Exposure parameters and health risk of Cryptosporidium and Giardia in the recreational water activities for urban residents in China

Knowledge gaps in the exposure parameters for recreational water activities make quantitative risk assessment related to water recreation difficult. Therefore, the annual exposure frequency and single exposure duration for the recreational water activities of residents from ten cities in the North and South of China were investigated. Questionnaire interviews were carried on recreational water activities comprising swimming (SW), boating (BA), playing in interactive fountains (PF), and watching fountains (WF). Quantitative microbial risk assessment for the exposure of urban residents to Cryptosporidium and Giardia was also performed. For the four recreational water activities, the participation rates of urban residents in SW and WF were higher than the others. For SW and BA, the mean annual exposure frequency and single exposure duration for males were significantly higher than those for females. PF and WF showed the opposite. The annual exposure frequency for above 35-year-old residents was higher than that for young residents (18–35 years). However, the single exposure duration for young residents was highest in SW, BA, and PF. The mean annual exposure frequency and single exposure duration for North China residents were higher than those for South China residents in all recreational water activities, except for SW. Overall, the annual exposure frequency and single exposure duration in recreational water activities for all urban residents followed a lognormal distribution. In the four recreational water activities, the total annual infection risk of male exposure to Cryptosporidium was 1.0 × 10⁻², with the confidence intervals between 95 and 5% of [4.3 × 10⁻⁴, 3.7 × 10⁻²], whereas that for females was 6.8 × 10⁻³ and [4.2 × 10⁻⁴, 2.4 × 10⁻²]. Also, the annual infection risk of males to Giardia was 8.8 × 10⁻³ and [5.1×10⁻⁴, 3.2×10⁻²], and that of females was 5.3 × 10⁻³ and [4.0 × 10⁻⁴, 1.8 × 10⁻²]. These results demonstrated that SW and PF made the highest contribution to the total annual infection risk. Sensitivity analysis highlighted that the characterization of exposure parameters plays a critical role in health risk assessment, which may provide a scientific basis for recreational water quality standards formulation.