Bathing water quality analysis, management and policy: an integrated assessment for Ireland

Every bathing season in Ireland several bathing sites are closing and receiving warnings against bathing. In this report, their water quality status is assessed, and the broader picture of each case is investigated. A database is formed including location-maps, the restrictions they were/are subject to, the official justification, past and current annual water quality status, (sub)catchment where they are located, main water bodies flowing in, the closest WasteWater Treatment Plants with their characteristics and performance based on EU treatment standards, the closest meteorological stations and the rainfall data related with stormwater overflow events (correlation analyses) and the surrounding land cover. For each case, possible causes were discussed; the actions so far and the relevant literature are analyzed to provide key policy recommendations which are useful for the review of the European Bathing Water Directive.

Modelling the Quality of Bathing Waters in the Adriatic Sea

The aim of this study is to develop a relocatable modelling system able to describe the microbial contamination that affects the quality of coastal bathing waters. Pollution events are mainly triggered by urban sewer outflows during massive rainy events, with relevant negative consequences on the marine environment and tourism and related activities of coastal towns. A finite element hydrodynamic model was applied to five study areas in the Adriatic Sea, which differ for urban, oceanographic and morphological conditions. With the help of transport-diffusion and microbial decay modules, the distribution of Escherichia coli was investigated during significant events. The numerical investigation was supported by detailed in situ observational datasets. The model results were evaluated against water level, sea temperature, salinity and E. coli concentrations acquired in situ, demonstrating the capacity of the modelling suite in simulating the circulation in the coastal areas of the Adriatic Sea, as well as several main transport and diffusion dynamics, such as riverine and polluted waters dispersion. Moreover, the results of the simulations were used to perform a comparative analysis among the different study sites, demonstrating that dilution and mixing, mostly induced by the tidal action, had a stronger effect on bacteria reduction with respect to microbial decay. Stratification and estuarine dynamics also play an important role in governing microbial concentration. The modelling suite can be used as a beach management tool for improving protection of public health, as required by the EU Bathing Water Directive.

Are the existing guidelines sufficient for the assessment of bathing water quality? The example of Polish lakes

The safety of beachgoers and swimmers is determined by the presence or absence of microbial contaminants and cyanobacterial toxins in the water. This study compared the assessment of bathing waters according to the Bathing Water Directive, which is based on the concentration of fecal contaminants, with some modifications, and a new method based on the concentration of chlorophyll-a, which corresponds to the World Health Organization (WHO) guidelines used for determining cyanobacterial density in the water posing threat to people health. The results obtained from the method based on chlorophyll-a concentration clearly showed that the number of bathing waters in Poland with sufficient and insufficient quality were higher in 2018 and 2019, compared to the method based on microbial contamination. The closing of bathing waters based only on the visual confirmation of cyanobacterial blooms might not be enough to prevent the threat to swimmers’ health. The multivariate analyses applied in this study seem to confirm that chlorophyll-a concentration with associated cyanobacterial density might serve as an additional parameter for assessing the quality of bathing waters, and in the case of small water reservoirs, might indirectly inform about the conditions and changes in water ecosystems.

Skip the Dip—Avoid the Risk? Integrated Microbiological Water Quality Assessment in the South-Eastern Baltic Sea Coastal Waters

The bathing water microbiome consists of pathogenic and non-pathogenic microorganisms, such as bacteria, viruses, and protozoa. However, the targets of the Bathing Water Directive (2006/7/EC) focus exclusively on fecal pollution. This study aims to investigate fecal indicator bacteria (FIB), naturally thriving cyanobacteria, and Vibrio bacteria in the Lithuanian coastal Baltic Sea and Curonian Lagoon bathing sites, combining information into an integrated microbial risk assessment scheme. The results show that officially monitored indicators, such as FIB, do not exceed the acceptable ‘low’ risk threshold. Simultaneously, cyanobacteria and Vibrio cholerae abundance in the Curonian Lagoon sites reveal a ‘high’ probability of adverse health effects. In coastal bathing sites, a positive correlation was found between Escherichia coli, cyanobacterial harmful algae bloom (cHAB), and V. cholerae, indicating that all target microorganisms may occur at the same time, with consequently high risks for the health of bathers. Therefore, implementing new target organisms in national or even regional bathing water monitoring programs is recommended, in order to safeguard the health of beachgoers.

Austria-wide survey on resistant, potentially pathogenic bacteria at Austrian bathing sites, 2017

Summary There is growing concern about human-induced antibiotic resistance and on the occurrence of antibiotic-resistant, potentially pathogenic bacteria in the environment. The aim of this study was to investigate the incidence of resistant, clinically relevant bacteria at bathing sites. In total, 27 of 263 bathing sites authorized under the EU Bathing Water Directive (3 per Austrian state) were sampled during the summer of 2017. Samples were tested for antibiotic-resistant bacteria by enrichment in thioglycollate broth and cultivation on chromogenic media. The screening for potentially pathogenic antibiotic-resistant bacteria was negative in 23 of the 27 samples. Antibiotic-resistant bacteria were detected from 4 of the 27 bathing sites: one Pseudomonas aeruginosa and three resistant Enterobacteriaceae (piperacillin/tazobactam-resistant Enterobacter cloacae with high-level expression of AmpC beta-lactamase, carbapenem-resistant Enterobacter mori, extended-spectrum beta-lactamase-producing Escherichia coli). Despite the occurrence of resistant bacteria, we consider the public health risk at Austrian bathing sites as low.

Efficiency of Private Household Sand Filters in Removing Nutrients and Microbes from Wastewater in Finland

Sand filters have been shown to be an economic and effective solution for wastewater treatment in private households, although the removal of phosphorus (P) may be insufficient. However, P removal can be improved by adding a P-adsorbing material, such as biotite, into the sand filters. The physico-chemical characteristics and the microbial quality of the effluents of family-scale sand filters without adsorbing media (SF), sand filters with a biotite layer (B), and sand filters with a modular filter (MB) were followed for one year. Sand filters with a biotite layer displayed the highest capacity to remove nitrogen (N) and biological oxygen demand BOD7. The efficiency of these filters did not depend on the age of the filter or the season. The P load of the effluent did not differ between sand filters with and without a biotite layer, but the modular sand filter failed to adequately reduce P. The treatment efficiency of sand filters without biotite decreased with increasing age. These private household sand filters can be a good way to treat domestic wastewaters, since these generally comply with the minimum requirements of a Finnish Decree (157/2017). However, enteric viruses (noro- and adenoviruses) were commonly found in the effluents, and the numbers of Escherichia coli were often above 103 colony forming units (CFU) 100 mL−1 (limit for the the EU Bathing Water Directive 2006/7/EC) for good water quality), signifying a risk of microbial contamination of nearby drinking water wells, as well as bathing and irrigation waters.