CORRELATION BETWEEN OOCYSTS AND WATER QUALITY PARAMETERS
Final Report to the Department of the Environment on a consultancy, October 1993 to February 1994
Report No DWI0275

May 1994

SUMMARY

As part of the National Cryptosporidium Research programme the National Rivers Authority funded a study in the spring of 1993 to determine if there was a relationship between the occurrence of Cryptosporidium oocysts in river waters and farming events. The Department of the Environment funded an extension of the study to include a correlation of the concentration of oocysts with levels of chemical and microbiological parameters associated with water quality. The results were inconclusive. More intensive studies were subsequently planned for an autumn period when oocyst levels in water were likely to be low and for a spring study when levels were likely to be high. The former, which is reported here, was funded by the DoE, and administered by the Drinking Water Inspectorate. It is anticipated that the latter study will be funded by the NRA and take place in the spring of 1994.

The autumn study took place during a period of high rainfall and high daily mean river flow, but with rapid fluctuations during the day. There were strong correlations between the presence of oocysts and some parameters indicative of faecal pollution, BOD and faecal bacteria for example. There were no pollution incidents of any consequence during this period but the excessive rain may have led to unusually high levels of diffuse run-off.

Particle size distribution analyses were also carried out on the samples. The pattern of results were similar for all samples whether oocysts were present or not. This is probably a reflection of the material washed into the river as a result of the excessive rains.

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