An Epidemiological Assessment of the Cantara Metam Sodium Spill

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An Epidemiological Assessment of the Cantara Metam Sodium Spill Acute Health Effects and Methyl Isothiocyanate Exposure Richard A. Kreutzer , David J. Hewitt , and William M . Draper 1

1,3

2

Environmental Epidemiology Section, California Department of Health Services, 5900 Hollis Street, Suite E, Emeryville, CA 94608 Hazardous Materials Laboratory, California Department of Health Services, 2151 Berkeley Way, Berkeley, CA 94704 1

2

This chapter describes an environmental epidemiology case study involving acute health effects of the pesticide metam sodium released in a railroad transportation accident in northern California.

A total

of 23,500 kg of metam sodium spilled into the Sacramento River, destroying nearly all aquatic life in a 45-mi stretch of river and exposing 2129 residents of Dunsmuir products, (MITC).

to metam sodium's volatile decomposition

which include the potent irritant methyl isothiocyanate Reported

health effects, including

nonspecific

complaints (headache and dizziness) and irritation (eye,

neurologic respiratory

tract, gastrointestinal tract, and skin) were consistent with

MITC

exposure. In Dunsmuir, 14% of residents sought medical attention. The case study demonstrates how health effects in a 1-month period following the spill were ascertained by using questionnaires, pesticide illness reports from private physicians, and hospital inpatient and emergency room medical records. An environmental fate and transport model suggests that the highest air concentrations of MITC in Dunsmuir were less than 160 ppb and may have occurred over 12 h after the spill as a result of a rapid photochemical conversion of metam sodium to MITC in sunlight.

The Cantara Metam Sodium Spill T h e S a c r a m e n t o R i v e r i n n o r t h e r n C a l i f o r n i a has l o n g b e e n r e n o w n e d for its b e a u t y a n d e x c e l l e n t t r o u t f i s h i n g . O r i g i n a t i n g n e a r M t . Shasta, i t flows 3

Current address: 13500 Cheral Parkway, Apartment 790D, Little Rock, AK 72211.

0065-2393/94/0241-0209$08.36/0 © 1994 American Chemical Society

Draper; Environmental Epidemiology Advances in Chemistry; American Chemical Society: Washington, DC, 1994.

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ENVIRONMENTAL EPIDEMIOLOGY


south to L a k e Shasta ( F i g u r e 1). H u m a n p o p u l a t i o n along this segment of the r i v e r is generally sparse. O n Sunday, J u l y 14, 1991, at 21:40 h , a S o u t h e r n Pacific R a i l r o a d train consisting of 97 cars a n d four locomotives d e r a i l e d o n a tight b r i d g e c u r v e s p a n n i n g the Sacramento R i v e r , k n o w n as the " C a n tara L o o p " , located 6 m i n o r t h of D u n s m u i r . A locomotive, six e m p t y freight cars, a n d an u n l a b e l e d tank car left the tracks. T h e tank car c a m e to rest i n a p a r t i a l l y i n v e r t e d position i n the shallows d i r e c t l y b e n e a t h the b r i d g e (J). C r e w m e m b e r s r e p o r t e d odors c o m i n g f r o m the d e r a i l e d cars shortly after the d e r a i l m e n t . A t 04:30 o n J u l y 15, r a i l r o a d officials r e p o r t e d a n o n l e a k i n g p u n c t u r e i n the d e r a i l e d tank car above the water l i n e . It was e s t i m a t e d that approximately 1500 gal of m e t a m s o d i u m m i g h t have l e a k e d into the river. A s reports of h e a l t h effects a n d d e a d fish d o w n s t r e a m b e c a m e

Figure 1.

Map of affected area.


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KREUTZER ET AL.

Cantara

Metam

Sodium

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available later that m o r n i n g , the extent of the s p i l l was reevaluated. T w o additional s u b m e r g e d holes i n the car w e r e found w h e r e it was r e s t i n g o n the r i v e r b e d . B y approximately n o o n o n J u l y 15, it was estimated that n e a r l y all of the 19,500 gal of pesticide transported i n the tank car w e r e released, p r o b a b l y w i t h i n 1 h of the d e r a i l m e n t (I).

Early Reports of Public Health and Environmental Effects T h e p l u m e t r a v e l e d e n masse s o u t h w a r d at a p p r o x i m a t e l y 1 m p h u n t i l the early hours of J u l y 17 w h e n it r e a c h e d L a k e Shasta, 45 m i f r o m the s p i l l site. A q u a t i c life along this section of the r i v e r was severely affected. T h e C a l i fornia D e p a r t m e n t of F i s h a n d G a m e ( C D F G ) r e p o r t e d fish kills i n the h u n d r e d s of thousands. T h e largest p o p u l a t i o n center o n the affected segment of the r i v e r is the t o w n of D u n s m u i r (population 2129, 1990 census) (2) ( F i g u r e 1). S e v e r a l m u c h smaller c o m m u n i t i e s (Castella, S w e e t b r i e r , L a M o i n e , P o l l a r d F l a t s , D e l t a , a n d Lakehead) and campgrounds are located farther d o w n s t r e a m . W i t h i n 8 h of the s p i l l , the c o u n t y h e a l t h d e p a r t m e n t h a d r e c e i v e d f r o m D u n s m u i r residents n u m e r o u s complaints of i r r i t a t e d eyes a n d unpleasant odors. T h e tail e n d of a l i g h t y e l l o w - g r e e n p l u m e was r e p o r t e d to pass t h r o u g h D u n s m u i r a r o u n d 07:45 (I). T h e M t . Shasta h o s p i t a l , located a few m i l e s u p s t r e a m f r o m the s p i l l site, began seeing patients w i t h exposurer e l a t e d illnesses i n its e m e r g e n c y r o o m b y 11:00 o n J u l y 15. A t e m p o r a r y shelter for v o l u n t a r y evacuees was established at the D u n s m u i r H i g h S c h o o l o n the afternoon of J u l y 15 a n d r e m a i n e d o p e n u n t i l 20:00 o n J u l y 20. P a r a medics w e r e stationed at the shelter to assess, treat, a n d triage h e a l t h c o m plaints.

