Risk factors and monitoring for water quality to determine best management practices for splash parks.

Splash parks have been associated with infectious disease outbreaks as a result of exposure to poor water quality. To be able to protect public health, risk factors were identified that determine poor water quality. Samples were taken at seven splash parks where operators were willing to participate in the study. Higher concentrations of Escherichia coli were measured in water of splash parks filled with rainwater or surface water as compared with sites filled with tap water, independent of routine inspection intervals and employed disinfection. Management practices to prevent fecal contamination and guarantee maintaining good water quality at splash parks should include selection of source water of acceptable quality.

Human exposure to endotoxins and fecal indicators originating from water features.

Exposure to contaminated aerosols and water originating from water features may pose public health risks. Endotoxins in air and water and fecal bacteria in water of water features were measured as markers for exposure to microbial cell debris and enteric pathogens, respectively. Information was collected about wind direction, wind force, distance to the water feature, the height of the water feature and the tangibility of water spray. The mean concentration of endotoxins in air nearby and in water of 31 water features was 10 endotoxin units (EU)/m(3) (Geometric Mean (GM), range 0-85.5 EU/m(3) air) and 773 EU/mL (GM, range 9-18,170 EU/mL water), respectively. Such mean concentrations may be associated with respiratory health effects. The water quality of 26 of 88 water features was poor when compared to requirements for recreational water in the Bathing Water Directive 2006/7/EC. Concentrations greater than 1000 colony forming units (cfu) Escherichia coli per 100 mL and greater than 400 cfu intestinal enterococci per 100 mL increase the probability of acquiring gastrointestinal health complaints. Regression analyses showed that the endotoxin concentration in air was significantly influenced by the concentration of endotoxin in water, the distance to the water feature and the tangibility of water spray. Exposure to air and water near water features was shown to lead to exposure to endotoxins and fecal bacteria. The potential health risks resulting from such exposure to water features may be estimated by a quantitative microbial risk assessment (QMRA), however, such QMRA would require quantitative data on pathogen concentrations, exposure volumes and dose-response relationships. The present study provides estimates for aerosolisation ratios that can be used as input for QMRA to quantify exposure and to determine infection risks from exposure to water features.

Health risk assessment for splash parks that use rainwater as source water.

In the Netherlands, rainwater becomes more and more popular as an economic and environmentally sustainable water source for splash parks, however, the associated public health risk and underlying risk factors are unknown. Since splash parks have been associated with outbreaks of infectious diseases, a quantitative microbial risk assessment was performed using Legionella pneumophila as a target pathogen to quantify the risk of infection for exposure due to inhalation and Campylobacter jejuni for ingestion. Data for L. pneumophila and C. jejuni concentrations in rainfall generated surface runoff from streets were extracted from literature. Data for exposure were obtained by observing 604 people at splash parks, of whom 259 were children. Exposure volumes were estimated using data from literature to determine the volume of exposure through inhalation at 0.394 µL/min (95% CI-range 0.0446-1.27 µL/min), hand-to-mouth contact at 22.6 µL/min, (95% CI-range 2.02-81.0 µL/min), ingestion of water droplets at 94.4 µL/min (95% CI-range 5.1-279 µL/min) and ingestion of mouthfuls of water at 21.5·10(3) µL/min (95% CI-range 1.17 ·10(3)-67.0·10(3) µL/min). The corresponding risk of infection for the mean exposure duration of 3.5 min was 9.3·10(-5) (95% CI-range 0-2.4·10(-4)) for inhalation of L. pneumophila and 3.6·10(-2) (95% CI-range 0-5.3·10(-1)) for ingestion of C. jejuni. This study provided a methodology to quantify exposure volumes using observations on site. We estimated that using rainwater as source water for splash parks may pose a health risk, however, further detailed quantitative microbial analysis is required to confirm this finding. Furthermore we give insight into the effect of water quality standards, which may limit infection risks from exposure at splash parks.

Quantitative assessment of infection risk from exposure to waterborne pathogens in urban floodwater.

Flooding and heavy rainfall have been associated with waterborne infectious disease outbreaks, however, it is unclear to which extent they pose a risk for public health. Here, risks of infection from exposure to urban floodwater were assessed using quantitative microbial risk assessment (QMRA). To that aim, urban floodwaters were sampled in the Netherlands during 23 events in 2011 and 2012. The water contained Campylobacter jejuni (prevalence 61%, range 14- >10(3) MPN/l), Giardia spp. (35%, 0.1-142 cysts/l), Cryptosporidium (30%, 0.1-9.8 oocysts/l), noroviruses (29%, 10(2)-10(4) pdu/l) and enteroviruses (35%, 10(3)-10(4) pdu/l). Exposure data collected by questionnaire, revealed that children swallowed 1.7 ml (mean, 95% Confidence Interval 0-4.6 ml) per exposure event and adults swallowed 0.016 ml (mean, 95% CI 0-0.068 ml) due to hand-mouth contact. The mean risk of infection per event for children, who were exposed to floodwater originating from combined sewers, storm sewers and rainfall generated surface runoff was 33%, 23% and 3.5%, respectively, and for adults it was 3.9%, 0.58% and 0.039%. The annual risk of infection was calculated to compare flooding from different urban drainage systems. An exposure frequency of once every 10 years to flooding originating from combined sewers resulted in an annual risk of infection of 8%, which was equal to the risk of infection of flooding originating from rainfall generated surface runoff 2.3 times per year. However, these annual infection risks will increase with a higher frequency of urban flooding due to heavy rainfall as foreseen in climate change projections.

