Estimation of Inhalation Exposure to N-Nitrosodipropylamine during the Application and Incorporation of the Herbicide Trifluralin Edgar W. Day, Jr.,* Donald G. Saunders, James W. Mosler, Edward M. McKlnney, Fred L. Powers, Richard D. Griggs, and Richard Frank Lilly Research Laboratories, Division of Ell Lllly and Company, Greenfield, Indiana 46140
The discovery of N-nitrosodi-n-propylamine (NDPA), a volatile nitrosamine in the herbicide trifluralin, prompted an investigation into the possible exposure of field workers to the contaminant. The potential for inhalation of the nitrosamine during and following application of the herbicide was evaluated. Experiments were conducted in which personal air monitors were attached to workers while applying herbicide containing 2-6 ppm of NDPA. To more closely approximate the inhalation rate of field workers, additional experiments were conducted with high-volume pumps mounted on tractors and placed in treated fields. Sampling and analytical techniques are described. The results of these experiments demonstrated an extremely low level of exposure potential. Introduction In September 1976, Fine et al. (1) reported on their discovery of the presence of volatile nitrosamines in certain pesticide formulations. The United States Environmental Protection Agency subsequently examined a number of pesticide products (2,3) and observed N-nitroso compounds in several products, including a number of dinitroaniline herbicides. One of the products analyzed was Treflan EC (trifluralin, Elanco Products Co., Division of Eli Lilly and Co.) which was found to contain approximately 150 ppm of N-nitroso-di-n-propylamine (NDPA). In conjunction with the initial observation (1,4), no NDPA was detected in the air, water, or crops following application of Treflan to a tomato field. NDPA has been shown to be carcinogenic in laboratory animals (5-8) and is thus a potential hazard to man. Data reported previously (9-11) indicated that consumers of crops grown in fields treated with NDPA-containing trifluralin were not subject to any detectable exposure to the nitrosamine. Likewise, potable waters from treated areas and the principal US manufacturing site (10, 11)demonstrated no nitrosamine exposure. Ross et al. (9) took air samples during the application of trifluralin and did not detect nitrosamines. However, the sampling system employed was not mobile and did not truly reflect the potential exposure of the applicator to the nitrosamine contaminant. In order to evaluate exposure to the nitrosamine contaminant in the spray suspension, it was deemed necessary to sample the environment in the vicinity of the tractor (or truck) driver during the application of the product in 0013-936X/82/0916-0131$01.25/0
typical use situations. Exposure via inhalation was of particular interest since nitrosamines are known to exhibit high vapor pressures and readily volatilize from soil (12, 13). Reported herein are the techniques used and the analytical results from a number of experiments conducted to measure the possible inhalation exposure of workers to NDPA resulting from the use of trifluralin. Operators were monitored while applying herbicide with several equipment configurations and in a number of typical geographic locations. Workers responsible only for the herbicide mixing and spray tank loading operations were monitored separately in two experiments. In one experiment, air samplings were taken during a second disking conducted 3 days after treatment. The air over this treated field was also monitored for NDPA and trifluralin during a 9-day period to estimate the potential exposure to workers who may enter a field after herbicide application. Experimental Section Two sets of experiments were conducted. Set I consisted of nine experiments in which the breathing zone of the operators was monitored with battery-powdered personal air samplers while the herbicide wa8 being applied. Set I1 consisted of seven experiments in which the air sampling rate more closely approximated the breathing rate of tractor driver. A summary of the general experimental conditions in the 16 experiments is presented in Table I. Applicator or grower equipment was used to apply the herbicide at the recommended rate for the crops and soil type. In some cases, application and incorporation of the herbicide were a simultaneous operation while in others they were carried out sequentially. In the latter case, both the spray applicator driver and the incorporation driver were monitored. Air Sampling Apparatus and Procedures. Set I. In the first set of experiments, air samples were taken with portable air sampling pumps (Bendix Model BDX44) connected to activated charcoal tubes (No. 226-09, SKC, Inc.). The pumps were clipped to the belt of the worker, and the charcoal tubes were clipped to the front of the worker's shirt to collect air from his breathing zone. Field collection efficiencies were determined in each of the experiments by placing 10 pL of a hexane solution containing 0.022 pg of NDPA and 0.20 pg of trifluralin just inside each of four freshly opened charcoal tubes. The pumps were turned on before placing the solutions in the
0 1982 American Chemical Society
Environ. Sci. Technol., Vol. 18,
No. 3, 1982 131
Table I. Field Conditions for NDPA Air Monitoring Experiments expt no.
