quantification of biologically effective environmental uv irradiance

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Adv Space Res Vol 26, No 12, 1983-1994.2000 pp 0 2001 COSPAR Pubhshed by Elsevler Science Ltd All nghts reserved

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QUANTIFICATION OF BIOLOGICALLY EFFECTIVE ENVIRONMENTAL UV IRRADIANCE

G Hot-neck

German Aerospace Center (DLR), Institute of Aerospace Medlcmne, Radzatlon Biology, D-51170 Koln, Germany

ABSTRACT

To determme the impact of envnonrnental W radiation on human health and ecosystems demands momtormg systems that weight the spectral nradrance according to the biological responses under considera- tion In general, there are three different approaches to quantify a btologrcally effective solar u-radiance (1) weighted spectroradiometry where the brologrcally weighted radiometrrc quantrties are derived from spectral data by multtphcatron wrth an action spectrum of a relevant photobtologrcal reaction, e g erythema, DNA damage, skm cancer, reduced productivity of terrestnal plants and aquatic foodweb, (ii) wavelength mtegratmg chemical-based or physical doslmetrrc systems wrth spectral sensmvmes similar to a brological response curve, and (111) brologrcal dosimeters that directly we&t the madent W components of sunhght 111 relation to the effectiveness of the dfierent wavelengths and to mteractrons between them Most brological dosrmeters, such as bactena, bacteriophages, or btomolecules, are based on the W sensmvrty of DNA If precisely charactertzed, brologrcal dosrmeters are apphcable as field and personal dosrmeters 0 2001 COSPAR Published by Elsevler Science Ltd All rights reserved

INTRODUCTION

Stratosphenc ozone is a protective filter of our atmosphere by absorbmg most of the brologrcally harmful W radiation of our sun m the W-C (190-280 nm) and short wavelength-region of the W-B (280-3 15 nm) Although the W-C and W-B regions contribute only 2 % of the entn-e solar nradnmce prior to at- tenuation by the atmosphere (Frederick et al 1989) they are mamly responsrble for the hrgh lethahty of extraterrestnal sunlight to hvmg orgamsms (Homeck and Bra&, 1992) With decreasing stratosphenc ozone concentration, the spectral drstrrbution of ground based W radratron changes srgmficantly more and more W-B radiation reaches the surface of the Earth A depletion of the stratospheric ozone layer was first observed m sprmgtime over Antarctica - commonly termed as “ozone hole” -, and 1s now rdentr- fied globally outside the tropics durmg all seasons of the year (Frederrck, 1993) Hence, the ozone problem winch is predommantly caused by man-made CFCs (chlormated fluorocarbons) (Rowland, 1989) has reached global dimensions Effects are expected (1) for human health, such as increase m skm cancer (Ur- bath, 1989), suppression of the mnnune system (Hurks et al, 1997) vu-us mductron (Yarosh, 1992) and ocular damage (Zrgman, 1993) (11) for terrestrral plants productrvny (Tevrm and Teramura, 1989) and ecosystem balance (SCOPE, 1992) as well as (111) for aquatic ecosystems, both phyto- and zooplankton (Hader, 1997) To determine the imphcatrons of mcreased levels of solar W-B radiation for crrtrcal processes of our biosphere m quantitative terms, an mstrumentatron for W-measurement 1s required that

1983

1984 G Homeck

weights the spectral nradrance according to the brologrcal responses under consrderatron In thrs paper, the different methods to measure the brologrcally effective W nradrance wrll be discussed

BIOLOGICAL SPECTRAL RESPONSES

The brologrcal effecttveness of W radiation changes dramatrcally wrth wavelength With decreasing wavelength, the brologrcal effectiveness increases progressrvely and almost exponentrally Thrs phenomenon 1s described by an action spectrum (Prgure 1) It 1s thrs highly wavelength specrficity of biologrcal action spectra m the W-B range and the wavelength specrfic absorptron characterrstrc of atmospherrc ozone that give nse to the global concern on the impact of a depletion of the stratosphenc ozone layer and thereby an increase m W-B upon the biosphere The shape of the action spectrum of the brologrcal phenomenon under consrderatton determmes whether an incremental change m W-B results m srgmficant changes m the brologlcal effectiveness of solar W radiation Thrs phenomenon stresses the need for a brologrcal weighting of solar W n-radiance for assessing its effects on brologrcal systems

