Health Hazard Evaluation Report 2015-0111-3271 Page 1

Evaluation of Potential Hazards during 

Harvesting and Processing Cannabis at an 

Outdoor Organic Farm

HHE Report No. 2015-0111-3271

April 2017

James Couch, PhD, CIH, CSP, REHS/RS

Kerton Victory, PhD, MSc

Brian Lowe, PhD

Nancy C. Burton, PhD

Brett J. Green, PhD

Ajay Nayak, PhD

Angela R. Lemons, MS

Donald Beezhold, PhD

U.S. Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health
Page 2 Health Hazard Evaluation Report 2015-0111-3271

Contents

Highlights...............................................i

Abbreviations ..................................... iii

Introduction......................................... 1

Methods ............................................... 4

Results and Discussion........................ 6

Conclusions........................................ 16

Recommendations............................. 17

Appendix A ........................................ 19

Appendix B ........................................ 21

Appendix C ........................................ 23

References ......................................... 25

Acknowledgements........................... 31

The employer is required to post a copy of this report for 30 days at or near the 

workplace(s) of affected employees. The employer must take steps to ensure 

that the posted report is not altered, defaced, or covered by other material.

The cover photo is a close-up image of sorbent tubes, which are used by the HHE 

Program to measure airborne exposures. This photo is an artistic representation that may 

not be related to this Health Hazard Evaluation. Photo by NIOSH.
Health Hazard Evaluation Report 2015-0111-3271 Page i

We evaluated cannabis 

harvesting and processing tasks 

at an outdoor organic cannabis 

farm. If hand trimming tasks are 

performed for longer periods 

than we observed, the repetitive 

hand motions create a risk for 

hand and wrist musculoskeletal 

disorders. Tetrahydrocannabinol, 

the psychoactive component 

in cannabis, was detected on all 

surface wipe samples. Botrytis 

cinerea, a plant pathogen that can 

cause allergic reactions in exposed 

individuals, was the predominant 

fungal species identified. 

Highlights of this Evaluation

The Health Hazard Evaluation Program received a request from a union representative for 

an outdoor organic cannabis farm. The representative was concerned about the potential 

occupational and safety hazards associated with harvesting and processing cannabis.

What We Did

● We visited the farm in August and October 2015.

● We observed work practices and evaluated ergonomic aspects of harvesting and 

processing tasks.

● We collected air samples for microbes and endotoxin (products released by some bacteria).

● We collected surface wipe samples for 

tetrahydrocannabinol.

● We interviewed employees about their work, 

health, and safety concerns.

● We observed demonstrations for machine 

trimming and nitrogen sealing.

What We Found

● Employees were concerned about repetitive 

hand motions when trimming cannabis. 

● Some hand trimming activities required a lot of 

hand motions, but not a lot of force. 

● Botrytis cinerea was the main fungal species in 

the air.

● Actinobacteria was the most frequently 

identified bacterial phyla in the air.

● We found tetrahydrocannabinol in every 

surface wipe sample. 

● Endotoxin concentrations were all below the 

occupational exposure limit.

What the Employer Can Do

● Change hook line hanging heights to correspond with typical stem length and employee 

working technique.

● Provide frequent breaks for employees when they are trimming cannabis by hand.

● Develop a plan to rotate employees among jobs that use different muscle groups.
Page ii Health Hazard Evaluation Report 2015-0111-3271

● Train employees on tool cleaning, lubrication, sharpening, and maintenance.

● Develop a cleaning schedule to remove tetrahydrocannabinol from work and tool surfaces.

What Employees Can Do

● Wear nonlatex gloves when handling cannabis, cannabis products, or equipment that 

contacts cannabis.

● Wash your skin with soap and water after removing gloves.

● Clean work surfaces after processing cannabis material.
Health Hazard Evaluation Report 2015-0111-3271 Page iii

Abbreviations

μg Microgram

μg/100 cm2 Micrograms per 100 square centimeters

μg/mL Micrograms per milliliter

μL Microliter

ACGIH® American Conference of Governmental Industrial Hygienists

CFR Code of Federal Regulations

cm2 Square centimeters

DECOS Dutch Expert Committee on Occupational Safety

DNA Deoxyribonucleic acid

EU Endotoxin unit

EU/m3 Endotoxin units per cubic meter

lbs Pounds

mL Milliliter

NA Not applicable

ND Not detected

NIOSH National Institute for Occupational Safety and Health

OEL Occupational exposure limit

OSHA Occupational Safety and Health Administration

PCR Polymerase chain reaction

PEL Permissible exposure limit

rDNA Ribosomal deoxyribonucleic acid

REL Recommended exposure limit

THC delta-9-tetrahydrocannabinol

TLV® Threshold limit value
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Health Hazard Evaluation Report 2015-0111-3271 Page 1

Introduction

The Health Hazard Evaluation Program received a request from the United Food and Commercial 

Workers International Union to evaluate potential hazards associated with harvesting and 

processing cannabis, commonly known as marijuana, at an outdoor organic farm. We visited the 

farm in August and October 2015. We evaluated ergonomic, chemical, and microbial hazards and 

conducted medical interviews with employees about their health concerns.

Background

The farm was located in the state of Washington, which has legalized cannabis for medicinal and 

recreational use. At the time of our evaluation, the farm was operated by the owner and three 

employees. The 5-acre farm grew organic cannabis, vegetables, and fruits without pesticides. The 

farm grew Cannabis sativa, Cannabis indica, and a Cannabis sativa/indica hybrid.

Chemical and Biological Exposures in Outdoor Farming 

Environments 

Outdoor farming environments have numerous potential occupational exposures of concern. 

We focused our evaluation on three exposures: endotoxins, microbial biodiversity (fungi 

and bacteria), and delta-9-tetrahydrocannabinol (THC). Endotoxins are lipopolysaccharide 

compounds that may be released by the outer cell walls of Gram-negative bacteria and can 

cause adverse respiratory effects such as chronic bronchitis and asthma [Castellan 1995; Park 

2006]. Fungi can produce health effects by four mechanisms: infections (e.g., pulmonary 

aspergillosis), irritant reactions (e.g., burning, blistering skin), allergic reactions (e.g., allergic 

rhinitis), and toxic reactions (e.g., gastrointestinal symptoms from ingesting mycotoxins) 

[Trout et al. 2004]. THC is the psychoactive component in cannabis.

Process Description 

According to the farm owner, seeding and cultivation began in February with each cannabis 

plant grown from seed. Seedlings were cultivated in the greenhouse before they were 

transplanted to the ground inside hoop houses. Hoop houses are large, semicircular structures 

that are often made of fabric, which allows sunlight and air to reach plants. The number 

of plants in each hoop house depended on plant type and size. After transplantation to the 

hoop house, a screen of green netting was constructed, and the cannabis plant grew through 

the screen. The screen allowed the cannabis plant to grow an even canopy, maximizing air 

movement and light to each stem. 

