Biomarkers of Human Exposure to Pesticides - ACS Publications

Chapter 15

Dermal Absorption and Disposition of Formulations of Malathion in Sprague—Dawley Rats and Humans 1

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Curtis C. Dary , Jerry N. Blancato , Mark Castles , Viyayapal Reddy , Michael Cannon , Mahmoud A. Saleh , and Gordon G. Cash Downloaded by NORTH CAROLINA STATE UNIV on September 8, 2012 | http://pubs.acs.org Publication Date: November 23, 1993 | doi: 10.1021/bk-1992-0542.ch015

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Exposure Assessment Research Division, Environmental Monitoring Systems Laboratory, U.S. Environmental Protection Agency, Las Vegas, NV 89109 Department of Life Sciences, Midwest Research Institute, Kansas City, MO 64110 Environmental Chemistry and Toxicology Laboratory, Department of Chemistry Texas Southern University, Houston, TX 77004 Office of Pesticides and Toxic Substances, Chemical Management Division, U.S. Environmental Protection Agency, Washington, DC 20460 2

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Dermal absorption of neat malathion, a 50% emulsifiable concentrate (50% EC), and a 1% and 10% aqueous mixture of the 50% EC formulation was examined in human volunteers. The absorption and elimination profiles of[ C]-malathionequivalents in the urine of the human were compared with the rat. Constants of absorption and elimination were calculated. Distribution of[ C]-malathionequivalents in selectedtissueswere examined in the rat. The 50% EC formulation was absorbed as readily as the neat malathion. The absorption of the organic based formulations was influenced by the increase in the surface area of the site of application. The total cumulative absorption was concentration dependent. The rate of absorption of the neat malathion, the 50% EC formulation, and 10% aqueous mixture was less than the rate of elimination resulting in a depletion of the body burden. The rate of absorption and elimination of the 1% aqueous mixture were coincident The elimination of malathion was efficient and independent of surface area, concentration, and formulation. The disposition of malathion favored organs of metabolism and elimination, liver and kidney. A substantial portion of the dose remained at the site of application. The results suggest that acute human toxicity could occur from handling the concentrate when a substantial portion of the exposed skin is contaminated. Acute toxicity from contact with surfaces treated with the aqueous mixtures would be unlikely. Repeated exposure, however, could burden organs of metabolism and elimination, skin, liver and kidney. 14

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Human exposure to insecticides used in the residential non-occupational marketplace may occur during mixing the concentrate by the untrained consumer or from contact with treated surfaces upon re-entry in treated microenvironments. The rate

0097-6156/94/0542-0231$09.25/0 © 1994 American Chemical Society

In Biomarkers of Human Exposure to Pesticides; Saleh, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.

Downloaded by NORTH CAROLINA STATE UNIV on September 8, 2012 | http://pubs.acs.org Publication Date: November 23, 1993 | doi: 10.1021/bk-1992-0542.ch015

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BIOMARKERS OF HUMAN EXPOSURE TO PESTICIDES

of dermal absorption, disposition, and elimination of a contacted dose would greatly impact on the analysis ofrisk(1). Without such information, understanding the human activities that relate to therateof contact and transfer ofresiduesare not as meaningful (2-5). Dislodgeable residues, even if contacted and entirely transferred to the skin, may not be appreciably absorbed and when absorbed may bereadilyand efficiently eliminated (5-7). Understanding bioavailability of selected pesticides could greatly reduce the need and the associated cost of environmental monitoring (4). The elimination half-times and cumulative percent of the dermal dose of certain pesticides excreted indicate a peat deal of variation in therateof clearance (1,8). The percent of the dermal dose variesfrom0.18% for diquat and 0.50% for aldrin to as much as 12.5% and 15.9% for azinphos-methyl (Guthion) and propoxur (Baygon) respectively (1). These results suggest that no more than 15% of a dermal dose of a given pesticide is absorbed and eliminated in urine. However, intravenous and intraperitoneal doses are efficiently eliminated in urine (8-9). The human studies protocol using the indirect method of adjustment for incomplete metabolism (8-9) does not account for evaporative and mechanical loss and retention of the dose at the skin surface and the epidermis (10). This study was designed to determine the rates of absorption and elimina tion of malathion as an organic concentrate and aqueous mixture when applied to the ventral forearms of human volunteers. The additional aim was to account for the dermal dose on the surface of the skin and epidermis of the human. When additional information on the disposition of malathion intissuesappeared compel ling, a limited dermal absorption study was conducted in the rat. The overall purpose of the study was to compare the absorption kinetics of the organic based concentrates that impact on mixer/loader activities and contact and transfer of surface (wet) aqueous mixtures that mightresultfrom exposure upon re-entry. Methods Human Exposure Study. Twelve healthy men and women ages 21 to 35 years were selected to participate in this study. The subjects were briefed on the goals, procedures, risks and benefits of participation. Each subject received a physical examination. The subjects were reported to have no history of acute or chronic disease or disability or previous exposure to malathion within the last six months. The subjects were admitted to the study upon receiving their written informed consent. Recruitment, selection and testing complied with U.S. EPA Order 1000.17, "Policy and Procedures for Protection of Human Subjects in Biomedical and Behavioral Research". Experimental Design. The subjects were divided into two groups of six. Each subject within a group would receive a nominal dose of a particular dosing solution of [ C]-malathion applied to a 4.6cm2 area of the ventral forearm (Table I). After completing the exposure and urine collection period for the first application, the subjects were allowed torestfor two weeks prior to the application of the second dosing solution. Pre-dose urine was examined for residual radioactiv ity prior to dosing. Thus individuals in group A thatreceivedneat malathion in the first application received the 1.0% aqueous mixture in the second application as members of group C. Individuals in group Β receiving the concentrated commercial formulation in the first application received the 10.0% aqueous mixture in the second application as members of group D. 14

