However, Parry and Hern 

### (8)reported negligible iodate at 

### IC when they used an open glass tube as a bubbler; this

seems to indicate that iodate would not be formed 

### at IC with an impinger. We feel, nevertheless, that the four data points these investigators presented 

### at unspecified values of other parameters do not provide sufficient information todraw a definiteconclusion.

The acidification procedure, outlined here, provides a satisfactory method for the analysis of high ozone concentrations. This is in agreement with Schmitz 

### (15). The procedure would not be suitable for lower levels of ozone (less than 50 ppm) because the iodide solution is slowly oxidized after acidificationandthis would lead toa significanterror. However, this shortcoming might be overcome by using buffered acidification to a controlled pH level where the rate of iodate decomposition (Equation 3) is rapid, but where oxidation remains negligible. This acidification might also be performed in stages to minimize the total time during which thepHis low.

Literature Cited (1)Federal Register, Vol. 36, No. 84, Part 11, p 8195, April 30,

1971. (2) Byers, D. H., Saltzman,B. E., “Determinationof Ozone in Air

by Neutral and Alkaline Iodide Procedures,”p 93 in “Ozone Chemistry and Technology,”Am. Chem. SOC., Adu. Chem. Ser., No. 21 (1959). (3) Birdsall,C. M., Jenkins,A. C., Spadinger,E., Anal. Chem.,24, 662 (1952). (4) Ingols, R. S., Fetner, R. H., Eberhart, W. H., “Determining

Ozone in Solution,”p 102 in “Ozone Chemistry and Technology,” Am. Chem. SOC., Adu. Chem.Ser.,No. 21(1955). (5) Boyd, N.W.,Willis, C.,Cyr,R.,Anal. Chem.,42,670 (1970). (6) Hodgeson,J.A.,Baumgardner,R. E., Martin,B. E.,Rehne,K.
(7) Kopczynski, S.L., Bufalini,J.J.,ibid.,43, 1126 (1971). (8) Parry,E. P.,Hern,D. H.,Enuiron.Sci. Technol.,7,65 (1973). (9) Dietz,R. N., Pruzansky,J.,Smith,J. D.,Anal. Chem.,45, 402

(1973). (10) Kolthoff, I. M., Belcher, R., “Inorganic Analysis,”Vol. 111,

“Titrimetric Methods: Oxidation and Reduction Reactions,”p 281,Interscience, 1957. (11)Saltzman,B: E., Gilbert,N.,

### J. Am.Znd.Hyd.,20, (1959). (12) Saltzman,B. E., “Selected Methods for the Measurementof

Air Pollutants,” Public Health Service Publication, No. 999- AP-11,pD-1, 1965. (13) Jacobs,M. B., “The Chemical Analysis ofAir Pollutants,”pp

218-20, Interscience, 1960. (14) Hendricks,R. H., Larsen,L. B.,J.Am. Znd. Hyg. Assoc., 27,

80 (1966). (15) Schmitz,L. R.,Enuiron.Sci. Technol..7,647 (1973).

A., ibid., 43,1123 (1971).

(16) Vogel, A. I., “A Textbook of Quantitative Inorganic Analy-
(17) Lanee. N. A.. Ed.. “Handbookof Chemistrv.”D 1124.Handsis,”p345,Wiley, 1961.
“, 

# . book PLblishers’,Inc:, 1949.

Received for review SeDtember 11. 1974. AcceDted Februarv 18. 1975. Work supported’ by National Science Foundation Grant GK-37469.



## Ambient Air Analysis with Dichotomous Sampler and X-ray Fluorescence Spectrometer

Thomas 

### G. Dzubay’ and Robert K. Stevens Chemistry and Physics Laboratory, Environmental Protection Agency, Research Triangle Park, N.C. 2771 1

Aerosol samples were collected in 

### St. Louis using a dichotomous sampler operating on the principle of virtual impaction and were analyzed for a wide variety of elements by X-ray fluorescence. A striking difference was observed between theparticles collected in the0-2-gm range and the particles collected in the 2-10-pm range. Although nearly equal mass was collected in thetwo size ranges,the deposit of small particles was black and the deposit of the coarse particles was a light tan. At least 75% of the 

### S,Zn, Br, and Pb occurred in particles smaller than 2 pm, and at least 75% of the Si, Ca, 

### Ti, and Fe occurred in particles larger than 2pm.

A major task in the field of air pollution monitoring is the development of devices for determining the mass and composition of airborne particulate matter as a function of size and time. This instrumentation is presently needed for human studies research in which attempts are being made to determine toxic threshold levels for aerosol constituents in ambient air. It is also needed for aerosol formation and transport studies essential to the development of cost-effective control strategies.



