Directory UMM :Data Elmu:jurnal:E:Environmental Management and Health:Vol09.Issue3.1998:

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A.F. Mage d and E.A. Saad Rado n e xhalatio n rate fro m so me fe rtilize rs, c lay and po tato e s in Egypt

Enviro nme ntal Manage me nt and He alth

9 / 3 [1 9 9 8 ] 1 3 1 –1 3 5

r a t e fr om fer t ilizer s, p ot a t o cr op a n d clay. T h e t h ick n ess of CR-39 is a b ou t 500µm , w h ich is sp ecia lly d esign ed for t h e r e gist r a t ion of a lp h a p a r t icles. T h e t r a ck s d et ect ed by t h ese CR-39 fi lm s en la r ged by p r ocessin g t h e d et ect or s in a n a lk a lin e solu t ion . T h e ca lib r a t ion fa ct or (Ma ged et a l.,1993) for r a d on m ea su r em en t s u sin g CR-39 d et ect or in a p la st ic h ollow h old er w a s 1.37 t r a ck cm-2_{.k Bq}-1_.h-1_.m3_{. T h e CR-39 d et ect or w a s cu t}

in t o 1.5 ×1.5cm p ieces a n d a ffixed t o a h ollow h old er. Sa m p les of som e fer t ilizer s, d r y p ot a -t oes a n d clay of a b ou -t 1gm w er e gr ou n d , -t h en p r essed a t 10 t on s (d isc d ia m et er 1.3cm ) for t en m in u t es. T h e sa m p le w a s t h en p la ced in sid e t h e h ollow h old er. T h e exp osu r e t im e w a s a b ou t t wo m on t h s. T h e t r a ck s d u e t o a lp h a p a r t icles fr om r a d on t h a t h a d en t er ed t h e a ir sp a ce in t h e h ollow h old er w er e r e gis-t er ed in gis-t h e CR-39 p la sgis-t ic d egis-t ecgis-t or. T h e fi lm s w er e et ch ed in 6 M N a OH solu t ion a t 70ºC for 18 h ou r s, t h en w er e h eld for a b ou t fi ve m in -u t es in r -u n n in g w a t er. T h e n -u m b er of a lp h a t r a ck s w a s r ecor d ed by op t ica l m icr oscop e a t t a ch ed t o a n im a ge a n a ly sis sy st em Qu a n -t im e-t 500.

Theoretical approach

T h e t im e r a t e ch a n ge of r a d on con cen t r a t ion in d oor s ca n b e d escr ib ed a s follow s:

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w h er e C(t) is t h e r a d on con cen t r a t ion in d oor s a t t im e t(Bq .m-3), E is t h e r a d on exh a la t ion r a t e p er u n it a r ea (Bq .m-2_.h-1_{), S is t h e su r fa ce}

a r ea fr om w h ich r a d on is exh a led (m2_{), V is}

t h e in d oor volu m e (m3_{), A is t h e ot h er r a d on}

sou r ces (Bq .h-1_{), C}

ois t h e ou t d oor r a d on con -cen t r a t ion (Bq .m-3_),λ

vis t h e a ir exch a n ge r a t e (ven t ila t ion ) con st a n t (h-1_{), T}

ia n d Toa r e t h e in d oor a n d ou t d oor t em p er a t u r e r esp ec-t ively, P_ia n d P_oa r e t h e in d oor a n d ou t d oor a t m osp h er ic p r essu r e r esp ect ively ; λis t h e r a d on d ecay con st a n t (h-1_).

Un d er eq u ilib r iu m con d it ion s eq u a t ion 1 ca n b e sim p lifi ed a s follow s :

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It is ev id en t fr om eq u a t ion (2) t h a t t h e m a in va r ia bles t o t h e exh a la t ion r a t e p er u n it a r ea (E) a r e t h e in d oor r a d on con cen t r a t ion C(t) a n d t h e a ir exch a n ge r a t e con st a n t (λ_v). It is p ossible t o p r ed ict t h e exh a la t ion r a t e p er u n it a r ea by m ea su r in g t h ese t wo p a r a m e-t er s, C(e-t) a n d λ_v.

