The recorder used was a Westronics MT-22, dual pen having 1mV full-scale sensitivity. Samples of oil, each 100 pl, were diluted with n-hexane in ratios of 1 to 25 and 1 to 50. The amounts injected for examination ranged from 1- 5 pl. Portions (100 pl.) of the pollution and suspected source samples were cleaned and dried by dissolving them in nhexane and passing them through a 1-in. column of anhydrous sodium sulfate. The volumes of each were reduced to 5 ml on a water bath a t 70°C, and aliquots ranging from 1-5 p1. were injected into the gas chromatograph. Water Partitioning. Three 1-ml samples were obtained from each “standard” oil sample and added to 800 ml of Mississippi River water in clean 1-qt glass jars. The samples and 800 ml of Mississippi River water blank were stirred for 1 hr with the aid of 2-in. Teflon-coated magnetic stirring bars and magnetic stir-jacks. The samples and the Mississippi River water blank were then extracted with 30 ml of n-hexane and dried on a 5-cm, column of anhydrous sodium sulfate. “Standards” of each oil were prepared by diluting 100 pl. of the oil to a volume of 5 ml with n-hexane. The n-hexane extracts of the samples and Mississippi River water blank were reduced to a volume of 25 ml on a water bath a t 70°C and aliquots, ranging from 1-5 pl., of the extracted samples, blank and corresponding “standard,” were injected for analysis. The gas chromatographic responses were compared for reproducibility (Figures 14 and 15). Weathering. One gram of the refinery sample (Figure 8) was laboratory “weathered” by placing the sample in a water bath a t 70°C for 4 hr to remove the more volatile components and reduce the sample 25% by weight by evaporation. A 100-p1. portion of the “weathered” sample was diluted to a volume of 5 ml with n-hexane and 5 pl. were injected into the gas chromatograph for analysis.
Aliphatic, Aromatic Separation. Another portion of the “weathered” refinery crude oil sample and a similar amount of the oil spill sample were each dissolved in 5 ml of ethyl ether and transferred to columns containing 2.5-cm layers of silica gel. The ethyl ether was evaporated’ from the column with the aid of a small reverse flow of prepurified nitrogen gas. The columns were eluted with 75 ml of isooctane, then with 75 ml of benzene, collecting the eluates separately. The two eluates collected from each sample contained the aliphatic and aromatic fractions, respectively. The eluates were reduced to a volume of 25 ml on a water bath and 5 pl. of each eluate were injected into the gas chromatograph for analysis. The use of a proprietary product is for information and does not necessarily imply endorsement of the product by the U S . Environmental Protection Agency. Acknowledgments The authors thank Micro Tek Instrument Corp., a subsidiary of Tracor, Inc., for the use of a Micro Tek M T 220 gas chromatograph equipped with a Melpar detector. Literature Cited Amer. SOC.Test. Mater., Philadelphia, Pa., ASTM Designation D, 129-62 (1962). Bowman, M . C., Beroza, Morton, A . O.A.C., 49, 1154 (1966). Bowman, M . C., Beroza, Morton, ibid., 50,940 (1967). Breidenbach. A. W.. “The Identification and Measurement of Chlorinated Hydrocarbon Pesticides in Surfa\ce Waters,” USDI, FWPCA (1966). Brodv. Sam S.. Chanev. John E.. Research Div.. Meloar Inc.. Fails C h u k h , Va. “ Gamble. L. W., Jones. W. H.,Anal. C h e m , 27.1456-9 (19551. Getz, Melvin E., Gas Chromatog., 5 , 377 (1967). Kawahara, F . K., Enuiron. Sei. Technol., 3, 150-3 (1969). Received for reuieu, December 23, 1971. Resubmitted October 26, 1973. Accepted November 7, 1973.
Migration and Redistribution of Zinc and Cadmium in Marine Estuarine System Charles W. Holmes,’ Elizabeth Ann Slade, and C. J. McLerran U.S. Geological Survey, Corpus Christi,
Tex.7841 1
~
A survey of trace-element levels in the estuarine sediments of Texas shows that Corpus Christi Bay has anomalously high concentrations of zinc and cadmium. Maps of elemental abundance within the bay indicate large concentration gradients, the highest values being near the harbor entrance. Seasonal determinations of metal levels in the harbor and bay waters also revealed variations with time. During summer, stagnation of the harbor water increases the concentration of metals so that significant quantities precipitate in the reducing environment of the bottom water. In winter, the exchange of water between the bay and the harbor increases, and metals are redissolved from harbor deposits, washed into the bay, and adsorbed by particles settling to the bottom. 0
1 To whom
correspondence should be addressed.
