Workplace Concentrations and Exposure Assessment of Monoterpenes in Rosemary- and Lavender-growing Greenhouses

Abstract

Objectives: Monoterpenes can positively or negatively affect human health depending on their concentrations. To assess the atmospheric risk for greenhouse workers, monoterpene concentrations and personal exposure in herb-growing greenhouses were measured. Methods: Monoterpene concentrations in a commercial greenhouse, where rosemary (Rosmarinus officinalis L.) and lavender (Lavandula angustifolia L.) were grown in pots, were measured every 4 hours on 11 days spread across a year. In a small experimental greenhouse, typical horticultural tasks were conducted to determine the factors increasing monoterpene concentrations. Results: Concentrations of α-pinene, camphene, β-pinene, limonene and cineole in the farmer's greenhouse were higher in winter than in summer because of longer ventilation periods of the greenhouse in summer. Further, the concentrations of these compounds were high (but <2 parts per billion in volume [ppbv]) when horticultural tasks were conducted inside the greenhouse. In a small experimental greenhouse, moving pots and cutting shoots increased ambient monoterpene concentrations to 10 ppbv. Spraying water also increased monoterpene concentrations but to a lesser extent. When performing tasks, greenhouse workers were exposed to monoterpene concentrations 2–3 times higher than the concentration in the ambient greenhouse air. Conclusions: Our measurement results reveal that monoterpene emissions are stimulated by horticultural tasks, even by spraying water. Our calculation result suggests that if ventilation is limited, the concentrations can reach levels high enough to cause sensory irritation in greenhouse workers. Greenhouse workers should be cautious when performing tasks for hours in tightly closed herb-growing greenhouses.

Introduction

Greenhouse farming is highly effective at enhancing crop growth and increasing farmer income; therefore, greenhouse farming has been spreading across the world for several decades. Greenhouses are covered with transparent glass or plastic films to increase the inside temperature and to protect crops from external environmental conditions such as strong wind or precipitation. Because of their airtight structure, the CO₂ concentration in greenhouses tends to drop below the concentration required to maintain a high photosynthetic rate of crops. Ventilation by opening the roof and side windows is effective in maintaining an adequate CO₂ concentration but may cause the air temperature inside the greenhouse to decrease to unfavorable levels.

Plants are known to emit a variety of volatile organic compounds (VOCs). Monoterpenes are a major group of compounds produced as secondary metabolites by many trees, crops, and herbs. Monoterpenes are evaporated from the storage organs present on leaf surfaces and inside the leaves. Major monoterpenes include α- and β-pinene, sabinene, camphene, and limonene. In particular, α-pinene and limonene are ubiquitous in the indoor air of residential houses, schools and workplaces¹⁾ and have been of great concern because of their effects on human health.

Monoterpenes have a variety of effects on humans, and the effects depend on their concentrations. At typical ambient concentrations in and around forests (<10 parts per billion in volume [ppbv]), monoterpenes positively affect humans by reducing stress and fatigue, as shown by measurements of variations in brain waves and blood pressure and volumes²⁾. This therapeutic effect of monoterpenes is considered to be a benefit of forest therapy³⁾.

The medicinal use of essential oils obtained from trees and plants has been investigated. Inhalation of essential oils increases sleeping time, relieves tension, decreases symptoms associated with anxiety and stress, and plays a significant role in regulating the central nervous system⁴⁾.

However, at higher concentrations, e.g., several tens parts per million in volume [ppmv], monoterpenes caused eye, nose and throat irritation^5,6). Wolkoff et al.⁷⁾ proposed a threshold limit value (TLV) and human sensory irritation threshold for α-pinene of 63 and 3.6 ppmv, respectively. At higher concentrations above 3,000 ppmv, these compounds caused mortality in rat and mouse⁶⁾. On the other hand, monoterpenes showed inhibitory effects against chemically induced mammary, lung, and forestomach tumors in rats and mice when added at concentrations of 5–95% to the diet fed to these animals during the initiation and promotion stages of the tumors⁸⁾.

