| Abstract | Infections of excreta-related pathogens are mostly due to poor sanitation and hygiene where especially contamination of the environment is apparent. Typically, Salmonella, E. coli or helminthes are dominated species in faecal matters, faecal sludge, wastewater etc, thereby human can be exposed and infected. The risk of infection depends on contact intensity and the pathogenic contamination at various sources and pathway. This study endeavors to integrate the Pathogen Flow Analysis (PFA) and Quantitative Microbial Risk Assessment (QMRA) for assessing E. coli and Salmonella concentrations and the associated health risks in a vegetable farmland system. Development of the integrated PFA and QMRA was based on pathway analysis and mathematic modeling. PFA model is applied at pathway of flows in Material Flow Analysis (MFA) system to calculate pathogens concentrations at exposure points. Meanwhile, QMRA applies the results of PFA associated with exposure amount and frequency to estimate health risks of the related activities. Results of the integrated PFA and QMRA could thus be used for health and sanitation planning. In experimental Phase 1, the lab-scale experiments were undertaken in order to determine the die-off rates (k20) of E. coli and Salmonella at different conditions in canal water, soil and on lettuce leaves. During the first 7 days of experiments, k20 of E. coli and Salmonella were 0.865 and 0.531 d-1in canal water and 0.121 and 0.687 d-1 in soil, respectively. In the period of 7-28 days, k20 of E. coli and Salmonella were decreased drastically at 0.078 and 0.086 d-1in canal water and 0.057 and 0.071 d-1 in soil, respectively. However, at the ambient condition, temperature and light intensity could affect the die-off rate, which are accorded to adjusting factor (Ct) for die-off rates (kT) calibration at various light intensities. It was found that Ct of both E. coli and Salmonellain canal water during the first 7 days were 1.0-1.2 and 1.2-1.7 times of kT at 0% light protection and 100% light protection, respectively, while Ct of 1.7-2.8 and 1.9-3.4 at 0% light protection and 100% light protection during the period of 7-28 days. In soil, Ct were 1.0-1.3 and 1.2-1.6 times of kT at 0% light protection and 100% light protection in the first 7 days, and were 1.0-1.2 and 1.4-2.7 times of kT at 0% light protection and 100% light protection in the later 7-28 days, respectively. For the pathogen reduction rates on vegetable at ambient condition it could be observed at the rates of 1 to 4 log per day at 50 to 0 % of light protection, and increased of 2 and 7 log after the first and second washings, respectively. Field investigations in Phase 2 at a lettuce farm in Pathumthani province, Thailand were undertaken to calibrate the die-off rates (kT) with the results of plot experiments and validating the calibrated model with another filed data. According to model validation, it could reveal the differences of geometric mean of E. coli and Salmonella concentrations were at 41 and 20 % in furrows, and 15 and 24 % in soil plots; with the correlation coefficient at 0.752 and 0.989 in furrow, and 0.980 and 0.958 in soil plots, respectively. The differences of geometric mean within 1 log are similar to other studies. The kinetic parameters obtained from Phase 1 and 2 were then applied in PFA model of lettuce farm system for assessing of pathogen concentrations, and consequently for determination of health risks by QMRA. Based on the integrated PFA and QMRA by using STELLA dynamic model, it could indicate that health risks from E. coli and Salmonella in fishing and vegetation in canal and swimming activities resulted in the highest risk at 1.29E-01 and 1.32E-01. Health risks from the irrigated water in farmland were attributed to 7.94E-04 and 5.39E-05 while health risks from the consumption of washed vegetable were 8.24E-06 and lower than 1.0E-04, lower than the acceptable risk of 1.0E-04. After testing with sanitation scenarios such as municipal wastewater treatment plant, infectious risks of both E. coli and Salmonella could be decreased at 90% in fishing, swimming and vegetation activities. The field investigations of kinetic coefficients of the pathogen die-off in this study, which emphasized on vegetable farmland, could demonstrate a promising application of the integrated PFA and QMRA. It is recommended that a comparative study of epidemiology and QMRA be undertaken with additional comprehensive field investigations. |