and =
25 e -0.53
(In 2 rpu
+ 0.69)’
(9)
When we allow the prelog function in Equation 3 to approximate 0.94, substitute Equations 1, 3, 8, and 9 into Equation 5, and rearrange, the following difference function is obtained:
riving the ( B s s / B o ) to o visual opacity relationship would probably negate the effort involved. Experimental verification of this discrepancy was observed on a glass furnace stack. The observed parameters were:
E = 1.96 x 10-7ft 4 rgw = 0.25 p = -2 [I - (Z/Zo)]i = 9 - 12% (obsd) [l - (Z/Zo)]u = 35% i 10% (obsd) [l - (Z/Io)lU= 30 - 33% (predic)
ug
where 6, - represents the fraction difference between visual and instrumental readings. Equation 2 has been converted to read in fractions rather than percent; ( W D / p ) and ( W D / p ) ’ are in units compatible with their respective parameters. An example of the discrepancies obtained is plotted for various ( W D / p ) ratios in Figure 1. By varying the constants in Equations 8 and 9, 6 functions for different refractive indices and viewing angles can be determined. Closer approximations could be obtained with computer solutions of the theoretical equations for k and ( B s s / B o ) o as functions r g W . However, the experimental error in de-
The implications of this type of discrepancy will become quite serious in light of the increasing use of instruments vs. human observers for the determination of opacities. A detailed examination of the philosophies behind the use of opacity measurements is indicated.
Literature Cited Ensor, D. S., Pilat, M. J., “The Relationship Betweep, the Visibility and Aerosol Properties of Smoke Stack Plumes, Second International Clean Air Congress of the IUAPPA, 1970. Halow, John S., Zeek, Susan J., “Predicting Ringelmann Number and Optical Characteristics of Plumes,” J. Air Pollut Contr. ASS.,23 ( 8 ) ,676-84 (1973).
Received for review July 30, 1973. Accepted November 30, 1973.
Mercury-Organic Matter Associations in Estuarine Sediments and Interstitial Water Steven E. Lindberg’ and Robert C. Harriss Department of Oceanography, Florida State University, Tallahassee, Fla. 32306
Sediment from the Florida Everglades and Mobile Bay estuary reveal significant associations between sediment Hg and sediment organic matter and between dissolved interstitial Hg and dissolved organic carbon. The bulk of dissolved Hg and dissolved organic carbon exists in the 100,000 molecular weight fraction in Mobile Bay pore water. Mercury in sediments and interstitial water occurs a t higher concentrations in the Everglades than in Mobile Bay, which receives anthropogenic mercury effluents. When normalized to organic content of the sediment or dissolved organic carbon concentration of the pore water, higher relative mercury concentrations occur in Mobile Bay. Interstitial dissolved mercury is enriched from 2.6 to 36 times over the associated surface water values, and in sulfide-rich pore waters far exceeds the thermodynamic solubility of HgS. Enrichment may be due to formation of organic and polysulfide complexes with mercury. The quantitative importance and potential ecological effects of anthropogenic additions of mercury to natural aquatic environments have been well documented in the recent scientific literature (Harriss, 1971; Wallace et al., 1971). As a result of several cases of acute mercury contamination in ,Japan and Sweden, most large industrial sources have been identified and the discharge of mercury to natural waters reduced to negligible flux rates relative to natural sources. However, much of the mercury released prior to the implementation of pollution control To whom correspondence should be addressed
regulations has accumulated in the sediments of watersheds receiving discharges. For example, the combination of high reactivity with particulates (Cranston and Buckley, 1972) and physical conditions conducive to high sedimentation rates has trapped large quantities of mercury in near shore sediments. The mobility and ultimate fate of mercury in the sedimentary environment are controlled to a large extent by its interstitial water chemistry. The present investigation is a study of sediment mercury and its interstitial water chemistry in an undisturbed estuarine environment, the western section of the Florida Everglades, and in an estuary known to receive industrially derived mercury effluents, Mobile Bay, Ala.
