Summary of Ciba Crop Protection Groundwater Monitoring Study for

Chapter 19 Summary of C i b a C r o p Protection Groundwater Monitoring Study for Atrazine and Its Degradation

Downloaded by STANFORD UNIV GREEN LIBR on September 30, 2012 | http://pubs.acs.org Publication Date: May 14, 1998 | doi: 10.1021/bk-1998-0683.ch019

Products in the United States 1

2

2

3

K. Balu , P. W. Holden, L. C. Johnson, and M. W. Cheung 1

Waterborne Environmental Inc., 7031 Albert Pick Road, Suite 100, Greensboro, NC 27409 Waterborne Environmental Inc., 897-B Harrison Street, SE, Leesburg, VA 20175 Novartis Crop Protection, Inc., P.O. Box 18300, Greensboro, NC 27419

2

3

Ciba Crop Protection (Ciba) has completed a private well monitoring program in cooperation with nineteen states to determine the levels of atrazine and its degradation products in groundwater in vulnerable regions of major use areas within the United States. The nineteen states were selected based on high atrazine use. In each state, between 30 - 200 wells were selected for monitoring based on high atrazine use, groundwater vulnerability and previous atrazine detections. Along with atrazine, the following major degradation products were monitored: desethylatrazine, deisopropylatrazine, diaminochlorotriazine, hydroxyatrazine, desethylhydroxyatrazine, deisopropylhydroxyatrazine and ammeline. A total of 1,505 wells were sampled and analyzed for chlorotriazines by GC/MS and hydroxytriazines by LC/MS/MS at the Limit of Quantitation/Limit of Detection (LOQ/LOD) of 0.10 ppb for each analyte. Of the 1,505 wells analyzed, 76.1% showed no detections of atrazine and 0.5% had atrazine concentrations exceeding the EPA Maximum Contaminant Level (MCL) of 3 ppb. Frequencies of detections of desethylatrazine and diaminochlorotriazine were similar to atrazine (28.8% and 24.1%), respectively. Deisopropylatrazine was detected in 14.9% of the wells sampled. The hydroxytriazine degradation products, hydroxyatrazine, desethylhydroxyatrazine, deisopropylhydroxyatrazine and ammeline, were detected in 4.5%, 2.8%, 0.3% and 0.5% of the wells, respectively. The wells selected for this study were biased for positive detections of atrazine and its degradation products since they were located in areas with high groundwater vulnerability or they had ©1998 American Chemical Society In Triazine Herbicides: Risk Assessment; Ballantine, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

227

228


previous detections of atrazine. Hence, these monitoring data cannot be used to extrapolate exposure estimates accurately for the general population served by rural drinking water wells. Although an extensive data base is currently available on atrazine levels in groundwater (1-11), data on the degradation products of atrazine are relatively scarce. Atrazine is degraded in the soil environment by microbial degradation with the formation of dealkylated chlorotriazines, desethylatrazine, deisopropylatrazine, and diaminochlorotriazine. Desethylatrazine and deisopropylatrazine have been monitored in groundwater in a very limited number of studies (12-13). Atrazine is also degraded by abiotic processes to hydroxyatrazine which is quite polar and remains bound in the soil matrix (14). Additional degradation products of atrazine that have been found in soil are dealkylated hydroxytriazines (desethylhydroxyatrazine, deisopropylhydroxy atrazine, and ammeline), which are even more polar than hydroxyatrazine. Structures of atrazine and its degradation products are provided in Figure 1. No monitoring data have been reported in the literature for the hydroxytriazine degradation products of atrazine in groundwater. The objective of this study was to determine the levels of atrazine and its chloro- and hydroxytriazine degradation products in groundwater samples collectedfrombroad geographic regions in the United States in cooperation with various state agencies. Nineteen states were selected for monitoring which included: Florida, Hawaii, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Michigan, Minnesota, Mississippi, Ohio, Pennsylvania, Texas, Virginia, Washington, West Virginia and Wisconsin. These states were selected based on 1) high atrazine use within the state, 2) presence of areas considered vulnerable to ground-water contamination where atrazine is used, and 3) the need to cover broad geographic areas in the United States. Well selection and sampling were conducted in cooperation with each state's department of agriculture or its affiliates such as land grant universities. Experimental Well Selection Criteria: The wells included in this study were selected through discussions with the representatives of the state agencies and its affiliates. The wells selected for this study were not based on a statistically defined random selection and hence, it is not possible to accurately extrapolate the results of this study to the general population of wells in the United States. The sampling design for this study was a targeted process of well selection meeting certain criteria chosen by each state following the general guidelines summarized below: a) Wells were selected in areas that met hydrogeologic vulnerability criteria for the requirements of a small-scale retrospective groundwater study (e.g., permeable soils, shallow water tables defined as those less than 50 feet from land surface, absence of layers in the vadose zone with low permeability, high product use areas, etc.).