Health effects of envnonmental W radratron on humans are manifold wrth the mductron of pre-mahgnant and mahgnant skm lesions as the most harmful effects Since the skm 1s the drrect target of solar W radratron, the action spectrum for the mammal erythema (Prgure 1) has been recommended as reference action spectrum by The Comrmsslon International de 1Bclalrage (CIE) It has been obtamed by averagmg over the spectral responses of vatlous mdlvlduals of different skm types (McKinley and Dlffey, 1987)

IO'

104

IUS I I I I I I I l-

250 275 300 325 350 375 400 425

Wavelength I nm

Fig 1 Actron spectrum for the mrnnnal erythema which has been recommended by CIE as reference a&on spectrum for assessmg the health impact of envuonmental UV rtiation (data from McKmley and D&y, 1987)

Reference wavelength IS h = 298 nm

Although the mnumal erythema 1s 1s used as a reference blomarker, it nught not be the proper mdlcator for the assessment of human health nsks from environmental W radlatlon With regard to human skm cancer, DNA 1s thought to be the prmapal molecular target of envtronmental W radiation (Figure 2) W- induced DNA lessons can lead to oncogemc alterations that play important roles m the mductlon of skm

Blologlcally Effechve UV 1985

cancer There 1s stnkmg evrdence that W-Induced DNA damage 1s the rmtratmg event m unrnunosuppres- sron, tumor promotron, vnus mductron and finally m photocarcmogenesrs (Yarosh, 1992) Likewise, DNA damage plays a central role m adverse effects of W-B radratron to terrestrral plants (Coohrll, 1989) and aquatic ecosystems (Hader and Worrest, 199 1) Therefore, the action spectrum for DNA damage, e g py- rumdme drmer formatron 111 DNA of human skm u-radiated m vrvo wrth W (Freeman et al 1989) or a generahzed action spectrum for DNA damage (Setlow, 1974) might be a more reahstrc brologrcal waghtmg fimctron when assessing the health nsks from an mcreasmg W-B portron m the ground-based W spectrum

promotion progression

Frg 2 Role of DNA lessons rn W-mdduced health risks (based on Yarosh, 1992)

In Figure 3 different action spectra for W-induced health effects are comprled, mcludmg DNA damage (Setlow, 1974), squamous cell carcinoma m race (deGrug1 et al, 1993), and mahgnant melanoma m fish (Setlow et al, 1993) For comparrson, the CIE action spectrum for mnumal erythema 1s also mcluded Wrth mcreasmg wavelength, all action spectra shown sharply decrease m the W-B regron and then level off m the W-A regron Whereas the slope of the action spectra 1s quite smular m the W-B range, the drfferent spectra vary by orders of magmtude m the W-A regron In thrs W regron, m addrtton to DNA, other endogenous chromophores may be involved leading to mdrrect effects on the DNA (Urbach, 1992) The action spectrum for malignant melanoma shows apprecrably hrgh sensrtrvrty in the W-A regron Thrs 1s mterpreted as mdrcatmg that light absorbed m melanm 1s effective m mducmg melanomas (Setlow et aE , 1993) However, rt IS not clear, whether thrs anrmal model 1s also valid for humans

Action spectra, like those shown m Figure 3 have been used as brologrcal weighting fiurctrons to qua&y the brologrcally harmful envrronmental W nradrance Thrs 1s descrtbed m the followmg chapter

1986 G Homeck

10'

250 275 300 325 350 375 400 425

Wavelength I nm

Fig 3 Action spectra for blologuxl responses to environmental UV rtiatlon A DNA damage (from Setlow, 1974), B skm cancer (from de GIU~J~ et al 1993), C rnmmal eqthema (from McKmley and Dlffey, 1987), D mahgnant melanoma (from Setlow et al 1993) Reference wavelength 1s h = 300 nm

MEASUREMENT OF BIOLOGICALLY EFFECTIVE W IRRADIANCE

We&ted hectroradiometry

To quantlfL the blologlcal effectiveness of environmental W radiation, the physical dose parameters have to be converted mto blologlcaily meanmgfU dose parameters Biologically weighted radlometnc qua&ties are derrved from the spectral data by multlplymg them with a blologlcal waghtmg function, 1 e an a&on spectrum of a relevant photoblologlcal reaction, e g DNA damage, erythema formation, skm cancer, reduced productlvlty of terrestnal plants, or W sensltlvlty of aquatic ecosystems The resultmg btologlcal effectiveness spectrum IS shown m Figure 4 The blologcally effective n-radiance Eef (W/mz), IS then determmed as follows (Setlow, 1974)

