Analytical Methods in Oceanography - ACS Publications

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17 Occurrence and Implication of Sedimentary

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Fluorite in Tampa Bay, Fla. D E A N F . M A R T I N and W I L L I A M H . T A F T University of South Florida, Tampa, Fla.

Phosphate processing caused large amounts of gaseous fluoride to be emitted as a waste product through stacks. Scrubbers were installed by a plant located on Tampa Bay, Fla., and the collectedfluoridewas then discharged into the Bay. In July 1973, the daily discharge offluorideentering the Bay was approximately 24,000 lb. A study of water and sediment samples in Tampa Bay adjacent to a discharge canal of the plant revealed (1) a deltaic deposit of sedimentaryfluorite,(2) remarkably low pH meter readings (3.3) that indicated the buffer capacity of 50 X 10 m of estuarine water was virtually exhausted, (3)fluorideconcentrations as much as 40 times the concentration in normal seawater, and (4) temperature differentials in relatively shallow water (0.6 m) that were the reverse of what would normally be expected. 6

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' T p h e geochemistry of fluoride i n estuarine waters has received increasing attention ( J , 2, 3, 4, 5) because of concern about the primary sources of fluoride i n continental waters—rainwater of ultimate marine origin, volcanic emanations coupled with atmospheric precipitation, rock weathering, and industrial. Generally, rock weathering is considered least as a primary source of fluoride. Kilham and Hecky (6) demonstrated the significance of weathering of fluoride-rich volcanic rocks i n East Africa. The Africa site is far removed from industrialized regions and may provide the best area for studying the preindustrial fluoride cycle and estimating the impact of man. Tampa Bay, F l a . , may w e l l represent another area that is ideal for studying the impact of man on the fluoride cycle, particularly i n an estuarine environment. Indeed, we believe that the present study provides 202 In Analytical Methods in Oceanography; Gibb, T.; Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

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MARTIN AND TAFT

203

the basis for studying a situation at what may be the ecologically worst stage, followed by improvement. In Florida, fluoride and phosphate are chemically and industrially associated. Phosphate deposits i n Florida occur as sedimentary phos­ phorite of Miocene age (10-15 million years o l d ) . The principal mineral is apatite, C a ( P 0 ) 3 F , containing about 4% fluorine. The deposits are centered i n a 500-sq mile area around Bartow. M i n i n g was initiated i n 1890, and i n 1972, Florida produced more than 30 million tons of phos­ phate valued at about $170 million. Florida supplies over three-fourths of United States needs and roughly one-third of the world needs (7). The processing of this resource underwent a number of changes as environmental degradation was noted and new technology became avail­ able to resolve those problems. According to Hendrickson (8) as much as eight tons of gaseous hydrogen fluoride per day was discharged into the atmosphere within an area of 100 sq miles as a result of treatment of the ores with sulfuric and phosphoric acid. That time has long passed, and phosphate processing companies have assumed considerable ecologi­ cal responsibility. F o r example, complaints by local residents, orange growers, cattlemen, and commercial florists led one such company, Gardinier, Inc. (then owned by U.S. Phosphoric) to install scrubbers i n about 1963. Rather than being released into the air, collected fluoride was discharged into Tampa Bay. The amount of fluoride discharged into the Bay varied with the amount of phosphate produced, but in July of 1973, the daily discharge amounted to about 24,000 lb. In addition, the effluent contained about 27,000 l b of phosphate and 3,000 l b of nitrate per day. This paper describes results of analyses of Tampa Bay water near the Gardinier plant i n July 1973 and July 1974 before and after reductions i n amounts of pollutants had been promised. Clearly, the discharge of 24,000 l b of fluoride on a daily basis seems excessive, and i n July 1973 when the first sampling took place, Gardinier had hoped to reduce the discharges by 97% within six months. The data collected i n July 1973 serve as a benchmark against which to measure the results of pollution abatement, and the data collected in July 1974 measure the progress of environmental restoration. 5

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Sedimentary Fluorite

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Physical Observations The location of Gardinier's plant i n relation to Tampa Bay is indi­ cated i n Figure 1. T w o canals discharge processing wastes into the Bay. A deltaic deposit of fluorite that may be the only such deposit of sedi­ mentary fluorite known in the world is located at the mouth of both canals. In cross-section, the fluorite deposit is about 3 i n . thick at the

In Analytical Methods in Oceanography; Gibb, T.; Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

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ANALYTICAL METHODS IN OCEANOGRAPHY

Figure 1.