### To perform elemental analysis on an increasing number of samples in more than one size range, a rapid analytical procedure is required. The use of X-ray fluorescence spectroscopy is well suited to meet this need for elementsheavier than A1 in atomic weight (I,2).A wide variety of elements can be determined in a few minutes without sample preparation. The composition of the sample is determined by irradiating with 

### a beam of X-rays and observing the emission of characteristic 

### K and L X-rays.By use of secondary fluorescers to produce a nearly monochromatic but variable energy X-ray source, a wide variety of elements throughout the periodic table can be analyzed (3). If particles are collected on the surface of a membrane filter, then

no sample preparation is required.

The sample collection device must be designed with consideration given to the nature of the aerosol and to the effects of the aerosol on human health. Recent measurements by Whitby et al. (4)show that the volume and hence the

mass of aerosol in ambient air has a bimodal distribution with a relative minimum at particle diameters of about 2 pm. It has been established that particles smaller than 3.5 pm in diameter can penetrate deeply intothehuman respiratory system, and that larger particles are trapped in the upper respiratory passages 

### (5). For these reasons, it is desirable to use a dichotomous sampler to collect particles in two size ranges rather than tocollect total particulates on a single filter. Separation atparticle diameters of about 2 gm would be appropriate for aerosol research; separation at3.5 pm is needed for monitoring aerosols to protect human health. Ractionation of particles into several additional size ranges is desirable only if the increased cost of analyzing more stages and the decreased deposited mass per stage
can be tolerated.

For size fractionation,a wide variety of conventional impactor devices is available in which particles are collected on a surface placed behind a circular or slit-shaped orifice.

Volume 9,Number 7, July 1975 663Collection in these devices may not be quantitative if particles bounce off the intended collection surfaces. Particle bounce errors can be reduced by applying an adhesivecoating to the collection surface (6). However, Lundgren has demonstrated thatthe effectiveness of theadhesive coating

can become nullified when a monolayer of particles has been deposited 

### (7).

The problems inherent in collection by impaction onto surfaces can be eliminated by using a virtual impactor in which particles are impacted into a slowlypumped void (8, 9). Figure 1 illustrates a dichotomous sampler (a device which collects particles in two size ranges) which operates

on the principle of virtual impaction. In this device, the air being sampled passes through an inlet jet and is deflected around a coarse particle receptor. Coarse particles, unable to follow the curving air stream, enter the coarse particle receptor and are collected on a filter. Fine particles that

move with the air stream are collected on a second filter. Theuse of filters in a virtual impactor eliminatestheparticle bounce problem associated with impaction surfaces.

Tominimize wall losses in thevirtual impactor, it is necessary to maintain a small flow of air intothe coarse particle receptor. In the device illustrated in Figure 

### 1, critical flow orifices are used to maintain a 

### 7:l concentration ratio between inlet and coarse particle air streams. For this flow ratio, 14.3%of the fine particle mass is deposited on the

coarse particle filter.

To reduce the contamination of fine particles on the

coarse particle filter,two virtual impactors,which have the

same fractionation cutpoint diameters, can be operated in series. Figure 2 illustrates a practical two-stage device developed by Peterson (10).An internal orifice maintains a 7:l concentration ratio for each stage, and external orifices maintain an overall concentration ratio of 49:l for the inlet and coarse particle air streams.

### For this flow ratio, only 2% of the fine particle mass is collected on the coarse particle filter. Attempts have been made to develop a single-stage virtual impactor with a 49:l concentration ratio, but wall losses were much worse than those obtained using a twostagedevice (10,11).

In the present work, a prototype dichotomous sampler

was field tested and evaluated for usefulness as an ambient air monitor. Aerosols collected in the dichotomous sampler and in a second automatic filter changing device were analyzed for elemental content with an X-ray fluorescence spectrometer. 

### Experimental

The dichotomous sampler used in this study is illustrated in Figure 2 and was built by Environmental Research Corp. 

