Calculation Procedure for Total Aluminium Guideline

Use this procedure to calculate (interpolate) intermediate concentrations in Table 2 if desired.

1. calculate the modelled survival of aluminium controls (i.e. [Al]=0) by:
   • deleting the aluminium terms from equation 4
   • substituting the pH and DOC of interest
   • calculating transformed logit y
   • substitute transformed logit y in equation 1 and solve for "p", the proportion surviving
2. calculate the LC₂₅ relative to the control survival (i.e. 0.75p)
3. calculate the logit of the LC₂₅ using equation 1
4. substitute this value for logit y in equation 4 and solve for aluminium concentration. This is the guideline aluminium concentration for that pH and DOC.

Do not extrapolate outside the range of the table (pH 5.2 to 6.4, DOC 0.5 to 10) because the modelled control
survival becomes unacceptably low, and/or the effects of higher DOC are unknown. A computation spreadsheet
is available by email from ceqg-rcqe@ec.gc.ca