Should we study sediments microbial quality in natural aquatic environments?

CHÁVEZ DÍAZ LUCÍA; DOLORES GUTIÉRREZ CACCIABUE; HUGO RAMIRO POMA; WAMAN HARO; 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. Dependingon the chemical and microbiological quality, recreational aquatic environments,like rivers and lakes, may become a risk to the population. In particularpathogens including bacteria, viruses, and parasites may transmit waterbornediseases.The aims of the study were to characterize water and sediments from tworecreational natural aquatic environments in Salta, Argentina, and to evaluatethe importance of sediments as potential reservoir of microorganisms.Water and sediment samples (3 replicates per occasion) were collectedfrom December 2015 to September 2016 from two recreational natural aquaticenvironments: Wierna River (WR, 5 samples: WR1, WR2, WR3, WR4, WR5) and GeneralBelgrano 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 characterizationbacteria 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 fromsediments with 1% Tween 80 and 15 min of handshaking. Adenovirus andenterovirus were quantified by real-time PCR from ultrafiltration waterconcentrates and from sediments after extraction of nucleic acids withcommercial kits.The main physico-chemical variations were observed in temperature(according to the season) for both environment, turbidity in WR (2-999 NTU) anddissolved oxygen (WR: 2-7 mg/l, GB: 2-10 mg/l). Culturable bacteria were mainlyin the sediments (75-99%) rather than in the water column of each correspondingsample. The highest counts were for TAM in both environments (2.8x103 CFU/mland 2.4x104 CFU/g for water and sediments in WR and 8x102 CFU/ml and 1.8x105CFU/g for water and sediments in GB). More than 50% of the samples werenegative for TC, THC, EC and ENT in water. Although water samples from WR5 andGB2 had the highest bacterial contamination, only in RW2 and GB3 exceeded thelimits for EC and ENT established for recreational water by the USEPA (2002)(Argentina does not have legislation), being all these associated with rainevents. Respecting viruses, only adenovirus was found in WR3 and WR4 watersamples and in water and sediments in GB4. In these cases the counts for ENTand EC in water were below the USEPA limits, showing that the presence of viruswas not related to the concentration of bacterial indicators.Concluding, sediments were the main reservoir of microorganisms. As theycan be resuspended and microorganisms returned to the water column due to theturbulence of rain events or recreational activities, they should also beanalyzed at the time the water quality of a recreational natural aquaticenvironment is assessed in order to protect public health.