Monoterpene concentrations in greenhouses where monoterpene-emitting herbs are grown may depend on environmental conditions, since emission is influenced by temperature and light intensity⁹⁾. In laboratory measurements, monoterpene emissions have been shown to be increased by vibration stimulus¹⁰⁾, mechanical wounding¹¹⁾ and leaf wet conditions¹²⁾. Therefore, greenhouse tasks including handling and watering plants may stimulate the monoterpene storage organs of the plants and accelerate monoterpene emissions. Further, the airtight structure of greenhouses may be responsible for increasing monoterpene concentrations. However, with the exception of a study on a tomato-growing greenhouse¹³⁾, no study of the effect of environmental conditions, horticultural tasks and ventilation rate on greenhouse monoterpene concentrations has been reported. To assess the atmospheric risk for greenhouse workers, it is important to obtain data on monoterpene concentrations in herb-growing greenhouses.

In the present study, monoterpene concentrations in a farmer's greenhouse were measured throughout the day on 11 days across a year. Because some horticultural tasks seemed to cause an increase in monoterpene concentrations, typical tasks were performed in a small experimental greenhouse to identify the source factors. Samples were also collected near greenhouse workers when they were performing a selected horticultural task to quantify the degree of personal exposure to the monoterpenes.

Materials and Methods

Measurements of monoterpene concentrations in a farmer's greenhouse

1) Greenhouse and plant materials

A glass, gable roof-type greenhouse belonging to a farmer in Mishima City, Shizuoka Prefecture, Japan, was used for this experiment. The greenhouse was 12 m wide and 45 m long with a ridge height of 3.2 m. The roof was pitched at a 30° angle. Saplings of 2 herb species, namely, rosemary (Rosmarinus officinalis L.) and lavender (Lavandula angustifolia L.), with heights of 10–40 cm, were grown in approximately 10,000 pots (10–20 cm in diameter), and the pots were densely arranged on the floor. Rosemary occupied three-fourths of the area.

2) Sampling date and horticultural tasks

Gas sampling was performed every 4 hours for 24 hours on 11 days between April 9th and December 2nd in 2005 (Table 1). Farmers sometimes worked in the greenhouse for purposes such as removing pots for shipping, planting seedlings and opening or closing windows of the greenhouse. Water was automatically, but irregularly, supplied with a rotary spraying device. The farmers maintained a logbook to record the time and duration of all tasks performed in the greenhouse.

Table 1. Measurement date and record of horticultural tasks

	Roof window Time opened	Spraying water Time	Shipping		Planting
			Time	Plant name	Time	Plant name
9-Apr	9:30–24:00
10-Apr	Whole day
13-Apr	9:00–15:30
14-Apr
27-Apr	0:00–10:30
28-Apr	8:00–10:00
6-May	Whole day	11:00–12:00
7-May	Whole day	8:00–9:00
13-May	Whole day		10:30–11:00	Rosemary	9:00–12:00	Rosemary
					14:30–17:00	Rosemary
14-May	Whole day
20-May	Whole day	12:20–13:20	14:00–14:30	Rosemary
21-May	Whole day
3-Jun	Whole day
4-Jun	8:00–10:00
1-Jul	Whole day	12:00–13:00
2-Jul	Whole day
21-Aug	Whole day
22-Aug	Whole day
7-Oct			10:30–11:00	Rosemary
			15:00–16:00	Rosemary and lavender
8-Oct		6:40–7:40
2-Dec			9:15–10:00	Rosemary
3-Dec

