o n s i d e r a t i o n s To meet EPA*s g o a l of i m p r o v i n g the c o n s i s t e n c y and q u a l i t y o f r i s k assessments, the s o f t w a r e must n o t o n l y be easy t o use, but must a l s o generate r e s u l t s t h a t can be r e l i e d upon i n a r e g u l a t o r y c o n t e x t . Users must have c o n f i d e n c e i n the a c c u r a c y o f the i n f o r m a t i o n c o n t a i n e d i n the system, whether database parameters o r r u l e s and a l g o r i t h m s . F u r t h e r , the l o g i c used by the s o f t w a r e i n r e a c h i n g any c o n c l u s i o n must be e x p l i c i t . A " b l a c k box" approach, even i f i n f a l l i b l e , would be o f v e r y l i m i t e d u t i l i t y i n the r e g u l a t o r y environment. A u t h o r i t a t i v e Databases. E f f o r t s t o ensure the a c c u r a c y o f the i n f o r m a t i o n i n R i s k * A s s i s t a n t databases i n v o l v e b o t h the s e l e c t i o n o f data sources and Q u a l i t y A s s u r a n c e procedures f o r d a t a e n t r y . As noted below, an e f f o r t was made t o l o c a t e the most a u t h o r i t a t i v e source f o r each database. Database e n t r i e s are r e p e a t e d l y checked against o r i g i n a l sources. F i n a l l y , the u s e r i s s u p p l i e d w i t h a c i t a t i o n of the o r i g i n a l l i t e r a t u r e s o u r c e , and so i s a b l e t o c o n f i r m database c o n t e n t s i f n e c e s s a r y . T o x i c Hazards and Exposure Parameters. S u p p l y i n g EPA u s e r s w i t h a u t h o r i t a t i v e i n f o r m a t i o n on t o x i c and c a r c i n o g e n i c hazards has been relatively straightforward. (1) I n t e g r a t e d R i s k I n f o r m a t i o n System (IRIS) - Wherever p o s s i b l e , R i s k * A s s i s t a n t o b t a i n s i n f o r m a t i o n on c h e m i c a l hazards from the EPA's I n t e g r a t e d R i s k I n f o r m a t i o n System ( I R I S ) . A l l i n f o r m a t i o n on c h e m i c a l hazards c o n t a i n e d i n IRIS i s s u b j e c t t o r i g o r o u s peer r e v i e w and r e p r e s e n t s and Agency-wide s t a n d a r d v a l u e ( 1 0 ) . (2) H e a l t h E f f e c t s Assessment Summary Tables (HEAST) - Because o f the r i g o r o u s p e e r - r e v i e w p r o c e s s , IRIS does not y e t c o n t a i n i n f o r m a t i o n on a l l c h e m i c a l s o f p o t e n t i a l i n t e r e s t t o u s e r s of R i s k * A s s i s t a n t , o r on a l l a s p e c t s o f the t o x i c i t y o f the c h e m i c a l s t h a t i t does i n c l u d e . A c c o r d i n g l y , f o r c h e m i c a l s t h a t are not c o v e r e d by I R I S , t o x i c h a z a r d d a t a from the HEAST are p r o v i d e d . These d a t a do not have the Agency-wide a p p r o v a l of IRIS d a t a , but have been reviewed by EPA. R e g u l a t o r y Standards. A u t h o r i t a t i v e database sources f o r r e g u l a t o r y standards a r e , l i k e t o x i c h a z a r d s o u r c e s , easy t o come by. Both the f e d e r a l and s t a t e governments p r o v i d e p u b l i s h e d v e r s i o n s o f such standards t h a t are r e l i a b l e sources f o r database e n t r y . The key i s s u e f o r these databases i s c h e c k i n g f o r a c c u r a t e e n t r y , and p e r i o d i c review f o r currency.


13.

SCHAUMETAK


C h e m i c a l P r o p e r t i e s . Because no s i n g l e source c o n t a i n s i n f o r m a t i o n on a l l r e l e v a n t p r o p e r t i e s , i n f o r m a t i o n from a v a r i e t y of sources i s c o n t a i n e d i n t h e s e d a t a b a s e s . A c c o r d i n g l y , a l l e n t r i e s are r e f e r e n c e d t o the o r i g i n a l source of the i n f o r m a t i o n .


