Environ. Sci. Techno/. 1995, 29, 406-412
Atrarifle Expesures throwjh AssesGeRts for Ohio. Illinois. R . PETER R I C H A R D S * AND DAVID B . B A K E R Water Quality hboratory, Heidelberg College, T i f i n , Ohio 44883
B R I A N R . CHRISTENSEN Montgomery- Watson Inc., Wayzata, Minnesota 55391
D E N N I S P . TIERNEY Ciba Plant Protection, Ciba-Geigy Inc., Greensboro, North Carolina 27419
A systematic exposure assessment process has been developed for evaluating and describing the distribution, within large populations, of human exposures through drinking water to substances of potential health concern. This process involves dividing the population into groups of known size, within which the drinking water exposure is the same or similar, and estimating the exposure concentration for each group based on the best available data. Using this process, assessments of human exposures to atrazine though drinking water have been carried out for the populations of the states of Ohio, Illinois, and Iowa. The assessments indicate that atrazine exposure through drinking water does not represent a significant human health threat based on the current understanding of atrazine toxicity. Exposures to atrazine above the lifetime health advisory level of 3.0 ppb do not exceed 0.25% of the assessed population in any of the three states, and between 94% and 99% of the assessed populations have exposure concentrations less than 1 ppb.
Introduction Considerable concern has been voiced in recent years over possible health effects from herbicides ingested in drinking water. Atrazine is one of the most extensively used herbicides throughout the midwest Corn Belt and is known to occur in rivers draining agricultural watersheds (1-41, in groundwater (5, 6), and even in rainfall (7) and fog (8). Atrazinebreaks down more slowlythan most other current generation herbicides and typically is detectable in surface waters for alonger period of time after application. Atrazine is not removed from drinking water by conventional treatment (91,thus tap water concentrations are similar to raw water concentrations unless carbon filtration is employed. The presence of herbicides in drinking water sources became more significant for water utilities in 1993, when monitoring requirements under the 1986 amendment to the Safe Drinking Water Act (SDWA) went into effect (10). Water utilities using surface waters must measure concentrations of designated herbicides, including atrazine, quarterly during the first compliance year. If the running average of four consecutive samples at a facility is less than the established drinking water standard for a regulated substance, the sampling frequency is decreased to twice per year for facilities serving more than 3300 people and once per year for facilities serving less than 3300 people. If, however,the running average of four consecutivesamples at a facility exceeds the established drinkingwater standard, more intensive monitoring and public notification are required, and the EPA can require the utility to find an alternative water supply or to treat the water to reduce the contaminant concentration. A rational assessment of the risk from a compound requires knowledgeof its toxicologyplus a methodology to systematically integrate disparate sources of information on concentrations and the populations exposed to them and to present this information in a concise fashion that documents the overall level of exposure and facilitates identification of the populations most heavily exposed.The purpose of this paper is to illustrate one such exposure assessment procedure and to report the results of its application to assess atrazine exposures in the populations of three midwestern states (Ohio,Illinois, and Iowa) which have a high percentage of corn acres treated with atrazine.
MCLs, HAL, and Human Health Risks The EPA has developed standard procedures for evaluating the health hazards associated with ingesting pesticides and other compounds. If direct evidence of human health effects is lacking, the evaluation relies on tests carried out using laboratory animals. These tests and other available information lead to the establishment of a series of health advisorylevels (HALs),which are concentrations in drinking water at which adverse health effectswould not be expected to occur from exposure for the specified length of time. Atrazine HALs are given in Table 1. To account for uncertainty in extrapolating from animal testing studies to humans and for possible variations in sensitivity among humans, safety factors are applied to the No Observed Adverse Effect Level (NOAEL) for the animal test species found to be most sensitive to the pesticide. A
406 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 29, NO. 2, 1995
0013-936x/95/0929-0406$09.00/0
0 1995 American Chemical Society
TABLE 1
Health Advisory levels (HALs) for Atrazine exposure duration
population segment
1 day 10 day 7 year 7 year 70 year
child child child adult adult
HAL (ppb) safety factor 100 100 50 200 3
100 100 100 100
1000
exposure concenuauon IS esumatea tor eacn segment. These segments may be as broad as the population using sources anywhere on an entire river or as narrow as the population served by a particular water utility or an individual well depending on the availability of data and the level of detail of the study, With increasing detail, the segments become smaller and more numerous and approximate more closely the distribution which would be obtained if each person's individual exposure history were knOWn.