3) Sampling method

To collect monoterpenes, an automatic gas sampling system was fabricated and used for measurements. This system consists of a data logger/controller (CR10X, Campbell Scientific, Logan, UT, USA), relay board (SDM-CD16AC, Campbell Scientific, Logan, UT, USA), digital flow controller (3850MS, Kofloc, Kyoto, Japan), pump (MP-11N, Sibata Scientific Technology Ltd., Saitama, Japan), 17 Teflon solenoid valves (USB2-M5-2, CKD, Komaki, Aichi, Japan), and 8 glass adsorbent tubes (130 mm × 7 mm, Shimadzu, Kyoto, Japan). This system has 7 sampling lines and 1 purge line. Glass tubes containing 200 mg Tenax-TA (60/80 mesh) were previously conditioned at 280°C under a flow of purified helium at 50 ml min⁻¹ for several hours. Air samples were first drawn into the purge line for 5 minutes and then pulled into the adsorbent tubes through polytetrafluoroethylene (PTFE) tubes (6 mm in diameter) for 10 minutes using the pump at flow rates of 200 ml min⁻¹. To prevent the degradation of monoterpenes with ozone, an ozone scrubber was applied at the inlet of the PTFE tube¹⁴⁾. The gas sampling system was placed 5 m from the entrance and 6 m from either side of the greenhouse. A gas inlet for the device was fixed at 0.5 m above the ground.

Monoterpenes were collected in different tubes at different sampling events. The sucking line was changed by switching on 1 set of the solenoid valves placed in the front and back of the adsorbent tubes. The starting time, duration and interval of sampling was controlled with the program input into the CR10X. Air temperature, relative humidity and global radiation were measured with T-type thermocouples, a humidity sensor (THT-B120, Sinnyei Technology Co., Ltd., Kobe, Japan), and a pyranometer (MS-62, EKO Seiki, Tokyo, Japan), respectively.

4) Analytical method

Monoterpenes were identified and quantified using a gas chromatography-mass spectrophotometer (GC-MS; QP5050A, Shimadzu). The adsorbent trap was rapidly heated to 250°C within 1 minutes using a thermal desorption system (FLS-3, Shimadzu), and the desorbed VOCs were introduced into the GC-MS system. Compound separation was achieved using an SPB-5 capillary column (50 m × 2.5 mm, 1 μm, 1 film thickness; Sigma-Aldrich Japan, Tokyo, Japan). GC analytical procedures and parameters are described in detail elsewhere¹⁵⁾. The detection limit (S/N=3) of the GC-MS system was 0.03–0.04 pmol, and that of the measured concentration was 7–9 pptv.

Measurements of monoterpene concentrations in an experimental greenhouse

1) Greenhouse and plant material

A glass greenhouse at the University of Tokai (Shizuoka Prefecture, Japan) was used for this experiment. Its width, length, and height were 4 m, 5.5 m and 3 m, respectively. One hundred pots (20 cm in diameter and 30 cm in depth) of rosemary (Rosmarinus officinalis L.) with heights of 50–70 cm were prepared and arranged in 5 rows and 10 columns on 2 parallel benches (1.2 m × 4 m) in the greenhouse. The 2 benches were placed 50 cm above the ground and 50 cm apart from each other. Each pot was placed 20 cm away from the adjacent pots.

2) Experimental procedure

To investigate the effect of horticultural tasks on greenhouse monoterpene concentrations, 3 kinds of tasks were performed in the greenhouse: moving pots, cutting shoots and watering. The task of moving pots imitates pot shipping done by farmers. Fifty pots were moved to a new spot in the array by 2 workers. Farmers often cut the shoots of rosemary to propagate clones of the plant. Fifty shoot tips of 5–7 cm in length were cut from the plants. The plants were large enough to provide many shoot tips for this task. Moving pots and cutting shoots were completed in approximately 10 minutes, while watering was completed in 5 minutes. These tasks were performed on different days, and each task was repeated on 3 separate days. The top windows of the greenhouse were left open throughout the experiments, and the number of ventilations was approximately 14 h⁻¹. To avoid days when wind might enhance gas exchange between the greenhouse and the outside, calm days were chosen for the measurements. The experiments were conducted from May to July 2006.

