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The parameters involved in this equation were obtained from the recommendations of previous studies (Teunis et al. 2008). The D50 of 8.60 × 107 and α of 1.78 × 10−1 were suggested for E. coli, while the D50 of 1.64 × 10−9 and α of 4 × 10−2 were suggested for norovirus. For further comparison of infection risk obtained by QMRA with the USEPA recommended risk level for microbial contamination, the annual infection risk was estimated by using Equation (13) based on the annual exposure frequencies summarized in Table 2:
formula
13
Results for the infection risks obtained by the QMRA method are summarized in Table 9. The average annual infection rate for river cleaning, boating, and road flushing was estimated at 5.00 × 10−1, 4.68 × 10−1, and 5.02 × 10−1, respectively, of which exposure through road flushing led to the highest infection risk for water reuse in Lake Cui. This finding was consistent with that for the disease burden calculations. Norovirus had the highest infection risk of 9.78 × 10−1 compared with that of 1.03 × 10−3 for E. coli. This result was inconsistent with the result of the disease burden evaluation shown in Figure 3. Thus, we may conclude that a higher infection risk may not necessarily indicate a greater disease burden. On the other hand, the average infection risk per year for E. coli and norovirus for river cleaning, boating, and road flushing exceeded the USEPA reference risk level of 10−4. Thus, the infection risk obtained from QMRA was regarded as unacceptable. When compared with the WHO recommended threshold of 10−6 DALYs pppy for disease burden estimation, the total disease burden estimated for these two pathogens from all pathways was below the WHO standard shown in Figure 3. Thus, the disease burden obtained by the DALY was regarded as acceptable. Therefore, infection should not be regarded as the end point of a certain health damage due to environmental pollution. In addition, the infection risk should not be determined as the only prediction of health impact according to QMRA. Compared with the infection risk obtained from the traditional QMRA, the DALY is much more suitable for use in comprehensively describing and quantifying the health impact caused by microbiological contaminants due to water reuse.
Table 9

Results of infection risks obtained by QMRA

Pill/yE. coliNorovirusAverage
River cleaning 4.53 × 10−5 9.99 × 10−1 5.00 × 10−1 
Boating 1.69 × 10−5 9.35 × 10−1 4.68 × 10−1 
Road flushing 3.02 × 10−3 1.00 5.02 × 10−1 
Average 1.03 × 10−3 9.78 × 10−1  
Pill/yE. coliNorovirusAverage
River cleaning 4.53 × 10−5 9.99 × 10−1 5.00 × 10−1 
Boating 1.69 × 10−5 9.35 × 10−1 4.68 × 10−1 
Road flushing 3.02 × 10−3 1.00 5.02 × 10−1 
Average 1.03 × 10−3 9.78 × 10−1  
Figure 3

Comparison of infection risk obtained by QMRA with disease burden obtained by DALY.

Figure 3

Comparison of infection risk obtained by QMRA with disease burden obtained by DALY.

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