David Kay

Modelling faecal coliform dynamics in streams and rivers

Abstract A series of field experiments are reported which have provided empirical evidence to improve the understanding of faecal coliform entrainment mechanisms within stream channels. A new conceptual model of faecal coliform dynamics is proposed and preliminary modelling results presented. The model is based on the assumption that the entrainment and deposition of organisms from storage within the stream bed is governed by the relationship between flow and the channel bed. The organisms are assumed to be associated with particulates of low settling velocity. Channel bed storage is modelled by a series of longitudinal sub-store units which are sequentially accessed as flow rises, each store unit is rapidly depleted of organisms after the onset of entrainment. Deposition to sub-stores where entrainment is not occurring is assumed to occur at a constant rate. Further investigations are required to confirm the results and examine the application of the model to natural flow events or alternative determinands.

Reduction of coliform bacteria in two upland reservoirs: The significance of distance decay relationships

Abstract This paper reports on the coliform bacterial densities observed between September 1976 and September 1977 in two British upland reservoirs having multiple-use catchment areas. The level of catchment use is defined in terms of agricultural and recreational activity and the rate of bacterial reduction in the reservoir impoundments is investigated. The applicability of previous studies (which examined rates of coliform reduction in different situations) to the British upland reservoir is discussed and a set of calculated purification rates, observed during different limnological conditions, are presented.

The enterovirus test in the assessment of recreational water-associated gastroenteritis

Abstract This study reports the results of a series of analyses designed to identify possible mathematical relationships between the numbers of fecal streptococci vs the numbers of enteroviruses present (as measured by the enterovirus assay) in marine recreational waters in order to indirectly assess the relationship between enteroviral densities and subsequent risk of gastroenteritis among bathers exposed to marine waters contaminated with domestic sewage. A database consisting of 2066 parallel fecal streptococci and enterovirus enumerations taken from 416 different marine water locations throughout the United Kingdom was used in the analyses. Polychotomous logistic regression was used to model the probabilities of zero enterovirus, a possible infectious dose and a probable infectious dose of enterovirus being present over increasing fecal streptococci densities. The results of the polychotomous logistic regression analyses showed that the probability of the absence of enterovirus (i.e., zero enteroviruses being present) remained higher than the probability of the presence of either a possible or probable infectious dose in 101 of seawater up to a fecal streptococci density of 1000/100 ml of sample (actual estimated probabilities for the three groupings of enterovirus densities described above, at a fecal streptococci density of 1000 equaled 0.44, 0.44, and 0.12, respectively). In addition, the probability of zero enteroviruses being present remained higher than the probability of one or more enteroviruses being present in 101 of seawater up to a fecal streptococci density of 450/100 ml of sample. Since previously published epidemiological studies have shown an excess risk of gastroenteritis to occur among bathers exposed to as few as 32 fecal streptococci per 100 ml of sample, these results suggest that the actual viruses enumerated by the enterovirus assay are not etiologically related to recreational water-associated gastroenteritis. Since gastroenteritis has been the most consistently reported bathing water associated illness, these findings suggest the enterovirus assay to be of limited use in assessing marine recreational water quality given the increasing tendency to formulate water quality standards based on increased risk of gastroenteritis among bathers relative to non-bathers.

Copper in drinking water--an investigation into possible health effects.

A study was carried out to examine the possible relationship between levels of copper in drinking water and the incidence of specified childhood liver complaints presenting at a major UK paediatric liver unit. Public drinking water supplies were generally found to have levels of copper which were well below the EC standard of 3,000 micrograms/l. In private supplies, a slightly greater number of samples were found to exceed the prescribed concentration; in one instance a value of 26,000 micrograms/l was recorded. Data describing infant patients reporting to Kings College Hospital, London with specified liver complaints were examined. Where the address of patients could be determined (220 out of 240 cases), all patients were found to live in areas served by public drinking water supplies and were, thus, unlikely to have experienced elevated drinking water copper concentrations.

An investigation into the possible links between shigellosis and hepatitis A and public water supply disconnections

Abstract A retrospective study was conducted to determine if water supply disconnection could be implicated as a causative factor in the incidence of laboratory confirmed cases of shigellosis and hepatitis A in the Hull area. Data on all disconnections and cases of shigellosis and hepatitis A, between April 1988 and March 1993, were obtained. Over the period of the study, 908 disconnections took place, there were 1591 cases of shigellosis and 1034 cases of hepatitis A. Whilst there was a statistical correlation between rates of both disease outcomes and rates of disconnection in the 20 Hull postcode areas, a detailed examination of the two data sets failed to identify a causative relationship between disconnection and either illness in any household. A correlation analysis examining for statistical association between sociodemographic factors and illness indicated the importance of the general living standards and the elevated susceptibility of the poor and economically disadvantaged to these two diseases.

Chapter 4:Impacts of Agriculture on Water-borne Pathogens

Microbial indicators of water quality are used to quantify the risk derived from faecally contaminated surface and drinking waters. The historical focus in this area has centred on human-derived sewage contamination of bathing, shellfish and drinking waters. However, emerging catchment-scale water legislation in North America and Europe, in particular, is driving a more holistic approach in which quantification of microbial pollution from all sources is undertaken, to inform and prioritise appropriate remedial action designed to ensure health risk is minimised. This involves integrated management of agricultural livestock-derived pollution alongside sewage effluents to ensure compliance of impacted sites with appropriate regulatory standards. The evidence-base for the design of best management practices by farmers which will remove and/or attenuate microbial flux from catchment systems is very limited when compared to the chemical parameters associated with ecological impairments, such as phosphorus and nitrogen. However, early empirical investigations do suggest the potential to realise very significant water quality benefits from simple interventions, such as stock exclusion fencing of stream banks and well-designed constructed wetland systems. Further process-based investigation of these areas is underway and this research effort is becoming imperative as emerging experience of catchment-scale legislation strongly suggests the importance of microbial pollution as the principal reason for non-compliance with water quality standards in North America.