Why The Catfish Consumption Advisory?

Type: Tidal
Region: Southern
Location: Leesylvania State Park

I launched my kayak at Leesylvania State Park on Saturday targeting largemouth and snakehead. I ended up catching this 20" catfish. I released it due to the sign at the kayak/canoe launch stating not to eat them if they are over 18". I know the state lines show the area to be in VA, but could you please educate me on why over 18" isn't safe, but under 18" is ok.

DNR Response: There is a consumption advisory in both Maryland and Virginia (tidal Potomac) on Channel Catfish over 18 inches in length due to measured amounts of Polychlorinated biphynel (PCB�s). Both PCB�s and Mercury can accumulate in the tissue of certain fish species as they get larger and feed on smaller fish that contain these contaminants. To test for this, fish are collected and tested for both PCB�s and Mercury at different lengths. If the level of contaminants is greater than set by the EPA, the jurisdictional State issues a consumption advisory. Interestingly, different species of catfish hold varying levels of contaminants. That is why they each may have different size limits set for an advisory.