Release of Chemicals into the Environment - ACS Publications

1 Release of Chemicals into the Environment STEPHEN L . BROWN and DAVID C. BOMBERGER

Downloaded by KAOHSIUNG MEDICAL UNIV on June 10, 2018 | https://pubs.acs.org Publication Date: August 30, 1983 | doi: 10.1021/bk-1983-0225.ch001

SRI International, Menlo Park, CA 94025

This paper is a review of methods f o r estimating r e l e a s e s of chemicals i n t o the environment in the course o f e x t r a c t i o n of raw m a t e r i a l s , manufacturing, use, storage, t r a n s p o r t a t i o n , and d i s p o s a l , as w e l l as by accidents o r n a t u r a l processes. I t discusses source types, forms of substances released ( s o l i d s , l i q u i d s , and gases), r e c e i v i n g media ( a i r , water, soil), time p a t t e r n of r e l e a s e (continuous versus i n t e r m i t t e n t , c y c l i c versus random), and geographic patterns of r e l e a s e (point, l i n e , area, and volume sources). The paper reviews s e v e r a l ad-hoc approaches to estimating r e l e a s e s and illustrates t h e i r use with a case study of benzene. The authors i d e n t i f y key o p p o r t u n i t i e s f o r f u r t h e r research. This symposium concerns models f o r p r e d i c t i n g the f a t e of chemicals i n the environment. S t r i c t l y speaking, the t o p i c of t h i s paper does not f a l l i n t o the usual d e f i n i t i o n of f a t e models. However, every f a t e model has a t l e a s t one source term. Although the source term f o r one f a t e model may be the output of another f a t e model (as when a i r transport models provide the d e p o s i t i o n rates that are the inputs to an aquatic f a t e model), the chain always has to be traced to the o r i g i n a l sources, whether they are n a t u r a l o r a s s o c i a t e d with human a c t i v i t i e s . In t h i s paper, we c h a r a c t e r i z e the v a r i o u s sources f o r chemicals i n the environment and d i s c u s s methods f o r d e s c r i b i n g the releases from them i n terms s u f f i c i e n t l y q u a n t i t a t i v e f o r use by f a t e models. We f i r s t describe human a c t i v i t i e s that can cause r e l e a s e s of chemicals; these are u s u a l l y of greatest concern to f a t e models, because they suggest where i n t e r v e n t i o n s can be made and environmental concentrations can be reduced. We then c l a s s i f y releases by t h e i r form, medium of entry, and s p a t i a l and temporal patterns. A f t e r b r i e f l y noting the most usual q u a n t i t a t i v e 0097-6156/83/0225-0003$06.00/0 © 1983 American Chemical Society

Swann and Eschenroeder; Fate of Chemicals in the Environment ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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F A T E OF C H E M I C A L S I N T H E E N V I R O N M E N T

expressions of r e l e a s e , we d i s c u s s s e v e r a l approaches to e s t i m a t i n g these q u a n t i t i e s . F i n a l l y , we d e s c r i b e an ad-hoc approach f o r an example chemical and note some areas f o r f r u i t f u l future r e s e a r c h .