During our visit, the farm had approximately 40 plants that each grew to over 8 feet tall 

and over 6 feet wide. At harvesting, an employee used hand pruners to first remove large 

outer stems and then continue removing more stems working inward toward the main 

cannabis plant trunk. The large stem, also known as a cola, was cut in such a way as to form 

a natural hook at the end furthest from the flower. The stems were transported by hand to 

the big leafing area. During our visit, the big leafing area was in the same hoop house as the 

harvested cannabis plants.
Page 2 Health Hazard Evaluation Report 2015-0111-3271

In the big leafing area, a cotton line (also known as the hook line) was hung approximately 

6–7 feet high from two posts approximately 10 feet apart, and drooped in the middle as 

stems were added. The cola was hung directly on the hook line via the natural hook cut into 

the plant during harvesting. The length of these colas was typically 12–18 inches, but one 

measured 42 inches. At the hook line, outer leaves (which contain little THC) were removed 

by pulling the leaves off or by cutting with hand pruners. The process of removing these large 

leaves is known as big leafing. Employees performed big leafing while the cola hung from 

the cotton line or by removing the cola and holding it with one hand while big leafing with 

the other. The trimmed colas were taken to the drying area and the big leaf trimmings were 

collected in a large container. Employees were required to wear powder-free latex gloves 

during big leafing activities.

The drying area was a separate building that contained wire fencing material stretched 

between building support columns. Using the natural hook, colas were placed on the wire 

fencing and allowed to dry. Dehumidifiers and fans were used to speed the drying process. 

Professional judgment and moisture meters were used to determine if the product was dry 

enough for destemming. 

Destemming is the process of removing the flower from the cola’s stem. Employees used two 

destemming methods. Some employees used bonsai tree trimming scissors to cut individual 

flowers one at a time. Other employees used a mint tin can with a half-inch hole drilled 

through the metal (Figure 1). The stem was inserted through the hole, and the flowers were 

removed by pulling the cola through the tin’s drilled hole. As the cola was pulled through the 

can, the flowers fell into a container lined with a plastic bag. Flowers were collected from 

both methods and moved to hand trimming. Employees were required to wear powder-free 

latex gloves during destemming activities.

Hand trimming is the final flower trimming step. It requires small, fine cuts to remove 

unwanted plant material and make the flower presentable. Employees used two hand 

trimming methods. Employees choose a hand trimming method based upon personal 

preference and would switch between the two throughout the day. Employees performed the 

first hand trimming method while seated at a foldable banquet table covered with a plastic 

tablecloth. They used a Trim StationTM to perform the second. The Trim Station was a plastic 

device with dedicated bins to hold the unfinished and trimmed product and tools. Curved 

cutouts underneath helped hold the device on the user’s lap (Figure 2). The Trim Station also 

contained a black foam ball for cleaning the trimming tool, a jar of trimming tool lubricant, 

and a plastic bag attached below the trimming area to collect trimmings. Employees used a 

variety of trimming tools including scissors, bonsai tree pruning scissors without a spring 

return, and hand pruners with a spring return. The bonsai tree pruning scissors without a 

spring return appeared to be the preferred tool for this work.
Health Hazard Evaluation Report 2015-0111-3271 Page 3

Figure 1. An employee removes the flower from the stem by pulling the stem through a small, drilled 

hole in a tin can. Photo by NIOSH.

Figure 2. An employee using a Trim Station for the final stage of flower hand trimming. The employee 

is wearing a CyberGlove on the right hand and a latex glove on the left hand. Photo by NIOSH.

The farm was investigating the use of machine trimmers to automate the trimming process 

and final packaging with nitrogen sealing to preserve freshness. We observed demonstrations 

of machine trimming and nitrogen sealing but neither were operational at a production scale 

during our visit. 
Page 4 Health Hazard Evaluation Report 2015-0111-3271

Methods

Our objectives were to:

1. Identify potential health hazards to employees related to harvesting and 

processing cannabis.

2. Determine whether employees were experiencing work-related health symptoms or 

had health concerns.

Our evaluation included the following: (1) ergonomic evaluation of work tasks, (2) air sampling 

for endotoxins, (3) assessment of airborne microbiological diversity (fungi and bacteria), (4) 

surface wipe sampling for THC, and (5) confidential medical interviews with employees. 

Ergonomic Evaluation

We observed harvesting tasks and recorded them by photograph and video. Employees 

confirmed that the harvest activities we observed were typical for the farm.

During big leafing tasks, we asked each of the four employees to simulate the pinch force 

used to pull leaves off the stem. The pinch force was estimated by having the employee 

duplicate that amount of force on a digital pinch force gauge (baseline, 100-pound [lb] 

capacity). Each employee performed three trials and these measurements were averaged.

During the destemming process, employees used either bonsai tree trimming scissors or the 

tin can method. To assess the force required to remove a bud with the bonsai tree trimming 

scissors, we asked the three employees performing the destemming process to reproduce that 

force by closing the scissors onto a digital force gauge (Figure 3). The force measurement 

represents a simulation of the force required based on the employee’s estimate of the exerted 

force. Each employee performed three trials and these measurements were averaged.

Figure 3. Bud snipping force was estimated by having the employee reproduce the force with the 

handles of the scissors transmitting the force to the pinch gauge. Photo by NIOSH.
Health Hazard Evaluation Report 2015-0111-3271 Page 5

For the tin can method, we taped the end of the stem to a digital force gauge after the end 

was inserted through the tin can’s orifice. This was done to measure the minimum force 

required to strip buds from the typical length stem when pulling the stem through the tin 

can. A single employee assisted by holding the tin can while an investigator pulled the stem 

through the device, using the minimum pull force necessary to strip the buds. We collected 

10 measurements to estimate the bud stripping minimum pull force.

For final hand trimming, we evaluated repetitive motion of the hand and fingers with a 

CyberGlove System, a virtual reality electrogoniometer glove. This form-fitting glove has 

embedded sensors that span the finger and thumb joints. The device interfaced with a laptopbased data acquisition system with custom-developed software (LabView v 10). All four farm 

employees wore the electrogoniometer glove during hand trimming; the time ranged from 9 

minutes to 35 minutes. For the employee with the most years of trimming experience (most 

experienced), we recorded a single 9-minute segment of trimming work time. The three other 

employees had data recording times of 35, 27, and 25 minutes. For these three employees, 

54 intervals of 10 seconds each (equal to 9 minutes work time) were randomly selected from 

the total data recording time to compare to the 9-minute work time for the most experienced 

trimmer. We counted the motions of the thumb and fingers (closures of the scissors) for 540 

seconds of work time for each participant. This was done manually from the time series 

plotting the hand/finger joint position. Each closure of the scissors has a distinct signature 

most observable in the index finger metacarpophalangeal joint (knuckle at the base of the 

finger) and thumb opposition sensors. We created a time history plot from this data, and we 

manually counted peaks corresponding to reversals in joint angle closure.

