Should we study sediments microbial quality in natural aquatic environments?

CHÁVEZ DÍAZ LUCÍA; WAMAN HARO; DOLORES GUTIÉRREZ CACCIABUE; HUGO RAMIRO POMA; OSCAR GAMBONI; VERÓNICA RAJAL

Chapel Hill, Raleigh, Carolina del Norte

Simposio; 19th International Symposium on Health-Related Water Microbiology (WaterMicro 2017); 2017

International Water Association (IWA)

Recreation is one of the many uses of water natural resources. Depending on the chemical and microbiological quality, recreational aquatic environments, like rivers and lakes, may become a risk to the population. In particular pathogens including bacteria, viruses, and parasites may transmit waterborne diseases. The aims of the study were to characterize water and sediments from two recreational natural aquatic environments in Salta, Argentina, and to evaluate the importance of sediments as potential reservoir of microorganisms. Water and sediment samples (3 replicates per occasion) were collected from December 2015 to September 2016 from two recreational natural aquatic environments: Wierna River (WR, 5 samples: WR1, WR2, WR3, WR4, WR5) and General Belgrano Reservoir (GB, 6 samples: GB1, GB2, GB3, GB4, GB5, GB6). Physicochemical variables in water (pH, turbidity, dissolved oxygen, temperature, conductivity, hardness) and sediments (organic matter, humidity, ash, conductivity) were measured. For the microbiological characterization bacteria and viruses were analyzed. Total aerobic mesophiles (TAM), total (TC) and thermotolerant coliforms (THC), E. coli (EC), enteroccocci (ENT) and P. aeruginosa (PA) were culture-based enumerated. Bacteria were detached from sediments with 1% Tween 80 and 15 min of handshaking. Adenovirus and enterovirus were quantified by real-time PCR from ultrafiltration water concentrates and from sediments after extraction of nucleic acids with commercial kits.The main physico-chemical variations were observed in temperature (according to the season) for both environment, turbidity in WR (2-999 NTU) and dissolved oxygen (WR: 2-7 mg/l, GB: 2-10 mg/l). Culturable bacteria were mainly in the sediments (75-99%) rather than in the water column of each corresponding sample. The highest counts were for TAM in both environments (2.8x103 CFU/ml and 2.4x104 CFU/g for water and sediments in WR and 8x102 CFU/ml and 1.8x105 CFU/g for water and sediments in GB). More than 50% of the samples were negative for TC, THC, EC and ENT in water. Although water samples from WR5 and GB2 had the highest bacterial contamination, only in RW2 and GB3 exceeded the limits for EC and ENT established for recreational water by the USEPA (2002) (Argentina does not have legislation), being all these associated with rain events. Respecting viruses, only adenovirus was found in WR3 and WR4 water samples and in water and sediments in GB4. In these cases the counts for ENT and EC in water were below the USEPA limits, showing that the presence of virus was not related to the concentration of bacterial indicators.Concluding, sediments were the main reservoir of microorganisms. As they can be resuspended and microorganisms returned to the water column due to the turbulence of rain events or recreational activities, they should also be analyzed at the time the water quality of a recreational natural aquatic environment is assessed in order to protect public health.