Environmental quality standards uncertainty

Knowledge of the measurement uncertainty, together with the value of the limit of quantification (LOQ) (and limit of detection (LOD) ) is the basis for checking compliance with Environmental Quality Standards (EQS) and assessment of fitness for purpose of the data against the predefined objectives of the monitoring programme. 

In the proposal of Commission Directive (European Commission, 2008) it is stated that Member States will need to ensure that the minimum performance criteria for all methods of analysis applied are based on a relative target uncertainty of 50 % (k = 2), estimated at the level of relevant Environmental Quality Standards and a limit of quantification equal to or below a value of 30 % of relevant Environmental Quality Standards. 

There may be occasions when a standard is set at a concentration below current analytical limits of detection (LODs) or limits of quantification (LOQs). This could be because high uncertainty leads to the application of large assessment factors to toxicity data to derive a standard or because analytical techniques for a particular environmental matrix have higher LODs/LOQs than those available for the medium in which the standard was derived (e.g., sewage effluent versus laboratory water). An inability to measure concentrations of a chemical at the standard does not necessarily render the standard totally useless. For example, a water quality standard set in a receiving watercourse may be below the LOD/LOQ, but measurement of concentrations from an effluent may be above these limits. Appropriate modeling may allow good estimation of whether the standard in the watercourse has been exceeded. 

Figure 2 summarizes the basic difference between the 1975 national stationary source demand for low sulfur coal and oil, based on State Implementation Plan (SIP) estimates of that necessary to achieve primary ambient air quality standards and the projected 1975 supply of these fuels (6, 7, 8, 9, 10, 11). The net result is a forecast coal/oil supply deficit on the basis of sulfur content and including foreign imports, of approximately 8 XlO Btu. This is equivalent to a combined annual shortage of about 230 million tons of coal and 300 million barrels of primarily residual oil. Table II shows the regional distribution of these shortages. In the judgment of the author, uncertainties in factors such as sulfur content analyses, production potentials, and the commercial impact of environmental standards by 1975 limit the accuracy of these supply deficit forecasts to about 20%. 

A broad range of technical requirements is important in a laboratory quality system. These include aspects such as the selection of appropriately qualified and experienced personnel sampling, sample handling and preparation laboratory accommodation and environmental conditions equipment and reagents calibration reference standards and reference materials traceability (of standards and of samples) the selection or development, validation, and control of methods estimation of the uncertainty of measurements reporting of results and quality control and proficiency testing. 

Certified reference materials are intended primarily for calibration and in quality control of analytical techniques. A certified reference material is a reference material, accompanied by a certificate, one or more of whose property values are certified by a procedure that establishes its traceability to an accurate realization of the unit in which the property values are expressed and for which each certified value is accompanied by an uncertainty at a stated level of confidence. They are used to test, validate, and optimize new analytical techniques as well as in quality control of routine laboratory work. Table 3 gives a list of environmental samples that provide certified values of PAH content. These are available from various bodies as certified reference materials. In measuring the concentration of a substance for certification purposes, more than two independent and reliable analytical methods are used. Certified reference materials when used for standardization of analytical methods will make comparisons between PAH data obtained by a variety of workers using... 

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