National risk assessment of irrigation on farmland near wastewater treatment plants in Korea

There are more than 130 agricultural water sources that are located near wastewater treatment plants (WWTPS) in Korea. The majority of the stream flow in these farmlands is dependent on effluent from the WWTPS during the dry season. This explains the indirect or direct reuse of effluent from WWTPs. Most of the farm workers use the effluent without any additional treatment because they have a lack of knowledge regarding water reuse. In addition, insufficient consideration is given to health and hygiene safety. This study reviewed the safety issues in these farmlands. A total of 53 farmlands located near WWTPs were investigated to determine if farm workers used effluent as irrigation water on their paddy rice fields. Total coliform, fecal coliform, Escherichia coli (E. coli), and the concentration of some heavy metals in paddy water and soils were measured. Quantitative microbial and toxic risk assessment methods were used to review the safety of wastewater irrigation. E. coli concentrations were used to estimate the microbial risk of enteric disease in the paddy fields. The microbial risk was 5.9 × 10−4, which did not satisfy the minimum safety standards. Carcinogenic risk was 3.99 × 10−5 and non-carcinogenic risk was 6.34 × 10−1. These values were too high to be considered safe, even though the measurements of E. coli and some toxic metals were of short duration.