3) Gas sampling

The automatic gas sampling system was used to periodically collect monoterpenes in the greenhouse. A gas sample was collected in the adsorbent tubes every 10 minutes before, during and after moving pots and cutting shoots and every 5 minutes for watering. The sampling flow rate was 200 ml min⁻¹, and the duration was 5 minutes. The sampling system was placed near the center of the greenhouse, and the gas inlet was fixed at 1 m above the ground.

Sampling near workers performing a horticultural task

1) Experimental procedure

To evaluate the amount of individual exposure to monoterpenes for horticultural workers, samples from the vicinity of the workers were collected during shoot cutting. Shoot cutting was chosen because of the close distance between the workers and herbs. The task was conducted for 10 minutes by 1 worker in the experimental greenhouse, during which 60–80 shoots of rosemary were cut. The experiment was repeated with 3 different workers. The experiments were conducted in May 2011.

2) Gas sampling and analytical methods

A portable pump (MP-Σ30, Shibata Scientific Technology Ltd., Saitama, Japan) was placed on the workers' backs, and the adsorbent tubes were fixed on their shoulders at a distance of approximately 15 cm from the mouth. Samples were first collected for 5 minutes for a control measurement. Then the worker began cutting shoots, and 2 consecutive 5-min samples were obtained. The ambient air in the greenhouse was simultaneously sampled using another portable pump (the same model as used for the personal sampling).

Monoterpenes were identified and quantified using GC-MS. The samples underwent 2-stage thermal desorption (TurboMatrix ATD, Perkin-Elmer), and compound separation was achieved using an SPB-5 capillary column (50 m × 25 mm, 1 μm film thickness). The analytical procedures and parameters are described in detail elsewhere¹⁶⁾.

3) Estimation of monoterpene concentrations in a closed greenhouse

We used a previously described simple mass balance model¹⁷⁾ and calculated monoterpene emission rates to estimate monoterpene concentrations under closed conditions. Because the monoterpene concentrations of the two samples collected during horticultural tasks were in same level, a steady-state mass balance model was employed.

  

where F is the total monoterpene emission rate (nmol s⁻¹), N is the number of ventilations (h⁻¹), V is volume of the greenhouse (L), and C_in and C_out are the total monoterpene concentrations (nmol l⁻¹) inside and outside the greenhouse.

Results

Monoterpene concentrations in the farmer's greenhouse

Typical results for concentration measurements are shown in Fig. 1. The major monoterpenes detected in the analysis were α-pinene, camphene, β-pinene, limonene and cineole. The minor monoterpenes detected consisted of linalool, 3-carene, and linalyl acetate.

Fig. 1.

Diurnal changes in the monoterpene concentrations, air temperature, relative humidity and solar radiation in the farmer's greenhouse.

During the measurements, 3 horticultural tasks were conducted: watering, planting, and shipping. Watering on May 6th and October 7th increased the concentrations of the 5 major monoterpenes by 1.5–2.5 times (Fig. 1). Watering on July 1st was also accompanied by increased monoterpene concentrations. Shipping drastically increased monoterpene concentrations on October 7th (Fig. 1). Shipping was also performed on May 13th and December 2nd, and similar increases were observed. Planting was monitored only on May 13th (Fig. 1), but it greatly raised monoterpene concentrations, and in particular, the cineole concentration increased more than 20-fold.

Ventilation was also a key factor controlling the monoterpene concentrations. On April 13th, the roof windows were opened only from 9 00 to 15 30 hours. Monoterpene concentrations dropped during this period, increased again after the windows were closed, and then gradually decreased under low temperature conditions from night to the early morning. On April 27th, monoterpene concentrations were high when the windows were kept closed. The windows were left open during measurements performed from May to August, except for the measurement performed on June 3rd, to keep the inside temperature as low as possible.

The relative humidity at night was very high; the humidity at night was over 95% from May 13th to December 2nd. Relatively high concentrations of monoterpenes were observed in the early morning measurements obtained at 4 00 hours on June 3rd and July 1st. The relevance of high humidity to high monoterpene concentration is discussed later.