During a survey of the trace-element distribution in the sediments of Texas bays and lagoons, anomalous zinc and cadmium levels were found in Corpus Christi Bay. Because zinc has been found to be detrimental to fish and other aquatic life (Pettyjohn, 1972) and because cadmium is a known toxin to man, these elements pose a threat to the estuarine system. Although zinc does not appear to be highly concentrated in the marine food chain (IDOE, 1972), it may pose a greater hazard in the dissolved state where it can interact freely with nectonic life. Cadmium, on the other hand, does become concentrated in the food chain and is therefore a hazard in any chemical state. This report presents data on the distribution of these elements in the sediments, their seasonal variations, and the pathways by which they move within the estuarine system. Volume 8,Number 3, March 1974
255
Corpus Christi Bay is approximately 4 meters deep and nearly equidimensional, covering an area of approximately 300 km2 (Figure 1). In the saucerlike central part of the bay, the sediments consist of fine silts and clays; sands composed mainly of shell debris rim the bay on shallow shelves. A dredged ship channel 15 meters deep and 123 meters wide nearly bisects the bay and terminates in a narrow, 13-km-long, landlocked harbor, along which petrochemical and other industries are located. Current measurements and drogue studies at the entrance of the harbor show a significant inwardly directed current below 6 meters; outflow occurs in the surface zone. The strength of both currents is much greater than can be accounted for by industrial uptake and discharge or by the movement of the tidal prism.
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Figure 1.
Location of study area
Km
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2
Figure 2.
4
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Distribution of zinc in the sediments of Corpus Christi Bay (dot = sample locality)
UM 0.24 0.49 0.74 0.99 1.90 0
Km
-8
Figure 3.
256
Distribution of cadmium in the sediments of Corpus Christi Bay (dot = sample locality)
Environmental Science & Technology
Methods In the initial phase of the study, 287 sediment samples were taken from the bay and harbor with a clamshell sampler designed to obtain a m3 sample. In addition to these, 156 water samples were taken with a PVC water sampler. The sediment samples were air dried, ground to less until than 200 mesh, and leached with boiling 16N "03 NO2 fumes ceased; they were then analyzed for zinc and cadmium by atomic absorption spectrophotometry. The deviation in this procedure determined on replicate samples was found to be less than 10%. Subsequent analyses on replicate samples by a spectrographic method (Grimes and Marranzino, 1968) demonstrated that this digestion procedure accounted for approximately 85% of the zinc and cadmium in the sediments. These results roughly agree with those of Jones (1973), who reported that 75% of
lbO
I
the zinc and 60% of the cadmium in the bottom sediments of Cardigan Bay, Wales, were acid soluble. Zinc concentrations in the water were determined by chelating and extracting the metal with an ammonium pyrrolidine-dithiocarbonate (APDC) methyl-isobutylketone (MIBK) mixture and subsequent atomic absorption analysis (Brooks and others, 1967). The deviation determined on replicate samples by this procedure was approximately 20%. Cadmium in the water was determined directly by anodic stripping voltammetry (ASV) (Matson, 1968), with a deviation on replicate samples of less than 8%. In an attempt t o determine the mineral association of the zinc in the bay and harbor sediments, 18 representative samples were analyzed for the metal-mineral associations. These samples were shaken for approximately 1 hr in a solution of 1M hydroxylamine-hydrochloride and 25% (v/v) acetic acid, a procedure which dissolves nonsilicate ferromanganese minerals and carbonate minerals and extracts the adsorbed trace elements but has no effect on the silicate or authigenically formed sulfide minerals (Chester and Hughes, 1967). Subsequent leaching of the residual material with 16N H N 0 3 allowed for an estimation of the amount of zinc and cadmium bound with organic or sulfide compounds. Replicate analyses of these samples established the analytical deviation to be less than 10%. The pH of the sediment and water was determined with a combination glass electrode calibrated against commercially available buffer solutions. The Eh (redox potential) was measured with a combination platinum electrode calibrated with "Zobell" solution (Langmuir, 1971). The temperature and salinity were determined by an in situ induction salinometer.
CADMIUM
Results and Discussion In the sediments of the bay, zinc concentrations ranged from a maximum of 235 ppm near the entrance of the harbor to a minimum of 6 ppm in the northeastern part of the bay (Figure 2 ) and cadmium concentrations ranged from a high of 1.9 to a low of 0.1 ppm (Figure 3). In the harbor sediments, zinc ranged from a maximum of 11,000 ppm, approximately 8 km from the harbor entrance, to a minimum of 235 ppm at the entrance, cadmium ranging from 130 ppm to 2 ppm (Figure 4). Correlation between the zinc and the cadmium concentrations in the bay and harbor sediments was calculated to be 0.80, indicating an identical source and their chemical similarity.
0 1 2 3 4 5 6 7 8 9 loll 1213 DISTANCE FROM
ENTRANCE
O F HARBORCKM)
Figure 4. Zinc and cadmium concentrations in the sediments of
Corpus Christi harbor SEPTEMBER 0
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DISTANCE FROM ENTRANCE OF HARBOR ( K m )
Figure 5. Zinc and cadmium concentrations in the water during
summer conditions for Corpus Christi harbor (concentration in ppb [wg/I.] Dot = sampie site)
,
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a
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10
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DISTANCE rROM ENTRANCE OF HARBOR (h)
Figure 6. Zinc and cadmium concentration in the water during winter conditions in Corpus Christi harbor (concentration In ppb [wg/l ] Dot = sample site)
Volume 8, Number 3, March 1974
257
C
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Figure 7. Vertical summer distribution of zinc and Eh in Itle water at four stations in Corous Christi harbor. June 1972 Station A is 4.2 km from harbor entrance, station I3 is 7.4 km, station C is 1 1 I
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