Human A c t i v i t i e s That Cause Releases Chemicals are d i s t r i b u t e d i n the environment by a wide v a r i e t y of n a t u r a l processes, i n c l u d i n g p h y s i c a l (e.g., weathering), chemical (e.g., photochemical), and b i o l o g i c a l (e.g., r e s p i r a t i o n ) processes. Although many of these processes are best thought of as c l o s e d c y c l e s , not e n t a i l i n g a t r u e "source," many can be thought of as source to s i n k processes, such as the r e l e a s e of carbon d i o x i d e by v o l c a n i c a c t i o n and i t s s i n k i n oceanic carbonates. These n a t u r a l processes form important background source terms f o r chemicals, but they are u s u a l l y not of primary I n t e r e s t because they are o f t e n not c o n t r o l l a b l e . Human a c t i v i t i e s that r e l e a s e chemicals, however, are o f primary i n t e r e s t , because some chemicals are r e l e a s e d , i n f a c t created, s o l e l y by human a c t i v i t i e s and would not otherwise be found i n the environment. Without t r y i n g to make an exhaustive l i s t of a l l the types of human a c t i v i t i e s that cause r e l e a s e s , we can l i s t many d i f f e r e n t a c t i v i t i e s that are d i s t i n c t and s i g n i f i c a n t . Figure 1 shows a s e l e c t i o n of such a c t i v i t i e s , i n d i c a t i n g how they a r e connected through the l i f e c y c l e of a chemical and the media to which they most commonly cause r e l e a s e s . The l i f e c y c l e of some chemicals begins with e x t r a c t i o n of raw m a t e r i a l s . A c t i v i t i e s such as c o a l and m i n e r a l mining, o i l production, and f o r e s t r y can e i t h e r r e l e a s e chemicals d i r e c t l y or open the land f o r r e l e a s e s by n a t u r a l processes that otherwise would be slower. Sometimes chemicals a r e prepared f o r d i s t r i b u t i o n without chemical r e a c t i o n s , as when limestone i s mined and r e f i n e d before use. In other cases, the raw m a t e r i a l s are converted to other chemicals i n a manufacturing process. In both cases, wastes are discharged to a i r , water, and ( i f l a r g e q u a n t i t i e s o f . s o l i d or s e m i - s o l i d wastes a r e involved) to l a n d . Both before and a f t e r p r o c e s s i n g , chemicals are s t o r e d and transported, o f t e n many times and through many stages o f p r o c e s s i n g and manufacturing. Both storage and t r a n s p o r t a t i o n can e n t a i l "normal" low l e v e l s of r e l e a s e and o c c a s i o n a l high l e v e l s o f r e l e a s e from a c c i d e n t s . (Manufacturing upsets a l s o can cause major a c c i d e n t a l r e l e a s e s , such as the r e l e a s e of d i o x i n s from a t r i c h l o r o p h e n o l r e a c t o r a t Seveso, I t a l y i n 1976.) The major r e l e a s e mechanism f o r many chemicals, however, i s a s s o c i a t e d w i t h use of the chemical or o f chemical-containing products. Primary uses i n c l u d e combustion of f u e l s , i n d u s t r i a l uses, commercial uses, household and other consumer uses, d e l i b e r a t e a p p l i c a t i o n s i n the environment ( f o r example,


BROWN A N D BOMBERGER

Chemical Release

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1.

Figure 1. Human a c t i v i t i e s leading to release of chemicals i n t o the environment. Key: A, a i r ; W, water; GW, groundwater; L, land.


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p e s t i c i d e s ) , and many o t h e r s . In some cases (spray can p r o p e l l a n t s , f o r example), v i r t u a l l y a l l of the chemical used i s r e l e a s e d to the environment. In other uses (such as i n v i n y l asbestos f l o o r t i l e s ) , most of the chemical c o n s t i t u e n t s are e s s e n t i a l l y i s o l a t e d from the environment f o r long periods of time. Such i s o l a t e d r e s e r v o i r s are a l s o " s i n k s " f o r the chemical. Even with such uses as f l o o r t i l e s , however, the time e v e n t u a l l y comes f o r d i s p o s a l , and m a t e r i a l s f i n d t h e i r way i n t o p u b l i c sewage systems, dumps, and other l e s s - f o r m a l d i s p o s a l facilities. Secondary processes r e l e a s e chemicals from these f a c i l i t i e s i n t o a l l environmental media. Form of Substances Released Chemicals may be r e l e a s e d i n s o l i d , l i q u i d , or gaseous forms and r e l e a s e may be to a i r , surface water, groundwater, and land. (We i n c l u d e r i v e r s , l a k e s , and the oceans as surface waters; both i n t e r s t i t i a l water i n s o i l s and deeper a q u i f e r s as groundwater; and a p p l i c a t i o n to s o i l as w e l l as shallow or deeper b u r i a l as land r e l e a s e s . The d i s t i n c t i o n between a land r e l e a s e and a groundwater r e l e a s e i s l a r g e l y a r b i t r a r y . ) The forms i n which the chemicals appear i n those media are v a r i e d , as shown i n Table I. Table I FORMS OF SUBSTANCES IN RECEIVING MEDIA Media