To est im a t e t h e m a xim u m r a d on con cen t r a -t ion in a closed ch a m b er, w e se-t λ_veq u a l t o 0.05h-1, w h ich is a ver y p oor ven t ila t ion r a t e. T h er efor e, eq u a t ion (2) ca n fu r t h er b e sim p li-fi ed a s follow s:

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T h e exh a la t ion r a t e p er u n it a r ea (E) ca n t h en b e est im a t ed by m ea su r in g C a n d V/S. Me dite rrane an Se a

Cairo

1

2

Sinai

3 N

R e

d S

e_a

EGYPT

5 0 km Figure 1

The thre e Egyptian fac to rie s o f pho s phate fe rtilize rs . 1 – Kafr EL Z iat, 2 – Abu Z aable and 3 – As s uit

C(T) = C_S

C(0 ) = C_B

X = T

X = 0 X E

C(X) Figure 2

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9 / 3 [1 9 9 8 ] 1 3 1 –1 3 5

Con sid er t h e ca se of r a d on exh a lin g fr om a d isc of t h ick n ess T con t a in in g a u n ifor m con cen t r a t ion of 226_{Ra a n d in a d d it ion , t h e}

r a d on con cen t r a t ion a b ove a n d b elow t h e d isc a r e m a in t a in ed a t C_Sa n d C_Br esp ect ively. T h is con fi gu r a t ion is sh ow n in F igu r e 2. At eq u ilib r iu m st a t e, t h e exh a la t ion r a t e of r a d on fr om t h e su r fa ce of t h e d isc a t X= T is a s follow s (Colle et a l.,1981),

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w h er e ε is t h e p or osit y, r a t io of p or e volu m e t o bu lk volu m e; λis t h e d ecay con st a n t of r a d on 7.6 ×10-3_h-1_,l_{is t h e d iffu sion len gt h of r a d on}

in t h e d isc; θis t h e r a d on p r od u ct ion r a t e Bq .m-3_{; C}

Bis t h e r a d on con cen t r a t ion a t X = 0; a n d C_Sis t h e r a d on con cen t r a t ion a t

X = T.

It is p ossible t o see t h a t t h e exh a la t ion r a t e of r a d on fr om t h e su r fa ce of t h e d isk is p r o-p or t ion a l t o t h e o-p or osit y of t h e m ed iu m , t h e d iffu sion len gt h of r a d on , a n d t h e d ecay con -st a n t of r a d on . T h e t h r ee t er m s in p a r en t h e-sis in eq u a t ion (4) in d ica t e t h a t t h e r a d on p r od u ct ion r a t e a n d r a d on con cen t r a t ion b elow t h e d isc w ill in cr ea se t h e su r fa ce exh a -la t ion r a t e, w h ile t h e r a d on con cen t r a t ion a b ove t h e d isc w ill d ecr ea se t h e r a d on fl u x on it s su r fa ce. T h e t h ick n ess of fer t ilizer or clay sa m p les t est ed is t h in n er t h a n 1cm , bu t t h e effect ive d iffu sion of 222Rn in soil a ir, a ssu m -in g fr ee com m u n ica t ion b et w een p or e sp a ces, is a b ou t 2m (UN SCE AR, 1982) . It is of in t er est t o n ot e h er e t h a t clay soils, a lt h ou gh ver y p or ou s, a r e n ot ver y p er m ea ble even w h en d r y b eca u se fr ee com m u n ica t ion b et w een t h e p or e sp a ce is p r oh ib it ed by t h e t ext u r a l com -p osit ion of t h e soils (F igu r e 3).