Air Sampling for Endotoxins

We collected breathing zone air samples on all four employees during their entire work shift 

for 3 days. Each sample was collected using three-piece 37-millimeter closed-face cassettes, 

preloaded with 0.45-micrometer-pore-size endotoxin-free polycarbonate filters. Samples 

were collected at an air flow rate of 2 liters per minute. Samples were analyzed for endotoxin 

content with the kinetic-chromogenic procedure using the limulus amebocyte lysate assay 

[Cambrex 2005]. For these analyses, one endotoxin unit (EU) was equivalent to 0.053 

nanograms of endotoxin. The limit of detection was 0.50 EU per sample. We also collected 

11 area air samples for endotoxin, including two in the harvesting hoop house, three outside 

the drying building, and six inside the drying building. We collected three task-based area air 

samples for endotoxin during various machining activities. 

Air Sampling for Microbes

We collected 26 full-shift, personal breathing zone and area air samples using a National 

Institute for Occupational Safety and Health (NIOSH) two-stage bioaerosol sampler. We 

collected full-shift personal breathing zone air samples from four employees over 3 days 

(12 samples in all). We collected 14 area samples: eight in the drying room, three in the 

greenhouse, and three outdoors. Complete details of the sampling and microbiological 

diversity analysis are in Appendix B. In brief, we processed the deoxyribonucleic acid (DNA) 

in the samples and used it to identify varieties of fungi and bacteria by comparing our results 
Page 6 Health Hazard Evaluation Report 2015-0111-3271

to the National Center for Biotechnology Information database. The results are reported in 

terms of relative abundance, which is the percentage of each type out of the total in the sample.

Surface Sampling for Tetrahydrocannabinol

We collected 33 surface wipe samples in areas with cannabis processing, before any 

housekeeping. We also sampled the hand trimming scissor blades after hand trimming 

but before cleaning, and after cleaning. For each sample we noted the location and recent 

activities in the area. Where possible, we used a 100-square-centimeter (cm2) template to 

sample a consistent surface area. The hand trimming scissor wipe sample area included both 

blade surfaces (less than 100 cm2). Surface wipe samples were analyzed for THC using a 

contract laboratory’s internal method. The method used liquid chromatography and tandem 

mass spectrometry with a limit of detection of 40 ng per sample.

Employees cleaned scissors by either wiping them with an alcohol pad or placing them into a 

jar of Scissor BUD-eTM cleaner and then wiping them by inserting and removing the scissors 

multiple times into a black foam ball. While the act of taking a surface wipe sample from the 

hand trimming scissor blade does remove THC, the “before cleaning” sample is an indication 

of the THC amount on the hand trimming scissor blades after trimming. The sample collected 

after the employee cleaned the scissors is an indication of the THC amount left after cleaning 

and if THC is still present after normal cleaning procedures.

Medical Interviews

We interviewed all four employees about their health and safety concerns related to cannabis 

processing. We discussed work history and exposure, use of personal protective equipment, 

and symptoms when working with cannabis. Employees were also asked about long-term 

health and safety concerns related to their job.

Results and Discussion

Ergonomic Evaluation

During harvesting activities, we observed an employee using hand cutters to remove the cola 

from the erect cannabis plant. We observed multiple cuts on a single plant. The number of 

cuts depends on the harvest size. Stems were typically cut at a vertical point below the waist 

level of the farmer. In many cases, stem removal involved considerable horizontal reaching 

(Figure 4A). The screen of green netting material creates a barrier restricting how close the 

farmer can stand with respect to the horizontal distance from the feet to the cutting point. 

Because of this restriction, the hands are farther from the lower spine (horizontally) when 

bending to cut plant stems. This creates stooped postures with significant trunk bend with 

the weight of the trunk and arms creating pressure on the lower spine. This stooping posture 

is considered a higher risk posture than that in which the feet were closer to the base of the 

plant and the horizontal distance to the hands was reduced. It does not appear that substantial 

vertical hand forces are associated with this task due to the light weight of the stems and the 

cutter. However, any significant pulling on the stem in the upward vertical direction from a 
Health Hazard Evaluation Report 2015-0111-3271 Page 7

posture such as that in Figure 4B would worsen the biomechanical forces around the lower 

spine. If the stem is cut cleanly, it does not appear that an upward pulling force is necessary. 

Figure 4. Cola removal from the cannabis plant. The screen of green netting restricts how close the 

harvester can position himself from the base of the plant. Photos by NIOSH.

We observed four employees performing the big leafing process. The working posture in this 

process was a function of multiple factors:

● Standing vs. sitting

● Height and arm length of employee 

● Height of hanging line

● Length of stems, which determines the vertical range of hand positions 

● Employee work technique 

We observed two big leafing techniques. The first was performed with the cola hanging on 

the line (Figure 5A). Leaving the cola on the hook line, some employees had to reach above 

shoulder height. Figure 5B shows a work zone that was above the employee’s shoulder 

height. The second big leafing technique was performed when the employee lifted the stem 

from the line and performed the big leafing process while holding the stem with his hand at 

mid-torso level. Because the weight of the cannabis stem is minimal, it likely contributes 

little to shoulder muscle fatigue. Supporting the mass of the arms accounts for almost all of 

the effort. Depending on the technique used, the optimal vertical height for the hook line will 

vary. A combination of repetitive work above shoulder height could also increase the risk for 

shoulder problems. 
Page 8 Health Hazard Evaluation Report 2015-0111-3271

Figure 5. (A) Employee on left is shown big leafing from a stem as it hangs on the line. Employee on the 

right is big leafing the stem by first removing it from the line and holding by hand. (B) The red highlight 

displays the work zone, which is greater than the employee’s shoulder height. Photos by NIOSH. 

We asked each employee to use a digital pinch gauge to estimate the pinch force needed to 

pull leaves off the stem. On the basis of three measurements per person, the estimated peak 

level pinch forces in the removal of leaves for each employee were 8.3 ± 2.0, 3.4 ± 0.83, and 

3.4 ± 0.32 pounds (lbs). 

We asked each employee to use a digital pinch gauge to estimate the pinch force needed for 

destemming. On the basis of three measurements per person for destemming with scissors, 

the peak level cutting force estimates were 3.9 ± 1.1, 3.2 ± 0.61, and 1.9 ± 0.22 lbs. For 

destemming with a tin can, the peak pull force averaged 6.2 ± 2.9 lbs over 10 measurements. 

When using the tin can, it appeared that the pull force is a function of the length of the stem, 

as longer stems tend to have more buds that are stripped using the pulling motion. Higher 

pull forces increase the musculoskeletal stress during the task, which may lead to higher risk 

of cumulative musculoskeletal disorders. 

The tin can destemming method required more hand force than cola removal and big leafing 

because of the can’s lightweight construction and flexion within the can. The tin can’s metal 

is not designed for destemming activities or for prolonged use in this manner. An alternate 

tool made of more durable, sturdy materials that could be attached to a table or work station 

would create less hand stress and fatigue. 

