Water Quality Parameters-TU WQW 2023.pptx

Parameters to be measured in water samples

1. Wat e r Q uality Parameters

2. W a t e r Q u a li t y P a r a m e t e r s Physi c al Color T a st e Odor T u r b i d i t y T e m p e r at u re Conductivity Suspende d Solids Che m i c al pH T o ta l D i ss o l ve d S o li d s Major Ions Minor or T race el ements Hardness Salinity Alkalinity M i cr obiolo g i c al P a thog e ni c micro organisms: V ir u s e s, B a ct e ri a , Pr o t o z o a Indi ca to r m i cr o organisms: T o t a l C o li f o rm, F e c a l C o li f o rm

3. Ph y s i ca l P a r a m e t e r s Color Suspended Part icl es O rgan i c Ma tt er Odor C a n b e du e t o d issolved subs tances D ecayed organ ic subs tance s - f ou l smell I norgan ic Subs tance s – ear t h y smell T u r b i d i t y Mudd ines s in W at er Suspended par ticl e s – Cl a y , sil t , organ ic ma tt er T e m pe r a t u re S u s pende d P a rt icl e s

4. P h ysica l Parame t er s - T e m p era t u r e E s s en t i a l f o r a l l en vi ronmen t a l s t ud i e s C on t ro l s man y e c o l og ic a l pro c e ss e s i n cl ud i n g c hem ic a l rea c t ions T e mpera t ur e o f s ur f a c e wa t e r i s in f luen c e d b y a t mo s pheri c c ond i t i on s T e mpera t ur e o f groundwa t e r i s c on t rolle d b y t herma l c hara ct er i st ic s o f bedro ck s an d t h e dep t h

5. P h ysica l Parame t er s - Co l or C o l o r o f w a t e r i s du e t o t h e s u s pende d par t icl e s an d organ ic matt er R ang e f ro m li gh t t o dar k bro wn B r o w n i sh co l or i n w a t er i s due t o p r esence o f ir on G r een i sh co l or i n ponds i s due t o t he p r esence o f o r gan i c sub st ances i nc l ud i ng a l gae

6. Ph y s i ca l P a r a m e t e r s – T a s t e a n d Odo r T a s t e an d odo r i n wa t e r c a n b e c au s e d b y organi c ma t erial s , i norgan i c c ompound s , o r d iss o lv e d ga ss e s T he se ma t er i a ls ma y c om e f ro m na t ura l , dome st i c, o r agr ic u l t ura l s our c e s D ecayed o r gan i c sub st ances g i ve f oul s m e l l I no r gan i c sub st ances g i ve ea r t hy s m e l l

7. Ph y s i ca l P a r a m e t e r s – T u r b i d i t y R e f er s t o cl oud i ne s s o r mudd i ne s s i n w a t e r I t i s t h e m ea s u r e o f t h e abili t y o f ligh t t o pa s s t h r oug h wa t e r D u e t o s u s pende d par t icl e s f ro m cl a y , sil t , an d organ i c ma tt e r

8. P h ys i ca l P a r a m ete r s – E l ect r i ca l C o ndu ct i v i t y T h e e l e c t r ic a l c ondu c t ivi ty ( E C ) o f w a t e r i s a m ea s u r e o f t h e ab ili ty o f a s o l u t i o n t o c a rr y o r c ondu c t a n e l e c t r ic a l c u rr ent Si n c e t h e e l e c t r ic a l c u rr en t i s c a rr i e d b y i on s i n s o l u t i on , t h e c ondu c t ivi ty i n c r ea s e s a s t h e c on c en t r a t i o n o f i on s i n c r ea s e s I t is on e o f t h e m a in pa r a m e t e rs u s e d t o de t e rmi n e t h e s u i t ab ili t y o f w a t e r f o r irri ga t i o n an d f ir e f i gh t i n g P u r e w a t e r i s no t a goo d c ondu c t o r o f e l e c t r ici ty T y p ic a l c ondu c t ivi t y o f w a t e r is a s f o ll o w s: Ul t r a - pu r e w at e r: 5. 5 × 10 − 6 S/ m; Dri nk i ng w a t e r: . 005– 0. 05 S/ m; S ea w a t e r: 5 S/ m.