S p e c i a l i z e d Databases. Some p o t e n t i a l u s e r s of R i s k * A s s i s t a n t may have developed independent e s t i m a t e s of t o x i c r i s k a s s o c i a t e d w i t h c h e m i c a l s , p a r t i c u l a r l y f o r c h e m i c a l s not i n c l u d e d i n EPA t o x i c h a z a r d d a t a b a s e s . Such u s e r s (such as S t a t e governments), who t y p i c a l l y w i l l have access t o c o n s i d e r a b l e t o x i c o l o g i c a l e x p e r t i s e may w i s h t o use these h a z a r d v a l u e s i n R i s k * A s s i s t a n t a n a l y s e s . Such s p e c i a l i z e d h a z a r d databases can r e a d i l y be i n c o r p o r a t e d i n t o the system. Referenced C a l c u l a t i o n s . Exposure assessment i n v o l v e s numerous c a l c u l a t i o n s , c o v e r i n g b o t h c r o s s - m e d i a t r a n s f e r s of c h e m i c a l s and the d e r i v a t i o n of exposures from c o n c e n t r a t i o n s and s c e n a r i o - s p e c i f i c parameters. I n g e n e r a l terms, such c a l c u l a t i o n s can be viewed as the l i m i t i n g case ( i n s i m p l i c i t y ) o f e i t h e r t h e o r e t i c a l o r e m p i r i c a l models. A l l c a l c u l a t i o n s i n R i s k * A s s i s t a n t f o r d e r i v i n g exposures from c o n c e n t r a t i o n s i n an a p p r o p r i a t e medium (e.g. i n h a l a t i o n exposures from a i r c o n c e n t r a t i o n s ) are o b t a i n e d from the Exposure F a c t o r s Handbook ( 4 ) . E q u a t i o n s f o r e v a l u a t i n g c r o s s - m e d i a t r a n s f e r f o r p a r t i c u l a r exposure s c e n a r i o s (e.g. v o l a t i l i z a t i o n from domestic w a t e r t o h o u s e h o l d a i r ) are o b t a i n e d from l i t e r a t u r e s o u r c e s . For such e q u a t i o n s , the o r i g i n a l r e f e r e n c e i s p r o v i d e d f o r the u s e r . E x p e r t Systems as "Automated Documents." Sometimes a u s e r needs t o make a d e c i s i o n based upon the c o n s i d e r a t i o n o f c a t e g o r i c a l o r q u a l i t a t i v e i n f o r m a t i o n , r a t h e r than c a l c u l a t i o n s i n v o l v i n g n u m e r i c a l parameters. E x p e r t Systems comprise s e v e r a l t y p e s of computer programs t h a t address t h i s type o f i n f o r m a t i o n . R i s k * A s s i s t a n t w i l l c o n t a i n a v a r i e t y of s m a l l e x p e r t systems t h a t a s s i s t u s e r s i n d i f f e r e n t a s p e c t s of the r i s k assessment p r o c e s s . E x p e r t systems sometimes r e p r e s e n t an attempt t o i n c o r p o r a t e the views and judgments of a p a r t i c u l a r e x p e r t i n a g i v e n d i s c i p l i n e . T h i s r a i s e s i s s u e s c o n c e r n i n g the p r o c e d u r e s used t o i d e n t i f y the e x p e r t on whom t o base the system and the p o s s i b i l i t y t h a t o t h e r e x p e r t s of e q u a l competence would reach a l t e r n a t i v e c o n c l u s i o n s , t h a t can l i m i t the u t i l i t y of an e x p e r t system f o r use i n a r e g u l a t o r y context. E x p e r t systems can a l s o be " d e l p h i c " i n t h e i r o p e r a t i o n , r e a c h i n g c o n c l u s i o n s from a n t e c e d e n t s by p r o c e s s e s t h a t are non-obvious t o the user. Sometimes these p r o c e s s e s are not even o b v i o u s t o the e x p e r t and knowledge e n g i n e e r who d e v e l o p e d the system, but are d e r i v e d by e x p e r t system s o f t w a r e from a s e r i e s o f s p e c i f i c s i t u a t i o n s p r e s e n t e d t o the e x p e r t f o r e v a l u a t i o n . For the r e g u l a t o r y c o n t e x t i n w h i c h EPA e v a l u a t e s hazardous waste s i t e s , n e i t h e r r e l i a n c e on the s i m u l a t e d judgement o f a s i n g l e i n d i v i d u a l nor a " d e l p h i c " d e c i s i o n p r o c e s s are a c c e p t a b l e . Thus f o r purposes o f t h i s system the d e c i s i o n was made t o use e x p e r t systems technology t o i n c o r p o r a t e e x p l i c i t p r o c e d u r e s from r e g u l a t o r y or guidance documents. Such documents have a l r e a d y been r e v i e w e d and deemed a p p r o p r i a t e b e f o r e p u b l i c a t i o n , and by t h e i r n a t u r e they include e x p l i c i t decision c r i t e r i a . The i n c o r p o r a t i o n of r e g u l a t i o n s