In Triazine Herbicides: Risk Assessment; Ballantine, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.


Ν

ΝΗ

^Ν

ΝΗ

2

2

deethylhydroxyatrazine

ΗΝ

Ζ Χ

deethylatrazine

Ν

ΝΗ

Χ

Atrazine

ΗΝ

ΗΝ

Ν

ΝΗ

^

Ν

ΝΗ

^

ΝΗ

Ν

ΝΗ

χ 2

2

ΗΝ

Ν

Χ ΝΗ

2

diaminochlorotriazine

2

ΗΝ

.

Ν

diaminohydroxytriazine deisopropylhydroxyatrazine Figure 1. Structure of Atrazine and Major Degradation Products

ΗΝ

I XI ^

deisopropylatrazine

2

2

ΗΝ

. χ

Ν

Ν

IX .

Ή

hydroxyatrazine

ΗΝ



230 b) Priority was given in some states to wells with previous detections of atrazine. This criterion was used in order to obtain sufficient data for the degradation products of atrazine under conditions when atrazine is detected in the wells. Hence, the well selection in this study is biased towards wells with previous detections of atrazine. A number of states used immunoassay analysis as a screening tool to facilitate selection of wells. However, many wells with no previous detections of atrazine were also included in areas of high groundwater vulnerability. c) Priority was given for selection of rural drinking water wells adjacent to farms. In some states, observation or irrigation wells close to atrazine use areas were also chosen for monitoring. d) To the extent possible, wells with known point-source contamination due to spills, back-siphoning incidents, or damaged well casings were avoided. However, it is difficult to avoid this problem entirely in a study of this magnitude. A source investigation was conducted separately by Ciba for wells where atrazine concentrations exceeded the life-time M C L value of 3 ppb. e) Approximately 10% of the wells in many states were resampled to address temporal variability of the concentrations. f) To the extent possible, wells were sampled in various regions of each sate to obtain a representative cross-section of the state. Field Phase: The general approach for study initiation in each state was quite similar. A preliminary discussion was held with the key staff to discuss the details of the monitoring program. Following this, each state developed a statespecific protocol. Well sampling was performed by trained staff from the state agency or its designated group, except in Florida, Minnesota and Texas where the sampling was done by independent consultants. A well sampling training session for selected personnel in each state was conducted after completion of the state-specific protocol prior to the initiation of sampling. The training session included an explanation of the purpose and design of the sampling program, an overview of the purpose and need for Good Laboratory Practices (GLP), a discussion of the study's Standard Operating Procedures (SOPs), and an introduction to the field equipment and data collection forms. Every effort was made to ensure that the field phase of the study was conducted in compliance with the GLP requirements of the Federal Insecticide, Fungicide and Rodenticide Act (FIERA). Sampling was initiated by having the well owner sign a permission-tosample form. The wells in each state were identified by a unique well identification number along with the latitude/longitude of the wells. Data collection forms were used to standardize the information collected for all wells sampled. After the well-water system was chosen, the system was purged until the water quality was constant as determined by monitoring three physico chemical parameters at five-minute intervals: pH, electrical conductivity and temperature. Purging was considered complete when all three parameters were stable between two consecutive five-minute sampling intervals. This purging