Solids

Liquids

Gases

Combinations

Air

Particulate

Vapor Particulate

Gas

Adsorbed gas or l i q u i d

Water

Suspended Dissolved

Dissolved

Dissolved

Cosolution

Groundwater

Dissolved

Dissolved

Dissolved

Land

Particulate Bulk Contained

Contained Absorbed Adsorbed

Contained

In a i r , s o l i d s appear as p a r t i c u l a t e s , l i q u i d s as e i t h e r p a r t i c u l a t e s or vapors, and gases of course i n gas form. Combinations are a l s o p o s s i b l e , as when gases are adsorbed on particulates. Some s o l i d s would a l s o have s u b s t a n t i a l vapor pressures, and so on, but we have t r i e d to s i m p l i f y the e x h i b i t . In water, a d i s s o l v e d s t a t e i s t y p i c a l f o r substances that are normally s o l i d , l i q u i d , or gaseous, but s o l i d s can a l s o simply be


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suspended. Groundwater i s somewhat l e s s l i k e l y to c o n t a i n d i s s o l v e d gases, but that too i s p o s s i b l e . Land r e c e i v e s s o l i d s as s c a t t e r e d p a r t i c u l a t e s or i n bulk as w e l l as i n c o n t a i n e r s . L i q u i d s may f i l l i n t e r s t i t i a l v o i d s of otherwise dry s o i l s , be adsorbed to s o i l p a r t i c l e s , or remain contained. Gases can a l s o be contained or adsorbed. Whether " r e l e a s e " occurs when containers are placed i n l a n d f i l l s or not u n t i l a f t e r they are breached i s , again, l a r g e l y a matter of d e f i n i t i o n .


Source C h a r a c t e r i s t i c s Environmental f a t e models r e q u i r e i n f o r m a t i o n on the d i s t r i b u t i o n of r e l e a s e s over time and space. B a s i c a l l y , sources can be described i n terms of t h e i r d i m e n s i o n a l i t y and r e l e a s e s i n terms of t h e i r temporal d i s t r i b u t i o n . D i m e n s i o n a l i t y i s best i l l u s t r a t e d by d e f i n i n g sources of a i r p o l l u t i o n (Figure 2 ) . Point sources, such as the mouths of smokestacks, r e l e a s e p o l l u t a n t s at (almost) a s i n g l e point i n space, which can be described by i t s geographic coordinates and height above the surface (or above sea l e v e l ) . L i n e sources are unidimensional, although they do not have to be s t r a i g h t l i n e s ; f o r example, on a roadway, cars form moving point sources t h a t , i n aggregate, look much l i k e a n e a r l y uniform l i n e source. As represented i n Figure 2 by only one house, a group of residences burning wood f o r heat can o f t e n be b e t t e r t r e a t e d as a twodimensional area source than as a l a r g e set of point sources; the d i s t r i b u t i o n of gas s t a t i o n s i n an urban area i s a l s o probably s u f f i c i e n t l y w e l l simulated by an area source. Our concept of a volume source (see Figure 2) i s i n t e n t i o n a l l y vague, because few good examples e x i s t . However, photochemical smog i s produced over a volume of a i r ; i s t h i s j u s t part of a f a t e model or should i t be considered a source? L i n e , area, and volume sources are a l s o described by t h e i r geographic d i s t r i b u t i o n , shape, and o r i e n t a t i o n . For surface water, an o u t f a l l i s a p o i n t source, whereas runoff to a r i v e r i s a l i n e source and d e p o s i t i o n from the a i r i s an area source. S i m i l a r ideas can be a p p l i e d to the groundwater and land media. There are a l s o s e v e r a l p o s s i b i l i t i e s f o r the temporal d i s t r i b u t i o n of r e l e a s e s . Although some r e l e a s e s , such as those stemming from a c c i d e n t s , are best described as instantaneous r e l e a s e of a t o t a l amount of m a t e r i a l (kg per event), most r e l e a s e s are described as r a t e s : kg/sec (point source), kg/sec-m ( l i n e source), kg/sec-m^ (area source). (Note here that a l i t t l e dimensional a n a l y s i s w i l l o f t e n i n d i c a t e whether a f a c t o r or constant i n a f a t e model has been i n a d v e r t e n t l y omitted.) The patterns of r a t e s over time can be q u i t e d i v e r s e (see Figure 3). Many r e l e a s e s are more or l e s s continuous and more or l e s s uniform, such as stack emissions from a base-load power p l a n t . Others are i n t e r m i t t e n t but f a i r l y r e g u l a r , or at l e a s t p r e d i c t a b l e , as when a coke oven i s opened or a chemical vat



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Point Source

Line Source

y\\^\\\>^\\mvvNvm\\\\\v\\\\\V|

Area Source

Volume Source

Figure 2.