187

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and guidance documents i n t o e x p e r t systems i s the approach t a k e n by Risk*Assistant. A key f e a t u r e o f ongoing e x p e r t systems r e s e a r c h i n t h i s p r o j e c t i s developing expert system r e p o r t s t h a t c l e a r l y document the r e a s o n i n g used t o proceed from a n t e c e d e n t c o n d i t i o n s t o a c o n c l u s i o n . Having such i n f o r m a t i o n i s n e c e s s a r y i n the r e g u l a t o r y c o n t e x t , where d e c i s i o n s based on " d e l p h i c " p r o c e s s e s are l i k e l y t o be c h a l l e n g e d as " a r b i t r a r y and c a p r i c i o u s . "


A p p l i c a t i o n s of R i s k * A s s i s t a n t As n o t e d above, the programs and databases c o n t a i n e d i n R i s k * A s s i s t a n t are d e s i g n e d t o s e r v e b o t h e x p e r t s and n o v i c e s i n the exposure and r i s k assessment p r o c e s s , w i t h the r e c o g n i t i o n t h a t i n d i v i d u a l s w i t h e x p e r t i s e i n one d i s c i p l i n e may be charged w i t h the r e s p o n s i b i l i t y o f c o n d u c t i n g or r e v i e w i n g exposure and r i s k assessments t h a t i n c o r p o r a t e d a t a from many d i f f e r e n t d i s c i p l i n e s . P o t e n t i a l users include r e g i o n a l EPA s t a f f and t h e i r c o u n t e r p a r t s i n s t a t e and l o c a l e n v i r o n m e n t a l a g e n c i e s and o t h e r i n d i v i d u a l s ( p r i v a t e , c o r p o r a t e ) concerned w i t h e v a l u a t i n g the h e a l t h r i s k s posed by hazardous waste s i t e s . G e n e r a t i o n of R i s k Assessments. Much of the r i s k assessment w o r k l o a d f a c e d by EPA r e g i o n a l p e r s o n n e l and s t a t e p e r s o n n e l does not i n v o l v e the development of d e t a i l e d r i s k assessments t h a t attempt t o be as a c c u r a t e as p o s s i b l e i n c h a r a c t e r i z i n g p a r t i c u l a r s i t u a t i o n s . These p r o f e s s i o n a l s need t o use r e l a t i v e l y s i m p l e r i s k assessments t o s e t r i s k management p r i o r i t i e s . They need t o be a b l e t o d e c i d e w h i c h s i t u a t i o n s r e q u i r e immediate a t t e n t i o n , w h i c h can be d e f e r r e d f o r l a t e r a c t i o n because they pose l i t t l e r i s k even under w o r s t - c a s e c o n d i t i o n s , and w h i c h r e q u i r e more d e t a i l e d e v a l u a t i o n . R i s k * A s s i s t ant can h e l p t o make such d e c i s i o n s i n a c o n s i s t e n t manner, w h i l e m a i n t a i n i n g s e n s i t i v i t y to important features of p a r t i c u l a r s i t u a tions . S c r e e n i n g w i t h QUICK*RISK. For u s e r s who need t o s e t assessment p r i o r i t i e s f o r a l a r g e number o f s i t e s , QUICK*RISK p r o v i d e s a means t o a c c o m p l i s h the t a s k r a p i d l y . The u s e r need o n l y s p e c i f y p r o b a b l e contaminant c o n c e n t r a t i o n s i n e n v i r o n m e n t a l media, and QUICK*RISK a p p l i e s a p p r o p r i a t e l y c o n s e r v a t i v e exposure a s s u m p t i o n s . Although o n l y one s c e n a r i o i s c o n s i d e r e d f o r any medium, f u r t h e r d e t a i l i s p r o b a b l y not needed f o r the i n i t i a l s e l e c t i o n of s i t e p r i o r i t i e s , and QUICK*RISK p r o v i d e s for consistent evaluation. Assuming that c o n c e n t r a t i o n e s t i m a t e s were a v a i l a b l e , s e v e r a l hundred s i t e s c o u l d be e v a l u a t e d i n a s i n g l e day. QUICK*RISK a l s o p r o v i d e s u s e r s w i t h the a b i l i t y t o respond q u i c k l y to requests f o r r i s k i n f o r m a t i o n regarding poorly charact e r i z e d s i t u a t i o n s . For example, a t e l e p h o n e i n q u i r y about p o t e n t i a l r i s k s a s s o c i a t e d w i t h w a t e r c o n t a m i n a t i o n c o u l d be answered i n a m a t t e r o f seconds. More D e t a i l e d A n a l y s e s . When d e a l i n g w i t h a more l i m i t e d number o f s i t e s (dozens, r a t h e r than h u n d r e d s ) , R i s k * A s s i s t a n t a l l o w s the u s e r t o take s p e c i f i c s i t e c o n d i t i o n s i n t o account w h i l e m a i n t a i n i n g a c o n s i s t e n t approach t o r i s k assessment. The assessments can be