### (St. Paul, Minn.). It was evaluated for wall losses andfractionation characteristicsby 

### Loo andJaklevic (12) using monodisperse aerosols of dioctylphthalate. It

was demonstrated that particles smaller than 2.0pm (50% cutpoint diameter) were collected on the fine-particle stage, and particles ranging from 2.5-10 pm (50%cutpoint diameters)were collected on the coarse particle stage.Wall losses were very low for particles smallerthan 1pm and for particles between 3.5 and 

### 8gm. Thewall losses were about 25%in the 2-3-pm range of diameters and were large for particles larger than 10gm (12).

The dichotomous sampler was operated with the flow rate divisions indicated in Figure 2. Flow rates were checked at the beginning and end of each measurement using a dry test meter. The inlet flow rate was maintained at49 l./min within an accuracy of f3%.A second sampling device which automatically changed the filter every 2 hr

was also used. This device also operated at a flowrate of 49 7 LMIN

COARSE PARTICLE RECEPTOR



# It1

TO PUMP Figure 1. Schematic view of dichotomous sampler that contains a single-stagevirtual impactor Flow rate at inlet is 7 I./mln, and the concentration ratio for coarse particles is 7: 1. Coarse particles are collected on filter C; fine particles are collected
on filter F

INLETULMlN

FIRSTSTAGE I1JETS)

INTERNAL FLOWORIFICE

SECONO STAGE

I1JET1 7 LMlN

yilN2 -TO

# -

FLOW

FINEPARTICLES

MONITOR

~

IU LMlNl

INCHES

COARSE PARTICLES I1 LMlNi Figure 2. Drawingof dichotomous sampler with two substages used in present work Each substage has the same fractionation cutpoint diameter. The internal flow orifice and orifices in exit flow lines (not shown) together maintain a 7:l concentration ratio for each stage

l./min, and used a single collection surface without size fractionation.

Measurements of trace element composition were made using an energy dispersive X-ray fluorescence spectrometer (3) which is illustrated in Figure 3. In this device, an X-ray beam from the tungsten anode excites the secondary fluorescer which in turn excites the sample with its nearly monochromatic characteristic X-rays (13). The three fluorescersused are Cu,Mo, and Tb,for which the corresponding anode potentials of the X-ray tube are 35, 50, and 

### 70 kV, respectively. Each sample was analyzed for 5 min with each fluorescer with an electron current of 400 pA in the X-ray tube. The fluorescent X-ray lines emitted by the sample were detected in a lithium-drifted silicon detector which used electronic collimation to enhance the signal

664 Environmental Science & Technology

# I nv

Figure 3. Schematic view of X-ray fluorescence spectrometer using secondary fluorescer and solid state detector

above background (3). Because of the very compact geometrical arrangement of the components in Figure 

### 3,anadequate count rate was obtained with X-ray power dissipation of less than 30 

### W.

The ability of the system to detect a wide variety of elements in the atmosphere is illustrated in Figure 

### 4, which is

a plot of theranges andtypical valuesof the concentrations of various elements in urban air (15). The detection limits (3a peak area above background) for X-ray fluorescence

are superimposed on the plot. These detection limits are expressed in ng/cm2 for each element assuming that it is deposited on a cellulose membrane filter which has a mass per unit area of 5 mg/cm2.The discontinuities in the detection limit curve using the molybdenum fluorescer are due to iron and copper impurities in theX-ray collimator above the detector.The detection limits can be converted 

### tounits of mass per unit volume by dividingthe values on Figure 4 by the air volume sampled per unit area of filter.For a flow rate of 49 l./min through an 8-cm2area of filter,the conversion factors are 0.74 m3/cm2 for a 2-hr sampling interval and 

### 8.8 m3/cm2 for a 24-hr sampling interval.

For X-ray analysis it is necessary that particles be collected on a filter having very low levels of impurities. Figure 5 shows a spectrum of a Teflon membrane filter with a

105

104

k 103 

### d n E

0 

# 5 102


### E 

## y 101



# 2 100 

# 5 z c

0 u -l

2 w
10-1

10-2

I0-3 r: 

## 8

CIIMIIEL Figure 5. X-ray spectra of clean polyethylene-backed Teflon filter and clean glass fiber filter using molybdenum secondary fluorescer for excitation In Teflon filter spectrum, peaks in channels 188and 238 are due to iron and copper impurities in collimators of X-ray spectrometer
polyethylene backing which is excellent in this regard. Figure 5 also shows a spectrum of clean glass fiber filter which contains large amounts of impurities and is unacceptable for X-ray fluorescence analysis. Membrane filters, made of mixed esters of cellulose and having 0.8-fimpore size, make

a good choice and were used in this work. Their elemental purity is similar tothat of theTeflon shown in Figure 5 except for impurities 

### of Ca and C1. High-porosity Teflon with superior gravimetric characteristics became available after theexperimentalphase of this work was completed.