Dimensionality of sources.



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Figure 3.

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Time patterns of

release.



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purged. Some are continuous but c y c l i c , such as automobile emissions over a day, and some are more or l e s s random, e i t h e r continuous or i n t e r m i t t e n t , as might occur when r a i n f a l l s i n t o a waste treatment pond and causes i t to overflow i n t o surface waters. A c c i d e n t a l r e l e a s e s , o f course, are concentrated i n t o i n d i v i d u a l events t h a t , nonetheless, may cause r e l e a s e s p e r s i s t i n g over a p e r i o d o f time. These temporal patterns are c h a r a c t e r i z e d by a v a r i e t y o f q u a n t i t a t i v e measures of the r a t e s of r e l e a s e . Any p a t t e r n , o f course, can be described i n d e t a i l as a f u n c t i o n of time [ r ( t ) = 1 kg/sec, t = 8 am to 5 pm; r ( t ) = 0 otherwise]. However, i t i s o f t e n s u f f i c i e n t to c h a r a c t e r i z e some t y p i c a l r a t e or one o f special interest. In a i r p o l l u t i o n , annual average emission rates are o f t e n s u f f i c i e n t i f the goal i s to p r e d i c t annual average c o n c e n t r a t i o n s . But i f the highest 24-hour, 8-hour, 3-hour, or 1-hour averages f o r concentrations are d e s i r e d , s i m i l a r l y time-segregated emission r a t e s may be needed (see Figure 4 ) . For some of the i n t e r m i t t e n t or a c c i d e n t a l r e l e a s e s , i t may be s u f f i c i e n t or even d e s i r a b l e to give i n t e g r a t e d r e l e a s e s , wherein the r e l e a s e r a t e s a r e i n t e g r a t e d over some time of i n t e r e s t . Such cases a l s o may be approximated by equivalent constant r e l e a s e r a t e s over the same time p e r i o d . Approaches to Estimating

Releases

The preceding d e s c r i p t i o n s make i t very easy to c h a r a c t e r i z e how r e l e a s e information i s d e s i r e d ; u n f o r t u n a t e l y , however, i t i s not so easy to estimate such q u a n t i t i e s from r e a d i l y a v a i l a b l e information. Some of the major types o f estimating techniques are i l l u s t r a t e d i n Figure 5. A l l r e l e a s e information can be tracked back to measurement, and d i r e c t measurement i s f r e q u e n t l y the p r e f e r r e d way of e s t i m a t i n g emissions. Stack gas sampling i s a case i n p o i n t : we measure concentrations i n stack gas, measure gas flow r a t e s , and compute emission r a t e s with e s s e n t i a l l y no e r r o r other than that caused by i n a c c u r a t e instruments or i n s u f f i c i e n t samples to c h a r a c t e r i z e a f u l l annual sample. Other examples are automotive exhaust sampling, discharge pipe sampling (aqueous e f f l u e n t s ) , and manifests f o r land d i s p o s a l by weight and volume. Measured disappearance r a t e s f o r storage or t r a n s p o r t a t i o n can be i n f e r r e d to be r e l e a s e r a t e s . A p p l i c a t i o n r a t e s f o r p e s t i c i d e s and f e r t i l i z e r s are sometimes adequate surrogates f o r kg/m^ r e l e a s e r a t e s to s o i l s . A second major estimating technique i s the m a t e r i a l s balance a p p r o a c h — t h e o r i g i n a l focus of t h i s paper. A chemical engineering standard, the m a t e r i a l s balance can reduce to the simple mass balance, as when the measured mass of a chemical i n products l e a v i n g the plant i s subtracted from the raw m a t e r i a l e n t e r i n g the p l a n t to y i e l d the l o s s . This l o s s i s then p a r t i t i o n e d among r e l e a s e s to v a r i o u s media or other s i n k s . I f




Figure 4.