10-foldsafetyfactoris applied to account for the uncertainty involved in extrapolating from animal studies to humans, and a 10-fold safety factor is applied to protect sensitive members of the population (e.g., infants, children, and the elderly). The EPA also classifies compounds according to the form of health risk they represent and the degree of certainty associated with the health risk. A additional 10fold safety factor was used in calculating the lifetime HAL for atrazine because the EPA ranks atrazine as a class C (possible) carcinogen. The lifetime HAL is considered to include childhood. For the calculation of the lifetime (70 year) HAL, the EPA further assumes that only 20% of atrazine exposure comes from drinking water and introduces an additional 5-fold factor into the HAL to account for this assumption. However, over the 30 years of its use, atrazine has not been detected in edible portions of plants or livestock, nor has it been detected during FDA monitoring of food in the American diet through market-basket studies (11). Nonoccupational dermal exposure to atrazine may occur through swimming, exposure to rainfall, etc., but such exposure is infrequent and intermittent. Concentrations are unlikely to be higher than those in drinking water, and total exposure is much less. Furthermore, dermal absorption is an inefficient uptake pathway compared to gastrointestinal absorption. These results suggest that at least 95% of non-occupational exposure to atrazine occurs through drinking water. Thus, the 20% assumption provides an additional safety factor which approaches 5-fold for atrazine. Further detailsabout the derivationof atrazine HALs are given in an EPA publication (12). In addition to HALs, the EPA may also establish a maximum contaminant level (MCL) for a substance, under authorityof the federal SDWA. MCLs are legally enforceable drinking water standards based on an assumed lifetime exposure and are the standards to which a water utility's average concentrations will be compared. For atrazine, the MCL is equal to the lifetime HAL of 3.0 ppb.
Methods Instantaneous raw drinkingwater concentrationsof atrazine which exceed short-term HALs are very rare. Instances of concentrations exceeding a short-termHAL when averaged over the HAL time interval have been even more infrequently reported. Thus, any potential adverse effects of atrazine exposure through drinking water are likely to be due to chronic exposures over a lifetime. Consequently, the concentration of interest is the long-term average concentration to which people are exposed. Each person has a unique history of exposure and, therefore, a unique long-term average exposure concentration, and no assessment can hope to evaluate each of these unique concentrations. Therefore,in the method we have developed, the population is divided into segments of known size and with similar exposures, and an average
Atrazine concentrations are highly seasonal,particularly in rivers (1-4, 13, 14). However, since exposures occur over multi-year time scales and the risk is related to the multi-year average exposure concentration, seasonal fluctuations are not important in this exposure assessment. They are important in estimating the exposure concentration from available data, however, especially since many monitoring programs focus on the summer months when raw water concentrations are highest. Time weighting of the concentrations is often required to prevent bias, and some data sets cannot be used because fall and winter months are totally unrepresented in the data. The exposure assessment is plotted as an exposure frequency distribution, a variable-width bar graph with concentration on the vertical axis and population on the horizontal axis. Each bar represents one segment of the population. The width of the bar indicates the percent of the total population which falls in the segment, and the height of the bar indicates the exposure concentration for the segment. The bars are presented in order of decreasing concentration. The procedure is computerized, which facilitatesupdating specific assessments, performing sensitivity analyses, and evaluating alternativefuture scenarios. Assessments were made for three different states using this method. Each was done slightly differently due to differences in the kind and amount of information available for each state. However, in each case the goal was to produce an assessment for the entire state population. For reasons given earlier, the assessments are for possible chronic effects only, and these are related to long-term average concentrations. Population data were taken from Public Water Supply Inventories (PWSIs)maintained by each state. Private well populations were estimated as the differencebetween the PWSI total population and the 1990 state population. Atrazine concentration data and data on local land use, geology, and other possible explanatory variables were obtained from state EPAs, the U.S. Geological Survey, Heidelberg College Water Quality Lab, other colleges and universities, and Ciba-Geigy and Monsanto Corporations. The most complete data set for each geographic region was used to obtain the estimated exposure concentration. All nondetects were treated conservatively and replaced by half the detection limit for the calculation of average concentrations. Public groundwater-based populations were grouped into five concentration ranges based on average atrazine concentrations in samples from each utility, and the population in each range was assigned the average concentration from all samples for all utilities in the group. Populations served by utilities for which no data were available and private well populations in Illinois were distributed among the concentration ranges by proportionality. In Ohio and Iowa, private well concentration data (1.516)were available,and the private well population was VOL. 29, NO. 2, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
407
c‘
._ o 5.0 +
F?
