Setting site-specific water-quality standards by using tissue residue criteria and bioaccumulation data. Part 1. Methodology.
We have developed a method for determining site-specific water-quality standards (SSWQSs) for substances regulated based on tissue residues. The method uses a multisite regression model to solve for the conditional prior probability density function (PDF) on water concentration, given that tissue concentration equals a tissue residue threshold. The method then uses site-specific water and tissue concentration data to update the probabilities on a Monte Carlo sample of the prior PDF by using Bayesian Monte Carlo analysis. The resultant posterior PDF identifies the water concentration that, if met at the site, would provide a desired level of confidence of meeting the tissue residue threshold contingent on model assumptions. This allows for derivation of a SSWQS. The method is fully reproducible, statistically rigorous, and easily implemented. A useful property of the method is that the model is sensitive to the amount of site-specific data available, that is, a more conservative or protective number (water concentration) is derived when the data set is small or the variance is large. Likewise, as the site water concentration increases above the water-quality standard, more site-specific information is needed to demonstrate a safe concentration at the site. A companion paper demonstrates the method by using selenium as an example.
Toll
John E
JE
Toll Environmental, Seattle, Washington 98105, USA. john@tollenvromental.com
Tear
Lucinda M
LM
DeForest
David K
DK
Brix
Kevin V
KV
Adams
William J
WJ
D000818:Animals; D001499:Bayes Theorem; D001822:Body Burden; D008954:Models, Biological; D015233:Models, Statistical; D009010:Monte Carlo Method; D011786:Quality Control; D014874:Water Pollutants, Chemical / Q000378:metabolism / Q000592:standards*; D014881:Water Supply / Q000592:standards*
D014874:Water Pollutants, Chemical