Chemical Release

C h a r a c t e r i s t i c s of r e l e a s e .

Release

Models

Bounding

Figure 5.

Approaches to estimating r e l e a s e s .


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chemical transformations are e n t a i l e d , the technique becomes known as a m a t e r i a l s balance. More complicated balances can s t a r t with the e x t r a c t e d or manufactured volume (kg/yr) of a chemical and t r a c e i t to a l l i t s intended uses, i n c l u d i n g f i n a l d i s p o s a l . Proper accounting of a l l flows can y i e l d important information about the r a t e s of r e l e a s e i n v a r i o u s branches of the d i s t r i b u t i o n t r e e ; however, r e l a t i v e l y small u n c e r t a i n t i e s i n the product flows can cause huge r e l a t i v e u n c e r t a i n t i e s i n the r e l e a s e flows. Mathematical models are a l s o used f o r e s t i m a t i n g r e l e a s e s , but these are u s u a l l y r e l a t i v e l y simple. For example, i f i t i s known that X kg of a c h l o r o f l u o r o c a r b o n i s manufactured annually, and Y percent enters spray cans, and Z percent of a spray can i s u s u a l l y l e f t unexhausted, then XY(IOO-Z)/10 kg of that CFC are released to the atmosphere per year. The average discharge r a t e (kg/sec) nationwide then can be computed e a s i l y . (For s i m p l i c i t y i n t h i s example, we ignore the c o n t r i b u t i o n s from l e a k i n g discarded cans and changes i n production and use l e v e l s . ) Other models might s t a r t w i t h concentrations of heavy metals i n c o a l , amounts of c o a l used per kWh e l e c t r i c i t y produced, kW c a p a c i t y and load f a c t o r , scrubbing e f f i c i e n c i e s , and so on to produce an estimate of stack emission r a t e s f o r a c o a l - f i r e d e l e c t r i c power p l a n t . In these cases, the model s t a r t s with measured q u a n t i t i e s (production l e v e l , c o a l c o n c e n t r a t i o n ) , and p r e d i c t s the r e l e a s e r a t e s . In other cases, an environmental f a t e model i s a p p l i e d i n a w e l l - c h a r a c t e r i z e d s i t u a t i o n and i t s outputs are compared with measurements to c a l i b r a t e the source term. For example, a groundwater model can be developed with semiempirical, a d j u s t a b l e constants, one of which i s the source strength. S u f f i c i e n t comparisons of p r e d i c t e d groundwater concentrations with c o n c e n t r a t i o n measurements from t e s t w e l l s can achieve a good estimate of the source s t r e n g t h , which can then be used to estimate c o n c e n t r a t i o n s at other places and times. Most other techniques f o r e s t i m a t i n g r e l e a s e r a t e s are ad-hoc, i n the sense that one uses the most obvious s u p p o s i t i o n s , c a l c u l a t i o n s , and so on f o r a given s i t u a t i o n . Some of these techniques set bounds on r e l e a s e r a t e s . For example, the percentage of a manufactured product that w i l l be t o l e r a t e d as waste depends on i t s p r i c e , because the p r o f i t margin can be markedly degraded i f too much i s l o s t . At the same time, however, h i g h - p r o f i t m a t e r i a l s can supply the resources to i n s t a l l more e f f e c t i v e c o n t r o l s . The r e s u l t s are rule-of-thumb bounds on the f r a c t i o n s of production l i k e l y to be l o s t (see lower r i g h t diagram of F i g u r e 5). Another u s e f u l r u l e i s t h a t , given equal p r i c e s , a smaller f r a c t i o n w i l l be l o s t from high-volume processes than from low-volume ones. Continuous processes i n h e r e n t l y have smaller l o s s e s than batch processes, but there i s probably no such t h i n g as a "completely c l o s e d p r o c e s s . " From such arguments, r e l e a s e r a t e s would very r a r e l y exceed 10% of production f o r economic reasons, and very r a r e l y would they be 4


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lower than 0.01% of production on f e a s i b i l i t y grounds. values might be i n the range of 0.1% to 1%.