13.

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Ρβφπηυ^ Risk Assessmentsfor Hazardous Waste

produced q u i c k l y (an e x p e r i e n c e d u s e r c o u l d p e r f o r m s e v e r a l i n a d a y ) , y e t s t i l l c o n t a i n enough t o p r o v i d e c o n f i d e n c e i n t h e d e c i s i o n made and a sound b e g i n n i n g f o r a f u l l - f l e d g e d r i s k assessment i f one i s required.


Summary o f S i t e I n f o r m a t i o n . The case d e s c r i p t i o n s e c t i o n o f R i s k * A s s i s t a n t provides a s u f f i c i e n t l e v e l of d e s c r i p t i v e d e t a i l t o enable a u s e r t o form a c l e a r c o n c e p t u a l model o f t h e s i t e and t o present relevant information c o n c i s e l y . I t a l s o e n a b l e s a summary e v a l u a t i o n o f t h e adequacy o f t h e d a t a base on a s i t e . I d e n t i f i c a t i o n o f Pathways. The e x p e r t system w i l l guide a u s e r t o c o n s i d e r t h e v a r i e t y o f exposure pathways t h a t s h o u l d be c o n s i d e r e d f o r a s i t e , and thus t o p e r f o r m a q u a l i t a t i v e r i s k assessment. I t h e l p s t o ensure t h a t s i g n i f i c a n t c u r r e n t o r p o t e n t i a l exposure pathways a r e n o t i g n o r e d . Assistance i n Modeling. R i s k * A s s i s t a n t does n o t p e r f o r m t r a n s p o r t m o d e l i n g , because o t h e r EPA-developed systems a l r e a d y p r o v i d e t h e s e capabilities. I t does, however, a s s i s t t h e u s e r i n s e l e c t i n g t h e a p p r o p r i a t e t r a n s p o r t models f o r a s i t e , i f m o d e l i n g proves t o be appropriate. An e f f o r t i s underway t o f a c i l i t a t e t h e a u t o m a t i c t r a n s f e r o f i n f o r m a t i o n between R i s k * A s s i s t a n t and EPA m o d e l i n g s o f t w a r e , such as PC-GEMS ( 3 ) . C a l c u l a t i o n o f Exposure. A g r e a t advantage o f R i s k * A s s i s t a n t i s t h a t i t a l l o w s u s e r s t o c o n s i d e r a wide range o f f a c t o r s t h a t w i l l i n f l u e n c e q u a n t i t a t i v e exposure e s t i m a t e s (e.g., s p e c i f i c exposure f a c t o r s f o r d i f f e r e n t p o p u l a t i o n s , pathways, and s c e n a r i o s ) w i t h a minimum o f e f f o r t . Thus, a u s e r can r a p i d l y produce a l t e r n a t i v e exposure e v a l u a t i o n s , i n c l u d i n g b e s t e s t i m a t e s , r e a s o n a b l e w o r s t - c a s e exposure e s t i m a t e s , and w o r s t case exposure e s t i m a t e s . Moreover, t h e system p r o v i d e s the u s e r w i t h i n f o r m a t i o n on the degree o f u n c e r t a i n t y c o n t r i b u t e d by v a r i o u s assumptions used i n t h e a n a l y s i s , w h i c h can guide t h e u s e r ' s f u t u r e d a t a c o l l e c t i o n e f f o r t s so t h a t they r e s u l t i n maximum r e d u c t i o n o f u n c e r t a i n t y . C a l c u l a t i o n o f L i f e t i m e Excess Cancer R i s k and Hazard I n d i c e s f o r C h r o n i c Exposure. F o r each exposure e s t i m a t e , i t i s e x t r e m e l y easy t o generate c o r r e s p o n d i n g r i s k e s t i m a t e s . Thus, t h e u s e r can q u i c k l y s p e c i f y t h e f u l l range o f r i s k s t h a t may r e a s o n a b l y be a t t r i b u t e d t o a site. I f reasonable w o r s t - c a s e o r w o r s t - c a s e assumptions i n d i c a t e m i n i m a l r i s k , i t may be p o s s i b l e t o d e f e r t h e a c t i o n u n t i l more p r e s s i n g problems a r e a d d r e s s e d . A l t e r n a t e l y , the R i s k * A s s i s t a n t a n a l y s e s may i n d i c a t e c u r r e n t o r p o t e n t i a l r i s k s t h a t s h o u l d be immediately ameliorated. When a wide range o f r i s k s may a p p l y t o a s i t e , i t may be important t o conduct a d d i t i o n a l s t u d i e s t o reduce t h e uncertainties associated with a s i t e . Reviews o f R i s k Assessment Generated by O t h e r s . I n many c a s e s , i t w i l l be i m p o r t a n t f o r EPA and s t a t e s t a f f t o r e v i e w r i s k assessments generated by t h i r d p a r t i e s (e.g., c o n t r a c t o r s o r p o t e n t i a l l y respon s i b l e p a r t i e s ) . R i s k * A s s i s t a n t f a c i l i t a t e s such r e v i e w s , by p r o v i d i n g