231


process is identical to procedures used during EPA's National Pesticide Survey (NPS) of drinking water wells (2). After purging the well, samples were collected in two 1-liter amber glass bottles. Samples were shipped to Ciba under refrigerated conditions using frozen blue ice packs in specially designed insulated containers. Analytical Phase: Residues of parent atrazine and the chlorotriazines, desethylatrazine, deisopropylatrazine, and diaminochlorotriazine were determined using a gas chromatograph with a mass selective detector (GC/MSD). In this method, sodium chloride was added to the water sample. The sample was then buffered using a pH 10 buffer solution, and partitioned with ethyl acetate. The organic phase was dried in anhydrous magnesium sulfate and evaporated to dryness. The sample was then reconstituted in acetone and analyzed by gas chromatography-mass spectrometry (GC/MSD) using selected ion monitoring for quantitation. Water samples were initially analyzed for hydroxytriazine dégradâtes: hydroxyatrazine, desethylhydroxyatrazine, deisopropylhydroxyatrazine and ammeline, by Alta Analytical Laboratories using a thermospray liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS) system (Finnigan TSQ-700) and quantified by selected ion monitoring (SIM). In this method, water samples were extracted by passing an acidified sample through SCX solid phase extraction (SPE) column and eluting with a methanol-waterammonia mixture (75:20:5). The method was subsequently revised to a direct aqueous injection, whereby an aliquot of the sample was evaporated under nitrogen and reconstituted with HPLC-grade water for LC/MS/MS analysis. Because of problems of quantitation of ammeline by direct aqueous injection, this method was further revised using the S C X solid phase extraction cleanup followed by analysis by LC/MS/MS system. The Limit of Determination (LOD) for atrazine and the chlorotriazine degradation products by GC/MS and the hydroxytriazine degradation products by LC/MS/MS was 0.10 ppb. The method performance for the chloro- and hydroxytriazine degradation products was demonstrated by analysis of laboratory fortification samples in each analytical set. The residue results in the field samples were reported after corrections for the procedural recovery in each analytical set. R E S U L T S A N D DISCUSSION National Summary: The frequency distributions of atrazine and the chlorotriazine degradation products, desethylatrazine, deisopropylatrazine and diaminochlorotriazine, for all wells from the nineteen states participating in the atrazine study are shown in Figure 2. These results show that out of 1,505 wells analyzed, 23.9% showed detections of atrazine. Desethylatrazine was detected in more wells than atrazine (28.8%), while diaminochlorotriazine detections were similar to atrazine detections (24.1%). Fewer detections of deisopropylatrazine were observed with 14.9% of the wells having detections. Greater frequency of



232 atrazine and metabolite detections in this study was anticipated because the targeted well selection process, which included sampling in vulnerable groundwater regions and previous detections of atrazine, was biased. In contrast, the NPS by the EPA was conducted as a statistically designed study by random selection of community water systems and rural domestic wells. In the NPS study, atrazine was detected in 0.7% of the rural domestic wells at the detection limit of 0.12 ppb (2). Eight wells (0.5%) out of the 1,505 in the Ciba study had atrazine concentrations exceeding the M C L federal standard of 3.0 ppb. Of these eight wells, three were located in Wisconsin, two were in Kansas and one well each was located in Indiana, West Virginia and Minnesota. The highest atrazine concentration (12 ppb) was found in a well in Wisconsin. Source investigations of these eight wells through site visits were conducted. Follow-up sampling of these wells confirmed that the detections exceeded 3 ppb. The three wells in Wisconsin had shown detections exceeding 3 ppb in the previous sampling program by the Wisconsin Department of Agriculture Trade and Consumer Protection (DATCP) (75). High concentrations in one well in Kansas and the well in West Virginia appeared to be caused by point-source contamination associated with a former mixing/loading site. Detection in the well in Indiana was probably caused by a very shallow water table (< 6 feet) and sandy soil. The reason for the high detection of atrazine exceeding 3 ppb in one well in Minnesota is unknown. The frequency distributions for the hydroxytriazine degradation products (hydroxyatrazine, desethylhydroxyatrazine, deisopropylhydroxyatrazine and ammeline) are shown in Figure 3. These results show that hydroxyatrazine was detected in 68 out of 1,505 wells (4.5%). The maximum concentration of hydroxyatrazine was found in a well in Indiana at 6.5 ppb. This well was also found to contain high levels of atrazine at 9.1 ppb as described above. Desethylhydroxyatrazine was detected in 42 wells (3.8%). Deisopropylhydroxyatrazine and ammeline were detected in only four and six wells in the entire study (0.3 and 0.5%, respectively). The low detections of hydroxytriazine degradation products in groundwater are in agreement with the adsorption/desorption studies which show that these degradation products are tightly bound in the soil substrate and are immobile. Regional Summary: A summary of atrazine monitoring data in the nineteen states participating in this program is shown in Figure 4. This graph also indicates the total number of wells in each state. The percentage of wells which show detections in each state is shown as % above the LOD. A brief discussion of these results is provided below: Two hundred private rural wells were sampled in Wisconsin by DATCP. Approximately 135 wells were selected by DATCP to meet the following objectives: a) to study the presence of atrazine and its degradation products in shallow private wells located near irrigated fields in the Central Sands regions of Wisconsin (43 wells); b) to resample wells from the DATCP Rural Well Survey that had previously exceeded Wisconsin's Enforcement Standard of 0.3 ppb for