date
location
current (or planned) crop
I-1 1-2 I-3 1-4 I-5 1-6 1-7 1-8 1-9 11-1 11-2 11-3 11-4 11-5 11-6 11-7
5/77 6/77 6/77 6/77 6/77 6/77 6/77 7/77 7/77 917 7 9/77 10177 10177 10177 10177 10177
Flat Rock, IN Horn Lake, MS Hernando, MS Fulton, KS Breckenridge, MI Dixon, CA Davis, CA Cutler, CA Cutler, CA Huron, CA Huron, CA Queen Creek, A 2 Chandler Hts, AZ Ferris, TX Ferris, TX Knightstown, IN
(soybeans) (soybeans) (soybeans) (soybeans) (dry beans) sugar beets tomatoes plums nectarines (cotton) (cotton) pecan grapefruit (cotton) (cotton) (soybeans)
acreage treated
appl/incorpa
40 40 70 70 40 45 20 30 31 70 80 45 30 80 65 16
separate simultaneous simultaneous separate simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous separate
a Indicates whether application and incorporation of the herbicide were accomplished in separate or simultaneous operations.
tubes so that all of the volatilized materials could be collected on the charcoal. These pumps and tubes were placed upwind from the treatment field along with two pumps and tubes which had not been spiked. These latter tubes served as blanks (controls) for each experiment. Set 11. The sampling of air in the vicinity of workers in the set I1 experiments was accomplished by pulling air through glass tubes packed with charcoal using an electric pump (Bendix Model 25004) powered by a gasoline generator. The tubes were 18 cm X 1.8-cm i.d. glass packed with an 8-g front section and a 2-g back section of charcoal separated with glass wool. The charcoal (PCB grade, 20-50 mesh, Calgon, Corp., Pittsburgh, PA) was baked 16 h at 200 "C, and portions were extracted and analyzed for thermal energy analyzer (TEA) responsive substances before use. The tubes were packed just before the initiation of each experiment and were wrapped in aluminum foil to exclude direct sunlight. Eight tubes were packed for each experiment. Four of the tubes were mounted on the tractor approximately 0.5 m from the head of the operator and were connected to a single pump. Before placement in an inverted position, 0.5 pg of dipropylamine (DPA) in 0.1 mL of hexane was placed just inside the inlet of two of the tubes and air flow commenced immediately. This enabled the DPA to volatilize onto the charcoal to permit a check on potential artifact formation during the experiments. For sampling the air over a treated field (experiment 11-7), two blank and two DPA-spiked tubes were mounted in an inverted position about 0.5 m above the surface of the soil, and the pump was operated between 8:OO a.m. and 8:OO p.m. if weather conditions permitted. During all experiments, four other packed tubes were used at the control site, which was located upwind but adjacent to the experimental field. The tubes were mounted on a ring stand and connected to a Model 25004 pump via rubber tubing. One of the tubes was a blank, one was spiked with 0.5 pg of DPA, and the other two were fortified with NDPA (0.05 pg) and trifluralin (0.2 pg) to determine field collection efficiencies. The driver of the application equipment in the set I1 experiments performed none of the mixing and loading operations. Exposure to the worker performing these tasks was evaluated in experiments 11-3 and -4. Four charcoal tubes were attached to the shirt of this worker. The tubes were connected to another pump via a harness of rubber tubing which permitted him to carry out his required tasks. 132
Envlron. Scl. Technol., Vol. 16, No. 3, 1982
7 *.
C.
B.
0.
2 z 0
6
4
2
0
6 4 2 0
J-f
2 0 z
AP
-1111 6 4 2 0 6 4 2 0
TIME (MINUTES1
Figure 1. GC-TEA chromatograms, small (600 mg) charcoal tubes: (A) direct standards, NDPA (0.054 pg/mL) and DMNA (0.038 pg/mL); (B) blank charcoal extract; (C) field recovery, experiment 11-5, 105%; (D) air sample from breathing zone of operator, experiment 11-5, response for 0.11 pg of NDRA on contents of single tube. All injection volumes, 50 pL. TEA attenuation, X4.
This sampling was conducted during each fill operation (approximately every 1.5-2.0 h) with the same set of tubes. Thus, the results are the cumulative exposure for 1 day of mixing and loading. Analytical Methodology. All samples collected in these experiments were analyzed for both NDPA and trifluralin. All NDPA measurements were made with a gas chromatography-thermal energy analyzer (GC-TEA) system using appropriate modifications of the methods of West and Day ( I I ) , and trifluralin determinations were carried out by electron capture gas chromatography methods similar to those of Tepe and Scroggs (14).Some representative GC-TEA chromatograms are presented in Figures 1and 2.
Results and Discussion Collection Efficiency, The efficiency of activated charcoal as a collection medium for NDPA was determined in the laboratory before the field experiments. The collection was nearly quantitative using both the small pumps with the small tubes and the large pumps with the large tubes for 0.1-1.0 pg of NDPA. The efficiency for the collection of trifluralin vapor was also quantitative at the
Table 11. Field Collection Efficiencies for NDPA and Trifluralin amt added, p g air sampling expt no. NDPA trifa time, h
a
I-1
0.022
0.20
5.5
0.55
1-2
0.022
0.20
7.5
0.68
1-3
0.022
0.20
6.0
0.58
1-4
0.022
0.20
5.0
0.50
I-5
0.022
0.20
7.8
0.75
1-6
0.022
0.20
7.8
0.77
I-7
0.022
0.20
8.0
0.77
1-8
0.022
0.20
7.0
0.69
1-9
0.022
0.20
8.0
0.78
11-1 11-2 11-3 11-4 11-5 11-6 11-7 11-7(2nd)
0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05
0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20
6.5 7.3 6.5 6.0 3.5 3.0 4.0 3.0
5.23 5.69 5.54 5.11 2.52 2.16 2.83 2.30
Trifluralin.
