Application of quantitative microbial risk assessment is still a some what controversial issue in drinking water, because validation of risk assessment models is not easily done, if at all possible. Theoretical risk estimates are made to meet a specified risk target (such as 1 infection per 10,000 people per year) for a particular situation, but whether this corresponds to reality is generally unknown……and the actual incidence of infection must also be estimated with a number of assumptions……
Schijven, J.F., P.F.M. Teunis, S.A. Rutjes, M. Bouwknegt, and A.M. de Roda Husman 2011. QMRAspot: A tool for Quantitative Microbial Risk Assessment from surface water to potable water. Water Research. Aug. 23. doi:10.1016/j.watres.2011.08.024
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In the Netherlands, a health based target for microbially safe drinking water is set at less than one infection per 10,000 persons per year. For the assessment of the microbial safety of drinking water, Dutch drinking water suppliers must conduct a Quantitative Microbial Risk Assessment (QMRA) at least every three years for the so-called index pathogens enterovirus, Campylobacter, Cryptosporidium and Giardia. In order to collect raw data in the proper format and to automate the process of QMRA, an interactive user-friendly computational tool, QMRAspot, was developed to analyze and conduct QMRA for drinking water produced from surface water. This paper gives a description of the raw data requirements for QMRA as well as a functional description of the tool. No extensive prior knowledge about QMRA modeling is required by the user, because QMRAspot provides guidance to the user on the quantity, type and format of raw data and performs a complete analysis of the raw data to yield a risk outcome for drinking water consumption that can be compared with other production locations, a legislative standard or an acceptable health based target. The uniform approach promotes proper collection and usage of raw data and, warrants quality of the risk assessment as well as enhances efficiency, i.e., less time is required. QMRAspot may facilitate QMRA for drinking water suppliers worldwide. The tool aids policy makers and other involved parties in formulating mitigation strategies, and prioritization and evaluation of effective preventive measures as integral part of water safety plans.
Natural gas migration into water wells can indeed occur naturally. Click here for an update on drilling in Lennox Township where drilling and methane investigations continue.
An interesting analysis of corrosion byproducts that confirms what has been deduced from prior studies….arsenic associated with solid deposits….and mobilization of manganese.
Peng, C.Y. and G.V. Korshin 2011. Speciation of trace inorganic contaminants in corrosion scales and deposits formed in drinking water distribution systems. Water Research. 2011 Aug 18. doi:10.1016/j.watres.2011.08.017
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Abstract: Sequential extractions utilizing the modified Tessier scheme (Krishnamurti et al., 1995) and measurements of soluble and particulate metal released from suspended solids were used in this study to determine the speciation and mobility of inorganic contaminants (As, Cr, V, U, Cd, Ni, and Mn) found in corrosion scales and particles mobilized during hydraulic flushing events. Arsenic, chromium and vanadium are primarily associated with the mobilization-resistant fraction that is resistant to all eluents used in this study and also bound in highly stable crystalline iron oxides. Very low concentrations of these elements were released in resuspension experiments. X-ray absorbance measurements demonstrated that arsenic in the sample with the highest As concentration was dominated by As(V) bound by iron oxides. Significant fractions of uranium and cadmium were associated with carbonate solids. Nickel and manganese were determined to be more mobile and significantly associated with organic fractions. This may indicate that biofilms and natural organic matter in the drinking water distributions systems play an important role in the accumulation and release of these inorganic contaminants.
It is interesting to me that this paper claims…
“no consensus among the scientific community exists on what risk, if any, pharmaceuticals and endocrine disruptors pose to human health.”
How do they know? Did they talk to everyone in the “scientific community”? Did they count noses? Statements like this are foolish, and do not have any bearing on the science itself. At best, they can report their perception of what has been published (but only to the degree of what they have read) and who they have talked with (which is a finite number of people, not the “scientific community.”)
Touraud, E., B. Roig, J.P. Sumpter, and C. Coetsier 2011. Drug residues and endocrine disruptors in drinking water: Risk for humans? Int J Hyg Environ Health. 2011 Aug 30.
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Abstract: The presence of pharmaceuticals and endocrine disruptors in the environment raises many questions about risk to the environment and human health. Environmental exposure has been largely studied, providing to date a realistic picture of the degree of contamination of the environment by pharmaceuticals and hormones. Conversely, little information is available regarding human exposure. NSAIDS, carbamazepine, iodinated contrast media, β-blockers, antibiotics have been detected in drinking water, mostly in the range of ng/L. it is questioned if such concentrations may affect human health. Currently, no consensus among the scientific community exists on what risk, if any, pharmaceuticals and endocrine disruptors pose to human health. Future European research will focus, on one hand, on genotoxic and cytotoxic anti-cancer drugs and, on the other hand, on the induction of genetic resistance by antibiotics. This review does not aim to give a comprehensive overview of human health risk of drug residues and endocrine disruptors in drinking water but rather highlight important topics of discussion.