For final hand trimming, the scissor closure motion count measured by the electrogoniometer 

glove in the 540-second sampling period ranged from 336 to 1,030. Table 1 shows the 

equivalent repetition rates in motions per second. The most experienced trimmer (more 

than 10 years) exhibited a higher frequency of hand motions than the two least experienced 

trimmers (less than 1 year) as displayed in Figure 6. The employee with intermediate 

experience (more than 1 year but less than 10 years) fell between the highest and lowest 

experienced employees but more closely resembled the lowest experienced employees. That 

the number of cuts per unit time is greater (i.e., faster trimming) with the more experienced 

employee(s) was an expected finding.
Health Hazard Evaluation Report 2015-0111-3271 Page 9

Table 1. Summary of repetitive hand motions in hand trimming*

Employee 

experience

Total observation 

time (minutes)

Sampling time 

(minutes)

Average rate 

(motions/second)

Peak rate 

(motions/second)†

Most 9.0 9.0 1.91 3.2

Intermediate 35 9.0* 0.95 1.9

Low 25 9.0* 0.62 1.3

Low 27 9.0* 0.79 1.5

*To comprise these 9-minute sampling periods, 54 10-second intervals were selected randomly

from the total observation time.

†Calculated from highest count of motions observed in any 10-second interval. Thus, 32 motions 

observed in a 10-second interval is a peak rate of 3.2 per second.

Figure 6. Line graph of hand motion example by level of hand trimming experience. The traces 

represent thumb opposition joint motion (blue line) and index finger metacarpophalangeal joint motion

(orange line) while the y-axis represents reflecting joint angle movement (raw sensor value).
Page 10 Health Hazard Evaluation Report 2015-0111-3271

We did not observe any employee performing hand trimming for a full workday. During our 

visit, only small amounts of product were trimmed because it was late in the harvest season. 

Employees noted that during the peak season, hand trimming was performed for an entire 

work day. High frequency motion in hand trimming could increase the risk for hand, wrist, 

and finger musculoskeletal disorders. 

Employees noted that, during hand trimming, the trimmer becomes harder to open and close 

as sticky residue builds up on it. Most often, employees reported cleaning trimmers only after 

noticeable resistance was observed. The additional resistance increases the hand, wrist, and finger 

forces needed for hand trimming and could increase the risk of musculoskeletal disorders.

Air Sampling for Endotoxin

Personal air sampling results for endotoxin are shown in Table 2. Endotoxin concentrations 

ranged from 2.8 to 37 endotoxin units per cubic meter (EU/m3). Endotoxin concentrations 

were highest for all four employees on day 1, when harvesting occurred. Employee 1 

harvested the cannabis plant while employees 2, 3, and 4 performed big leafing activities 

nearby in the same hoop house. During big leafing (Day 2), the maximum endotoxin 

concentration measured was 24 EU/m3. Day 2 had the lowest endotoxin concentrations for all 

four employees. No samples exceeded the Dutch Expert Committee on Occupational Safety 

(DECOS) recommended limit of 90 EU/m3 [DECOS 2010]. No occupational exposure limit 

(OELs) for endotoxin have been established in the United States. 

The airborne endotoxin concentrations at the cannabis farm were below those found in other 

agricultural settings such as an indoor flower greenhouse with 38 employees (range: 0.84 

to 1,100 EU/m3); two indoor herb processing plants with 70 and 90 employees (median 

endotoxin concentration: 3×105 EU/m3); four peppermint and nine chamomile herb farm 

indoor processing operations (median for endotoxin peppermint farms: 1×106 EU/m3; median 

endotoxin for chamomile farms: 1.8×104 EU/m3); and an indoor hemp processing plant with 

seven employees (mean endotoxin concentration: 1.9×104 EU/m3) [Dutkiewicz et al. 2001; 

Fishwick et al. 2001; Skórska et al. 2005; Thilsing et al. 2015].

Endotoxin concentrations in area air samples, provided in Table A1, Appendix A, ranged 

from not detected to 15 EU/m3. The highest area air sample endotoxin concentrations were 

found in the hoop house on the first day of sampling during harvesting and big leafing 

activities. Endotoxin was not detected in the three outdoor area air samples collected outside 

the drying house. Endotoxin concentrations during task-based sampling for three machining 

processes (Table A2, Appendix A) were 2.0 EU/m3 for the large tumbling machine trimmer, 

3.6 EU/m3 for the horizontal machine trimmer, and 13 EU/m3 for nitrogen sealing. The 

nitrogen sealing demonstration took place in the hoop house where harvesting had been 

performed 2 days earlier, while the two machine trimming demonstrations were performed in 

the drying house. 
Health Hazard Evaluation Report 2015-0111-3271 Page 11

Table 2. Personal breathing zone air sampling for endotoxins on October 27–29, 2015

Job/Activity Sample time

(minutes)

Total volume

(liters)

Concentration

(EU/m3)

Harvesting – October 27, 2015

Employee 1 466 950 37

Big leafing/gross trimming – October 27, 2015

Employee 2 471 938 20

Employee 3 469 934 22

Employee 4 466 928 24

Big leafing/gross trimming/destemming – October 28, 2015

Employee 1 415 818 6.1

Employee 2 414 798 2.9

Employee 3 418 812 3.8

Employee 4 409 795 2.8

Destemming/hand trimming – October 29, 2015

Employee 1 486 951 17

Employee 2 479 964 15

Employee 3 480 929 21

Employee 4 483 940 19

ACGIH® TLV® NA

NIOSH REL NA

OSHA PEL NA

DECOS 90

ACGIH = American Conference of Governmental Industrial Hygienists

NA = Not applicable 

OSHA = Occupational Safety and Health Administration

PEL = Permissible exposure limit 

REL = Recommended exposure limit

TLV = Threshold limit value

Air Sampling for Microbes

Bacterial Analysis

A total of 1,077 bacterial sequences were identified; these were clustered into 639 taxonomic 

units. Figures 7A–7D show the relative abundance by phylum (7A), class (7B), most 

common bacterial taxa (7C), and sampling location (7D). The relative abundance is the 

percentage of each bacterial species compared to the total number of bacterial species. The 

bacterial sequences were derived from the bacterial phyla listed in Figure 7A. The most 

predominant phyla identified in the area and personal samples included Actinobacteria 

(45%), Proteobacteria (26%), Firmicutes (15%), and Bacterioidetes (9%) (Figure 7A). An 

additional 11 bacterial phyla were identified in the analysis and accounted for 4% of bacterial 

sequences (Figure 7A). 
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Figure 7B depicts the relative abundance of individual bacterial classes for the four most 

prominent bacterial phyla. Bacterial classes with over 10% relative abundance included 

Actinobacteria (43%), Alphaproteobacteria (16%), and Bacilli (13%) (Figure 7B). Analysis 

of the individual species is shown in Figure 7C. The most abundant species identified in 

the area and personal samples accounted for 7% of bacterial sequences and consisted of 

three genera: Arthrobacter spp. (2.5%), Nocardioides spp. (2.5%), and Bacillus spp. (2.1%) 

(Figure 7C). In some field and media negative controls, bacterial DNA derived from species 

such as Bradyrhizobium elkanii were identified and subtracted from the personal and area air 

sampling results to identify potential contaminant bacterial DNA and normalize all results. 

