In 2010, ARCHE and Watts Crane Associates developed a user-friendly BLM tool to facilitate the practical application of BLM normalization for different regulatory applications, such as the European Water Framework Directive (WFD, 2000/60/EC). The BLM tool is based on the chronic BLMs for Ni and estimates of risks associated with the presence of Ni in a particular freshwater environment, based on a limited set of routinely screened BLM input parameters. Because the full BLM calculations are not rapid, a quick and easy to use Microsoft Excel™-based tool was devel-oped to allow the calculation of many BLM parameters simulta-neously.
The BLM tool consists of two main pages, i.e., an introductory page and an input/output (results) page. The introductory page gives the user information on how to use the tool, on which input parameters are needed to run the BLM tool, and on which output (results) are generated by the model. The ambient water quality information required to run the BLM tool is listed below.
- Dissolved Organic Carbon (DOC) as mg/L
- Ca2+ as mg/L or Hardness as (mg/L CaCO3)
- Dissolved Ni concentration as µg/L
It is important to note that the BLM tool provides accurate predictions only within well-defined water chemistry boundaries. Accu-rate predictions are only estimated for Ca2+ concentrations between 3.8 and 88 mg/L, and for pH between 6.5 and 8.2.
An example of the application of the BLM screening model for Ni is presented in Figure 5. In this instance, three examples have been selected (Example 1, 2, and 3). The dissolved Ni concentrations vary between 2 and 10 µg/L, the pH between 6.5 and 8, the Ca2+ concentration between 20 and 40 mg/L, and the DOC between 1 and 10 mg/L.
Entering the required input parameters for the BLM screening tool resulted in the calculation of the bioavailable PNEC value (as µg/L), the BioF6 for Ni, the bioavailable Ni (as µg/L), and the risk characterization ratio (RCR).
The site-specific PNEC value is estimated using the approach as described in this fact sheet. Through the use of a BioF, differences in bioavailability are accounted for by adjustments to the monitor-ing data but the environmental quality standard (EQS) remains the same. The BioF is calculated as follows:
BioF = Generic PNEC7/site-specific PNEC
The model also provides bioavailable predicted environmental concentrations (PEC) values which are calculated as follows:
bioavailable PEC = Dissolved Ni concentration * BioF
Finally the screening model also provides calculations of the risks associated with the presence of Ni in the freshwater environment. The RCR is calculated as the ratio between the PEC and the PNEC values.
Figure 5: Example of results calculated in the BLM screening tool8
6. The BioF is the bioavailability factor is based on a comparison between the expected bioavailability at the reference site and that relating to site-specific conditions.
7. Generic PNEC is a PNEC estimated using realistic worst case conditions, representing a PNEC of ‘high bioavailability.’
8. The Local EQS (dissolved) (µg/L) is the calculated dissolved concentration of metal that is equivalent the EQSbioavailabe at the local water conditions at the site. This can be considered to be equivalent to a site-specific PNEC for dissolved nickel.