Metam Sodium Chemistry and Properties M e t a m s o d i u m (sodium m e t h y l d i t h i o c a r b a m a t e or s o d i u m m e t h y l c a r b a m odithioate) was patented i n 1958 as a soil fumigant a n d n e m a t i c i d e (3). A t h i g h concentrations, m e t a m s o d i u m also is an h e r b i c i d e , a n d it is w i d e l y u s e d as a w o o d preservative. A g r i c u l t u r a l usage of m e t a m s o d i u m has i n creased substantially i n recent years, because other p r e v i o u s l y u s e d f u m i gants such as 1,3-dichloropropene w e r e r e m o v e d f r o m the m a r k e t d u e to h e a l t h concerns (4). T h e fumigant activity of m e t a m s o d i u m is a t t r i b u t e d to its volatile b r e a k d o w n p r o d u c t , m e t h y l isothiocyanate ( M I T C ) — m e t a m s o d i u m itself is an i n volatile salt. M I T C also is a registered pesticide that has a s p e c t r u m of activity similar to that of m e t a m s o d i u m . S u r p r i s i n g l y , a l k y l isothiocyanates, i n c l u d i n g M I T C , o c c u r naturally i n plants, b u t they are u s u a l l y sequestered as glucosinolates.



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M e t a m s o d i u m is c o m m o n l y f o r m u l a t e d as a 3 2 . 7 % - b y - w e i g h t aqueous solution, the m i x t u r e that was s p i l l e d into the Sacramento R i v e r . It is p r e p a r e d c o m m e r c i a l l y b y reacting c a r b o n d i s u l f i d e , m e t h y l a m i n e , a n d s o d i u m h y d r o x i d e . A t h i g h concentrations, m e t a m s o d i u m solutions r e m a i n slightly basic, a n d the pesticide is r e l a t i v e l y stable. A t v e r y h i g h a n d l o w p H values, m e t a m s o d i u m decomposes v i a different pathways ( F i g u r e 2). B e l o w p H 4.0, m e t a m s o d i u m [pKa = 2.89 (5)] is protonated, a n d free m e t h y l d i t h i o c a r b a m i c a c i d r a p i d l y converts back to the starting materials, m e t h y l a m i n e a n d carbon disulfide. A t h i g h p H values (>11), m e t a m s o d i u m loses a second p r o t o n , a n d the d i a n i o n decomposes to M I T C a n d sulfide. Typically, the concentrated m e t a m s o d i u m formulations are d i l u t e d w i t h water a n d are a p p l i e d d i r e c t l y to soil. U n d e r these conditions, m e t a m sod i u m is r a p i d l y c o n v e r t e d i n h i g h y i e l d to M I T C (6). T h e fate of m e t a m s o d i u m i n natural water is not as w e l l - u n d e r s t o o d . T h e a c i d - and base-catalyzed d e c o m p o s i t i o n reactions ( F i g u r e 2) are not i m portant at p H 7.0, w h e r e m e t a m s o d i u m occurs as its conjugate base [ C H N H — C ( S ) S ~ ] . D i s s o l v e d oxygen may oxidize m e t a m s o d i u m to a d i sulfide, b u t this oxidation is not t h e r m o d y n a m i c a l l y favored b e l o w p H 9.5 (7). A t n e a r - n e u t r a l or slightly acidic p H , m e t a m s o d i u m decomposes v i a a m o n o m o l e c u l a r cleavage reaction, g i v i n g rise to M I T C a n d h y d r o g e n sulfide ( F i g u r e 2). T h e cleavage reaction is b e l i e v e d to i n v o l v e a planar i n t e r m e d i a t e i n w h i c h a h y d r o g e n is b o n d e d to b o t h sulfur a n d n i t r o g e n . I n a d d i t i o n to d e c o m p o s i t i o n b y cleavage, m e t a m s o d i u m is subject to p h o t o c h e m i c a l d e c o m p o s i t i o n i n natural water. M e t a m s o d i u m is estimated to have a half-life of b e t w e e n 30 m i n a n d 1.6 h for d i l u t e solutions i r r a d i a t e d i n s u m m e r s u n light (8, 9). T h e p h o t o d e c o m p o s i t i o n products of m e t a m s o d i u m i n c l u d e M I T C , w h i c h accounts for 2 1 - 2 4 m o l % of m e t a m s o d i u m reacting (

An Epidemiological Assessment of the Cantara Metam Sodium Spill

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