In t h is ca se, sin h T/l ≅_T_/l_{, cosh T}_/l ≅ _{1 +}

T/ 5 , eq u a t ion (4) ca n b e sim p lifi ed a s follow s, (5)

T h e eq u a t ion (5) m a t h em a t ica l a p p r oa ch is b a sed on a n id ea l st ea dy st a t e con d it ion . In a r ea l sit u a t ion , t h e in it ia l r a d on exh a la t ion r a t e (E_o) in a closed ch a m b er is la r ge b eca u se a t t = 0, C_S= 0. La t er, r a d on exh a la t ion r a t e, E(t) d ecr ea ses r a p id ly a s C_Bin cr ea ses w it h t im e, a n d E(t) w ill r ea ch a con st a n t va lu e a s b ot h C_Sa n d C_B, in eq u a t ion (5), a lso r ea ch a con st a n t va lu e. To m ea su r e su ch a low r a d on exh a la t ion r a t e, a p a ssive m et h od w a s d evel-op ed a n d t h e m a t h em a t ica l m od el n eed s t o b e sim p lifi ed t o a sses t h e aver a ge r a d on exh a la -t ion r a -t e in -t o a closed ch a m b er.

Experimental approach

If a d isk of fer t ilizer s, or clay or d r y p ot a t oes (1gm ), is set in sid e a h ollow h old er (volu m e is 3 ×10-5_m3_{a n d su r fa ce a r ea is 1.33}_×₁₀-4_m2_{) t h e}

t im e va r y in g r a d on con cen t r a t ion in t h e h ollow h old er C(t) w ill follow t h e d iffer en t ia l eq u a t ion .

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w h er e S is t h e a r ea of t h e d isk (m2_{), V is t h e}

volu m e of t h e h ollow h old er (m3_{), a n d}_λ_{is t h e}

d ecay con st a n t of r a d on .

000000000000000000000000000000000 000000000000000000000000000000000 000000000000000000000000000000000 000000000000000000000000000000000 000000000000000000000000000000000

00000 00000 00000 00000

SOIL

00000 00000 00000 00000

CAPILLARITY BREAKING LAYER

000000 000000 000000 000000

CLAY

TRANSPORT OF SOIL GAS

DIFFUSION OF RADON

0000000000000000000 0000000000000000000 0000000000000000000

00000 00000 00000 00000

SOIL

00000 00000 00000 00000

CAPILLARITY BREAKING LAYER

000000 000000 000000 000000

ESKER GRAVEL

TRANSPORT OF SOIL GAS Figure 3

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9 / 3 [1 9 9 8 ] 1 3 1 –1 3 5

To ob ser ve t h e dy n a m ic va r ia t ion of r a d on level in a closed ch a m b er (volu m e is 0.24m3_),

t h e p it ch blen d e sa m p le (su r fa ce a r ea is 7.85 ×

10-3_m2_{) w a s p la ced in a closed ch a m b er w ell}

eq u ip p ed w it h a silicon b a r r ier d et ect or. T h e r a d on con cen t r a t ion in t h e ch a m b er w a s m ea su r ed d a ily u n t il it r ea ch ed eq u ilib r iu m . It sh ow ed t h a t t h e exh a la t ion r a t e d ecr ea sed a s t h e r a d on con cen t r a t ion in t h e a ir in cr ea sed a s sh ow n in F igu r es 4 a n d 5.

E xp er im en t a l d a t a sh ow ed t h a t E(t) ca n b e exp r essed a s follow s a t eq u ilib r iu m :

(7) T h e α-va lu e of F igu r e 5 is 0.5m .h-1_{w h ich w a s}

ca lcu la t ed fr om p it ch blen d e m in er a l in a closed ch a m b er a t eq u ilib r iu m . Su b st it u t in g E(t) in eq u a t ion (6) by eq u a t ion (7) gives

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Let

T h e β va lu e is 0.02h-1_{for p it ch blen d e in sid e}

t h e closed ch a m b er. T h en a solu t ion of eq u a -t ion (8) is

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In t e gr a t in g eq u a t ion (9) fr om t = 0 t o t = t gives

