Although the current EU bathing directive has certainly had a positive effect on the condition of our beaches and waters there are still concerns, particularly when considering urban beaches, which are subjected to higher environmental pressure due to their location, but also experience seasonal increases in visitors increasing the risk of human exposure to possible infection. One of the main concerns of the EU bathing directive has been to monitor and control pollution relating to sewage but when sampling methods have been designed, they have not taken into consideration possible small scale temporal variations.
Recent research has focused on this aspect in a study conducted in North West Portugal. Four beaches were chosen, to be sampled hourly for a period of 11 hours, on several different occasions. All samples were analysed to determine numbers of microbial indicators, Escherichia coli and intestinal enterococci.
It was found that waters with lower salinity due to the beaches being closer to river run off had significantly higher numbers of both indicators. In addition during the summer months, reduced rainfall lead to a higher concentration of microbes in the run off. Wind direction was also found to have a significant influence on readings, driving contaminated surface waters from river mouths towards the monitored beaches at times. As wind direction may change regularly, it is important that this be taken into consideration when samples are taken as this could have significant effects on the readings acquired.
Although water quality varied at all sample sites throughout the day, the highest readings for indicator species were generally found in the morning. Readings could be as high as 5100 cfu 100 ml-1, and as low as 21 cfu 100 ml-1 with in one 11-hour period. These readings could mean the difference between the beach being closed or being given a rating of excellent.
The current directive requires a minimum of four samples to be taken from each bathing area during any season however there appears to be no specification regarding times that samples should be taken. Previous studies have shown that if samples are taken five times per week they highlight 80% of non-conformity events however only 5% of these events were detected when sampling was monthly.
I believe that this study along with previous evidence highlights the need for not only an increase in sampling efforts to ensure that those beaches considered more at risk from pollution are maintained at a safe level but also a requirement to have a greater understanding of the local area. If these studies were carried out on a more local basis rather than by a national organizations it would allow for a greater understanding of how daily variations and seasonal patterns may affect the cleanliness of bathing waters. This could allow local authorities to better inform visitors highlighting the safest times for swimming or watersports.
Amorim, E., Ramos, S., & Bordalo, A. A. (2014). Relevance of temporal and spatial variability for monitoring the microbiological water quality in an urban bathing area. Ocean & Coastal Management, 91, 41-49.