All of the sites showed variable but significant levels of E. coli in both the watercress and

Question

water samples and therefore the potential for enteric waterborne human pathogens to be
present. Campylobacter was detected in the growing waters in at least one sample from each
of the sites (80% of the samples) and in 11% of the watercress samples.
The results demonstrate that urban, semi-urban, rural and bush/scrub catchments are subject
to variable levels of faecal contamination which may include pathogens such as
Campylobacter. The source of this contamination is likely to be both point and non-point
discharges. Watercress gathered from surface waters in these catchment types is at significant
risk of contamination by enteric pathogens and therefore, persons consuming raw watercress
gathered from these catchment types are at potential risk of gastrointestinal illnesses. There is
also the risk of cross-contamination of other foods during preparation. In rural areas there is
also the potential for fascioliasis in persons consuming raw watercress due to contamination
with Fasciola hepatica cysts.
The water sample results also showed levels of E. coli well above the alert/red mode action
for freshwater recreational contact safety, with all of the sites, except for the Golf Course site,
exceeding the action/red mode level on one or more occasions. Persons gathering watercress
could potentially be at risk of illness through contact with faecally contaminated water.
Although the study only looked at surface waters in the Wellington Region, it is considered
that the significance of the microbiological results can be applied nationally. Catchments in
other areas of New Zealand would be exposed to similar sources of faecal contamination
either from rural livestock, urban runoff or feral animals such as possums and goats. As
Campylobacter was found in all of the catchments including the Golf Course Site, it is
reasonable to assume that it would be widespread in other New Zealand catchments due to the
number of animal species that carry and excrete Campylobacter.
As demonstrated by our study, the significant variability of E. coli counts in watercress makes
it difficult to assess microbiological contamination to determine suitability of raw watercress
for human consumption. In regard to raw watercress, controls on the quality of the growing
waters would be the most appropriate method of reducing health risks for consumers.
However, E. coli concentrations do not correlate well with protozoan pathogens such as
Cryptosporidium. Therefore, using faecal indicators in growing waters alone to determine
suitability for human consumption may not accurately represent the risk. Strict quality
controls on source water/growing conditions in addition to applying a strict faecal indicator
standard to the growing waters (e.g. New Zealand Drinking Water Quality Guidelines (2000)
E. coli standard) would be required to ensure minimal potential for watercress contamination.
The heavy metal results did not show watercress contamination above the NZ Food
Regulations limits at any of the sites, except for zinc on one occasion. However, there were
higher levels of specific metals in a number of urban streams, relative to rural streams and the
control site. In streams subject to industrial discharges or natural processes, watercress may
bio-accumulate heavy metals to concentrations in excess of acceptable regulatory levels
thereby potentially causing adverse health effects depending on the amount consumed. For
example, there are areas, associated with geothermal activity, in the central North Island,
where studies have revealed levels of arsenic in the watercress in excess of WHO guidelines.
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6. RECOMMENDATIONS
1. Watercress harvested from any uncontrolled surface water source in New Zealand should
not be consumed unless the watercress is thoroughly cooked in boiling water to destroy
potential human pathogens.
2. Watercress should not be eaten raw unless it can be demonstrated that the growing
environment is strictly controlled and effectively monitored to ensure the water source is
of suitable standard e.g. controlled hydroponic cultivation. A suitably strict standard
should be applied to the growing waters e.g. New Zealand Drinking Water Quality
Guidelines (2000) E. coli standard of less than 1 E. coli/100mls, to monitor acceptable
watercress microbiological quality.
3. Further research should be undertaken to assess the risk of contracting waterborne
illnesses through contact with contaminated water when gathering watercress from
uncontrolled surface waters.
4. The potential for fascioliasis in New Zealand from consumption of wild watercress should
be the subject of a targeted study. This would involve further research on such factors as
the geographic distribution of the host snails and the geographic distribution of Fasciola
hepatica in livestock.
5. There are areas in New Zealand, specifically the central North Island, where studies have
revealed high levels of arsenic in the watercress as a result of geothermal activity. In these
areas it is recommended that watercress collected from local waterways is not consumed.
6. To minimise potential health risks, watercress should not be gathered for consumption
from waterways subject to significant historical/current industrial discharges
write the main points

Answer 1

1. Watercress harvested from any uncontrolled surface water source in New Zealand should not be consumed unless thoroughly cooked to destroy potential pathogens.
2. Watercress should not be eaten raw unless the growing environment is strictly controlled and monitored to ensure water quality.
3. Further research is needed to assess the risk of waterborne illnesses from gathering watercress from uncontrolled surface waters.
4. Study on the potential for fascioliasis in New Zealand from consuming wild watercress is recommended.
5. Avoid consuming watercress from areas with high levels of arsenic, such as in the central North Island.
6. Watercress should not be gathered for consumption from waterways with significant industrial discharges.