The elemental concentrations were determined by a minicomputer interfaced to the X-ray spectrometer. For the analysis, it was assumed that an observed X-ray spectrum was a superposition of characteristic X-rays of each individual element in the sample. Individual spectra of 40 pure element standards were accumulated and stored in the computer memory. These individual spectra as well as

104

103

N 

### E

t 

## I



# . 102 

# :

A 101 

# E

100 

## t; Y

0

10-1

10.2

I 0-3

Figure 4. Detection limit curves using Cu, Mo,and Tb fluorescers expressed in ng/cm* Conditions of analysis and substrate are specified in the text. Also shown are ranges and typical values of urbantrace element concentrationscompiled by Cooper ( 74)

Volume 9, Number 7, July 1975 665a stored clean filter background spectrum were compared with the unknown aerosol spectrum using a stripping procedure to determine the concentration of each element 

### (3). By making a judicious choice of theorder in which the elements were stripped, theprohlem of interfering

### K, and Kg X-raylines was largely eliminated.

The analyzer was calibrated using thin single-element concentration standards according to a procedure developed by Giauque et al. 

### (I). These standards consisted of

vacuum evaporated foils obtained from Micromatter Co. (Seattle,Wash.) and dried solution deposits on memhrane filters obtained from Columbia Scientific Industries (Austin, Tex.). The elemental depositswere uniform across the 37-mm diameter of each standard and ranged in mass per unit area from 

### 10-150 eg/cm2. They were known to an accuracy of 

### f10% or better.

For airborne particulates uniformly deposited onto a 37-mm diameter filter, the concentration (in eg/cm2) of a specific element on the filter was determined by comparison of the observed count rate with that of the known foil of the sameelement. A smooth curve was fitted to thecalibration points and used to determine elements for which foils were not available or not accurately known. By use of the smooth calibration curve, the root mean square deviation of the X-ray analysis of each calibration foil from the gravimetric value was 

### 5% for the elements with atomic numbersbetween 

### 19and 38.

From these considerations it is estimated that for elements well above the detection limit, the 

### 1-0 accuracy for X-ray analysis of elements with atomic numbers above 

### 20 (Ti and heavier) is 

## +lo%.This is compatible with the results from a recent study by Hammerle etal. (15) in which X-ray fluorescence and neutron activation analyses were applied to aerosol samples, and 20% agreement was obtained. For the lighter elements the energies of the characteristic X-rays are sufficiently low that significant self-ahsorption can takeplace within the larger collected particles and within the filter media for fine particles thatpenetrate intothe filter, Self-absorptibn corrections were made,using a procedure developed by DzuhayandNelson 

### (16).

For thetwo size ranges of the dichotomous sampler,the total aerosol mass was determined by gravimetrically comparing the weights of each filter before and after sampling. 

### A 210Poradioactive source was placed inside the microbalance chamber near the weighing pan to eliminate electrostatic effects. Gravimetric accuracy was 

### f50Fg for the filters, which had typical depositmasses ofabout 

### 1-2 mg.



### Results 

### andDiscussion Samples were collected over the period between August 26 and August 31, 

### 1973,in St.Louis ata site on the Washington University campus. Figure 

### 6 shows a photograph of two filters used in the dichotomous sampler for the 23-hr period beginning at

### 0915hr on August 

### 30. X-ray spectrafor these filters are shown in Figure 7, and the elemental and gravimetric analyses are shown in Table 

### I. The results for five days of continuous measurements using 2-hr sampling periods with unfractionated aerosol are shown in Figures 

### 8 and

### 9.

Thefilters shown in Figure 

### 6indicatethe strikingdifference between small and large particles. The large particles produce a light tan deposit, and yet they have almost as much total mass as the small ones, which make a black deposit. This is consistentwith the notion that the large particles contain large amounts of earthen crustal materials, whereas the small particles consist of combustion 