9. P h ysica l Parame t er s – S o li d s S o li d s o cc u r i n w a t e r e i the r i n s o l u t i o n o r in s u s pen si o n T he se t wo t y pe s o f s o li d s c a n b e i den t i f i e d b y u si n g a g l a ss f i be r f il t e r t ha t t h e w a t e r s amp le pa ss e s t hroug h S u s pende d s o li d s ar e re t a i ne d o n t h e t o p o f t h e f il t e r an d Diss o lv e d s o li d s pa ss t hroug h t h e f il t e r wi t h t h e w a t e r

10. Che m ica l P a r a m e t e r s pH R ef er s t o C onc . O f H + I ons R ange s f rom – 14 T otal D isso lve d Solids C oncen t rat i o n o f non -vol at ile subs tances TD S determ i ne s sui t ab ili t y o f w at e r f o r ou r us e an d consump t i on Inorgani c C h l or i de , Sod i um , C a lci um , Fl uor i de , Magnes i um , Bicarbona t e , C arbona t e , Sul fat e I ron, H ardness , C onduc tivi t y , Ni tra tes , Phospha t e , Boron, Dissolved O xygen Organ i c Benzene, T richl oroe t hy l ene , 1, 2 - d ichl oroe t hane , T o l uene , 2, 4 - d i n i t ropheno l, naphtha l ene , DD T , PC B Mi xt ure s o f rel at e d compounds Pest ici des , V o l at ile O rgan i c C ompound s (V O C s), Bi o l og ical O xygen D eman d (B O D ), C hem ical O xygen D eman d (C O D ), T ot a l O rgan i c C arbo n ( T O C ), T ot a l O rgan i c H a l ogens , T ri ha l ome t hane s (THMs)

11. Ch em i ca l P arame t er s – pH R e f e r s to t h e e f f e c t i v e c on c en t r a t i o n o f h y d r oge n i on s i n w a t e r p H = - Log [ H + ] p H < 7 is A ci d ic an d p H > 7 is A lk a li n e Ex cess i ve l y h i g h an d l o w p H ca n b e det rim enta l fo r th e us e of w a t e r Hi g h p H m a k e s th e ta st e b i tte r an d de cr ea s e s th e e f fe ct iv ene ss of th e c h l o ri n e d isi nfe ct i on, the r eb y c au si n g th e nee d fo r add i t i ona l c h l o ri n e T h e a m ount of o xy ge n in w ate r i n cr ea s e s a s p H ris e s Lo w p H w ate r will c o rr od e o r d iss o lve m eta ls an d othe r s ub st an c e s

12. Ch em i ca l P arame t er s – A c i d i ty Ac i d i t y i s th e m easu r e o f ac i d s i n a so l ut i on T h e a ci d i t y o f w a t e r i s i t s quan t i ta t iv e c apa ci t y to neu t r a liz e a s t r on g ba s e to a s e l e c t e d p H l e v e l Ac i d i t y i n w ate r i s usua ll y du e t o ca r bo n d i ox i de , mi ne r a l ac i ds , and h y d r o lyz e d s a l ts s u c h a s f e rri c an d a l u mi nu m s u l fat es Ac i d s ca n i nf l uenc e m an y p r ocesse s suc h a s co rr os i on , che mi cal r ea c t i on s an d b i o l og ic a l a c t ivi t i e s

13. Ch em i ca l P arame t er s – A lka li n i ty T h e a lk a li n i t y o f w a t e r i s i t s a ci d - neut r a lizi n g c apa ci ty c o m p ris e d of the tota l o f a l l t i t r a ta b l e ba s e s M ea s u ri n g a lk a li n i t y o f w a t e r i s ne c e ss a r y to de t e rmi n e t h e a m oun t o f lim e an d s od a neede d f o r w at e r s of t en i n g ( e.g. , f o r c o rr o si on c on t r o l i n c ond i t i on i n g t h e bo il e r f ee d w a t e r ) A l ka li n i t y o f w ate r i s m a i n l y cause d b y th e p r esenc e o f hyd r ox i de i on s ( O H − ) , b ic a r bona te i on s (HC O 3 − ) , an d c a r bona te i on s (C O 3 2 − ), o r a mix t u r e o f t w o o f t he s e i on s i n w at e r .

