4. Conclusions
1. The concentration of HAdV is stable in raw sewage throughout
the year, with mean values of 8.38 105 GC/L.
2. Secondary biological treatment reduces pathogen concentrations
between 2.0 and 3.1 log10 (as GC/L). Because conventional
WWTPs discharge secondary effluents into rivers, the Llobregat
River is persistently impacted by human faecal pollution as
evidenced by the presence of HAdV, JCPyV and FIB in riverwater
samples.
3. Seasonal NoV GGII patterns are observed at all sampling sites
including wastewater and environmental samples. From the
most upstream sampling site to the seawater impacted by the
river discharge, NoV GGII was detected during spring, autumn
and especially in winter when more outbreaks are identified in
the population.
4. A new quantitative PCR method has been developed for the
detection of the emergent MCPyV related to Merkel cell
carcinoma in water matrices. This is the first study reporting
detection and quantification of MCPyV in seawater samples
(with 18% prevalence and mean concentration of 1.18 102 GC/
L). The high prevalence of MCPyV in sewage (75%) suggests that
the human population commonly sheds this virus.
5. Temperature and precipitation predictions to 2100 for the
selected Mediterranean river catchment suggest an increase in
temperatures throughout the year and increased precipitation
during winter with a decrease in precipitation between May and
October. The highest virus concentrations are detected in summer
when minimum precipitation and river flow occurs. The
reduced dilution of treated effluents by rivers will result in
elevated summer pathogen concentrations, with the potential
for increased concentrations in winter resulting from intermittent
combined sewage overflows discharging during the more
frequent storm events.