Materials and Methods Sediment cores were obtained manually from near-shore marsh areas with a piston-fitted polycarbonate tube and immediately extruded into polyethylene Whirlpak bags kept near ambient temperature until squeezing (2-6 hr). Interstitial water was extracted using a nitrogen-operated, Teflon-lined squeezer similar to that described by Presley et al. (1967). Salinity was determined in the field laboratory on freshly extracted pore water with a Goldberg refractometer (precision +0.5 O/OO); 25 ml of pore water samples for dissolved Hg analysis were stored in Pyrex containers after acidification with “ 0 3 to pH < 1 and addition of 6% KMn04; 5-ml samples for determination of dissolved organic carbon (DOC) were placed in glass ampules containing 100 mg of K ~ S 2 0 8and 0.1 ml of H3P04, and were then purged of inorganic COz and sealed; sediment samples were kept a t 0°C until laboratory analysis. Volume 8, Number 5, May 1974
459
Analysis for mercury was performed using the flameless atomic fluorescence technique developed by Muscat et al. (1972). The method consists of either wet digestion of an aqueous sample followed by reduction-aeration and detection of mercury vapor (Hg") by atomic fluorescence, or dry combustion (8OOOC) of an oven-dried (SOT), homogenized, and pulverized sediment sample and similar detection of Hg". Either technique afforded a limit of detection of 1ng with an average analytical variation of *3%. DOC in the interstitial water was determined using the techniques of Menzel and Vaccaro (1964). The coefficient of variation was found to be &4%. Sediment organic content, expressed as a percent of the total dry weight (6OoC), was determined by weight loss a t 550°C for 2 hr. Total dissolved sulfide (ZS2-) was determined using a modification of the silver-silver sulfide electrode technique of Berner (1963). The recent development of a sulfide antioxidant buffer (Orion, 1969) permits determination of total sulfide concentration down to 0.1 mg/l. Analytical precision was *lo%. Molecular weight fractionations were performed using an Amicon model 50 stirred ultrafiltration cell with Amicon Diaflo ultrafiltration membranes. The technique is a form of membrane pressure dialysis based on the exclusion principle of gel column chromatography. Fractionation is accomplished by the selective permeability of the membranes to solutes of given molecular dimensions. Procedural details as well as limitations of the technique have been described elsewhere (Blatt et al., 1967). The ultrafilters used provided the following molecular weight ranges: 100,000. Boundaries of molecular weight exclusion for each membrane must be regarded only as relative ranges and are better characterized as Amicon cutoff limits. However, for purposes of discussion, they will be referred to as molecular weight ranges.
Results and Discussion The interstitial water and sediment data collected during this study are summarized in Table I. For the Everglades samples no consistent trends in dissolved interstitial or total Hg concentrations with core depth are apparent. The large variability in dissolved Hg (cores 3E and 5E) suggests that distribution is influenced by a number of interacting factors in this environment. Parameters that may influence Hg distribution in these cores such as salinity, ZS2-, DOC, and sediment organic content show similar variations. In contrast, the single core taken from Mobile Bay exhibits decreasing concentrations of total Hg and interstitial Hg with depth to apparent background levels near 20 cm. The observed gradients correlate with a recent (10-20 years) increment in the release of Hg-containing industrial effluents to this estuary. To elucidate the geochemistry of Hg in these sediments, correlation and stepwise regression analyses were applied to the data. The concentration of Hg in the sediment is significantly related to the organic content of the sediment for the combined samples ( r = 0.80). No significant change in the correlation coefficient is noted when the data are divided into more homogeneous groups such as Everglades samples, Everglades surface samples (0-10 cm), and Everglades subsurface samples ( > l o cm). Similar correlations have been found in soils by Anderson (1967), in fresh water sediments by Kennedy et al. (1971), and in estuarine sediments by Bothner and Piper (1971). For the Everglades samples the concentration of dissolved Hg in the pore water is significantly correlated with the concentration of DOC ( r = 0.55). The correlation increases significantly when calculated for the Everglades surface samples ( r = 0.81) but decreases to an insignificant level for the Everglades subsurface samples ( r = 0.46). These results provide some insight into the pro-
Table I. Summary of Interstitial Water and Sediment Data Core
1 Ea
2 E
3E
4 E 5E
6 E 7 E 1 MBb
2 a
MB
Core depth, c m
Salinity,
0-10 10-20 20-30 30-40 0-10 10-20 20-30 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 0-10 0-10 10-20 20-30 30-40 0-10 10-20 0-10 0-10 10-20 20-30 30-40 0-10
Everglades. t' Mobile Bay.
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Environmental Science & Technology
DOC, d m l
0100
14.7 19.7 20.3 20.8 20.8 19.7 19.7 19.7 19.7 16.9 16.9 20.8 22.0 22.0 22.5 16.4 18.8 18.8 19.3 18.8 19.7 24.6 27.2 3.0 2.4 2.4 2.4 2.5
0.1 1.4 0.1 0.1 0.1