Figure 2 shows maximum, average, and minimum concentrations of α-pinene, limonene, and cineole in the farmer's greenhouse. Maximum and average concentrations of α-pinene in April and December were higher than those in other months. These concentrations tended to be low during the summer because the roof windows were left open. An exception was June 3rd, when the roof windows were closed and high concentrations of the 3 monoterpenes were observed. No clear trends in the variation in the minimum α-pinene concentration were observed.

Fig. 2.

Seasonal variation in average, maximum and minimum monoterpene concentrations in the farmer's greenhouse. The cineole concentration in the sample collected on April 9th was not measured because a wrong m/z value was entered during the gas chromatography-mass spectrometer setup.

Limonene and cineole showed seasonal variations similar to those of α-pinene with regard to maximum, average and minimum concentrations. Again, their concentrations were low in the ventilated greenhouse during summer (May 20th, July 1st and August 21st).

Monoterpene concentrations in the experimental greenhouses

The concentrations of α-pinene, camphene, β-pinene, limonene, and cineole were all less than 0.1 ppbv before the start of the horticultural tasks (Fig. 3), but rose rapidly just after the start of the tasks. The highest concentrations of the 5 monoterpenes were observed when pots were moved. In all 3 instances of pot moving, the α-pinene, limonene and cineole concentrations were 6.1–9.2, 1.4–2.8 and 2.0–3.8 ppbv, respectively. Cutting shoots also led to a large increase in monoterpene concentrations. The concentration of α-pinene rose up to 2.8–5.2 ppbv in the triplicate measurements. Watering, to a less extent, increased the monoterpene concentrations, but never to more than 1 ppbv.

Fig. 3.

Monoterpene concentrations in the experimental greenhouse measured before, during and after the horticultural tasks. The first, second and third panels show results for pot moving, shoot tip cutting and watering, respectively. The arrows indicate the periods during which each task was performed.

Monoterpene concentrations near the workers performing a horticultural task

The total monoterpene concentration in samples obtained from the vicinity of the worker during the shoot cutting task ranged from 12.9 ppb to 18.6 ppb (Table 2). The concentrations were not largely different between workers, and the concentration was 2–3 higher than the ambient concentration in the greenhouse.

Table 2. Change in monoterpene concentrations due to shoot cutting

	Worker A		Worker B		Worker C
	Vicinity	Ambient	Vicinity	Ambient	Vicinity	Ambient
During work	13.5	6.9	18.6	6.0	12.9	5.1
Background	0.1	0.2	0.2	0.1	0.2	0.1

Unit: ppbv.

Monoterpene concentrations estimated under closed conditions

Monoterpene emission rates calculated from equation (1) during the tasks of moving pots, cutting shoots, and watering were calculated to be 204, 99, and 13 nmol s⁻¹, respectively. Assuming that the number of ventilations is zero, horticultural tasks continue for 1 hour, and monoterpene adsorption onto the materials in the greenhouse and absorption by soil can be ignored, the total monoterpene concentrations under completely closed greenhouse conditions were determined to be 282, 135 and 18 ppbv for the tasks of moving pots, cutting shoots and watering, respectively.

Discussion

Factors affecting monoterpene concentrations in the farmer's greenhouse

Opening and closing the roof windows is a major factor affecting monoterpene concentrations in the greenhouse. A drastic concentration difference was observed between samples obtained on April 13th and 27th (Fig. 1). Although the number of ventilations could not be measured in the farmer's greenhouse, this difference can be attributed to the large difference in the ventilation rate between closed- and open-window conditions.

