NOTES
Bromine Accumulations in Pine Trees Growing around Bromine Production Plants Frank H. Tainter'" and Dona C. Bailey Department of Plant Pathology, University of Arkansas, Fayetteville, Ark. 72701
Soil and pine foliage samples were collected from 92 plots located around five bromine production plants in Union and Columbia Counties, Arkansas, during January-February 1977. Analysis of pine tissues for the major salt components of brine showed that bromine was the only component accumulating in these tissues and that the amount of bromine decreased exponentially with the distance from the emission sources. Bromine content in plots closest to the sources ranged from 170 t o 550 ppm in 1-year-old needles and from 140 to 1000 ppm in 2-year-old needles. Some visible injury was evident in trees growing closer than 0.48 km from the sources, but tissues with bromine contents of 800 to 1000 ppm from the closest plots exhibited no visible injury. Bromine did not accumulate in organic litter or in the soil. The bromine industry in south-central Arkansas is relatively new, having grown phenomenally since the first facilities were constructed just over 2 decades ago. This industry is confined to the oil fields and processes brines, or "salt water", from the Smackover limestone formation. The brines are pumped from a depth of ca. 2150 m. The brine, which leaves the well head a t ca. 110 "C, is pumped through buried pipes t o plant sites, and temporarily stored in open ponds. It is utilized as soon as practical so as to minimize heat loss. T o extract bromine, the brine is pumped to the top of a granite tower and ejected through spray nozzles. As chlorine and steam are passed upward through the brine spray, the bromine is liberated, passes out with the steam, and then is condensed. T h e chlorine is recycled. The condensate containing the bromine is separated into aqueous and halogen layers, the former being recycled, while the latter is further purified by fractional distillation ( I ) . The extraction towers are vented to the atmosphere due to the refractory nature of construction materials, which requires that large pressure changes within the tower be minimized. The vented gases pass through scrubbers which consist of fresh brine flowing through a packed column. This type of scrubber is not efficient when inert gases are excessive, and the gaseous effluent from such scrubbers is the major source of bromine discharge during manufacture of elemental bromine. At most bromine extraction sites this type of discharge has occurred more or less regularly and to varying degrees. Once past the extraction stage, the discharge of bromine and brominated compounds from storage and subsequent processes is well controlled, although occasional discharges result from equipment failure, line ruptures, etc. In 1976, representatives from the bromine-producing companies and the Department of Plant Pathology designed research which would estimate the scope and degree of bromine accumulations in pine trees growing around the production sites. Except for a brief mention by Rerge (21, there was no published information regarding accumulations of bromine gas by plants. The cooperating companies included: Ethyl Corporation (ETH) near Magnolia, Columbia County; Present address, Department of Forestry, Clemson University, Clemson, S.C. 29631. 730
Environmental Science & Technology
Arkansas Chemicals Inc. (ACI) near El Dorado; Great Lakes Chemical Corporation (GLE) near El Dorado and Marysville (GLM); and Velsicol Chemical Corporation (VCC) near El Dorado, all in Union County. Experimental
Five 0.0809-ha (% acre) circular plots were established on each of four transect lines starting a t each of the five plant sites and radiating outward in NW, NE, SE, and SW bearings, respectively. On each transect line, the plots were located in the nearest predominantly pine stand a t 0.48, 0.96, 1.6, 6.4, and 12.9 km from the extraction towers. An organic litter and a 0-15 cm depth soil sample were taken a t the plot center. Foliage and twig samples were collected from the three dominant or codominant pine trees nearest the plot center with a .22 caliber rifle by shooting off three branches in the upper one-third of the crown and a t equidistant points around the crown perimeter. Subsamples of vegetation were washed with Na4EDTA according to ASTM ( 3 ) standards for preparing plant tissues for fluoride analysis. The washed samples were oven-dried at 80 "C, ground in a Wiley mill t o pass a 40-mesh screen, packaged, coded, and sent to Zethus Research Corporation (332 Patton Drive S.W., Atlanta, Ga. 30336) for analysis of bromine concentration by neutron activation. T o determine if ions other than bromine could be accumulating in pine tissues, portions of the samples were also analyzed for manganese, calcium, potassium, chlorine, and sodium, the other major components of brine. Single regression analyses of the data were calculated. Results
Needles. Bromine contents decreased exponentially with distance from the source. Concentrations in 1-year-old needles from the closest sets of plots were 170 ppm a t E T H arid GLM, 235 ppm a t ACI, 540 ppm a t GLE, and 550 ppm a t VCC, with the average for all sites represented by the power curve ~ 2 = 0.83 and cy = 0.01), where x is equation ' 5 = 1 4 9 . 2 ~ - O(. R the distance in kilometers from the source. In 2-year-old needles, concentrations in the closest plots were 140 ppm at GLM, 240 ppm a t ETH, 350 ppm a t ACI, 950 ppm a t VCC, and 1000 ppm a t GLE, with the average represented by the equation P = 260.3x-OT ( R 2= 0.62 and cy = 0.01). Twigs. A similar exponential decrease of bromine content was shown in twigs. In 1-year-old twigs from the closest plots, bromine concentrations were 32 ppm a t E T H , 47 ppm at GLM, 70 ppm a t ACI, 140 ppm a t VCC, and 185 ppm at GLE, with the average represented by the equation P = 41.6x-09 ( R 2= 0.86 and cy = 0.01). Concentrations in 2-year-old twigs from the closest plots were 24 ppm a t ETH, 45 ppm a t GLM, 60 ppm a t ACI, 118 ppm a t VCC, and 150 ppm a t GLE, with the average repre( R 2 = 0.86 and cy = sented by the equation Y = 37.6~-O.~ 0.01).
