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Several risk scoring and ranking methods have been applied for the prioritization of micropollutants, including pesticides, and in the selection of pesticides to be regulated regionally and nationally. However, the effectiveness of these methods has not been evaluated in Japan. We developed a risk prediction method to select pesticides that have a high probability of being detected in drinking water sources where no monitoring data is available. The risk prediction method was used to select new pesticides for the 2013 Primary List in the Japanese Drinking Water Quality Guidelines. Here, we examined the effectiveness of the method on the basis of the results of water quality examinations conducted by water supply authorities across Japan, and studied ways to improve the risk prediction method. Of the 120 pesticides in the 2013 Primary List, 80 were detected in drinking water sources (raw water entering water treatment plants). The rates of detection of the newly selected pesticides and previously listed pesticides were not significantly different: 64% and 68%, respectively. When the risk predictor was revised to incorporate degradability of dry-field pesticides and current pesticide sales data, the rate of detection of pesticides selected as having a high risk of detection improved from 72% to 88%. We prepared regional versions of the Primary List using the revised risk predictors and verified their utility. The number of listed pesticides varied greatly by region, ranging from 32 to 73; all regional lists were much shorter than the national Primary List. In addition, 55% to 100% of the pesticides detected in each region were included in a Regional Primary List. This work verifies the ability of the risk prediction method to screen pesticides and select those with a high risk of detection.

We evaluated the removal of enteric adenovirus (AdV) type 40 and poliovirus (PV) type 1 by coagulation, using water samples from 13 water sources for drinking water treatment plants in Japan. The behaviors of two widely accepted enteric virus surrogates, bacteriophages MS2 and φX174, were compared with the behaviors of AdV and PV. Coagulation with polyaluminum chloride (PACl, basicity 1.5) removed AdV and PV from virus-spiked source waters: the infectious AdV and PV removal ratios evaluated by means of a plaque-forming-unit method were 0.1-1.4-log10 and 0.5-2.4-log10, respectively. A nonsulfated high-basicity PACl (basicity 2.1) removed infectious AdV and PV more efficiently than did other commercially available PACls (basicity 1.5-2.1), alum, and ferric chloride. The MS2 removal ratios tended to be larger than those of AdV and PV, partly because of differences in the hydrophobicities of the virus particles and the sensitivity of the virus to the virucidal activity of PACl; the differences in removal ratios were not due to differences in the surface charges of the virus particles. MS2, which was more hydrophobic than the other viruses, was inactivated during coagulation with PACl. Therefore, MS2 does not appear to be an appropriate surrogate for AdV and PV during coagulation. In contrast, because φX174, like AdV and PV, was not inactivated during coagulation, and because the hydrophobicity of φX174 was similar to or somewhat lower than the hydrophobicities of AdV and PV, the φX174 removal ratios tended to be similar to or somewhat smaller than those of the enteric viruses. Therefore, φX174 is a potential conservative surrogate for AdV and PV during coagulation. In summary, the surface hydrophobicity of virus particles and the sensitivity of the virus to the virucidal activity of the coagulant are probably important determinants of the efficiency of virus removal during coagulation.

Vacuum ultraviolet (VUV) treatment is a promising advanced oxidation process for the removal of organic contaminants during water treatment. Here, we investigated the formation of disinfection by-products from coexisting organic matter during VUV or ultraviolet (UV) treatment following pre-chlorination, and their fates after post-chlorination, in a standard Suwannee River humic acid water and a natural lake water. VUV treatment after pre-chlorination decreased the total trihalomethane (THM) concentration but increased total aldehyde and chloral hydrate concentrations; total haloacetic acid (HAA) and haloacetonitrile (HAN) concentrations did not change. UV treatment after pre-chlorination produced similar changes in the by-products as those observed for VUV treatment, with the exception that the total THM concentration was not changed, and the total HAN concentration was increased. The final concentrations of by-products after post-chlorination were increased by VUV or UV treatment, except for the total HAA concentration, which remained unchanged after UV treatment. The increases were greater after VUV treatment than after UV treatment, probably because the larger amount of hydroxyl radicals generated during VUV treatment compared with during UV treatment transformed coexisting organic matter into precursors of by-products that were then converted to by-products during post-chlorination.