233 (0.07%) (0.47%) (3.19%) (8.37%)

(0.53%)-| (4.58%) h (0.00%) (12.03%)

(11.83%) (11.69%)

(71.16%) (76.08%)


Atrazine

Deethylatrazine

• (0.00%) • (0.00%)

• (0.07%)

(0.73%)" (4.85%)(9.30%)-

(1.13%)—ι (4.12%) (9.77%) (8.97%)

(75.95%)

• (85.12%) Deisopropylatrazine

0.10-0.29 •

Diaminochlorotriazine

Concentration (ppb) 0.30-0.99 Γ | 1.00-2.99 • 3.00-9.99

10.00-19.99

Figure 2. Frequency Distribution of Atrazine and its Chlorotriazine Degradation Products (Total Number of Samples = 1505) (0.07%)

Γ

(0.20%) (1.13% (3.12%)

(0.60%) Η (2.19%)

(95.48%)

(0.00%) (0.00%)

• (97.21%)

Hydroxyatrazine

Deethylhydroxyatrazine (0.08%) (0.16%)—j (0.00%) (0.24%)

(0.13%)(0.13%)—i— (0.00%)

(99.73%) Deisopropylhydroxyatrazine

(99.53%) Diaminohydroxytriazine

Concentration (ppb) •

0.10-0.29

I

I 0.30-0.99

g!

1.00-2.99

•

3.00-9.99

Figure 3. Frequency Distribution of Hydroxytriazine Degradation Products of Atrazine (Total Number of Samples = 1505)



Figure 4. Summary of Atrazine Data for Ciba-Geigy/State Ground Water Monitoring Study



235 atrazine plus three chlorinated metabolites (44 wells); and c) to evaluate trace level triazine detections detected by immunoassay by splitting the sample with Ciba (48 wells). The remaining 65 wells were sampled for a variety of other reasons, such as responding to the well owner's request. Atrazine was detected in 97 wells (48%). A comparison of the changes in concentrations of atrazine and its chlorotriazine degradation products in 44 wells sampled earlier by DATCP showed significant decline in these levels over a three year period (75). One hundred-fourteen wells were sampled in Hawaii, primarily in the sugar cane producing areas using atrazine. Many of these wells had been sampled earlier for atrazine and some of its degradation products, and were chosen based on previous detections of atrazine by Hawaii Sugar Planters' Association (HSPA). Atrazine was detected in 37 wells (32%) with a maximum concentration of 1.8 ppb. The maximum concentration for desethylatrazine, deisopropylatrazine and diaminochlorotriazine in Hawaii were 1.5, 0.53 and 0.47 ppb, respectively. Atrazine was detected in 17 of the 31 wells sampled in Iowa (55%). The well selection in Iowa was based on documented atrazine detections in previous monitoring studies conducted by the Iowa Department of Agriculture. From a list of 100 wells with previous detections of atrazine, 31 wells were chosen based on well depth criteria. Atrazine was detected in 32 out of 89 wells in West Virginia. Significant detections in West Virginia were in corn producing areas of Mason and Jefferson counties where thirty wells were included based on positive detections of atrazine in a previous sampling program by the West Virginia Department of Agriculture. Six of these wells were sampled two to five times each to address temporal variability. The results of these additional samplings were in good agreement with the analysis in the first sampling. Atrazine was detected in 46 of the 187 wells sampled in Pennsylvania. Significant numbers of detections in Pennsylvania were in the karst valleys of the state's Ridge and Valley province and other limestone valleys of southeast Pennsylvania. Forty-nine wells were sampled in Maryland in high atrazine use areas. Of those, 24 wells were located in the coastal plains and the karst regions of the state and 15 of these wells were USGS observation wells in the eastern shore region. Atrazine was detected in 17 wells (35%). Well selection in Virginia included the Delmarva Peninsula, the southeast portion of the state and several counties in the Blue Ridge Mountain regions. Fifty-eight wells were sampled in Virginia which included five shallow USGS observation wells in Delmarva Peninsula. Atrazine was detected in only eight wells with a maximum concentration of 0.61 ppb. Thirty wells were sampled in Washington State in atrazine use areas of Christmas tree production. Priority was given to wells with previous detections of atrazine, such as the detections of triazines in the Chehalis River Basin using the immunoassay screens. Atrazine was detected in three out of the 30 wells sampled in Washington State with a maximum concentration of 0.22 ppb. Of the 91 wells sampled in high atrazine use areas in Mississippi, one well showed detection of atrazine at 0.60 ppb. Resampling of this well confirmed the


