ENGLISH ABSTRACT: The increased consumption of fresh produce has been shown to be related to increases in
foodborne disease outbreaks and these have in many cases been ascribed directly to carry-over of
pathogens from contaminated irrigation water. In South Africa, rivers are the main source of
irrigation water but many have been found to be unsuitable for irrigation of fresh produce because
of the unacceptably high levels of faecal contamination.
The main aim of this study was to do a baseline evaluation of the microbiological quality of
the Plankenburg and Eerste Rivers and to determine which bacterial contaminants are present.
Two sampling sites were selected for the Plankenburg (Plank-1 and -3) and one for the Eerste
River (Eerste-1). The microbiological analysis included aerobic colony count (ACC), aerobic and
anaerobic sporeformers, Staphylococcus, Salmonella, Listeria, enterococci, coliforms, faecal
coliforms and E. coli using standard methods. The faecal contamination levels for both rivers
exceeded the DWAF and WHO guidelines of <1 000 E. coli per 100 mL water for irrigation of fresh
produce intended to be consumed raw. The Plankenburg River sites always had higher coliform
contamination levels (1 200 - 13 000 000 MPN per 100 mL water) than the Eerste River site (230 -
79 000 MPN per 100 mL water). There was also a high incidence of index organisms including
Salmonella, Staphylococcus, Listeria and endosporeformers. The isolation of intestinal
enterococci suggested the presence of potential pathogens that can cause disease outbreaks.
The baseline data also showed large variations in microbial loads over the 15 month study with the
faecal coliform counts ranging for Plank-1 from 1 200 to 7 000 000 MPN.100mL-1, Plank-3 from 10
to 460 000 MPN.100mL-1 and Eerste-1 from 28 to 79 000 MPN.100mL-1. The water temperatures
at all three sites ranged from 12.1° to 21.7°C with COD values in most cases below 100 mg.L-1.
As the baseline study showed large variations in microbial loads over the 15 month study
period an assessment using the Colilert-18 system of the weekly, daily and hourly variations, for 6
weeks over a period of 4 months was conducted at site Plank-2. This site was specifically used as
it is an irrigation source point for nearby fresh produce farmers and is about 2 km further
downstream from an informal settlement. The weekly variation trend for total coliforms (TC)
showed a decrease over the entire sampling period with the highest count of 3 200 000 MPN.100
mL-1 during the warmer period. The E.coli (Ec) counts showed a similar trend with the highest
count of 440 000 MPN.100 mL-1 also in March. The daily variation trends were the same for both
the TC and Ec and counts found to increase from Monday to Thursday followed by a decrease to
Sunday. The highest counts were on Thursday with average TC and Ec counts of 1 900 000 and
160 000 MPN.100 mL-1, respectively. The hourly variation trends were similar for both TC and Ec
with counts increasing from 06h00 to 12h00 followed by a decrease to 18h00. The increases in TC
and Ec counts found during the weekly, daily and hourly variation trend studies clearly suggests
that the 15 month sampling that was done once a month on Mondays at 08h00 could be
considered an underestimation of the contamination levels of the Plankenburg and Eerste Rivers. The overall weekly variation trend for the water temperature showed a decrease over the
sampling period while the daily and hourly variation trends showed an increase from 06h00 to
18h00. The overall weekly trend for pH differed from that of the temperature with an increase over
the sampling period. The analysis of covariance showed no correlation (p < 0.05) between the
physico-chemical (temperature and pH) and the microbial variables (TC and Ec). Therefore it was
concluded that temperature and pH had no direct impact on either the total coliform or E. coli
counts.
Both the Plankenburg and Eerste Rivers were found to be unsuitable for the irrigation of
fresh produce intended to be consumed raw due to the high levels of faecal contamination that
exceeded DWAF and WHO guidelines. Irrigation with such water could pose a health risk because
of presence of potential pathogens that could be carried-over to fresh produce.
AFRIKAANSE OPSOMMING: Die toenemende gebruik van vars produkte hou direk verband met die toename in
voedseloordraagbare siektes. Alte dikwels kan dit toegeskryf word aan die teenwoordigheid van
patogene in besproeiingswater. In Suid Afrika is riviere die hoofbron van besproeiingswater maar
dit is al gevind dat meeste ongeskik is vir gebruik as besproeïngsbron as gevolg van die
onaanvaarbare hoe vlakke van fekale besmetting.