Overall, no substantial differences in bacterial phyla relative abundance were observed 

among the different sampling locations. Gram-positive bacteria belonging to the phylum 

Actinobacteria, also known as Actinomycetes, comprised 47% in personal air samples, 

51% in greenhouse samples, 46% in drying room samples, and 23% in outdoor area samples 

(Figure 7D). Approximately, 40% of bacterial phyla were endotoxin-producing Gramnegative bacteria. These gram-negative endotoxin-producing bacteria, as well as the Grampositive Actinomycetes, are known to cause adverse health effects, such as hypersensitivity 

pneumonitis, chronic bronchitis, organic dust toxic syndrome, asthma, and allergic sensitization 

[Lacey and Crook 1988; Mackiewicz et al. 2015; Park et al. 2006; Pepys et al. 1963].

Figure 7. Four bar charts that depict bacterial relative abundance by phylum (A), class (B), most 

common bacterial taxa (C), and sampling location (D).
Health Hazard Evaluation Report 2015-0111-3271 Page 13

Fungal Analysis

Fungal DNA sequences derived from 985 sequences were clustered into 216 taxonomic 

units. Figures 8A–8D are horizontal bar graphs showing the relative abundance by phylum 

(8A), class (8B), most common fungal taxa (8C), and sampling location (8D). The relative 

abundance is the percentage of each fungal species compared to the total number of fungal 

species. The fungal sequences were placed into four fungal phyla and included the Ascomycota 

(53%), Basidiomycota (46%), Zygomycota (1.2%), and Glomeromycota (0.5%) (Figure 

8A). Figure 8B shows the relative abundance of classes derived from the two most prevalent 

fungal phyla, the Ascomycota and Basidiomycota. The Agaricomycetes (Basidiomycota) 

and the Leotiomycetes (Ascomycota) were the most abundant classes accounting for 42% 

(Agaricomycetes) and 38% (Leotiomycetes) of fungal sequences. The Agaricomycetes 

represent a class of fungi that decays wood and produces a wide diversity of fruiting structures 

such as mushrooms. In contrast, the Leotiomycetes are a class placed in the Ascomycota 

and includes a diverse group of fungi, many of which are plant pathogens that break down 

agricultural products. In the present study, Botrytis cinerea, a plant pathogen of Cannabis sativa

that causes grey mold, was the most common fungal sequence in the analysis of personal and 

area samples and accounted for 34% of fungal sequences (Figure 8C). 

Figure 8D depicts the analysis of fungi in area and personal samples. Sequences placed in the 

Basidiomycota were the predominant class identified in outdoor samples (91%) and within 

the drying room (70%) (Figure 8C). Greenhouse samples included similar proportions of 

Ascomycota (49%) and Basidiomycota (47%), as well as some Zygomycota (2.7%). Personal 

air samples were dominated by sequences placed in the Ascomycota (87%, Figure 8D), and 

the most prevalent species was the fungal plant pathogen Botrytis cinerea. This was the major 

fungal species identified in the air samples, making up almost 60% of the fungi detected in 

personal air samples, 19% of the drying room area air sample, 18% of the greenhouse area 

air sample, and 6% in the outdoor sample. Botrytis cinerea is the most significant fungal 

pathogen of Cannabis and can affect the seedlings, stems, and buds [McPartland 1996; 

Rodriguez et al. 2015]. Botrytis has been observed to be among the most frequently detected 

fungal genera (10%–32% relative abundance) in European greenhouse environments 

[Monsó et al. 2002; Radon et al. 2002]. Personal exposure to B. cinerea has been shown to 

cause allergic sensitization in occupational settings such as green bell pepper greenhouses 

[Groenewoud et al. 2002a], chrysanthemum greenhouses [Groenewoud et al. 2002b], and 

table grape farms [Jeebhay et al. 2007]. 
Page 14 Health Hazard Evaluation Report 2015-0111-3271

Figure 8. Four bar charts that depict the fungal relative abundance by phylum (A), class (B), most 

common fungal taxa (C), and sampling location (D).

Microbiological exposures including endotoxin, bacterial, and fungal species may place 

workers at risk of allergic sensitization and respiratory issues. For example, B. cinerea has 

previously been linked to a hypersensitivity pneumonitis condition commonly known as wine 

grower’s lung [Popp et al. 1987].
Health Hazard Evaluation Report 2015-0111-3271 Page 15

Tetrahydrocannabinol

All 27 surface wipe samples were collected in cannabis production areas and had 

detectable levels of THC. The surface wipe results ranged from 0.17 to 210 micrograms (μg) 

per 100 cm2 (μg/100 cm2). Table A3, Appendix A shows all 27 surface wipe sample levels. In 

an evaluation of 30 indoor cannabis grow operations to investigate potential law enforcement 

employee exposures, surface THC levels ranged from not detected to 2,000 μg/100 cm2 with 

a geometric mean of 0.37 μg/100 cm2 [Martyny et al. 2013]. 

We collected six hand trimming scissor blade surface wipe samples. For three employees, 

a sample was collected after hand trimming but before cleaning as well as after cleaning. 

The THC levels before cleaning ranged from 61 to 180 μg per sample, while the levels after 

cleaning ranged from 25 to 67 μg per sample. Table 3 shows the wipe sample result for each 

employee both before and after cleaning. We cannot determine if the reduction in THC is due 

to the cleaning procedure or the removal due to surface wipe sampling. 

Table 3. Scissor surface wipe sampling for THC before and 

after cleaning on October 28, 2015*

Sample Micrograms per sample

Employee 1

Before cleaning 180

After cleaning 67

Employee 2

Before cleaning 61

After cleaning 41

Employee 3

Before cleaning 110

After cleaning 25

*Scissors were sampled after hand trimming but before 

cleaning and sampled again immediately after cleaning. 

Raw cannabis plant material consists of various cannabinoid acids: (1) 

tetrahydrocannabinolic acid, (2) cannabidiolic acid, and (3) cannabichromenic acid [Burstein 

2014]. THC is the psychoactive component of cannabis, and previous cannabis exposure 

assessments have typically involved sampling for THC [Martyny et al. 2013]. However, raw 

cannabis plant material contains a number of precursor acids that must be decarboxylated in 

order to form the psychoactive and medicinal components. Decarboxylation most commonly 

occurs through heat application but may also result from aging. Because of the lack of heat 

applications, surface wipe sample results may under report the range of THC compounds 

present including the THC precursor acid (tetrahydrocannabinolic acid). 

THC surface wipe sample results should be considered semiquantitative. Samples with high 

concentrations required multiple dilutions while samples with lower concentrations did not 

require as many or any additional dilutions to quantify the THC concentrations. The contract 
Page 16 Health Hazard Evaluation Report 2015-0111-3271

laboratory noted that the recovery was dependent on the THC concentration and that the 

reported values were likely an underestimate of the actual concentrations. Therefore, the 

THC concentrations should be considered as semiquantitative and used to designate areas of 

higher THC contamination. Currently, there are no OELs for THC.