14. Ch em i ca l P arame t er s – Sali n i t y S a lini t y i s a mea s ur e o f t h e c on t en t o f s a l t s i n s o i l o r w a t e r S a l ts a re h i gh l y s o l ub l e i n s u rf a ce an d g r ound w a t e r an d c a n b e tr an s po rt e d wi th w a t e r m o v e m en t . S a li n it y co m es due t o S od i um and C h l o ri de I t i s a s t r on g c on t r ibu t o r t o c ondu c t i v i t y an d he l p s de t e rmi n e m an y a s pe c t s o f t he c hem i s t r y o f na t ura l w a t er s an d t h e b i o l og ic a l pro c e ss e s wi t h i n t he m S a li n i t y , a l on g wi t h t e m pe r a t u r e an d p r e ss u r e , he l p s go v e r n ph ysic a l c ha r a c t e ris t ic s o f w a t e r s u c h a s den s i t y an d hea t c apa c i t y T he U n i t e d S t a t e s G eo l og i c a l S ur v e y ( U SGS ) c l a ss i f i e s w a t e r o f v ar y i n g c on c en t ra t i on s o f s a l t a s: F r e s h w a t e r : < 1 , 00 pa rts pe r m illi o n ( pp m) S li gh t l y s a li n e w a t e r : 1 , 00 pp m – 3 , 00 ppm M ode r a t e l y s a li n e w a t e r : 3 , 00 pp m – 10 , 00 ppm Hi gh l y s a li n e w a t e r : 10 , 00 pp m – 35 , 00 ppm

15. Ch em i ca l P arame t er s – H ar dn e s s H ardne s s i s a t er m u s e d t o e x pre s s t h e proper t i e s o f h i gh l y m i nera li z e d w a t er s Di sso l ved mi ne r a l s i n w a t er cause p r ob l e m s such as sca l e depos it s i n ho t w a t er p i pes and d i f fi cu lt y i n p r oduc i ng l a t her wit h soap C a l c i u m ( Ca 2+ ) an d m agne s i u m (Mg 2+ ) i on s c au s e t h e g r ea t e s t po r t i o n o f ha r dne s s i n na t u r a ll y o cc u rri n g w a t e r s T hey en t er w a t er m a i n l y fr om con t a ct wit h so i l and r o ck, pa rti cu l a rl y lim e st one depos it s T h e s e i on s ar e pre s en t a s b i c arbona t e s , s u l f a t e s , an d s ome t i me s a s c h l or i de s an d n i t ra t e s G ene r a ll y , g r ound w a t er i s ha r der t han su rf ace w a t e r . T h er e ar e t w o t y pe s o f hardne ss : T e m po r a r y ha r dness w h i ch i s due t o ca r bona t es and b i ca r bona t es can be r e m oved by bo ili ng , and P e rm anen t ha r dness w h i ch i s r e m a i n i ng a ft er bo ili ng i s caused m a i n l y by su lf a t es and ch l o ri des

16. Ch e mi ca l P a r a m e t e r s – Di ss ol v e d O x y ge n Diss o lv e d o xy ge n (D O ) i s t h e a m oun t o f o xy ge n t ha t i s p r e s en t i n w a t e r W a t e r bod i e s r e c e i ve o xy ge n fr o m t h e a tm o s phe re an d fr o m aqua t i c p l an ts R unn i n g w a t e r , s u ch a s t hat of a s wi f t m o v i n g s tr ea m , d i ss o l v e s m o re o xy ge n t ha n t h e s t il l w a t e r of a pon d o r l a ke D O i s c on si de r e d a n im po rt an t m ea s u r e o f w a t e r qua li t y a s i t i s a d ir e c t i nd ic a t o r o f a n aqua t ic r e s ou rc e ’ s ab ili t y to s uppo r t aqua t i c li f e W h il e ea c h o r gan is m ha s i t s o w n D O t o l e r an c e r ange , gene r a l l y , D O l e v e l s be l o w 3 milli g r a m s pe r li te r (m g / L ) a r e o f c on c e r n an d w a t e r s wi t h l e v el s be l o w 1 m g /L a r e c on si de r e d h y po xi c an d u s ually de v o i d of li fe Lo w l e v e l s of o xy ge n ( h y po xi a ) o r n o o xy ge n l e v e l s ( ano xi a ) c a n o cc u r w he n e xc e s s o r gan i c m a t e ri a ls , s u c h a s l a r g e a l ga l b l oo ms, a r e de c o m po s e d b y micr oo r gan isms.