Example of an Ad-Hoc Approach:

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Typical

Benzene

Although benzene has r e c e n t l y come under i n c r e a s i n g c o n t r o l because of i t s a l l e g e d r o l e i n leukemia and other n e o p l a s t i c d i s e a s e s , i n past years i t has been widely d i s p e r s e d i n commercial uses and has entered the environment through many routes. In 1977, SRI attempted to c h a r a c t e r i z e "Human Exposures to Atmospheric Benzene" (1) . Most of the f o l l o w i n g examples come from t h a t r e p o r t , even though s e v e r a l l a t e r s t u d i e s have updated and r e f i n e d that work, and recent events have changed exposure patterns. F i r s t , p o i n t s of r e l e a s e of benzene were i d e n t i f i e d : petroleum r e f i n i n g and coke oven operations (production and e x t r a c t i o n r e l e a s e s ) , use as a chemical intermediate ( t r a n s p o r t a t i o n , storage, use, and waste r e l e a s e s ) , use i n g a s o l i n e ( u s e - r e l a t e d r e l e a s e ) , and use i n f i n i s h e d products (use-related r e l e a s e ) . Benzene a l s o can be a contaminant of most of the d e r i v a t i v e s made from i t and i t s use as a s o l v e n t was s u b s t a n t i a l before h e a l t h concerns arose. The complexity of the chemical systems dependent on benzene i s shown i n F i g u r e 6. A l i s t of p o t e n t i a l r e l e a s i n g products appears i n Table I I . Table I I MANUFACTURED PRODUCTS USING BENZENE AS A SOLVENT (1) Rubber t i r e s Miscellaneous rubber products Adhesives Gravure p r i n t i n g inks Trade and i n d u s t r i a l p a i n t s Paint removers Coated f a b r i c s Synthetic rubber Leather and l e a t h e r products F l o o r coverings Next, v a r i o u s q u a n t i t a t i v e techniques were used to estimate r e l e a s e s by type of use. For use of benzene as an intermediate, we r e l i e d on the "emission f a c t o r " technique, which estimates the r a t i o of benzene r e l e a s e to t o t a l d e r i v a t i v e production and then a p p l i e s t h i s r a t i o to the production r a t e at s p e c i f i c l o c a t i o n s . Emissions f a c t o r s were estimated from crude engineering assessments of the chemical processes e n t a i l e d (such as open versus c l o s e d systems, continuous versus batch, and so on). These crude estimates could be checked by comparing estimates of ambient c o n c e n t r a t i o n s based on them against a c t u a l measurements


14

FATE OF CHEMICALS I N T H E E N V I R O N M E N T


BENZENE

F i g u r e 6a. Benzene d e r i v a t i v e s w i t h p e r m i s s i o n f r o m R e f . 2.)

and

t h e i r uses.

(Reproduced



Chemical Release


1.

F i g u r e 6b. Benzene d e r i v a t i v e s w i t h p e r m i s s i o n f r o m R e f . 2.)

and

t h e i r uses.

(Reproduced



16

or by mass balance on measured input and output. Even so, such estimates were probably accurate to no b e t t e r than a f a c t o r of ten (Table I I I i s a sample l i s t ) . Emissions were then c a l c u l a t e d f o r about 80 p l a n t s , l o c a t e d i n over 20 s t a t e s , that consumed about 7 b i l l i o n pounds of benzene. Table I I I


EMISSION FACTORS AND CHARACTERIZATIONS FOR MANUFACTURING PLANTS THAT USE BENZENE

Chemical

Emission Factor (10~3 kg of benzene per kg of product)

Emission Characterization

SRI estimates (1) : Aniline Cyclohexane Detergent a l k y l a t e ( l i n e a r and branched)

23.60 0.25 2.20

Fugitive Fugitive Fugitive

PEDCo estimates (3): Cumene Dichlorobenzene (p- and o-)

Ethylbenzene M a l e i c anhydride Mono chlo rob enz ene Nitrobenzene Phenol Styrene

0.25 8.60

0.62 96.70 3.50 7.00 1.00 1.50

Fugitive Chlorinator, by-product recovery systems Scrubber-vent Product recovery scrubber Unknown Point absorber Unknown C o l l e c t i o n vent, emergency vent