+ C
c
4.0
a, m
0
MCL
Q
3.0 Q
a,
c
I;: 2.0
1.o
.o 0
10
20
40
30
60
50
70
100
90
80
Percent of Assessed Population
Lakes
Rivers
Groundwater
Reservoirs
FIGURE 1. Atrazine exposure exceedency plot for the state of Ohio. Each rectangle represents one water source; its width is proportional to the papulation served by the source. and its height is pmpofional to the estimated exposure concentration for the source.
assessed separatelybyaprocedure parallel to that used for the public water supplies. Surface water-based populations served by non-impounded portions of interior rivers were usually assessed at a whole-basin level, since adequate local concentration data were usually not available. Surface water-based populations SeNed by lakes or reservoirs were usually assessed individually. Populations served by the Mississippi, Ohio, and Missouri rivers were assessed in segments defined by the location of monitoring stations for which adequate concentration records were available. Timeweighted concentrations were used to compensate for seasonally focused sampling programs. If local data were not available,populationswith water sources on headwater streams and impoundmentswere not assessed in instances where theirexposureconcentrationswerelikelytobehigher than those along the mainstream. These omissions were consistent with a general pbilosophyof resolving ambiguity in the direction of a “worst reasonable case” result; it was deemed better to consider them unknownthan to attribute too low an exposure concentration to them. Some other populations were also excluded because no locally appropriate concentration data were available. Omitted populations constituted 5.1,4.7,and 4.4% of the total state population for Ohio, Illinois, and Iowa, respectively. Because our purposes are to illustrate a novel approach to exposure assessment and to show the general characteristics of our results, we have chosen not to identify the populations represented by each segment of our graphs, except in terms of the type of water supply used. More 408 m ENVIRONMENTAL SCIENCE &TECHNOLOGY I VOL. 29, NO. 2,1995
TABLE 2
Population-Weighted Average Exposure Concentrations for Surface Water and Groundwater Sources and for All Assessed Sources Combined nato
Ohio
source
LakeErie other surfacewater public groundwater private groundwater all assessed sources Illinois Lake Michigan other surface water groundwater all assessed sources Iowa surfacewater public groundwater private groundwater all assessed sources
QOQUhtiOn
SoNed
IIV COnCn
(Qpb)
2 493 319 2 891 518 2 862 000 2 000 000 10 247 447
0.070 0.840 0.025 0.052 0.271
5 385 973
0.100 0.998 0.028 0.187
1 381 070 4 121 341 10 888 390 575 086 1 417 446 677 550
2 670 082
0.402 0.116 0.113 0.177
detailed descriptions of the specilic approaches used in dealingwitheachstate’savailabledataarefoundinRichards et al. (17).
Results The results of the assessments are presented in Figures 1-3andsunmarhedinTable2. Themostsigniiicantresult of these assessmentsis that, accordingto the data currently available,onlyverysmallpopulation segments areexposed to average atrazine concentrations exceeding the MCL of
i 0 ._ c
MCL
311 11’11
0
I,, 0
10
,
I
20
30
Lake Michigan
10
5
0
e
I
I
I
I
40 50 60 70 Percent of Assessed Population
Rivers
Reservoirs
I
I
80
90
,
100
Groundwater
FIGURE2 Alrazins sxpDsunsxcmdsncyplotforthenaMoflllinois.Iheinwtistha lensndoflfisgnphwiththe horizontalscale expanded to allow baler resolution of small population segments.