Test and Control Articles. [i4C]-Malathion(31.^Ci/mg) was obtained from Sigma Chemical Company, St. Louis, Missouri. The radiochemical purity was confirmed as 98.3% by reverse phase HPLC with a Perkin-Elmer In Biomarkers of Human Exposure to Pesticides; Saleh, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.


d

Mixture of radiolabeled malathion with 1% diluted commercial product (1% malathion) in tap water.

Mixture of radiolabeled malathion with 10% diluted commercial product (5% malathion) in tap water.

d

100

15

50

c

1.2

34.2 μg/cm

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20

Mixture of radiolabeled malathion with undiluted commercial product (EC Malathion 50).

5.5

157.1 Gig)

5.6

5.4

Dose Volume (μΐ)

b

5.70

2.45

25.7

24.6

(mg/cm )

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Malathion

Mixture of radiolabeled and nonradiolabeled malathion (neat).

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6

7.25

7.24

Dose Levels Malathion (mg)

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10% mixture

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D

6

0

50% E C

Β

1% mixture

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Neat*

A

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Table I. Experimental Design and Dosing Solutions Number Nominal of Dosing Groups Subjects Solution c (μΟί)



234

BIOMARKERS OF HUMAN EXPOSURE TO PESTICIDES

LC55B variable wavelength detector at 230 nm and a Radiomatic Flo-One HewlettPackard radiochemical detector. The system was equipped with a Spherisorb ODS2 reverse-phase Q s column ( 150 mm χ 4.6 mm, ID 5 μπι). A Cig guard column (Brownlee, 15 mm χ 3.8 mm, ID) was placed ahead of the analytical column. The mobil phase (0.2% trifuoroacetic acid in water [A] / 0.1% trifluoroacetic acid in acetonitrile [B] ) was delivered at 1.0 mL/min with a Perkin-Elmer Model 250 binary pump. The HPLC/radiochemical column eluent was collected and diluted with scintillation cocktail for liquid scintillation counting (LSC) on a Packard Tricard Model 4530. Standards were preparedfromaliquots of the sample solution used for chromatographic analysis. The radiochemical purity was determined as the percentage of the malathion peak to the total radioactivity. Columnrecoverywas determined as the percentage of radioactivity elutedfromthe column as compared to the direct measurement of 100 pL of the standard by LSC. The non-labeled malathion was obtained from Chem Service Inc., West Chester, Pennsylvania. The commercial product, Ortho Malathion 50, containing 50% malathion by weight was purchased over the counterfroma department store in the Kansas City area. Dose Preparation. The dosing solutions were prepared separately three to four hours before dosing. The [i C]-malathion in toluene wasreducedto near dryness andresuspendedin non-labeled malathion to yield a predetermined amount of radioactivity for each dosing solution (Table I). Before dose application, aliqouts of the dosing solution were counted to determine final radioactive content. 4

Dose Application. Baseline urine samples were collected prior to dosing. In preparation to dosing, each subject's arm was washed once with soap and water and allowed to air dry. A 4.6 cm test area was outlined with a graphite pencil on the ventral forearm. The dose was applied within the test areafromthe lure tip of a glass Hamilton Gas-Tight microliter syringe. The weight of the loaded syringe was obtained prior to application and again following the delivery of the dose to determine the final weight of the dose delivered. The final dose adminis tered was adjusted for loss of dosing solution due to running of the neat and concentrated commercial formulation(Table Π). The application site was observed for four hours after application for spreading of the test substance beyond the test area. The area of application was adjusted to reflect spreading of the neat and commercial formulation(Table II). At the conclusion of the four hour period of observation, the test area was covered with an occlusive patch. 2

Sample Collection. Collection intervals were based on the time from dose application. Urine was collected at four hour intervals up to 12 hours post application(Table Π). After 12 hours of exposure, urine was collected and pooled at 12 hour intervals. The site was examined after 24 hours and gently washed two times with soap and water andrinsedthree times to remove only the residual amount of the applied dose and not any of the material that had penetrated the integument. The gauze sponges used to clean the site and the occlusive patches and contaminated bench paper were extracted in methanol to obtain residual site concentrations. Radiochemical Analysis. Aliquots of urine(2.0g) were prepared in duplicate for LSC. The well mixed samples were prepared in 10 mL Ultima Gold® (Packard, Downers Grove, Illinois) scintillation cocktail. The vials were kept at 8*C for 24 hours prior to LSC for 10 minutes on a Packard, Model 2000CA liquid scintillation spectrophotometer. Counts per minute(CPM) were corrected for In Biomarkers of Human Exposure to Pesticides; Saleh, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.


17.50 20.90 18.80 13.90 7.85 11.80

Bl B2 B3 B4 B5 B6

Sub.

Slte

Biomarkers of Human Exposure to Pesticides - ACS Publications

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