(10) E q u a t ion (10) sh ow s t h e cu m u la t ive r a d on a ct iv it y by u sin g a p a ssive cu m u la t ive r a d on m on it or. T h er e a r e t wo u n k n ow n p a r a m et er s, E_oa n d β, so it is n ot p ossible t o get b ot h p a r a -m et er s by a sin gle -m ea su r e-m en t . To si-m p lify t h e m ea su r in g p r oced u r es, set E(t) = con -st a n t , t h en eq u a t ion (9) ca n b e sim p lifi ed a s

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T h is is t h e ca se of n o b a ck d iffu sion . F igu r e 6 sh ow s t h e d iffer en ce of r a d on gr ow t h cu r ves of eq u a t ion s (9) a n d (11). Accor d in g t o t h e dy n a m ic ob ser va t ion of t h e r a d on exh a la t ion r a t e fr om p it ch blen d e m in er a l, it w ill r ea ch eq u ilib r iu m w it h in 15 d ay s. At eq u ilib r iu m E(t) it ca n b e ca lcu la t ed by r ew r it in g eq u a t ion (6) a s follow s:

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F igu r e 5 sh ow s t h e r a d on exh a la t ion r a t es of p it ch blen d e m in er a l ca lcu la t ed fr om eq u a -t ion (12). F r om -t h is fi gu r e a n d Ta bles I-II, i-t is

7 0 6 0 5 0 4 0 3 0 2 0 1 0 0

0 5 1 0 1 5 2 0

Growth Time (day)

Radon Concentration (kBqm–3)

Figure 4

The e xpe rime ntal gro wth o f rado n in a c lo s e d ro o m

7 0 0

6 0 0

5 0 0

4 0 0

3 0 0

2 0 0

1 0 0

0

Exhalation rate (kBqm2_h–1₎

Random Concentration (kBqm–3₎

0 1 0 2 0 3 0 4 0 5 0 6 0 7 0

Figure 5

Exhalatio n rate s c alc ulate d by e quatio n (1 2 ) o f pitc hble nde mine ral. Re gre s s io n c urve at e quilibrium s ho ws lo w s lo pe (αvalue in e quatio n (7 ))

3 0 0 0

2 5 0 0

2 0 0 0

1 5 0 0

1 0 0 0

5 0 0

0

0 5 1 0 1 5 2 0 2 5 3 0

Growth time (day) Radon concentration (kBqm–3₎

Key

Equatio n 9 with bac k diffusio n Equatio n 1 1 no bac k diffus io n Figure 6

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9 / 3 [1 9 9 8 ] 1 3 1 –1 3 5

p ossible t o see t h a t t h e in it ia l r a d on exh a la -t ion r a -t e is ver y h igh a n d sh ow s a d iscr e-t e p h en om en on . T h e cor r ela t ed p a r a m et er s a r e su m m a r ized in Ta bles I a n d II. T h e d iffer en ce b et w een t h e r a d on exh a la t ion r a t es ca lcu -la t ed fr om eq u a t ion (12) a n d t h e h ollow h old er m et h od a t eq u ilib r iu m u sin g eq u a t ion (13) a r e com p a r ed in Ta ble II. T h e h ollow h old er m et h od w h ich m ea su r ed d a t a w it h in t wo m on t h s of exp osu r e w a s a lit t le b it h igh er t h a n t h a t ca lcu la t ed fr om eq u a t ion (12). F igu r e 7 sh ow s t h e exp er im en t a l r ela t ion b et w een t h e r a t io of volu m e of t h e h ollow h old er p er su r fa ce a r ea fr om w h ich r a d on is exh a led a n d t h e t im e of r ea ch in g eq u ilib -r iu m . In p -r a ct ica l a p p lica t ion , t h e CR-39 p la s-t ic d es-t ecs-t or ca n b e u sed in a ca lib r a s-t ed h ollow h old er t o m ea su r e t h e a ccu m u la t ed a ct iv it y a n d est im a t e t h e aver a ge r a d on exh a la t ion

r a t es fr om fer t ilizer s, clay a n d p ot a t oes. In t h is ca se eq u a t ion (10) ca n b e sim p lifi ed a s