E, = &% (2) 5 (a)da (1)

with En(A) = solar spectral u-radiance (Wmm2 nm-‘), S&l) = a&on spectrum (relative umts), and h = wavelength (nm) Integration of the blologcally effective n-radiance EM over time (e g , a full day) gves the blologcally effective dose Hef (Jrn-“),R (e g , dady dose) (Horneck, 1995) The advantages of the weighted spectroradlometry method he m rts high accuracy, the capablhty to ident@ mfluences by various parameters, to u&e a large vatlety of blologlcal weighting fimcttons and to use the data for the evaluation of model calculattons &gh demands are made on the mstrument speaficatlons, such as high accuracy - espe- clally at the edge of the solar spectrum m the W-B range, high stray light suppression, high reproduclbd- lty and temperature stab&y Frequent cahbratlon mth standard lamps and field mtercompatlsons vvlth other spectroradlometers are mdlspensable (SCOPE, 1992, McKenzie et al, 1993, Webb et al, 1994)

Blologtcally Effecttve UV 1987

I r

I I I I I I z 250 275 300 325 350 375 400 b

Wavelength / nm

Frg 4 Solar spectral rrradrance at the Earth’s surf&e and a brolo8rcal werghtlng iimctron (actron spectrum) The solar etfectrveness spectrum 1s defined as the product of the rrradrance trmes the actron spectrum The area under the curve IS the brologrcally effkctrve nradrance (see Eq 1)

Spectroradtometers are bulky mstruments and require a large Investment of resources Therefore, there wrll be only a few sites of measurements at selected statrons For field measurement especially at remote sates or for personal dosrmetry, more snnple devrces are requn-ed

Wavelength-Integratmn W Doslmetrv

Wavelength Integrating W detectors wrth a spectral sensmvrty smnlar to the standard erythema functron are wrdely used The most common detectors are based on the excrtatton spectrum of magnesrum tungsten phosphor wrth associated optrcal filter combmatrons (Berger, 1976), or on photosensmve films, such as the polysulphone frhn (Davrs et al, 1976) or polycarbonate plastics (Wong et al, 1989), or on solid state photodrodes m combmatron with optrcal filters (Drffey, 1987) Because the spectral sensmvrty of most chemrcal or physical broad band radiometers does not closely match wrth the most relevant action spectra, then readmgs must be corrected consrdermg the solar W spectrum, the spectral response of the W detector and the actton spectrum of concern The brologrcally effective W dose He, (Jm-z)~ IS determmed accordmg to the followmg equation

H &

= jE” 0) %(4dA

I

F El (A) v, VP

(2)

wrth En(A) = solar spectral nradrance (Wm-* run-‘), S,@J = actron spectrum (relative umts) u&J = response fkctron of the sensor (relatrve units), F = equivalent dose of monochromatrc radratron (I,) producing the same response of the detector (Jm’*), and h = wavelength (mn) Broad band radiometers are relatively cheap, wrdely used devtce wrth a contmuous data acqmsmon A comprehenstve data collectron exrsts from long-term measurements at several sites m USA (Berger and Urbach, 1982, Scotto et al,

1988 G Homeck

1988), from alpme sites (Blumthaler and Ambach, 1990), m deserts (Kolhas et al, 1988) and m northern hrgh latitudes (Jokela et al , 1993) Polysulphone films as simple means of contmuously mtegratmg W exposure are rugged, econonucal and can be mrmaturrzed whrch enables them to a wade apphcatron m medr- cal context, especrally as persona1 dosrmeter (CIE, 1992, Dtiey, 1987, Krms et al, 1998)

Brolosncal W Dosrmetry

Brologrcal dosrmeters automatically weight the madent W components of sunhght relative to the brologrcal effectiveness of the different wavelengths and any mteractrons between them Ideally, the spectral response of the brologrcal dosimeter 1s tdentrcal to that of the action spectrum of the photobiologrcal effect under consideratton In this case; the brologrcally effective dose Heff 1s equivalent to the mcrdent dose of monochromatrc radiation at a standard wavelength h, whrch would produce the same response as the ac- tual radratton under consideratron (Tyrrell, 1980) It IS given by the followmg relation

He8 =F (3) wrth Heff = brologrcally effective dose (Jmm2),s and F = equivalent dose of monochromatrc W radratron producmg the same brologrcal response (Jm-‘)

