Wastewater effluent impacts: introduction

Rivers, lakes and coastal waters have long been used as receptacles for diluting and dispersing domestic waste.   Water pollution related to sewage discharge probably can be traced back to the foundation of the first cities 7000 years ago along the Tigris-Euphrates and Indus rivers.  However, it only became a severe problem during the industrial revolution when wastes produced from industrial processes along with domestic sewage from an increasing urban population were poured untreated into the nearest waters.  Classic examples of long-term water pollution from domestic sewage are described for the Thames River, England (Gameson and Wheeler 1977), and Boston Harbor and Chesapeake Bay, USA (National Research Council 1993).  Yet, while there have been considerable efforts since the 1970s by developed nations to improve sewage treatment, discharge of untreated or poorly treated sewage is still a concern in many parts of the world, particularly developing countries and those experiencing transition economies (e.g., Russia and central Europe).  In the case of developing countries, >90% of urban sewage is discharged directly into surface water without treatment (World Resources Institute 1996).  However, even in many developed countries, only a portion of municipal sewage receives conventional treatment.  For example, only 60% of the total population of countries belonging to the Organisation for Economic Co-operation and Development was connected to a sewage collection system and served by domestic wastewater treatment in the late 1980s (OECD 1995).

The impacts of domestic wastewater discharge on receiving water are numerous.  Sewage poses a direct health risk from pathogens such as bacteria (e.g., cholera, salmonella, shigellas), viruses (e.g., hepatitis, enteroviruses, poliovirus, Norwalk) and parasites (e.g., protozoans such as Giardia and Cryptosporidium, helminths) (World Health Organization 1993; World Resources Institute 1996).  Indirect human health risks include consumption of fish or shellfish rendered toxic by bacteria, metals or organic compounds associated with sewage (Waldichuck 1989), or exposure to microbially-contaminated waters during recreational activities (Edsall and Charlton 1996).  In addition to human health risks, domestic wastewater discharge poses environmental risks.  Loading of nitrogen and phosphorus can lead to eutrophication resulting in radical changes in productivity and biodiversity, inputs of contaminants can cause acute or chronic toxicity of organisms in receiving waters, while high loads of oxygen-demanding material can reduce dissolved oxygen to levels that threaten the survival of aquatic organisms (e.g., Meybeck et al. 1989; National Research Council 1993).

The aim of this study was to review the consequences of municipal wastewater discharge to Canadian lakes, rivers and coastal waters.  Canada is often seen as a privileged country because of the abundance and quality of its water resources.  However, concerns raised by international agencies about sewage disposal world-wide (United Nations 1992a; UNEP1995) and bypublic groups about the Canadian situation (Sierra Legal Defence Fund 1994; Kapitain 1995; Nantel 1995, 1996a,b) emphasized the need to evaluate the current status of municipal wastewater discharges and their effects on the Canadian environment.  In this review, we summarized the current risks to human health and the environment from municipal wastewater discharge in Canada.  Whereas the historical focus of municipal wastewater management has been on discharges from municipal wastewater treatment plants (MWTPs), it is now recognized that municipal wastewater management should also take into account stormwater discharges and combined sewer overflows.  Thus, in this paper, we examined the effect of discharges from MWTPs, stormwater and combined sewer overflows.  Discharges from lagoons and septic systems have not been considered as their risks to human health and the environment are difficult to generalize due to a paucity of Canadian information.

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