Analysis of microcosm and mesocosm studies used to calibrate
CASM_Atrazine and determine a threshold screening level of concern
(LOC):   The EPA has asked the Panel to consider the approach used to
determine the LOC (Charge Question #2), as well as consideration of
uncertainty (Charge Questions #4 and #9-ii) .  This document provides a
review of the microcosm and mesocosm studies used to calibrate
CASM_Atrazine, specifically assessing them against three study quality
criteria; inclusion of treatment replication, use of statistics to
identify adverse effects, and whether recovery was measured and/or
reported.  Using all three criteria, the uncertainty surrounding the
selection of the screening LOC was estimated.  It was determined that
the screening LOC selected for this program represents a highly
conservative (lower-bound) no-effect threshold for assessing
atrazine-induced effects on primary producer communities in Midwestern
streams.