3.0 ppb, and most are exposed to average concentrations less than 1.0 ppb. Another importantresult is that average exposures from surface waters other than the Great Lakes are substantially higher than average exposures from groundwater. Large rivers such as the Ohio and Mississippi andmost groundwater sourcesprovide waterwith relatively low concentrations of atrazine. Average concentrations forrawwater takenfromtheGreatLakes arenotwellknown, but the available data point to average concentrations in the range of0.05 or less to about 0.10 ppb, concentrations whicharecorroboratedbyrecent open-lakesampling (18). The highest concentrations of atrazine are associated with a few small groundwater-based public water supplies and privatewells. Adarydataaccompanyingthe atrazine measurements show that these wells are usually shallow and oftendrawonbigblyvulnerable alluvial aquifers. High concentrations in surface waters are often associated with small inland reservoirs, particularly those which impound streamwater from small, agriculturalwatershedsandwhich have intermittent outflow. Intermediate average concentrations, almost always less than the MCL of 3.0 ppb, are associatedwithriversdrahingagriculturalbasinsandwith reservoirs and lakes created by damming such rivers. Pumped storage reservoirs often have lower concentrations, because these reservoirsoftenhavefairlylongholdingtimes and because pumping can be carried out at times when the atrazine concentration of the source is low.
Discussion SourcesOfAtrazineinGroundwater. High concentrations
of atrazine in groundwater are often the result of point
source contamination from a nearby agriculturalchemical dealer(l9,20)orofaccidentsorimproperpesticide handling practices on the farm (16.21, 22). Some of the highest groundwater concentrations observed in this study are known to be of point sources origin, and it seems likelythat point Sourcesor improper practices are responsiblefor most of the concentrations above the MCL Nonpoint sources are responsible for at least some occurrences of atrazine in groundwater, particularly in vulnerable areas with porous soils andlor shallow water tables. Dug and driven (sand point) wells and springs, shallow wells, and sandy soils are associated with more frequent detections and higher concentrations of atrazine in private wells (15,211. Sources of Uncertainly and Possible Bias in the Aapeapments. For Lake Michigan, Lake Erie, and many groundwatersites,most or allanalysesforatrazineproduced nondetections. We used half the detection limit for these results. The actual concentrations in these samples were probably lower on average than half the detection limit, otherwise more detections would be expected. Thus, our procedure probably overestimates concentrationsfor these sources. While the estimated concentrations are still low compared to some other sources, the large populations served by these sources give them considerable weight in determining overall average concentrations. AU concentration data are for untreated water. Treatment of drinking water with activated carbon, often used for taste and odor control in surfacewater-based supplies, also reducestheatrazine concentrationinfinishednisheddrinldng VOL. 29, NO. 2,1995 I ENVIRONMENTALSCIENCE &TECHNOLOGY m 409
14.03.
14.01
0
10
Rivers
20
30
40 50 60 Percent of Assessed Population
Lakes
Groundwater
70
80
90
100
0
Too narrow to shadesee detail
AGURE 3. Atrazine exposurn exceedency plot for the state of Iowa. The inset is an expansion of the left end of this graph.
water (91. Thus, exposure concentrations based on raw water data may be overestimates for some sources. We did not attempt an assessment for certain surface water-based communities located within interior watersheds in Illinois and Iowa that utilized small tributaries or impoundments of small tributaries as water sources, because atrazine concentration data were not available for these water supplies. We also felt that available data from monitoring programs on the main rivers might provide an unrealisticallylow estimate of the exposure concentration forthese communities. The concentrationsinthese interior waters are generally higher than those in the Great Lakes, theOhio,Mississippi,andMissouririvers, andgroundwater. Thus, excluding these communities from the assessment had the effect of reducing the estimated overall surface water concentrationsslightly. However, since the excluded populations were less than 5% of the corresponding total populations, this effect is undoubtedly a small one. Our poor knowledge of the exposure concentrations for