Intrmsrc Bromarkers for W Exuosure Intrmsrc bromarkers grve a record of the mdrvrdual radiation exposure (e g , of humans, ammals, plants or ecosystems) m measurable umts For momtormg persona1 exposure to envrronmental W radiation, the followmg intrmsrc blomarkers may be apphcable (1) photopro- ducts mduced m the skm (e g , cyclobutadrpyrumdmes, (6-4) ppmrdme-pyrnmdone adducts and their De- war valence isomer) (Freeman, 1989, Chadwrck et al, 1995, Young et al, 1997) and then reparr rates, (n) gene mutatrons m the skm (e g , ~53 mutatrons that occur predommantly assoaated wrth skm cancer) (Daya-GrosJean et al, 1995, Ananthaswamy et al, 1998), (111) second messengers m skin cells (e g , regulation of matrix metalloprotemases) (Brennersen et al, 1996), (iv) antibody titers m the blood, and (v) lens turbrdrty that can be measured by fluorescence The first three methods mentioned are mvasrve, require bi- opsy and are therefore not apphcable for large scale screemng of W exposure of humans However, they should be used to calibrate extrmsrc brologrcal doslmeters

102

IO' - DNA - --. Uracll -- T7 - - - Spore - Bofilm

I I

300 350

Wavelength I nm

Fig 3 Relauve actron spectra of drfferent brologrcal dosnneters (from Hoi-neck, 1997)

Blologtcally Effectwe UV 1989

Extrmsrc Biolo~;lcal W Dosnneters Extrmsrc biological dosimeters are especially suited for long-term momtormg of global changes m environmental W radiation and its biological implications They are also useful m momtormg W exposure of mdivlduals durmg out-door activities (e g , sknng, lnkmg, gardening, or leisure) or those at specral risk So far, biological W dosrmeters of different levels-of complexny are available, mcludmg (1) biomolecules (e g , the uracil molecule or DNA) (Grof et al., 1996, Regan et al, 1992, Yoshida and Regan, 1997) (n) vnuses (e g bacteriophage Tl, T2, T4, or T7) (Ronto et al, 1994) and (111) bacteria (e g E cob, spores of BaczZZus subtzlrs, or EugZena graczlzs phytoplankton) (Munakata, 1993, 1995, Horneck et al , 1996, reviewed m Horneck 1997) The most commonly used biological W doslmeters are listed m Table 1 Then- action spectra (Figure 5) agree quite well with that for DNA damage (Setlow, 1974) Since W-Induced cancer is probably nntiated by photochermcal changes of the DNA (Yarosh, 1992) a predommant mechanism of W-B, these simple brological dosnneters are suitable to es- timate the potential carcmogemc risk of an Increased solar W radiation

The biological W dosimeters are simple, robust and functional mdicators of systems at risk (e g , DNA damage, photosynthetic Impairment, reduced biological activity, or loss m vitality) Most of them are well characterized concernmg then photoblological (e g , action spectra) and radiometnc properties and have been cross-calibrated vvlth other W radiometers (Munakata et al , 1996, Furusawa et al , 1998)

Table 1 Characteristics of the Most Commonly Used Biological W Dosimeters

Biological detector

Biological endpoint

Dosage unit Apphcation Reference

Uracil Drmer formation

DNA Inactivation, dimer formation

Bacteriophage Inactivatron of T7 plaque formers

Bacterial cells (E colz sp )

Bactenal spores (B subabs sp )

Biofilm

Inactivation, mu- tagenesis, role of repair processes, interactions

Inactivation, mu- tagenesis, spore photoproduct formation

Loss of biological activity

Dose to reduce absorb- ance by e-l

Effective dose, eqmva- lent to 254 nm (Jm-‘)

Average number of hits m the population

(Iln(N/Nol)

Inactivation rate constant, dose equivalent to that at 254 nm, % survival, % enhancement of survival by removal of W-B

Inactivation rate constant, mutation doubling constant, dose equivalent to that at 254 nm

Dose equivalent to that at 254 nm

Long-term momtormg

Clear tropical marme water (O-3 m depth)

Long-term/contmuous momtormg, measurements in lakes, rivers, ocean

Dnu-nal profiles, daily totals, vertical dose distribution m natural water

Grof et al, 1996 .

