1Centre for Astronomy and Atmospheric Research, University of Southern Queensland, Toowoomba, 4350, Australia. Ph: 61 7 46 312226. Fax: 61 7 46 312721. Email: parisi@usq.edu.au
2Centre for Medical and Health Physics, School of Physical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, 4001, Australia.
(*To whom correspondence should be addressed)
Abstract
The ranges of conditions and environments of a dosimetric spectrum evaluator previously developed and employed in the evaluation of the UV source spectrum have been considered in this paper. The complete system of four dosimeter materials can be employed for a total UV exposure of up to approximately 10 J cm-2. The exposure times required were influenced by the UV environment. The exposure times ranged from 20 minutes to 3 hours for filtered solar erythemal UV, 5 to 30 minutes for solar erythemal UV, 30 to 53 minutes for quartz tungsten halogen lamp erythemal UV, 10 to 15 minutes for plant damage solar UV and 90 minutes for plant damage UV from fluorescent sun lamps. In these environments, employing the system in open and well-ventilated conditions minimises changes in the dose response of the system due to temperature. The results in this paper provide a guide for the range of conditions and exposure times required for different environments for future research employing the dosimetric spectrum evaluator.
INTRODUCTION
Ultraviolet (UV) radiation is a genotoxic and has a causative role in human skin cancer, premature skin photo-aging and wrinkling and some eye disorders (Longstreth et al., 1995). Additionally, increased ultraviolet irradiances due to stratospheric ozone depletion may affect plant growth (Caldwell et al., 1995). An improved characterisation and understanding through UV measurements of the solar UV exposures to humans and plants is required.
The measurement of UV radiation in photobiological experiments has been
reviewed in another paper (Wong and Parisi, 1998). Spectroradiometers and
radiometers may be employed for ambient UV measurements on a horizontal
plane. However, UV dosimeters must be employed for simultaneous multi-site
measurements of the UV irradiances to specific sites on the object of study.
Dosimeters based on polysulphone (Diffey, 1989) and CR-39 (Wong et al.,
1992) have been employed for erythemal UV measurements. A dosimetric spectrum
evaluator based on four different UV dosimeter materials has been developed
(Parisi et al., 1997, Parisi and Wong, 1996a) and employed in photobiological
research (for example, Parisi et al., 1998a). Each of the materials is
sensitive to different UV wavelengths and measurement of the change in
the optical absorbance of each of the materials at a set wavelength for
each material allows broad scale evaluation of the UV spectrum. The minimum
irradiance required on this type of detector is 0.01 mW
cm-2. This paper investigates the range of conditions and exposure
times of the spectrum evaluator system for different UV environments.
MATERIALS AND METHODS
Dosimeter System
The technique for the spectrum evaluator based on the four different
dosimeter materials, polysulphone, nalidixic acid, 8-methoxypsoralen and
phenothiazine has been described elsewhere (Parisi et al., 1997). The physical
size of the spectrum evaluator holder is approximately 3 cm x 3 cm. Each
different material is over a 0.6 cm diameter hole in the holder. The system
provides the time averaged spectrum over the exposure period and incorporates
any changes in the source UV spectrum during the period. The evaluated
source spectrum agrees to better than 20% with that measured with a calibrated
spectroradiometer. The exposure times for the spectrum evaluator are a
compromise between a sufficient UV exposure to produce a measurable change
in optical absorbance of the material, but not long enough to either saturate
the most sensitive dosimeter material or allow an unacceptable large change
in the source spectrum.
Environments
The spectrum evaluator has been employed to evaluate the UV spectrum
for both natural and artificial UV sources at any orientation over the
object of study in a number of environments. The system has been employed
to measure the biologically effective UV irradiances received to specific
body sites on humans and on a horizontal plane in a number of different
environments, namely, in a car interior (Parisi and Wong, 1998), glass
enclosure (Parisi and Wong, 1997a) and greenhouse (Parisi and Wong, 1997b)
for solar UV, outside for winter and summer sun and in the laboratory employing
a quartz tungsten halogen (QTH) lamp (Parisi et al., 1997) as the UV source.
For plant studies, the system has been employed over a plant canopy, both
in the field (Parisi and Wong, 1996b, Parisi et al., 1998b) and in a greenhouse
(Parisi et al., 1996). In the greenhouse, artificial UV was provided with
Philips TL40/12 sunlamps. The effect of ambient air temperature in each
of these environments on the response of the dosimeter material is also
discussed.
The biologically effective UV irradiance (UVBE) has been calculated as follows:
UVBE = ò uv Sl Al dl (1)
where Sl is the source UV spectrum and Al is the action spectrum for the biological process. In this paper, the action spectrum for human erythema (CIE, 1987) and the generalised plant damage action spectrum (Caldwell, 1971) are employed.
RESULTS
Saturation
The dose response to UV radiation of each of the dosimeter materials
has been measured (Parisi and Wong, 1996a). The approximate total UV exposure
for which the dose response of each of the materials starts to saturate
is provided in Table 1. Phenothiazine is the most sensitive of the four
materials with 8-methoxypsoralen the least sensitive. Phenothiazine saturates
for total UV exposure of approximately 10 J cm-2, whereas, 8-methoxypsoralen
has a linear dose response for a total UV exposure of up to 40 J cm-2.
Similarly, nalidixic acid and polysulphone have an approximate linear response
to about 15 J cm-2 of total UV before the response starts to
saturate. These are the approximate exposure limits before the individual
dosimeters start to saturate. As a combined system of dosimeters, the exposure
limit for the system is approximately 10 J cm-2.