Organic Litter, Bromine concentrations in organic litter collected from the closest plots were 65 ppm a t ETH, 90 ppm 0013-936X/80/09 14-0730$01.00/0
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1980 American Chemical Society
I-YR-OLD
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Figure 2. The bromine content of organic litter and soil collected from in proplots around GLE ( O ) ,in production since 1965, and GLM (A), duction for 12 months
240
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n 0
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Figure 1. The bromine content of needle and twig samples collected in from plots around GLE ( 0 )in production since 1965, and GLM (A), production for 12 months
a t GLM, 130 ppm a t ACI, 180 ppm a t VCC, and 620 ppm a t GLE with the average represented by the equation P = 9 7 . 7 ~ - o ( R 2= 0.68 and cy = 0.01). Soil. Bromine concentrations in soil from the closest plots were 3 ppm a t GLM, 5 ppm a t ETH, 1 2 ppm a t ACI, 17 ppm a t GLE, and 20 pprn a t VCC. The relationship of bromine content of soil around the GLM plant was represented by the linear equation ? = 3.4 ( - 0 . 2 ) ~( R 2= 0.37 and CY = 0.01). The power equation representing the four remaining sites was Y = 7 . 7 ~ - o ( R 2= 0.62 and cy = 0.01). Sets of sample regression curves representing the preceding four categories of tissues and soil are given in Figures 1 and 2. Two bromine extraction plants are compared: GLE, an old, long-established plant in production since 1965, and GLM, a newly established plant in operation for 12 months a t the time of sampling T h e relationship between bromine contents of 1- and 2-
+
year-old needles from all sources was nearly linear, with the bromine content of 2-year-oLd needles approximately double t h a t of 1-year-old needles ( Y = 1.9x1.O;R 2 = 0.94; CY = 0.01) a t any given distance from the sources. The ratio of the bromine content of 2-year-old twigs to that of 1-year-old twigs was also relatively constant for all the sources ( P = l . 2 ~ O . ~R; 2 = 0.97; a: = 0.01). T h e bromine content of organic litter as a function of bromine content of 2-year-old needles was expressed by $' = 1.2x0.* (R2= 0.78; CY = 0.01), with the bromine content of litter being ca. one-half that of 2-year-old needles. Concentration of Salt Brine Components Other Than Bromine. The concentration of manganese, calcium, chlorine, and sodium in 1-year-old needles showed no relation to distance from any of the sources. Potassium content had a significant (a: = 0.05) but unexplained increase from 4200 ppm a t 0.48 km to 5000 ppm at 12.9 km from the pooled sources. The low coefficient of determination ( R 2 = 0.21), however, indicates only a small association between the two variables. Injury. No injury attributable to bromine accumulations was observed in pine foliage within the closest sample plots, even in needles with bromine contents of 800-1000 ppm. There were few trees growing closer than 0.48 km to most of the extraction towers. However, visible injury including total necrosis, needle banding, and needle tip-burn which could be attributed to bromine was found on some of these trees.
Discussion The extensive literature regarding uptake of bromide salts by vegetation indicates that the bromide ion is absorbed into the root system of some plant species to a greater degree than into others, and, that once in the plant, it can be accumulated and redistributed. There is little published information regarding the aerial uptake by plants of elemental bromine gas. It is, therefore, difficult to relate these results with what is known about root absorption of the ion as a salt. Volume 14, Number 6, June 1980
731
This research has elucidated a partial understanding of the behavior of aerially absorbed bromine in pine tissues. Pine needles continued to accumulate bromine during their second year at about the same rate as during their first year. But only a small proportion of bromine was translocated from first-year needles into first-year twigs. Second-year twigs did not accumulate bromine during their second year, or if they did, it was translocated out a t an equal rate. Elemental bromine is a strong oxidant and one might expect more injury than was observed. The strong neg,ative exponential character of the accumulation curves would tend to limit possible injury to vegetation growing close to the sources. Although the degree of visible injury resulting from a particular bromine emission episode was not determined, the 800-1000 ppm concentrations in needles exhibiting no visible injury suggest that needle tissues can detoxify and accumulate relatively large concentrations of bromine with no visible ill effects. Bromine did not accumulate in the organic litter layer to a concentration greater than that found in living pine needles in the canopy above the plots. Loblolly and shortleaf pine needles are normally cast a t the end of 2 years of age, so that bromine content of organic litter should reflect the content of a mixture of primarily 2-year-old needles and some twigs and other organic debris. In general, this content ranged from less than to less than 1/3 of that of 2-year-old needles sam-
pled in the same plots. This finding and the low levels of bromine in soil suggest that, as the litter was decomposed, the resulting bromides were quickly leached away. The negative exponential power curves of bromine accumulations are compatible with Berge’s (2) prediction. He reasoned that, since bromine gas was five times as dense as air, it should be sharply confined to the immediate vicinity of the sources. This is strikingly shown by our regression equations. Most of the bromine accumulated was within 1 or 2 km from the source. For example, even though plots around GLE and VCC had accumulations of 550 ppm a t 0.48 km, compared to 150-250 ppm for ACI, GLM, and ETH, at 2 km accumulations by l-year-old needles at all five sources were reasonably tightly grouped at 40-100 ppm.
