Environmental variability assessment procedure

Additionally, the integration of geographic information system (GIS) with analytical data is an effective procedure in addressing the problem of spatial and temporal variability of the different parameters involved in the environmental fate of chemicals. Based on accurate local estimations, GIS-based models would then also allow deriving realistic and representative spatially averaged regional PECs. Table 4 shows some studies that have used GIS-based methodologies to perform a site-specific risk assessment of PECs in different exposed ecosystems. 

Variability and uncertainty affect every element of every risk assessment. For example, participants in the European Workshop on Probabilistic Risk Assessment for the Environmental Impacts of Plant Protection Products (EUPR A) were asked to list sources of uncertainty affecting current procedures for assessing pesticide risks to aquatic... 

In most cases, chemical analysis of environmental samples relies on an extraction step, followed by determination of the target chemical species in the extract obtained. Complete extraction is not possible for most contaminants, unless very onerous procedures are followed. As a result, the extent and variability of extraction must be known as otherwise the held concentrations of contaminant may be underestimated. When dealing with water samples it is possible to introduce a recovery spike into the sample, preferably immediately on sampling in the held, in which case the efficiency of the whole testing procedure, including extraction, can be assessed. For soil samples, with the exception of more volatile organic contaminants, dispersion of the spike throughout the sample is very poor, so that this approach does not work. 

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