### and secondary aerosols. From the analysis of the two filters in Table 

### I, it appears that the large particles contain atleast

666 EnvironmentalScience&Technology 2;hr period beg;& at 1015hr, August 30, 1973,in a St. Louis residential neighborhood Volume Sampled is 68 m3. Filtersare mounted in 5.1 X 5.1-cm frames used for automatic manipulation within X-ray analyzer. Elemental analysis for these samples is given in Table i

Figure 7.X-ray fluorescencespectrum with copper secondaryfluorescer excitation for particles collected in two size ranges on filters shown in Figure 6 Elemental analysis is given in Table I. Peaks labeledCI are partlydueto slgnificantbutvariableamountsof chlorine inthe filter blanks

Table 

### 1. Analysis of St. Louis Aerosol on Filters Shown in Figure6 Samplescollectedfor a 23-hr August30. 1973 Ele- Fine+ Coarse,= ment ng/mB ng/mr Element

Si mn+ ifin mn+ inn 7" 

### _. S K Ca Ti V Cr Mn Fe


### co 

# ___ .I" 3700f 600 6001200 As 160Zt60 240+80 Se llOf40 1700+300 Br 64& 7 210f 30 Rb 4+2 <3 Sr <3 <3 

### Cd 5+2 6Zt2 Sn 130+ 14 400+40 Ba <2 <2 Pb 

## .. 

# .. .

FiW,G ns/mz 45dz 6 20f 10 

### 7f 2 

### 114& 12 <1 <2 <13 <14 <30 460 f50 CO.W*W ns/mr 15+ 2 <4 <2 30* 4 <1 4+ 2 <13 <14 <30 llOf12 19,200f



### nnn Ni <2 

### <2 Gravi- 26.600+ 

### cu <3 <3 metric 800

... aThe collected size ranges are 0-2 pm for fine particles and 2.5-10

for coarse particles.Table 

### II. MaximumAmount of Various Sulfate Compounds Deduced from Observed Elemental Sulfur and Metal Concentrations Listed inTable I for Particles Smaller Than 2 Mm
It is assumed that all of the sulfur is in the form of sulfate Compound Sulfate, %a Compound Sulfate, %a

K2S04 <2% Fe~(S04)~ 

### <3% CaS04 <3% ZnS04 <1% TiZ(SO& <2% PbS04 

### <2%

a If only fraction F of the elemental sylfur were in the form of sulfate, then these percentages areto bemultiplied by 1/F.

75% of the Si, Ca, Ti, and Fe at the sampling site. At least 75%of the 

### S,Zn, Br, and Pbis contained in thesmallparticles. These same features were observed in all the data from the dichotomous sampler over the August 26-31 sampling period. Similar results have been reported by Lee et al. (17)for a variety of elements. The concentrationslisted in Table I for V, Cr,Mn,Ni, Cu,Zn, Rb, and Sr are significantly lower than the typical urban values shown in Figure 

### 4. This may be due to the residential nature of the sampling site and to the relatively clean air conditions at the time of measurement. Variable amounts of chlorine in the filter blanks prevented analysisfor that element.

Inthese datathemost abundantobservedelement is sulfur. Certain sulfate compounds such as zinc ammonium sulfate, sulfuric acid, and ammonium sulfate have been shown by Amdur (18) to be pulmonary irritants. If one makes the assumption that all sulfur is in the form of sulfate,then one can deducethemaximum possible fraction of the sulfate that is associated with thevarious observed cations as shown in Table 11. One notes that the biologically active zinc sulfate compounds can only be minor components. Table I1 suggests that significant amounts of sulfate may be bound to light element cations such as H+ or (NHJ+. Additional work needs to be done to demonstrate the accuracy of the X-ray analysis for sulfur, to determine the percentage of sulfur in the form of sulfate and to verify that the observed sulfur is not the result of SO2 being converted tosulfate on thefilter.

The diurnal patterns of the elements plotted in Figures 

### 8 and 

### 9 give valuable clues about the source of these pollutants. For example, the enormous fluctuation in the titanium concentration is indicative of a local discrete source. The lack of major fluctuations in the sulfur concentration indicates a lack of a single local or discrete source. The Br to Pb ratio and the lead concentration seem to be influenced by rush hour traffic patterns.