Study site on Hillsborough Bay portion of Tampa Bay

initial discharge point and rapidly diminishes to translucent flakes at the outer edges of the deposit, roughly 350 m into the Bay. Temperature and p H data were obtained at the time of sampling. Temperatures were obtained using the same mercury thermometer i n 1973 and 1974. In July 1973, the temperature increased rapidly during equilibration while water temperature was read at the surface (30-sec period). Thus, the temperatures i n Table I should be regarded as mini­ m u m values. The thermal problem was not noticeable during the July 1974 sampling. A l l p H values were obtained i n the field w i t h a Beckman model G p H meter, standardized w i t h p H 7 buffers. The field values were checked again i n the laboratory and generally agreed within 0.2 units. Salinity was obtained using the Harvey method (9) and was checked w i t h a hand-held refractometer (9). Silicate and phosphate analysis were obtained by a Technicon AutoAnalyzer II using standard procedures described i n the E P A Methods Manual (10). Fluoride was determined mainly by using an Orion fluoride electrode (model 90-01) with a Corning model 10 expanded p H meter. The pro­ cedures described earlier (9, I I , 12) were modified as follows. T o a 10 m l sample of water i n a plastic beaker was added 40 m l of stock seawater (30% ), followed by 10 m l of total ionic strength buffer ( T I S B , p H — 5.5, ionic strength 1.9) (13). Initial reading (=E ) was recorded after c

X

In Analytical Methods in Oceanography; Gibb, T.; Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

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Sedimentary Fluorite

MARTIN AND TAFT

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constancy was obtained (usually less than 5 m i n ) . Readings ( = E ) were also recorded after addition of stock fluoride solution (1000 p p m F") i n 0.1-ml increments (or addition of 2, 4, 6, 8, 10 p p m F " ) . The data were plotted on semi-logarithmic paper: E (in m V ) as a function of log p p m added fluoride. The linear relationship was extrapolated to obtain the value of apparent initial fluoride, ( F " ) knowing E The apparent fluoride concentration ( F ~ ) i n the original sample was calculated using Equation 1: x

x

b

i t

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0

(F-ppm)

0

= ^

^

(1)

where ( F ~ ) is the apparent fluoride concentration i n the stock seawater (a value obtained by using 10 m l of distilled water instead of sample), s

Table I.

Station IB 2S 2B 3S 3B 4S 4B 5S 5B 6S 6B 7S 7B

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SO 2S 3S 5B 7S 8 GFD

C

Physical and Chemical Properties of Tampa Bay Water Samples

Salinity (°M

t(°C)

27.8±0.3 21.1±0.1 27.1±0.3 21.1±0.1 22.6± 31.1±0.1 29.6±0.3 23.8±0.2 31.7± 22.4±0.4 31.9±3.5 21.2±0.1 34.8±0.6

36 28 34 28 28.5 30 34 33 35 33 33 28.5 31

1973 3.3 3.95 3.3 5.70 4.60 3.8 3.2 3.5 3.2 3.6 3.2 5.5 3.4

33 28 29 31 30 32

1974 6.68 6.90 7.22 7.21 7.60 2.28

30 15 13 16 15 32

pH°

POt-P (PPm) 36.7 32 33 20.1 22.5 31.3 35.5 35.4 33.6 35.5 40.3 23 33.7

F(ppm)

Distance from Dischar* Canal (i

44.1 18.7 46.1 10.3 17.1 19.0 46.9 25.5 49.2 25.6 34.8 10.7 40.0

43.0 23.3 34.8 18.5 14.0 21.5 30.8 36.5 25 34.2 35.0 16.3 36.3

15 155 155 305 305 115 115 155 155 305 305 265 265

5.0 1.4 1.6 1.1 0.8 61.2

2.1 2.6 2.6 2.0 1.8 330±6« 346±20'

0 15 32 265 425 0

SiOi-Si (PPm)

pH meter reading, B. S, surface; B, bottom (Ca. 0.6 m at time of collection, August 23, 1973). SC, southernmost canal. Sample collected near gypsum field ditch (see Figure 2). « Fluoride ion electrode method, internal standard, dilutions at 0.1, 0.02, 0.01. ' Colorimetric method with internal standard, dilution at 0.004. a

b c

d

In Analytical Methods in Oceanography; Gibb, T.; Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

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ANALYTICAL METHODS IN OCEANOGRAPHY

Figure 2. Location of specific sampling sites in relation to southern and northern discharge canals ( F " ) i is the apparent initial fluoride i n the TISB-diluted sample, and D . F . is the dilution factor, 0.2. The accuracy of the method was indicated b y the value of (F~) , which was 1.05 ppm, and which would correspond to a value of 1.3 p p m for the sample of salinity, S — 35%