17. Ch e m i ca l P a r a m ete r s – Ch e m i ca l O xy g e n D e m a n d ( C O D) C OD i s a mea s ur e o f t h e o xy ge n equ i v a l en t o f t h e organ i c ma tt e r i n a w a t e r s amp l e t ha t is suscep t i b l e t o ox i da t i o n b y a s t ron g che m i ca l ox i dant C O D is wi de ly u s e d a s a m ea s u re of th e s u sc ept i b ili t y t o o xi dat i o n of th e o r gan ic an d i no r gan ic m ate ri a ls p r e s ent in w ate r bod i e s an d in th e m un ici pa l an d i ndu st ri a l w a st e s C OD i s a w a t e r qua li ty mea s ur e u s e d no t on l y t o de t erm i n e t h e amoun t o f b i o l og i c a lly act i v e subs t ance s suc h a s bac t e r i a bu t a l s o b i o l og i ca ll y i nac t i v e o r gan i c m a tt e r i n w a t er C OD i s o ft e n u s e d a s a mea s uremen t o f po ll u t an ts i n w a t e r , w a s t e w a t e r , an d aqueou s haza rdou s w ast es O n e app lic at i o n of th e C O D te st is t o m ea s u re s o l ub le C O D in w a st e w ate r , si n ce c ha r a ct e riz at i o n of tota l C O D in w a st e w ate r is cri t ic a l fo r a cc u r at e m ode li n g of b i ot r an sf o rm at i o n in w a st e w ate r t r eat m ent p r o c e ss e s

18. Ch e m i ca l P a r a m ete r s – B i o l og i ca l O xy g e n D e m a n d ( B O D) B i ochem i ca l oxyge n dema n d ( B O D ) r ep r e s en t s t h e a moun t o f oxyge n consume d b y bac t e r i a an d o t he r m i c r oo r gan i s m s w h il e t he y deco mpos e o r gan i c m a tt e r unde r ae r ob i c ( oxyge n i s p r esen t ) cond i t i on s a t a spec i f i e d t e m pe r a t u re Diss o lv e d o r gan i cs: 1 . B i odeg r adab l e - s t a rc he s, f a t s, p r o t e i n s, a l c oho ls, a c i d s, a l deh y de s e t c. 2 . N on - b i odeg r adab l e (r e fr a c t o ry) B O D reduc t i o n i s use d a s a gaug e o f t h e e f f e c t i v ene s s o f w a s t e w a t e r t rea t men t p l an ts B O D o f w as t e w a t e r e f f l uen t s i s u s e d t o i nd i c a t e t h e s ho rt- te r m i mpa c t o n th e o xy ge n l e v e l s o f t h e r ece i v i n g w a t er

19. Ch e m i ca l P a r a m ete r s – To ta l O r g a n i c C a r bo n ( T O C ) T o ta l Ca r bo n T o ta l o r g a n i c car bo n ( T O C ) i s t h e a m oun t o f c a r bo n foun d i n a n o r gan i c c o m poun d an d i s often u s e d a s a non -s pe cifi c indica t o r o f w a t e r qua li t y A t y p ic a l ana lysi s f o r tota l ca r bo n (TC ) m ea s u r e s bo th t h e t o t a l o r gan i c c a r bo n ( T O C ) p r e s en t an d th e co m p l e m ent i n g tota l i no r gan i c ca r bo n (TI C) , t h e l a tt e r r ep r e s en t i n g t h e a m oun t o f no n - o r gan i c c a r bon , lik e c a r bo n i n c a r bona t e mi ne r als S ub tr a c t i n g t h e i no r gan i c c a r bo n fr o m t h e t o t a l c a r bo n y i e l d s T O C Pu r geable O r ganic Carbo n (POC) O r ganic Ca r bon Non - pu r geable O r ganic Carbo n (NPOC) Pa rt icula t es Dissolved ( D O C) Pa rt icula t es Inor ganic Ca r bon ( T I C) Dissolved