189

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EXPERT SYSTEMS FOR E N V I R O N M E N T A L APPLICATIONS


d a t a on s t a n d a r d p r o c e d u r e s and assumptions as w e l l as automated menus f o r comparing v a l u e s a c t u a l l y used t o s t a n d a r d v a l u e s . When a r i s k assessment under r e v i e w d e v i a t e s from t h e use o f s t a n d a r d f a c t o r s , t h e r e may i n many cases be a v a l i d reason f o r so d o i n g ; t h e assessment may r e f l e c t p a r t i c u l a r c o n d i t i o n s a t o r n e a r a specific site. The a b i l i t y t o a n n o t a t e f i n d i n g s i n R i s k * A s s i s t a n t p r o v i d e s a ready means f o r r e v i e w e r s t o i n d i c a t e t h e importance and/or v a l i d i t y o f d e v i a t i o n s from s t a n d a r d p r o c e d u r e s . S a m p l i n g / A n a l y s i s C h e c k l i s t . T h i s module o f R i s k * A s s i s t a n t , d e v e l o p e d s p e c i f i c a l l y f o r t h e r e v i e w o f Superfund r i s k assessments, prompts t h e u s e r t o c o n s i d e r key i s s u e s i n q u a l i t y a s s u r a n c e and q u a l i t y c o n t r o l f o r s a m p l i n g conducted a t a waste s i t e . I t p r o v i d e s a c o n c i s e summary of whether the s t a n d a r d s d e v e l o p e d under EPA's Superfund program have been met. Q u a n t i t a t i o n and D e t e c t i o n L i m i t s Reviews. Because t h e q u a l i t y o f l a b o r a t o r y analyses of chemical contamination i s c r i t i c a l t o the v a l i d i t y o f any c o n c l u s i o n s about r i s k , EPA i n i t i a t e d the C o n t r a c t L a b o r a t o r y Program (CLP) t o ensure c o n s i s t e n t , h i g h q u a l i t y a n a l y s e s . By comparing r e p o r t e d q u a n t i t a t i o n l i m i t s f o r samples a t a s i t e t o q u a n t i t a t i o n l i m i t s s p e c i f i e d by CLP, R i s k * A s s i s t a n t w i l l p r o v i d e a r e p o r t on a key f e a t u r e o f a n a l y t i c a l q u a l i t y s e n s i t i v i t y . Comparison o f T o x i c Hazard V a l u e s w i t h S t a n d a r d V a l u e s . For the d e r i v a t i o n of v a l i d r i s k estimates, i t i s c r u c i a l that current hazard e s t i m a t e s from a u t h o r i t a t i v e s o u r c e s a r e employed i n r i s k c a l c u l a t i o n s . R i s k * A s s i s t a n t e n a b l e s a r e v i e w e r t o e a