G.6, 1

L V O _ E S MANC.AUESE D I 3 X DE x 0’

Figure 2. Absorbance of crystal violet in final solvent solution vs. Fmoles of manganese dioxide in original 100-ml samples

manganese dioxide suspension to 100-ml aliquots of a solution 10-3M in bicarbonate and lO-5M in manganous perchlorate. The amounts of added manganese dioxide were then estimated using the extraction procedure and calibration graph (Figure 2) as 1.00 x 1W2 and 3.01 X pmoles, respectively, again indicating no appreciable interference in the method from manganous manganese.

Samples of High Ionic Strength Since the coloration produced by the oxidation of 4,4’4”-

methylidynetris (N,N-dimethylaniline) in solution can be attributed to the formation of the resonant cation of crystal violet, the methods with and without extraction were ex- amined for use with samples of high ionic strength. One half- and 1 .O-ml quantities of 1 .OO x 10-4M stock manganese dioxide suspension were added to 50-ml aliquots of a solution 10-3M in sodium bicarbonate and 0.65M in sodium chloride, and the procedure followed as described under “Analysis Without Extraction.” Similarly 0.1- and 0.3-mi quantities of the stock suspension were added to 100-ml aliquots of the sodium bicarbonate-sodium chloride solution, and the pro-

Table 11. Comparison of Absorbances for Samples of Low and High Ionic Strength

Absorbance Measured absorbance with low

MnOz in sample, with high ionic ionic strength #moles strength samples samples

1 . 0 x 10-2 0 . 090a 0 . 160b 3 . 0 x 10-2 0 . 334a 0 . 478b 5 .0 x 0. loxc 0 . 208d

10.0 x 10-2 0,259‘ 0.417d a With extraction. From Figure 1 . c Without extraction.

d From Figure 2.

cedure detailed under “Analysis with Extraction” carried out. The measured absorbances (after subtraction of blank values) are compared in Table I1 with values estimated from Figures 1 and 2.

The results indicate that in cases where the sample con- tributes considerable ionic strength to the final 100-ml solution in the analysis without extraction, or to the aqueous phase in the analysis with extraction, when compared with the ionic strength contribution of the acetic acid-acetate buffer (ap- proximately 0.04 for 5 ml of 6M buffer a t p H 4.0 in 100 ml), calibration curves need to be constructed for the particular conditions encountered. Such would be the case, for instance, with seawater samples.

Literature Cited Morgan, J. J. , Stumm, W., J . Amer. Water Works Ass., 57,

107 (1965). Ormerod, J. G., Limnol. Oceanogr., 11, 635 (1966).

Receiwd for reciew September 13,1971. Accepted December 31, 1971.

Mercury: Vertical Distribution at Two Locations in the Eastern Tropical Pacific Ocean

Herbert V. Weiss’ and Sachio Yamamoto Naval Undersea Research and Development Center, San Diego, CA 92132

Thomas E. Crozier and James H. Mathewson Department of Chemistry, San Diego State College, San Diego, CA 921 15

rn Mercury concentrations a t two locations off the west coast of Mexico have been determined in the water column. At a station 60 km from the shore, pronounced fluctuations and greater mercury concentrations, 22-173 nglkg, were measured compared with samples taken 150 km from the coast in which the concentration range was 12-27 ng/kg.

urrent interest in environmental contamination by C mercury has led to extensive investigations of mer- cury levels in a variety of organisms and environments (Ackefors et al., 1970). However, little information has been gathered about the distribution of mercury in the oceans. Mercury concentration was measured in the sea a t two sta- tions 60 and 150 km off the west coast of Mexico to determine

644 Environmental Science & Technology

the mercury levels in areas remote from direct input by man. Samples of seawater were collected in July 1970, over the western edge of the Middle America Trench in 3450 meters of water (16”00’N, 101 “40’W, Station V) and directly over the Trench in 4800 meters of water (17”52’N, 103”50’W, Station IX). Vertical profiles of mercury were constructed (Figure 1).

Sample Collection Samples of seawater were collected at depths between the

surface and near the bottom in 8-1. “Niskin” bottles attached to a standard hydrowire. One-liter, unfiltered samples were drawn off within 2 hr after collection into polyethylene bottles which were capped, frozen immediately, and kept

To whom correspondence should be addressed.

frozen until analyzed. Laboratory tests were performed to determine the influence of sample storage on mercury re- covery. Half-liter volumes of seawater were spiked with lg7Hg in the divalent state and frozen. After about one week of storage the samples were thawed at room temperature. Following this treatment, mercury activity was quantitatively recovered by the separation procedure described below.

