Micro-organisms are a ubiquitous and intimate part of our daily existence. Every day large numbers of them are discharged into the wastewater system from healthy and unhealthy people through diverse human activities. Risks arising from the wastewater generated will depend on the general state of health of the population. Inadequate hygiene and sanitation systems can cause contamination of foods and water used for drinking. Epidemics of cholera and typhoid11 can occur and spread rapidly, particularly in poor and deprived areas. The South
11 P. West, ‘The ecology and survival of Vibrio cholera in natural aquatic environments’, in ‘Cholera update’, PHLS Microbiol. Digester, 1992, 9, 13—42.
Table 4 Quality of bathing water 1989—92, % compliance with CEC directive
SeaWater 1989 1990 1991 1992
Belgium 94 90 85 90
American pandemic of 1991 and Rwanda of 1994 are recent illustrations.
Hostilities such as the Gulf War can often result in the breakdown of sanitary systems and increase risk of water-borne disease.
Wastewater treatment has generally been directed towards the reduction of aesthetic and obvious polluting aspects of wastewater discharges, rather than microbiological aspects of the processes. Most treatments achieve some reductions in faecal, including pathogenic, micro-organisms and some plants may be augmented with various tertiary treatments including lagooning, sand filtration, membrane filtration, and disinfection which further reduce bacterial levels.
Tertiary treatment or chemical disinfection are used particularly where microbiological standards apply in the receiving waters. These standards tend to be most depending where recreational use is to be made of the receiving water, as with inland waterways and resort bathing waters.
Microbiological standards relating to coastal and esturial waters include European directives on bathing water quality and the water quality in shellfisheries. Public and media concern about sewage disposal in these areas has related not just to compliance with these standards but also to more obvious aesthetic signs of pollution, including material washed up on beaches or floating in or on the water. This has an adverse psychological effect on the public well-being and recreational value, quite apart from any subsequent morbidity associated with faecal contamination of the water. The ‘Good Beach’ guide statistics and ‘Blue Flag’ awards include standards relating to cleanliness and provision of facilities such as toilets at the beach site, in addition to the achievement of microbiological quality standards. European compliance with the Bathing Water Directive is given in Table 4. Gradual improvement in the UK in bathing water quality is evident.
In fact, the microbiological standards of the Bathing Water Directive were set arbitrarily and not on the basis of knowledge of public health significance.
Subsequent epidemiological studies aiming to relate standards to health criteria have been widely criticized by scientists on statistical grounds.12 In practice, these
12 R. Philipp, ‘Risk assessment and microbiological hazards associated with recreational water sports’. Rev. Med. Microbiol., 1991, 2, 208—214.
studies are both difficult and expensive to perform. The most recent and largest study of this kind13 concluded that there was a correlation between faecal micro-organism numbers (particularly Enterovirus) and gastro-intestinal symptoms.
The correlation in those who had been exposed to the water was only significant, however, when counts significantly exceeded the mandatory, imperative standards of the Bathing Water Directive. Other categories of symptom such as eye, ear, nose, throat, and skin disorders were correlated with degree of water contact, duration, and intimacy of exposure, rather than concentrations of microbial indicators of faecal pollution. The Bathing Water Directive microbiological standards are being reviewed and amended, giving greater importance to faecal Streptococci in line with experience, although European consensus has yet to be achieved.
Viruses are of topical interest in relation to exposure risks from wastewater use and discharged. Public Health Laboratory figures show that Hepatitis A, responsible for infectious jaundice, has increased since 1987.14 Shellfish consumption can increase risk but no link has yet been made with recreational water exposure.
There is no evidence supporting risk to the public from exposure to recreational waters or sewage from HIV, the causative agent of AIDS.
Bathing waters can suffer from potential microbiological hazards other than from sewage discharge. Notably, environmental contamination can result from gulls which have a prevalence of enteric bacterial pathogens such as Salmonella and Campylobacter in their faeces.15
The position is similar where inland waters are used for recreation. The concentration of faecal organisms is the principal factor in the risk of disease.
Recreational exposure, including canoeing, swimming, sailing, and fishing differs only slightly from marine waters in the degree and intimacy of exposure. Rivers act as repositories for large bodies of treated wastewater, surface water, and agricultural run-off. Sewage effluents, although subject to stringent discharge consents, still have significant inputs of faecally derived microbes. Abstraction of river water for drinking purposes places constraints on the location of the water purification works and the type of treatment required.
The often quoted risks of Leptospirosis, or Weil’s disease, must be kept in context. Sewage workers may have an increased risk from indirect exposure to rats and this has led to confusion with the risk of exposure to sewage. In fact the disease is usually contracted by exposure to the urine of infected rats or of urine-contaminated stagnant water. Infection occurs through cuts and abrasions or via the mucous membranes.16
13 E. B. Pike, Health Effects of Sea Bathing (WMI 9021)—Phase III Final Report to the Department of the Environment, 1992, Report No. DoE, 3412 (P).
14 PHLS Working Group, ‘The present state of hepatitis A infection in England and Wales’, PHLS Microbiol. Digest, 1991, 8, 122—126.
15 D. J. Gould, ‘Gull droppings and their effects on water quality’, Water Research Centre Tech.
Report 37, 1977.
16 S. Moore, ‘Occupational exposure to Leptospirosis. Reducing the risk of Weil’s disease’, Occupational Hlth. Rev., Dec. 1991/Jan. 1992, 30—32.