The safety factor used in setting the MCL is sufficiently large (1000-fold)so that the EPA believes there is a margin of safety between the MCL and the threshold dose for adverse human health effects. In Figure 4, the range of exposure concentrations from this studyis compared with the MCL (equal to the lifetime HAL), the NOAEL, and the Lowest Obsemed Adverse Effect Level ( L O W ) . To make this comparison, the concentrations were converted to dose rates, in milligrams of atrazine per kilogram of body weight per day, using the same assumptions as the EPA uses in calculakg the lifetime HAL from the NOAEL: a body weight of 70 kg (154 Ib) and a drinking water consumption rate of 2 L (2.2 qtllday. Tbe assessed populations. on a state-wideaverage basis, are exposed to concentrations less than one-tenth of the MCL, and only a fraction of a percent of the population in each state is exposed to concentrations above the MCL. Several of the communities with the highest exposure concentrationseitherhave alreadytakenremedialmeasures smallcomm~tieswhi~relyonsmallinlandsurfacewater or are planning to do so in the near future. Thus, even sources in each state also adds to the uncertainty of these individuals in these communities are unlikely to have assessmentsand detracts from their completeness. Priority lifetime average exposures greater than the MCL. Given should be given to obtaining data which will permit these these remedial measures and given the sue of the safety communities to be added to the assessments. factor built into the MCL, even individuals in these communities are unlikely to have any adverse health effect I m p l i c a t i o n s o f t h e A f o rHuman Health. The from exposure to atrazine through drinking water. MCL is not a threshold for human health effects, but a regulatory concentration designed to leave a considerable Increasing the Knowledge Base. Much of the surface margin for safety between it and the human health water portion of these assessments was done using data threshold. For atrazine, the MCLcorresponds to 115000of which were imperfectly suited for the purpose. Given the theNOAELdoseforthemost sensitiveanimalspeciestested. size of the population served by Lake Michigan waters, it 410. ENVIRONMENTAL SCIENCE k TECHNOLOGY I VOL. 29,
NO. 2.1995
Minurnurn exposure concentration: groundwater, no detections (0.025 ppb) Average groundwater, Illinois (0.028 ppb) - Average groundwater, Ohio (0.036 ppb) - Average groundwater, Iowa (0.i 13 ppb)
. Average surface water, Illinois (0.283 ppb) *
NOAEL (15 PPm)
Average surface water, Iowa (0.402 ppb)
- Average surface water, Ohio (0.483 ppb) MCL (3 PPW
Maximum exposure concentration (13.5 PPb)
SAFETY FACTOR
-I 10.'
I
-6
10
'
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-5
10
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-4
' ' """I
10
' """'I
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Exposure rate, mg/kg/day FIGURE 4. Relationship between exposure concentrationsobserved in this study, the MCL the NOAEL and the LOAEL. Concentrationshave been converted to dose rates in milligrams of atrazine per kilogram of body weight per day; the correspondingconcentrations are listed in parentheses with the arrow labels.
is important to have concentration data from Illinois water utilities using Lake Michigan water rather than having to rely on data from an adjacent state. Even more important is the development of better databases for inland rivers and reservoirs. The available data are often detailed enough to give reliable average concentrations for the points of sampling, but these do not always correspond closely to the points from which water is taken for human consumption. As mandated testing for atrazine at water treatment plants is phased in (IO),data specificto the treatment plants will begin to be available, and this important component of the assessment can be put on more certain grounds. It would be particularly useful to sample at more than the minimum required frequency (quarterly) until the levels and seasonal fluctuations of atrazine in these plants are better understood.
Conclusions The exposure assessment process is a useful technique for evaluatingand trackingthe overall quality of a state's water resources, identifying population segments at risk, and prioritizing remediation efforts, if needed. This process has been used to provide a preliminary estimate of exposures to atrazine in drinking water in the states of Ohio, Illinois, and Iowa. The currently available data do not document exposures to atrazine through drinking water at levels which pose a significant health threat given the current understanding of atrazine toxicity. Most population segments evaluated had exposure concentrations less than the lifetimehealth advisorylevel only 0.05% ofthe assessed Ohio population, none of the assessed Illinois population, and 0.21% of the assessed Iowa population had exposures above this standard. 94% of the assessed Ohio population, 97% of the assessed Illinois population, and 99% of the assessed Iowa population had exposure concentrations less than 1 ppb. 76% of the
assessed Ohio population, 88% of the assessed Illinois population, and 81% of the assessed Iowa population had exposure concentrations less than 0.3 ppb. Exposures from inland surface water sources are generally higher than those from groundwater sources. Average exposures from water from Lakes Michigan and Erie are less than 0.1 ppb; most samples from these sources did not have detectable levels of atrazine. Uncertaintyin this assessment could be reduced if more data were available from water utilities, particularly those on inland lakes and reservoirs. These data will become available in the future as a consequence of monitoring requirements of the SDWA. These data should be used as the basis for more detailed and more accurate exposure assessments, which should be periodically updated.