(13) w h er e E is aver a ge r a d on exh a la t ion r a t e of fer t ilizer s or clay or p ot a t oes (Bq .m-2_.h-1_{), C is}

t h e m ea n r a d on con cen t r a t ion m ea su r ed by CR-39 (Bq .m-3_{), t is exp osu r e t im e (t wo}

m on t h s), Vis t h e volu m e of t h e h ollow h old er (m3_{) a n d}_λ_{is t h e r a d on d ecay con st a n t (h}-1_).

Conclusion

T h e u se of fer t ilizer s con t a in in g p h osp h a t e in m a ssive q u a n t it ies h a s led t o t h e r ed ist r ibu -t ion -t h r ou gh ou -t -t h e en v ir on m en -t of la r ge a m ou n t s of u r a n iu m , r a d iu m a n d r a d iu m d ecay p r od u ct s. T h e r esu lt in g p ot en t ia l r a d io-logica l im p a ct s a r e d u e t o d ir ect exp osu r e, su r fa ce r u n -off in h a la t ion a n d in gest ion of food s gr ow n w it h fer t ilizer s. Gy p su m , a by -p r od u ct of t h e -p r od u ct ion of -p h os-p h a t e fer t il-izer s, con t a in s m u ch of t h e r a d iu m or igin a lly in t h e p h osp h a t e r ock . T h e r esu lt in g w a st e gy p su m p iles a r e a sou r ce of r a d on em ission t o t h e en v ir on m en t . In ou r m ea su r em en t s t h e aver a ge r a d on exh a la t ion r a t es for p r ocessed fer t ilizer s, clay a n d p ot a t oes a r e 1.8, 0.6 a n d 0.07Bq .h-1_.m-2_{r esp ect ively, fr om on e gr a m by}

t h e h ollow h old er m et h od . We b elieve t h a t t h e exh a la t ion r a t e p er gm m ay b e con st a n t for t h ick n ess of t h e or d er of on e m et er. T h is is b a sed on t h e d iffu sion len gt h of 222_{Rn in}

p or ou s m ed ia b ein g a s h igh a s 200cm . T h e exh a la t ion r a t e of 222_{Rn fr om 200 b a gs of fer}

-t ilizer s ea ch of 50k g k e p -t in a n u n ven -t ila -t ed Table I

Dynamic o bs e rvatio n o f rado n e xhalatio n rate s and re late d parame te rs o f pitc hble nde

a_E

o bEo α β cE1 dE2 eEh

(k.Bq-2_.h-1_{) (k.Bq}-2_.h-1₎ _(m.h-1₎ _(h-1) _(k.Bq-2_.h-1₎ _(k.Bq-2_.h-1_{) (k.Bq}-2_.h-1₎

6 5 5 9 1 0 .5 0 .0 2 1 8 .6 1 8 .8 1 3 .7

Notes:

a_E

ois the extrapolation of equation (7 ) b_E

ois c alc ulated from equation (1 1 ) c_E

1is the average exhalation rate at equilibrium inside c losed c hamber: equation (1 2 ) d_E

2is the average exhalation rate at equilibrium, c alc ulated from equation (1 1 ) e_E

his measurable by CR-3 9 in hollow holder inside the c losed c hamber at equilibrium:

equation (1 3 )

Table II

The rado n e xhalatio n rate s fro m pho s phate raw mate rials , pro c e s s e d fe rtilize rs , c lay and po tato c ro p

Name C (Bq.m-3₎ _E

h(Bq.m-2.h-1) E1 (Bq.m-2.h-1)