20. Ch e mi ca l P a r a m e t e r s – T r ih a lo me t h a n e s T r i ha l o m e t hane s ( T H M s ) a r e a g r ou p o f d i s i n f ec t i o n byp r oduc t s t ha t a r e a r esu l t o f r eac t i o n be t w ee n t h e ch l o r i n e use d f o r d i s i n f ec t i n g t a p w a t e r an d na t u r a l o r gan i c m a tt e r i n th e w a te r A t e l e v ate d l e v e l s, T HMs ha ve bee n a ss o ci ate d wi t h negat ive hea l t h e f fe ct s s u ch a s c an c e r an d ad v e rse r ep r odu ct ive out c o m e s Leve l s o f T H M s gene r a ll y i nc reas e i n t h e su mm e r m on t h s du e t o t h e w a rm er te mpera tu re s , bu t c a n a l s o b e a f fe c te d b y s ea s ona l c hange s i n s our c e w a te r qua li ty o r b y changi n g amoun ts of d i s i nfect i o n added W a t e r sys t e m s o ft e n c a n e x pe r i en c e t e m po r a r y i n cr ea s e s i n TT H M du e t o s ho r t - te r m i n c rea s e s i n c h l or i n e d i s i n f e c t i o n C h l o ri n e d isi nfe ct i o n i n cr ea s e s c a n o cc u r w he n the re is a w ate r m a in b r ea k, w he n w ate r syst e ms a re unde r r epa i r , o r w he n the re is a potent i a l micr ob i a l ( e x a m p l e: ba ct e ri a ) p r ob l e m o r th r eat

21. C h e m i ca l P arame t ers – Amm o ni a , N it r i t e , N it ra t e , Pho s ph a t e A mm on i a co m e s fr o m deco m pos i t i o n of o r gan i c m atte r li k e p r ote i ns, a mi n o ac i d s etc., Its c on c en tr a t i o n a l so i n cr ea s e s du r i n g w a t e r d i s i n f e c t i o n p r o c e ss u s i n g c h l o r a m i n e Ni t ri t e i s v e r y un st ab l e i n t e rm ed i a te f o rm e d du ri n g c on v e rsi o n o f NH 2 i n to n i t r a t e . In ae r ob i c c ond i t i o n n i tr i te i s o x i d i z e d i n to n i tr a te w he r ea s i n anae r ob i c c ond i t i on, n i tr i te i s r edu c e d to a mm on i a. I f c on c en tr a t i o n of n i tr i te i s g r ea t e r i n d r i n k i n g w a t e r , i t b r i ng s s e r i ou s hea l th ha z a rd to t h e c on s u m e r s. Ni t r a te i s m o s t st ab l e o xi d iz e d f o r m o f n i t r oge n In w a t e r n i tr a te c o m e s fr o m o r gan i c m a tt e r de c o m po s i t i o n an d fr o m a tm o s phe r i c n i tr oge n f i x a t i on. h i g h c on c en tr a t i o n of n i tr a te f a c ili t a t e s hea vy g r o w th of aqua t i c p l an ts c au s i n g eu tr oph i c a t i o n Phosphat e i s p r esen t i n th e fo rm of H 2PO4 - , po l yphosphat e an d a s o r gan i c phosphate. C o m e s fr o m ag r i c u l t u r a l w a s t e s, s e w ag e an d fr o m i ndu s tr i a l e f f l uent P ho s pha te i s not t o x i c to hu m a n be i ng s but i t i s i m po rt ant c he m i c a l i n na t u r a l w a t e r sys t e m li ke pon d be c au se i ts h i g h c on c en tr a t i o n f a c ili t a t e s eu tr oph i c a t i o n

22. M i c r o b i o l og i ca l P a r a m e t e rs P a t hog e ni c M i c r oo r g a ni s ms V ir u s e s B a c t e ria Pr o t o z o a Indi ca t o r M i c r oo r g a ni s ms F e c a l C o li f o rms T o t a l C o li f o rms

23. M i c r ob i o l og i cal P a r a m ete r s – P at hog e n i c M i c r oo r g a n i s m s BAC T ER I A C on si de r e d t o b e si ng l e -c e ll e d p l an t s be c au se o f t he ir c e ll s t r u c t u re an d t h e w a y t he y i nge st f o o d O cc u r in t h r e e ba sic c e ll s hape s: r od - shaped or bac ill u s, sphe r e - shaped or coccu s, and sp ir a l- shaped or sp ir e ll us U nde r f a v o r ab le c ond i t i on s o f f oo d s upp l y , t e m pe r a t u r e , an d p H , ba c t e ria c a n r ep r odu ce r ap i d ly W a t e r bo r n e d is ea s e s a re c au s e d b y ba c t e ri a : T ypho i d and P a r a t ypho i d f eve r , Lep t osp ir os i s, T u l a r e mi a , S h i ge ll os i s, and C ho l e r a

