A risk assessment approach was developed to arrive at a comparative risk analysis of the various recommended wastewater irrigation microbial health guidelines for unrestricted irrigation of vegetables normally eaten uncooked. The guidelines compared are those of the WHO and the USEPA/USAID. The laboratory phase of the study determined the degree of contamination of vegetables irrigated by wastewater. Based on these estimates of the risk of ingesting pathogens, it is possible to estimate the risk of infection/disease based on the risk of infection and disease model developed for drinking water by Haas et al. (1993). For example, the annual risk of infectious hepatitis from regularly eating vegetables irrigated with raw wastewater is shown to be as high as 10−3. The study indicates that the annual risk of succumbing to a virus disease from regularly eating vegetables irrigated with effluent meeting WHO guidelines (1,000 FC/100mL) is negligible and of the order of 10−6 to 10−7 The risk of the more infectious, but less serious, rotavirus is 10−5 to 10−6. The USEPA considers an annual risk of 10−4 to be acceptable for microbial contamination of drinking water. The additional health benefit that might result from a further reduction of risk gained by adhering to the USEPA/USAID Reuse Guidelines (1992), which require no detectable faecal coliforms/100mL, appears to be insignificant in relation to the major additional costs associated with the expensive technology required to treat effluent to such a rigorous standard. Our preliminary estimates show that meeting the USEPA Guidelines would result in an extra expenditure of $3–30millions/case of disease prevented.
This paper presents a preliminary attempt at obtaining an order-of-magnitude estimate of the global burden of disease (GBD) of human infectious diseases associated with swimming/bathing in coastal waters polluted by wastewater, and eating raw or lightly steamed filter-feeding shellfish harvested from such waters. Such diseases will be termed thalassogenic--caused by the sea. Until recently these human health effects have been viewed primarily as local phenomena, not generally included in the world agenda of marine scientists dealing with global marine pollution problems. The massive global scale of the problem can be visualized when one considers that the wastewater and human body wastes of a significant portion of the world's population who reside along the coastline or in the vicinity of the sea are discharged daily, directly or indirectly, into the marine coastal waters, much of it with little or no treatment. Every cubic metre of raw domestic wastewater discharged into the sea can carry millions of infectious doses of pathogenic microorganisms. It is estimated that globally, foreign and local tourists together spend some 2 billion man-days annually at coastal recreational resorts and many are often exposed there to coastal waters polluted by wastewater. Annually some 800 million meals of potentially contaminated filter-feeding shellfish/bivalves and other sea foods, harvested in polluted waters are consumed, much of it raw or lightly steamed. A number of scientific studies have shown that swimmers swallow significant amounts of polluted seawater and can become ill with gastrointestinal and respiratory diseases from the pathogens they ingest. Based on risk assessments from the World Health Organization (WHO) and academic research sources the present study has made an estimate that globally, each year, there are in excess of 120 million cases of gastrointestinal disease and in excess of 50 million cases of more severe respiratory diseases caused by swimming and bathing in wastewater-polluted coastal waters. Filter-feeding shellfish/bivalves, which are often harvested from wastewater-polluted areas of the sea, can effectively filter out and concentrate the microbial pathogens in the seawater. It can be roughly estimated that annually there are some 4 million cases of infectious hepatitis A and E (HAV/HEV), with some 40 thousand deaths and 40 thousand cases of long-term disability, mainly chronic liver damage, from consuming raw or lightly steamed filter-feeding shellfish/molluscs harvested globally from polluted coastal waters. The total global health impact of the thalassogenic diseases--human infectious diseases associated with pathogenic microorganisms from land-based wastewater pollution of the seas--is estimated to be about 3 million 'disability-adjusted life years' (DALY)/year, with an estimated economic loss of some 12 billion dollars per year. Due to the preliminary nature of the estimates in this study it is appropriate to assume that all of the above figures are no more than first approximations and th...
Studies reported here are part of a program to reevaluate current nitrate and nitrite standards for water and food. Included are field studies among infants in areas with varying concentrations of nitrates in water supplies as well as experimental studies on laboratory animals. Findings are reported and discussed. The detection of irreversible electrical brain activity changes in rats receiving low doses of nitrites in drinking water is of particular concern.
Although chlorine is the most widely used agent for disinfecting water, its use presents problems because of its relatively low effectiveness as a virucide and because of potentially toxic compounds that may be formed. Ozone is shown to have a much more rapid virucidal effect and may soon find its place in treating water and wastewater, alone or in combination with chlorine.
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