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.

A method is described for second-step concentration of viruses from water. This method, combined with an adsorption-elution method, yields a mean recovery of about 75%

Carp were maintained for a month in well-oxygenated water fertilized with organic manure. During the experiment the thickness of the epidermis increased from 140 to 180 pm. Fish from pulluted water were dark, an adaptation to the dark, turbid water. The number of cytoplasmic extensions from the dermal pigment cells increased continuously from 6 per unit length in control specimens to over 80 in the experimental specimens at the end of the month. Apart from background adaptation, this activity of the pigment cells may be a stress reaction. Holocrine secretion of mucous cells was pronounced, with a progressive reduction on the first day after the transfer, to almost total disappearance of this cell type from the epidermis after 3 days. A thick mucous coat became visible on the outside of the epidermis. Eight days after the transfer, a slightly subnormal mucous cell count was observed, indicating the development of newly differentiated mucouscells.This subnormal cell count lasted until the end of the experiment. The pavement cells actively secreted glycocalyx, while newly differentiated pavement cells with still-intact secretory granules replaced the exhausted cells at the epidermis surface throughout the experimental period. Granulocytes, both baso-and neutrophilic, as well as macrophages, infiltrated the epidermis; despite the high bacterial count in the water, no bacteria were observed either inside the skin or entangled in the mucous coat.

The inactivation efficiencies of silver ions, hydrogen peroxide and their combination was studied as part of a performance evaluation of the combined disinfectant for drinking water applications. The major advantages of such combined disinfectant include, low toxicity of its components, long lasting residual effect and low disinfection by product formation. Specific strains of E. coli (E. coli-B (SR-9) and E. coli K-12) were used in this study as target microorganisms and the separate and combined inactivation efficiencies of silver and hydrogen peroxide were evaluated at different concentrations and exposure durations. Both, silver and hydrogen peroxide exhibited a significant inactivation performance even at concentrations that do not pose any health risk according to the EEC, WHO and the USEPA (the USEPA Maximum Contaminant Level (MCL) of silver is 90 ppb, and currently, there is no MCL for hydrogen peroxide but it is approved as a food additive in the USA). Combinations of 1:1000 silver:hydrogen peroxide (w) exhibited higher inactivation performance as compared with each of the disinfectants alone and in some cases a synergistic effect was observed, i.e., the combined disinfectant exhibited higher inactivation performance than the sum of the inactivation levels of the separate disinfectants. Thus, for example, one hour exposure to 30 ppb silver, 30 ppm hydrogen peroxide and their combination yielded 2.87, 0.65 and 5 logs of inactivation respectively. While the rate of inactivation shown by this combined disinfectant, now available commercially in a stabilized formulation is relatively slow, it may well hold promise as a secondary disinfectant providing long lasting residuals and biofilm control required for distribution systems. Its disinfection action may be similar to chloramines, the use of which has been recently outlawed in France and in Germany and which are now under careful scrutiny in other countries due to the formation of undesirable by-products.

This study was designed to compare the die-off of E.coli and F*bacteriophages with that of enteric pathogenic viruses in groundwater and raw wastewater at various temperatures. At low temperatures, the die-off of E.coli was greater than that of HAV and poliovirus 1. Under conditions compatible with bacterial growth no die-off of E.coli was observed. Under most experimental conditions no die-off was observed for F*bacteriophages. The survival of HAV and poliovirus 1 was strongly affected by temperature. Regardless of the water type, the highest die-off of viruses was observed at 30°C, whereas at 10°C the titer of HAV and poliovirus 1 was reduced by 1 to 2 log10 after 90 days incubation. The data presented in this study indicated that E.coli cannot serve as an index for the survival of HAV and poliovirus 1 in ground and wastewater. Since F+bacteriophages were not affected by the tested conditions, their acceptance as indicators for viral pollution of water sources needs further evaluation.