Monoterpene emission from secretory organs is temperature dependent because volatilization of monoterpenes increases with increasing vapor pressure, which is influenced by temperature. For a short range (<20°C) of temperature, a simple model, named the G93 model, can be used to describe the temperature dependency of monoterpene emission⁹⁾. Using this equation, the monoterpene emission rates in summer are estimated to be 5 times higher than those in winter. However, in this study, average and maximum monoterpene concentrations in summer were lower than those in winter (Fig. 2); this may be because the windows were kept open during summer. Closing of the windows from late autumn to spring might have helped accumulation of monoterpenes inside the greenhouse.

Three horticultural tasks—watering, planting and shipping herbs—were performed in the greenhouse. All of the tasks seemed to increase atmospheric monoterpene concentrations in the greenhouse. The mechanisms were assessed by performing an experiment in a small-scale greenhouse and are discussed in the next section.

Effect of typical horticultural tasks on monoterpene concentration

In the farmer's greenhouse, watering, planting and shipping were irregularly performed by the farmers, and these tasks seemed to stimulate monoterpene emissions from the herb species. To investigate the degree of the effect of the horticultural tasks on monoterpene accumulation in the greenhouse, moving pots, cutting shoots and watering were performed in an experimental greenhouse. Moving pots and cutting shoots were considered to be similar to shipping and planting, respectively.

Of the 3 tasks, moving pots maximally increased monoterpene concentrations in the greenhouse. This task causes leaves and branches to touch each other. The vibrational stimulus has been reported to increase monoterpene emission from a herb (Melissa officinalis)¹⁰⁾. M. officinalis, as well as R. officinalis and L. angustifolia used in our study, has oil glands on abaxial leaf surfaces. Therefore, vibration might directly stimulate the oil glands and cause emissions.

Further, cutting shoots increased monoterpene emissions. Holding the shoots with fingers seemed to stimulate emissions from oil glands on leaves, and cutting the shoots with scissors can mechanically damage the monoterpene storage organ in stems, the resin duct, and directly enhance emission from this organ. A previous study using a real-time monitoring instrument, a proton-transfer reaction mass spectrometer, showed that damage due to wounding immediately increased monoterpene emission from the Sitka spruce (Picea sitchensis), and the highest rate of emission was recorded within 3 minutes after cutting¹¹⁾.

Watering also increased emissions. Fine water droplets might vibrate the leaves and stimulate oil glands, even though this stimulus is very soft. Croteau¹²⁾ found that sprinkler irrigation significantly increased monoterpene emissions from peppermint (Mentha × piperita). This might be because the falling water droplets injure the glandular cells and stimulate monoterpene emission. Another possible reason is leaf wetness that might result in increased emission of monoterpenes from the oil gland¹²⁾.

The total monoterpene concentration in the vicinity of workers was 2–3 times higher than the ambient concentration (Table 2). This is because the emission source was close to the workers (∼50 cm). Similar ratios were observed for the monoterpene concentration in ambient air and in the vicinity of workers in indoor Finnish workplaces¹⁸⁾. Our results suggest that risk assessment using only ambient concentration data might underestimate the risk to workers handling emission sources.

Estimated effects of monoterpenes in greenhouses on workers

Monoterpenes are ubiquitous in the indoor environment, where they are emitted from woody products, solvents, fragrances in cosmetics, food additives and other products^3,18). Monoterpenes are also emitted by wood processing in sawmills¹⁹⁾, joinery shops²⁰⁾ and thermomechanical pulp plants²¹⁾. High monoterpene concentrations of several to several tens ppmv were observed in these sites. When harvesting a fragrant plant, Myoga (Zingiber mioga), in field agriculture, high concentrations of α- and β-pinene and limonene were reported to cause eye and skin irritations²²⁾.

Compared with these reports, the herb greenhouses showed low monoterpene concentrations of several ppbv. Monoterpene concentrations in the vicinity of workers performing horticultural tasks were only several times higher than those in the ambient air. The measurements in the experimental greenhouse were performed with the roof windows open. Since the monoterpene concentrations depended on the degree of gas exchange between the inside and outside of a greenhouse, the concentrations might have been higher under less ventilated conditions.