Estimates a l s o were made f o r 65 coke p l a n t s i n 12 s t a t e s . Coke ovens produce benzene as a by-product, but not a l l of i t can be recovered. I t has been estimated that benzene c o n t r i b u t e s about two-thirds of one percent of the c o a l gas generated. P o t e n t i a l p o i n t s of emissions from one type of coke b a t t e r y are i l l u s t r a t e d i n F i g u r e 7. Emissions from coke ovens were d e r i v e d from estimated emission f a c t o r s (based on coke oven product assays and benzene y i e l d s ) and c o a l charging r a t e s . Because the content i n g a s o l i n e at that time accounted f o r a l a r g e f r a c t i o n of t o t a l benzene production, a l l p a r t s of the g a s o l i n e marketing chain (Figure 8) were considered to be


BROWN AND BOMBERGER

Chemical Release


1.


17

18


REFINERY STORAGE


SHIP, R A I L , B A R G E

PIPELINE

BULK TE RMINALS

TANK TRUCKS

BULK PLANTS

TRUCKS

COMMERCIAL, R U R A L USERS

SERVICE STATIONS

AUTOMOBILES, TRUCKS

Figure United

8. The g a s o l i n e m a r k e t i n g d i s t r i b u t i o n s y s t e m i n t h e S t a t e s , ( R e p r o d u c e d w i t h p e r m i s s i o n f r o m R e f . 3.)



1.


19

Chemical Release

p o t e n t i a l r e l e a s e p o i n t s . Benzene can be emitted i n r e f i n i n g , storage, d i s p e n s i n g ( s e r v i c e s t a t i o n s ) , or use (automotive emissions). R e f i n i n g r e l e a s e s were t r e a t e d much as were those from use as an " i n t e r m e d i a t e , " except that the emission f a c t o r s were s c a l e d to b a r r e l s of o i l processed by using the estimated concentrations of benzene i n t o t a l hydrocarbon emissions and emission f a c t o r s per b a r r e l o f o i l f o r hydrocarbons. Storage emissions are a l s o based on emission f a c t o r s . Both o f the preceding source types were t r e a t e d as p o i n t or small area sources. S e r v i c e s t a t i o n s and automobiles, however, were t r e a t e d as l a r g e area sources. Automotive t a i l p i p e emissions were based on emission f a c t o r s per m i l e d r i v e n and gas tank emissions were based on emissions per t r i p and t r i p s per v e h i c l e day. For s e r v i c e s t a t i o n s , ambient c o n c e n t r a t i o n s were p r e d i c t e d by models and compared w i t h measurements to c a l i b r a t e the emission r a t e s . For solvent o p e r a t i o n s , benzene use had to be estimated by a s e r i e s of tenuous assumptions about the amount of benzene i n "other uses," the percent o f that used f o r s o l v e n t s , and the l o s s of benzene from those o p e r a t i o n s . As an upper l i m i t , i t might be assumed that a l l o f the purchased benzene i s e v e n t u a l l y l o s t to the atmosphere. However, some measured concentrations suggest that perhaps only 10% i s l o s t a t the p l a n t . The remainder might be i n c i n e r a t e d a f t e r becoming unusable or sent elsewhere f o r d i s p o s a l . A general r u l e f o r v o l a t i l e s o l v e n t s i s that they e v e n t u a l l y reach the environment unless they are destroyed d e l i b e r a t e l y or degrade n a t u r a l l y . The d i s t r i b u t i o n o f solvent emissions g e o g r a p h i c a l l y i s much more d i f f i c u l t to determine. For completeness, we must mention that benzene a l s o occurs n a t u r a l l y i n foods such as f r u i t s , f i s h , vegetables, nuts, meats, d a i r y products, eggs, and a l c o h o l i c beverages. Exposures are estimated by m u l t i p l y i n g measured concentrations by usage o f the food product. In the SRI r e p o r t (2) the r e l e a s e i n f o r m a t i o n on benzene was used w i t h atmospheric d i s p e r s i o n models and data on geographic d i s t r i b u t i o n of p o p u l a t i o n to o b t a i n aggregate exposure estimates (shown i n Table I V ) . Table IV COMPARISON OF BENZENE EXPOSURES AMONG SOURCES (1)