s i l y compare t h e v a l u e s used i n a p a r t i c u l a r assessment w i t h s t a n d a r d v a l u e s from IRIS o r HEAST. Exposure Assessment Review. Because so much o f t h e d i f f e r e n c e among a l t e r n a t i v e r i s k assessments r e f l e c t s t h e use o f d i f f e r e n t assumptions about exposure, R i s k * A s s i s t a n t p r o v i d e s an e x p l i c i t program f o r comparing exposure assessments t o s t a n d a r d p r o c e d u r e s . T h i s program i s an a d a p t a t i o n o f the one used t o g e n e r a t e exposure assessments, w h i c h was d e s i g n e d e x p l i c i t l y f o r r e v i e w i n g such assessments, i t c o n s i d e r s s e v e r a l key components o f t h e exposure assessment p r o c e s s , including: (1)

Data S e l e c t i o n - Were average o r maximum c o n c e n t r a t i o n s used (or were b o t h u s e d ? ) . D i d t h e a v e r a g i n g p r o c e s s use a r i t h m e t i c o r g e o m e t r i c means? Were any c h e m i c a l s e x c l u d e d from t h e a n a l y s i s , and what was t h e r a t i o n a l e f o r e x c l u d i n g them?

(2)

Pathways C o n s i d e r e d - Were any s i g n i f i c a n t c u r r e n t o r p o t e n t i a l exposure pathways e x c l u d e d from a n a l y s i s ? What i s the consequence o f i n c l u d i n g these pathways on t o t a l exposures? Were any i n a p p r o p r i a t e pathways c o n s i d e r e d ? How much do t h e s e pathways c o n t r i b u t e to' t h e t o t a l exposure?

(3)

S c e n a r i o s and Routes o f Exposure - Were a l l a p p r o p r i a t e s c e n a r i o s c o n s i d e r e d ? F o r example, i f domestic w a t e r


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r e p r e s e n t s an exposure pathway, were b a t h i n g and contaminat i o n o f h o u s e h o l d a i r by v o l a t i l e c h e m i c a l s c o n s i d e r e d as w e l l as d i r e c t consumption? Were a l l r e l e v a n t r o u t e s o f exposure ( o r a l , d e r m a l , i n h a l a t i o n ) c o n s i d e r e d ? (4)

S e l e c t i o n o f Parameter V a l u e s - F o r the s c e n a r i o s e v a l u a t e d , were s t a n d a r d f a c t o r s employed? Were t h e s e average v a l u e s or r e a s o n a b l e w o r s t - c a s e v a l u e s ? I f a l t e r n a t i v e v a l u e s were used, what was the j u s t i f i c a t i o n ? Was the r e a s o n i n g c o r r e c t ?