24. M i c r ob i o l og i cal P a r a m ete r s – P at hog e n i c M i c r oo r g a n i s m s V I RUSES S m a ll e st b i o l og i cal st r u ct u r es kno w n t o con t a i n a l l gene ti c i n f o rm a ti on necessa r y f or t he i r o w n r ep r odu ct i on T hey can on l y be seen by a po w e rf ul e l e ct r on i c mi c r oscope V ir uses a r e pa r as it es t ha t need a ho st t o li ve T hey can pass t h r ough filt e r s t ha t do no t pe rmit t he passage o f ba ct e ri a W a t e r bo r ne v ir al pa t hogens a r e kno w n t o cause i n f e ct i ous hepa titi s and po li o m ye liti s M o st o f t he w a t e r bo r ne v ir uses can be dea ct i va t ed by t he d i s i n f e ct i on p r ocess condu ct ed i n t he w a t er t r ea t m en t p l an t

25. M i c r ob i o l og i cal P a r a m ete r s – P at hog e n i c M i c r oo r g a n i s m s PR O T OZO A P ro t ozoa are single-celled microscopic animal Consume solid organic par t icle s, ba ct eria , and algae f or f ood , and t hey are in t urn inge st ed as f ood by higher level mul t icellular animals A qua t ic pro t ozoa are f loa t ing f reely in wa t er and some t imes called zooplan kt on T hey f orm cyst s t ha t are di f f icul t t o ina ct iva t e by disin f e ct ion

26. M i c r ob i o l og i cal P a r a m ete r s – I nd i c at o r Or g a n i s m s A ve r y i m po r t an t b i o l og i ca l i nd i ca t o r o f w a t e r an d po ll u t i o n i s t h e g r ou p o f bac t e r i a ca ll e d co li f orm s P a t hog e n i c co li f orm s a lw ay s e x i s t i n t h e i n t e s t i na l sys t e m o f humans , an d m illi on s ar e exc r e t e d wi t h bod y w ast es C onsequen tl y , w a t er t ha t has been r ecen tl y con t a mi na t ed wit h se w age wil l a lw ays con t a i n co lif o rm s A pa r t i cu l a r spec i e s o f co li f o rm s f oun d i n do m es t i c se w ag e i s Es cher i ch i a co l i o r E . co l i E ven if t he w a t er i s on l y s li gh tl y po ll u t ed , t hey a r e ve r y li ke l y t o be f ound . T he r e a r e r ough l y 3 milli on o f E. co l i ba ct e ri a i n 100 m L vo l u m e o f un tr ea t ed se w age C o li f or m ba c t er i a ar e aggre ss i v e organ i s m s an d s ur v i v e i n t h e w a t e r l onge r t ha n mo s t pa t hogens.

27. M i c r ob i o l og i cal P a r a m ete r s – I nd i c at o r Or g a n i s m s F e ca l c oli f o r m b a cter i a ar e a sub-grou p o f tot a l co li f or m bac t er i a T hey appear i n g r ea t quan t i t i es i n t he i n t e s t i nes and f eces o f peop l e and an i m a l s T he p r esence o f f ecal co li f o r m i n a d r i nk i ng w a t er sa m p l e o ft en i nd i ca t es r ecen t f ecal con t a m i na t i on , m ean i ng t ha t t he r e i s a g r ea t er r i sk t ha t pa t hogens a r e p r esen t t han i f on l y t o t al co li f o r m ba c t e r i a i s de t e c t ed E . c oli i s a s u b -grou p o f t h e f eca l co li f or m group M o st E. co l i ba c t e r i a a r e ha rm l ess and a r e f ound i n g r ea t quan t i t i es i n t he i n t e s t i nes o f peop l e and w a r m - b l ooded an i m a l s S o m e s t r a i n s, ho w eve r , can cause ill ness T he p r esence o f E. co l i i n a d r i nk i ng w a t er sa m p l e a l m o st a lw ays i nd i ca t es r ecen t f ecal con t a m i na t i on , m ean i ng t he r e i s a g r ea t er r i sk t ha t pa t hogens a r e p r esen t

28. T HA N K Y OU