Literature Cited ( 1 ) Yaron, F. In “Bromine and Its Compounds”; Jolles, Z. E., Ed.; Academic Press: New York, 1966; pp 3-42. ( 2 ) Berge, H. “Phytotoxische lmmissionen (Gas-Rauch-und Staubschaden)”; Paul Parey: Berlin and Hamberg, 1963; Chapter 10, pp 53-54. (3) A m . SOC. T e s t . Mater., Book A S T M Tentatiue S t a n d . 1975,26, $24-737.
Receiced for review August 14, 1978. Resubmitted November 8 , 1979. Accepted March 10, 1980. T h i s work was supported i n part b y A r kansas Chemicals Inc., E t h y l Corporation, Great L a k e s Chemical Corporation, and Velsicol Chemical Corporation.
Removal of Thiosulfate/Sulfate from Spent Stretford Solution Tsoung-Yuan Yan” and Wilton F. Espenscheid Mobil Research and Development Corporation, P.O. Box 1025, Princeton, N.J. 08540
now containing tetravalent vanadium and reduced ADA is regenerated by oxidation with air and recycled to the gas absorber. The ADA also acts as a catalyst for the regeneration step. The net reaction is the indirect oxidation of hydrogen sulfide to form water and sulfur, which is recovered. The reactions can be represented as follows:
Thiosulfate accumulation presents a serious disposal problem in the Stretford process for removing hydrogen sulfide from contaminated gas streams. A method for treating spent Stretford solution to dispose of thiosulfate and recover the chemicals that it contains is presented. In this technique the solution is acidified with sulfuric acid to decompose the thiosulfate to sulfur and sulfur dioxide, and limed to remove added sulfate and restore the pH of the solution. The extent of reaction and recovery of chemicals has been investigated for each step of the method, and the feasibility of the process scheme as a whole has been investigated.
.
oxidation regeneration
Low concentrations of sulfur contaminants occur in gas streams such as coke oven gas, natural gas, and the tail gas from the Claus process ( I ) . The latter process, which is widely used in petroleum refineries to convert hydrogen sulfide byproduct to sulfur, generates large volumes of waste tail gas. Direct discharge of this gas, which contains residual HzS, to the atmosphere results in pollution levels unacceptable to an increasing number of communities. A highly effective process for removing low concentrations of hydrogen sulfide from contaminated gas streams is the Stretford process (2). In this method, the gas stream is contacted with aqueous sodium carbonatelbicarbonate solution that contains pentavalent vanadium and anthraquinonedisulfonic acids (ADA). The hydrogen sulfide is oxidized to sulfur with accompanying reduction of the vanadium and ADA. After the sulfur is separated, the spent aqueous solution 732
Environmental Science & Technology
+
16V5+ 8H2S 4V4+
-
16V4+
+ 16H+ + Sa
ADA + 4H+. + 02 --+ 4V5+ + 2H20
In practice, t h e process performs its intended function of removing hydrogen sulfide from waste gas streams or other gas streams such as natural gas extremely well. Nonetheless, the process suffers one serious drawback. During each cycle of the process, a small percentage of sulfide is converted irreversibly to thiosulfate and, to a lesser extent, sulfate. This accumulation of thiosulfate reduces the solubility of vanadium and ADA in the solution, and decreases the rate of oxidative regeneration. To maintain these salts a t an acceptable level of 20-30 wt %, a continuous purge becomes necessary. This results in a loss of the valuable chemicals: ADA, sodium vanadate, and sodium carbonate. More important, however, high thiosulfate concentrations present a serious problem for disposing this purge stream because of their high chemical oxygen demand (COD). Thiosulfate is stable and has high water solubility. The methods for its destruction andlor removal from the process stream are costly. Proposed processes for disposal of this effluent have included evaporation, incineration, and even
0013-936X/80/0914-0732$01 .OO/O
@ 1980 American Chemical Society