(5)

R e s u l t s of U s i n g A l t e r n a t i v e V a l u e s - How do the v a l u e s o b t a i n e d from the exposure assessment performed compare t o v a l u e s o b t a i n e d u s i n g assumptions? How much u n c e r t a i n t y i s a s s o c i a t e d exposure assessment?

exposure actually standard w i t h the

Communication. I n a d d i t i o n t o i t s use f o r a n a l y s e s , R i s k * A s s i s t a n t produces s e v e r a l s t a n d a r d t y p e s o f r e p o r t s t h a t a l l o w u s e r s t o s y n t h e s i z e and summarize i n f o r m a t i o n on r i s k i n a c o n s i s t e n t f o r m a t . Any assumptions t h a t are used i n an a n a l y s i s a r e n o t e d i n t h e s e r e p o r t s . These r e p o r t s e n a b l e a u s e r t o e f f e c t i v e l y communicate key s i t e i n f o r m a t i o n w i t h o t h e r p e r s o n n e l , i n c l u d i n g r i s k management decision-rmakers and o u t s i d e r i s k assessment c o n s u l t a n t s . Record Keeping. R i s k * A s s i s t a n t w i l l s t o r e and r e t r i e v e d a t a e n t e r e d f o r e v e r y exposure and r i s k assessment t h a t has been performed and w i l l a u t o m a t i c a l l y t r a n s f e r d a t a from one program t o a n o t h e r , e l i m i n a t i n g the need f o r r e p e t i t i v e d a t a e n t r y . I t i s easy t o r e t r i e v e and r e v i e w i n f o r m a t i o n from p a s t assessments and t o conduct m u l t i p l e assessments on the same s e t o f d a t a w i t h d i f f e r i n g assumptions. R i s k * A s s i s t a n t * s e l e c t r o n i c notepad s t o r e s any a n n o t a t i o n s c o n c e r n i n g an assessment. R e f e r e n c e . R i s k * A s s i s t a n t i s a ready r e f e r e n c e source t h a t reduces the n e c e s s i t y o f f l i p p i n g t h r o u g h numerous r e f e r e n c e books or searching s e v e r a l e x t e r n a l databases.

Literature Cited 1. The Risk Assessment Guidelines of 1986, U.S. Environmental Protection Agency, Office of Health and Environmental Assessment: Washington, DC, EPA/600/8-87/045, August 1987. 2. Risk Assessment in the Federal Government: Managing the Process. National Research Council (NRC), National Academy Press: Washington, DC, 1983. 3. PC-GEMS Users Guide, U.S. Environmental Protection Agency, Office of Toxic Substances, Exposure Evaluation Division: Washington, DC, February 29, 1988. 4. Exposure Factors Handbook, U.S. Environmental Protection Agency, Office of Health and Environmental Assessment: Washington, DC, EPA/600/8-89/043, March 1989.


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192

5. Proposed Guidelines for Exposure-Related Measurements -- Request for Comments; Notice, Federal Register 53(48830-48853), December 2, 1988. 6. Superfund Public Health Evaluation Manual, U.S. Environmental Protection Agency: Washington, DC, 1986.


7. Risk Assessment Guidance for Superfund: Human Health Evaluation Manual Part A. U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response: Washington, DC 20460. OSWER Directive 9285.701a, July, 1989. 8. Selection Criteria for Mathematical Models Used i n Exposure Assessments: Surface Water Models, U.S. Environmental Protection Agency, Office of Health and Environmental Assessment: Washington, DC, EPA/600/888/042, July 1987. 9. Selection Criteria for Mathematical Models Used i n Exposure Assessments: Ground Water Models, U.S. Environmental Protection Agency, Office of Health and Environmental Assessment: Washington, DC, EPA/600/888/075, August 1988. 10. Integrated Risk Information System Support Document, Vol I, I I , U.S. Environmental Protection Agency, Office of Health & Environmental Assessment: Washington, DC, EPA/600/8-86/032a, March 1987. RECEIVED

February 7, 1990


Computerized System for Performing Risk Assessments for Chemical

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