% collection efficiency
av vol of air, m3
NDPA
triP
65,70 70,100 49,65 50,55 75,95 75,85
91,68 86,86 91,100 95,91 105,95 114,105 109,109 123,118 68,105 109,105 127,118 114,118 109,109 118,114 105,100 95,86 95,86 100,91 88,40 68,58 36,72 100,72 64,72 86,96 98,104 100,94
b
95,85 75,95 115,120 115,115 95,115 160,115 70,75 9,lO 85,95 85,85 95,85 b
90,78 b
54,55 97,89 108,81
125,85
Interferences or contamination observed in these samples.
Table 111. Results of Monitoring the Breathing Zones of Field Workers during the Application of Treflan Low-Volume Sampling Experiments obsd. concn in air: pg/m3 expt Treflan rate, NDPA in spray boom sampling av air no. lb/acre Treflan, ppm position field worker time, h vel: m3 N D P A ~ trifC
a
1-1
1.0
4.6
rear
I-2
1.0 0.5 1.0
3.8
1-3 1-4
3.8 3.0
rear belly rear
1-5 1-6 1-7 1-8 1-9
0.5 0.75 0.75 2.0 2.0
4.6 3.4 3.3 2.0 2.0
front bellv rear front front
Average of two or four values.
applicator incorporator applicator applicator applicator incorp 1 incorp 2 applicator applicator applicator applicator applicator
ND ND ND ND ND ND ND
0.14 0.40 0.75 0.59 0.19 0.34 0.39 0.76 0.67 0.67 0.70 0.79
1.5 4.0 8.0 6.0
2.0 4.0 4.0 7.75 8.0
0.016 ND
8.0 ND 7.0 ND 8.5 ND ND = none detected at a test sensitivity of 0.005 p g per adsorber tube.
1-pg level and greater than 90% a t the 20- and 100-pg levels. The laboratory findings were generally supported by the recoveries observed in the field, which are listed in Table 11. In the nine set I experiments, the NDPA field recoveries ranged from 68% to 127% with an average of 102%. For trifluralin, the range was 49-120% (ignoring the anomalous values in experiments 1-8 and 1-7) with an average of 97%. The collection efficiencies using the larger equipment ranged from 36 to 104% for NDPA and from 54 to 125% for trifluralin. The averages were 78% and 87% for NDPA and trifluralin, respectively. The variations and losses observed in field are most likely due to experimental handling difficulties under field conditions rather than deficiencies in the trapping medium itself. Low-Volume Sampling. The results of monitoring the breathing zones of the workers in the set I experiments are presented in Table 111. In each of these nine trials, the herbicide was applied at the recommended rate for the specific crop and soil type in accordance with the farmer’s
-
6 4 2 0
0-6
,29.3 1.1 9.8 4.3 62.7 2.3 5.0 22.7 13.5 10.5 7.9 11.9 Trifluralin.
--
6
4
2
0
6 4 2 0
TIME (MINUTES)
Figure 2. GC-TEA chromatograms, large charcoal (8 g) tubes: (A) direct standard NDPA, 0.025 pg/mL; (B)fieid control charcoal, experiment 111-4; (C) field recovery, 0.05 pg NDPA (72% efficiency); (D) air sample, breathing zone of tractor driver, response of 0.024 pg of NDPA. All Injection volumes, 50 pL. TEA attenuation, X4. Environ. Scl. Technol., Vol. 16, No. 3, 1982
133
Table IV. Results of Monitoring the Breathing Zones of Field Workers during the Application of Treflan High-Volume Sampling Experiments expt no.
Treflan rate, Ib/acre
NDPA in Treflan, ppm
11-1
0.69
3.7
driver
7.1
12.9
5.44
11-2
0.69
3.7
driver
7.3
12.6
5.54
11-3
2.0
3.6
driver
7.1
13.3
5.65
mixer
1.1
12.0
0.78
driver
6.9
13.2
5.42
mixer
1.0
10.9
0.63
11-4
2.0
3.6
worker monitored
sampling sampling time, h rate, L/min
amt collected,a Mg air v01, m3 NDPAb trifC
11-5
1.3
6.4
driver
6.4
12.7
4.89
11-6
1.3
3.5
driver
5.6
12.7
4.25
11-7
1.0
4.3
driver (a p + inc) driver (2nd disking)e
4.8
12.0
3.42
2.8
12.3
2.03
B
0.020 0.025 0.019 0.032 ND ND ND ND ND ND 0.037 0.028 0.008 0.006 0.009 ND 0.029 0.026 0.01 2 0.011 ND ND ND ND
185 203 130 164 22 18 13 6.5 25 30 117 87 13 14 17 18 139 111 84 83 6.7 5.7 0.24 0.32
av concn in air, pg/m3 NDPA trifC 0.0037 0.0046 0.0034 0.0058