Source Chemical manufacturing Coke ovens Gasoline s e r v i c e s t a t i o n s People u s i n g s e l f - s e r v i c e People l i v i n g i n the v i c i n i t y Petroleum r e f i n e r i e s Solvent operations Storage and d i s t r i b u t i o n Urban exposures from automobile emissions

(10

6

Exposure ppb -person-years) 15.9 8.8 1.6 90.0 3.4 0.1 Minimal 102.2


F A T E OF CHEMICALS I N T H E

20

ENVIRONMENT

Although s e v e r a l f i g u r e s i n Table IV are s i g n i f i c a n t , the estimates are probably accurate to the f i r s t d i g i t at best. However, they do suggest that widespread but l o w - l e v e l exposures from automobiles and s e r v i c e s t a t i o n s provide the m a j o r i t y of benzene molecules that enter human bodies. Whether these are the most b i o l o g i c a l l y s i g n i f i c a n t emissions depends on the behavior of dose-response r e l a t i o n s h i p s at low dose l e v e l s .


Research

Opportunities

Because the techniques of e s t i m a t i n g r e l e a s e s are so d i v e r s e and underdeveloped, there are many o p p o r t u n i t i e s f o r improvement. However, the o p p o r t u n i t i e s are d i f f i c u l t to d e s c r i b e i n s p e c i f i c terms. We t h e r e f o r e note only a few broad areas: Measurement—Much u n c e r t a i n t y about r e l e a s e r a t e s could be reduced by markedly i n c r e a s i n g the number and v a r i e t y of measurements made. Releases during use, i f not c l e a r l y 100% of use or n e a r l y so, are e s p e c i a l l y needed. We can c l e a r l y use many more model-measurement comparisons to c a l i b r a t e our source term assumptions, as w e l l as the model parameters. .

S t a t i s t i c s — W e need b e t t e r access to the data that are a v a i l a b l e from measurements. For example, annual production volumes are sometimes equal, or n e a r l y so, to annual r e l e a s e r a t e s on a nationwide b a s i s . But concern f o r p r o p r i e t a r y information has c u r t a i l e d access to such d a t a — i n our o p i n i o n , out of p r o p o r t i o n to the harm that might come to i n d u s t r y from p u b l i c knowledge. A c t u a l i n - p l a n t emission and e f f l u e n t r a t e s are obviously much more s e n s i t i v e , but b e t t e r summarization of d i s t r i b u t i o n s of such r e l e a s e s could be made f o r s c i e n t i f i c use. Surveys of degree of use to combine w i t h measured r e l e a s e s i n such uses are a l s o needed. M a t e r i a l s b a l a n c e — T h i s technique, i n p r i n c i p l e , i s developed to i t s f u l l e s t extent, but i t i s e x t r a o r d i n a r i l y s e n s i t i v e to u n c e r t a i n t i e s i n the data i t uses. B e t t e r c h a r a c t e r i z a t i o n of a l l pathways and chemical r e a c t i o n s would help, as would more accurate measurements of flows through these paths. Modeling—Most r e l e a s e s have been worked out with only one type of model. V a r i a n t approaches should be t r i e d and compared. O p p o r t u n i t i e s should be sought to e n r i c h models without overcomplicating them.

.

Ad-hoc approaches—Methods of estimating should be borrowed from other problems whenever a p p l i c a b l e . For example, s t a t i s t i c a l techniques f o r q u a l i t y c o n t r o l theory can probably be a p p l i e d to chemicals by viewing discharges as " f a u l t y " production.


1.


Literature 1.

2. 3.

Chemical Release

Cited

Mara, Susan J . , and Lee, Shonh S. "Human Exposures to Atmospheric Benzene," SRI I n t e r n a t i o n a l , Menlo Park, CA, 1977. Hedley, W. M. " P o t e n t i a l P o l l u t a n t s from Petrochemical Processes," Monsanto Research Corporation, 1975. PEDCo Environmental "Atmospheric Benzene Emissions," PEDCo Environmental, Inc., 1977.


R E C E I V E D April 15, 1983.


Release of Chemicals into the Environment - ACS Publications

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