Aerial Fallout of DDT in Southern California David R. Young, Deirdre J. McDermott, and Theodore C. Heesen Southern California Coastal Water Research Project 1500 East Imperial Highway El Segundo, Cal. 90245

DDT and its metabolites are among the m o s t serious contaminants yet identified in the m a r i n e environment (RISEBROUGH et al. 1967; DE LONG et al. 1973; M C D E R M O T T et al. 1974). In past years, ver~ large quantities of DDT wastes were released into the JWPCP* sewer system of the County Sanitation Districts of Los Angeles County (MAC GREGOR 1974). These wastes, apparently p r o d u c e d b y Montrose Chemical Company (during the m a n u f a c t u r e of this pesticide) were subsequently discharged via the JWPCP submarine outfalls off Palos Verdes Peninsula to the m a r i n e ecosystem of the Southern California Bight (Figure i). During the last 3 years we have investigated the input rates of DDT and other chlorinated h y d r o c a r b o n s to the Bight via a number of d i f f e r e n t routes (YOUNG et al. 1974; R I S E B R O U G H et al. 1974). Here we report the results for one of the routes, dry aerial fallout. In v i e w of the very low rainfall in southern California, a p p r o x i m a t e l y 30 cm/yr, dry aerial fallout dominates aerial inputs along this section of the Pacific Coast. Utilizing a glass plate and mineral oil c o l l e c t i o n technique first developed b y Dr. Vance McClure (National M a r i n e Fisheries Service, La Jolla, California), approximately 1,000 samples w e r e taken in replicate 1-week collections made during two 13-week periods** at 14 coastal stations and 6 island stations b e t w e e n Point C o n c e p t i o n and the U . S . / M e x i c o border. These samples have y i e l d e d a large b o d y of data on several DDT compounds in dry aerial fallout, at levels free of apparent c h r o m a t o g r a p h i c interferences or significant contributions from analytical blanks.

Joint Water Pollution Control Plant July-September 1973 and March-June 1974

604 Bulletin of Environmental Contamiaation & Toxicology, VoL 16, No. $ {9 November 1976 by Sprlnger-Verlag New York Inc.

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F I G U R E i. Average flux of total DDT (10 -9 g/sq m/day) via dry aerial fallout collected in the Southern California Bight during 1973-74.

M A T E R I A L S AND METHODS The c o l l e c t i o n device for sampling dry aerial fallout was a piece of cleaned w i n d o w glass (0.i square meter) sprayed with a m i x t u r e of p h a r m a c e u t i c a l mineral oil (Squibb brand) diluted b y five parts p e s t i c i d e - g r a d e hexane. A pair of cleaned plates wrapped in aluminum foil were taken to the c o l l e c t i o n site, unwrapped, and p l a c e d on a h o r i z o n t a l surface above the ground. Generally this was the roof of a o n e - s t o r y structure located on or near the b e a c h b u t removed from obstructions with large profiles w h i c h m i g h t cause excessive turbulence. E v e r y effort was made to isolate the sampling plates from n e a r b y painted surfaces, e s p e c i a l l y if the paint was flaking. If this was impossible, samples of the p o t e n t i a l l y c o n t a m i n a t e d m a t e r i a l were taken for analysis. Once the places were unwrapped and in place, they were sprayed with a very light coat of the diluted m i n e r a l oil using a TLC sprayer (Chromatosprayer brand). The criterion followed was to apply enough oil so that the plate would trap small p a r t i c l e s b u t not larger objects such as insects and feathers. Usually, spraying from a d i s t a n c e of about 0.3 meter for a period of about 5 seconds was sufficient. After the h e x a n e evaporated, 605

this left roughly 0.3 ml of oil on the plate. At the end of the one week sampling period, a cleaned piece of teflon, cut w i t h a straight edge, was used to scrape the mineral oil and fallout particles from the plate. The oil was transferred from the edge of the teflon strip to the inner rim of a pointed, g r a d u a t e d p y r e x centrifuge tube. After several minutes of scraping, the plate was re-sprayed with diluted mineral oil and rescraped; this procedure was repeated for a third scraping. (Tests have indicated that this threestep process recovers more than 95% of the fallout material.) Then, the sample tube was covered with aluminum foil under a screw cap and returned to the laboratory. Before leaving the site the scraped sampling plates were r e - s p r a y e d to b e g i n the next sampling period. A e r i a l fallout samples were processed through a "cleanup column" b e f o r e b e i n g analyzed b y gas chromatography. The clean-up column was a disposable 5 ml pipet packed with specially prepared and activated silica gel. MCB Silica Gel (SX-144-6) 100-200 mesh was w a s h e d with a i:i solution of methanol/benzene. Three m i l l i l i t e r s of solution were used per one gram of adsorbent. After rinsing, the silica gel was dried in a Rotovapor and a c t i v a t e d at 180~ overnight and then stored under hexane. The column was packed b y inserting a plug of silane treated glass wool, adding several mls of h e x a n e and slurrying the silica gel w i t h a pipet. Using the markings on the 5 ml pipet as a guide, adsorbent was added until the volume of the compacted bed was 1.7 ml • 0.i ml. A vibrator was held against the column b r i e f l y to compact the adsorbent. The fallout samples came into the laboratory in centrifuge tubes containing up to 1 ml of m i n e r a l oil. The sides of the tube were w a s h e d down with enough h e x a n e to b r i n g the volume to 3 mls. The sample was then introduced into the column using a pipet to transfer it from the centrifuge tube. The initial elution was with 1.7 ml of hexane to remove the m i n e r a l oil from the column; this fraction was discarded. The DDT compounds were then eluted with 5.7 ml of 20% b e n z e n e / hexane. Dilutions of this fraction were made to appropriate volumes for analysis b y electron capture gas chromatography. RESULTS AND D I S C U S S I O N The results for p,p'-DDT, o,p'-DDT, and p,p'-DDE (plus p , p ' - D D D for the second survey) have b e e n converted to e s t i m a t e d m e a n daily fluxes (10 -9 g/sq m/day) for each sampling, applying respective collection efficiency factors of 60, 64, 36 and 63 percent. The W i l c o x O n 606