These results illustrate the utility of using the combination of dichotomous sampler, X-ray fluorescence analyzer and gravimetric analysis for particulate monitoring. For future studies of this type, a newly developed dichotomous sampler will be available. Through careful design by 

### Loo (II), the wall losses in the 0-15-wm range of diameters are reduced to a very low level. Tendichotomous samplerswith automatic sample changers are presently being installed in a network for use in theRegional Air Pollution Studyin 

### St. Louis. A second low loss dichotomous samplerhas been developed for routine field use (19).
Acknowledgments

The authors are grateful to 

### F. S. Goulding,

### J. 

### M. Jaklevic, B. V. Jarrett,

### J.Meng, and 

### H. A. Rook for valuable advice and discussions, to 

### J.A. Cooper for providing the plot TIME OF DAY Figure 8. Plot of 2-hr average concentrationsof S,Fe, and Ti for the five-day period between August 26 and August 31, 1973, in St. Louis Size fractionation was not used

0 0 0 0 0 0 ~SUN4~ON~TUf~WEO~T~U~FFRI~
TlUE OF DAY Figure 9. Plot of 2-hr average concentrations of Zn, Pb, and the Br-Pb ratio for period between August 26 and August 31, 1973, in St. Louis Smooth curve is a repetitive 24-hr pattern and guide to the eye. Size fractionationwas not used

of elemental abundances used in Figure 

### 4,to W. 

### E. Wilson for providing space in his mobile laboratory in 

### St. Louis to operate the sampling equipment, and to W. 

### C. Peters and C. R. Sawicki and

### L. E. Hines for valuable assistance.

Literature Cited
(1) Giauque, R. D., Goulding, F. S., Jaklevic, J. M., Pehl, R. H.,

Anal. Chem.,45,671 (1973). (2) Rhodes, J. R., Pradzynski, A. H., Hunter, C. B., Payne, J. S.

Lindgren,J. L.,Enuiron, Sci. Technol.,6,922(1972). (3) Goulding, F. S., Jaklevic, J. M., "X-Ray Fluorescence Spectrometer for Airborne Particulate Monitoring," EPA Rep. No. EPA-R243-182.Auril 1973. (4) Whitby, K. T.,Hisar,R.B., Liu, B. Y. H.,J. ColloidInterface
(5) Liuumann.M.. Harris. W. B.. HealthPhvs.. 8.155 119621.

Sci.,39, 177 (1972).
(6) Mi;, K. R.',J.Sei.Instrum.,22,187 (19&).' (7) Lundgren,D. A,,J.AirPollut. Contr.Assoc., 17,225(1967). (8)Hounam, R. F., Sherwood, R. J.,Am. Ind. Hyg.Assoc. J., 26,
(9) Conner,W. D.,J.Air Pollut. Contr. Assoc., 16,35 (1966). '

122 (1965).

Volume 9, Number 7, July 1975 667(16) Dzubav. T. G., Nelson, R. O., in “Advances in X-Rav Analv(10) Peterson, C., Environmental Research Corporation, private

communication. 1973. (11) Loo,B. W., tobe published. (12) Loo,B. W.,Jaklevic,J.M., “An Evaluationof theERC Virtual ImDactor.” Lawrence Berkelev Laboratorv Publication LBL2468,-Berkeley Calif., 1974. (13) Jaklevic, J.M., Giauoue. R. D.. Malone. D. F.. Searles. W. L.

in “Advances in X-Ray Analysis,’’Heinrich et al:, Eds., Vol. 15, p 266,1972. (14) CooDer. J. A.. Battelle Pacific Northwest Laboratorv ReDort “.

~ BNWL‘-SA-4690, June 1,1973. (15) Hammerle,R. H., Marsh, R. H., Rengan, K., Giauque,R. D.,

Jaklevic,J.M.,Anal.Chem.,45, 1939(1973). ses,” Vol-18, p 619, W. L. Pickels, C. 

### S.Barrett, J. B. Newkirk, C. 0.Ruud,Eds., 1974. (17) Lee. R. E.. Goranson. S. S.. Enrione. R. E.. Morean. G. B..

.. I.

Enuirok. Sci. ’Technol.,6,1025 (1972). ’ (18) Amdur, M. O.,Proc.Am.Phil. Soc., 14,3 (1970). (19) Peterson, C., EPA Report, “Development and Testing of Dichotomous Sampler,”tobe published, 1975. Received for review July 11, 1974.Accepted April 10, 1975.Mention of commercial products isfor identification only and does not constitute endorsement by the Enuironmental Protection Agency of the U.S.Gouernment.