Table 1 - The approximate total UV exposure at which the dose response
of each of the materials start to saturate.
| Material |
|
| Phenothiazine |
|
| Nalidixic acid |
|
| Polysulphone |
|
| 8-methoxypsoralen |
|
Environments
The different environments in which the spectrum evaluator has been
employed and the range of biologically effective irradiances for human
erythema and generalised plant damage that have been encountered are provided
in Table 2. The environments can be divided into a number of categories.
Namely, filtered solar UV in a greenhouse, glass enclosure and a car interior
with erythemal irradiances ranging from 0.01 to 0.93 mW
cm-2. The spectrum evaluator has been orientated at the appropriate
angles both over a rectangular prism and a manikin to approximate the human
body shape. The second category of environment was solar UV for both summer
and winter with the spectrum evaluator attached to human volunteers and
erythemal irradiances of 3.1 to 25 mW cm-2.
The third category was for UV from a QTH lamp in the laboratory on a horizontal
plane with irradiances of 18 to 43 mW cm-2.
For plants, the irradiances can be grouped into natural sunlight in winter
and autumn and artificial UV provided with sunlamps in a greenhouse. For
sunlight, the plant damage irradiances were 9 to 17 mW
cm-2 and 10 to 43 mW cm-2
in winter and autumn respectively with plant damage irradiances of 2 to
20 mW cm-2 in the greenhouse.
Table 2 - The range of different environments and the biologically
effective irradiances for which the spectrum evaluator has been employed.
| Object | Environment | Source | UVBE (mW cm-2) |
| Human model | Greenhouse | Spring Sun | 0.06 - 0.32 |
| Human model | Glass enclosure | Sun | 0.18 - 0.93 |
| Human model | Car interior | Winter Sun | 0.01 - 0.14 |
| Humans | Winter | Sun | 3.1 - 4.2 |
| Humans | Summer | Sun | 17 - 25 |
| Horizontal Plane | Laboratory | QTH lamp @ 10 cm | 43 |
| Horizontal Plane | Laboratory | QTH lamp @ 14 cm | 18 |
| Plants | Winter | Sun | 9 - 17 |
| Plant model | Autumn | Sun | 10 - 43 |
| Plants | Greenhouse | Sunlamps | 2 - 20 |
Exposure Times
The ranges of exposure times employed for the spectrum evaluator for
the different irradiances and environments are provided in Figure 1. The
categories of the different irradiance environments are shown with different
symbols. The exposure times ranged from 20 minutes to 3 hours for the filtered
solar erythemal UV, 5 to 30 minutes for the solar erythemal UV, 30 to 53
minutes for the QTH lamp erythemal UV, 10 to 15 minutes for the plant damage
solar UV and 90 minutes for the plant damage lamp UV. For general applications,
the results of the exposure times for the different UV sources have been
summarised in Table 3.
Table 3 – The range of biologically effective irradiances for erythema(a)
and plant damage(b) and the approximate exposure times that
may be employed.
| UV Source | UVBE (mW cm-2) | Exposure Time (minutes) |
| Filtered solar UV | 0.06 – 0.32(a) | 60 |
| Filtered solar UV | 0.18 – 0.93(a) | 20 |
| Filtered solar UV | 0.01 – 0.14(a) | 180 |
| Solar UV | 3.1 – 4.2(a) | 30 |
| Solar UV | 17 – 25(a) | 5 |
| QTH lamp | 43(a) | 30 |
| QTH lamp | 18(a) | 53 |
| Fluorescent sunlamps | 2 – 20(b) | 90 |
| Autumn sun | 10 – 43(b) | 10 |
| Winter sun | 9 – 17(b) | 15 |
Temperature
The effects of temperature on the individual dosimeter materials have
been measured over the temperature range 34.5 to 61.3 oC (Parisi
and Wong, 1996a). Over this range, there was no significant temperature
effect for polysulphone and 8-methoxypsoralen and phenothiazine showing
no effect up to 50 oC, with an effect for higher temperatures.
For nalidixic acid, there was a small increase with temperature in the
change in absorbance of 0.001 /oC. As a combined system of dosimeters,
any temperature effects can be minimised by using the system at approximately
constant temperatures below 50 oC. These can be maintained by
employing the system in the open or well-ventilated conditions.
CONCLUSION AND DISCUSSION
The ranges of conditions and environments of a dosimetric spectrum evaluator previously developed and employed in the evaluation of the UV source spectrum have been considered in this paper. The complete system of four dosimeter materials can be employed for a total UV exposure of up to approximately 10 J cm-2. For the different environments, the exposure times required for the spectrum evaluator were found to be a compromise between producing a measurable change in optical absorbance of the dosimeter material and reducing the saturation of the dosimeter material and minimising any changes in the source spectrum. The exposure times ranged from 5 minutes to 3 hours and were dependent on the UV irradiances and the general shape of the UV spectrum, which was influenced by the UV environment. In these environments, employing the system in open or well-ventilated conditions up to temperatures of 50 oC minimises changes in the dose response of the system due to temperature. The results presented in this paper provide a guide for the ranges of conditions and exposure times required for the different environments for future research employing the dosimetric spectrum evaluator.
Acknowledgments – The authors would like to thank Ken Mottram, Ron Matthews, Oliver Kinder, Graeme Holmes and Dennis Cracknell in the USQ physics discipline whose technical expertise contributed to these projects.
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