Dynamics of artificially immobilized Nitrosomonas europaea: Effect of biomass decay.

The dynamics of growth and death of immobilized Nitrosomonas europaea were studied. For this, the death rate of suspended cells was determined in the absence of ammonium or oxygen by following the loss of respiration activity and by fluorescein-diacetate (FDA)/lissamine-green staining techniques. The death rates obtained (1.06 x 10(-6) s(-1) or 4.97 x 10(-6) s(-1) in the absence of oxygen or ammonium, respectively) were incorporated in a dynamic growth model and the effects on the performance of the immobilized-cell process illustrated by model simulations.These model simulations and experimental validation show that if decay of biomass occurs the biomass concentration in the center of the bead decreases. As a result, the systems react slower to changes in substrate concentrations than if all cells remain viable.To show that cells in the center of the bead died, the FDA and lissamine-green staining techniques were adapted for immobilized cells. It was shown that biomass decay occurred, especially in the center of the bead; the amount of cells decreased there, and the remaining cells were all stained with lissamine green indicating cell death. After the substrate availability was decreased, also cells near the surface of the bead lost their viability. The number of viable cells increased again after increasing the substrate concentration as the result of cell multiplication. At low substrate concentrations and low hydraulic retention times, as for example in the treatment of domestic wastewater, the death rate of cells is thus an important parameter for the performance of the immobilized-cell system. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 630-641, 1997.

Relevance of rheological properties of gel beads for their mechanical stability in bioreactors.

The mechanical stability of biocatalyst particles in bioreactors is of crucial importance for applications of immobilized-cell technology in bioconversions. The common methods for evaluation of the strength of polymer beads (mostly force-to-fracture or tensile tests) are, however, not yet proven to be relevant for the assessment of their mechanical stability in bioreactors. Therefore, we tested fracture properties of gel materials and investigated their relevance for abrasion in bioreactors. Abrasion of gel beads was assumed to be a continuous fracturing of the bead surface. At first, three rheological properties were considered: stress at fracture; strain at fracture; and the total fracture energy. If stress at fracture is the most important property, beads having a similar fracture energy, but a smaller stress at fracture, would abrade faster in a bioreactor than beads with a larger stress at fracture; if fracture energy the determining factor, beads that require less energy to fracture would abrade faster than those having a larger fracture energy for the same fracture stress. To determine this, beads of kappa-carrageenan and agar (at two different polymer concentrations) were tested for abrasion in four identical bubble columns under the same operating conditions. Agar beads were expected to abrade faster than those of carrageenan because agar had either a lower stress at fracture or a lower fracture energy. However, no correlation between fracture properties and abrasion rate was found in any of the combinations tested. Carrageenan beads abraded faster than those of agar in all combinations. Furthermore, both the stress and strain at fracture of agar and carrageenan beads decreased during the run and those of carrageenan decreased faster, suggesting that the gels are liable to fatigue in different ways. This hypothesis was confirmed by oscillating experiments in which gel samples were subjected to repeated compressions below their fracture levels. Their resistance to compression clearly decreased with the number of oscillations. Fatigue is probably related to the development of microcracks and microfracture propagation within the material. We concluded that: (a) the use of tests based on bead rupture do not provide relevant information on the mechanical stability of gel beads to abrasion; and (b) abrasion of polymer beads is likely to be related to fatigue of the gel materials. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 517-529, 1997.

Effects of diffusion limitation on immobilized nitrifying microorganisms at low temperatures.

Activation energies of suspended and immobilized nitrifying bacteria were determined and compared to determine if diffusion limitation results in decreased sensitivity for temperature. The activation energy for the respiration activity of suspended Nitrosomonas europaea and Nitrobacter agilis was found to be 86.4 and 58.4 kJ mol(-1), respectively. The activation energy for oxygen diffusion in the support material, kappa-carrageenan, determined from the effect of temperature on the effective diffusion coefficient (D), was 17.2 kJ mol(-1). Consequently, the apparent actvation energy of diffusion limited cells should be lower. It was indeed shown that due to the effect of diffusion limitation and to temperature effects on the Monod constant K(s), the immobilized-cell activity was less sensitive to temperature. The apparent activation energy for immobilized Ns. europaea was between 28.6 and 94.2 kJ mol(-1) and for immobilized Nb. agilis between 1.4 and 72.9 kJ mol(-1), depending on the oxygen concentration and temperature. (c) 1995 John Wiley & Sons, Inc.

Molecular detection of Norwalk-like caliciviruses in sewage.

In this study, Norwalk-like virus (NLV) RNA was detected by reverse transcriptase PCR (RT-PCR) in sewage water concentrates. Sequence analysis of the RT-PCR products revealed identical sequences in stools of patients and related sewage samples. In 6 of 11 outbreak-unrelated follow-up samples, multiple NLV genotypes were present. Levels as high as 10(7) RNA-containing particles per liter were found. These data show that high loads of NLVs may be present in sewage and warrant further studies addressing the efficacy of NLV removal by sewage water treatment processes.