236


detection. Fifty-two wells were sampled in corn and sugarcane use areas of Florida including the sandy regions in north central Florida, the Florida panhandle, sugarcane use areas south of Lake Okeechobee and corn growing regions in southern Dade county. Atrazine was detected in four wells (8%) with a maximum concentration of 0.25 ppb. Fifty wells were chosen in Louisiana in representative crop growing regions for rice, sugarcane, cotton and soybeans. Also, twenty wells were monitored in Texas in the Brazos River alluvium area, southern High Plains and Ogollala aquifer area (south of Lubbock), and Gulf Coast. No detections of atrazine or its degradation products were found in either Louisiana and Texas. Ratio of Atrazine Degradation Products to Atrazine: Ratios of the levels of desethylatrazine, deisopropylatrazine and diaminochlorotriazine as a function of atrazine levels were computed to determine a relationship between these variables. Detections below the LOD were excluded in this analysis. It has been proposed that a ratio of desethylatrazine to atrazine (DAR) greater than unity is an indicator of nonpoint source contamination (14). The DAR hypothesis is predicted on the assumption that atrazine degrades slowly in the vadose zone to desethylatrazine and the later has higher mobility than the parent compound. Adams and Thurman (12) hypothesized that a small D A R ratio may be an indicator of point-source contamination of an aquifer. Distribution of the desethylatrazine to atrazine ratios for all the detections of atrazine shows that the high values of atrazine (> 3.0 ppb) have a DAR value close to zero. Similarly, when atrazine is near the detection limit of 0.10 ppb, the DAR ratio for some wells were significantiy greater than unity. However, these data were extreme values in the distribution and the correlation between the D A R and atrazine concentrations was poor (R square value of 0.051). The DAR hypothesis may be valid as a generalized statement; however, a number of factors may cause variation of the DAR. Some of these factors include preferential flow (such as macropores), surface water interactions, lack of degradation in highly permeable soils, history of atrazine use at the site, etc. The ratios of deisopropylatrazine to atrazine and diaminochlorotriazine to atrazine were calculated to attempt a relational analysis. The conclusions from these distributions were similar to results of D A R ratios. An evaluation was made of the distribution of desethylatrazine with deisopropylatrazine in all the wells in the nineteen states participating in this program. The ratio of deisopropylatrazine to desethylatrazine (referred to as D2R) has been suggested by Thurman (12) as typically less than unity because of preferential degradation of atrazine by desethylation instead of deisopropylation. A D2R ratio greater than unity suggests the formation of deisopropylatrazine from other sources such as cyanazine or propazine instead of atrazine. The distribution of deisopropylatrazine vs. desethylatrazine shows that a large number of wells have D2R ratios less than unity (desethylatrazine levels > deisopropylatrazine). However, a small number of wells in the extreme show D2R ratios > 1 which may be caused by sources other than atrazine. Pesticide


237 use history in the area where these wells were found could assist in determining the source for the greater detection of deisopropylatrazine.