We did not collect air samples for THC. A previous study of 30 indoor grow operations 

indicated that measurable airborne THC levels were unlikely [Martyny et al. 2013]. The 

study reported only one detectable air sample (0.70 μg per sample) while the rest did not 

detect THC (limit of detection 0.10 μg per sample). 

Medical Interviews

We interviewed all four employees at the farm including the owner/operator. They reported prior 

work with cannabis with a range of less than 1 year to 17 years. Employees stated that harvesting 

season (summer–fall) is the busiest time at the farm. All interviewed employees reported 

performing several tasks at the farm including cultivating, cutting, and trimming of cannabis. 

All interviewed employees stated that they always used powder-free latex or work gloves 

when handling cannabis. However, we did observe employees not wearing gloves while 

handling cannabis. The use of powdered latex gloves may lead to adverse health effects 

ranging from allergic dermatitis to anaphylaxis and occupational asthma [Meade et al. 2002; 

Sussman et al. 2002]. 

Employees were also asked whether they experienced symptoms that might be related to 

working with cannabis. None reported any symptoms or health effects, such as rashes on the 

skin or allergic reactions, which have been previously shown to be associated with cannabis 

exposure [Decuyper et al. 2015]. No employee reported hand, wrist, or shoulder symptoms or 

other musculoskeletal problems. However, employees did express concerns about whether they 

might develop long-term musculoskeletal problems as a result of the way they trim the cannabis. 

Employees also raised concerns about slips, trips, and falls. They also mentioned concerns about 

the safety of the proposed use of automated trimmers during operation and cleaning. 

Research on occupational health issues in the cannabis industry is limited. A study of 30 

indoor grow facilities in Colorado evaluated potential exposures to first responders [Martyny 

et al. 2013]. That study identified potential dermal exposures to THC, fungal spores 

(predominantly Cladosporium and Penicillium species), pesticides (primarily pyrethroids), 

carbon monoxide, and carbon dioxide. The state of Colorado has issued occupational safety 

and health guidance for the cannabis industry [CDPHE 2017].

Conclusions

We evaluated hazards associated with harvesting and processing cannabis at a small outdoor 

organic farm. The four employees reported no health effects. Our findings indicate that 

the employees have exposures to highly repetitive and forceful work, most notably during 

hand trimming activities. These exposures increase their risk of musculoskeletal disorders. 

THC surface wipe concentrations indicate the potential for dermal and ingestion exposures. 

However, the health implications from occupational exposure to THC is unknown. Airborne 
Health Hazard Evaluation Report 2015-0111-3271 Page 17

exposure to Actinobacteria and fungus like B. cinerea can increase the risk of allergic and 

respiratory symptoms. The employer should take measures to minimize these hazards.

Recommendations

On the basis of our findings, we recommend the actions listed below. We encourage the farm 

to discuss our recommendations and develop an action plan. Those involved in the work can 

best set priorities and assess the feasibility of our recommendations for the specific situation 

at the farm. 

Our recommendations are based on an approach known as the hierarchy of controls. This 

approach groups actions by their likely effectiveness in reducing or removing hazards. In 

most cases, the preferred approach is to eliminate hazardous materials or processes and 

install engineering controls to reduce exposure or shield employees. Until such controls 

are in place, or if they are not effective or feasible, administrative measures and personal 

protective equipment may be needed. 

Engineering Controls

Engineering controls reduce employees’ exposures by removing the hazard from the process or by 

placing a barrier between the hazard and the employee. Engineering controls protect employees 

effectively without placing primary responsibility of implementation on the employee. 

1. Improve the tin can bud removal method to eliminate tool flexion during destemming. 

Replace the tin can with a new tool made of more durable materials that can be 

attached to a table or work station to lessen hand stress and fatigue.

2. Remove the screen of green netting during harvesting to allow the harvester to stand 

closer to the cannabis plant. This change will reduce exposure to awkward postures. 

3. Standardize procedures so that hook line hanging heights are in an optimal work zone 

consistent with employee size and working technique. Determine a hook line hanging 

height that is compatible with the typical stem length and working technique preferred 

(sitting or standing) so that the upper arms are not in an elevated static posture. The 

hook line height should keep the hands below shoulder height to the extent possible. 

4. Consider hook line configurations that have standing and sitting options or alternate 

sitting/standing. 

5. Provide as much natural ventilation as possible by raising the sides of the hoop house 

and opening doors when it is occupied.

Administrative Controls

The term administrative controls refers to employer-dictated work practices and policies 

to reduce or prevent hazardous exposures. Their effectiveness depends on employer 

commitment and employee acceptance. Regular monitoring and reinforcement are necessary 

to ensure that policies and procedures are followed consistently.

1. Develop a job rotation plan to move employees working in high hand and finger 
Page 18 Health Hazard Evaluation Report 2015-0111-3271

motion frequency tasks to other jobs that require using different muscle-tendon groups. 

An effective job rotation plan will reduce the risk of musculoskeletal disorders.

2. Provide frequent breaks for employees working in high hand and finger motion 

frequency tasks such as hand trimming.

3. Develop a cleaning schedule to remove THC from work and tool surfaces. 

4. Provide training to employees on the cleaning, lubrication, sharpening, and 

maintenance of tools according to manufacturer recommendations. 

5. Encourage employees to report any work-related symptoms to their supervisor and to 

their healthcare provider.

Personal Protective Equipment

Personal protective equipment is the least effective means for controlling hazardous 

exposures. Proper use of personal protective equipment requires a comprehensive program 

and a high level of employee involvement and commitment. The right personal protective 

equipment must be chosen for each hazard. Personal protective equipment should not be 

the sole method for controlling hazardous exposures. Rather, personal protective equipment 

should be used until effective engineering and administrative controls are in place.

1. Wear nonlatex gloves when handling cannabis or equipment that may be contaminated 

with THC. Many types of glove materials are available, such as nitrile, polyvinyl 

chloride, neoprene, and polyvinyl alcohol. Each glove material provides different 

levels of protection from chemicals, and varying levels of cut, tear, abrasion, puncture, 

and thermal resistance. 

2. Wash your skin with soap and water after removing gloves.
Health Hazard Evaluation Report 2015-0111-3271 Page 19

Appendix A: Tables

Table A1. Area air sampling for endotoxin on October 27–29, 2015

Job/Activity Sample time

(minutes)

Total volume

(liters)

Concentration

(EU/m3)*

Harvesting/big leafing/gross trimming – October 27, 2015

Front of harvesting hoop house 435 860 13

Back of harvesting hoop house 434 868 15

Trimming area of drying house 450 895 ND

Next to drying plants in drying house 450 909 ND

Outside new drying house 421 836 ND

Big leafing/gross trimming/destemming – October 28, 2015

Trimming area of drying house 423 830 ND

Next to drying plants in drying house 412 812 ND

Outside new drying house 409 795 ND

Destemming/hand trimming – October 29, 2015

Trimming area of drying house 522 1022 1.5

Next to drying plants in drying house 525 1016 1.7

Outside new drying house 504 978 ND

ACGIH TLV NA

NIOSH REL NA

OSHA PEL NA

DECOS 90

ND = Not detected

*The minimum detectable concentration of endotoxin ranged from 0.51 EU/m3 to 0.63 EU/m3.

