Groundwater age distributions at a public drinking water supply well field derived from multiple age tracers (⁸⁵Kr, ³H/³He, and ³⁹Ar)

Groundwater age is a key aspect of production well vulnerability. Public drinking water supply wells typically have long screens and are expected to produce a mixture of groundwater ages. The groundwater age distributions of seven production wells of the Holten well field (Netherlands) were estimated from tritium-helium (3H/3He), krypton-85 (85Kr), and argon-39 (39Ar), using a new application of a discrete age distribution model and existing mathematical models, by minimizing the uncertainty-weighted squared differences of modeled and measured tracer concentrations. The observed tracer concentrations fitted well to a 4-bin discrete age distribution model or a dispersion model with a fraction of old groundwater. Our results show that more than 75 of the water pumped by four shallow production wells has a groundwater age of less than 20 years and these wells are very vulnerable to recent surface contamination. More than 50 of the water pumped by three deep production wells is older than 60 years. 3H/3He samples from short screened monitoring wells surrounding the well field constrained the age stratification in the aquifer. The discrepancy between the age stratification with depth and the groundwater age distribution of the production wells showed that the well field preferentially pumps from the shallow part of the aquifer. The discrete groundwater age distribution model appears to be a suitable approach in settings where the shape of the age distribution cannot be assumed to follow a simple mathematical model, such as a production well field where wells compete for capture area.

Water quality and health in a Sahelian semi-arid urban context: an integrated geographical approach in Nouakchott, Mauritania

Access to sufficient quantities of safe drinking water is a human right. Moreover, access to clean water is of public health relevance, particularly in semi-arid and Sahelian cities due to the risks of water contamination and transmission of water-borne diseases. We conducted a study in Nouakchott, the capital of Mauritania, to deepen the understanding of diarrhoeal incidence in space and time. We used an integrated geographical approach, combining socio-environmental, microbiological and epidemiological data from various sources, including spatially explicit surveys, laboratory analysis of water samples and reported diarrhoeal episodes. A geospatial technique was applied to determine the environmental and microbiological risk factors that govern diarrhoeal transmission. Statistical and cartographic analyses revealed concentration of unimproved sources of drinking water in the most densely populated areas of the city, coupled with a daily water allocation below the recommended standard of 20 l per person. Bacteriological analysis indicated that 93% of the non-piped water sources supplied at water points were contaminated with 10-80 coliform bacteria per 100 ml. Diarrhoea was the second most important disease reported at health centres, accounting for 12.8% of health care service consultations on average. Diarrhoeal episodes were concentrated in municipalities with the largest number of contaminated water sources. Environmental factors (e.g. lack of improved water sources) and bacteriological aspects (e.g. water contamination with coliform bacteria) are the main drivers explaining the spatio-temporal distribution of diarrhoea. We conclude that integrating environmental, microbiological and epidemiological variables with statistical regression models facilitates risk profiling of diarrhoeal diseases. Modes of water supply and water contamination were the main drivers of diarrhoea in this semi-arid urban context of Nouakchott, and hence require a strategy to improve water quality at the various levels of the supply chain.

Water quality in dental chair units. A random sample in the canton of St. Gallen

This study aimed to identify the microbial contamination of water from dental chair units (DCUs) using the prevalence of Pseudomonas aeruginosa, Legionella species and heterotrophic bacteria as a marker of pollution in water in the area of St. Gallen, Switzerland. Water (250 ml) from 76 DCUs was collected twice (early on a morning before using all the instruments and after using the DCUs for at least two hours) either from the high-speed handpiece tube, the 3 in 1 syringe or the micromotor for water quality testing. An increased bacterial count (>300 CFU/ml) was found in 46 (61%) samples taken before use of the DCU, but only in 29 (38%) samples taken two hours after use. Pseudomonas aeruginosa was found in both water samples in 6/76 (8%) of the DCUs. Legionella were found in both samples in 15 (20%) of the DCUs tested. Legionella anisa was identified in seven samples and Legionella pneumophila was found in eight. DCUs which were less than five years old were contaminated less often than older units (25% und 77%, p<0.001). This difference remained significant (0=0.0004) when adjusted for manufacturer and sampling location in a multivariable logistic regression. A large proportion of the DCUs tested did not comply with the Swiss drinking water standards nor with the recommendations of the American Centers for Disease Control and Prevention (CDC).

Bone healing around titanium implants in two rat colitis models

OBJECTIVE Crohn's disease is a chronic inflammatory process that has recently been associated with a higher risk of early implant failure. Herein we provide information on the impact of colitis on peri-implant bone formation using preclinical models of chemically induced colitis. METHODS Colitis was induced by intrarectal instillation of 2,4,6-trinitro-benzene-sulfonic-acid (TNBS). Colitis was also induced by feeding rats dextran-sodium-sulfate (DSS) in drinking water. One week after disease induction, titanium miniscrews were inserted into the tibia. Four weeks after implantation, peri-implant bone volume per tissue volume (BV/TV) and bone-to-implant contacts (BIC) were determined by histomorphometric analysis. RESULTS Cortical histomorphometric parameters were similar in the control (n = 10), DSS (n = 10) and TNBS (n = 8) groups. Cortical BV/TV was 92.2 ± 3.7%, 92.0 ± 3.0% and 92.6 ± 2.7%. Cortical BIC was 81.3 ± 8.8%, 83.2 ± 8.4% and 84.0 ± 7.0%, respectively. No significant differences were observed when comparing the medullary BV/TV and BIC (19.5 ± 6.4%, 16.2 ± 5.6% and 15.4 ± 9.0%) and (48.8 ± 12.9%, 49.2 ± 6.2 and 41.9 ± 11.7%), respectively. Successful induction of colitis was confirmed by loss of body weight and colon morphology. CONCLUSIONS The results suggest bone regeneration around implants is not impaired in chemically induced colitis models. Considering that Crohn's disease can affect any part of the gastrointestinal tract including the mouth, our model only partially reflects the clinical situation.

Natural Tracers in recent groundwaters from different Alpine aquifers

Groundwater with underground residence times between days and a few years have been investigated over more than 20 years from 487 remote sites located in different aquifer types in the Alpine belt. Analysis of the data reveals that groundwaters evolved in crystalline, evaporite, carbonate, molasse, and flysch aquifers can be clearly distinguished based on their major and trace element composition and degree of mineralisation. A further subdivision can be made even within one aquifer type based on the trace element compositions, which are characteristic for the lithologic environment. Major and trace element concentrations can be quantitatively described by interaction of the groundwater with the aquifer- specific mineralogy along the flow path. Because all investigated sites show minimal anthropogenic influences, the observed concentration ranges represent the natural background concentrations and can thus serve as a “geo-reference” for recent groundwaters from these five aquifer types. This “geo-reference” is particularly useful for the identification of groundwater contamination. It further shows that drinking water standards can be grossly exceeded for critical elements by purely natural processes