Regan et al, 1992

Ronto et al, 1994

Karentz and Lutze, 1990

Dnu-nal profiles, darly Munakata, totals, long term 1993, 1995 momtormg, personal dosimetry

Long term momtor- Qumtern et mg, personal dosime- al, 1992, try, trend estimation Hoi-neck et

al, 1996

1990 G Horneck

Scope of Apphcatmn ofBmloglcal Doslmetry Bmloglcal UV dostmeters have the potential to be used as personal and field dosimeters complementary to physical UV measurements Their advantages he in the fact 0) that they &rectly weight the incident radlatmn according to its DNA damaging capacity, (n) that they give an integral record of the bmloglcally effective UV dose over a designated period regardless of variations m the weather conditions, 0ii) that they can be used simultaneously at many different sites, and (iv) that they can be attached to mowng targets (e g , persons) with varying onentatmn to the sun A few examples of apphcatmns ofblologacal dosimeters are given m the following

Biological film dosimeters, such as the spore dosimeter (Munakata et al, 1998) and the bmfilm (Rettberg and Horneck, 1998) have been integrated m badges to measure the in&wdual UV exposure with regard to its bmloglcal effectweness Bmloglcal dosimeters have also been used to determme the datly and annual profiles ofbmloglcally effectwe environmental UV radmtion m Hungary (Ront6 et al 1994, 1995), m Bra- zd and Japan (TyrreU, 1978, Munakata, 1993), and m Antarctica (Qumtem et al 1994) Using the spore dostmeter, Munakata (1993) showed m a 14 years study a trend of increase of the bmloglcally effecuve dose of solar UV radmtmn m Tokyo from 1980 to 1993 Using the bmfilm dosimeter m a more than 1 year lasting UV-momtonng campaign m AntarcUca, Qumtern et al (1994) provided experimental proof of an enhanced level of bmlogacally effectwe UV radmtmn during periods of stratospheric ozone depletmn In a space experiment, the bmfilm dosimeter was used to deterrmne the biologically effectwe UV lrra&ance of extraterrestrial sunhght filtered through a set of different cut-off filters to simulate the terrestrial UV radmtmn chmate at different ozone concentratmns Homeck et al (1996) showed that the stratospheric ozone layer reduces the bmlogical effectiveness of extraterrestrial solar radiatmn by three orders of magmtude

CONCLUSIONS

In order to assess the risks to human health and the bmsphere from an increased UV radmuon as a conse- quence of increasing stratospheric ozone depletmn, bmlogJcal dostmetry bears the potenUal of providing ad&tmnal mformatmn to physical measurements and model calculaUons Tl~s is based on the fact, that the bmloglcal dosimeters directly weight the incident UV components of sunhght m relatmn to the bmloglcal effectiveness of the different wavelengths and potential interactmns between them However, m order to provide rehable data, a set of criteria has to be met, wtuch are of photobmloglcal and ra&ometnc nature Such a catalogue of criteria for rehable bmloglcal UV dosmaeters has been elaborated within the BIODOS project of the European Commlssmn It includes the following 7 reqmrements

A biological dosimeter must/should 1 m&cate a biological effect of possible risk or benefit by solar ra&ation

• The reaction must be UV specific (m UV-B and UV-A range) • The reaction should be general • The reaction must indicate a biologically slgmficant process, e g in human health, ecosystem balance,

agricultural and fishery productlwty 2 have a spectral response (UV-B and UV-A) m agreement with a specific photoblologlcal process

• with respect to monochromatic radmtmn • w~th respect to polychromatlc ra&atlon These acUon spectra (mono- and polychromaUc) must be described with the tughest accuracy possible

3 quantify the bmloglcal effectiveness of solar UV ra&ation in measurable umts that can be • compared with other measurements (e g calculated data from spectroradmmetry, other ra&ometers) • converted into other umts ofphotobmloglcal/me&cal importance (e g MED) The error budget shall be estimated

4 produce reproducible data • the procedure must be standardised

BIologlcally Effectwe UV 1991

l the biological sensrtive system must be well defined, e g genetically well defined strams l the operation of the dosimeter must be independent of environmental condmons (e g temperature,

relative hunudity, ram etc ) l stab&y with time The dosimeter should be positioned m a defined manner, dependmg on the purpose (e g horizontally, personal dosimetry)

5 comply with the general requirements for radiometers l absolute responsivzty to W-B, W-A and W-B plus W-A (cahbratron) 0 relative spectral response 0 hnearity of response (law of reciprocity) 0 angular response The feaszbihty of the biological dosimeter should be proven by mtercompanson with biologically weighted spectroradiometry

6 be robust l have a long shelf hfe l be resistant agamst environmental extremes durmg pre- and post-exposure storage (e g heat, cold,

humidny etc ) 7 be suttable for routme measurements

l easy handling 0 safe to the environment 0 automatic registration 0 cost-effectiveness

If sufficiently characterized and cahbrated according to the 7 cntena mentioned above, biologzcal doame- ters are applicable m field measurements and as personal dosimeters

ACKNOWLEDGMENT

The study was supported by a grant of the European Commission (ENV4-CT950044)

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