The total monoterpene concentration under completely closed greenhouse conditions was estimated to increase up to 0.3 ppmv for the tasks. The results of the personal exposure measurement (Table 2) indicate that the concentrations of the monoterpenes in the vicinity of the workers are several times higher than ambient levels, and therefore the above calculation suggests that, under the closed conditions, the concentrations near workers may rise up to a sub-ppm level. Although the above simple approximation does not consider monoterpene loss or the extent of air mixing in the greenhouse, these results suggest that the monoterpene concentration greatly depends on the ventilation conditions in the greenhouse.

Limonene and α- and β-pinene in concentrations of ppmv and sub-ppmv have been reported to cause eye, nose and throat irritation^5,6). Wolkoff et al.⁷⁾ proposed that the TLV, air quality guideline and human sensory irritation threshold for α-pinene should be 63, 1.6 and 3.6 ppmv, respectively. The corresponding values for limonene were shown to be 32, 0.7 and 79 ppmv. For the other 3 monoterpenes, data on threshold values for negative effects on human health are unavailable. Our results suggest that under well-ventilated conditions monoterpene concentrations in herb greenhouses have no negative effect on workers. However, the calculations showing the effect of ventilation and the concentrations measured near the workers suggest that continuous work including shipping plants and cutting shoot tips in airtight greenhouses for hours may increase the concentrations close to the sensory irritation threshold. Caution is advised when performing horticulture tasks.

Monoterpene concentrations in greenhouses have been previously reported only by Jansen et al.¹³⁾ for tomato plants (Lycopersicon esculentum). These authors reported that the concentration of β-phellandrene, which is a monoterpene species, increased to the ppbv level when removing shoots and picking fruits and that monitoring of the concentrations of monoterpenes and sesquiterpenes could be used for assessing plant health. They did not discuss the monoterpene risk to workers in the greenhouse in their report. To our knowledge, this is the first study on the risk of atmospheric monoterpenes for greenhouse workers.

Conclusion

Monoterpene concentrations in a rosemary- and lavender-growing greenhouse were greatly influenced by ventilation rate and horticultural work. Typical tasks such as moving pots and cutting shoots were performed in a small experimental greenhouse, and these tasks increased ambient monoterpene concentrations to 10 ppbv. Spraying water also increased the monoterpene concentrations, but to a lesser extent. The concentrations to which workers were exposed were 2–3 times higher than those in the ambient air inside the greenhouse. Our measurement and calculation results revealed that monoterpene emissions are stimulated by horticultural tasks, including spraying water, and that monoterpene concentrations near workers might rise to levels high enough to cause sensory irritation in greenhouse workers. Workers should be cautious when performing horticultural tasks for hours in tightly closed herb-growing greenhouses.

Acknowledgments:

This research was partially supported by the Ministry of Education, Culture, Sports, Science and Techmology, Japan (Grant-in-Aid for Scientific Research (B) No. 21310026 and Grant-in-Aid for Scientific Research on Innovative Areas No. 20120005). It was also supported by the Japan Society for the Promotion of the Science (A3 Foresight Program “CarboEastAsia”).