## Distribution 

# of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) in 

## Aquatic 

# Model Ecosystem

Allan R. Isensee* and Gerald 

### E. Jones Agricultural EnvironmentalQuality Institute,Agricultural Research Center, ARS, United States Departmentof Agriculture, Beltsville,

### Md.20705

Several organismsin a model ecosystem were exposed to 14C-labeledTCDD for up to 31 days to determine the distribution and bioaccumulation potential in the aquatic environment. TCDD accumulation by all organisms was directly related to water concentration (0.05-1330 ppt) and averaged 2.0-2.6 X 

## lo4(snail,

### Gambusia,and daphnid) and 4-9 X 

### lo3 (duckweed, algae, and catfish) times the water concentration. 

### No metabolites of TCDD were found in submerged soil,water, snails,

### Gambusia,or catfish.

Discovery in 1970 of the highly toxic contaminant 

### 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the herbicide 

### (2,4,5-trichlorophenoxy) acetic acid (2,4,5-T) spawned

a great deak of concern about the potential hazard to man and the environment. This concern subsequently stimulated numerous studies

### to assess thebehavior of TCDDin the environment [as summarized by Helling et al. (I)].These studies revealed that TCDD is immobile in soils, is not translocated in plants, has a half-life in soil of about 1year, and is slowly photodecomposed in water but not on soil. The results of these studies, combined with the knowledge that presently produced 2,4,5-T contains <0.1 ppm TCDD, indicate that TCDD is not entering or being distributed in the environment in large quantities. However, concern still lingers over the TCDD hazard to man for several reasons: (1)it has an extremely high mammalian toxicity [LD50 

### of 10pg/kg for rabbits (2)];0.6 wg/kg for guinea pigs 

### (3); (2)it is a teratogen (4,5); and (3)concentrations of TCDDranging from about 20-1000 parts per trillion (ppt)have been found in fish and crustaceans from South Vietnamese waters (6). Since this concern exists and the total environmental impact is still in question,we felt thatfurther information on the probable environmental distribution would be useful. This study was therefore initiated to determine the availability, distribution, and bioaccumulation potential of TCDD in a model ecosystem.

This model ecosystem was designed tosimulatetheusual mode of entry of pesticides into water and the simultaneous exposure of several organisms representing parts of natural food chains. The bulk of pesticides (or their contaminants) that enter yater unintentionally do 

### so via erosion of pesticide contaminated soil or plant remains from agricultural land. The amount of pesticide that enters water from the submerged soil will depend on its solubility and desorption from soil. Simultaneous exposure of several organisms should ensure that accumulation by all processes-i.e., absorption, adsorption, and consumption of lower by higher food chain organisms, would be represented. 

### As designed, this model ecosystem exposes both a test chemical and organisms to some of the major conditions that might realistically be expectedto occur in the environment. The system is not designed to determine the effects of a chemical on the organisms (though some primary effectscan be assessed)butrather,how does the chemical behave when subjectedtolikely environmental conditions. 

### Experimental

One single concentration andtwo multiple concentration experiments were performed. In each, 14C-TCDDwas adsorbed to soil, and placed in the bottom of glass aquaria (25.4 X 5.2 X 17.8 cm). Table I summarizesthe treatment, rate, and replication details of the three experiments. In

Table I. Soil TCDD Application Ratesand Replications

Total TCDD Type and amount, Final soil

added per grams, of soil com- TCDD No. of tank.

### !.w bined with TCDDa concn., ppmb replicates

149

0

63 63 63 63

0

10

1 0.1 0.01 0 Experiment I L-2 0 L-20

L-20 L-20+ M-100 L-20 + M-200 L-20+ M-400 L-20

M-100 M-100 M-100 M-100 M-100 Experiment II

Experiment Ill 7.45 0

3.17 0.53 0.29 0.15 0

0.1 0.01 0.001 0.0001 0 3 1

2 2 2 2 2

2 2 2 2 2

a L = Lakeland sandy loam, M = M,atapeake silt loam. In II, L was grst treated with TCDD, then dry mixed with M in,treatment tanks.

Soil concentrations based on total quantity of soil in tank.

668 Environmental Science & Technology