Our wa­ter

The bad bug that does good work

NZ Lifestyle Block - - Contents - WORDS ELAINE MO­RI­ARTY

Go­ing down to the river to cool off, col­lect mahinga kai (eg, fresh­wa­ter fish and plants), and even drink the wa­ter is a rite of pas­sage in New Zealand. As a mi­grant, it has taken me a while to truly un­der­stand this and see how wai (wa­ter) re­ally is at the heart of every New Zealan­der.

The qual­ity of our rivers is un­der the mi­cro­scope. It seems that every week, a new guide­line or pol­icy state­ment is is­sued and that every politi­cian and politi­cal party has a so­lu­tion.

But what do all the num­bers mean, and have our rivers re­ally be­come un­safe for swim­ming?

When peo­ple re­fer to the qual­ity of a river and whether you can swim in it, they of­ten re­fer to a bac­te­ria known as E. coli. E. coli typ­i­cally will not make you ill. It is a nec­es­sary bac­te­ria to have in your body, in­volved in a num­ber of vi­tal func­tions such as ab­sorp­tion of food and pro­duc­tion of vi­ta­min K.

The most abun­dant source of E. coli is hu­man or an­i­mal fae­ces. One gram of cow fae­ces con­tains ap­prox­i­mately 10 mil­lion E. coli. Sci­en­tists use it as an in­di­ca­tor of fae­cal pol­lu­tion when they test wa­ter sam­ples be­cause it is rel­a­tively easy and cheap to do.

Wa­ter sam­ples are not tested for the bugs that would make the pub­lic sick if they drank the wa­ter, for two rea­sons: • they are usu­ally only present in low num­bers; • the cost is higher to find and count them.

The as­sump­tion is made that when E. coli is present in high num­bers in a wa­ter sam­ple, there is a good chance that re­ally nasty bugs are also there, in­clud­ing a num­ber of path­o­genic bac­te­ria such Campy­lobac­ter, the cause of the 2016 wa­ter­borne out­break in Have­lock North.

When fae­ces are fresh, mea­sur­ing how many E. coli are in a sam­ple is a re­ally handy way to es­ti­mate the num­ber of nasty bugs. The re­la­tion­ship be­tween Campy­lobac­ter and E. coli be­comes un­stuck when the fae­ces are older when they en­ter the wa­ter­way, or have un­der­gone treat­ment such as from a wastew­a­ter treat­ment plant. In th­ese cir­cum­stances, E. coli present may still be rel­a­tively high but the pathogen may not be present. This can lead to the per­cep­tion of a higher risk of be­com­ing ill than is re­ally present.

The guide­lines in place in NZ for

E. coli is used as an in­di­ca­tor of fae­cal pol­lu­tion be­cause tests are cheap and easy to do

suit­abil­ity of fresh­wa­ter for swim­ming are based upon the re­la­tion­ship be­tween E. coli and Campy­lobac­ter and a level of ac­cept­able risk of ill­ness in swim­mers from con­tact with fresh­wa­ter. The greater the num­ber of E. coli, the greater the risk.

Cur­rently, if there are more than 550 E. coli in 100ml of wa­ter, a sign is placed on the river bank and the river is closed for recre­ational pur­poses. Sci­en­tists then visit the site and try to es­tab­lish where the E. coli is com­ing from and the best way to re­duce the con­tam­i­na­tion.

We use a tool­box of tech­niques at the In­sti­tute of En­vi­ron­men­tal Sci­ence and Re­search (ESR). We can an­a­lyse a wa­ter sam­ple which con­tains a high num­ber of E. coli and de­ter­mine the source of the pol­lu­tion, a tech­nique known as fae­cal source track­ing. While some sources can be fixed, eg a bro­ken sewer pipe, sources such as birds are a bit trick­ier.

Tak­ing a mea­sure of E. coli is the best tool we have for de­ter­min­ing if wa­ter is safe to swim in, but there are is­sues. At cer­tain times of the year the con­cen­tra­tion of E. coli is higher in some rivers than oth­ers. For at least 48 hours af­ter heavy rain­fall, the lev­els in­crease dra­mat­i­cally and this can be due to a num­ber of dif­fer­ent sources of pol­lu­tion im­pact­ing the river: • stormwa­ter run­ning off the road and into the river; • an­i­mal fae­cal ma­te­rial be­ing washed in from pad­docks and river banks; • hu­man sewage.

To pro­tect your health, avoid con­tact with rivers for at least 48 hours af­ter heavy rain­fall. All lo­cal coun­cils have in­for­ma­tion on wa­ter qual­ity and suit­abil­ity for swim­ming at the most pop­u­lar sites on their web­sites, so check th­ese out be­fore you jump on in.

If E. coli num­bers get too high, the af­fected wa­ter­way is closed and sci­en­tists visit to try and es­tab­lish where the con­tam­i­na­tion is com­ing from.

DR ELAINE MO­RI­ARTY is a Se­nior Re­search Sci­en­tist for the In­sti­tute of En­vi­ron­men­tal Sci­ence and Re­search (ESR), with ex­per­tise in micro­organ­isms. She works with govern­ment, com­mu­nity groups, iwi, farm­ers and other land-based in­dus­tries on a range of wa­ter qual­ity is­sues.

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