References

• 1)  Wolkoff P, Nielsen GD. Organic compounds in indoor air—their relevance for perceived indoor air quality? Atmos Environ 2001; 35: 4407-17.
• 2)  Yatagai M. Tree aroma and its function on relaxation and rest. Aroma Research 2000; 1: 2-7 (in Japanese with English summary).
• 3)  Park BJ, Tsunetsugu Y, Kasetani T, et al. Physiological effects of Shinrin-yoku (taking in the atmosphere of the forest)—using salivary cortisol and cerebral activity as indicators. J Physiol Anthropol 2007; 26: 123-8.
• 4)  Edris AE. Pharmaeutical and therapeutic potentials of essential oils and their individual volatile constituents: a review. Phytother Res 2007; 21: 308-23.
• 5)  Kasanen JP, Pasanen AL, Pasanen P, Liesivuori J, Kosma VM, Alarie Y. Evaluation of sensory irritation of Δ3-carene and turpentine, and acceptable levels of monoterpenes in occupational and indoor environment. J Toxicol Environ Health A 1999; 57: 89-114.
• 6)  Mølhave L, Kjaergaard SK, Hempel-Jørgensen A, et al. The eye irritation and odor potencies of four terpenes which are major constituents of the emissions of VOCs from Nordic soft woods. Indoor Air 2000; 10: 315-8.
• 7)  Wolkoff P, Wilkins CK, Clausen PA, Nielsen GD. Organic compounds in office environments: sensory irritation, odor, measurements and the role of reactive chemistry. Indoor Air 2006; 16: 7-19.
• 8)  Crowell PL, Gould MN. Chemoprevention and therapy of cancer by d-limonene. Crit Rev Oncog 1994; 5: 1-22.
• 9)  Guenther A, Zimmerman PR, Harley PC. Isoprene and monoterpene emission rate variability: model evaluations and sensitivity analysis. J Geophys Res 1993; 98: 12609-17.
• 10)  Mochizuki T, Endo Y, Matsunaga S, et al. Factors affecting monoterpene emission from Chamaecyparis obtuse. Geochem J 2011; 45: e15-e22.
• 11)  Tani A, Hayward S, Hewitt CN. Measurement of monoterpenes and related compounds by proton transfer reaction-mass spectrometry. Int J Mass Spectrom 2003; 223/22: 561-78.
• 12)  Croteau R. Effect of irrigation method on essential oil yield and rate of oil evaporation in peppermint grown under controlled conditions. Hort Science 1977; 12: 563-5.
• 13)  Jansen RMC, Hofstee JW, Wildt J, et al. Health monitoring of plants by their emitted volatiles: trichome damage and cell-membrane damage are detectable at greenhouse scale. Annals of Applied Biology 2009; 154: 441-52.
• 14)  Hoffmann T. Adsorptive preconcentration technique including oxidant scavenging for the measurement of reactive hydrocarbons in ambient air. Analytical Chemistry 1995; 351: 41-7.
• 15)  Tani A, Nozoe S, Aoki M, Hewitt CN. Monoterpene fluxes measured above a Japanese red pine forest at Oshiba plateau, Japan. Atmos Environ 2002; 36: 3391-402.
• 16)  Okumura M, Tani A, Kominami Y, et al. Isoprene emission characteristics of Quercus serrata in a deciduous broad-leaved forest. J Agric Meteorol 2008; 64: 49-60.
• 17)  Hodgson AT, Rudd AF, Beal D, Chandra S. Volatile organic compound concentrations and emission rates in new manufactured and site-built houses. Indoor Air 2000; 10: 178-92.
• 18)  Edwards RD, Jurvelin J, Saarela K, Jantunen M. VOC concentrations measured in personal samples and residential indoor, outdoor and workplace microenvironments in EXPOLIS-Helsinki, Finland. Atmos Environ 2001; 35: 4531-43.
• 19)  Eriksson KA, Stjernberg NL, Levin JO, Hammarstroem U, Ledin C. Terpene exposure and respiratory effects among sawmill workers. Scand J Work Environ Health 1996; 22: 182-90.
• 20)  Eriksson KA, Levin JO, Sandstroem T, Lindstroem-Espeling K, Linden G, Stjernberg NL. Terpene exposure and respiratory effects among workers in Swedish joinery shops. Scand J Work Environ Health 1997; 23: 114-20.
• 21)  Goyer N. Chemical emissions in a thermomechanical pulp production plant. Appl Occup Environ Hyg 1994; 9: 428-32.
• 22)  Wei Q, Harada K, Ohmori S, Minamoto K, Wei C, Ueda A. Toxicity study of the volatile constituents of Myoga utilizing acute dermal irritation assays and the Guinea-pig Maximization test. J Occup Health 2006; 48: 480-6.