Table A2. Task-based area air sampling for endotoxin on October 28–29, 2015

Job/Activity Sample time

(minutes)

Total volume

(liters)

Concentration

(EU/m3)

Next to large tumbler 131 252 2.0

Next to machine trimming 198 388 3.6

Nitrogen sealing 46 89 13

ACGIH TLV NA

NIOSH REL NA

OSHA PEL NA

DECOS 90
Page 20 Health Hazard Evaluation Report 2015-0111-3271

Table A3. Surface wipe sampling for THC on 

October 28, 2015

Location Level 

(μg per 100 cm2)

Drying building

Table surface in front of dry trimmer 0.51

Table surface to right of dry trimmer 0.81

Dry trimmer exit chute 100

Preparation table 0.67

Preparation table near drying cannabis 2.5

Wood chest 3.9

Top of heater (not turned on) near 

hand trimming 5.9

Table surface directly in front of dry 

trimmer #2 120

Table surface to the right of dry 

trimmer #2 6.9

Table surface to the left of dry 

trimmer #2 5.5

Dry trimmer #2 chute 37

Dry trimmer #2 inside lid 1.8

Dry trimmer #2 outside lid 1.5

Hand trimming table 130

Hand trimming table #2 20

White chair seat at trimming table 140

Hoop house

Folding table 0.17

Trimming station after hand trimming 45

Trimming station after hand 

trimming #2 1.0

Grey table near hand trimming station 210

Grey table near hand trimming 

station #2 0.27

Folding chair at trimming station* 2.9

White chair near hood line* 5.2

Metal chair in sitting area* 2.7

Wood table in sitting area 1.4

Round table in sitting area 2.8

Chair near big leafing 2.9

*The 100 cm2 template could not be used so an estimated 

100 cm2 was sampled.
Health Hazard Evaluation Report 2015-0111-3271 Page 21

Appendix B: Methods

Air Sampling for Microbial Genomic Analysis

We collected aerosols at 2 liters per minute using a two-stage sampler with two cyclones 

depositing into microcentrifuge tubes and onto a polytetrafluoroethylene filter. The bioaerosol 

samplers allowed for the collection of particles across three size fractions: > 4.1 micrometers, 

1.0–4.1 micrometers, and < 1.0 micrometer aerodynamic diameter. The three size cut samples 

taken with each bioaerosol sampler were aggregated for genomic DNA analysis. 

Genomic DNA Extraction from Air Samples

We processed air samples separately for fungal and bacterial DNA extraction using the 

Roche High Pure Polymerase Chain Reaction (PCR) Template kit as previously described 

[Rittenour et al. 2012, 2014]. For air samples, including field and media blank controls, 

we combined each stage from the NIOSH BC251 air sampler prior to DNA extraction. We 

sectioned the after filter into six pieces with a scalpel using aseptic methods. We placed these 

pieces into a 2-milliliter (mL) bead-beater tube containing 300 milligrams of glass beads as 

described above. We placed the tubes in liquid nitrogen for 30 seconds and processed in a 

bead beater for 30 seconds. This process was repeated one more time. The High Pure PCR 

Template kit lysis buffer (650 microliters [μL]) was then sequentially added to the first and 

second stage tubes and vortexed to collect the fungal and bacterial DNA from the samples. 

The lysis buffer was added to the 2 mL bead-beater tube containing the macerated filter 

material. We processed the tubes with a bead beater for 30 seconds and then centrifuged for 

1 minute at 20,000 × g, a measure of relative centrifugal force. We collected the supernatant 

and incubated with 40 μL Cell Lytic B lysis reagent (Sigma Aldrich) for 15 minutes at 37°C. 

We mixed the sample with the kit’s binding buffer (200 μL) and proteinase K (40 μL) and 

incubated at 70°C for 10 minutes. We washed the sample and eluted in 100 μL of isopropanol 

as recommended by the manufacturer.

Fungal ITS and Bacterial 16S rDNA Amplification, 

Cloning, and Sanger Sequencing

We targeted fungal ribosomal deoxyribonucleic acid (rDNA) for PCR amplification 

as previously described [Rittenour et al. 2012, 2014]. Briefly, fungal rDNA sequences 

were amplified with the primer pair Fun18Sf (TTGCTCTTCAACGAGGAAT) and ITS4 

(TCCTCCGCTTATTGATATGC). The fungal internal transcribed spacer-1 (ITS1) and ITS2 

regions were amplified with Platinum Taq DNA polymerase (Invitrogen) according to the 

methods previously described [Rittenour et al. 2012, 2014]. For fungal amplification, three 

replicate PCR reactions (50 μL) were run for each sample by using 5 μL of DNA template. 

These replicates were then combined, and the rDNA amplicons were purified with a Qiagen 

PCR purification kit, according to the manufacturer’s instructions. We ran the purified 

product (8 μL) on a 1% agarose gel containing 1 μg/mL ethidium bromide and examined for 

amplicons with ultraviolet light.
Page 22 Health Hazard Evaluation Report 2015-0111-3271

We amplified bacterial 16S rDNA sequences with the use of the highly conserved primer 

pair p8FPL (AGTTTGATCCTGGCTCAG) and p806R (GGACTACCAGGGTATCTAAT) 

[McCabe et al. 1999]. We amplified the bacterial 16S rRNA genes with Invitrogen Platinum 

Taq DNA polymerase by a modified method of [McCabe et al. 1999]. The PCR conditions 

included initial denaturation at 95°C for 4 minutes, followed by 33 cycles of denaturation 

at 94°C for 1 minute, annealing at 55°C for 1 minute, extension at 72°C for 2 minutes, and 

completion with a final extension at 72°C for 10 minutes. We ran three 50-μL replicate PCR 

reactions for each sample with the use of 5 μL of DNA template. We combined the replicates, 

and the rDNA amplicons were purified with a Qiagen PCR purification kit according to 

the manufacturer’s instructions. We ran the purified product (8 μL) on a 1% agarose gel 

containing 1 μg/mL ethidium bromide and examined for amplicons with ultraviolet light.

We separately cloned fungal and bacterial amplicons into the pDRIVE vector using a 

Qiagen PCR cloning kit. We generated clone libraries by transforming cloned plasmids into 

chemically competent Escherichia coli cells as previously described [Rittenour et al. 2012, 

2014]. We selected positive colonies (as determined colorimetrically by the inactivation of 

the lacZ gene) and cultured for 16 hours at 37°C in liquid Luria-Bertani media containing 

100 μg/mL of ampicillin. Resultant cells were centrifuged at 1800 × g (relative centrifugal 

force) and the pellet resuspended in 200 μL of 15% glycerol, and sent for Sanger sequencing 

of the bacterial 16S insert from Genewiz, Inc. Inserts were sequenced in both directions, 

allowing for sequence analysis of the 16S region. 