Analytical Procedure The samples, whose weights ranged from 300 to 900 grams,

were analyzed by thermal neutron activation of mercury. The mercury was separated from sea salts by coprecipitation with copper sulfide from acid solution (Weiss and Crozier, 1972): The copper sulfide was dissolved in concentrated nitric acid, transferred to a 15-ml polyethylene vial and irra- diated for 1 hr in a thermal neutron flux of 1.8 X 10l2crn-2 sec-l, in the Lazy Susan of the Triga Reactor at the Gulf Energy and Environment Service facility in San Diego.

In experiments performed at 5OoC and a flux of lo1* neutron cm-* sec-', Bate (1971) demonstrated that mercury radio- activity is lost from plastic containers when irradiations of 12 to 65 hr are carried out. In our preliminary recovery ex- periments at the nanogram level, under the experimental con- ditions of the present study no significant loss occurred.

After the irradiation, mercuric nitrate carrier was added to the samples and interfering nuclides were removed, The 77- keV X-ray emitted in the decay of 65-hr 197Hg was measured with a NaI(T1) detector coupled to a 400-channel analyzer about one week after irradiation. All reagents used prior to irradiation contained negligible amounts of mercury. The limit of detection (defined as a count rate in excess of three standard deviations above the background count rate) is 4 ng. The error of analysis is 1 2 z .

Results The mercury profiles appear in Figure 1. At Station V,

mercury concentrations ranged from 12 to 27 ng/kg; the average was 19 ng/kg. The concentrations for Station IX ranged from 22 to 173 ngikg. The frequency and amplitude of the variations at this station were significantly greater than that at Station V. This difference perhaps is ascribable to varying particulate content which may be associated with a location closer to shore. A minimum and maximum in con- centrations appear in both stations at 100 and 400 meters and the surface values in each are approximately the same. The mercury content for waters from Station IX were uniformly

500

1000

- 1500- '0 w u

2 2000- - I

2500- n

3000

3500-

4000-

4500-

Hg IN SEAWATER n g k g

0 20 40 60 EO 100 120 140 I60 180

-

-

-

L

Figure 1. Vertical distribution of mercury in the eastern tropical Pacific Ocean

greater than for samples collected at Station V. A consistent increase or decrease in concentration from the top of the water column to the bottom was not apparent.

The mercury concentrations found in the location farther out to sea agree closely with the 14 to 21 nglkg determined for waters from the English Channel (Burton and Leather- land, 1971) and with 30 ng/kg reported for the North Sea (Stock and Cucuel, 1934). On the other hand the values for the near-shore station approximate the 80 to 270 ngikg found in the RamaDo Deep (Hosohara, 1961).

Temperature and salinity data indicate that the samples analyzed at each of the two stations were from the same water mass; yet, pronounced differences in their mercury content exist. The basis for these differences will be sought in future investigations.

Literature Cited Ackefors, H., Loforth, G., Rosen, C. F., Oceanogr. Mar. Biol.

Bate, L. C., Radiochem. Radioanal. Lett., 6,139 (1971). Burton, J . D., Leatherland, T. M., Nature, 231, 440 (1971). Hosohara, K., J. Chem. SOC. Jap. Pure Chem. Sect., 82, 1107

Stock, A., Cucuel, F., Naturwissenschaften, 22, 390 (1934). Weiss, H. V., Crozier, T. E., Anal. Chim. Acta., 58,231 (1972).

Receiced for reciew October 8,1971. AcceptedJanuary 10, 1972.

Annu. Rec., 8, 203 (1970).

(1 961).

Modification of Technique for Determination of Aluminum in Water by Atomic Absorption Spectrophotometry

Deh Y. Hsu and Wesley 0. Pipes1 Department of Civil Engineering, Northwestern University, Evanston, IL 60201

he determination of aluminum using an atomic ab- T sorption spectrophotometer is complicated by the formation of refractory aluminum oxides in the flame. Either nitrous oxide or air enriched with oxygen must be used to increase the flame temperature. Even at the high flame temperawre, the sensitivity of the aluminum determination

is not as good as the sensitivity obtained for other metals such as Cu, Fe, and Mg. Sachdev and West (1970) reported a simple solvent extraction procedure for preparation of samples for the determination of some bivalent and trivalent

1 To whom correspondence should be addressed.

Volume 6, Number 7, July 1972 645