s i g n e d - r a n k test was used to determine if there was a s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e b e t w e e n the two seasonal values of total DDT fallout onto the Bight. None was d e m o n s t r a t e d at the 95 p e r c e n t confidence level; therefore, the w e e k l y data for the individual components were averaged over the entire 26-week collection period. Figure 1 p r e s e n t s the r e s u l t a n t m e a n for total DDT. The average ratio of p , p ' - D D T to o,'p-DDT observed in the B i g h t was 2.5 to i, and these two isomers constituted a p p r o x i m a t e l y 70 p e r c e n t of the "total" m e a s u r a b l e flux of D D T compounds onto the Bight. In contrast, we have observed that a p p r o x i m a t e l y three-quarters of the total DDT in ocean b o t t o m sediments around the site of the JWPCP o u t f a l l s is m a d e - u p of p , p ' - D D E and the p r i n c i p a l components of the w a s t e w a t e r s discharged are p , p ' - D D E and p,p'-DDD. During the first seasonal collections a few w e e k l y samples also w e r e taken in Ensenada, Mexico. The r e s u l t s indicated that one of the h i g h e s t coastal flux values for total DDT observed in the Bight during summer 1973 o c c u r r e d at Ensenada. This is an agricultural r e g i o n of the B a j a California peninsula, and these higher fallout values appear to r e f l e c t greater or m o r e r e c e n t local usage of DDT than to the north. One of the m o s t striking results of this B i g h t - w i d e survey was that, w i t h the e x c e p t i o n of the Ensenada results, the total DDT fallout values g e n e r a l l y increased toward Los Angeles. This was surprising, as the major a g r i c u l t u r a l areas of the coastal plain lie to the north and south of this h i g h l y - u r b a n i z e d region. Because the results of our research h a d indicated that dry aerial f a l l o u t was a r e l a t i v e l y important source of DDT compounds to the Bight, we c o n d u c t e d a fallout survey w i t h i n the Los Angeles Basin to further investigate this finding. B e t w e e n 26 A p r i l a n d 24 M a y 1974, we sampled 24 b a s i n stations during 4 successive weeks. Because of the p a s t h i s t o r y of dramatic DDT p o l l u t i o n of the Bight, a p p a r e n t l y as a result of waste d i s c h a r g e s from M o n trose Chemical Company, four stations w e r e established w i t h i n a few b l o c k s of this industrial p l a n t located in a suburb of Los Angeles. Four sites also were established around the s a n i t a r y landfill in Rolling Hills Estates on the Palos Verdes Peninsula, operated b y the C o u n t y S a n i t a t i o n D i s t r i c t s of Los Angeles County. It is r e p o r t e d that this landfill r e c e i v e d DDT wastes from the M o n t r o s e p l a n t up until about 1972. In addition, four sites w e r e e s t a b l i s h e d around a private s a n i t a r y landfill owned b y B e n K. K a z a r i a n and located near the 607

city of West Covina where the M o n t r o s e wastes are now taken. In this survey, the DDT constituents were clearly identified at levels at least an order of m a g n i t u d e above those found in process blanks. The results showed two regions of r e l a t i v e l y h i g h DDT fallout, located in the v i c i n i t y of the Montrose plant and the R o l l i n g Hills sanitary landfill. The h i g h e s t of the values in each r e g i o n generally occurred at the south or southeast stations. As the p r e v a i l i n g coastal winds are from the northwest, this suggests two separate sources. In light of the large gradients in DDT fallout rates that w e r e observed, and the implications regarding the sources, the survey was repeated during 2 weeks in September 1974; two additional stations were included in the pattern around the M o n t r o s e plant. The September DDT data were similar to those of the previous spring and indicate little seasonal effect. The occurrence of an occasional anomalous value can strongly bias a small-sample mean, so for this b a s i n study, we assumed the m e d i a n of the six w e e k l y values to b e m o s t r e p r e s e n t a t i v e of the fallout flux at a given station. The values for total DDT are illustrated in Figure 2. ~ZUMA

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