Sequencing results were downloaded as “.ab1” chromatogram files from Genewiz Inc. 

Vector sequence data were trimmed and forward and reverse sequences were assembled 

using Biomatters Geneious R7 Software. Then we sequenced the DNA to identify which 

varieties of bacteria were present in the air. Sequence data were then clustered into operational 

taxonomic units with MOTHUR software version 1.32.1 using a 97% similarity cutoff as 

described in previous publications [Rittenour et al. 2012, 2014; Schloss et al. 2009]. Sequences 

representative of each operational taxonomic unit were then used in a Basic Local Alignment 

Search Tool search against the National Center for Biotechnology Information database.
Health Hazard Evaluation Report 2015-0111-3271 Page 23

Appendix C: Occupational Exposure Limits and 

Health Effects

Endotoxins

Endotoxins are found throughout the agricultural environment. Endotoxins are found in the 

cell wall of Gram-negative bacteria and are released when the bacterial cell is lysed (broken 

down) or when it is multiplying. In experimental studies, human volunteers exposed via 

inhalation to high levels of endotoxin experience airway and alveolar inflammation as well as 

chest tightness, fever, and malaise, and have an acute reduction in lung function, as measured 

by the forced expiratory volume in one second [Castellan 1995]. Airborne endotoxin 

exposures between 45 and 400 EU/m3 have been associated with acute airflow obstruction, 

mucous membrane irritation, chest tightness, cough, shortness of breath, fever, and wheezing 

[Thorne and Duchaine 2007]. Chronic health effects that have been associated with airborne 

endotoxin exposures include asthma, chronic bronchitis, bronchial hyper-reactivity, 

chronic airway obstruction, hypersensitivity pneumonitis, and organic dust toxic syndrome 

[Duquenne et al. 2013; Rylander 2006]. Some studies suggest that high environmental and 

occupational endotoxin exposures may protect exposed individuals from developing atopic 

sensitization [Rylander 2006].

Rylander and Jacobs have suggested an occupational threshold concentration for endotoxin 

equivalent to 100 EU/m3 of air to prevent airway inflammation [Rylander and Jacobs 1997]. 

No accepted OELs have been developed in the United States because of the variability of 

sampling and analytical methods, and because of a lack of data showing a consistent doseresponse relationship [AIHA 2005; Duquenne et al. 2013]. In 2010, DECOS recommended 

a health-based OEL for airborne endotoxin of 90 EU/m3 as an 8-hour time-weighted average 

[DECOS 2010].

THC

THC is the psychoactive component of cannabis. The health effects from an effective dose 

of cannabis may include mood changes, diminished memory, and disorientation [NIDA 

2016]. Health effects from long-term occupational exposures are unknown, in part because 

occupational exposures to THC are thought to be predominantly through skin absorption 

and ingestion. Past THC and health effects research has focused primarily on inhalation in 

nonoccupational settings.

The adverse health effects associated with nonmedicinal and chronic consumption of 

THC derived from Cannabis sativa and Cannabis indica have been extensively studied 

and reviewed [Hall and Degenhardt 2014; Volkow et al. 2014]. In contrast, the short-term 

and long-term health effects of occupational exposure to Cannabis spp. material are not 

well described in the literature. In addition to THC and cannabinol, cannabis production 

employees may be exposed to a variety of plant-derived materials such as leaves, buds, sap/

exudate, flowers, and pollen when handling the plant during cultivation and processing 

procedures. They can also encounter other contaminant and plant pathogen sources such as 
Page 24 Health Hazard Evaluation Report 2015-0111-3271

bacteria and fungi. These secondary exposures may result in occupational byssinosis, a lung 

disease associated with textile fibers (cotton, hemp, etc.) [Valic et al. 1968; Zuskin et al. 1990].

Hemp

Hemp, also derived from Cannabis sativa, is used for a variety of purposes including fiber, 

rope, paper composites, food, and oil and oil-based products [USDA 2000]. Occupational 

hemp exposure can result in a variety of clinical symptoms including sinusitis, byssinosis, 

and reductions in lung function [Zuskin et al. 1990, 1992, 1994]. Employees who directly 

handle the plant are particularly at risk [Barbero and Flores 1967; Valic and Zuskin 1971; 

Zuskin et al. 1990, 1994]. Transdermal applications of medicinal cannabis demonstrate 

that occupational dermal absorption is a potential exposure route [Goldsmith 2015]. Other 

studies have also demonstrated dermal reactions such as an urticarial rash (hives) in subjects 

who directly contact cannabis [Basharat et al. 2011; Ozyurt et al. 2014]. Urticaria has also 

occurred in forensic specialists and law enforcement officers following the handling of 

cannabis [Herzinger et al. 2011; Majmudar et al. 2006; Mayoral et al. 2008; Williams et 

al. 2008]. Several of these plant components have recently been shown to produce high 

molecular weight proteins that can result in the allergic sensitization following personal 

exposure [Nayak et al. 2013]. 
Health Hazard Evaluation Report 2015-0111-3271 Page 25

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Keywords: North American Industry Classification System 111910 (Tobacco Farming), 

Washington, cannabis, marijuana, ergonomics, fungal, bacteria, hand, endotoxin, THC, 

surface wipe, chemical, biological, physical, metagenomics
Health Hazard Evaluation Report 2015-0111-3271 Page 31

The Health Hazard Evaluation Program investigates possible health hazards in the workplace 

under the authority of the Occupational Safety and Health Act of 1970 (29 U.S.C. § 669(a)

(6)). The Health Hazard Evaluation Program also provides, upon request, technical assistance 

to federal, state, and local agencies to investigate occupational health hazards and to prevent 

occupational disease or injury. Regulations guiding the Program can be found in Title 42, Code 

of Federal Regulations, Part 85; Requests for Health Hazard Evaluations (42 CFR Part 85).

Disclaimer

The recommendations in this report are made on the basis of the findings at the workplace 

evaluated and may not be applicable to other workplaces.

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Acknowledgments

Analytical Support: Charles Neumeister, Jennifer Roberts, Bureau Veritas North America

Desktop Publisher: Shawna Watts 

Editor: Ellen Galloway 

Industrial Hygiene Field Assistance: Bradley King

Logistics: Donnie Booher, Kevin Moore

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have also received a copy. This report is not copyrighted and may be freely reproduced. 

Recommended citation for this report:

NIOSH [2017]. Evaluation of potential hazards during harvesting and processing 

cannabis at an outdoor organic farm. By Couch J, Victory K, Lowe B, Burton N, Green 

B, Nayak A, Lemons A, Beezhold D. Cincinnati, OH: U.S. Department of Health and 

Human Services, Centers for Disease Control and Prevention, National Institute for 

Occupational Safety and Health, Health Hazard Evaluation Report Report 2015-0111-

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