I Raw material of fertilizers

Assuit 1 ,2 4 4 2 .3 5 2 .1 3

Abu Zaabel 9 3 6 1 .7 7 1 .6 1

Kafr El Ziat 7 6 7 1 .4 5 1 .3 1

II Processed fertilizers

Assuit 1 ,0 5 5 1 .8 6 1 .8 0

Abu Zaabel 7 6 8 1 .3 6 1 .3 1

Kafr El Ziat 1 ,2 2 2 2 .1 6 2 .0 9

III Clay 3 3 4 0 .5 9 0 .5 7

IV Potato crop

Assuit (medium amount of fertilizer) 1 5 0 .0 6 0 .0 3

Assuit (high amount of fertilizer) 2 3 0 .0 9 0 .0 4

Kafr El Ziat (low amount of fertilizer) 1 0 0 .0 4 0 .0 2

Kafr El Ziat (medium amount of fertilizer) 2 5 0 .1 0 0 .0 4

Kafr El Ziat (high amount of fertilizer) 1 1 0 .0 5 0 .0 2

Notes:

E_his measured by CR-3 9 plastic detec tor in hollow holder from equation (1 3 ) E₁is c alc ulated from equation (1 2 )

The analysis unc ertainty of a passive trac k-etc h radon detec tor is ±1 5 per c ent

4 0 0

3 5 0

3 0 0

2 5 0

2 0 0

1 5 0

1 0 0

5 0

0

0 5 1 0 1 5 2 0 2 5 3 0

Volume/ Area

Time of reaching equilibrium (hours)

3 5 Figure 7

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9 / 3 [1 9 9 8 ] 1 3 1 –1 3 5

st or e r oom of volu m e 10 ×10 ×5m3_{w ill lea d t o}

a con cen t r a t ion of m or e t h a n 1.5 ×103_{k Bq .m}-3

a ft er 24 h ou r s of st or a ge. T h e Com m ission of t h e E u r op ea n Com m u n it ies r ecom m en d s t h e u se of a con ver sion r a t io by w h ich 1Bq .m-3of

222_{Rn cor r esp on d s t o a n effect ive d ose eq u iva}

-len t of 0.05 m Sv.y-1_{. T h e a lp h a d ose d er iv in g}

fr om t h e in h a la t ion of t h e sh or t lived d a u gh -t er s of 222_{Rn p r esen t in t h e a ir m ay b e ca lcu}

la t ed on t h e b a sis of t h e level of t h e con cen t r a -t ion of 222Rn a n d w a s fou n d t o b e 75m Sv.y-1_.

T h e level r ecom m en d ed for t h e p u blic va r ies fr om 10-148Bq .m-3 _{(0.5-7.4m Sv.y}-1_{). T h e con cen}

-t r a -t ion in s-t or e r oom s es-t im a -t ed on -t h e b a sis of m ea su r em en t s of fer t ilizer s sa m p les in d ica t es t h a t p eop le wor k in g in su ch en v ir on m en t s m ay b e su b ject ed t o sign ifi ca n t in h a la -t ion h a za r d s. I-t is -t h en p ossible -t o es-t a blish a d a t a b a se for t h e b est u se of fer t ilizer s in t h e en v ir on m en t in im p r ov in g eit h er t h e y ield of cr op s or t h e m et h od of st or a ge. T h is m et h od m ay b e u sed t o m ea su r e t h e exh a la t ion r a t e of a n y d r y m a t er ia l.

References

Colle, R., Ru b in , R.J ., Kn a b L.J . a n d H u t ch in son J .M.R.(1981), R a d on T ra n sp or t th r ou gh a n d E x h a la tion fr om B u ild in g M a ter ia ls, a R ev iew a n d A ssessm en t, US De p a r t m en t of

Com m er ce, N a t ion a l Bu r ea u of St a n d a r d s, Wa sh in gt on , DC.

H a r t ley, J .N. a n d F r eem a n , H .D.(1986), R a d on Flu x M ea su rem en ts on Ga rd in ier a n d R oyster Ph os-p h og yos-p su m Piles n ea r T a u os-p e a n d M u lb er r y,

Flor id a, E PA 520/ 5-85-029, USE PA, Mon t gom er y, AL.

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