Conclusions and Research Needs Ciba has completed a large-scale groundwater monitoring program for atrazine and its degradation products in the United States. This monitoring has been conducted in nineteen major atrazine use states with over 1,500 wells selected based on high atrazine use, groundwater vulnerability, and previous atrazine detections. The well selection in this study was highly biased for positive detections because of the targeted well selection process used by these states and hence, these monitoring data cannot be used for accurate extrapolation of exposure estimates for the general population using rural drinking water wells. This study has provided extensive groundwater monitoring data for atrazine and its chloro and hydroxytriazine degradation products in a very large geographic area where these detections are expected. This study was conducted in cooperation with the various state agencies and involving the states very effective for addressing the data gaps on atrazine degradation products in groundwater. The state agencies and their affiliates have also benefited from this program through training in the sample collection and GLPs related to the field phase of groundwater monitoring. Results from this study can be used to facilitate the design and implementation of site-specific water management plans and product stewardship activities to protect groundwater. Acknowledgment The authors wish to thank the nineteen state agencies and affiliates who participated in this study, Environmental and Public Affairs of Ciba and Quality Associates, Inc., for the technical support of the field phase. The authors also wish to thank the Biochemistry Resources Department of Ciba for performing the GC/MSD analyses of chlorotriazines; and Alta Analytical Laboratory Inc. and ABC Laboratories Inc. for performing the LC/MS/MS analyses of hydroxyatrazines. Literature cited 1.

2. 3.

Balu, K., Paulsen, R. T. In Interpretation of Atrazine in Ground Water Data Using a Geographic Information System; Weigmann, D. L., Ed.; Pesticides in the Next Decade: The Challenges Ahead, Proceeding of the Third National Research Conference on Pesticides, Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, Blacksburg, VA, November 8-9, 1990. U.S. Environmental Protection Agency, National Survey of Pesticides in Drinking Water Wells, Phase 1 Report, Report No. EPA/570/09-90/015. Holden, L. R., et al. Environ. Sci. And Technol. 1992, Vol. 26, pp. 935943.


238 4. 5.


6.

7.

8. 9. 10. 11. 12. 13. 14. 15.

Kross, B. C. et. al., The Iowa State-wide Rural Well Water Survey - Water Quality Data, Initial Analysis, Iowa Geological Survey Technical Information Series Report No. 19, 1990, pp. 1424. LeMasters, Gary, and D. J. Doyle, Grade A Dairy Farm Well Water Quality Survey, Wisconsin Department of Agriculture, Trade and Consumer Protection, Madison, Wisconsin, 1990, pp. 36. Detroy, M. G., P. Κ. B. Hunt, and M. A. Holub, Ground-Water Quality Monitoring Program in Iowa: Nitrate and Pesticides in Shallow Aquifers, Proceedings of the Agricultural Impacts in Ground Water, National Water Well Association, Dublin, Ohio, 1988, p. 255-278. Klaseus, T. G., G. C. Buzick and E. C. Scheider, Pesticides and Groundwater: Survey of Selected Minnesota Wells, Minnesota Department of Health and Minnesota Department of Agriculture, Minneapolis, MN, 1988, pp. 95. California Environmental Protection Agency, Sampling for Pesticides Residues in California Well Water - 1993 Update, Department of Pesticide Regulations, Sacramento, CA, 1993, pp. 167. Spalding, R. F.; Burbach, M. E.; Exner, M. E. Ground Water Monitoring Review. 1989, Vol. 9, pp. 126-133. Maas, R. P., et. al. J. Environ.Qual.1995, Vol. 24, pp. 426-431. Domagalski, J. L.; Dubrovsky, Ν. M. Journal of Hydrology, 1993, Vol. 130, pp. 299-338. Adams, C. D.; Thurman, E. M. J. Environ. Qual. 1991, Vol. 20, pp. 540-547. Mills, S. Margaret; Thurman, Ε. M. Environ. Sci. Technol. 1994, Vol. 28, pp. 600-605. Winkelmann, D. Α.; Kline, S. J. Environmental Toxicology and Chemistry, 1991, Vol. 10, pp. 347-354. Postle, J., 1994. "Report on the DATCP/Ciba-Geigy 200 Well Sampling Program," Wisconsin Department of Agriculture, Trade and Consumer Protection, Madison, WI.


Summary of Ciba Crop Protection Groundwater Monitoring Study for

Recommend Documents