Die hoofdoel van hierdie studie was om ‘n basislyn evaluasie van die mikrobiologiese
kwaliteit van die Plankenburg en Eerste Riviere te doen en ook vas te stel watter bakteriese
kontaminante teenwoordig is. Twee bemonsteringpunte is geselekteer vir die Plankenburg (Plank-
1 en -3) en een vir die Eerste Rivier (Eerste-1). Mikrobiologiese analises met standaard metodes
het die volgende ingesluit: aërobe kolonie telings (AKT), aërobe en anaërobe spoorevormers,
Staphylococcus, Salmonella, Listeria, enterococci, koliforms, fekale koliforms en E. coli met
gebruik van standaard metode. Die fekale besmettingsvlakke vir beide riviere het die DWAF en
WHO leistreep van <1 000 E. coli per 100 mL water vir besproeiing van vars produkte wat rou
geëet kan word oorskry. Die Plankenburg Rivier bemonsteringspunte het in alle gevalle ‘n hoër
kolivorm besmettingsvlak (1 200 - 13 000 000 MPN per 100 mL water) as die Eerste Rivier punt
(230 - 79 000 MPN per 100 mL water) gehad. Daar was ook ‘n hoër voorkoms van
indeksorganismes insluitend Salmonella, Staphylococcus, Listeria en endosporevormers. Die
voorkoms van ingewand enterococci was ‘n addisionele aanduiding van die voorkoms van
patogene wat ernstige gesondheidsrisikos vir die verbruiker kan inhou. Die basislyn data het groot
variasies in die mikrobe vlakke oor die 15 maand van studie getoon. Die faecal koliforms vir Plank-
1 het gewissel van 1 200 tot 7 000 000 MPN.100mL-1, vir Plank-3 van 10 tot 460 000 MPN.100mL-1
en vir Eerste-1 van 28 tot 79 000 MPN.100mL-1. Die water temperature het gewissel van 12.1° tot
21.7°C met die CSB waardes in meeste gevalle minder as 100 mg.L-1.
Aangesien daar sulke groot variasies in mikrobe ladings oor die 15 maande tydperk
voorgekom het, is die Colilert-18 sisteem gebruik om die weeklikse, daaglikse en uurlikse variasies
vas te stel vir 6 weke oor ‘n periode van 4 maande by die Plank-2 bemonsteringspunt. Daar is
spesifiek op die bemonsteringspunt gefokus omdat dit as ‘n besproeiingsbron gebruik word deur
groente produsente. Dit is ook gelee ongeveer 2 km stroomaf van ‘n informele nedersetting.
Die weeklikse variasies in totaal koliforms (TC) het ‘n afname oor die hele
bemonsteringsperiode getoon, met die hoogstes telling van 3 200 000 MPN.100 mL-1 gedurende
die warmer tydperk. Die E.coli (Ec) tellings het ‘n soortgelyke neiging getoon, met die hoogste
telling van 440 000 MPN.100 mL-1 ook in Maart. Die daaglikse neigings was dieselfde vir beide die
TC en Ec en die tellings het vermeerder van Maandag tot Donderdag, met ‘n afname tot Sondag.
Die hoogste telling was op Donderdag met gemiddelde TC and Ec tellings van 1 900 000 and 160
000 MPN.100 mL-1, respektiewelik. Die uurlikse variasie profiel was soortgelyk vir beide TC and Ec
met tellings wat vermeerder het van 06h00 tot 12h00 gevolg deur ‘n afname tot 18h00. Die toename in TC en Ec getalle soos vasgestel gedurende die weeklikse, daaglikse en uurlikse
variasie het duidelik getoon dat die bemonsterings wat een maal per maand op Maandae om
08h00 gedurende die 15 maande tydperk uitgevoer is, tot ‘n erg onderskatting van die besmettings
vlakke in die Plankenburg en Eerste Riviere gelei het.
Die algehele weeklikse variasies vir die water temperatuur het ‘n verlaging oor die
bemonsteringstydperk getoon terwyl die daaglikse en uurlikse variasie neigings ‘n verhoging van
06h00 tot 18h00 getoon het. Die weeklikse neigings vir pH het van die van die temperatuur verskil.
Die analises van kovariante het geen korrelasie (p < 0.05) tussen die fisiese-chemiese
(temperature en pH) parameters en die mikrobe veranderlikes (TC en Ec) getoon nie. Dus is daar
afgelei dat temperatuur en pH geen direkte impak op die totale kolivorm of E. coli tellings gehad
nie.
Die data van die studie het duidelik getoon dat water van beide die Plankenburg en Eerste
Riviere nie geskik is vir gebruik vir besproeiing van vars produkte wat rou geëet gaan word nie. In
beide gevalle het die fekale besmettingsvlakke die DWAF en WHO leistreep oorskry. Besproeiing
met sulke water hou ‘n gesondheidsgevaar in as gevolg van die teenwoordigheid van potensiële
patogene wat oorgedra kan word na vars produkte.
