Aquacultured eastern oysters (Crassostrea virginica) are placed in a two-tiered structure with one chamber a fixed distance from the bottom of the water, and another on a sliding float held a fixed distance from the surface. This allows determination of where, within the water column, pollutants are circulating.
Oyster racks are deployed to a variety of sites within the monitoring region two to three weeks prior to the start of monitoring. Racks are also deployed at control sites during the entire monitoring period. Prior to deployment a subset of oysters are analyzed to determine baseline toxicity. The first oysters are collected from the field at both test and control sites and analyzed the day before the causal event (e.g. dredging) begins. Oysters are then collected biweekly, with the last oysters collected two weeks after the completion of the event.
Oysters are shelled, homogenized and analyzed for total toxicity in ORCA's lab using the Microtox® Basic Solid-Phase bioassay. Homogenized oysters from each sample are also sent to an EPA approved laboratory for analysis of individual pollutants (selected based on the particular concerns of the monitoring project).