Literature Cited (1)Thurman, E. M.; Goolsby, D. A.; Meyer, M. T.; Kolpin, D. W. Environ. Sci. Technol. 1991, 25, 1794. (2) Goolsby, D.A.; Coupe, R. C.; Markovchick, D. J. Distribution of selected herbicides and nitrate in the Mississippi River and its major tributaries, April through June 1991; Water-Resources Investigation Report 91-4163;U.S. Geological Survey: Reston, VA, 1991. (3) Baker, D. B. Sediment, NutrientandPesticide Transportin Selected Lower GreatLakes Tributaries;US.EPA Chicago, IL, 1988;EPA905/4-88-001. (4) Richards, R. P.; Baker, D. B. Environ. Toxicol. Chem. 1993, 12, 13. (5) National Pesticidesurvey: Project Summary, US.Environmental Protection Agency, Office ofwater, Office of Pesticides and Toxic Substances: Washington, DC, 1990. (6) Holden, L. R.; Graham, J. A.; Whitmore, R. W.; Alexander, W. J.; Pratt, R. W.; Liddle, S. K.; Piper, L. L. Environ. Sci. Technol. 1992, 26, 935. (7) Richards, R. P.; Gamer, J. W.; Baker, D. B.; Krieger, K. A. Nature 1987, 327, 129. (8) Glotfelty, D.E.; Sieber, J. N.; Liljedahl, L. J. Nature 1987, 325, 602.
(9) Miltner, R. J.; Baker, D. B.; Speth, T. S.; Fronk, C. A.J. Am. Water Works Assoc. 1989, 81, 43.
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(10) Pontius, F. W. 1. Am. Water Works Assoc. 1990, 82, 32. (11) Food and Drug Administration, I; AOAC Int. 1993, 76 (Septl Oct), 127A. (12) U S . Environmental Protection Agency. Drinking Water Health Advisory: Pesticides; Lewis Publishers: Chelsea, MI, 1989. (13) Glotfelty, D. E.; Williams, G. H.; Freeman, H. P.; Leech, M. M. In Long Range Transport of Pesticides; Kurtz, D. A., Ed.; Lewis Publishers: Chelsea, MI, 1990; pp 199-222. (14) Baker, D. B.; Richards; R. P. In LongRange TransportofPesticides; Kurtz, D. A,, Ed.; Lewis Publishers: Chelsea, MI, 1990; pp 241270. (15) Baker, D. B.; Wdrabenstein, L. W.; Richards, R. P. In Proceedings of the Fourth National Conference on Pesticides: New Directions in Pesticide Research, Development, and Policy; Weigman, D. L., Ed.; Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University: Blacksburg,VA, 1994;pp 470-494. (16) The Iowa Statewide Rural Well-Water Survey: Water Quality Data: Initial Analysis; Technical Information Series 19; Iowa Department of Natural Resources: Iowa City, IA,1990. (17) Richards, R. P.; Baker, D. B.; Christensen, B. R.; Tiemey, D. P. In Proceedings of the Fourth National Conference on Pesticides: New Directions in Pesticide Research, Development, and Policy;
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Weigman, D. L., Ed.; Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University: Blacksburg, VA, 1994; pp 222-243. (18) Schottler, S. P.; Eisenreich, S . J. Abstract. In International Association for Great Lakes Research and Estuarine Research Federation Program and Abstracts; University of Windsor: Windsor, Ontario, 1994. (19) Ciba-Geigy Corp. Unpublished investigations. (20) Ohio Department of Agriculture. Unpublished investigations. (21) The Iowa Statewide Rural Well-Water Survey: Site and Well Characteristics and Water Quality; Technical Information Series 23; Iowa Department of Naturd Resources: Iowa City, IA,1992. (22) Frank, R. Agriculture Canada, presented at Heidelberg College, 1990.
Received for review April 19, 1994. Revised manuscript received September 12, 1994. Accepted September 14, 1994.@
ES9402415 Abstract published in Advance ACS Abstracts, October 15, 1994.
