Down the drain – is it a case of out of sight, out of mind?

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One of the problems of the modern human being is his/her restricted view of the world. Waste water is very good example. Waste water, once it has disappeared down the drain, does not exist any more to most people. Therefore it is difficult to create a sense of personal responsibility, even if most of us are critical about industrial waste. Consequently, the emissions from industrial plants are monitored by legislative and regulatory controls, and the release of many dangerous chemicals has been totally banned. Urban wastewaters are fortunately also cleaned properly in many civilized countries and untreated wastewaters do not enter waterways except when there is an accident or some other unanticipated release.

There are both chemical and microbiological risks connected with wastewaters. Globally, the microbiological risks are by far the more important and this is the case even in the advanced European societies; people die from microbiological contamination, but chemical releases additionally cause many ecological problems.

Chemical factors

There are many different types of compounds present in wastewaters. The drains bring water into wastewater treatment plants with hormones, drugs, detergents, other cleaning chemicals, cosmetics, pesticides; in fact everything possible from the domestic and industrial activities, including mishandled hazardous waste. These place a stress on the wastewater treatment systems.

The most important source of drugs is the urine from patients. The greatest attention has been focussed on hormones that cause feminization of male fish. This has been studied in England downstream of major towns. Female sex hormones are mostly natural hormones and to a smaller extent synthetic hormones from birth control pills. Other drugs have not been shown to cause problems in water ecosystems, although the impact of antibiotics has been a cause of concern though only studied to a limited extent. A problem caused by antibiotics could be selection pressure favouring resistant bacteria.

Many compounds popular in personal hygiene and household use, as well as cosmetics, end up in wastewater. This is well illustrated by the fact that suntan protection chemicals (UV-screens) have been detected in fish caught from the waters around popular beach resorts.

There are some data on the importance of these problems in both Europe and North America, but climatic conditions may have a profound influence, and a comprehensive risk assessment is difficult. Most industrial releases are now well controlled in the developed countries, but there are many compounds present in consumer products which pass through the conventional waste water treatment processes. It is likely that the most important problems are ecotoxicological, but in some instances also health considerations might require more research especially with respect to persistent compounds. Consumption of fish is the most likely source of exposure by human beings.

Microbiological factors

Outbreaks of waterborne diseases occur throughout Europe. These problems are more endemic in Eastern Europe, and the European office of the World Health Organisation estimates that 13,500 children aged less than 14 years die due to poor water conditions in its region. In most western European countries, almost all of the populations have been connected to safe water supplies. However, even when there is access to good quality drinking water, outbreaks do occur due to broken pipes or uncontrolled small water supplies. Many outbreaks go unnoticed; this seems to vary from country to country. It is noteworthy that Finland which has a well-established surveillance system and high-quality water supplies, has reported the highest number of outbreaks in Europe. This suggests that in many countries the majority of outbreaks go unnoticed.

Typical microbes that enter the water supply via wastewater are norovirus (calicivirus) and Campylobacter jejuni. In some countries, there is also a risk of more serious infections such as viral hepatitis, shigella infections, and parasitic infections (e.g. cryptosporiosis). Viruses need a specific host (human or animal), and cannot reproduce outside this organism in the natural environment. However, one patient with norovirus diarrhoea excretes huge numbers of viruses, in fact a number that could theoretically infect the entire human population of the world. So even if most of the viruses are destroyed in the wastewater treatment processes, enough may remain to infect other individuals.

The high number of viruses explains the following infection episode in Finland. An epidemic was contracted from imported raspberries irrigated in their country of origin with sewage water. Several school classes became ill after eating the berries. Enough viruses from diarrhoeal stools entered the waste water plant and passed through the treatment processes to cause another epidemic several months later in a village downstream which had a simple drinking water purification system that did not stop or kill the viruses. In that village almost everyone, about 90 % of the population, fell ill.

Also recreational waters have been linked to diseases. It has been estimated that globally 20 million people suffer gastrointestinal disease from swimming and bathing in wastewater-polluted coastal waters. Youngsters and tourists are more vulnerable, because they do not have immunity towards local endemic diseases. Children also tend to swallow water when they swim which increases the risk.

Wastewaters cause significant ecological problems. Health problems caused by chemicals in surface waters seem to be rare, but can occur due to accidental releases or other irregularities. Microbiological risks are significant if wastewater treatment is not good.

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